JP6825704B2 - Power converters, lighting fixtures, electrical equipment - Google Patents

Description

The present invention relates to power converters, luminaires and electrical appliances.

Lighting fixtures that use LEDs (Light Emitting Diodes) as a light source have regulations regarding harmonics of input current. For example, in Japan, the Japanese Industrial Standards set limits on the harmonics of the input current. Therefore, the luminaire is provided with a PFC (Power Factor Direction) circuit for suppressing the harmonics of the input current and improving the power factor. A current critical mode is generally used as a method of controlling a PFC circuit in a luminaire. Patent Documents 1 and 2 describe the content of power factor improvement control in the current critical mode. Dedicated control ICs for realizing control in the current critical mode are on the market.

Japanese Patent Application Laid-Open No. 10-294191 Japanese Patent Application Laid-Open No. 2015-213044

In the control in the current critical mode, it is necessary to detect that the current of the inductor used in the power factor improvement circuit becomes zero. As a zero current detecting means for detecting that the inductor current has become zero, for example, a secondary winding provided in the inductor is used. However, immediately after the start of operation of the power factor improving circuit, the output voltage of the secondary winding is small, and zero current cannot be detected accurately.

Therefore, it is conceivable to use a dedicated control IC having a protection function that repeats the switching operation at a constant cycle when the output voltage of the secondary winding cannot be detected. For example, Patent Documents 1 and 2 describe means for switching and controlling a switching element at a predetermined fixed frequency immediately after the power factor improving circuit starts operation, and then changing to a current critical mode.

However, in the above-mentioned control, when the control is changed from the fixed frequency to the current critical mode, the switching frequency of the switching element suddenly changes, and the output voltage of the power factor improving circuit fluctuates greatly. For example, when controlling a light source such as an LED, if the output voltage of the power factor improving circuit fluctuates greatly, the current supplied to the light source fluctuates and the light source flickers.

In order to avoid such an adverse effect, if the number of turns of the secondary winding is increased to obtain a larger output, the loss generated in the secondary winding increases, the inductor becomes large, and zero current is generated. The loss in the circuit to be detected increases.

The present invention has been made to solve the above-mentioned problems, and to provide a power conversion device, a lighting fixture, and an electric device capable of reducing the amount of change in the switching frequency of the switching element of the power factor improving circuit. The purpose.

The power conversion device according to the present invention includes a rectifier circuit that rectifies AC power, a switching element, and an inductor, and a power factor improving circuit that inputs the output of the rectifier circuit and outputs a DC voltage, and the inductor. A detection winding for detecting the voltage generated in the above and a control unit for inputting the voltage detected by the detection winding to drive the switching element, the control unit operates the power factor improving circuit. When the first control for changing the switching frequency of the switching element is executed when started, and then the second control for switching the switching element in synchronization with the voltage obtained by the detection winding is executed. The amount of change in the switching frequency when shifting from the first control to the second control is smaller than the difference value between the switching frequency at the start of the first control and the switching frequency at the start of the second control. It is characterized by doing.

The lighting equipment according to the present invention has a rectifier circuit that rectifies AC power, a switching element, and an inductor, and a power factor improving circuit that inputs the output of the rectifier circuit and outputs a DC voltage, and the inductor. A detection winding for detecting the generated voltage and a control unit for inputting the voltage detected by the detection winding to drive the switching element are provided, and the control unit starts the operation of the power factor improving circuit. When this is done, the first control for changing the switching frequency of the switching element is executed, and then the second control for switching the switching element in synchronization with the voltage obtained by the detection winding is executed. The amount of change in the switching frequency when shifting from the first control to the second control is made smaller than the difference value between the switching frequency at the start of the first control and the switching frequency at the start of the second control. A power conversion device characterized by the above, and a light source which is an LED (Light Voltage) or an organic EL (Electro Voltage) connected to the output of the power conversion device.

The electric device according to the present invention has a rectifier circuit for rectifying AC power, a switching element and an inductor, and a power factor improving circuit for inputting the output of the rectifier circuit and outputting a DC voltage and the inductor. A detection winding for detecting the generated voltage and a control unit for inputting the voltage detected by the detection winding to drive the switching element are provided, and the control unit starts the operation of the power factor improving circuit. When this is done, the first control for changing the switching frequency of the switching element is executed, and then the second control for switching the switching element in synchronization with the voltage obtained by the detection winding is executed. The amount of change in the switching frequency when shifting from the first control to the second control is made smaller than the difference value between the switching frequency at the start of the first control and the switching frequency at the start of the second control. The present invention includes a power conversion device, and a load connected to the output of the power conversion device.

Other features of the present invention will be clarified below.

According to the present invention, immediately after the power factor improving circuit starts operating, the switching element does not use the zero current detector for detecting that the inductor current of the power factor improving circuit has become zero. Since the switching frequency is fluctuated and then the switching element is controlled in synchronization with the signal obtained by the zero current detection unit, it is possible to prevent the switching frequency of the switching element from suddenly changing.

It is a circuit diagram of the lighting equipment which concerns on Embodiment 1. FIG. It is a circuit diagram of a zero current detection part. It is a circuit diagram of a current control circuit. It is a waveform figure which shows the control example of a current control circuit. It is a waveform figure which shows the operation of the power factor improvement circuit. It is a waveform diagram of the current discontinuous mode. It is various waveform diagrams after the start of a boosting operation by a power factor improvement circuit. It is a waveform diagram which shows another control pattern of a switching frequency. It is a flowchart which shows the operation of the lighting equipment which concerns on Embodiment 1. FIG. It is a hardware block diagram of the control part. It is a software configuration diagram of a control unit. It is a waveform diagram of the current continuous mode. It is a waveform figure when the current continuous mode is included in the period of 1st control. It is a waveform diagram which shows the control which concerns on Embodiment 2. It is a waveform diagram which shows another control pattern of a switching frequency. It is a flowchart which shows the operation of the luminaire according to Embodiment 2. It is a circuit diagram of the lighting equipment which concerns on Embodiment 3. It is a waveform figure which shows the vibration of Vpfc.

