JP3248218B2 - Inverter device for motor drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device suitable for driving an electric motor.

[0002]

2. Description of the Related Art Conventionally, a current-type inverter device and a voltage-type inverter device have been provided as inverter devices for driving a motor. FIG. 5 is an electric circuit diagram showing a configuration of a three-phase current source inverter device. A thyristor bridge rectifier circuit 51 having a three-phase AC power supply as an input, a reactor 52 for functioning as a constant current source, and a reactor 52
And a current-type three-phase full-bridge inverter 53 that obtains a three-phase AC current by switching the current obtained by the above and supplies the three-phase AC current to a motor 54 as a load. In addition, a diode 53b of a forward connection is connected to a series circuit of three pairs of thyristors 53a (of each phase) constituting the current type three-phase full-bridge inverter 53, and a commutation capacitor 53c is connected between the phases. ing.

FIG. 6 is an electric circuit diagram showing the configuration of a three-phase voltage source inverter device. Three pairs of (each phase) switching which constitute a voltage type three-phase full-bridge inverter 62 between terminals of a DC power supply 61 are shown. A series circuit of the elements 62a is connected, and a diode 62b is connected in parallel with each switching element 62a. Reference numeral 63 denotes a three-phase motor as a load. The DC power supply 61 simply shows a converter that receives a three-phase AC power as an input.

The three-phase current source inverter device switches the thyristor 53a of each phase so that the current waveform supplied to the load becomes a square wave.
Since the voltage waveform becomes a sine wave shape by switching the 3a in this manner, the number of times of switching of the thyristor 53a per cycle can be reduced, and a good waveform can be obtained. Focusing on the advantage that the number of times of switching per cycle can be reduced, it is applied to driving of a large motor.

The three-phase voltage source inverter switches the switching elements 62a of each phase so that the voltage waveform supplied to the load becomes a square wave. Can be simplified.

[0006]

In the above three-phase current source inverter device, the commutation capacitor 53c must be connected between each phase, so that not only the circuit configuration is significantly complicated, but also the power source is connected to a constant current source. In order to function as, the inductance of the reactor 52 must be increased, and since the current waveform is made into a square waveform, depending on load conditions, inconveniences such as overvoltage and instability may occur.

In the three-phase voltage source inverter, since the voltage waveform is controlled in the form of a square wave, there are many harmonic components included in the voltage waveform as it is, so that the noise becomes large and the efficiency becomes poor. Moreover, there is a possibility that an overcurrent occurs, and if the overcurrent occurs, a disadvantage that the switching element is destroyed occurs. In order to solve such inconvenience, generally, the switching element 62a of each phase is PWM-controlled so that the voltage waveform approaches a sine wave. However, the number of switching operations per cycle is inevitably increased. I have to. Therefore, the number of switching times that the three-phase full-bridge inverter 62 can follow is restricted.

That is, there has been a strong demand for an inverter device for driving a motor which has advantages and disadvantages in both the three-phase current source inverter device and the three-phase voltage source inverter device, has a simple circuit configuration, and can exhibit good characteristics.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has a simple circuit configuration and is characterized by the characteristics of a current-source inverter device and a voltage-source inverter device depending on the size of a load and the magnitude of an input voltage. It is an object of the present invention to provide a novel inverter device for driving a motor.

[0010]

According to a first aspect of the present invention, there is provided an inverter device for driving a motor, comprising: a bridge rectifier circuit having an AC power supply as an input; and a DC voltage obtained by the bridge rectifier circuit. Includes a step-down chopper circuit for stepping down a voltage, a voltage-type bridge inverter to which a DC power obtained by the step-down chopper circuit is input, and a regenerative power bypass diode reversely connected in parallel between the input and output of the step-down chopper circuit. .

[0011]

According to the first aspect of the present invention, a DC voltage rectified by the bridge rectifier circuit can be obtained, and the current flowing through the reactor can be controlled to DC by the step-down chopper circuit. By operating the voltage-type bridge inverter, a desired alternating current can be supplied to the motor as a load.

Here, the step-down chopper circuit functions as a constant current source when viewed from the voltage-type bridge inverter. However, when the regenerative power bypass diode is conducting, the output current of the step-down chopper circuit is reduced. Is not constant, the input voltage and the output voltage of the step-down chopper circuit become substantially equal, and conversely, the output current of the step-down chopper circuit becomes constant when the regenerative power bypass diode is not conducting. Therefore, if the conduction period of the regenerative power bypass diode is short, the output current of the step-down chopper circuit becomes substantially direct current, and the load current and voltage have the waveforms of the current source inverter device. Conversely, if the conduction period of the regenerative power bypass diode is long, the period during which the output voltage of the step-down chopper circuit becomes constant increases and becomes almost DC, and the load current and voltage become waveforms of the voltage type inverter device. That is, it has the characteristics of the current source inverter device and the voltage source inverter device.

As is clear from the above description, one regenerative power bypass diode can be substituted for the series diode conventionally connected in series to the thyristor as a switching element, and the inverter provided between the respective phases can be used. Since the diversion capacitor can be omitted, the circuit configuration as a whole can be simplified.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is an electric circuit diagram showing an embodiment of an inverter device for driving a motor according to the present invention.
, A step-down chopper circuit 3 that uses a DC voltage obtained by the three-phase diode bridge rectifier circuit 2 as a power supply, and performs a predetermined switching operation with the output of the step-down chopper circuit 3 as an input. Source three-phase full-bridge inverter 4 for supplying three-phase power to a motor 6 as a load, and a step-down chopper circuit 3
And a regenerative power bypass diode 5 reversely connected in parallel to the power supply.

