JP3570173B2 - Control circuit provided in a device that generates direct current from alternating current - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control circuit provided in a device that generates direct current from alternating current, and particularly to a circuit that improves the power factor of the device.
[0002]
[Prior art]
In recent years, power electronics technology has been widely used in various fields such as industrial equipment, home electric appliances, and OA equipment. These devices often convert a commercial AC power supply into a DC voltage and operate an internal circuit using the DC voltage, or charge a battery using the DC voltage. As an example, a charger for charging a battery using a commercial AC power supply will be described and its configuration will be described.
[0003]
FIG. 7 is a configuration diagram of an example of an existing charger. Here, a charger having a voltage boosting type converter function is used.
This charger rectifies a commercial alternating current (full-wave rectification) using a rectifier 21, and charges a battery while adjusting a supply current by switching a switching element 22 by a PWM method by a control circuit 10. The control circuit 10 includes an output error amplifier 11, a multiplier 12, a current error amplifier 13, and a comparator 14, and generates a control signal for adjusting a current.
[0004]
The output error amplifier 11 amplifies an error between the output voltage and the target voltage value. The target voltage value is given, for example, according to the standard and state of the battery charged by this charger. The multiplier 12 multiplies the input voltage rectified by the rectifier 21 and the output of the output error amplifier 11. The current error amplifier 13 amplifies an error between the current detected by the current sensor 23 and the output of the multiplier 12. The comparator 14 compares the level of the triangular wave generated by the triangular wave generation circuit 24 with the output level of the current error amplifier 13, and outputs a pulse signal having a duty determined by the result of the comparison.
[0005]
In the charger having the above configuration, a control signal for making the output of the multiplier 12 and the current detected by the current sensor 23 coincide with each other is generated by the control circuit 10, and the current is adjusted by feedback control using the control signal. Is done. As described above, the current detected by the current sensor 23 is controlled by the feedback control so as to match the output of the multiplier 12, so that the output of the multiplier 12 is used as the “target current” of the charger. Plays a role.
[0006]
[Problems to be solved by the invention]
However, there is no multiplier having ideal characteristics for use in the above-described configuration. That is, as shown in FIG. 8A, the ordinary multiplier has poor linear characteristics particularly when the input voltage is small. Therefore, in the configuration shown in FIG. 7, when the input voltage is multiplied by the output of the output error amplifier 11 by the multiplier 12, an output waveform obtained from the input voltage is distorted. This is shown in FIG.
[0007]
FIG. 8B is a diagram illustrating an output waveform of the multiplier 12. In the above charger, the input voltage has a waveform that draws a sine curve. Therefore, the waveform obtained by multiplying the input voltage by the output of the output error amplifier 11 should ideally be a sine curve. However, in practice, since the linear characteristic of the multiplier 12 is poor, a part of the waveform output from the multiplier 12 is distorted.
[0008]
Here, the output of the multiplier 12 is the “target current” of the charger as described above. For this reason, the waveform of the input current is adjusted to match the output of the multiplier 12, and is distorted similarly to the output waveform of the multiplier 12. When the waveform of the input current is distorted in this way, a slight difference occurs between the phase of the input current and the phase of the input voltage, and the power factor deteriorates. When the power factor deteriorates, the effective value of the input current when the same power is output increases.
[0009]
Further, as shown in FIG. 8B, when a state occurs in which the waveform is distorted and the inclination with respect to the time axis is large, as is well known to those skilled in the art, the harmonic component (harmonic current) of the current increases. I do. It is said that harmonic currents cause malfunctions of other electronic devices, and are considered to be regulated. Therefore, it is desirable to keep the harmonic current as low as possible. Note that there is a close relationship between the power factor and the harmonic current, and generally, when the power factor deteriorates, the harmonic current increases.
[0010]
An object of the present invention is to provide a circuit that improves a power factor when generating a direct current from an alternating current and suppresses a harmonic current.
[0011]
[Means for Solving the Problems]
The control circuit of the present invention is provided in a device that generates DC from AC using a switch, and has the following units. The pulse generation means generates a pulse signal having a frequency higher than the frequency of the alternating current and having a duty corresponding to an error between a specified value and the output of the device. The chopper section chops the AC voltage waveform signal using the pulse signal generated by the pulse generating section. The averaging means averages the output of the chopper means. The control signal generating means outputs a control signal for controlling the switch based on an error between an output of the averaging means and a current flowing through the device.