The power conversion device, the luminaire, and the electric device according to the embodiment of the present invention will be described with reference to the drawings. The same or corresponding components may be designated by the same reference numerals and the description may be omitted. The description of the embodiment does not limit the present invention.

Embodiment 1.
FIG. 1 is a circuit diagram of a lighting fixture 100 according to a first embodiment. The lighting fixture 100 includes a rectifier circuit 3, a power factor improving circuit 5 that suppresses harmonics of a current input from an AC power supply 1 to improve the power factor, and a smoothing capacitor 6 that smoothes the output voltage of the power factor improving circuit 5. And have.

The configuration of the luminaire 100 will be described in detail. An input filter 2 is provided between the AC power supply 1 and the rectifier circuit 3. The input filter 2 has a function of reducing high-frequency noise superimposed on the current input from the AC power supply 1. The input filter 2 has a coil 21 and a capacitor 22. A series circuit having the coil 21 and the capacitor 22 is connected in parallel to the AC power supply 1. One end of the coil 21 is connected to one end of the AC power supply 1, and the other end of the coil 21 is connected to one end of the capacitor 22 and the rectifier circuit 3. The other end of the capacitor 22 is connected to the AC power supply 1 and the rectifier circuit 3.

The rectifier circuit 3 has a function of converting AC power supplied from AC power supply 1 into DC power. That is, the rectifier circuit 3 is a circuit that rectifies AC power. The rectifier circuit 3 is arranged between the input filter 2 and the power factor improving circuit 5. The rectifier circuit 3 is composed of a diode bridge in which four diodes are combined. The configuration of the rectifier circuit 3 is not limited to this, and may be configured by combining a MOSFET (Metal Oxide Semiconductor-Field Effect Transistor) which is a unidirectional conductive element.

A capacitor 4 is connected in parallel to the output of the rectifier circuit 3. One end of the capacitor 4 is connected to the positive electrode side of the DC bus, and the other end of the capacitor 4 is connected to the negative electrode side of the DC bus. The capacitor 4 has a function of smoothing the output voltage of the rectifier circuit 3.

The power factor improving circuit 5 is arranged between the rectifier circuit 3 and the current control circuit 7. The power factor improving circuit 5 is a circuit in which the output of the rectifier circuit 3 is input and a DC voltage is output. The power factor improving circuit 5 includes a switching element 51, an inductor 52, and a diode 53. The switching element 51 is, for example, a MOSFET. The switching element 51 switches the path of the current output from the rectifier circuit 3.

The inductor 52 is formed by winding a primary winding 52a and a secondary winding 52b on the same core. A voltage having a different polarity is applied to the primary winding 52a as the switching element 51 is turned on and off. A voltage corresponding to the applied voltage of the primary winding 52a and the turns ratio n is output to the secondary winding 52b. The secondary winding 52b functions as a detection winding that detects the voltage generated by the inductor 52.

The power factor improving circuit 5 boosts the output voltage of the rectifier circuit 3 and outputs it to the smoothing capacitor 6 by turning the switching element 51 on and off. It also has the function of suppressing the harmonics of the input current and improving the power factor.

FIG. 1 shows an example in which the power factor improving circuit 5 is configured by a boost chopper circuit. The drain of the switching element 51 is connected to the inductor 52 and the diode 53 on the positive electrode side of the DC bus. The source of the switching element 51 is connected to the capacitor 4 and the smoothing capacitor 6 on the negative electrode side of the DC bus. The gate of the switching element 51 is connected to the control unit 9. A control signal output from the control unit 9 is input to the gate of the switching element 51, and on / off of the switching element 51 is controlled. Therefore, the power factor improving circuit 5 is controlled by the control unit 9.

The inductor 52 is arranged between the capacitor 4 and the switching element 51 on the positive electrode side of the DC bus. One end of the inductor 52 is connected to one end of the capacitor 4, and the other end of the inductor 52 is connected to the switching element 51 and the diode 53. The diode 53 is arranged between the switching element 51 and the smoothing capacitor 6 on the positive electrode side of the DC bus. The anode of the diode 53 is connected to the inductor 52 and the switching element 51, and the cathode of the diode 53 is connected to the smoothing capacitor 6.

In addition to the boost chopper circuit, the power factor improving circuit 5 can be configured by a circuit such as a buck-boost chopper circuit, a flyback circuit, a flyforward circuit, a SEPIC, a Zeta converter, and a Cuk converter.

The smoothing capacitor 6 is arranged between the power factor improving circuit 5 and the current control circuit 7 on the DC bus. One end of the smoothing capacitor 6 is connected to the positive electrode side of the DC bus, and the other end of the smoothing capacitor 6 is connected to the negative electrode side of the DC bus. A current control circuit 7 is connected to the smoothing capacitor 6. The current control circuit 7 is a circuit that controls the magnitude of the current output to the LED 8.

A control unit 9 is connected to the switching element 51. The control unit 9 receives the voltage detected by the secondary winding 52b, which is the detection winding, to drive the switching element 51. The control unit 9 includes a switching control unit 91, an input voltage detection unit 92, a zero current detection unit 93, an output voltage detection unit 94, and a drive unit 95.

The switching control unit 91 is provided with the detection results of the input voltage detection unit 92, the zero current detection unit 93, and the output voltage detection unit 94. The switching control unit 91 has an output in which the output voltage Vpfc of the power factor improving circuit 5 is stored in the switching control unit 91 in advance based on the detection results of the input voltage detection unit 92, the zero current detection unit 93, and the output voltage detection unit 94. A control signal for on / off control of the switching element 51 is output so as to match the voltage target value. FIG. 1 shows that the value of Vpfc is equal to the voltage on the high voltage side of the smoothing capacitor 6.

