JPS5846895A - Inverter controlling system for induction motor - Google Patents

Abstract

PURPOSE:To reduce the capacity of a smoothing capacitor in a filter circuit by a method wherein a phase difference is selected between frequency signals supplied to inverters in response to a selection of carrier frequencies for pulse width modulation. CONSTITUTION:The system is constituted of pulse width modulation inverters 4A and 4B receiving power from a common filter circuit 3, induction motors 5A- 5H controlled by the respective inverters 4A and 4B, voltage control means 11A and 11B for controlling the inverter output voltages, and a frequency control means 9 for controlling inverter operating frequencies in response to revolving speeds. A phase shift circuit 28 is added to said system which provides a phase shift to frequency signals being fed to each inverter from frequency control means 11A and 11B, while said circuit 28 switches over the magnitude of the phase difference in accordance with the carrier frequency switching over of the pulse width modulation. The system being thus constructed, the ripple frequency in the output current from the filter circuit 3 is larger, realizing a smoothing capacitor 7 effectively functioning with a reduced capacity in the filter circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for an induction motor using a PWM (pulse width RH) inverter, and in particular to a method suitable for trains, etc., in which a plurality of OIl conduction motors are controlled by a plurality of PWM inverters. . - Recently, a system has been developed in which an induction motor is used as a motor for driving a train, and the speed of this induction motor is controlled by a PWM inverter with variable frequency and variable voltage. Its basic configuration is shown in Figure 1.

The DC voltage of the overhead wire 1 is taken in from a pantograph 2 and is applied to an inverter 4 through a filter circuit 3. The inverter 4 converts DC voltage into three-phase AC with variable frequency and variable voltage.For trains, it is recommended to use a PWM inverter using Ii thyristor or B GTO (gate turn-off thyristor) due to its weight and price. The 93-phase AC voltage generated by this inverter 4, which is considered practical in terms of the following points, is fed in parallel to four induction motors 5A, 5B, 50, and 5D that drive the wheels in this example.

The filter circuit 3 is composed of a smoothing reactor 6 and a smoothing condenser t7, and prevents rectification ripple from the substation from entering from the overhead wire 1, and at the same time prevents high frequency components generated by the inverter 4 from flowing into the overhead wire 1 and interfering with the signal system. t4 Role of preventing growth f: ″r.

Since the inverter 4 has variable frequency characteristics and variable voltage characteristics, it has two control inputs: frequency and voltage.

For this purpose, the control system includes a frequency control system consisting of a pulse generator 8 that detects the vehicle speed and a frequency control circuit 9 that determines the operating frequency of the inverter 40 by adding a slip frequency to the output frequency of the pulse generator 8; There are two systems of voltage control systems consisting of a voltage control circuit 11 that controls the output voltage of the inverter 4 according to the output of the voltage pattern circuit 1°.In addition, in electric trains, constant acceleration 21 is obtained by keeping the torque of the induction motor constant. This is the basic control method for
Generally, the output voltage of the inverter 4 is made proportional to the operating frequency. Therefore, in the example of FIG. 1, the inverter 4
There is also a method in which the output voltage of the induction motor is detected by a voltage detector 12Kto and feedback controlled using a Kllll ratio detector. be. In this case, a current pattern circuit will be used in place 9 of the voltage pattern circuit 1o, but since the output voltage sound of the inverter 4 will be controlled in any case, the voltage control distance is given to the inverter 4 by the voltage control path 11°. However, in order to improve the characteristics, there is also a method of controlling using a voltage detector, a current detector, one voltage pattern path, and a current control circuit.

Next, Figure @2 is a one-way diagram to clarify the operation of the PWM inverter. ◎ The same parts as in Figure 1 are given the same reference numerals. ◎ In Figure 2, 13.14 is a diagram of the inverter. 16.17 is a reverse conduction capacitor for arc extinguishing, 18.18 is a t reactor, and 20 is a gate signal generation circuit. ◎ Also, 21 is a pulse width modulator.

Now, a frequency signal is inputted to the frequency control input terminal 22 from the frequency control (b) path 9 (see FIG. 1), and the zero sine wave generation circuit 23 is synchronized with the frequency signal, for example, as shown in FIG. ) generates a sine wave voltage. Similarly, the triangular wave generating circuit 24 generates a triangular wave (car, rear) like the one shown in the center of FIG. 3, which has a frequency n times, in this example, nine times the frequency of the sine wave. The output voltage 0) of the sine wave generation circuit 23 is adjusted in amplitude t' by the amplitude adjustment circuit 25 and applied to one input terminal of the comparator 26.
7 receives a voltage control signal from the voltage control circuit 11 (see Figure 111), and in response to this signal, the comparator 26
The triangular wave (b) is applied to the other input terminal of the comparator 260. As a result, the comparator 26 outputs the voltage as shown in FIG.
◎ The gate signal generation circuit 20 outputs a pulse width modulation waveform like f1.
Accordingly, a gate signal for operating the main thyristors 13 and 14 of the inverter 4 is generated.