[0012]
In the above configuration, the chopper means is on / off controlled in accordance with the pulse signal. In the on state, the chopper means faithfully outputs a voltage waveform signal. Then, the output of the chopper means is smoothed by the averaging means. Therefore, the output of the averaging means has a waveform in which the amplitude of the input voltage waveform is changed according to the duty of the pulse signal. As a result, the phases of the input voltage and the input current completely match, and the power factor is improved. In addition, since the input current is adjusted by the control signal generating means so as to match the output of the averaging means, the input current changes smoothly, and the harmonic current is suppressed.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. In the following, as an example, a configuration and operation of a control circuit that improves a power factor and suppresses a harmonic current by using a charger that charges a battery using a commercial AC power supply will be described.
[0014]
FIG. 1 is a configuration diagram of a charger provided with a control circuit of the present embodiment. Among the reference numerals used in FIG. 1, those used in FIG. 7 indicate the same parts. That is, the control circuit of the present embodiment is basically configured such that the output error amplifier 11 and the multiplier 12 of the conventional control circuit 10 are replaced with a CPU 31, a chopper circuit 32, and an averaging circuit 33. Hereinafter, the configuration and operation of the control circuit of the present embodiment will be described.
[0015]
This charger uses a rectifier 21 to rectify commercial alternating current (full-wave rectification), and controls a switching element 22 by a PWM method by a control circuit 30 to charge a battery while adjusting a supply current. The control circuit 30 includes a CPU 31, a chopper circuit 32, an averaging circuit 33, a current error amplifier 13, and a comparator 14, and generates a control signal for adjusting a current.
[0016]
The CPU 31 generates a pulse signal having a duty determined based on an output voltage (battery voltage) of the charger, an output current of the charger (current supplied to the battery), and an instruction notified from the battery unit 40. I do. The frequency of this pulse signal is sufficiently higher than the input AC frequency (50/60 Hz), for example, about 20 kHz. The output voltage is divided to a level that can be processed by the CPU 31. The output current is detected by the output current sensor 25.
[0017]
An example of a process in which the CPU 31 generates the pulse signal will be described with reference to FIG. Here, it is assumed that battery unit 40 instructs the charger on the power value for charging the battery based on the current state of charge and the like. This instruction may be, for example, the wattage at the time of charging, or a ratio (percentage) of the wattage at the time of charging to the capacity of the battery unit 40. Shall be instructed. Further, the CPU 31 includes a duty value holding memory (not shown), and generates a pulse signal having the held duty.
[0018]
In step S1, the instruction notified from the battery unit 40 is recognized. In this embodiment, the power value W is recognized. In step S2, the output voltage (battery voltage) V of the charger is detected. In step S3, the output current I detected by the output current sensor 25 is recognized. In step S4, W / V is calculated from the power value W recognized in step S1 and the voltage V detected in step S2. This value is a target value of the current to be supplied to the battery unit 40. Then, the calculated value is compared with the output current I recognized in step S3.
[0019]
If W / V> I, it is determined that the current output current is smaller than the target value, and in step S5, the current duty value is retrieved from the duty value holding memory and is increased by a predetermined amount. Then, in step S6, the duty value holding memory is updated according to the correction in step S5. On the other hand, if W / V <I, it is determined that the current output current is larger than the target value, and in step S7, the current duty value is extracted from the duty value holding memory and the value is reduced by a predetermined amount. . Then, in step S8, the duty value holding memory is updated according to the correction in step S7. If W / V = I, it is considered that the current output current matches the target value, and the duty value holding memory is not updated. When the duty of the output pulse of the CPU 31 is increased, the output current of the charger increases accordingly. In step S9, a pulse signal having the duty value held in the duty holding memory is generated and output.
[0020]
The above processing is repeatedly executed at predetermined time intervals by, for example, a timer interrupt or the like. The method of correcting the duty may be a simple method as in the example of the flowchart, but may be corrected using, for example, PID calculation.
[0021]
Thus, CPU 31 generates and outputs a pulse signal for charging the battery with the power indicated by the instruction from battery unit 40. This pulse signal is supplied to the chopper circuit 32.
[0022]
Chopper circuit 32 includes transistors Q1 and Q2. The transistors Q1 and Q2 are an npn transistor and a pnp transistor, respectively, and are connected in series with each other. A signal obtained by dividing the voltage rectified (for example, full-wave rectified) by the rectifier 21 (hereinafter, this signal is referred to as a “voltage waveform signal”) is applied to the collector of the transistor Q1. The output of the CPU 31 is supplied to each control terminal (base) of the transistors Q1 and Q2. When the pulse signal output from CPU 31 is at "H" level, transistor Q1 is turned on and transistor Q2 is turned off. On the other hand, when the pulse signal is at "L" level, transistor Q1 is turned off. At the same time, the transistor Q2 is turned on.
