JPS6236476B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation control device for an AC motor, and particularly to a regenerative braking device.

Conventionally, in regenerative braking devices in which the regenerative bridge is configured with a thyristor, a step-up transformer is interposed between the regenerative thyristor bridge and the AC power supply in order to prevent malfunction of commutation of the thyristor bridge. ing. For this reason, devices using this system had the drawback of being large and expensive due to the large capacity step-up transformer. A device that solved this defect by using a transistor regeneration bridge was published in JP-A-Sho.
It is described in Publication No. 56-29479. Further, a device in which the above-mentioned defects are solved by a combination of a regenerative thyristor bridge and a switch transistor is described in Japanese Patent Laid-Open No. 56-29480. The devices described in the above-mentioned Japanese Patent Application Laid-open Nos. 56-29479 and 56-29480 all use transistors in the regenerative circuit. However, transistors are expensive, and if they are used, the device becomes expensive. Furthermore, it is difficult for the transistor type to support a 400V class AC power supply, which requires a switch element withstand voltage of at least 800V. Further, in the device described in Japanese Patent Application Laid-Open No. 56-29479, a diode for detecting that the AC motor is in the regenerative braking region is connected in series to the positive bus of the power circuit. Therefore, a large-capacity regenerative voltage detection diode must be used, which makes the device expensive, and there is a drawback that heat generation due to the forward voltage of the diode is large, causing a drop in efficiency.

Therefore, the present invention provides a regenerative bridge that is cheaper than a transistor, has high withstand voltage and high peak current capacity equivalent to an SCR, and does not require energizing a special component circuit to prevent commutation errors as required for an SCR. Highly reliable switching operation possible
By using GTOSCR, the aim is to provide a regenerative braking device for AC motors that is inexpensive, highly reliable, and compatible with 400V class power supplies, and furthermore, a regenerative voltage detector is installed in series with the power circuit. The purpose of this is to reduce the cost of the device by avoiding the above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described in detail below based on embodiments shown in the accompanying drawings.

In Fig. 1, 2 is an AC motor such as a three-phase induction motor, 4 is an input diode rectifier bridge composed of diodes D1 to D6, which rectifies the voltage of the RSR phase of the three-phase AC power supply, and 6 is a GTOSCR (Gate
Turn Off Thyristor) Regenerative GTOSCR bridge consisting of S1 to S6, 10 a smoothing capacitor, 12 a variable voltage variable frequency inverter consisting of GTOSCR, 14 a flywheel diode bridge consisting of diodes, 8 a power circuit The smoothing capacitor 20 connected between the positive bus 16 and the negative bus 18 is a DC current transformer, and is connected to a regenerative current control circuit 22. The output of the regenerative current control circuit 22 is connected to the AND gate 38, and outputs a signal of "1" when the regenerative current is less than a specified value. 24 is a rectifier made of a diode, and is provided branching off from the power circuit. 25 is a regenerative voltage detector consisting of a comparator, one end of which is connected to the positive bus 16 side of the smoothing capacitor 8, and the other input end of which is connected to the output end of the rectifier 24. 26 is a synchronous transformer whose input end is connected to an AC power source, and a diode rectifier bridge 28 is connected to its low voltage side. Said rectifier bridge 28 forms a similar circuit of said input diode rectifier bridge 4. 30 is a smoothing capacitor provided between the positive bus 34 and the negative bus 32, and 36 is a regeneration synchronization comparator, which is composed of comparators CP1 to CP6. One input end of the comparator CP1 is connected to the r-phase terminal of the synchronous transformer 26, and the other input end is connected to the minus bus 32 side. One input end of the comparator CP3 is connected to the s-phase terminal of the synchronous transformer 26, and the other input end is connected to the minus bus 32. One input end of the comparator CP5 is connected to the t-phase terminal of the synchronous transformer 26, and the other input end is connected to the minus bus 32. One input terminal of the comparator CP2 is connected to the r-phase terminal of the synchronous transformer 26, and the other input terminal is connected to the positive bus 34. One input terminal of comparator CP4 is the synchronous transformer 26
The other input terminal is connected to the positive bus 34. One input terminal of the comparator CP6 is connected to the t-phase terminal of the synchronous transformer 26, and the other input terminal is connected to the positive bus 34. The rst phase voltage of the synchronous transformer 26 corresponds to the RST phase voltage. The comparators CP1 to CP6 output a signal of "1" when the potential of one input cathode end N is lower than the potential of the other input anode end P. Reference numeral 38 denotes an AND gate, which is composed of six AND circuits A1 to A6 corresponding to the comparators CP1 to CP6. Each input terminal of the AND circuits A1 to A6 is connected to the output terminal of the corresponding comparator CP1 to CP6.
The output terminal of the regenerative voltage detector 25 is connected to each input terminal of the AND circuits A1 to A6, and the output terminal of the regenerative current control circuit 22 is connected to each input terminal of the AND circuits A1 to A6.
are connected to each input terminal of the 40 is a gate pulse amplifier, which consists of amplifiers PA1 to PA6, and the output terminal of each amplifier is connected to the corresponding GTOSCR.
It is connected to the gates of S1 to S6.