The voltage waveform of one phase of the output voltage of the inverter 4, for example, the U phase, is the voltage waveform of the main thyristors 13 and 14 of the upper and lower arms
Since it is done with the voltage generated by conduction, it is not a sine wave but a third wave.
The pulse voltage shown in Figure (C) is 0. However, the pulse width varies! Since we are performing ilI, the average value of the pulse voltage is! 1! Figure 3 (c) Trap The distribution will be sinusoidal as shown by the dotted line ◎The width of each pulse in the pulse width modulation waveform f→ will be It becomes wider and smaller. Since the amplitude of the output voltage 4h of the inverter 4 (sine wave voltage 0) becomes larger, the amplitude becomes higher, and as the amplitude becomes smaller, the amplitude becomes lower.

The output voltage tl of the input I↑-I4 conduction as described above.

When applying a motive power of 5A to 5DK, the flow and current waveform are as follows.
The result is a waveform with few low-order harmonic components, as shown in the figure).

In the above example, the operating frequency of the inverter 4 (sine wave voltage f
Carrier (triangular wave fC4) for oO frequency aK@t)
In this case, the ratio n of the frequencies is 9, and in this case, 9 pulses of the pulse width modulated wave are generated within one cycle of the L sine wave, so such a case is called a 9-pulse modulation mode. n
If the value of is increased, the low-order harmonic components contained in the induction motor current will be reduced, but if it is too large, the loss will increase due to the increase in the number of commutations. Practically, the maximum value of ijn is about 27, and the value of n must be decreased as the inverter's operating frequency increases, otherwise the output voltage cannot be increased. For example, the value of Fia is set to 27, and as the operating frequency of the inverter increases, the carrier frequency is switched and the value of n is decreased as 27 → 15 → 9 → 5 → 3 → 10 Figure 4 shows n- Fig. 5 shows the waveforms of sine wave 0), triangular wave (b), pulse width modulated wave (c), and induction motor current in the 15 pulse modulation mode.
0 Showing similar waveforms in pulse variation mode 0 In this way, when you change the value of n and change the modulation mode, the content of harmonic components will differ 0 Also, when you change the gR1il mode, the switching phase will also change. Therefore, the input current waveform of the inverter also changes.
Waveforms 1 of the inverter input current H) and its average value ←) and the filter circuit smoothing capacitor voltage (C) in each cooking mode are shown.

By the way, in a normal train, it is practical to control eight electric motors with a single unit control device, even from the examples of conventional chisel control systems.However, with the thyristors currently in practical use, , 1500V at current capacity 0 point,
It is difficult to collectively control eight induction electric motors 1a of about 100 to more than 100 kW.

Therefore, in the case of the inverter control method, it is considered common to use one inverter to control four induction motors, a total of two inverters. Even when two inverters are used in this way, it is more economical to use a common filter circuit. If the first filter circuit is used to support two inverters, the filter circuit will cost less than one inverter.
Because of the necessity of halving the inductance of the smoothing reactor and doubling the capacity of the smoothing capacitor, it is necessary to increase the size of the filter circuit, especially the smoothing capacitor, in accordance with the number of inverters that can be supported. The technical issue here is how to miniaturize smoothing capacitors.

In order to reduce the capacitance of the smoothing capacitor, the input frequency of the two inverters can be reduced by creating a phase difference between the frequency signals given to the two inverters and operating the two inverters at the same frequency but with different phases. It is possible to increase the ripple frequency of the sum of currents.

However, in the case of a PWM inverter, as mentioned above,
As the operating frequency of the inverter increases, the carrier frequency is switched so that the value of n decreases.
In the explanation of the above conventional technology, we will simplify the explanation. Therefore, 1 filter circuit, 2 PWM inverters, 8 induction motors
Next, we will explain the case of a machine, and the above problem can be solved by
One filter circuit handles multiple PWM inverter tubes, each PWM inverter is 1゛～～Multiple induction current 1III*
This is common when controlling.

It is an object of the present invention to provide an induction motor which eliminates the above-mentioned drawbacks of the prior art, uses a plurality of PWM inverters, and controls an induction motor with each PWM inverter, while reducing the capacitance of the filter circuit. To achieve this objective, the present invention provides a plurality of PWM inverters fed from a DC power source through a common filter circuit, and each of these inverters controlled by a a plurality of induction motors, voltage control means for controlling the output voltage and sound of the inverter, and frequency control means for controlling the operating frequency "a" of the inverter according to the rotational speed of the induction motor, In an inverter control system for an induction motor in which the inverter switches the frequency during pulse width modulation according to the operating frequency of the inverter, a phase shift circuit tube provides a phase difference to a frequency signal supplied from the frequency control means to each of the inverters. 15, wherein the phase shift circuit switches the magnitude of the phase difference in response to switching of the intermediate frequency of the pulse width modulation.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. 0 In FIG. 7, the same parts as in FIG. 1 are given the same reference numerals. In this example, one 7. Ilter circuit 3 to 2
Four PWM inverters, 4B, are connected. One inverter has four induction motors 5A to 5Dt-
1 The other inverter 4B also has four induction motors 5E.
~5Ht control. Output voltage distribution of inverters 4A and 4B, voltage pattern circuit 10 corresponding to each as before
A, 10B, voltage control circuits 11A, IIB, and voltage detection circuits 12A, 12B.