[0023]
The input waveform and output waveform of the chopper circuit 32 will be described with reference to FIG. A full-wave rectified voltage waveform signal is applied to the chopper circuit 32, as shown in the upper part of FIG. In this state, when a pulse signal is supplied from the CPU 31 shown in the middle part of FIG. 3 to the control terminals of the transistors Q1 and Q2, the output voltage of the chopper circuit 32 becomes as shown in the lower part of FIG. That is, when the pulse signal output from CPU 31 is at "H" level, transistor Q1 is on and transistor Q2 is off, so that the output potential of chopper circuit 32 is at the same level as the voltage waveform signal. On the other hand, when the pulse signal output from CPU 31 is at "L" level, transistor Q1 is off and transistor Q2 is on, so that the output potential of chopper circuit 32 is at the ground level.
[0024]
Thus, the voltage waveform signal is chopped in the chopper circuit 32 according to the pulse signal generated by the CPU 31. Here, the switching speed of the transistors Q1 and Q2 is sufficiently high as compared with the input AC frequency and the pulse signal generated by the CPU 31. Therefore, when the transistor Q1 is on, the chopper circuit 32 can faithfully output the voltage waveform signal rectified by the rectifier 21.
[0025]
The averaging circuit 33 is a general RC circuit, and includes a resistor R and a capacitor C. FIG. 4 shows a processing example by the averaging circuit 33. The averaging circuit 33 averages (smooths) the output of the chopper circuit 32. The output of the chopper circuit 32 changes according to the duty of the pulse signal generated by the CPU 31. Therefore, the output of the averaging circuit 33 is adjusted according to the duty of the pulse signal generated by the CPU 31. FIGS. 4A and 4B show output voltages of the averaging circuit 33 when the duty of the pulse signal generated by the CPU 31 is 30% and 80%, respectively.
[0026]
In FIG. 4A and FIG. 4B, the frequency of the pulse signal is drawn at a lower speed than the actual one in order to explain the concept of averaging. The output of the chopper circuit 32 is smoothly averaged by the averaging circuit 33 because the output is significantly larger than the AC frequency. That is, the averaging circuit 33 acts as a so-called smoothing circuit. Conversely, the frequency of the pulse signal generated by the CPU 31 is set to such a frequency that the averaging circuit 33 smoothly averages the pulse signal by RC. Further, as described above, the switching speed of transistors Q1 and Q2 is sufficiently high, and when transistor Q1 is on, chopper circuit 32 faithfully outputs its input voltage (voltage waveform signal). Therefore, the output of the averaging circuit 33 is proportional to the voltage waveform signal as shown in FIG. This proportional coefficient is determined by the duty of the pulse signal generated by the CPU 31. Then, the output waveform of the averaging circuit 33 becomes a sine curve of the same phase having a different amplitude from that of the voltage waveform signal, as shown in FIG.
[0027]
The output of the averaging circuit 33 is supplied to the current error amplifier 13. The current error amplifier 13 amplifies an error between the output of the averaging circuit 33 and the current sensor 23. The comparator 14 compares the level of the triangular wave generated by the triangular wave generation circuit 24 with the output level of the current error amplifier 13 in the same manner as the existing configuration shown in FIG. Is output.
[0028]
In the charger of the present embodiment shown in FIG. 1, a control signal for causing the current detected by the current sensor 23 to coincide with the output of the averaging circuit 33 is generated by the control circuit 30, and feedback control using the control signal is performed. Adjusts the current. That is, in this charger, the output of the averaging circuit 33 plays a role as “target current: target value of input current”.
[0029]
Next, the power factor and the harmonic current will be discussed. The power factor increases as the phase difference between the input voltage and the input current decreases. Here, the input current is adjusted so as to coincide with the output of the averaging circuit 33 which is the target current of the charger. As described above, the output of the averaging circuit 33 divides the input voltage by dividing the input voltage. The output waveform of the averaging circuit 33 is in a sine curve having the same phase as the input voltage and no distortion since it is proportional to the voltage waveform signal which is the obtained signal. Therefore, the phase of the input voltage almost completely matches the phase of the input current, and a high power factor can be obtained.
[0030]
The harmonic current increases due to a sudden change in the current, that is, a sharp rise in the current waveform. However, in the present embodiment, the target input current is generated using a chopper circuit having a very high response speed as compared with the multiplier and an averaging circuit for smoothing the output. Therefore, the target input current smoothly changes following the input voltage waveform. As a result, the actual current waveform matched with the target input current also changes smoothly without any distortion, so that the harmonic current is suppressed.
