JP3992242B1 - AC motor control device - Google Patents

Abstract

An object of the present invention is to reduce the loss for voltage conversion in an AC motor control device that performs VVVF control and to improve the efficiency of the entire device.
A control device for an AC motor using a capacitor storage power source and a three-phase inverter, and comprising a plurality of capacitors for charging / discharging and a switch circuit for switching the connection of the plurality of capacitors in series and parallel. Capacitor storage power source 1 that enables serial-parallel switching of capacitor connections, a three-phase inverter 4 that drives the AC motor 5 by converting the discharge output of the capacitor storage power source 1 into a three-phase AC, and a command from the AC motor 5 Control means 8 for controlling the three-phase inverter 4 by generating a PWM signal while switching the series connection of the plurality of capacitors by switching control of the switch circuit of the capacitor storage power source 1 according to the speed.
[Selection] Figure 1

Description

  The present invention relates to a control apparatus for an AC motor using a capacitor storage power source and a three-phase inverter.

In a speed control device that performs VVVF (variable voltage variable frequency) control on an AC motor, a converter that rectifies the AC voltage between an AC power source and the AC motor and converts the AC voltage into a predetermined DC voltage, and the converter output in each phase Correspondingly, a three-phase inverter that performs PWM (pulse width modulation) control is connected (for example, see Patent Document 1). In this device, considering that the efficiency of the motor is significantly reduced in the low speed range when the specification of the AC motor is adjusted to the high speed range, the specification of the AC motor is adjusted to the low speed range and a boost chopper is provided at the subsequent stage of the converter Therefore, the input voltage of the inverter is increased so that high-speed operation is possible. Furthermore, in order to reduce the efficiency of the circuit in the low speed region in this case, the DC voltage input to the inverter is lowered by turning off the boost chopper.
JP 2000-146392 A

  In an apparatus for controlling an AC motor by VVVF by combining an AC power source with a converter and a three-phase inverter, it is preferable to set the DC voltage input to the inverter to a voltage suitable for the speed. In addition, a switching loss (conversion loss) for voltage conversion occurs. Moreover, there is a problem that, even if the output voltage of the converter is boosted or lowered, if the step-up / step-down width is large, the conversion loss also increases.

  Therefore, in general, even if the power is the same, the smaller the current, the smaller the conversion loss.In other words, the higher the voltage, the smaller the conversion loss. There are many cases of pressure drop. However, even in this case, the conversion loss becomes the largest when the voltage is stepped down to the lowest usable voltage. In addition, since the purpose of the minimum operating voltage is to save energy, there is a contradiction between the purpose and the technology as the realization means.

  The present invention solves the above-described problem, and is intended to improve the efficiency of the entire apparatus by reducing a loss for voltage conversion in an AC motor control apparatus that performs VVVF control.

To this end, the present invention is a control device for an AC motor using a capacitor storage power source and a three-phase inverter, and switches the plurality of capacitors to a plurality of series-parallel connection stages by a plurality of capacitors for charge / discharge and a switching signal. Ri Do from the switch circuit, and a capacitor energy storage power supply for switching the terminal voltage of the capacitor energy storage power supply by switching the connection stage, a voltage detecting means for detecting the terminal voltage of the capacitor power storage power supply, detects the output speed of the AC motor compared with the speed detecting means, and the voltage-frequency signal generating means for generating a voltage signal and frequency signal corresponding to the command speed of the AC motor, the voltage corresponding to the command speed and the terminal voltage of the capacitor energy storage power supply a voltage terminal voltage of the capacitor energy storage power supply does not become lower than the voltage corresponding to the command speed A switching signal generating means for generating the switching signal for switching the connection stage the near of voltage, and a three-phase inverter for driving the AC motor by converting the discharge power of the capacitor energy storage power supply to a three-phase AC, corresponding to the command speed to the frequency, the capacitor energy storage power supply terminal voltage and the AC motor output speed of the speed error and the triangular wave carrier signal of a constant frequency to generate a sine wave signal having an amplitude corresponding to said sine wave signal to a specified speed of And a control means for generating a PWM signal based on the control and controlling the three-phase inverter.

