JP2016077150A - Inverter apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve use of an electrolytic capacitor even in a low temperature environment.SOLUTION: An inverter apparatus includes: an electrolytic capacitor 1 for smoothing a rectified voltage to a DC voltage; an inverter circuit 2 formed so as to supply the DC voltage smoothed by the electrolytic capacitor 1 and generating an AC voltage from the DC voltage to drive a motor 5; control means 3 for controlling drive of a plurality of switching elements 6u-6w, 7u-7w included in the inverter circuit 2; and temperature detection means 4 for detecting a temperature of the electrolytic capacitor 1 and outputting the detected temperature to the control means 3. The control means 3, when the temperature acquired by the temperature detection means 4 is lower than a previously determined target temperature, supplies a current restricted so that a ripple voltage of the DC voltage generated when smoothing the rectified voltage is included within an allowable value to the motor 5 before normal operation start of the motor 5 to increase the temperature of the electrolytic capacitor 1 up to the target temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an inverter device that generates an AC voltage from a DC voltage smoothed by an electrolytic capacitor to drive an electric motor, and particularly relates to an inverter device that is intended to be able to use an electrolytic capacitor even in a low temperature environment.

  This type of conventional inverter device selectively drives the three switching elements on the upper phase side and the three switching elements on the lower phase side of the inverter circuit, so that three phases of U, V, and W are generated from the DC voltage. A motor that drives a motor by generating voltage is provided with a smoothing capacitor that smoothes a DC voltage of a power source of an inverter circuit (see, for example, Patent Document 1). In this case, an electrolytic capacitor, a film capacitor, or the like is used as the smoothing capacitor.

JP 2009-138521 A

  However, in such a conventional inverter device, in particular, the in-vehicle inverter device may be used in a low temperature environment, and when an electrolytic capacitor is used in such an environment, the equivalent series resistance of the electrolytic capacitor increases. As a result, the ripple voltage increases, and the voltage applied to the switching element and the electrolytic capacitor exceeds the withstand voltage or becomes a reverse voltage, so that an electric compressor, for example, as an electric motor cannot be operated.

  Therefore, in an inverter device used in a low temperature environment, a large film capacitor having an extremely small equivalent series resistance has to be used as a smoothing capacitor. However, large film capacitors are expensive, and there is a problem that the inverter device becomes large and the manufacturing cost increases.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inverter device that can cope with such problems and can use an electrolytic capacitor even in a low temperature environment.

  In order to achieve the above object, an inverter device according to the present invention is provided with an electrolytic capacitor that smoothes a rectified voltage into a DC voltage, and the DC voltage that is smoothed by the electrolytic capacitor. An inverter circuit that generates an AC voltage from the motor to drive the motor, a control unit that controls driving of a plurality of switching elements included in the inverter circuit, and a temperature detector that detects the temperature of the electrolytic capacitor and outputs the detected temperature to the control unit And when the temperature acquired by the temperature detection unit is lower than a predetermined target temperature, the control unit smoothes the rectified voltage before starting the normal operation of the electric motor. A current limited so that a ripple voltage of the generated DC voltage is within an allowable value is applied to the motor, and the temperature of the electrolytic capacitor is set. Until serial target temperature is intended to warm.

  According to the present invention, in the low temperature environment, before starting the normal operation of the electric motor, the warm-up mode is implemented in which the electric motor is energized and the temperature of the electrolytic capacitor is increased to the temperature at which the normal operation of the electric motor can be started. A large ripple voltage causes a voltage exceeding the breakdown voltage to be applied to the switching element and the electrolytic capacitor, and it is possible to prevent the occurrence of an accident that destroys these elements. Therefore, an inexpensive and small electrolytic capacitor can be used even in a low temperature environment, and the inverter device can be miniaturized and the manufacturing cost can be reduced. In this case, since the warm-up mode is implemented by energizing the motor with a current that is limited so that the ripple voltage of the DC voltage that is the power supply voltage of the inverter circuit is within the allowable value, switching is also performed during the warm-up mode. It is possible to prevent destruction of the element and the electrolytic capacitor.

