JP2673994B2 - Thyristor Leonard device current limiting method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a current control method for a thyristor Leonard device for driving an electric motor.

[Conventional technology]

Thyristor Leonard devices are often used to drive DC motors, but the devices provide large load currents (continuous current region) and small load currents (interrupted current) even when a gate signal with the same firing angle is applied. Region), the output voltage thereof is different.

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 is needed for this.

FIG. 3 is a general connection block diagram of the thyristor Leonard device, which will be described.

1 is an AC power supply, 2 is a thyristor bridge, 3 is a DC motor with a load machine, 4 is a load current detector, 5 is a current setting device, 6 is an adder / subtractor, 7 is a current control amplifier, and 8 is a gate signal generator. A circuit, I ^* is a DC command signal, and I is a load current signal.

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

The gate signal generation circuit 8 supplies the gate signal of the 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 control block diagram of the thyristor Leonard device, in which 71 is a proportional amplifier, 72 is an integrating amplifier, and 73 is an adder, the same reference numerals as in FIG. The components are shown.

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

The current control amplifier 7 is composed of a proportional amplifier 71 having a gain K _p , an integral amplifier 72 having an integral time constant K _I , and an adder 73 for adding the outputs of the proportional amplifier 71 and the integral amplifier 72. The output V ^* of the phase width device 7 is a voltage command value.

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

The DC motor 3 including the load machine can be represented by characteristic constants such as the motor time constant K _M torque coefficient Kτ and the inertia J, but detailed description thereof will be omitted.

A general output characteristic of the thyristor Leonard device having the above-described structure is shown in FIG. 5, and shows the relationship between the firing angle and the output voltage.

Referring to FIG. 5, when the load current is sufficiently large and continuous, V _DC is the output voltage, V _IN is the power supply voltage, and the DC output voltage when the firing angle α changes is .

V _DC = 1.35V _IN × cos α (1) The above characteristics are indicated by the broken line a. However, when the load current is small and does not continue, it changes like a real battle and a 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.

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

Therefore, a conventional method for improving the stability will be described with reference to FIG. 6 of the control block diagram.

FIG. 6 shows the same components as those in FIG. 4 with the same components, with the addition of an integral time constant calculation circuit 9 composed of a limiter circuit 93. The characteristic diagram of the limiter circuit 93 is shown in FIG. It shows in FIG.

The integral time constant calculation circuit 9 obtains an integral time constant K _I proportional to the load current I, but the load current in the state where the load current is continuous
It does not increase above the value corresponding to I _O. In addition, it is limited even in the small current region where overflow and calculation accuracy drop significantly.

The method exhibits good stability under steady load, but has a problem in transient response as shown below.

FIG. 8 shows a transient characteristic curve of the above-described device with improved stability, where I ^* is a current command signal, I is a load current signal, and K _I is an integration time constant.

First, when the current command signal I ^* rises stepwise at time t _I , the load current is still small and the integration time constant K _I is also small, so the output to the current control amplifier 7 is changed by the change in the current command signal I ^*. It changes greatly and the load current rises rapidly and exceeds the current set value at once.

Further, the integral time constant K _I increases as the load current increases, but in the thyristor Leonard device, the load current largely overshoots because of a control delay of 60 electrical degrees of the power supply frequency.

Next, when the current command signal I ^* decreases stepwise at time t ₂ , the integration time constant K _I immediately after t ₂ is large, a sudden change in the output of the current control amplifier 7 is not allowed, and the load current I changes It will be a gradual change.

[Problems to be solved by the invention]

For these reasons, the improved method described above constantly obtains good characteristics, but overshoot occurs during transient changes, changes are extremely gentle, and the response speed at rising and falling is high. There were drawbacks such as differences.

[Means for solving the problem]

The present invention has been made in order to solve the above-mentioned problems, and has a fast response speed transiently without losing steady stability, and a current control method having no difference in the response speed of rising and falling. Specifically, the integrating amplifier of the current control amplifier is capable of varying the integrating time constant, and the integrating time constant of the integrating amplifier is proportional to the average value of the load current signal and the current command signal. It was made to change.

