JPS60160396A - Controller of current type inverter - Google Patents

Abstract

PURPOSE:To improve the stability at regenerative rotation time, to increase the stabilizing range and to improve the dynamic characteristic by differentiating the value divided by a frequency command value at the multiplied value of the voltage of an intermediate circuit by an input current. CONSTITUTION:An inverter is controlled by a multiplier 22 for multiplying the voltage VDC of a DC intermediate circuit of a current type inverter by an input current, a divider 23 for dividing the output of the multiplier 22 by the frequency command value from a voltage instruction unit 21, by differentiating the output of the divider 23 by a differentiator 24, subtracting by a subtractor 30 the differentiated value by the frequency command value through an oscillator 18 and a frequency divider 17. Thus, the stability is improved for any of the motor driven and regenerative states. Since the current is not directly differentiated by the conventional current differentiating stabilization system, the differentiating gain of the differentiator can be readily set.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a control device for a current source inverter that drives an induction motor.

<Prior Art> FIG. 1 is a diagram showing the configuration of a conventional example of a current source inverter (for simplification, only one phase) for driving an eight-phase induction motor and its control device. Thyristor for converter 2.
The DC current converted from AC by 8 passes through the DC reactor 4 to the inverter thyristors 5 and 6, the diode 7.8, and the commutating capacitor 9. It is converted into an alternating current by lO and supplied to the induction motor 11. The voltage of the induction motor 11 is converted to DC by a diode 18 and then passed through a filter 2.
9, it is smoothed and becomes a voltage feedback signal. The difference between this voltage feedback signal and the command value of the voltage command device 21 is amplified by the voltage controller 20 and becomes a current command. Based on this current command, current transformer 1, diode 12, current controller 19, phase shifter 14, pulse transformer 15, converter sirisk 2
．． 8 performs known current minor loop control.

Since the DC command is the current command of this current minor loop, the current IDC of the DC reactor 4, which is the current of the DC intermediate circuit, is proportional to the current command. On the other hand, the voltage command device 21
An AC signal with a frequency proportional to the frequency command value of oscillator 1
8, and becomes the ignition signal for the inverter sirisks 5 and 6 through the frequency divider 17 and pulse transformer 16.

This control is known as V//constant control of an induction motor.

However, in this conventional current source inverter, the voltage of the induction motor 11 is
It is known that rotation etc. become unstable. This phenomenon tends to occur when the frequency of the induction motor 11 is high. For this reason, stabilization has conventionally been achieved by turning on one of the switches 25 and 26. The case where the switch 26 is turned on is a stabilization method called "current differentiation." Since the detected current value of the current transformer 1 is in a proportional relationship with the current Ioc flowing through the DC reactor 4 and the current of the induction motor 11, the current of the current transformer 1 is differentiated by the differentiator 24, and the differential value is calculated by the subtracter 80. It is subtracted from the frequency command value of the voltage command device 21. This means that when the current of the induction motor 11 increases, the output (differential value) of the differentiator 24 becomes positive.If the frequency command value of the voltage command device 21 is constant, the input of the excavator 18 decreases, and the output (differential value) of the differentiator 24 becomes positive. Stabilization is achieved by lowering the frequency of the applied alternating current. The case where the switch 26 is turned off and the switch 25 is turned on is a stabilization method called "voltage differentiation."

When the voltage of the induction motor] 1 changes, its polarity is inverted by the polarity inverter 28, differentiated by the differentiator 24, and the result is subtracted from the frequency command value of the voltage command device 21 by the subtractor 80. Therefore, in this case, when the voltage of the induction motor 11 increases due to the action of the polarity inverter 28, the oscillator 18
The 0 input increases, the frequency of the induction motor 11 increases, and stabilization is performed.

Although these two conventional stabilization methods have a stabilizing effect to some extent, they have the effect of destabilizing the induction motor 11 during "regenerative" operation.

This is a method of detecting current and voltage using a current transformer 11 diode 12 or diode 18.