1 is a circuit diagram showing a schematic configuration of a first embodiment of an inverter device according to the present invention; It is a block diagram which shows the control circuit of the warming-up mode in the control means of the said 1st Embodiment. It is a flowchart shown about operation | movement of the warm-up mode of the said 1st Embodiment. It is explanatory drawing which shows the electricity supply state in the warming-up mode of the said 1st Embodiment. It is a flowchart shown about operation | movement of another warming-up mode of the said 1st Embodiment. It is a graph which shows the relationship between the electricity supply time in warm-up mode, the temperature of an electrolytic capacitor, and an equivalent series resistance. It is a block diagram which shows the control means of 2nd Embodiment of the inverter apparatus by this invention. It is a flowchart shown about operation | movement of the warm-up mode of the said 2nd Embodiment. It is a flowchart shown about operation | movement of another warming-up mode of the said 2nd Embodiment. It is a flowchart shown about operation | movement of another warming-up mode of the said 2nd Embodiment.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a schematic configuration of a first embodiment of an inverter device according to the present invention. This inverter device drives an electric motor by generating an AC voltage from a DC voltage smoothed by an electrolytic capacitor, and includes an electrolytic capacitor 1, an inverter circuit 2, a control means 3, and a temperature detection means 4. Configured.

  The electrolytic capacitor 1 smoothes the rectified voltage into a DC voltage, and is a large capacity aluminum electrolytic capacitor. Such an aluminum electrolytic capacitor is small and inexpensive, but generally has a large equivalent series resistance Ra due to the resistance of the electrolytic solution, the resistance of the electrolytic paper, and the like, and becomes larger in a low temperature environment. Have.

  An inverter circuit 2 is provided so that a DC voltage smoothed by the electrolytic capacitor 1 is supplied as a power supply voltage. This inverter circuit 2 generates a three-phase voltage Vu, Vv, Vw from a DC voltage and supplies it to a three-phase brushless motor (hereinafter simply referred to as “motor”) 5 as an electric motor. The three switching elements (IGBT) 6u, 6v, 6w and three switching elements (IGBT) 7u, 7v, 7w on the lower phase side are configured.

  A control means 3 is provided in connection with the inverter circuit 2. This control means 3 controls the on / off drive of the six switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 so as to operate the motor 5 appropriately, and the temperature of the electrolytic capacitor 1 is predetermined. When the temperature is lower than the target temperature, before starting the normal operation of the motor 5, the duty of the pulse width modulation (hereinafter referred to as "PWM") signal for driving the switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 on and off By controlling the ratio, a current that is limited so that the ripple voltage of the DC voltage is within an allowable value is supplied to the motor 5, and the temperature of the electrolytic capacitor 1 is adjusted by Joule heat generated in the equivalent series resistance Ra of the electrolytic capacitor 1. A warm-up mode for raising the temperature to the target temperature can be performed.

  FIG. 2 is a block diagram showing a control circuit for the warm-up mode in the control means 3. As shown in the figure, the warm-up mode control circuit is connected to the emitters of the lower-phase switching elements 7u to 7w of the inverter circuit 2 and is connected to the shunt resistor (not shown) or on the ground line of the inverter circuit 2. The current detection unit 8 detects the energization current of the motor 5 based on the current flowing through a shunt resistor (not shown) provided in the circuit, and the current value detected by the current detection unit 8 and the ripple voltage of the DC voltage are within an allowable value. A comparator 9 that compares a constant set current value that can be suppressed (hereinafter referred to as “warm-up mode current value”) and a PWM signal so that the difference between the energization current value and the warm-up mode current value can be corrected. And a PWM duty ratio calculation unit 10 for calculating the duty ratio.

  The control means 3 configured as described above executes the warm-up mode before starting the motor 5 when the temperature of the electrolytic capacitor 1 is lower than the target temperature. That is, among the three switching elements 6u to 6w on the upper phase side of the inverter circuit 2, for example, the switching element 6u is selected and turned on, the remaining switching elements 6v and 6w are selected and driven off, and the lower phase side Among the three switching elements 7u to 7w, the switching elements 7v and 7w are selected and turned on, and the remaining switching elements 7u are selected and driven off. At the same time, the current detection unit 8 detects the energization current of the motor 5, compares the detected current value with the warm-up mode current value by the comparator 9, and the PWM duty ratio calculation unit so that the difference can be corrected. 10 calculates the duty ratio of the PWM signal. Thus, the switching elements 6u, 7v, and 7w are turned on by the PWM signal having the calculated duty ratio to energize the motor 5. As a result, a current limited to the ripple voltage of the DC voltage within the allowable value flows through the inverter circuit 2 through the motor 5. On the other hand, during energization of the motor 5, the electrolytic capacitor 1 is heated by Joule heat generated in its equivalent series resistance Ra.

