JPS636000B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a system for converting alternating current power into direct current power, and converting this direct current power into direct current to direct current or direct current to alternating current to control a motor. This invention relates to an electric motor control device with improved efficiency.

[Background technology of the invention]

The motor control device to which the present invention is applied includes, for example, a system that performs AC-DC-DC conversion to control a DC motor, an AC-DC-DC-AC conversion, or an AC-DC-AC conversion. There is a method that controls an AC motor. In order to explain the prior art, an AC-DC-AC conversion type electric motor control device will be described with reference to FIG. In this diagram 1
1 is an input AC power supply, 12 is a forward converter that performs AC-DC conversion, 13 is a large-capacity filter capacitor, 14 is an inverter that performs DC-AC conversion and outputs variable frequency AC power, 15 is an AC motor, 16 is an inverse converter that performs DC-AC conversion, 1
7 is a DC reactor. In FIG. 1, AC power from an input AC power supply 11 is converted to DC power by a forward converter 12, smoothed by a filter capacitor 13, and converted again to AC power of a different frequency by an inverter 14 to drive an AC motor 15. Operates at variable speed. When power is supplied to the AC motor 15 from the input AC power supply 11, the power is supplied through the route explained above, but when power is regenerated from the AC motor 15 to the input AC power supply 11, the feedback power is once stored in the filter capacitor 13, and while smoothed by the DC reactor 17, the power is regenerated to the input AC power source 11 via the inverter 16.

[Problems with background technology]

As explained above, in the conventional electric motor control device, when power is supplied from the input AC power source 11, the forward converter 12 is operated;
The inverter 16 is operated when power is regenerated to. Further, the forward converter 12 may be configured with a diode bridge and not controlled (control angle α≒0), or may be configured with a thyristor bridge and operated within the range of control angle α = 0° to 90°. In most cases, in the operating range near the control angle α≈0, the engine operates with a leading power factor, and when the control angle lags to a certain extent and the load becomes heavy, the engine operates with a lagging power factor. Further, since the inverter 16 is constructed of a thyristor bridge and is operated within a control angle α of 90° to 180°, it has a lagging power factor. In the conventional motor control device operated in this manner, the reactive power on the input AC power source 11 side changes significantly depending on the operating state, and the apparent power of the input AC power source 11 can be supplied from the motor control device. The disadvantage was that the active power had to be very large compared to the average effective power.

In addition, due to the recent deterioration of the energy situation, if the apparent power on the input AC power source 11 side can be reduced, it is expected that efficiency will improve on the input AC power source 11 side and equipment investment costs will be reduced. There is a demand for the practical application of control devices.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a motor control device that can reduce reactive power on the input power source side.

[Summary of the invention]

In order to achieve this object, the present invention enables the forward converter and the inverse converter to be operated simultaneously, and cancels the reactive power generated in the forward converter operation with the reactive power generated in the inverse converter operation. It is characterized by the following.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. In this figure, the circuit components labeled with the same numbers as in Figure 1 are as follows:
This circuit element has the same function as that in FIG. 1, and its explanation will be omitted. In this figure, 18 is a chopper that performs DC-DC conversion, 19 is a transformer, 20 is a power factor control circuit, and 13
₁ is a filter capacitor, 18 ₁ is a semiconductor switch such as a gate turn-off thyristor, 18 ₂ is a diode, and 18 ₃ is a DC reactor.

The operation shown in FIG. 2 will be explained. The method of operating the AC motor 15 by supplying power from the input AC power source 11 and the method of regenerating the feedback power from the AC motor 15 to the input current power source 11 are the same as those shown in FIG. In this figure, since the forward converter 12 is constituted by a diode bridge, the control angle α≈0, and therefore, in normal operation, leading reactive power is generated. The chopper 18 can control its output voltage to an arbitrary value by controlling the conduction and non-conduction periods of the semiconductor switch ₁₈₁ . That is, when the semiconductor switch 18 ₁ is conductive, current flows from the filter capacitor 13 in the loop of the semiconductor switch 18 ₁ -DC reactor 18 ₃ -filter capacitor 13 ₁ -filter capacitor 13, and when the semiconductor switch 18 ₁ becomes non-conductive, the current flows through the diode 18. ₂ - DC reactor 18 ₃ -
The energy of the DC reactor 18 ₃ is released through the filter capacitor 13 ₁ -diode 18 ₂ loop. Its output power is controlled by a semiconductor switch 18.
It is well known that it is determined by the ratio of the conduction period to _one conduction period. In this figure, the converter 16 is a natural commutation rectifier that is operated in the range of control angle α = 90° to 180°, and generates delayed reactive power. On the ° side, reactive power can be generated with a large delay. The power factor control circuit 20 obtains an electric signal corresponding to the power factor of the input AC power source 11 from the voltage and current signals of the input AC power source 11, and controls the inverter 16 and chopper 18.