The input voltage detection unit 92 is a means for detecting the voltage of the capacitor 4. The voltage of the capacitor 4 is equal to the input voltage of the power factor improving circuit 5. Therefore, the input voltage detection unit 92 detects the input voltage of the power factor improving circuit 5. The input voltage detection unit 92 transmits a signal related to the detection result to the switching control unit 91.

The output voltage detection unit 94 is a means for detecting the voltage of the smoothing capacitor 6. The voltage of the smoothing capacitor 6 is equal to the output voltage of the power factor improving circuit 5. Therefore, the output voltage detection unit 94 detects the output voltage of the power factor improving circuit 5. The output voltage detection unit 94 transmits a signal related to the detection result to the switching control unit 91.

The input voltage detection unit 92 and the output voltage detection unit 94 can be a voltage divider circuit that divides the detected voltage into a voltage of a size that can be input to the switching control unit 91 by, for example, two resistors connected in series. ..

The zero current detection unit 93 is a means for detecting that the current of the primary winding 52a of the inductor 52 has become zero. The zero current detection unit 93 transmits a signal related to the detection result to the switching control unit 91.

FIG. 2 is a circuit diagram showing a configuration example of the zero current detection unit 93. The zero current detection unit 93 has a Zener diode 932 for voltage limiting and a resistor 931 for current limiting in order to limit the voltage of the secondary winding 52b to a size that can be input to the switching control unit 91. ..

Returning to the description of FIG. The switching control unit 91 includes a storage unit that stores the output voltage target value of the power factor improving circuit 5. The switching control unit 91 sends a signal for on / off control of the switching element 51 based on the voltage detection result of the smoothing capacitor 6 received from the output voltage detection unit 94 and the above-mentioned output voltage target value so that the two match. Output.

The signal output from the switching control unit 91 is converted into a voltage having a size capable of turning the switching element 51 on and off in the drive unit 95, and is output to the gate of the switching element 51.

The current control circuit 7 has a function of converting the DC voltage output from the power factor improving circuit 5 into a DC current that can be input to the LED 8. FIG. 3 is a circuit diagram showing a configuration example of the current control circuit 7. FIG. 3 shows a current control circuit 7 composed of a step-down chopper circuit.

The current control circuit 7 includes a MOSFET 71, an inductor 72, a diode 73, and a capacitor 74. The MOSFET 71 is arranged on the positive electrode side of the DC bus. The drain of the MOSFET 71 is connected to the diode 53 and the smoothing capacitor 6. The source of the MOSFET 71 is connected to the diode 73 and the inductor 72. It is preferable that the gate of the MOSFET 71 is connected to the control unit 9 to input an on / off control signal from the control unit 9 to the gate of the MOSFET 71. The cathode of the diode 73 is connected to the MOSFET 71 and the inductor 72. The anode of the diode 73 is connected to the smoothing capacitor 6 and the capacitor 74.

In addition to the step-down chopper circuit, the current control circuit 7 can be composed of circuits such as a buck-boost chopper circuit, a flyback circuit, a flyforward circuit, a SEPIC, a Zeta converter, and a Cuk converter.

FIG. 4 is a waveform diagram showing a control example of the current control circuit 7. FIG. 4 shows the waveforms of the current I8 flowing through the LED 8, the current I72 flowing through the inductor 72, and the control signal Cs to the MOSFET 71. When an on signal is input to the gate of the MOSFET 71, a current path is formed through the smoothing capacitor 6, the MOSFET 71, the inductor 72, and the capacitor 74, and the current of the inductor 72 increases.

When an off signal is input to the gate of the MOSFET 71, a current path is formed through the inductor 72, the capacitor 74, and the diode 73, and the current of the inductor 72 is reduced to zero. When the predetermined switching cycle Tsw has elapsed, the on signal is input to the MOSFET 71 again, and the switching operation is restarted.

As shown in FIG. 4, the current I72 flowing through the inductor 72 has a triangular wavy waveform. Then, the current output to the LED 8 is smoothed by the capacitor 74. Therefore, the current control circuit 7 outputs the average value of the currents of the inductor 72.

When controlling the current of the LED 8 to dimm the LED 8, the switching cycle Tsw that turns on the MOSFET 71 is made constant, and the on-time Ton is changed. That is, the on-time Ton is adjusted according to the target value of the output current. The ratio of the on-time Ton to the switching period Tsw is called the duty. Such a control method for obtaining a desired output by adjusting the on-time ton is called duty control.

The LED 8 is composed of a group of LEDs in which a plurality of LEDs are connected in series and parallel. One end of the LED group is connected to the positive electrode side of the DC bus, and the other end of the LED group is connected to the negative electrode side of the DC bus.

FIG. 5 is a waveform diagram illustrating an operation example of the power factor improving circuit 5 shown in FIG. FIG. 5 shows waveforms of the current I52 of the inductor 52, the zero current detection signal Sz output from the zero current detection unit 93, the drain voltage Vd of the switching element 51, and the gate voltage Vg of the switching element 51 from above. There is. However, for the sake of explanation, the period for turning on and off the gate voltage of the switching element 51 is described here longer than the actual period.

When the switching element 51 is turned on by the signal from the control unit 9, a closed circuit is formed by the AC power supply 1, the rectifier circuit 3, the inductor 52, and the switching element 51, and the AC power supply 1 is short-circuited via the inductor 52. .. Therefore, a power supply current flows through this closed circuit, the current of the inductor 52 increases, and energy is stored in the inductor 52.

When the on-time set by the switching control unit 91 elapses, the switching element 51 is turned off. As a result, a closed circuit is formed by the inductor 52, the diode 53, and the smoothing capacitor 6, the current of the inductor 52 is reduced, the energy stored in the inductor 52 is released, and the smoothing capacitor 6 is charged.