  In the vicinity of the electrolytic capacitor 1, temperature detecting means 4 is provided. This temperature detection means 4 detects the ambient temperature of the electrolytic capacitor 1 and outputs it to the control means 3, and is, for example, various temperature sensors such as a thermocouple or a resistance sensor. When the electrolytic capacitor 1 is mounted on the same substrate as the inverter circuit 2 or is accommodated in the same space, the temperature detecting means 4 is the switching element of the inverter circuit 2 that generates the largest amount of heat. The temperature of the electrolytic capacitor 1 may be estimated by detecting the temperature in the vicinity. However, in the following description, the temperature detecting means 4 detects the ambient temperature of the electrolytic capacitor 1 and electrolyzes it. A case where the temperature of the capacitor 1 is estimated will be described.

Next, the operation in the warm-up mode of the first embodiment configured as described above will be described with reference to the flowchart of FIG.
First, in step S1, when the operation switch is turned on (operation command), the power supply voltage is supplied to the inverter device and the control means 3 of the inverter device is activated.

  Next, in step S <b> 2, the temperature around the electrolytic capacitor 1 is detected by the temperature detector 4, and the detected output is sent to the controller 3. The determination unit (not shown) of the control means 3 estimates the detected temperature acquired by the temperature detection means 4 as the temperature of the electrolytic capacitor 1, and performs the operation in the warm-up mode that is preset and stored in a memory (not shown). It compares with the target temperature for determining whether to implement or not. If the detected temperature is lower than the target temperature, step S2 is “YES” and the process proceeds to step S3.

  In step S3, the PWM duty ratio calculation unit 10 of the control means 3 calculates the duty ratio of the PWM signal based on the warm-up mode current value set in advance and stored in the memory, and the calculated duty ratio is calculated. For example, the switching element 6u on the upper phase side of the inverter circuit 2 is turned on by the PWM signal, while the switching elements 7v and 7w on the lower phase side are turned on. As a result, as shown by a thick solid line in FIG. 4, the inverter circuit 2 and the motor 5 are supplied with a current limited so that the ripple voltage of the DC voltage is within the allowable value, and the operation in the warm-up mode is performed. The In this case, since the switching element to be turned on of the inverter circuit 2 is fixed to, for example, the switching element 6u on the upper phase side and the switching elements 7v and 7w on the lower phase side, for example, the motor 5 remains stopped. . In this way, while the limited current is applied to the motor 5, the electrolytic capacitor 1 is warmed by Joule heat generated in its equivalent series resistance Ra and raised in temperature. The energizing current of the motor 5 is a current flowing through a shunt resistor provided in connection with the emitters of the lower-phase switching elements 7u to 7w of the inverter circuit 2 or a shunt resistor provided on the ground line of the inverter circuit 2. Is detected by the current detector 8, and the PWM duty ratio calculator 10 compares the detected current with the warm-up mode current value by the comparator 9 and corrects the difference. Therefore, during the warm-up mode, a current that is limited so that the ripple voltage of the DC voltage is within the allowable value flows through the motor 5 at all times. In this case, the warm-up mode current value may change in correlation with the temperature of the electrolytic capacitor 1.

  Subsequently, returning to step S2, whether or not the temperature detected by the temperature detecting unit 4 is lower than the target temperature is determined again by the determining unit of the control unit 3. Thus, step S2 and step S3 are repeatedly executed until the detected temperature reaches the target temperature in step S2, that is, until “NO” is determined in step S2.

  When the detected temperature reaches the target temperature and step S2 is “NO”, the process proceeds to step S4, where the plurality of switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are sequentially turned on / off according to a predetermined procedure. The motor 5 is started by being turned off. As a result, the motor 5 performs normal operation.