From input AC power supply 11, forward converter 12 - filter capacitor 13 - inverter 14 - AC motor 1
When power is supplied through route 5, forward converter 12
The power factor control circuit 20 controls the output voltage of the chopper 18 and the control angle α of the inverter 16 in accordance with the magnitude of the leading reactive power generated. That is, forward converter 1
2 is a light load, the leading reactive power generated is large, so the output voltage of the chopper 18 is high, and the inverter 16
so that the control angle α is closer to the 180° side than the 90° side.
Conversely, if the forward converter 12 is heavily loaded, the output voltage of the chopper 18 is lowered to adjust the control angle α of the inverse converter 16.
By approaching the 90° side, the delayed reactive power generated in the inverse converter 16 is reduced.

On the other hand, when the feedback power from the AC motor 15 is regenerated to the input AC power source, the output signal of the power factor control circuit 20 is used to pass the feedback power to the forward converter 12 and perform inverse conversion with the chopper 18 to generate reactive power. vessel 16
By controlling this, the reactive power of the input AC power supply 11 can be reduced. That is, depending on the magnitude of the feedback power from the AC motor 15, the forward converter 12 - filter capacitor 13 - chopper 18 - filter capacitor 13 ₁ - DC reactor 17 - inverse converter 16
- Reducing the reactive power of the input AC power supply 11 by controlling the magnitude of the current flowing in the route of the transformer 19.

As described above, according to the present invention, the reactive power of the input AC power source 11 can be reduced regardless of whether the power is being supplied from the input AC power source 11 or the power is being regenerated.

FIG. 3 shows another embodiment of the invention. In this figure, circuit elements given the same numbers as in FIGS. 1 and 2 are circuit elements having the same functions as in FIGS. 1 and 2, and their explanation will be omitted. 12 ₁ and 12 ₂ are forward converters 13 ₂ and 13 ₃
is the filter capacitor, 16 ₁ is the inverter, 17 ₁
and 17 ₂ is a DC reactor. The operation in this figure is basically the same as in Figure 2, and the forward converter 12
Two sets of ₁ and 12 ₂ are provided, and their output sides are separated from each other. Also, the forward converter 12 ₁ , 1
2 ₂ is composed of a thyristor bridge, and the magnitude and polarity of the generated reactive power change depending on the control angle α. The DC reactors 17 ₁ and 17 ₂ smooth the current that charges the filter capacitors 13 ₂ and 13 ₂ . On the other hand, the inverse converter ₁₆₁ is a gate turn-off thyristor, a large-capacity power transistor, or a forced commutation type converter, and the control angle α is from 90°.
This is a converter that can operate within a range of 270°. In FIG. 3, a chopper 18 is provided corresponding to each of the filter capacitors 13 ₂ and 13 ₃ , and the output side of the chopper 18 is connected directly to the filter capacitor 13 ₁ and the DC reactor 17 as shown in FIG. It can also be connected to the inverter 16 ₁ . The inverse converter ₁₆₁ can generate delayed reactive power when the control angle α is controlled within the range of 90° to 180°, and can generate advanced reactive power when the control angle α is controlled within the range of 180° to 270°. Therefore, even if the reactive power generated by the forward converter 12 ₁ or 12 ₂ is leading reactive power or lagging reactive power, the inverter 16 is configured to cancel this reactive power.
₁ can be controlled, so the input AC power supply 1
It is clear that the reactive power of 1 can be reduced.

Note that the present invention does not limit the insertion location of the transformer 19, as long as the AC terminal sides of the forward converters 12, _{12 1} , 12 ₂ and the inverse converters 16, 16 ₁ are insulated. Further, the number of forward converters and the number of choppers are not particularly limited, and the circuit configuration of the choppers is not particularly limited. Various other modified circuits can be constructed without changing the gist of the present invention.

〔Effect of the invention〕

According to the present invention, a chopper is provided between the DC output terminal of the forward converter and the DC input terminal of the inverse converter, and the reactive power generated by the forward converter and the reactive power of reflected polarity are generated in the reverse rectifier. It is clear that it is possible to realize a motor control device that can reduce the amount of reactive power of the input AC power source by adjusting the amount of reactive power.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional motor control device, Fig. 2 is a circuit diagram of a motor control device showing an embodiment of the present invention, and Fig. 3 is a circuit diagram of a motor control device showing another embodiment of the present invention. FIG. 3 is a circuit diagram of the device. 11... Input AC power supply, 12, _{12 1} , 12 ₂ ... Forward converter, 13, _{13 1} , 13 ₂ , 13 ₃ ... Filter capacitor, 14... Inverter, 15... AC motor, 16, 16 ₁ ... Inverse converter, 17,17 _1,17
2 ...DC reactor, 18...Chopper, ₁₈₁ ...Semiconductor switch, ₁₈₂ ...Diode, ₁₈₃ ...DC reactor, 19...Transformer, 20...Power factor control circuit.

Claims (1)

[Claims] 1 Convert the AC power of the input AC power supply into DC power with a forward converter and drive a DC motor with this DC power, or convert the DC power into AC power with an inverter to drive an AC motor, and drive the DC motor with the DC power. Alternatively, when power is fed back from an AC motor, in a motor control device that regenerates power to the input AC power source using an inverter, a chopper is provided on the input side of the inverter, and the voltage of the input AC power source is A control device for an electric motor, which is provided with a power factor control circuit that receives current as input and controls the inverse converter and chopper, thereby making it possible to control reactive power in the direction of canceling the reactive power generated by the forward converter.