When the current of the inductor 52 decreases, the voltage of the secondary winding 52b also decreases. The zero current detection unit 93 connected to the secondary winding 52b detects that the current of the inductor 52 becomes zero when the voltage of the secondary winding 52b becomes smaller than a predetermined value, and relates to the detection result. The signal is transmitted to the switching control unit 91. The switching control unit 91 turns on the switching element 51 again after a predetermined delay time elapses after the current of the inductor 52 becomes zero. As a method of providing this delay time, the switching element 51 can be turned on near the bottom of the voltage vibration during the period when the drain voltage of the switching element 51 is free-vibrating. As a result, it is possible to suppress abrupt fluctuations in the drain voltage and suppress noise caused by switching. That is, after the voltage of the secondary winding 52b becomes 0, the switching element 51 is turned on after seeing the falling edge of the first vibration of the drain voltage. This operation is called the current critical mode.

By the on / off operation of the series of switching elements 51, the waveform of the current flowing through the inductor 52 becomes a triangular wave shape. The apex of the triangular wavy waveform becomes a sinusoidal envelope as shown by the dotted line. At this time, the current input from the AC power supply 1 is smoothed by the input filter 2, the average value of the inductor current is input, and a sinusoidal current waveform is obtained to improve the power factor.

The switching control unit 91 receives information on Vpfc, which is the output voltage of the power factor improving circuit 5, from the output voltage detection unit 94, and feedback-controls the on-time of the switching element 51 so that the target Vpfc can be realized.

When the feedback control is performed, if the on-time changes significantly, the envelope at the apex of the current I52 flowing through the inductor 52 does not become a sine wave, and the input current cannot be made a sine wave. Therefore, the response time of the feedback control is set so that the loop gain of the feedback control is 1 times (0 dB) or less in 1/2 cycle or more of one cycle of the AC power supply 1. In other words, the frequency is set to be 1 times (0 dB) or less at a frequency of 2 times or less the frequency of the AC power supply 1. For example, when the power supply frequency is 50 Hz, the constant current feedback control is set to 1 times (0 dB) or less in the half cycle (half wave) of 100 Hz or less, that is, the cycle of 10 msec or more and the constant current feedback control of the power cycle. Set so that it does not respond in a cycle shorter than 1/2. As a result, within 1/2 of the power supply cycle, fluctuations in the on-time of the switching element 51 are suppressed, and the envelope at the apex of the current I52 of the inductor 52 becomes a sinusoidal waveform.

Further, in the feedback control, the same effect can be obtained by setting the update cycle of the on-time to half or longer than half of the cycle of the AC power supply 1.

The output voltage of the secondary winding 52b of the inductor 52 is used to detect that the current of the primary winding 52a of the inductor 52 has become zero. The output voltage of the secondary winding 52b is determined by the voltage VL1 applied to the primary winding 52a and the turns ratio n of the secondary winding 52b to the primary winding 52a. The magnitude of the output voltage of the secondary winding 52b can be expressed by the product of VL1 and n.

The voltage VL1 of the primary winding 52a can be represented by the output voltage Vdb of the rectifier circuit 3 and the output voltage Vpfc of the power factor improving circuit 5. When the switching element 51 is on, the output voltage Vdb of the rectifier circuit 3 is applied to the primary winding 52a, so that VL1 = Vdb. On the other hand, when the switching element 51 is off, the difference between Vpfc and the output voltage Vdb of the rectifier circuit 3 is applied to the primary winding 52a, so that VL1 = Vpfc-Vdb.

Therefore, the output voltage VL2 of the secondary winding 52b when the switching element 51 is on is nVdb. The output voltage VL2 of the secondary winding 52b when the switching element 51 is off is n (Vpfc-Vdb). In the zero current detection unit 93, the output voltage VL2 of the secondary winding 52b is limited to a size that can be input to the switching control unit 91, and a signal is transmitted to the switching control unit 91.

Before the power factor improving circuit 5 starts the boosting operation, Vpfc, which is the output voltage of the power factor improving circuit 5, and the output voltage Vdb of the rectifier circuit 3 are equal. Therefore, immediately after the power factor improving circuit 5 starts the boosting operation, the output voltage VL2 of the secondary winding 52b is zero.

Further, while the power factor improving circuit 5 starts the boosting operation and the output voltage Vpfc of the power factor improving circuit 5 is rising, the output voltage VL2 of the secondary winding 52b is set during the period when the difference between Vpfc and Vdb is small. Not enough voltage can be obtained. Zero current cannot be detected unless the output voltage VL2 of the secondary winding 52b is sufficiently large.

Immediately after the power factor improving circuit 5 starts the boosting operation, there is a method of increasing the turns ratio n in order to obtain a voltage sufficiently large as the output voltage VL2 of the secondary winding 52b. However, when the turns ratio n is large, when Vpfc is sufficiently boosted and VL2 is large, the loss generated by the resistor 931 of the zero current detection unit 93 and the Zener diode 932 increases. Therefore, if the turns ratio n is increased, the circuit efficiency is lowered. Further, since the heat generation of the resistor 931 and the Zener diode 932 increases, it is necessary to take measures such as increasing the component size for heat dissipation.

Further, in order to increase the number of turns of the secondary winding 52b and increase the number of turns ratio n, it is necessary to lengthen the secondary winding 52b, which increases the cost. Further, the inductor 52 becomes large due to the increase in the number of turns of the secondary winding 52b. Therefore, it is not preferable to increase the number of turns of the secondary winding 52b in order to obtain a voltage having a sufficient magnitude as the output voltage VL2 of the secondary winding 52b.

Immediately after the power factor improving circuit 5 starts the boosting operation, it is possible to provide an amplifier circuit in the zero current detection unit 93 in order to obtain a voltage sufficiently large as the output voltage VL2 of the secondary winding 52b. .. However, since the number of parts increases by providing the amplifier circuit, the cost increases, the circuit becomes complicated, and the device becomes large. Therefore, it is not preferable to amplify the output voltage VL2 of the secondary winding 52b by the amplifier circuit.