[0031]
In the above embodiment, the CPU 31 has a role of converting an output error into a pulse signal having a duty corresponding to the output error, but this role may be provided by another configuration. For example, as shown in FIG. 6A, the present invention may be realized by a configuration in which an error amplifier 51 and a comparator 52 are provided. In this case, the error amplifier 51 detects and outputs an error between the externally specified target voltage and the actual output voltage of the charger, or detects the error from the externally specified target current and the current sensor 25. An error from the actual output current is detected and output. Further, the comparator 52 compares the output level of the error amplifier 51 with the level of the triangular wave, and outputs a pulse signal having a duty obtained based on the comparison result. It is assumed that the frequency of the triangular wave is sufficiently higher than the frequency of the input alternating current. Then, the output of the comparator 52 is supplied to the chopper circuit 32.
[0032]
In the above embodiment, the chopper circuit 32 is configured to include two switching elements (transistors Q1 and Q2) as an example. However, another configuration may be used. As another configuration, for example, as shown in FIG. 6B, a circuit including one switching element (transistor Q3) and a resistor can be considered. In this case, a pulse signal generated by the CPU 31 is supplied to a control terminal (base) of the transistor Q3 while supplying a voltage waveform signal to the transistor Q3.
[0033]
Furthermore, in the above embodiment, the averaging circuit 33 includes a resistor and a capacitor, but may have another form.
In the above embodiment, the charger is adopted as a device to which the control circuit of the present invention is applied. However, the present invention is not limited to this, and controls a process of generating a direct current from an alternating current. Can be widely used as a circuit.
[0034]
【The invention's effect】
According to the present invention, since the power factor is improved, the effective value of the input current when obtaining the same output power is reduced. Further, at this time, since the AC current waveform is not distorted, the harmonic current is suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a charger provided with a control circuit of the present embodiment.
FIG. 2 is a flowchart illustrating a process in which a CPU generates a pulse signal.
FIG. 3 is a diagram illustrating input and output of a chopper circuit.
FIG. 4 is a diagram illustrating input and output of an averaging circuit.
FIG. 5A is a diagram illustrating a relationship between an input voltage and an output of an averaging circuit, and FIG. 5B is a diagram illustrating a relationship between a voltage and a current.
FIG. 6A is a circuit diagram of another embodiment of a means for generating a pulse signal having a duty corresponding to an output error, and FIG. 6B is a circuit diagram of another embodiment of a chopper circuit. .
FIG. 7 is a configuration diagram of an example of an existing charger.
8A is a diagram illustrating characteristics of a multiplier, and FIG. 8B is a diagram illustrating an output waveform of the multiplier.
[Explanation of symbols]
13 Current Error Amplifier 14 Comparator 21 Rectifier 22 Switching Element 23 Current Sensor 24 Triangular Wave Generation Circuit 25 Output Current Sensor 31 CPU
32 Chopper circuit 33 Averaging circuit 40 Battery unit 51 Error amplifier 52 Comparator

Claims (4)

A control circuit provided in a device that generates DC from AC using a switch,
A pulse generation unit that generates a pulse signal having a frequency higher than the frequency of the AC and having a duty corresponding to an error between a specified value and an output of the device;
Chopper means for chopping the AC voltage waveform signal using the pulse signal generated by the pulse generation means,
Averaging means for averaging the output of the chopper means;
Control signal generating means for outputting a control signal for controlling the switch based on an error between an output of the averaging means and a current flowing through the device;
A control circuit having: The chopper means includes at least one switching element, and the switching element is turned on / off by a pulse signal generated by the pulse generating means in a state where the AC voltage waveform signal is supplied to the switching element. The control circuit according to claim 1, wherein the control circuit has a configuration. The averaging means has a configuration including a resistor and a capacitor, and the frequency of the pulse signal generated by the pulse generating means is a frequency at which the output of the chopper means is sufficiently smoothly smoothed by the averaging means. The control circuit according to claim 1. A battery charger for charging a battery using power obtained from an AC power supply,
A switch for determining whether to supply power to the battery,
A rectifier for rectifying alternating current obtained from the alternating current power supply;
Pulse generation means for generating a pulse signal having a frequency higher than the AC frequency of the AC power supply and having a duty corresponding to an error between a specified value and an output to the battery;
Chopper means for chopping a voltage waveform signal output from the rectifier using a pulse signal generated by the pulse generation means,
Averaging means for averaging the output of the chopper means;
Control signal generating means for outputting a control signal for controlling the switch based on an error between an output of the averaging means and an input current from the AC power supply;
Charger with.

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