(Operation)

As a parameter for changing the integration time constant of the integrating amplifier, the current command signal is used to speed up the response during sudden load changes,
In addition, overload can be suppressed by using the load current signal. Further, by making the two parameters act equally, it is possible to make the rate of change of both the rising edge and the falling edge the same.

〔Example〕

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

91 an adder, 92 is an amplifier gain (1/2), K _I 'is the integration time constant, the integration time constant calculating circuit 9', amplifier 92 of the adder 91 and the gain (1/2) of the It is configured by adding it to FIG.

In FIG. 1, the current command signal I ^* and the load current signal I are added by the adder 91, and the value of (1/2) is obtained by the amplifier 92. That is, I ^* and I average value are obtained, and an integrating amplifier is obtained according to the average value.
It changes the integration time constant of 72.

FIG. 2 shows a transient characteristic curve of the present invention, K ₁ is an integral time constant, and the same reference numerals as in FIG. 8 show the same components.

If the current command signal I ^* rises stepwise, the eighth
In comparison with the conventional method shown in the figure, in the conventional method shown in FIG. 8, the load current rises at once and overshoots due to the control by the small integration time constant K _{I in the} straightness of t ₁ .

However, those of this invention shown in Figure 2, integration time for the parameters of the constant K _I is the current command signal I ^* is applied, the integral time constant K _I at immediately after t ₁ 'is about half quickly By increasing the output current of the current control amplifier 7 and suppressing the change in the output of the current control amplifier 7, the change in the load current becomes slower than in FIG.

Next, when the current command signal I ^* drops stepwise at t ₂ , the conventional method shown in FIG. 8 keeps the current limit signal large because the load current is large even after t ₂ and the control is continued. The output of the amplifier 7 can only change gently, and the load current can only decrease gently.

However, those of this invention shown in FIG. 2, since the applied current command signal I ^* to the parameters of the integration time constant K _I, FIG. 8 and compared with integration time constant K _I 'is a current command Immediately after the change of the signal I ^* , it is rapidly reduced to about half to accelerate the change of the load current.

Also, when the current setting rises or falls, the integral time constant changes rapidly (1/2) of the current change and then converges, so that the load current becomes steady after the current command suddenly changes. The response time until reaching the same level is almost the same for both rising and falling.

As described above, as compared with the case where the integration time constant K I is changed only by the load current I by changing the integration time constant K _I by the average value of the load current signal I and the current command signal I ^* , the integration time constant K The change of _I can be accelerated in an appropriate direction, and a good transient response can be obtained.

(Effect)

As described above, the present invention uses the load current signal in a feedback manner and the current command signal in a feedforward manner in controlling the integration time constant K _I ,
In other words, rather than determining the integration time constant K _I of the control amplifier only the load current, by determining the average value of the load current and the current command signal, current command signal to the feed forward relative integration time constant K _I Can act. Therefore, it is possible to provide a thyristor Leonard device in which the integration time constant changes rapidly and appropriately, the response is fast, and a good response is obtained in which the response times of rising and falling are almost the same.

[Brief description of the drawings]

1 and 2 show a control block diagram and a transient characteristic curve according to the present invention. 3 and 4 are a connection configuration diagram and a control block diagram of a general thyristor leonard device, FIG. 5 is an output characteristic curve of a general thyristor leonard device, and FIG. 6 is a conventional system with improved stability. FIG. 7 is a control block diagram, FIG. 7 is a characteristic diagram of the limiter circuit, and FIG. 8 is a conventional transient characteristic curve diagram with improved stability. 71, 72 ... proportional amplifier of current control amplifier 7, integral amplifier, 92 ... amplifier of integral time constant calculating circuit 9 ', I ... load current signal, I ^* ... current command signal, K _I ... integral time constant.

Claims (1)

(57) [Claims] 1. A current control method for a thyristor Leonard device comprising means for changing an integration time constant of said integration amplifier of a current control amplifier comprising a proportional amplifier and an integration amplifier, wherein the integration time constant is a load current signal and a current command. A method for controlling current in a thyristor Leonard device, characterized in that the signal is changed in proportion to an average value.