JPH0219714B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention is directed to switching and controlling thyristor converters connected in antiparallel to each other with respect to the armature circuit of a DC motor without circulating current. This paper relates to a control method for a DC motor that performs quadrant operation.

[Prior art and its problems]

FIG. 1 is a block diagram showing the general configuration of this type of device. In FIG. 1, a power converter 2 connected to a 3-phase AC power source via an AC reactor 1 consists of two sets of thyristor converters 2A and 2B connected in a 3-phase bridge. They are connected in antiparallel to each other with respect to the armature of the DC motor 3. The rotational speed of the electric motor 3 is detected by a speed detection generator 4 and fed to a speed regulator 5 as a speed actual value signal N. The speed regulator 5 is generally configured as a PI regulator and receives a speed target value signal N ^* from a speed command unit (not shown).
Then, the current target value is commanded so that the actual speed value matches the target speed value. The output signal I ^* of the speed regulator 5 is subjected to absolute value conversion by an absolute value conversion circuit 6 and is guided to the current regulator 7 as a current target value signal |I ^* |. On the other hand, the armature current of the DC motor 3 is transferred to a current transformer 8 inserted into the AC side of the power converter 2.
A and a rectifier circuit 8B, the current detecting section 8 detects the non-polar current actual value signal |I|, and this current actual value signal |I| is also guided to the current regulator 7.

The switching command calculator 10 receives the torque polarity signal Tp from the speed regulator 5;
Tp is the output signal I ^* of the speed regulator 5 or an equivalent internal signal of the speed regulator 5 whose polarity can be determined, and the switching command calculator 10 determines the torque polarity from this torque polarity signal Tp. A function of determining the desired torque polarity, a function of determining whether the current actual value signal |I| from the current detection unit 8 is zero and creating a current zero detection signal, and information from the above-mentioned functions. A function to create a firing angle shift command signal Vs based on the function, and a converter selection signal to select which of the thyristor converters 2A and 2B to operate.
It has the function of creating Wa and Wb.

The current regulator 7 receives the current target value signal |I ^* | and the current actual value signal |I|, and outputs a firing angle command signal to match the current target value and the actual value according to the deviation between the two.
Vα is given to the firing angle adjuster 9. Furthermore, when the torque polarity is reversed, the firing angle shift command signal Vs guided from the switching command calculator 10 to the current regulator 7 has a sufficiently large value and the current is adjusted with a polarity opposite to that of the current target value signal |I ^* | Therefore, the current regulator 7 determines that the actual current value is excessive and changes the firing angle α.
to the maximum firing angle α _nax (maximum inverse conversion output voltage for thyristor converter 2A or 2B). Note that the maximum firing angle α _nax and the minimum firing angle α _nao (for converters, the maximum forward conversion output voltage)
is set by the output voltage limiter built into the current regulator 7.

The firing angle regulator 9 outputs a firing angle command signal output from the current regulator 7 to the thyristor converter 2A or 2B designated by the converter selection signals Wa and Wb from the switching command calculator 10. The firing angle is controlled according to Vα.

The switching command calculator 10 issues a command to switch the thyristor converter when the torque polarity signal Tp is reversed, and this switching operation will be explained with reference to the operating waveform diagram in FIG. This switching operation is
This is a case where the operating thyristor converter 2A is switched to the converter 2B.

In Fig. 2, at the instant of time t ₀ , the torque polarity signal
When the polarity of Tp is reversed, the switching command calculator 10
determines that the polarity of this signal Tp has been reversed (Fig. 2a) and immediately issues the firing angle shift command signal Vs (Fig. 2d). This firing angle shift command signal Vs
The firing angle signal output by the current regulator 7
A command is issued so that the firing angle α of Vα, which was less than 90 degrees, is shifted to the maximum firing angle α _nax (Fig. 2g), and the integrating capacitor in the current regulator 7 is set at this maximum point. Start charging to the value equivalent to arc angle α _nax .
The actual current value |I| changes as shown in FIG. 2b, and when the switching command calculator 10 detects this current zero (FIG. 2c), a certain period of time T ₁ is set to confirm this current zero.
After the period of time, the selection signal Wa for the operating thyristor converter 2A is turned off (Fig. 2 d), the operation of the converter 2A is stopped, and the operation is stopped for a certain period of time.
After T ₂ has elapsed, a selection signal Wb for operating the converter 2B is generated (FIG. 2f). This fixed time T ₂ is provided to allow time until the integration capacitor in the current regulator 7 is charged to a value corresponding to the maximum firing angle α _nax . this certain period of time
After T ₂ has elapsed, the selection signal Wb turns on, and converter 2B
The firing angle shift command signal is sent at the same time as the
Vs is also released (Fig. 2 d), and the firing angle command signal Vα
The firing angle gradually changes from the maximum firing angle α _nax corresponding to the maximum reverse conversion output point to the firing angle corresponding to the reverse conversion output point that can supply the desired armature current (Fig. 2g). ), the current in the converter 2B increases smoothly in regenerative braking mode without inrush current (Fig. 2b).

