JPS5819169A - Controlling method for pwm control converter - Google Patents

Abstract

PURPOSE:To control a PWM control converter with good responsiveness by removing a harmonic wave by a filter and setting a firing element ON or OFF whenever the deviation between the output current of the filter and the current command pattern is displaced from the prescribed range. CONSTITUTION:The output current i of an inverter 4 becomes a superposed wave of a sinusoidal current and a triangular current, the output signal of an arithmetic circuit 11 is sinusoidal current, the outputs of arithmetic units 14-16 are produced with the harmonic component as a deviation. When the deviation signal becomes larger than the prescribed value by comparators 17-19 having hysteresis characteristic, a firing element of P side of the converter 4 is fired, and when it becomes smaller than the prescribed value, the firing element on N side of the converter is fired. In this manner, control of good responsiveness can be performed without control delay and phase delay without causing loss with the harmonic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a PWM control converter, and in particular to a PWM control method that is optimal for controlling a load without response delay or phase delay.
The present invention relates to a control method for a control converter.

In recent years, self-extinguishing high frequency power semiconductor devices such as Q'l'Q' (Qate Turn Qff) thyristors have been developed and are often used in PWM control converters (inverters) for driving electric motors. In particular, since the chopping frequency of PWM control can be sufficiently increased compared to the conventional thyristor type, the output current waveform can be made closer to a sine wave, and an excellent system with less torque ripple can be realized.

However, this output current includes a high-order harmonic component derived from PWM control, and there is a problem in that loss increases due to the secondary current component of the motor induced thereby. In particular, since the secondary current component has a high frequency, it is known that the skin effect tends to increase the effective resistance of the secondary winding circuit and increase loss.

It is being A simple method to remove harmonic components is to insert a low-pass filter, but as is well known, the filter is generally constructed from a combination of a capacitor and an axle. For this reason, it has a time constant, which causes a response delay, resulting in a control delay and a phase delay in load control.

In order to improve the responsiveness and stability of the system, it is necessary to have a feedback loop, but if a filter is used to remove harmonics, there is an inconvenience that a response delay occurs due to the time constant of the filter, as described above. in this case,
If the feedback system is constructed without using a filter, there is the disadvantage that not only ripple cannot be sufficiently suppressed, but also the loss due to the secondary winding circuit cannot be reduced as described above.

In this way, a feedback system is necessary to improve responsiveness, and a filter is necessary to eliminate loss due to harmonics, but the current situation is that it is not possible to simply combine the two. Met.

An object of the present invention is to provide a method for controlling a PWM control converter with excellent controllability and excellent responsiveness and efficiency.

The present invention removes harmonics using a filter, and controls the ignition element of a converter (inverter) on and off every time the deviation value between the output current of the filter and the current command pattern deviates from a predetermined value range. This is what I did.

FIG. 1 is a block diagram showing one embodiment of the present invention. The example shown in the figure is a case where direct current is converted to alternating current using an inverter.

A diode rectifier 1 converts power from an alternating current power source AC into direct current power. The converted power is smoothed by a filter composed of a DC reactor 2 and a smoothing capacitor 3. The DC power after smoothing is converted into AC by a PWM control converter (inverter) 4 composed of a combination of diodes and GTO thyristors for the number of phases.The output of the PWM control inverter 4 is composed of a capacitor and a reactor. The harmonic components are removed by a filter 5 and supplied as a sine wave to an induction motor 6, which is a load.

An analog signal from a speed detector 8 connected to an induction motor 6 is subjected to a calculation unit 9 in which a deviation from a speed command circuit 7 is calculated, and after being amplified by a speed deviation amplifier 10, it is sent to a calculation circuit 11. The arithmetic circuit 11 generates a motor current command pattern signal (sine wave signal) based on the signal corresponding to the speed deviation output from the amplifier 10 and the output signal of the speed detector 8.