  According to the present invention, the voltage input to the inverter is adjusted to an appropriate voltage by switching the parallel connection of the plurality of capacitors of the capacitor storage power source according to the speed of the AC motor. It is only switching the parallel, and after switching, the loss for voltage conversion that occurs in the conventional device that converts the voltage input to the inverter to an appropriate voltage by a converter, a chopper, or the like can be eliminated. Also, when driving an electric vehicle or the like, it is possible to provide a means for efficiently performing power running and regenerative control by generating a DC voltage corresponding to the speed by switching the connection of a plurality of capacitors in series and parallel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an embodiment of the control apparatus for an AC motor according to the present invention, FIG. 2 is a diagram for explaining bank switching of connection of a plurality of capacitors constituting the capacitor storage power source, and FIG. 3 is a speed of the AC motor. FIG. 4 is a diagram illustrating a PWM signal generated by a sine wave signal and a carrier wave signal. In the figure, 1 is a capacitor storage power source, 2 is an AC power source, 3 is a converter, 4 is an inverter, 5 is an AC motor, 6 is a speed detector, 7 is a charge control unit, 8 is a motor control unit, and Vc is a capacitor power supply voltage. Indicates.

  In FIG. 1, a capacitor storage power source 1 is a bank switching type storage power source device including, for example, a plurality of electric double layer capacitors and a switch circuit that performs series-parallel switching of their connections. Then, using the AC power supply 2 as a charging power supply, each electric double layer capacitor of the capacitor storage power supply 1 is charged to a full charge voltage and stored through a converter 3 that rectifies and converts AC from the AC power supply 2. The AC motor 5 is driven at a command speed by controlling the speed of the AC motor 5 by discharging the DC output stored in each of the electric double layer capacitors through the inverter 4 that converts the DC output into three-phase AC.

  The charging control unit 7 controls the switching while performing so-called bank switching by switching the connection of a plurality of electric double layer capacitors by controlling the switching circuit of the converter 3 and the capacitor storage power source 1. . The motor control unit 8 is connected to the rotating shaft of the AC motor 5, for example, based on the signal of the speed detector (tachogen TG) 6 that detects the rotation speed of the AC motor 5, and the command speed for operating the motor. By controlling the switch circuit and the inverter 4, the banks of the plurality of electric double layer capacitors are switched, and the inverter 4 is controlled by a PWM signal generated according to the command speed and the input voltage, so that the AC motor 5 is set to a desired speed. It is something to control.

  For example, as shown in FIG. 2 (d), the bank-switching capacitor storage power source 1 is configured to start charging when the bank (cell) voltage of each electric double layer capacitor is low in the charge control by the charge control unit 7. C1 to C4 are connected in series, and as the voltage rises, the connection is switched sequentially from the series in parallel as shown in FIG. 2 (c) → (b) → (a). Such a capacitor power storage device has already been proposed by the present applicant and the like (see, for example, Japanese Patent No. 3487780 and Japanese Patent Laid-Open No. 2005-287110), and realizes efficient charging.

  In the capacitor storage power source 1 in which the banks of the electric double layer capacitors C1 to C4 are charged to the full charge voltage in this way, when the electric double layer capacitors C1 to C4 are all connected in parallel as shown in FIG. The voltage equal to the full charge voltage of the bank can be used as the capacitor power supply voltage Vc to be input to the inverter 4. Also, as shown in FIG. 2B, when switching to a connection in which the series circuit of the electric double layer capacitors C1-C2 and the series circuit of C3-C4 are switched in parallel, the voltage input to the inverter 4 is doubled, As shown in FIG. 2 (c), when switching to a connection in which C3 is parallel to C2 of the series circuit of electric double layer capacitors C1-C2-C4, the voltage input to the inverter 4 is tripled, and FIG. 2 (d) As shown in FIG. 4, the voltage input to the inverter 4 can be quadrupled by switching to the series connection of the electric double layer capacitors C1-C2-C3-C4.

  In the present embodiment, the motor control unit 8 performs bank switching control of the capacitor storage power source 1 and PWM control of the inverter 4 so that the voltage applied to the AC motor 5 through the inverter 4 and the control frequency become values proportional to the speed. Is. For example, in FIG. 3, when the speed of the horizontal axis is Ni, the voltage and frequency applied to the AC motor 5 are selected and controlled for Vi and fi on the vertical axis corresponding to the speed.