In the inverter device for driving a motor having the above configuration, the output current of the step-down chopper circuit 3 becomes substantially DC when the regenerative power bypass diode 5 is not conductive, but the regenerative power bypass diode 5 is conductive. In this state, the output current of the step-down chopper circuit 3 does not become constant, and the input voltage and the output voltage of the step-down chopper circuit 3 become substantially equal. Therefore, if the period during which the regenerative power bypass diode 5 conducts is short, the output current of the step-down chopper circuit 3 becomes substantially DC, and the load current and voltage have the waveform of the current source inverter device. Conversely, if the period during which the regenerative power bypass diode 5 conducts is long, the period during which the output voltage of the step-down chopper circuit 3 is constant increases, and becomes substantially DC, and the load current and voltage are similar to the waveform of the voltage type inverter device. become.

Next, each component will be described in detail. Since the three-phase diode bridge rectifier circuit 2 employs a diode 2a as a rectifier instead of a thyristor whose phase is controlled and uses a constant voltage source by an electrolytic capacitor 2b, the configuration can be simplified. The step-down chopper circuit 3 includes a reactor 3b, a switching element 3a that is switching-controlled to control the current of the reactor 3b to DC, and a diode 3c connected in parallel with the electrolytic capacitor 2b via the switching element 3a. Have been. Therefore, the current of the reactor 3b can be controlled by the switching element 3a and the diode 3c whose switching is controlled, and by setting the switching frequency of the switching element 3a high, the reactor 3
The capacity of b can be reduced. Further, when controlling the phase of the thyristor, conventionally, it was necessary to switch six thyristors, but one switching element 3a
Only switching is required. The PI control is performed based on the current command value and the actual reactor current, and the magnitude of a signal obtained as a result of the PI control is compared with a triangular wave signal having a predetermined frequency, and switching is performed based on the magnitude comparison result. The element 3a is controlled, and the overcurrent can be suppressed when there is a possibility that an overcurrent flows to the electric motor as typified at the time of starting. As a result, the electric motor can be started softly by preventing an excessive current from flowing at the time of starting.

The above voltage type three-phase full bridge inverter 4
Is a diode 4 in parallel with the switching element 4a of each phase.
Since only b is connected and no commutation diode between the phases is required, the configuration can be significantly simplified. The regenerative power bypass diode 5 includes a step-down chopper circuit 3
Of the switching element 3a and the reactor 3b are reversely connected in parallel with the series circuit. Therefore, only when the output terminal voltage of reactor 3b is higher than the voltage between the terminals of the electrolytic capacitor of three-phase diode bridge rectifier circuit 2, regenerative power bypass diode 5 becomes conductive.

FIG. 2 shows a load voltage and a load current when a 1.2 kW load is applied by driving the induction machine using the motor driving inverter device having the above-described configuration. The load voltage has a substantially sinusoidal waveform, which indicates that the characteristics of the current source inverter device are exhibited. FIG. 3 shows the load voltage and the load current when there is no load, and it can be seen that the load voltage has a substantially square wave shape, indicating the characteristics of the voltage type inverter device.

FIG. 4 is a graph showing changes in the load current and load voltage distortion with respect to the load. The more the load increases, the closer to the current source inverter, the smaller the waveform distortion, and the problem of vibration, noise, etc. disappears. I understand.

[0020]

As described above, according to the first aspect of the present invention, the step-down chopper is incorporated in the three-phase voltage source inverter, and the diode for regenerative power bypass is reversely connected in parallel with the step-down chopper, so that the circuit configuration is simplified. It is possible to obtain a characteristic effect that the characteristics of the current source inverter and the voltage source inverter can be obtained according to the load without changing the circuit configuration.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of an inverter device for driving a motor according to the present invention.

2 is a waveform diagram showing a load voltage and a load current when a 1.2 kW load is applied by driving an induction machine using the motor driving inverter device having the configuration shown in FIG. 1;

FIG. 3 is a waveform diagram showing a load voltage and a load current when an induction machine is driven by using the motor driving inverter device having the configuration shown in FIG. 1 and no load is applied.

FIG. 4 is a diagram showing load characteristics of load voltage and load current distortion.

FIG. 5 is an electric circuit diagram showing a configuration of a conventional three-phase current source inverter device.

FIG. 6 is an electric circuit diagram showing a configuration of a conventional three-phase voltage source inverter device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 three-phase AC power supply 2 three-phase diode bridge rectifier circuit 3 step-down chopper circuit 4 voltage-type three-phase full-bridge inverter 5 regenerative power bypass diode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H02P 7/63

Claims (1)

(57) [Claims] 1. A bridge rectifier circuit (2) having an AC power supply (1) as an input, a step-down chopper circuit (3) for stepping down a DC voltage obtained by the bridge rectifier circuit (2), and a step-down chopper circuit (3). ), And a regenerative power bypass diode (5) reversely connected in parallel between the input and output of the step-down chopper circuit (3). Characteristic inverter device for driving a motor.