The arithmetic circuit 11 has the number of output signals corresponding to the number of phases, and the deviation between each of these signals and the load current detected by the current transformer 12, 13 from the filter 5 is calculated and compared by the arithmetic unit 14, 15, 16. 17', 18, and 19 respectively. These comparators have hysteresis characteristics and produce an output signal when the input signal exceeds or exceeds a set value. Each output of comparator 17, 18, 19 is connected to gate amplifier 2.
0,21°22, and gate amplifiers 20~
Each output signal of 22 serves as a firing signal for the GTO thyristor, alternately turning the P and N sides on and off.

2(a), Φ)t(C), and (d) are operation waveform diagrams of each part of the apparatus of FIG. 1. 1 while referring to Figure 2.
The operation of the illustrated embodiment will be explained. Since the power supply system is well known, the explanation will be omitted here, and only the control system will be explained.

The output current i of the inverter 4 is
It increases when the O thyristor or diode conducts, and decreases when the N side conducts. Because such repetition is performed, the output current becomes a sinusoidal current superimposed with a triangular waveform current that repeatedly increases and decreases. When the output current passes through the filter 5 made up of a reactor and a capacitor, its triangular wave-like harmonics are attenuated. Arithmetic circuit 11
The output signal is a second signal based on the speed command signal and the actual speed.
It is a sine wave signal as shown in Figure (a), and on the other hand, the current transformer 12.
Each of the outputs 13 is a sine wave signal which is attenuated as shown in FIG. 2(b) but has a ripple component (harmonic signal) superimposed thereon. Arithmetic units (14 to 16) that use these signals as input signals
As shown in FIG. 2(C), only the harmonic component is output as a deviation.

The comparators 17 to 19 have hysteresis characteristics as shown in FIG.
6) generates an output signal (positive or negative) when it is exceeded (on either the positive or negative side). That is, the current command pattern signal (U phase) from the arithmetic circuit 11 and the current detection signal (U phase) from the current detector 12 are compared, and a deviation signal in which the former is higher than the latter by a predetermined value or more is determined. When the output from the arithmetic unit 14 is output, the thyristor or the diode is controlled to turn on as shown in FIG. Control the side to turn on. The V-phase and W-phase currents are similarly controlled. Regarding the W phase, the W phase current Iw is determined from the U phase current iu and the V phase current iv based on the relationship of the following equation, and one current detector is omitted.

iy = −(jt+ + jv) ... Concave curve, concave curve, concave curve (1) As a result of the above, the motor current of each phase is controlled to follow the current command pattern signal of each phase.

Incidentally, in the embodiment described above, the current detection signal is obtained from the output side of the filter 5, but if the current detection signal is obtained from the input side of the filter 5, the same problem as described in the prior art will occur. As mentioned above, the object of the present invention can be achieved by taking out the filter 5 from the outlet side, but the differences depending on which side the filter 5 takes out from are listed below.

l) Since the motor current is directly detected and controlled, it is possible to compensate for the current control delay and phase delay caused by the filter, and it is possible to faithfully control the motor current without delay in accordance with the command pattern signal. Therefore, since the torque of the motor can be controlled without delay with respect to the current command pattern signal, and the current can be controlled with no phase delay with respect to the current command pattern signal, the excitation current component and the torque acting current component of the motor current are independent. It is possible to perform so-called vector control with high precision.

2) Since the harmonics of the motor current are smaller than the input current of the filter, the hysteresis width of the comparator (the maximum deviation value of the actual current value from the current command value) can be set small.
Improves accuracy of current control.

Further, since the harmonic components are removed by the filter 5, it is possible to reduce the occurrence of the aforementioned loss of arrow inside the electric motor.

FIG. 4 is a block diagram showing another embodiment of the present invention.

This embodiment deals with the case where direct current is obtained from alternating current using a converter, and the same reference numerals are used in the figure for the same members as used in FIG. 1.

