JPH0471385A - Current limiting method for thyristor leonard system - Google Patents

Abstract

PURPOSE:To quicken response at the time of abrupt load variation by means of a current command signal and to suppress overshoot by means of a load current signal by a current limiting method which provides a quick transient response without sacrifice of steady state stability and has no difference between rising and falling response rates. CONSTITUTION:Since a current command signal I* is added to a parameter having integration time constant K1, current limiting signal kI' drops to about half level quickly immediately after variation of the current command signal I* and functions to vary the integration time constant quickly thus quickening variation of load current. The integration time constant varies quickly by an amount corresponding to half of current variation for both increase and decrease of current setting and then converges. Consequently, response time after abrupt variation of current command before settling of load current is substantially identical for both increase and decrease. When the integration time constant K1 is varied according to the average value of the load current signal I and the current command signal I* as mentioned above, variation of the integration time constant K1 can be quickened in appropriate direction as compared with the case employing only the load current I, resulting in a preferable transient response.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current limiting method for a thyristor Leonard device that drives an electric motor.

[Conventional technology]

Thyristor Leonard devices are often used to drive DC motors, but even if a gate signal with the same firing angle is given, this device is difficult to operate when the load current is large (current continuous region) and when the negative current is small (current (intermittent region), the output voltage has different properties.

This means that the control gain changes depending on the magnitude of the load current, and that the stability and response of the control system change depending on the load current. Some means will be needed.

FIG. 3 is a general connection configuration diagram of a thyristor 1 non-onard device, and this will be explained.

1 is an AC power supply, 2 is a thyristorby 1. 3 is a DC motor with a load device, 4 is a load current detector, 5 is a current setting device, 6 is an adder/subtractor, 7 is a current control amplifier, 8 is a gate signal generation circuit, ■ is a current command The signal ■ is the load current signal.

In the above configuration, the difference between the output signals of the current setter 5 and the load current detector 4 is obtained by the adder/subtractor 6 and applied to the current control amplifier 7.

The gate signal generation circuit 8 supplies a gate signal having a firing angle corresponding to the output of the current control amplifier 7 to the thyristor bridge 2, and the thyristor bridge 2 drives the DC motor.

FIG. 4 is a general P3 control block diagram of a thyristor Leonard device, in which 71 is a proportional amplifier, 72 is an integral amplifier, and 73 is an adder. The same components are shown.

*The adder 6 outputs a deviation current signal Δ■ between the current command signal I and the load current signal.

The current control amplifier 7 includes a proportional amplifier 71 with a gain Kp, an integral amplifier 72 with an integral time constant KX, and a proportional amplifier 7.
The output of the current control amplifier 7 is the voltage command value.

The gate generation circuit 8 generates a gate pulse with a firing angle α corresponding to the voltage command V*, and the Cyrisk bridge 2 generates a DC voltage V proportional to cos α by the gate pulse with a firing angle α.

The DC motor 3 with a load machine has a motor time constant KM,
Although it can be expressed by characteristic constants such as torque coefficient τ and inertia J, detailed explanation will be omitted.

The general output characteristics of the thyristor Leonard device constructed as described above are shown in FIG. 5, which shows the relationship between the firing angle and the output voltage.

Explaining FIG. 5, when the load current is sufficiently large and continuous, VDC is the output voltage, VIN is the power supply voltage, and the DC output voltage when the firing angle α changes is expressed by the following formula.

VDC= 1.35VIN
・・・・・・・・・・・・・・・・・・(1) The above characteristics are shown by the broken line A. However, when the load current is small and not continuous, it changes as shown by the solid line or the dashed-dotted line C, and this characteristic changes depending on the magnitude of the load current, the back electromotive force of the DC motor, and the armature resistance and inductance of the DC motor. do.

The above shows that the stability of the control circuit changes depending on the load condition.

Therefore, a conventional method for improving stability will be explained with reference to FIG. 6, which is a control block diagram.

In FIG. 6, the same reference numerals as in FIG. 4 indicate the same components, and an integral time constant calculation circuit 9 composed of a limiter circuit 93 is added. It is shown in Figure 7.

The integral time constant calculation circuit 9 obtains an integral constant KX proportional to the load current I, but the load current ■ is in a state where the load current is connected. The limited current limit signal kI is supplied to the integral amplifier 72 at a value higher than the value corresponding to
change the integral time constant of

Although this method shows good stability against steady loads, it has problems with transient response as shown below.

FIG. 8 shows a transient characteristic curve diagram of the above-mentioned device with improved stability, where ■ indicates a current command signal, ■ indicates a load current signal, and kI indicates a current limit signal.

First, when the current command signal I rises in an upward trend at time t1, the load current is still small and the current limit signal kI is not large enough. However, since the integral time constant KN is also small, the output of the current control amplifier 7 changes greatly depending on the change in the current command signal I, causing the load current to rise suddenly and exceeding the current set value at once. Therefore, the integral time constant Kl is The load current increases as the direct current increases, but since the thyristor Leonard device involves a control delay of 60 electrical degrees of the power frequency, the load current becomes large and operginate.