This embodiment is a frequency control system that is significantly different from the conventional one. That is, the frequency signal that determines the operating frequency of the inverter created by the frequency control circuit 9 is transmitted to one of the inverters 4.
M is connected to A, and K is inputted through the other inverter 4BKR phase shift circuit 28t.

The phase shift circuit 28 is for providing a predetermined phase difference between the frequency signal input to one inverter 4A and the frequency signal input to the other inverter 4B. It is summed to switch in response to switching of the width modulation carrier frequency.

The magnitude of the phase difference can be switched, for example, by using the carrier frequency switching signal of the pulse width modulator and in synchronization with the switching of the carrier frequency. For example, the ratio nO value of 27 → 1
If the change is 5 → 9 → 5 → 3 → 1, the above phase difference Δ-'' will be changed to 2 × 1 accordingly.In the case of 5-pulse modulation mode, the pulse width The modulated waveform has five pulses in an l-cycle circle, but since the frequency of the triangular wave is six times that of the sine wave, it is treated as n=6.

When the phase difference Δ# of the frequency signals given to the two PWM inverters 4A and 4B is switched as described above in accordance with the switching of the carrier frequency, the ripple frequency of the output current of the filter circuit 3 is equal to that of one PWM inverter. It will be about twice that of the case. For example, to explain the combination of n''-9 with reference to Figure 8, the input current of the four inverters on one side is (A)
The input current of the other inverter 4B has a waveform as shown in (←) whose phase is delayed by %x71B from (a). The output current of the filter circuit 3 is the sum of the two (-9), and the ripple frequency is twice that of the case of one inverter. Doubling the ripple frequency means that the capacity of the smoothing capacitor can be reduced to half, so even if one filter circuit handles two inverters, the capacity of the smoothing capacitor will be Since only one inverter is required, the smoothing capacitor can be downsized.

In addition, in the above embodiment, the number of inverters handled by one filter circuit is t.
% If the ratio of the carrier frequency to the inverter operating frequency is fn, then the phase difference between the operating frequencies for one inverter should be π/mn. There is no problem even if there is a slight deviation from w/mnK.

According to the present invention, when power is supplied through a common filter circuit to a plurality of PWM inverters, each of which is controlled by an induction motor horizontal tube, the frequency applied to each inverter according to the switching of the carrier frequency of pulse width modulation. In addition to increasing the ripple frequency of the output current of the filter circuit by switching the phase difference of the signal, the capacity of the smoothing capacitor in the filter circuit can be reduced. Therefore, the smoothing capacitor can be made smaller and lighter. It has the advantage that it can significantly reduce costs, and in the case of electric trains, it can help save electricity.

[Brief explanation of the drawing]

Figure 1 is a pull diagram showing the basic configuration of the conventional inverter control system for induction motors, Figure 2 is a pull diagram showing the basic configuration of the inverter control system for conventional induction motors, and Figure 2 shows the inverter when the circuit modulation mode of the PWM inverter section in Figure 1 is changed. A waveform diagram showing changes in input current and smoothing capacitor voltage of the filter circuit, and FIG. 7 is a block diagram showing an inverter control system for an induction motor according to an embodiment of the present invention. FIG. 7 is a waveform diagram showing waveforms of the input current of the inverter and the output current of the filter circuit in the OFi shown in FIG. 7; 1... Frame # (DC power supply), 3... Filter circuit, 4A, 4B... PWM inverter,
5A~5H...Induction motor, 6...Smoothing reactor, 1...5F smoothing capacitor, 8.
...Frequency control circuit, 11A, 11B...
・Voltage control four-way, 21...Pulse width modulator, 2
8... Phase shift) I circuit 〇 Fig. 4 Fig. 5rIA Fig. 6 (a) 27 pulse change 1l-h-do (n = 27)
(ω15 pulse cusp 1 layer mode - (n=15) 9/<J
Lsu1Il14-F (n=9) (d)5
Pulse change 14 tons - F (n = 6) = -tqA C i11

Claims (1)

[Scope of Claims] 1. A plurality of pulse width modulation inverters supplied with power from a DC power supply through a common 7' inverter circuit, a plurality of induction machines respectively controlled by these inverters, and an output voltage of the inverters. and a frequency control means for controlling the operating frequency of the inverter according to the rotational speed of the induction motor, and a frequency control means for controlling the operating frequency of the inverter according to the operating frequency of the inverter. A phase shift circuit is provided to provide a phase difference to the frequency signal applied from the frequency control means to each of the inverters, and the phase shift circuit changes the frequency signal according to the switching of the carrier frequency of the pulse width modulation. An inverter control method for an induction motor characterized by summation that switches the magnitude of phase difference. 2. In claim 1, when the number of inverters t''s is the ratio t-n of the carrier frequency to the operating frequency of the inverter, the phase difference tube x/mn. This is an inverter control system for induction motors.