It has been confirmed that the operation using the conventional control method described above sometimes results in unstable control, and as a result of various studies on this issue, it has been determined that the cause of this is unnecessary switching operations performed in conjunction with torque disturbances. It turned out to be because. In other words, when a load torque fluctuation occurs in which the desired torque polarity is reversed for a short period of time and then returned to the original state, in the conventional control method, as soon as the desired torque polarity is reversed, the firing angle shift command signal is sent to the current regulator. , and the integral capacitor in the current regulator is charged to a value equivalent to the maximum firing angle α _nax based on this firing angle shift command signal, so even if the desired torque polarity returns to its original value, Since it takes time for the charging state of the integrating capacitor to return to its original state, it takes a considerable amount of time to restore the armature current to its original state.

[Purpose of the invention]

An object of the present invention is to prevent unnecessary switching operations from being executed due to torque disturbances, thereby preventing control from becoming unstable.

[Key points of the invention]

The present invention is characterized in that the firing angle shift command signal is not issued when the desired torque polarity is reversed, but is issued after detecting zero current, and according to this, the firing angle shift command signal is issued after detecting zero current. The control is stable because the control does not respond quickly to load torque fluctuations that would cause the desired torque polarity to return to its original state.

[Embodiments of the invention]

The device for realizing the control method according to the present invention is basically the same as the conventional device shown in FIG.
The timing of Vs can be changed not at the moment when it is determined that the desired torque polarity has reversed, but when the current zero signal is generated.

FIG. 3 is an operation waveform diagram illustrating the basic operation of the process of switching the thyristor converter in accordance with the reversal of the desired torque polarity in the case of the control method of the present invention.

In FIG. 3, before time _t0 , the converter selection signal Wa is on and the converter 2A is in operation, and the selection signal Wb is off. It is determined that the polarity of the torque polarity signal Tp was positive, but at time _t0 , the polarity was reversed and became negative (Fig. 3a).
Conventionally, the firing angle shift command signal Vs is immediately issued, but in the case of the control method according to the present invention, the current actual value signal |I| drops to the inside of the dead zone of the current zero detection means, and the current This firing angle shift command signal Vs is issued at the time when the zero detection signal is generated (Fig. 3b, c, d). The operation after this point is the same as in the conventional example. That is, after the time _T1 for confirming zero current has elapsed, the converter selection signal Wa is turned off, the operation of the thyristor converter 2A is stopped (Fig. 3e), and the maximum of the integrating capacitor in the current regulator 7 is After a sufficient time _T2 has elapsed to complete charging to the firing angle α _nax equivalent value, the firing angle shift command signal Vs is released and at the same time the converter selection signal is released.
Wb is turned on and the operation of the converter 2B is started (Fig. 3 d, f). When the firing angle shift command signal Vs is released, the integral capacitor has been charged to the value equivalent to the maximum firing angle α _nax , so the current regulator 7
The output signal Vα does not change suddenly, and gradually changes from the maximum firing angle α _nax corresponding to the maximum inverse conversion output point to the inverse conversion output point that can supply the desired armature current in accordance with the armature voltage. Since the firing angle is reached,
The thyristor converter 2B operates smoothly without inrush current, and the DC motor 3 can smoothly switch from the drive operation mode to the control operation mode.