Next, the operation of this embodiment will be explained.

In a normal driving mode, the AC power supply voltage is rectified by the input diode rectifier bridge 4, and a constant DC voltage is smoothed by the smoothing capacitor 8 and is supplied to the variable frequency inverter 12, which is connected to an ignition circuit (not shown). ), variable voltage variable frequency operation is performed by a so-called PWM control method that simultaneously controls the pulse period and pulse width of each GTOSCR so that the induction motor 2 is operated at a frequency and voltage corresponding to the speed command signal. Next, when the speed command value is changed in order to decelerate, the newly commanded synchronous speed becomes lower than the speed at which the induction motor 2 has been rotating, so the induction motor 2 rotates with negative slip. Power is regenerated from the stator windings. With this regenerated power, the smoothing capacitor 8
to charge. As a result, the voltage on the positive bus 16 side of the power circuit becomes higher than in normal operation. As a result, the potential at the input anode end of the regenerative voltage detector 25 becomes higher than the potential at the input cathode end, and the regenerative voltage detector 25 outputs a signal of "1" and conducts each AND circuit of the AND gate 38. Make it possible. Thereby, it is possible to detect that the induction motor 2 is in the regenerative state. In this regenerative state, when each diode of the input diode rectifier bridge 4 is forward biased, the regenerative GTOSCR, which has the same phase and opposite poles in relation to the diodes D1 to D6 and the AC power supply, has a maximum forward voltage. If an ignition signal is applied during this period to make them conductive, a regenerative current can flow through the AC power supply, and the induction motor 22 acts as a generator and rapidly decelerates to the new speed command value. be done. This operation will be explained in detail below.

The R, S, and T phase AC phase voltages of the AC power supply are stepped down through the synchronous transformer 26 and converted into lower voltage r, s, and t phase voltages corresponding to the R, S, and T phases. A smoothing capacitor 30 and a load resistor 41 are connected to the output of each diode rectifier bridge 28, and an idle current flows therethrough. If the voltage of the diode is determined by Cp1 to Cp6 of the comparator 36, the forward voltage drop of the diode can be reduced only when the forward bias is applied to each diode.
The anode of each comparator becomes high by 0.7V, resulting in an output of “1”, which causes the comparator to
Regeneration synchronization signals a to f are generated at Cp1 to Cp6 as shown in FIG. 2C, and a very simple and highly reliable regeneration synchronization circuit can be constructed.

The regenerative synchronization signals a to f pass through the AND gate 38 and the gate pulse amplifier 40, are converted into gate control signals, and are sent to the corresponding GTOSCR S1 to
Applied to the gate of S6. GTOSCR S1~S
An example of the operation of No. 6 will be explained below.