FIG. 5 is a flowchart showing another operation in the warm-up mode of the first embodiment. Hereinafter, a description will be given with reference to FIG.
First, in step S10, when the operation switch is turned on (operation command), the power supply voltage is supplied to the inverter device, and the control means 3 of the inverter device is activated.

  Next, in step S <b> 11, the temperature around the electrolytic capacitor 1 is detected by the temperature detector 4, and the detected output is sent to the controller 3. In the determination part of the control means 3, the detected temperature acquired by the temperature detection means 4 is estimated as the temperature of the electrolytic capacitor 1, and it is determined whether or not to perform the warm-up mode operation stored in advance in the memory. Compare with target temperature for judgment. Here, when the detected temperature is lower than the target temperature, the determination in step S11 is “YES”, and the process proceeds to step S12.

  In step S12, the PWM duty ratio calculation unit 10 of the control means 3 calculates the duty ratio of the PWM signal based on the warm-up mode current value set in advance and stored in the memory, and the calculated duty ratio is calculated. For example, the switching element 6u on the upper phase side of the inverter circuit 2 is turned on by the PWM signal, while the switching elements 7v and 7w on the lower phase side are turned on. As a result, as shown by a thick solid line in FIG. 4, the inverter circuit 2 and the motor 5 are supplied with a current limited so that the ripple voltage of the DC voltage is within the allowable value, and the operation in the warm-up mode is performed. The In this case, since the switching element to be turned on of the inverter circuit 2 is fixed to, for example, the switching element 6u on the upper phase side and the switching elements 7v and 7w on the lower phase side, for example, the motor 5 remains stopped. . In this way, while the limited current is applied to the motor 5, the electrolytic capacitor 1 is warmed by Joule heat generated in its equivalent series resistance Ra and raised in temperature.

  In step S13, the elapsed time is counted by the timer, and when a predetermined time set in advance and stored in the memory has elapsed, the process proceeds to step S14. Note that the temperature and equivalent series resistance Ra of the electrolytic capacitor 1 and the energization time have a relationship shown in FIG. 6, for example. That is, as the energization time elapses, the temperature of the electrolytic capacitor 1 increases and the equivalent series resistance Ra decreases. In both cases, it is known that when the time t elapses, the value becomes constant. Therefore, in the control example shown in FIG. 5, the temperature of the electrolytic capacitor 1 and the elapsed time t at which the equivalent series resistance Ra is constant after the current of the current value for the warm-up mode is supplied to the motor 5 are previously experimentally determined. Then, the elapsed time t is stored in the memory.

  In step S13, when a certain time has elapsed and the temperature of the electrolytic capacitor 1 rises to the target temperature, the process proceeds to step S14, and the six switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are sequentially turned on / off according to a predetermined procedure. Driven, the motor 5 is started. As a result, the motor 5 performs normal operation.

  If the detected temperature has already reached the target temperature in step S11, the determination in step S11 is “NO” and the process proceeds to step S14. In this case as well, the six switching elements 6u˜ 6w and 7u-7w are sequentially turned on and off according to a predetermined procedure, the motor 5 is started, and the motor 5 performs normal operation.

  In the first embodiment, the current detector 8 is provided on the shunt resistor provided by being connected to the emitters of the lower-phase switching elements 7u to 7w of the inverter circuit 2 or on the ground line of the inverter circuit 2. Although the case where the current flowing through the shunt resistor is detected has been described, the current flowing through the shunt resistor (not shown) connected to the negative electrode side of the electrolytic capacitor 1 is detected, and the ripple voltage of the DC voltage is allowed based on the current. The motor 5 may be energized with a current limited to be within.

FIG. 7 is a circuit diagram showing a schematic configuration of the second embodiment of the inverter device of the present invention, and is a block diagram showing a circuit configuration of the control means 3. Here, a different part from 1st Embodiment is demonstrated.
The control means 3 in the second embodiment controls the inverter circuit 2 so as to carry out the warm-up mode until a certain time has elapsed since the start of the motor 5, and includes a current detector 8 and d, q Axis converter 11, rotor angle detector 12, rotation speed calculator 13, current calculator 14, comparator 9, applied voltage calculator 15, phase voltage converter 16, and PWM duty ratio calculator 10 and a warm-up mode switching unit 17.