Therefore, if zero current cannot be detected immediately after the power factor improving circuit 5 starts the boosting operation, it is conceivable that the switching element 51 is forcibly turned on again at a predetermined cycle after the switching element 51 is turned on. FIG. 6 is a waveform diagram when the switching element 51 is switched at a predetermined cycle. The control that exhibits the waveform shown in FIG. 6 is called a current discontinuity mode because the current I52 of the inductor 52 is discontinuous. In this control, the switching element 51 is switched in a predetermined on time and off time. The output voltage VL2 of the secondary winding 52b is not used. As a result, the switching element 51 can be turned on and off at a constant frequency even during a period in which the zero current after the start of the boosting operation of the power factor improving circuit 5 cannot be detected.

When the operation shown in FIG. 6 is continued for a certain period of time, a voltage having a sufficient magnitude as the output voltage VL2 of the secondary winding 52b can be obtained. After the boosting operation of the power factor improving circuit 5 is started, when the magnitude of the output voltage VL2 of the secondary winding reaches a magnitude at which zero current can be detected, the control shifts to the control using the output voltage VL2 of the secondary winding 52b. .. That is, the mode shifts to the current critical mode. Before and after this transition, there is a problem that the switching frequency of the switching element 51 changes abruptly. When the switching frequency of the switching element 51 changes abruptly, Vpfc fluctuates, the output current of the current control circuit 7 connected to the subsequent stage fluctuates, and the optical output of the LED 8 may flicker.

Therefore, in the first embodiment of the present invention, when the secondary winding 52b cannot detect zero current and the switching element 51 is forcibly turned on again, the switching frequency suddenly shifts to the current critical mode. We propose a method to prevent change.

FIG. 7 is a waveform diagram showing various waveforms after the start of the boosting operation by the power factor improving circuit 5 according to the first embodiment. In the period up to time t1, the smoothing capacitor 6 is charged via the diode 53. Since the LED 8 is off until the time t1, the smoothing capacitor 6 is charged and held up to the amplitude peak value of the AC power supply 1. Therefore, the output voltage Vpfc of the power factor improving circuit 5 becomes the peak voltage of the AC power supply 1.

At time t1, the power factor improving circuit 5 starts the boosting operation with the AC power supply 1 connected to the input filter 2. Immediately after the power factor improving circuit 5 starts the switching operation, the difference value ΔV (Vpfc−Vp) between Vp and Vpfc is small, and the output voltage VL2 of the secondary winding 52b required for zero current detection cannot be obtained. During the period P1 in which a sufficient output voltage VL2 cannot be obtained, the switching element 51 is turned on and off by the frequency control predetermined by the switching control unit 91. The "frequency control" is a control for turning on / off the switching element 51 at a predetermined cycle without referring to the output voltage of the secondary winding 52b.

FIG. 7 shows the difference value threshold. The difference value threshold value is the difference value ΔV when Vpfc becomes high and the output voltage VL2 of the secondary winding 52b rises to a detectable extent. When the difference value ΔV reaches the difference value threshold value, control by the current critical mode becomes possible. The period P1 is a period from the time t1 when the boosting operation is started to t2 when the difference value ΔV reaches the difference value threshold value. Frequency control is performed during period P1.

At time t2, Vpfc is boosted, the difference value ΔV rises, and the output voltage VL2 of the secondary winding 52b rises to a detectable level. The switching control unit 91 stores the difference value threshold value, and detects that the difference value ΔV exceeds the difference value threshold value. When the switching control unit 91 detects that the difference value ΔV exceeds the difference value threshold value, the switching control unit 91 changes the control of the switching element 51 from the frequency control to the current critical mode. The period after the transition to the current critical mode is shown as period P2.

FIG. 7 shows that the switching frequency was increased as the difference value ΔV increased during the period P1 in which the power factor improving circuit 5 was frequency-controlled. That is, in the period P1, the switching frequency of the switching element 51 is not constant, and the switching frequency of the switching element 51 is increased as time elapses. As a result, it is possible to reduce the change in the switching frequency when shifting from the frequency control to the current critical mode. It is preferable to change the switching frequency in the period P1 so that the switching frequency at the end of the frequency control matches the average switching frequency in the current critical mode control.

FIG. 8 is a waveform diagram showing another control pattern of the switching frequency. In the period P1 for frequency control of the switching element 51, the switching frequency is increased as the difference value ΔV becomes larger. In this example, ΔF1, which is the difference between the switching frequency f2 at the end of the frequency control and the average frequency f3 in the current critical mode control, is the switching frequency f1 at the time t1 when the frequency control is started and the average frequency f3 in the current critical mode control. It is smaller than the difference value ΔF2 of. This is an effect obtained by increasing the switching frequency in the period P1 and making f2 larger than f1. In either case of FIGS. 7 and 8, since the sudden change in the switching frequency at the time t2, which is the timing of the control change, can be suppressed, the output voltage fluctuation of the power factor improving circuit 5 can be suppressed.

The control unit 9 performs the above-mentioned control. That is, the control unit 9 executes the first control for changing the switching frequency of the switching element 51 when the operation of the power factor improving circuit 5 is started, and then the switching element is synchronized with the voltage obtained in the detection winding. The second control for switching 51 is executed. In this embodiment, the frequency control corresponds to the first control and the current critical mode corresponds to the second control. Then, in this case, the control unit 9 sets ΔF1, which is the difference in switching frequencies when shifting from the first control to the second control, between the switching frequency at the start of the first control and the switching at the start of the second control. Make it smaller than the difference value ΔF2 from the frequency. FIG. 8 discloses a control for making ΔF1 smaller than ΔF2. In FIG. 7, in the first control, the switching frequency of the switching element 51 is continuously changed, and the switching frequency of the switching element 51 at the end of the first control is set to the switching frequency of the switching element 51 at the start of the second control. It has been shown to match. The amount of change in the switching frequency when shifting from the first control to the second control is preferably zero. However, if ΔF1 is made smaller than ΔF2, the fluctuation of Vpfc can be suppressed, so that there is an effect of suppressing the flicker of the light source.