As shown in FIG. 4, the difference from the embodiment shown in FIG. 1 is that the current detection and filter positions are different, and the speed signal is changed to a DC voltage detection value (DC voltage command). That is, the filter 5 is inserted between the AC power source AC and the PWM control converter 4, and a current detection signal is obtained from its input side. On the other hand, the power supply voltage detector 23 converts the voltage of the alternating current power supply AC into a speed detection signal.
The obtained AC voltage signal is sent to the arithmetic circuit 11. Further, the voltage deviation is obtained by calculating the deviation between the output signal of the DC voltage command circuit 24 and the DC output voltage detection value by the voltage detector 28 in the arithmetic unit 25, and further amplifying it by a predetermined value in the voltage deviation amplifier 26. . Note that the capacitor 27 inserted on the DC output side is for smoothing.

Next, the operation of this circuit will be explained. The alternating current input current (i) of the converter 4 increases when the N-side GTO thyristor or diode conducts, and likewise decreases when the P-side conducts. Therefore, the AC input current is a sine wave current with a triangular wave current superimposed on it. When the AC input current passes through the filter 5, its triangular harmonics are absorbed and the amount transmitted to the AC power supply (system) is reduced. The current command pattern signal (R phase) from the arithmetic circuit 10 and the power supply current (R phase) detected by the current detector 11 are transmitted to the arithmetic units 14 to 14.
16, when the former is larger than the latter by a predetermined value or more, the N-side GTO thyristor or diode is controlled to turn on, and conversely, when the former is smaller than the latter by a predetermined value or more, the N-side GTO thyristor or diode is controlled to turn on. Similarly, P
The side is controlled to turn on. Regarding the T-phase, the T-phase current i is determined from the R-phase current iII and the S-phase current 1B based on the relationship of the following equation, and the current detector is omitted.

”T= (IR+l1l) ・・・・・・・・・
(2) As a result of the above, the power supply current of each phase is controlled to follow the current command pattern signal of each phase.

By the way, compared to the case where similar control is performed by detecting the AC input current of the converter 4, the harmonic component of the power supply current is smaller than that of the AC input current of the converter, so the hysteresis width of the comparator is small. Can be set. Therefore, the accuracy of current control is improved, and the power supply current can be precisely controlled to a predetermined phase with respect to the power supply voltage. Therefore, the power factor of the power source can always be controlled to 1.0 with high precision.

Further, the filter 5 can remove harmonic components, and can prevent the influence of harmonics on the AC power supply system.

As is clear from the above, according to the present invention, responsive control without control delay and phase delay can be realized without causing loss due to harmonics.

In the above embodiment, a description has been given of a device that drives an induction motor, but the present invention can also be applied to a device that controls a synchronous motor to obtain similar effects.

In that case, a signal from a position detector for detecting the rotational position of the motor is input to the arithmetic circuit 11 in FIG. 1 instead of the speed detection signal, and a current command pattern signal synchronized with the induced electromotive force of the motor is taken out. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
(b), (C), and (d) are operational waveform diagrams of each part of the embodiment of FIG. 1, FIG. 3 is an explanatory diagram of the operation of the comparator according to the present invention, and FIG. It is a block diagram showing an example. 1... Diode rectifier, 2... DC reactor,
3゜27... Smooth condenser, 4... PWM control converter, 5... Filter, 6... Induction motor, 7...
...Speed command circuit, 8...Speed detector, 9, 14, 1
5,16゜25... Arithmetic unit, 10... Speed deviation amplifier, 11... Arithmetic circuit, 12.13... Current transformer, 1
7, 18.19... Comparator, 20, 21.22...
Gate amplifier, 23... Power supply voltage detector, 24...
DC voltage command circuit, Figure 1 Figure 2 Time - Figure 3 Figure 3

Claims (1)

[Claims] 1. In a method of controlling a PWM control converter that supplies power to a load by performing a forward conversion or inverse conversion operation using a current command signal or a voltage command signal generated based on a command value and an actual value, the PWM control conversion Every time the deviation between the detected value of the current flowing to the non-PWM control converter side of the filter provided on the power supply side or the load side of the device and the command signal exceeds a predetermined setting value, the ignition control signal is switched to the PWM control converter side. A method for controlling a PWM control converter, the method comprising applying voltage to switching elements constituting the control converter.