  The current detection unit 8 is connected to the emitters of the lower phase side switching elements 7u to 7w of the inverter circuit 2 and based on the current flowing through a shunt resistor (not shown) of the motor 5, the three phase currents Iu, Iv, Iw of the motor 5. Are respectively detected. The d and q axis converter 11 converts the three-phase currents Iu, Iv and Iw into d and q axis currents Id and Iq. Further, the rotor angle detector 12 detects the rotor angle, and calculates the rotor angle using, for example, a hall sensor or based on the phase voltage and phase current. Furthermore, the rotational speed calculation unit 13 calculates based on the detected rotor angle and calculates the rotational speed of the rotor. The current calculation unit 14 calculates a current value based on the currents Id and Iq and the rotor angle, and calculates the phase lag or phase advance of the current. The comparator 9 compares the calculated rotor rotation speed with the target rotation speed and outputs the difference. Further, the applied voltage calculator 15 calculates the voltage for driving the motor 5 and adjusts the phase of the voltage. The phase voltage converter 16 converts the d and q-axis voltages Vd and Vq to the three-phase voltages Vu, Vv and Vw. Further, the PWM duty ratio calculation unit 10 calculates the duty ratio of the PWM signal based on the three-phase voltages Vu, Vv, and Vw, and the switching elements 6u to 6w of the inverter circuit 2 based on the PWM signal having the calculated duty ratio. , 7u to 7w are driven on. When the operation switch is turned on and an operation command is issued, the warm-up mode switching unit 17 compares the temperature input from the temperature detection means 4 with the target temperature of the warm-up mode and needs to execute the warm-up mode. In some cases, one of the current limit command for the warm-up mode, the rotational speed limit command, and the PWM carrier frequency limit command that can limit the ripple voltage of the DC voltage of the inverter circuit 2 within an allowable value is selected and output. It is like that. In this case, when the warm-up mode is performed based on the current limit command, the current limit command is output to the current calculation unit 14. Further, when the warm-up mode is performed based on the rotation speed limit command, the rotation speed limit command is output to the memory. Further, when executing the warm-up mode based on the PWM carrier frequency limit command, the PWM carrier frequency limit command is output to the PWM duty ratio calculation unit 10.

Next, the operation in the warm-up mode of the second embodiment configured as described above will be described.
First, the case where the warm-up mode is performed based on the current limit command will be described with reference to the flowchart of FIG.
In step S20, when the operation switch is turned on and an operation command is issued, the process proceeds to step S21, and it is determined whether or not to implement the warm-up mode.

  Specifically, in step S21, the ambient temperature of the electrolytic capacitor 1 input from the temperature detection means 4 (hereinafter simply referred to as “temperature of the electrolytic capacitor 1”) is set in advance by a determination unit provided in the control means 3. Compare with the target temperature stored in memory. When the temperature of the electrolytic capacitor 1 is lower than the target temperature, the determination in step S21 is “YES”, the warm-up mode switching unit 17 is turned on to select the current-limiting warm-up mode, and the warm-up mode switching unit The current limit command is output from 17 to the current calculation unit 14, and the process proceeds to step S22.

  In step S22, the current value calculated by the current calculation unit 14 is limited to a preset current value based on the current limit command. Here, the limited current value is a preset current value that is preset and stored in the memory, for example, can limit the ripple voltage of the DC voltage within an allowable value, and is lower than that during normal operation. Current value. Alternatively, it may be a current value set so as to change in correlation with the temperature of the electrolytic capacitor 1, and may be a current value that changes based on a table created in advance by experiment and stored in a memory. Thus, the current calculation is performed based on the currents Id and Iq converted from the three-phase currents Iu, Iv, and Iw by the d and q axis conversion unit 11 to the d and q axes and the rotor angle detected by the rotor angle detection unit 12. The current value calculated by the unit 14 is limited to the set current value. In addition, you may change the said electric current value, monitoring the temperature of the electrolytic capacitor 1, and the ripple voltage of DC voltage irrespective of the said table.

  The applied voltage calculation unit 15 calculates an applied voltage for driving the motor 5 based on the set current value and the rated target rotational speed. Further, the phase voltage converter 16 converts the voltage into three-phase voltages Vu, Vv, Vw, and the PWM duty ratio calculator 10 calculates the duty ratio of the PWM signal based on the three-phase voltages Vu, Vv, Vw. The switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are turned on based on the PWM signal having the calculated duty ratio. As a result, a current that is limited so that the ripple voltage of the DC voltage is within the allowable value is supplied to the motor 5, and the motor 5 is started. Thereafter, the motor 5 rotates while maintaining the rated number of rotations under the limited current value.