FIG. 9 is a flowchart showing the operation of the lighting fixture 100 according to the first embodiment. When the power factor improvement circuit 5 is turned on, the control unit 9 is activated in step S1. Next, in step S2, the input voltage detection unit 92 detects the input voltage peak value Vp. The input voltage peak value Vp is the voltage peak value at the location described as Vp in FIG. Next, in step S3, the output voltage detection unit 94 detects Vpfc.

After that, in step S4, the switching control unit 91 calculates the difference value ΔV (Vpfc−Vp). The calculation of the difference value ΔV is executed at a predetermined cycle. When the periodic calculation of the difference value ΔV is started, the boosting operation by the power factor improving circuit 5 is started in step S5. As a result, the frequency control described above starts.

After the start of the boosting operation of the power factor improving circuit 5, in step S6, the magnitude of the difference value ΔV and the difference value threshold value is determined. If the difference value ΔV is smaller than the difference value threshold value, frequency control is continued in step S7, Vpfc is detected again in step S8, and the difference value Δ is calculated using the latest Vpfc in step S9.

On the other hand, when the difference value ΔV is equal to or larger than the difference value threshold value, the frequency control shifts to the current critical mode in step S10. The switching frequency of the switching element 51 at the start of the current critical mode is determined by the load and the circuit constant. After that, the operation using the secondary winding 52b is continued, and the sequence is completed. In this way, the control unit 9 shifts from the first control to the second control when the difference value ΔV between Vp and the output voltage Vpfc reaches a predetermined difference value threshold value.

The switching control unit 91 can be configured by combining commercially available analog ICs. When the switching control unit 91 is configured by combining analog ICs, a circuit for calculating the difference value ΔV, determining the magnitude of the difference value ΔV and the difference value threshold value, and changing the control from the first control to the second control. Becomes complicated and the number of parts increases. Therefore, the switching control unit 91 can simplify the circuit configuration and suppress an increase in the number of parts by realizing the software as software using an arithmetic unit such as a microcomputer or a CPU.

Each function of the drive unit 95 and the switching control unit 91 of FIG. 1 is realized by the receiving device 9a and the processing circuit 9b of FIG. The receiving device 9a is a device that receives various information input to the switching control unit 91. The processing circuit 9b is dedicated hardware. The processing circuit 9b corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. Each function of the drive unit 95 and the switching control unit 91 may be realized by the processing circuit 9b, or the functions of each unit may be collectively realized by the processing circuit 9b.

FIG. 11 is a block diagram showing a control unit 9 realized by software. In this case, the input voltage detection unit 92, the zero current detection unit 93, and the output voltage detection unit 94 of FIG. 1 are the receiving device 30 of FIG. When the processing circuit is a CPU, each function of the switching control unit 91 and the drive unit 95 in FIG. 1 is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 34. The processor 32, which is a processing circuit, realizes the functions of each part by reading and executing the program stored in the memory 34. That is, there is a memory 34 for storing a program in which the operation described in the flowchart of FIG. 9 and the first embodiment is eventually executed. It can also be said that this program causes a computer to execute the above procedure or method. Here, the memory corresponds to, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD. It should be noted that a part of each function of the control unit 9 may be realized by dedicated hardware, and a part may be realized by software or firmware.

The above-mentioned configuration and control method can be variously modified without losing its characteristics. Hereinafter, some modification examples will be described. In the first embodiment, it is important to change the switching frequency of the switching element 51 in the period P1 immediately after the start of the boosting operation shown in FIG. 7, for example. The process of change is not particularly limited. The switching frequency of the switching element 51 may be continuously increased over the entire period P1, or the switching frequency of the switching element 51 may be increased in a part of the period P1. The switching frequency may be increased stepwise during the period P1.

In the first embodiment, the lighting fixture 100 using the rectifier circuit 3, the power factor improving circuit 5, the secondary winding 52b used as the detection winding, and the power conversion circuit having the control unit 9 for controlling the LED 8 will be described. did. That is, the output of this power conversion circuit was connected to the LED 8 via the current control circuit 7. However, this power conversion circuit can be generally used for devices to which power is input. For example, a load such as a motor can be connected to the output of this power converter. This power converter and load are collectively called electrical equipment.

In the first embodiment, after performing frequency control in the current discontinuous mode shown in FIG. 6, the mode shifts to the current critical mode. In other words, during the period of the first control, the switching element 51 was turned on and off in the current discontinuous mode. However, the switching element 51 may be turned on and off in the current continuous mode during the period of the first control. FIG. 12 is a waveform diagram when the switching element 51 is operated in the current continuous mode. The current continuous mode is a control method for turning on the switching element 51 before the current I 52 of the inductor 52 becomes zero. Similar to the current discontinuous mode, the current continuous mode is a control method of the switching element 51 that does not refer to the output voltage VL2 of the secondary winding 52b.

FIG. 13 is a waveform diagram when the control in the current continuous mode is adopted during the period of the first control. The power factor improving circuit 5 is operated in the current discontinuous mode during the period from time t1 to time ta, and the power factor improving circuit 5 is operated in the current continuous mode during the period from time ta to time t2. The current continuous mode is a mode that operates at a higher switching frequency than the current critical mode. The amount of change ΔF1 of the switching frequency when shifting from the first control to the second control is made smaller than the difference value ΔF2 between the switching frequency f1 at the start of the first control and the switching frequency f2 at the start of the second control. Therefore, it is possible to avoid a sudden change in the switching frequency when the control is changed.

As described above, the control unit 9 operates the switching element 51 in the current discontinuous mode or the current continuous mode during the first control period, and operates the switching element 51 in the current critical mode during the second control period. Can be done.

In the first embodiment, the case where the light source is the LED 8 has been described, but a light source different from the LED such as an organic EL (Electro Luminescence) may be used. The modified example described in the first embodiment can also be applied to the power conversion device, the luminaire, and the electric device according to the following embodiment. Since the power conversion device, the luminaire, and the electric device according to the following embodiments have much in common with the first embodiment, the differences from the first embodiment will be mainly described.

