JPS6223539B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a power exchanger control device, and particularly to electric motor control using a thyristor switch.
This invention relates to a method of combining output voltage control and current control of a chopper, which allows automatic switching between constant voltage control and constant current control depending on load conditions.

<Conventional technology> Conventionally, when controlling the speed of a DC motor using a thyristor chopper, the speed of the motor is changed by changing the duty factor _dF of the chopper and changing the average value of the voltage applied to the DC motor. ing. As shown in Figure 1, the method of changing the duty factor _dF of the chip is to generate a specific bias such as a sawtooth wave or triangular wave that changes linearly over time, and then set this bias to the set value. A method is adopted in which the chopper is turned on and off by slicing it into a square wave b, and differentiating the rising and falling edges of the square wave (to obtain waveforms c and d). The sawtooth generator and the comparator constitute a pulse width modulator, and the comparator is a normal one without hysteresis. The carrier frequency of the comparator output signal is equal to the frequency of the sawtooth wave, and the pulse width is proportional to the signal input voltage or voltage setting of the comparator. Since the average value e of the chopper output voltage is proportional to the set value, voltage control with good linearity can be performed. On the other hand, in order to protect the motor, thyristor chopper, and DC power supply, it is necessary to control the maximum value of the current flowing through the motor to a constant value. Conventionally, a device as shown in FIG. 2 has been used to combine current limiting with the voltage control described above. That is, when the detected motor current of the motor 1 exceeds the limit current setting value, the adder 2
It works as if the voltage setting value has been lowered. In this case, the chopper output characteristics are as shown in FIG. 3. When the motor current is small, the chopper operates at a constant voltage, and the voltage is maintained at the set value. When the current reaches the limit value, the chopper operates at a constant current. Constant current operation is dVa/d
Ideally, Ia = ∞, as shown by the dashed line in Figure 3, but since the constant current operation in this method is configured by a negative feedback circuit, the current is constant as shown in Figure 3. It has the disadvantage of having a slope.

By increasing the amplifier gain and increasing the loop gain of the negative feedback circuit, dVa/dIa can be increased as shown by the broken line in Figure 3, but care must be taken to prevent the circuit from becoming unstable (oscillating). Therefore, the time constant of the low-pass filter must be increased. Increasing the time constant of the low-pass filter slows down the response of constant current operation, that is, it takes time for the chopper output voltage to start decreasing after the current exceeds the limit value, making it difficult to detect and suppress instantaneous overcurrent. However, there was a drawback that the thyristor power could not be sufficiently protected.

Another constant current control method is an instantaneous current value control method that has excellent constant current characteristics.

FIG. 4 is a diagram showing the principle of a control device employing this method. In the figure, the current of the motor 1 is converted into a voltage by a current detector 3, and after passing through an amplifier 4, it is compared with the current setting. The comparator 5 has a constant hysteresis width, and the current waveform is as shown in FIG. Let me explain how it works. The instantaneous value i _a of the current reaches the lower limit I ₀ at time t ₁
-ΔI ₀ or less, the chopper 7 turns on, the voltage E _s is applied to the motor 1, and the current i _a increases. When the current i _a reaches the set upper limit I ₀ +△I ₀ (time t ₂ ),
The chopper 7 is turned off and the current i _a decreases thereafter. When the current i _a reaches the lower limit I ₀ −△I ₀ (time
t ₃ ), the chopper is turned on again, and this operation is repeated thereafter.

The on time, off time, and period of the chopper vary every cycle, but the instantaneous current value i _a is always within the range of I ₀ ±△I ₀ regardless of the motor speed and average terminal voltage, and the chopper output is shown in Figure 6. It shows good constant current characteristics. However, in order to use this method as a current limiter in the voltage control method mentioned above, it is necessary to switch between constant voltage operation and constant current operation, and it has the disadvantage that it is difficult to perform this switching smoothly and is not practical. .

<Object of the Invention> The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and provides a method of combining voltage control and current control that allows automatic switching with instantaneous current value control of the chopper to be extremely easy. .

<Example> An example of the present invention will be described below in detail with reference to the drawings.

FIG. 7 first shows a principle diagram of the voltage control section constituting the power converter control device of the present invention. In the figure, the output of the comparator 5 is connected to the low-pass filter 8, and the filter output is As in FIG. 5, instantaneous value control is performed by comparing the voltage setting value with a comparator 5 having hysteresis. Compared to the conventional device shown in Fig. 2, the comparator output The signal does not have a constant carrier frequency, unlike traditional pulse width modulators. The average value of the output voltage of the low-pass filter 8 is controlled to be equal to the set value.

