JPS59194688A - Control system of dc motor - Google Patents

Abstract

PURPOSE:To prevent the control from becoming unstable by providing a firing angle shifting command signal at the time point for generating a current zero detection signal in the step of switching-over a thyristor converter. CONSTITUTION:When a torque polarity signal Tp is positive, a selection signal Wa is ON, and a converter 2A operates. When the current actual value signal ¦H¦ decreases to the inside of insensitive unit of current zero detecting means in case that the polarity of the signal Tp inverts from positive to negative at the time point t0, a firing angle shift command signal Vs is outputted, and shifted to the maximum firing angle. After the lapse of the time T1, a selection signal Wa becomes OFF, and the operation of the thyristor converter 2A is stopped. After further the lapse of time T2, a firing angle shift command signal Vs is released, the selection signal Wb simultaneously becomes ON, and the operation of the thyristor converter 2B is started.

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention provides a direct current motor by switching and controlling thyristor converters connected in antiparallel to each other with respect to an armature circuit of a direct current motor without circulating current. This invention relates to a control method for a DC motor that performs four-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 three-phase AC power source via an AC reactor 1 consists of two sets of three-phase bridge-connected thyristor converters and two thyristor converters 2B, and this thyristor converter 2A and 2B are connected in antiparallel 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, receives a speed target value signal N* from a speed command section (not shown), and commands a current target value so that the actual speed value matches the target speed value. do. The output signal of the speed regulator 5 is converted into an absolute value by an absolute value conversion circuit 6 and is guided to the current regulator 7 as a current target value signal 1.Meanwhile, the armature current of the DC motor 3 is converted into power. Current transformer 8A inserted on the AC side of section 2
The current detecting section 8 consisting of a rectifier circuit 8B detects the current value as a non-polar 'actual current value signal III, and this actual current value signal III is also guided to the current regulator 7.

The switching command calculator 10 receives the torque polarity signal Tp from the speed regulator 5, but this torque polarity signal Tp is an output signal of the speed regulator 5, or an equivalent internal signal of the speed regulator 5 that can determine the polarity. The switching command calculator 10 has the function of determining the torque polarity from this torque polarity signal Tp and determining the desired torque polarity, and also has the function of determining whether the current actual value signal 1'I+ from the current detection section 8 is zero. A function to determine whether or not the current is zero and create a zero current detection signal, a function to create a firing angle shift command signal Vs based on the information from the above function, and a function to determine which of the thyristor converters 2A and 2B to operate. It has a function of creating converter selection signals Wa and wb to be selected.

The current regulator 7 receives the current target value signal 1 and the current actual value signal III, and adjusts the firing angle command signal Vα to match the current target value and the actual value according to the deviation between the two. Also, 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 target value signal 1
Since the current is inputted to the current regulator with a polarity opposite to that of 1, the current regulator 7 determines that the actual current value is excessive and operates to increase the firing angle α. Note that the maximum firing angle αmax and the minimum firing angle αmin (maximum forward conversion output voltage for the converter) are set by an output voltage limiter built in the current regulator 7.

The firing angle regulator 9 issues a firing angle command 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 the signal 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. Note that this switching operation is performed when the thyristor converter 2 is in operation.
This is a case where converter A is switched to converter 2B.

In Fig. 2, at the instant of time t0, the torque polarity signal T
When the polarity of signal Tp is reversed, the switching command calculator 10 determines that the polarity of signal Tp has been reversed (Fig. 2(a)).
The firing angle shift command signal Vs is immediately issued (Fig. 2 (d)
)) ○ Based on this firing angle shift command signal Vs, the firing angle signal ■ α that the bit flow regulator 7 outputs is 90.
The integrator capacitor in the current regulator 7 issues a command so that the firing angle α is shifted to the maximum firing angle α (Fig. 2 (g)), and the integral capacitor in the current regulator 7 Start charging. The actual current value III changes as shown in FIG. 2(b), and when the switching command calculator 10 detects this current zero (FIG. 2(c)), a fixed time T1 is set to confirm this current zero.
After the elapse of T2, the selection signal Wa for the thyristor converter 2A in operation is turned off, and the operation of the x converter 2A is stopped, and the converter 2B is activated after the elapse of a certain period of time T2. A selection signal wb is issued to make the selection (FIG. 2(f)). This fixed time T2 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 αmax. After this fixed time T2 has elapsed, the selection signal wb is turned on and the converter 2B starts operating, and at the same time the firing angle shift command signal V
s is also canceled (Fig. 2 (d)), and the firing angle of the firing angle command signal ■α is the maximum firing angle αma corresponding to the maximum inverse conversion output point.
Since the firing angle gradually changes from x to the firing angle corresponding to the inverse conversion output point that can supply the desired armature current (Figure 2 (g))
, the current in the converter 2B increases smoothly in the regenerative braking mode without inrush current (FIG. 2(b)).