Embodiment 2.
In the first embodiment, the frequency control is shifted to the current critical mode when the difference value ΔV reaches the difference value threshold value, but in the second embodiment, the control is shifted by paying attention to the output voltage Vpfc.

FIG. 14 is a waveform diagram showing the control according to the second embodiment. The smoothing capacitor 6 is charged via the diode 53 until the AC power supply 1 is connected and the power factor improving circuit 5 starts the boosting operation. Since the LED 8 is turned off during this period, the smoothing capacitor 6 is charged and held up to the amplitude peak value of the AC power supply 1. Therefore, the output voltage Vpfc of the power factor improving circuit 5 becomes the peak voltage of the AC power supply 1.

The input voltage peak value Vp is detected by the input voltage detection unit 92 before the time t1 when the operation of the power factor improvement circuit 5 starts. The detected Vp information is transmitted to the switching control unit 91. The switching control unit 91 stores a program or table for deriving a threshold value of Vpfc at which the output voltage VL2 can be detected from the information of Vp. The threshold value of Vpfc at which the output voltage VL2 can be detected is called the output voltage threshold value. The switching control unit 91 calculates the output voltage threshold value corresponding to the Vp information received from the input voltage detection unit 92 by the above-mentioned program or table.

At time t1, the power factor improving circuit 5 starts the boosting operation. At the initial stage of the boosting operation, the output voltage VL2 of the secondary winding 52b required for zero current detection cannot be obtained, so the power factor improving circuit 5 is frequency-controlled. When Vpfc is boosted after the power factor improving circuit 5 starts the switching operation, the output voltage VL2 rises to a detectable level.

The switching control unit 91 changes the control of the switching element 51 from the frequency control to the current critical mode when the Vpfc exceeds the output voltage threshold value calculated earlier. In other words, the control unit 9 shifts from the first control to the second control when the output voltage Vpfc reaches a predetermined output voltage threshold value. By changing the control at the timing when Vpfc reaches the output voltage threshold value in this way, the calculation of the difference value ΔV required in the first embodiment becomes unnecessary, so that the calculation load of the switching control unit 91 can be reduced.

Further, in the period P1 in which the power factor improving circuit 5 is frequency-controlled, the switching frequency is increased as Vpfc becomes larger to prevent the switching frequency from suddenly changing when shifting from the frequency control to the current critical mode. did. FIG. 14 shows that the switching frequencies were matched before and after the control was changed from the frequency control to the current critical mode. In this way, it is preferable to match the switching frequency at the end of frequency control with the average frequency of switching at the beginning of current critical mode control.

FIG. 15 is a waveform diagram showing another control pattern of the switching frequency. By increasing the switching frequency as Vpfc increases during the period of frequency control of the power factor improving circuit 5, the amount of change ΔF3 of the switching frequency when shifting from the first control to the second control is set at the start of the first control. It can be made smaller than the difference value ΔF4 between the switching frequency and the switching frequency at the start of the second control.

FIG. 16 is a flowchart showing a control method of the lighting equipment according to the second embodiment. When the power is turned on, the control unit 9 is activated in step Sa. Next, in step Sb, the switching control unit 91 receives Vp information from the input voltage detection unit 92. For example, it receives information that the effective value of Vp is 100V, 200V or 242V. Then, the switching control unit 91 calculates the output voltage threshold value corresponding to Vp. By storing the correspondence between Vp and the output voltage threshold value as a table in the switching control unit 91, the output voltage threshold value can be derived using the table. In this way, the output voltage threshold value is determined from Vp at the start of operation of the power factor improving circuit 5. If Vp is high, the output voltage threshold value is preferably high, and if Vp is low, the output voltage threshold value is preferably low.

Then, the process proceeds to step Sc. In step Sc, the power factor improving circuit 5 starts operating by starting the switching element 51 on and off based on the command from the switching control unit 91. In the initial stage of the operation of the power factor improving circuit 5, the switching element 51 is frequency-controlled. Next, in step Sd, the switching control unit 91 determines the magnitude of Vpfc and the output voltage threshold value detected by the output voltage detection unit 94. If Vpfc is smaller than the output voltage threshold value, the process proceeds to step Se and frequency control is continued. After that, Vpfc is detected again in step Sf, and the determination in step Sd is performed again. If it is determined in step Sd that Vpfc is equal to or higher than the output voltage threshold value, the process proceeds to step Sg and the current critical mode is entered. After that, the control in the current critical mode is continued.

In the second embodiment, the control unit 9 determines the output voltage threshold value by Vp, which is a value reflecting the input voltage to the power factor improving circuit 5. That is, the output voltage threshold is variable. However, when the Vp of the power converter is predetermined, the process of determining the output voltage threshold is unnecessary. For example, if the power conversion device is a product dedicated to AC100V, the process of determining the output voltage threshold is unnecessary, and one predetermined output voltage threshold can be used.

Embodiment 3.
FIG. 17 is a circuit diagram of the luminaire 200 according to the third embodiment. The luminaire 200 basically operates in the same manner as the luminaire 100 described in the first embodiment. In the first embodiment, the control unit 9 mainly controls the power factor improving circuit 5, but the control unit 9 of the third embodiment controls not only the power factor improving circuit 5 but also the current control circuit 7. The current control circuit 7 is a circuit that is connected to the output of the power factor improving circuit 5 and converts the DC voltage output from the power factor improving circuit 5 into a DC current.

The control unit 9 of the third embodiment includes a current detecting unit 10 for detecting the current flowing through the LED 8 and a current detecting unit 96 for receiving the output of the current detecting means 10. For example, a shunt resistor or a Hall sensor can be used as the current detecting means 10. The current detection unit 96 sends LED current information to the switching control unit 91. The switching control unit 91 controls the current output by the current control circuit 7 by controlling the MOSFET 71 on and off using the drive unit 95.