  In step S23, the elapsed time from the startup of the motor 5 is counted by a timer. Then, when a predetermined time has elapsed, the process proceeds to step S24.

  In step S24, the warm-up mode switching unit 17 is driven off based on the output signal of the timer indicating that a certain time has elapsed, and the current limitation based on the set current value is released. Thereby, the warm-up mode ends.

  In step S25, the control means 3 detects the three-phase current detected by the current detector 8 based on the current flowing through the shunt resistor provided connected to the emitters of the lower-phase switching elements 7u to 7w of the inverter circuit 2. The current value calculated by the current calculation unit 14 based on the currents Id and Iq converted from du and q axes from Iu, Iv, and Iw and the rotor angle detected by the rotor angle detection unit 12, and detected by the rotor angle detection unit 12 The applied voltage Vd to the motor 5 is applied to the motor 5 by the applied voltage calculator 15 based on the difference between the rotational speeds calculated by comparing the rotational speed calculated based on the rotor angle and the rated target rotational speed by the comparator. Vq is calculated. Further, the phase voltage converter 16 converts the applied voltages Vd and Vq on the d and q axes to the three-phase voltages Vu, Vv and Vw, and the PWM duty ratio calculator 10 based on the three-phase voltages Vu, Vv and Vw. After the duty ratio of the PWM signal is calculated, the switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are appropriately turned on by the PWM signal having the calculated duty ratio, so that the motor 5 is normally operated.

  In step S21, if the temperature of the electrolytic capacitor 1 has already reached the target temperature, step S21 is “NO”, the process proceeds to step S25, and the motor 5 performs normal operation.

Next, with reference to the flowchart of FIG. 9, implementation of the warm-up mode based on the rotational speed restriction command will be described.
In step S30, when the operation switch is turned on and an operation command is issued, the process proceeds to step S31, and it is determined whether or not to implement the warm-up mode.

  Specifically, in step S31, the temperature of the electrolytic capacitor 1 input from the temperature detection means 4 is set in advance by a determination unit provided in the control means 3 and compared with the target temperature stored in the memory. When the temperature of the electrolytic capacitor 1 is lower than the target temperature, the determination in step S31 is “YES”, and the warm-up mode switching unit 17 is turned on to select the warm-up mode with the rotational speed limit, so that the warm-up mode is switched. A rotation speed limit command is output from the unit 17 to the memory and set in advance and stored in the memory. For example, a constant set rotation speed that can limit the ripple voltage of the DC voltage within an allowable value (lower than that during normal operation) Read the number of revolutions) from the memory. Then, the process proceeds to step S32. The set rotational speed is a rotational speed that is set so as to change in correlation with the temperature of the electrolytic capacitor 1, and is a rotational speed that changes based on a table created in advance by experiment and stored in the memory. May be. In this case, the rotation speed may be changed while monitoring the temperature of the electrolytic capacitor 1 and the ripple voltage of the DC voltage, without depending on the table.

  In step S32, the motor 5 is started on the basis of the predetermined rotational speed read from the memory based on the rotational speed restriction command, and a current that can restrict the ripple voltage of the DC voltage within the allowable value is energized. In this state, the engine is operated with the rotation speed limited to the set rotation speed.