It has been confirmed that the operation using the conventional control method described above sometimes becomes unstable in control, and as a result of various studies, the cause was found to be something other than torque.

It turns out that this is because unnecessary switching operations are executed due to disturbances. 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 αmax based on this firing angle shift command signal, so even if the desired torque polarity returns to its original state, the above Since it takes time for the charging state of the integrating capacitor to return to its original state, a considerable amount of time is required to restore the armature current to its original state.

[Purpose of the invention]

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

[Key points of the invention]

The unique feature of the present invention is that the firing angle shift command signal is not generated when the desired torque polarity is reversed, but is generated 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 the firing angle shift command signal Vs issued by the motor can be changed not at the moment when it is determined that the desired torque polarity has been 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 the time point to, the converter selection signal W
a is on, the two converters are in operation, and the selection signal wb is off. The polarity of the torque polarity signal Tp is positive at t. If it is determined that the polarity has reversed and become negative at that point (FIG. 3(a)), conventionally the firing angle shift command signal V's would have been immediately issued, but
In the case of the control method according to the invention, the current actual value signal III
When the current zero detection signal is generated by decreasing to the inside of the dead zone of the current zero detection means, this firing angle shift command signal V
s is emitted (Fig. 3 (b), (e), (d)
> ). The operation after this point is the same as in the conventional example. That is, after the time T for confirming zero current has elapsed, the converter selection signal Wa is turned off and the operation of the thyristor converter 2A is stopped. Maximum firing angle α Charging to the equivalent value is a
After a time T2 sufficient to complete the firing, the firing angle shift command signal Vs is released, and at the same time, the converter selection signal 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 a value equivalent to the maximum firing angle αmax, so the output signal V of the current regulator 7 does not change suddenly, and the maximum inverse conversion output point is reached. Since the maximum firing angle α corresponding to aX gradually reaches the firing angle corresponding to the inverse conversion output point that can supply the desired armature current commensurate with the armature voltage, the thyristor converter 2B operates without inrush current. The DC motor 3 operates smoothly, and the DC motor 3 can smoothly switch from the drive mode to the brake mode. In FIG. 4, which is a waveform diagram of the operation, the operation according to the control method of the present invention is shown by a solid line, and the operation according to the conventional control method that is different from the operation according to the method of the present invention is shown by a broken line.

In Fig. 4, the polarity of the torque polarity signal TI) 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 II+ does not become zero (Fig. 4(a) ), (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 TI) is first reversed (Fig. 4(d)). ), and at the same time, the firing angle command signal va issues a command so that the firing angle α becomes the maximum firing angle αmax (Fig. 4 (
g)). Accordingly, the integral capacitor of the current regulator 7 is charged toward a value corresponding to the maximum firing angle αmax (maximum inverse conversion output voltage). Therefore, when the required torque and polarity are reversed again after a short period of time, it takes time to return the firing angle command signal va, which is the output of the current regulator 7, to its original state (the fourth (Fig. 4(g)), the armature current will remain at a low level for a short period of time (Fig. 4(b)).

By the way, according to the control method of the present invention, the firing angle shift command signal Vs is not issued when zero current is not detected, so the firing angle signal va also maintains a value commensurate with the actual current value. If the torque polarity signal Tp is reversed again before the current zero is detected, the 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 a good thing as the amount of 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 than in the conventional control system. .

Furthermore, in order to reduce the switching wasted time, 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 issued (Unexamined Japanese Patent Publication No. It is also possible to combine the following methods.

〔Effect of the invention〕

As described above, a fifth aspect of the present invention is that the firing angle shift command signal, which is to be performed in the process of switching the sirisk converter in response to a change in the operating mode of the motor, is changed to the current timing rather than the point at which the desired torque polarity is reversed. By generating the zero detection signal when it occurs, it is possible to avoid unstable control due to unnecessary response to torque disturbance, and stabilize control with only a slight increase in switching dead time. In order to maintain this stable control system, the i4
The use is zero

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a 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 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...Ignition angle regulator, 1゛0・Switching command calculator 0III...Current actual value signal, II" 1...Current target value signal, N...Speed actual value signal, N"...Speed target value signal, Tp...Torque polarity signal, ■o...
Firing angle command signal, Vs... Firing angle shift command signal, W
a*Wb...Converter selection signal. Figure 8 Figure 4

Claims (1)

[Claims] 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 Current zero confirmation wave of an operating thyristor converter due to reversal In a control method for a DC motor in which the operation of the operating thyristor converter is stopped and then the other thyristor converter starts operating, In order to prevent inrush current immediately after the thyristor converter starts operating, the output signal of the current regulator is driven to the maximum ignition equivalent value in advance during the converter switching process, and this is performed when the desired torque polarity is reversed. A control method for a direct current motor, characterized in that control is performed by waiting for the generation of a zero current detection signal.