If there is any change in the frequency at the timing of changing the control of the switching element 51 of the power factor improving circuit 5 from the frequency control to the current critical mode, the Vpfc vibrates. FIG. 18 is a waveform diagram showing that Vpfc vibrates as the control is changed. FIG. 18 shows that vibration is generated at Vpfc from the time t2, which is the timing of the control change, and the vibration is attenuated with the passage of time. This vibration is attenuated in, for example, about 100 msec.

In order to keep the output of the current control circuit 7 constant, it is necessary to respond to the vibration of Vpfc at high speed. Therefore, the control unit 9 of the third embodiment has a predetermined period before the transition from the first control to the second control, a predetermined period after the transition from the first control to the second control, and a force. The response speed of the current control circuit 7 is increased as compared with the state where the output voltage Vpfc of the power factor improving circuit 5 is stable at a constant value. The response speed of the current control circuit 7 is a speed at which the detection result of the current detection unit 96 is reflected in the control of the MOSFET 71. The higher the response speed of the current control circuit 7, the more quickly the detection result of the current detection unit 96 is reflected in the control of the MOSFET 71.

For example, the response speed of the current control circuit 7 in the period from 100 msec before the time t2 to 100 msec after the time t2 is made higher than the response speed of the current control circuit 7 after t3 when Vpfc reaches the target value. In other words, the response speed of the current control circuit 7 is made higher than the period after t3 only for a short period before and after the control change of the switching element 51. As a result, the output of the current control circuit 7 can be kept substantially constant.

The period for increasing the response speed of the current control circuit 7 is referred to as a high-speed response period. In order to execute the above-mentioned control, the switching control unit 91 must specify the high-speed response period. Since the switching control unit 91 is the control body of the power factor improving circuit 5, the high-speed response period can be easily specified. That is, since the switching control unit 91 periodically compares the difference value ΔV and the difference value threshold value, the timing of the control change is approaching, the timing of the control change has come, and a certain period after the control change. Can be detected that has passed. From these detection results, the above-mentioned high-speed response period can be easily specified.

In this way, by controlling the power factor improving circuit 5 and the current control circuit 7 using one control unit 9, the response speed of the current control circuit 7 can be increased when the control of the power factor improving circuit 5 is changed. .. As a result, it is possible to prevent the LED 8 from flickering due to fluctuations in the current flowing through the LED 8 due to a slight vibration of Vpfc generated when the control is changed in the power factor improving circuit 5.

The method described in the third embodiment is effective for any control in which the switching frequency can fluctuate to some extent at the timing of the control change of the switching element 51. Therefore, the method of the third embodiment can be combined with the control method of the switching element 51 described in the first and second embodiments or modifications thereof.

In addition, the effect of the present invention may be enhanced by combining the technical features described in each of the above embodiments.

5 Power factor improvement circuit, 51 switching element, 52 inductor, 52a primary winding, 52b secondary winding, 9 Control unit

Claims (11)

A rectifier circuit that rectifies AC power and
A power factor improving circuit that has a switching element and an inductor, receives the output of the rectifier circuit, and outputs a DC voltage.
A detection winding that detects the voltage generated by the inductor and
A control unit for inputting a voltage detected by the detection winding and driving the switching element is provided.
When the operation of the power factor improving circuit is started, the control unit executes a first control for changing the switching frequency of the switching element, and then the switching element synchronizes with the voltage obtained in the detection winding. When the second control for switching the above is executed, the amount of change in the switching frequency when shifting from the first control to the second control is the switching frequency at the start of the first control and the second control. A power conversion device characterized in that the difference value from the switching frequency at the start of is smaller than that of the switching frequency. In the first control, the switching frequency of the switching element is continuously changed, and the switching frequency of the switching element at the end of the first control matches the switching frequency of the switching element at the start of the second control. The power conversion device according to claim 1, wherein the power conversion device is used. It is provided with an output voltage detection unit that detects the output voltage of the power factor improving circuit.
The power conversion device according to claim 1 or 2, wherein the control unit changes the switching frequency of the switching element in the first control according to the output of the output voltage detection unit. An input voltage detection unit that detects the input voltage of the power factor improving circuit,
An output voltage detection unit for detecting the output voltage of the power factor improving circuit is provided.
Claim 1 or 2 characterized in that the control unit shifts from the first control to the second control when the difference value between the input voltage and the output voltage reaches a predetermined difference value threshold value. The power converter described in. It is provided with an output voltage detection unit that detects the output voltage of the power factor improving circuit.
The power conversion device according to claim 1 or 2, wherein the control unit shifts from the first control to the second control when the output voltage reaches a predetermined output voltage threshold value. It is provided with an input voltage detection unit that detects the input voltage of the power factor improving circuit.
The power conversion device according to claim 5, wherein the control unit determines the output voltage threshold value based on the input voltage. The power conversion device according to any one of claims 1 to 6, wherein the amount of change in the switching frequency when shifting from the first control to the second control is zero. The control unit is characterized in that the switching element is operated in the current discontinuous mode or the current continuous mode during the period of the first control, and the switching element is operated in the current critical mode during the period of the second control. The power conversion device according to any one of claims 1 to 7. A current control circuit that is connected to the output of the power factor improving circuit and converts the DC voltage output from the power factor improving circuit into a DC current is provided.
The control unit improves the power factor for a predetermined period before the transition from the first control to the second control and a predetermined period after the transition from the first control to the second control. The power conversion device according to any one of claims 1 to 8, wherein the response speed of the current control circuit is increased as compared with a state in which the output voltage of the circuit is stable at a constant value. The power conversion device according to any one of claims 1 to 9,
A luminaire comprising an LED (Light Emitting Diode) or an organic EL (Electro Luminescence) light source connected to the output of the power converter. The power conversion device according to any one of claims 1 to 9,
An electrical device comprising: a load connected to the output of the power converter.

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