When the electric motor 2 enters the regenerative braking area, the detector 25
outputs "1", and the gate of the AND gate 38 becomes conductive. Figure 2A shows the phase voltage of the AC power supply as seen from the negative bus 18 of the circuit, and N-R
NS indicates the waveform of the S phase, and NT indicates the waveform of the T phase. Figure 2 (b) shows the phase voltage waveform seen from the positive bus 16 of the power circuit, where P-S is the S phase,
T is in T phase and PR is in R phase. Although the phase voltage waveform is shown as a triangular wave type for convenience, it is actually a triangular wave type. In the figure, from time 1 to time 2, as shown in the timing of Figure 2 C, the comparator
The output levels of CP1, CP2, CP4, and CP5 are in the “0” state, and the comparators CP3 and CP6
is in the state of "1". As can be understood from the phase voltages in Figure 2 A and B, the diodes D4,
D5 is in a forward bias state. This allows GTOSCR of the same polarity as the forward biased diode D4.
S3, GTOSCR S with the same polarity as diode D5
6 becomes conductive, and regenerative current flows through the AC power supply. In this case, ON and OFF signals are alternately applied to the gates of GTOSCR S3 and S6 within the conduction time by the pulse output of the regenerative current control circuit 22, thereby controlling the regenerative current. Between hours 2 and 3
GTOSCRS S3 and S2 become conductive. In this way, when each diode of the input diode rectifier bridge 4 is forward biased, the regenerative GTOSCR bridge 6, which has the same polarity as the diodes of the input diode rectifier bridge 4,
GTOSCR is fired and becomes conductive.

As mentioned above, the present invention uses GTOSCR, which is cheaper and more versatile than transistors, as an element constituting the regeneration bridge, so it is possible to reduce the cost of the device and make it compatible with 400V class power supplies. Reliable regenerative braking can be performed without using a step-up transformer. In addition, since the regenerative voltage detector is not placed in series with the power circuit, there is no need to use a large-capacity detector.Furthermore, a diode rectifier bridge similar to the input diode rectifier bridge, and the anode and cathode of each diode of this A simple and reliable regeneration synchronization circuit can be constructed by using a regeneration synchronization comparator consisting of a comparator that discriminates between voltages, and this has the effect of reducing the cost of the device.

[Brief explanation of the drawing]

The figures show preferred embodiments of the present invention, with FIG. 1 being an electric circuit diagram and FIG. 2 being a waveform diagram for explaining the operation. 2...AC motor, 4...Diode rectifier bridge, 6...GTOSCR bridge for regeneration, 8,
10... Smoothing capacitor, 12... Inverter, 14... Flywheel diode bridge,
16...Plus bus, 18...Minus bus, 2
0... Direct current detection means, 22... Regenerative current control circuit, 25... Regenerative voltage detector, 26... Synchronous transformer, 28... Diode rectifier bridge, 3
0...Smoothing capacitor, 32...Minus bus, 34...Positive bus, 36...Regeneration synchronous comparator, 38...And gate.

Claims (1)

[Claims] 1 an input diode rectifier bridge 4 connected to an AC power supply, a regeneration GTOSCR bridge 6,
Power circuit positive bus 16 and negative bus 18
A smoothing capacitor 8 disposed between them, a variable voltage variable frequency inverter 12, an AC motor 2 whose rotation is controlled by the variable voltage variable frequency inverter 12, and an AC motor 2 provided branching off from the power circuit. Diode rectifier 24 connected to power supply
A regeneration system that compares the DC potential on the anode side of the smoothing capacitor 8 with the DC potential on the output side of the diode rectifier 24, and outputs a regeneration voltage detection signal when the potential on the anode side of the smoothing capacitor 8 becomes high. a voltage detector 25; a second diode rectifier bridge 28 similar to the input diode rectifier bridge 4 and connected to the alternating current power supply; and a comparator CP1 to determine the voltage between the anode and cathode of each diode of the bridge 28. a regeneration synchronizing signal for conducting each GTOSCR of the regeneration GTOSCR bridge which is composed of a CP6 and has the same opposite polarity as the forward biased diode when each diode of the input diode rectifier bridge 4 is forward biased; a regeneration synchronization comparator 36 to be generated, and a gate control signal connected to the regeneration synchronization comparator 36, conduction/cutoff controlled by the output signal of the regeneration voltage detector 25, and based on the regeneration synchronization signal of the regeneration synchronization comparator. Each GTOSCR of the regeneration GTOSCR bridge 6
A rotation control device for an AC motor, comprising an AND gate circuit 38 that supplies a gate electrode to the gate electrode of the AC motor.