* - Next, when the current command signal ■ decreases in an up-like manner at time t2, the current limit signal kI immediately after t2 is also large and becomes an integral time constant! is a large value, which does not allow sudden changes in the output of the current control amplifier 7 and obtains good characteristics in terms of changes in the load current. Also, there were drawbacks such as different response speeds between rising and falling edges.

[Means to solve the problem]

The present invention has been made in order to solve the above-mentioned problems, and is a current limiting method that has a fast response speed even in a transient state without losing steady stability, and has no difference in response speed between rising and falling edges. Specifically, the integrating amplifier of the current control amplifier has a variable integration time constant, and the integration time constant of this integrating amplifier is set to the average value of the load current signal and the current command signal. It is designed to change proportionately.

[For production]

The current command signal is used as a parameter to change the integral time constant of the integrating amplifier to speed up the response when the load suddenly changes.
Moreover, overshoot can be suppressed using the load current signal. Furthermore, by applying these two parameters equally, it is possible to make the speed of change in both the rise and fall the same.

〔Example〕

FIG. 1 is a control block diagram of a thyristor Leonard device according to the present invention, in which the same reference numerals as in FIG. 6 indicate the same components.

91 is an adder, 92 is an amplifier with gain (1/2), kI'
is a current limit signal, and the integral time constant calculation circuit 9' is constructed by adding an adder 91 and an amplifier 92 with a gain of (1/2) to the one shown in FIG.

* In FIG. 1, an adder 91 adds the current command signal I and a load current signal ■, and an amplifier 92 obtains a value of (1/2).

That is, a current limit signal kI' proportional to the average value of ■ and I,
1 is supplied to the integrating amplifier 72 to change the integration time constant of the integrating amplifier 72.

Figure 2 shows the transient characteristic curve of the present invention, kI'
is a current limit signal, and the same reference numerals as in FIG. 8 indicate the same components.

If we compare the case where the current limit signal rises in a stepwise manner with the conventional system shown in Fig. 8, the conventional system shown in Fig. 8 will increase the current limit signal kI in a step immediately after t1. The load current increases and overshoots.

However, the invention shown in Figure 2 ζ has an integral time constant! Since the current command signal "■" is added to the parameter, the current limit signal kI' immediately after t1 rises to about half, suppressing the sudden change in the integral time constant, and suppressing the output change of the current control amplifier 7. As a result, the change in load current becomes more gradual than in FIG.

Next, when the current command signal ■ decreases in an upward manner at t2, in the conventional system shown in FIG. The output can only change gradually, and the load current can only decrease slowly.

However, in the present invention shown in Fig. 2, the current command signal I* is added to the parameter of the integral time constant KI, so compared to Fig. 8, the current limit signal * kI' is the current command signal Immediately after the change in (2), it quickly decreases to about half, acting on a sudden change in the integral time constant, and accelerating the change in load current.

In addition, when the current setting increases or decreases, the integral time constant changes rapidly for (1/2) of the current change and then tends to converge, so the load current changes after the current command suddenly changes. The response time until reaching steady state is almost the same for both rise and fall.

As described above, by changing the integral time constant KI according to the average value of the load current signal *■ and the current command signal I, the integral time constant Kz can be changed compared to the case where the integral time constant is determined only by the load current ■. Changes can be accelerated in the appropriate direction and good transient response can be obtained.

〔effect〕

As explained above, in controlling the integral time constant KX, the present invention uses the load current signal in a feedback manner and the current command signal in a feedforward manner.
In other words, the integral time constant of the control amplifier! By determining the value not only from the load current but from the average value of the load current and the current command signal, the current command signal can act in a feedforward manner on the integral time constant. Therefore,
It is possible to provide a thyristor Leonard device in which the integral time constant changes quickly and appropriately, the response is fast, and a good response in which the rising and falling responses are almost the same can be obtained.

[Brief explanation of drawings]

1 and 2 show control diagrams and transient characteristic curves according to the present invention. Figures 3 and 4 are the connection configuration diagram and control block diagram of a general thyristor Leonard device, Figure 5 is the output characteristic curve P 11 line of a general thyristor 1/Onard device, and Figure 6 is the stability diagram. A control block diagram of an improved conventional method, FIG. 7 shows a characteristic diagram of a limiter circuit, and FIG. 8 shows a conventional transient characteristic curve diagram with improved stability. 71, 72...Current control amplifier 7 proportional amplifier, integral amplifier, 92... amplifier of integral time constant calculation circuit 9', ■... load current signal, I*...
...Current command signal, kI...Current limit signal.

Claims (1)

[Claims] 1. A thyristor Leonard device characterized in that the integral time constant of the integral amplifier of a current control amplifier consisting of a proportional amplifier and an integral amplifier is changed in proportion to the average value of a load current signal and a current command signal. current limiting method.