This is because only the magnitude of the voltage is detected. In other words, even if the induction motor 11 is in two different operating states, "electric" and "regenerative," the diode 12.18 detects the absolute values of current and voltage, so both states can be This is because it cannot be distinguished. In addition, since "current differentiation" operates based on changes in the primary current including the excitation current, the differential value varies greatly depending on the operating point of the induction motor 11. If you adjust the differential gain in a state where the induction motor 11 is in disorder, adjusting the differential gain will result in a change in the non-disturbance region. There were cases where disturbances occurred. In other words, "current differentiation" has the disadvantage that the stabilization region is narrow.

<Objective of the Invention> Therefore, an object of the present invention is to provide a control device for a current source inverter that improves stability even during "regenerative" operation, expands the stabilization range, and improves dynamic characteristics. It is in.

<Structure of the Invention> For this purpose, the present invention detects the voltage of the DC intermediate circuit of the inverter, multiplies this voltage and the input current of the DC intermediate circuit, and then divides this product by the frequency command value. This is an amount proportional to the torque of the induction motor, and the differential value of this amount is subtracted from the frequency command value. Therefore, in the case of T-electric motors, when the torque increases over time, the frequency of the induction motor decreases and attempts to lower the torque, so it stabilizes, and in the case of "regeneration", the absolute value of torque When the torque increases over time, the frequency increases, suppressing the increase in the absolute value of the torque and stabilizing it.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a current source inverter and its control device according to an embodiment of the present invention, and this embodiment is different from the conventional example of FIG. On the other hand, a multiplier 22 detects the voltage VDC of the DC intermediate circuit and multiplies this voltage VDC by the current IDC flowing through the DC intermediate circuit detected through the current transformer 1 and the diode 12; Output, that is, the product of voltage VDC and current IDC VDC@IDC
A divider 2B that divides by the frequency command value, and this divider 2
a switch 27 that selectively outputs the output of 8 to the differentiator 24;
It has been established.

The output of the divider 28 is differentiated by the differentiator 24, and the differential value is subtracted from the frequency command value by the subtracter 80.

If the frequency of the inverter is f, the output of the divider 28 is E
is . Here, KI, Kv, and Kf are constants.

On the other hand, the input power of the induction motor 110 is the inverter thyristor 5I6, the diode 7.8, and the commutating capacitor 9.
．． Ignoring losses such as IO, the DC intermediate circuit current II
It is equal to the product IDC·VDC of nc and the DC intermediate circuit voltage VDC. Moreover, this input power is the secondary input of the induction motor 11, Pz=2π/*n, T (T is the torque of the induction motor 11,
n is equal to the number of polar pairs). Therefore, the following formula % formula % (21) holds true. From formulas +1) and (2), the torque T is expressed by the following formula.

From equation (8), the output E of the divider 28 is an amount proportional to the torque T, and the output E of the divider 28 is an amount proportional to the torque T. The differential value is subtracted from the frequency command value of the voltage command device 21. Therefore, in the case of "electric", the output of the differentiator 24 is such that when the torque T of the induction motor 11 increases over time, the frequency of the induction motor 11 decreases, the output of the differentiator 24 becomes stable because the torque T is tried to decrease, and vice versa. When the torque T decreases, it acts to increase the frequency. Furthermore, in the case of "F regeneration", when the absolute value of torque T increases over time, the frequency acts to increase, so the increase in the absolute value of torque T is suppressed and stabilized. The polarity of the current IDC is constant, but the polarity of the voltage VDC is positive when it is "electric" and negative when it is "regenerative", so the output of the divider 28 depends on the operating state of the induction motor 11, that is, the The polarity changes depending on the polarity.

Figure 8 is an equivalent circuit diagram of the induction motor 11, where R17-R2 are the primary and secondary resistances, Jl and /2 are the primary and secondary leakage inductances, M is the mutual inductance, and e is proportional to the speed. It is a speed electromotive force that generates voltage. Assuming that the smoothness of the induction motor 11 is e, the speed electromotive force θ is replaced by knee, -R2 in a steady state, resulting in a known equivalent circuit.