  Therefore, in the motor control unit 8, for example, with respect to the speed of Ni in FIG. 3, the voltage Vi is supplied from the capacitor storage power source 1 as the voltage input to the inverter 4, for example, series-parallel shown in FIG. Bank switching control of the capacitor storage power supply 1 is performed so as to form a circuit. Further, a sine wave signal having a frequency fi is generated, and the amplitude of the sine wave signal is adjusted based on the error between the detected speed detected from the speed detector 6 and the command speed, as shown in FIG. And a triangular wave carrier signal to generate a three-phase PWM signal. Then, the inverter 4 is controlled by the PWM signal to generate a three-phase alternating current, and the alternating current motor 5 is driven to control to a command speed, for example, Ni.

  When the capacitor storage power supply 1 discharges by operating the AC motor 5 by PWM control of the inverter 4 according to the command speed, the bank voltage of each electric double layer capacitor gradually decreases, and the capacitor power supply input to the inverter 4 The voltage Vc decreases. Therefore, even if the series-parallel connection stage of the plurality of electric double layer capacitors in the capacitor storage power source 1 initially has the voltage relationship shown in FIG. 3, the capacitor power source voltage Vc corresponding to the speed corresponds to the speed of the AC motor 5. It becomes lower than the voltage to be applied. Therefore, the motor control unit 8 compares the capacitor power supply voltage Vc with the voltage applied to the AC motor 5 with respect to the capacitor storage power supply 1, and when the capacitor power supply voltage Vc decreases, the bank switching is performed, for example, as shown in FIG. The voltage drop is compensated by performing a control of sequentially shifting from 2 (a) to.

  Further, the PWM signal for controlling the inverter 4 in the motor control unit 8 is generated by comparing the triangular wave carrier signal and the sine wave signal as shown in FIG. 4, and this PWM signal is used for switching each phase of the inverter 4. It is a timing signal. When the voltage input to the inverter 4 fluctuates, that is, when the capacitor power supply voltage Vc input from the capacitor storage power supply 1 to the inverter 4 gradually decreases due to discharge, the voltage applied to the AC motor 5 decreases. 8 compensates for this decrease by increasing the amplitude of the sine wave signal in response to a decrease in the capacitor power supply voltage Vc. That is, the amplitude of the sine wave signal is adjusted according to the capacitor power supply voltage Vc.

  Next, an embodiment of a circuit for generating a bank switching signal and a PWM signal will be described. FIG. 5 is a diagram showing an embodiment of a circuit for generating a bank switching signal and a PWM signal in the motor control unit. 11 is a command speed holding unit, 12 is a voltage signal generating unit, 13 is a terminal voltage holding unit, and 14 is A bank switching signal generation unit, 15 is a frequency signal generation unit, 16 is a comparison operation unit, 17 is a proportional control unit, 18 is a sine wave signal generation unit, 19 is a carrier wave signal generation unit, and 20 is a PWM signal generation unit.

  In FIG. 5, a command speed holding unit 11 holds a command speed Ni given as a target value for controlling the speed of the AC motor 5, and is a register, for example. The voltage signal generator 12 generates a voltage signal of the voltage Vi on the vertical axis corresponding to the command speed Ni on the horizontal axis shown in FIG. 3 from the command speed Ni. The terminal voltage holding unit 13 detects and holds the capacitor power supply voltage Vc input to the inverter 4 from the output terminal of the capacitor storage power supply 1, and is a register, for example. The bank switching signal generator 14 compares the voltage signal Vi generated by the voltage signal generator 12 with the capacitor power supply voltage Vc held in the terminal voltage holding unit 13 so that the capacitor power supply voltage Vc does not fall below the voltage signal Vi. A bank switching signal is generated. For example, as shown in FIG. 3, a bank switching signal is generated for switching to the connection stage of the nearest voltage that makes the capacitor power supply voltage Vc not lower than the V line.