The comparator output voltage has a constant amplitude and has two states, only "1" or "0", and its average value and duty factor are proportional to each other, and the average value of the output of the comparator 5 and the output of the low-pass filter 8 are proportional to each other. Since the average values are equal, the duty factor of the comparator output will be proportional to the voltage setting value. The comparator output signal is supplied to the chopper 7 through the output circuit 6.
is turned on and off according to the comparator output "1" or "0", and the chopper output voltage average value becomes equal to the set voltage. One of the features of this device (devices shown in Figures 7 and 8) is that the state of the duty factor "1" or "0", which is difficult with conventional devices, is determined by the magnitude relationship between the set value and the input voltage of the low-pass filter. Therefore, it can be done automatically and safely.

FIG. 8 shows another principle diagram of the voltage control section constituting the power converter control device of the present invention, in which the connection of the input of the low-pass filter 8 is changed from the output of the comparator 5 to the terminal of the load 10, If the voltage at the load terminal is too large for signal processing, use a voltage divider 9 or the like to adjust it to an appropriate level. The operation is almost the same as in FIG. 7, and the output voltage of the low-pass filter is controlled to be equal to the voltage setting value. In this case, the average load voltage and the average low-pass filter output voltage are in a proportional relationship, so if the DC power source Es fluctuates or there is a large voltage drop in the chopper circuit, or when the chopper is off, a back electromotive force will be generated at the load terminal. Even when , the average load voltage is controlled to a constant value according to the set value.

The combination of voltage control and instantaneous current value control according to the present invention can be realized as shown in FIG.
That is, the outputs of the comparator ₅₁ of the voltage control section and the comparator ₅₂ of the current control section are combined by an AND gate A, and the output (or chopper output voltage) is passed through a low-pass filter 8 and input to the comparator ₅₁ . The operation of this method is shown in Figures 10 and 11.
FIG. 12 shows the voltage-current characteristics of the chopper output. To explain switching between constant voltage operation and constant current operation, assume that the voltage and current are set to V ₀ and I ₀ respectively as shown in Figure 12, and the load on the motor is light and line A in Figure 12 If the load characteristics are as follows, the waveforms at each part will be as shown in FIG. Since the load is light, the motor current is I ₀ +△I ₀
is never reached and therefore comparator 5
The output of ₂ is "1". And gate A
The output of will follow the output of comparator ₅₁ . In other words, the current control section is not related to the operation of the chopper, and only the voltage control section mentioned above works, and the chopper is turned on and off according to the output of the comparator ₅₁ , so that the average value of the chopper output voltage V _a is constant at V ₀ is maintained.

As the load becomes heavier and the motor current increases,
While the chopper is on, the motor current reaches I ₀ + △I ₀ before the low-pass filter output reaches V ₀ + △V ₀ , and the output of AND gate A becomes “0” according to the output of comparator ₅₂ . become. When the output of this AND gate A becomes "0", the low pass filter output decreases, so the voltage becomes V ₀ again.
+ΔV is not reached, the output of the comparator ₅₁ remains "1", and the AND gate output follows the output of the comparator ₅₂ .

In other words, if the load is as shown in line B in Figure 12,
As shown in FIG. 11, only the current control section operates, resulting in constant current operation. When the load becomes lighter again, the chopper output becomes a constant voltage through the same operation. Further, as shown in the figure, even if the voltage setting value V ₀ is changed, constant voltage operation and constant current operation are switched. The maximum value of V _a is Es.

As described above, according to the present invention, the voltage control section can be coupled with the current instantaneous value control section with extremely smooth operation, and excellent constant voltage/constant current output characteristics can be obtained as shown in FIG. . Of course the voltage
V ₀ and current I ₀ can be changed independently by voltage setting and current setting, making it ideal as a motor control system.