  Thereafter, the control means 3 generates the three-phase currents Iu, Iv, Iw in the current detection unit 8 based on the current flowing through the shunt resistor provided connected to the emitters of the lower-phase switching elements 7u-7w of the inverter circuit 2. Then, the d and q axis conversion unit 11 converts the three-phase currents Iu, Iv, and Iw into the d and q axes to obtain the currents Id and Iq. The rotor detected by the currents Id and Iq and the rotor angle detection unit 12 is detected. Based on the angle, the current calculation unit 14 calculates the current value and the phase lag or phase advance. On the other hand, based on the rotor angle detected by the rotor angle detector 12, the rotational speed calculator 13 calculates the actual rotor rotational speed. Then, the rotation speed is compared with the set rotation speed by the comparison section, and the difference is output. In the applied voltage calculation section 15, the difference between the current value calculated by the current calculation section 14 and the rotation speed output from the comparison section. Based on the amount, applied voltages Vd and Vq for driving the motor 5 are calculated. Further, the applied voltages Vd and Vq are converted into the three-phase voltages Vu, Vv and Vw by the three-phase voltage converter 16, and the PWM duty ratio calculator 10 calculates the PWM signal based on the three-phase voltages Vu, Vv and Vw. After calculating the duty ratio, the switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are turned on by the PWM signal having the duty ratio. Thereby, the motor 5 rotates while maintaining the set rotational speed. At this time, the energization current to the motor 5 is maintained at a current value that can limit the ripple voltage of the DC voltage within an allowable value.

  In step S33, the elapsed time from the startup of the motor 5 is counted by a timer. Then, when a predetermined time has elapsed, the process proceeds to step S34.

  In step S34, the warm-up mode switching unit 17 is turned off based on the output signal of the timer indicating that a predetermined time has elapsed, and the rotation speed limit based on the set rotation speed is released. Thereby, the warm-up mode ends.

  In step S35, the target rotational speed of the rated value is read from the memory, the rotational speed is controlled so as to be the target rotational speed, and the motor 5 is operated. Thus, the motor 5 shifts to normal operation.

  In step S31, when the temperature of the electrolytic capacitor 1 has already reached the target temperature, step S31 is “NO” determination, the process proceeds to step S35, and the motor 5 performs normal operation.

Furthermore, with reference to the flowchart of FIG. 10, the implementation of the warm-up mode based on the PWM carrier frequency restriction command will be described.
In step S40, when the operation switch is turned on and an operation command is issued, the process proceeds to step S41, and it is determined whether or not to implement the warm-up mode.

  Specifically, in step S41, the temperature of the electrolytic capacitor 1 input from the temperature detection means 4 is set in advance by a determination unit provided in the control means 3 and compared with the target temperature stored in the memory. When the temperature of the electrolytic capacitor 1 is lower than the target temperature, step S41 is determined as “YES”, the warm-up mode switching unit 17 is turned on, and the warm-up mode with PWM carrier frequency restriction is selected, and step S42 is performed. Proceed to

  In step S42, the warm-up mode switching unit 17 outputs a PWM carrier frequency limit command to the PWM duty ratio calculation unit 10, and can limit the ripple voltage of the DC voltage within an allowable value, for example, a constant PWM carrier frequency (normal operation) Carrier frequency is set to a carrier frequency lower than that). Then, the PWM duty ratio calculation unit 10 generates a PWM signal based on the set carrier frequency, calculates the duty ratio of the generated PWM signal based on the rated target rotational speed, and the calculated The switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are turned on by the PWM signal having the duty ratio to start the motor 5. Note that the set carrier frequency is a carrier frequency that changes in correlation with the temperature of the electrolytic capacitor 1, and may be a carrier frequency that changes based on a table that is created in advance by experiment and stored in the memory. . As a result, the motor 5 is operated with the carrier frequency limited (reduced) to the set carrier frequency in a state in which a current that can limit the ripple voltage of the DC voltage within an allowable value is applied. Note that the carrier frequency may be changed while monitoring the temperature of the electrolytic capacitor 1 and the ripple voltage of the DC voltage, regardless of the above table.

  Thereafter, the control means 3 calculates the duty ratio of the PWM signal generated by the set carrier frequency based on the detected three-phase currents Iu, Iv, Iw, the rotor angle, and the target rotational speed, and the calculated The switching elements 6u to 6w and 7u to 7w of the inverter circuit 2 are turned on by the PWM signal having the duty ratio. As a result, the motor 5 operates while maintaining the target rotational speed. At this time, the energization current to the motor 5 is maintained at a current value that can limit the ripple voltage of the DC voltage within an allowable value.

  In step S43, the elapsed time from the start of the motor 5 is counted by a timer. Then, when a predetermined time has passed, the process proceeds to step S44.

  In step S44, the warm-up mode switching unit 17 is driven off based on the output signal of the timer indicating that a certain time has elapsed, and the carrier frequency limitation (reduction) by the set carrier frequency is released. Thereby, the warm-up mode ends.