Fig. 4 is a waveform diagram of the operation when the torque polarity is reversed in a short time due to load torque fluctuation and then returns to the original polarity. , portions of the operation according to the conventional control method that differ from the operation according to the method of the present invention are indicated by broken lines.

In Fig. 4, the polarity of the torque polarity signal TP is reversed from positive to negative, and then reversed again after a short time to return to positive polarity, during which the actual current value |I| does not become zero (Fig. 4a , b) However, in the conventional control system, the firing angle shift command signal Vs is issued at the moment when it is determined that the polarity of the torque polarity signal Tp is first reversed (Fig. 4d), and at the same time the firing angle shift command signal The command signal Vα also issues a command so that the firing angle α becomes the maximum firing angle α _nax (Fig. 4g). Along with this, the integrating capacitor in the current regulator 7 adjusts the maximum firing angle α _nax
(maximum reverse conversion output voltage) is charged towards the equivalent value. Therefore, when the required torque polarity is reversed again after a short time, it takes time to return the firing angle command signal Vα, which is the output of the current regulator 7, to its original state (Fig. 4g), and the armature The current will remain at a low level for a considerable time (Figure 4b).

By the way, according to the control method of the present invention, since the firing angle shift command signal Vs is not issued when zero current is not detected, the firing angle command signal Vα also maintains a value commensurate with the actual current value. If the torque polarity signal Tp is reversed again before detecting zero current, operation will continue without any problem and there will be no control problem.

If you just want to avoid unnecessary switching operations due to torque disturbances such as load torque fluctuations, it is possible to delay the generation of the firing angle shift command signal Vs, for example after the current zero confirmation time has elapsed. This is not desirable since the wasted time increases accordingly. However, if the firing angle shift command signal Vs is given to the current regulator 7 at the time when the current zero detection signal is generated, as in the present invention, the increase in switching dead time can be made smaller compared to the conventional control method. .

Furthermore, in order to reduce the switching waste time, there is a means for switching the integration time of the current regulator 7 to a value smaller than the normal value for a predetermined time at the same time as the firing angle shift command signal Vs is generated (Japanese Patent Laid-Open No. 55-33259). It is also possible to combine the following:

〔Effect of the invention〕

As described above, according to the present invention, the firing angle shift command signal, which should be performed in the process of switching the thyristor converter in response to a change in the operating mode of the electric motor, is determined not when the desired torque polarity is reversed, but when current zero is detected. By causing the signal to occur at the moment it occurs,
It is possible to avoid unstable control due to unnecessary response to torque disturbance, and maintain control stability with only a slight increase in switching dead time. The cost to implement this method is zero.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the general configuration of a control system for four-quadrant operation of a DC motor, and FIG. 2 is an operation waveform diagram illustrating switching operation in the case of a conventional control system. 3 and 4 are operation waveform diagrams for explaining the switching operation according to the control method of the present invention, and FIG. 4 compares and explains the control method of the present invention with the conventional control method. 2A, 2B...Thyristor converter, 3...DC motor, 4...Speed detection generator, 5...Speed regulator, 6...Absolute value conversion circuit, 7...Current regulator,
8... Current detection unit, 9... Firing angle adjuster, 10...
...Switching command calculator. |I|...actual current value signal,
|I ^* |... Current target value signal, N... Actual speed value signal, N ^* ... Speed target value signal, Tp... Torque polarity signal, Vα... Firing angle command signal, Vs... Firing angle Shift command signal, Wa, Wb...Converter selection signal.

Claims (1)

[Claims] 1. Of a pair of thyristor converters connected in antiparallel to each other with respect to the armature circuit of a DC motor, only one thyristor converter corresponding to the torque polarity desired by the motor is operated each time, and the desired torque polarity is set. In a control method for a DC motor, in which the operation of the thyristor converter in operation is stopped after checking that the current in the thyristor converter in operation is zero due to the reversal of the thyristor converter, and then the operation of the other thyristor converter is started. To prevent inrush current immediately after the thyristor converter starts operating,
The feature is that in the process of switching the converter, the operation of driving the output signal of the current regulator to the maximum value equivalent to ignition is not performed at the time when the desired torque polarity is reversed, but is performed after waiting for the generation of the current zero detection signal. A control method for a DC motor.