FIG. 13 shows another embodiment of the method of coupling the voltage control section and instantaneous current value control section of the power converter control device according to the present invention, in which AND gate A in the circuit configuration of FIG. 9 is replaced with OR gate 0. It has been changed. In this case, in the voltage control circuit and the current control circuit, either the motor voltage or the motor current, whichever is always larger than the set value, will be ignored, and the output dynamics will be as shown in FIG. 14. That is, if the motor current is greater than the set value _I0 , only the voltage control circuit operates, and the chopper output exhibits constant voltage characteristics.
Conversely, if the output voltage is greater than V ₀ , constant current operation occurs. Figure 15 shows a method for obtaining multi-stage output voltage/current characteristics by combining multiple methods of coupling the voltage control section and current control section shown in Figures 9 and 13 above, and Figure 16 shows the characteristics. This shows that.
Since V ₁ , V _{2 .} . . and I ₁ , I ₂ .

5 ₁ to 5 _o are comparators, 8 is a low-pass filter, A ₁ to A _o are AND gates, and O ₁ to _{O o} are OR gates.

FIG. 17 shows another multistage coupling, and FIG. 18 shows its output characteristics.

FIG. 19 shows another principle diagram of the voltage control section constituting the power converter control device of the present invention, and shows the output voltage control circuit of the inverter, and shows the three parts of the output transformer T.
The output of the next winding is used for voltage detection. The comparator input has a waveform as shown in FIG. 20, and the transistor Tr ₁ or Tr ₂ is turned on according to "0" or "1" of the comparator output. The inverter output becomes a width-modulated square wave, and the average output voltage of the transformer T becomes similar to the reference signal.

<Effects of the Invention> Since the present invention is configured as described above, in motor control using a thyristor chopper, etc., a power converter such as a chopper can easily switch between constant voltage control and constant current control depending on the load condition. A control device can be obtained.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram of each part of the control device using the conventional chopper output voltage control method, and Figure 2 is a diagram of the waveforms of various parts of the control device using the conventional chopper output voltage control method.
Block diagram of control device using current control method, Part 3
The figure is an output characteristic diagram of Figure 2, Figure 4 is a block diagram of a control device using a conventional constant current control method, Figure 5 is an explanatory diagram of the operation of Figure 4, and Figure 6 is an output characteristic diagram of Figure 4. , FIG. 7 is a block diagram of a voltage control section constituting the power converter control device of the present invention, FIG. 8 is a block diagram of another voltage control section same as above, and FIG. 9 is a block diagram of the power converter control device of the present invention. A block diagram showing voltage control and current control coupling according to one embodiment of the present invention, FIG.
Figure 11 is an explanatory diagram of operation under light load.
12 is an output characteristic diagram of FIG. 9, and FIG. 13 is a block diagram showing voltage control and current control coupling according to another embodiment of the power converter control device of the present invention. Figure 14 is the output characteristic diagram of Figure 13, Figure 15 is a diagram showing the multi-stage combination of voltage control and current control in the same manner, Figure 16 is the output characteristic diagram in Figure 15, and Figure 17 is the same as in the same figure. 18 is the output characteristic diagram of FIG. 17, and FIG. 19 is a block diagram showing an example of a control device using a voltage control method using an inverter. FIG. 20 shows the operating waveform diagram of FIG. 19. In the figure, 1: electric motor, 3: current detector, 5 ₁ to 5
_o : Comparator, 6: Chopper on/off drive circuit, 7: Chopper, 8: Low-pass filter, 9: Voltage divider, 10: Load, A: AND gate, O: OR gate, Es: DC power supply.

Claims (1)

[Claims] 1 The system is designed to control the average voltage of the load by alternating on/off operations of a semiconductor chopper that drives the load such as a DC motor, and includes a low-pass filter, a reference voltage setting means, and a first input. and a first comparator for deriving a binary output having hysteresis at the output section, the output section of the low-pass filter and the reference voltage setting section of the reference voltage setting section. an output section is connected to a first input section and a second input section of the first comparator, respectively; an output section of the first comparator is connected to a first input section of the logic circuit; The second input part of the logic circuit is connected to the output part of the second comparator of the instantaneous current value control part which is connected to the current detection terminal of the load and controls the instantaneous current of the load. The voltage control instruction is the output of the first comparator, the output part of which is connected to the on/off drive circuit of the semiconductor chopper, and the input part of the low-pass filter connected to the output part or load terminal of the logic circuit. By combining the signal and the current control instruction signal, which is the output of the second comparator, in the logic circuit, the alternating operation of the semiconductor chopper is controlled depending on the magnitude of the load. It is characterized by being made to follow one signal,
Power converter control device.