A current source inverter is driven by a constant current source, and the current It(
(Fig. 8) is constant. Now, if we assume that an impact load is applied to the induction motor 11 and the speed rapidly decreases, the voltage e will fluctuate by Δe in response to this speed decrease, and due to this fluctuation Δe, a transient current will be generated as shown in FIG. Δ1 occurs. Since the primary side of the induction motor 110 is a current source, this transient current Δ1 flows only to the secondary side. Transient lightning 1st flow Δ1
changes the current 1m which is the current of the mutual inductance M, so the voltage of the mutual inductance M also changes. Since the voltage of the mutual inductance M is approximately equal to the primary voltage of the induction motor 11, the voltage of the induction motor 11 fluctuates.

The decay time constant of transient current Δ1 is T= (M+/2)
/R2 is a quadratic time constant that changes -8 Generally, the housing is large u-f, and the generated torque ``■'' also changes according to the fluctuation of the transient current Δ1. By controlling the frequency of the induction motor 11, the transient current A1 is reduced and the current 1m is kept constant.In other words, when the speed decreases and the voltage e decreases by Δθ, the current 12 increases. As a result, the torque T also tends to increase, but it is stabilized by lowering the frequency of the induction motor 1 to prevent fluctuations in the current 12, and reducing the transient current Δ1 to keep the current 1 m constant.

FIG. 4 is a diagram showing an example of transient fluctuations of the induction motor 11 during an impact load. #c4 diagram rll shows fluctuations in load torque, and an impact load is applied after time t=t o. Figure 4 (2+, (81) respectively show the speed and torque (output of divider z8) when switch 27 (Figure 2) is turned off, Figure 4 (4), (5)
show the fluctuations in speed and torque when the switch 27 is turned on, respectively. When switch 27 is turned off, both speed and torque are damped vibrations, but switch 2
If you turn on 7, the speed,!・It can be seen that both torque and torque become non-oscillatory, improving dynamic characteristics and increasing stability.

In Fig. 2, the detection of the voltage VDC of the current open circuit at 1 is as follows:
Although it is set to the output side of the DC reactor 4, it may also be the input side of the DC reactor 1, that is, the output of the current transformer 1. Further, although FIG. 2 has been described using an analog method, a digital method using a microcomputer is also possible.

<Effects of the Invention> According to the present invention, the stability is improved in both the operating conditions of r-electric and r-regenerative, and the stability is improved in both of the operating states of r-electric and r-regenerative.
Unlike the "current differential" stabilization method, this method does not promote disturbance in the "N raw" state. Furthermore, in the present invention, since the torque does not include excitation current, a wide linear region can be obtained. Therefore, even in an area where there is no disturbance, the switch 27 (second
When the system is turned on, the dynamic characteristics are improved as shown in Figure 4, and the stabilization area is expanded compared to the conventional system.

Further, unlike the conventional "current differentiation" stabilization method, the current is not directly differentiated, so setting the differential gain in the differentiator becomes easy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional example of a current source inverter and its control device, and FIG. 2 is a diagram of a current source inverter and a conventional example of a control device thereof.
FIG. 2 is a diagram showing the configuration of the control device according to the embodiment. 11; induction motor; 21; voltage command unit. 22; Multiplier; 23; Divider. 24; differentiator, 80; subtractor. Patent Applicant Yaskawa Electric Manufacturing Co., Ltd. Figure 3 Figure 4 Procedures Amendment (spontaneous) February 21, 1980 Commissioner of the Japan Patent Office 1. Indication of case 1989 Patent Application No. 12000 2. Invention Name: Control device for current source inverter 3, Person making the amendment Relationship to the case: Patent applicant (662) Yaskawa Electric Manufacturing Co., Ltd. 4, Agent address: 1-9-20-5 Akasaka, Minato-ku, Tokyo, Subject of the amendment Column 6 of "Detailed Description of the Invention" of the specification, contents of the amendment, page 3, line 13 of the specification, "JogJ is amended to [■])cJ."

Claims (1)

[Scope of claims] A control device for a current source inverter that drives an induction motor, comprising: a multiplier that multiplies the voltage of a DC intermediate circuit of the current source inverter and an input current; an output of this multiplier is divided by a frequency command value; A current source inverter comprising: a divider for differentiating the output of the divider; and a subtracter for subtracting the differential value obtained from the differentiator from the frequency command value. Control device.