  In step S45, the motor 5 is operated under the control of the carrier frequency during normal operation, and the motor 5 shifts to normal operation.

  In step S41, when the temperature of the electrolytic capacitor 1 has already reached the target temperature, step S41 is determined as “NO”, the process proceeds to step S45, and the motor 5 performs normal operation.

  In the second embodiment, the case where the warm-up mode is performed with the current, the rotational speed, or the carrier frequency limited to each independently has been described. However, the present invention is not limited thereto, and the current, the rotational speed, You may carry out combining the restriction | limiting of a carrier frequency suitably. For example, at least two of current limitation, rotation speed limitation, and carrier frequency limitation may be selected and the warm-up mode may be performed for a certain period of time. Further, when the function of only the warm-up mode of current limitation, rotation speed limitation, or carrier frequency limitation is installed, the warm-up mode switching unit 17 may not be provided.

  In the first and second embodiments, the shunt resistor provided in connection with the emitters of the lower-phase switching elements 7u to 7w of the inverter circuit 2 or the shunt provided on the ground line of the inverter circuit 2 is used. Although the case where the current flowing to the motor 5 is limited based on the current flowing through the resistor or the current flowing through the shunt resistor connected to the negative electrode side of the electrolytic capacitor 1 has been described, the present invention is not limited to this, and the lower phase side The ripple current is estimated from the current (detection current) flowing through the shunt resistor connected to the emitters of the switching elements 7u to 7w or the shunt resistor provided on the ground line of the inverter circuit 2, and the ripple current is an allowable value. The energization current to the motor 5 may be limited so as to be within. In this case, the ripple current can be estimated by the sum of the AC components of the detection current. Alternatively, the relationship between the detection current and the ripple current is measured in advance by experiments, and the ripple current can be estimated from this relationship.

  In the above description, the three-phase inverter circuit 2 has been described. However, the present invention is not limited to this, and the inverter circuit 2 may have any number of phases, for example, four phases. It is good to set appropriately according to.

DESCRIPTION OF SYMBOLS 1 ... Electrolytic capacitor 2 ... Inverter circuit 3 ... Control means 4 ... Temperature detection means 5 ... Motor (electric motor)
6u-6w, 7u-7w ... Switching element Ra ... Equivalent series resistance

Claims (6)

An electrolytic capacitor that smoothes the rectified voltage into a DC voltage;
An inverter circuit that is provided so that the DC voltage smoothed by the electrolytic capacitor is supplied, generates an AC voltage from the DC voltage, and drives an electric motor;
Control means for controlling driving of a plurality of switching elements included in the inverter circuit;
Temperature detecting means for detecting the temperature of the electrolytic capacitor and outputting it to the control means;
With
The control means, when the temperature acquired by the temperature detection means is lower than a predetermined target temperature, the DC voltage generated when the rectified voltage is smoothed before the normal operation of the electric motor is started. An inverter device, wherein a current limited so that a ripple voltage is within an allowable value is supplied to the electric motor, and the temperature of the electrolytic capacitor is increased to the target temperature.   The control means selects a specific switching element among the plurality of switching elements of the inverter circuit before starting the electric motor, drives it on, stops the electric motor, and allows the ripple voltage of the DC voltage to be an allowable value. The inverter device according to claim 1, wherein a current supplied to the electric motor is controlled based on a set current value that can be suppressed within.   The specific switching element selected may be a pulse current modulation signal having a duty ratio calculated based on a constant current value set and stored in advance or a current value that varies in correlation with the temperature of the electrolytic capacitor. The inverter device according to claim 2, wherein the inverter device is driven.   The duty ratio of the pulse width modulation signal is calculated so as to correct a difference between the preset current value stored and the energization current value of the motor. 3. The inverter device according to 3.   5. The energization of the electric motor with a current limited so that the ripple voltage of the DC voltage is within an allowable value is performed until a predetermined time set in advance has elapsed. The inverter device according to any one of the above.   The control means has a constant set current value that can limit the ripple voltage of the DC voltage within an allowable value or a setting that changes in correlation with the temperature of the electrolytic capacitor until a predetermined time has elapsed since the start of the electric motor. 6. The inverter device according to claim 5, wherein a current supplied to the electric motor is controlled based on a current value.