  When each electric double layer capacitor of the capacitor storage power supply 1 is charged to a full charge voltage, a plurality of electric double layer capacitors having a capacitor power supply voltage Vc that does not fall below the line of the voltage V corresponding to the speed N shown in FIG. The series-parallel connection stages are determined as shown in, for example, (a), (b), (c), and (d). However, since the capacitor power supply voltage Vc decreases with the discharge, the bank switching signal generator 14 compares the voltage of the V line with the capacitor power supply voltage Vc at a certain speed so that the capacitor power supply voltage Vc falls below the V line. Then, a series-parallel connection stage of a plurality of electric double layer capacitors is connected in series, for example, as shown in FIGS. 2 and 3 from (a) to (b),..., (C) → (d). A signal for shifting to the connection side is generated to perform bank switching control of the capacitor storage power source 1.

  The frequency signal generator 15 generates a frequency signal fi corresponding to the command speed Ni given as the control target value. The comparison calculation unit 16 compares the command speed Ni given as the control target value with the speed Nd of the AC motor 5 detected by the speed detector 6 and calculates the error Δn. The proportional control unit 17 The feedback signal α is generated from the speed error Δn. The sine wave signal generation unit 18 generates a sine wave signal based on the capacitor power supply voltage Vc held in the terminal voltage holding unit 13, the frequency signal fi generated by the frequency signal generation unit 15, and the feedback signal α generated by the proportional control unit 17. The carrier signal generator 19 generates a triangular wave carrier signal having a constant frequency, for example, 1500 Hz. The PWM signal generator 20 generates a sine wave signal and a carrier signal generated by the sine wave signal generator 18. The PWM signal is generated based on the carrier wave signal generated by the unit 19.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, a capacitor power storage device is charged from an AC power source and stored, and the voltage is adjusted by switching the connection of a plurality of electric double layer capacitors from the capacitor power storage device to a desired inverter. Although it has been described that the voltage is supplied, the converter unit that charges the capacitor power storage device from the AC power supply can also convert the voltage. You may enable it to use together with the supplied electric power. Further, when driving an electric vehicle or the like, it may be controlled to receive regenerative power by performing series-parallel switching of connections of a plurality of electric double layer capacitors according to the speed in the same manner during regeneration.

It is a figure explaining embodiment of the control apparatus of the alternating current motor which concerns on this invention. It is a figure explaining the bank switching of the connection of the some capacitor which comprises a capacitor electrical storage power supply. It is a figure which shows the relationship between the voltage applied to an AC motor corresponding to the speed of an AC motor, and a control frequency. It is a figure explaining the PWM signal generated with a sine wave signal and a carrier wave signal. It is a figure which shows embodiment of the circuit which generates the bank switching signal and PWM signal in an electric motor control part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Capacitor electrical storage power supply, 2 ... AC power supply, 3 ... Converter, 4 ... Inverter, 5 ... AC motor, 6 ... Speed detector, 7 ... Charge control part, 8 ... Electric motor control part, Vc ... Capacitor power supply voltage

Claims (1)

An AC motor control device using a capacitor storage power source and a three-phase inverter,
Ri Do from the switch circuit for switching a plurality of capacitors and a switching signal by the plurality of capacitors plurality of series-parallel connection stage charging and discharging a capacitor energy storage power supply by switching the connection stage switching the terminal voltage of the capacitor energy storage power supply ,
Voltage detecting means for detecting a terminal voltage of the capacitor storage power source;
Speed detecting means for detecting the output speed of the AC motor;
Voltage / frequency signal generating means for generating a voltage signal and a frequency signal corresponding to the command speed of the AC motor;
The voltage corresponding to the command speed is compared with the terminal voltage of the capacitor energy storage power source, and the terminal voltage of the capacitor energy storage power source is switched to the connection stage of the nearest voltage that is not lower than the voltage corresponding to the command speed. Switching signal generating means for generating a switching signal;
A three-phase inverter that converts the discharge output of the capacitor storage power source into a three-phase alternating current to drive an alternating current motor;
A triangular wave carrier signal having a constant frequency is generated by generating a sine wave signal having a frequency corresponding to the terminal voltage of the capacitor storage power source and an output speed speed error with respect to the command speed of the AC motor at a frequency corresponding to the command speed . And a control means for controlling the three-phase inverter by generating a PWM signal based on the sine wave signal.

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