JPH01190283A - Switch controlling method for forward/reverse power converter - Google Patents

Abstract

PURPOSE:To enable a current setting time to be shortened at the time of switching a converting means even if load current is in an intermittent state, by creating a voltage correcting quantity in accordance with motor current at the time point of switching the converting means, and by adding the voltage correcting quantity to ignition command signal. CONSTITUTION:Between a power source 2 and a motor 5, a power rectifying means 3 and a power inverting means 4 are connected to each other, and when power running or damping running is performed on one side and is switched to the other side, then arithmetic is performed on a counter-electromotive force in accordance with the rotational speed N of the motor 5 at the time point of switching, first by a counter-electromotive force arithmetic circuit 11, and the counter-electromotive force is converted to ignition command signal by an ignition command generating circuit 12. Besides, a voltage correcting quantity I' in accordance with motor current I at its time point is converted to an ignition angle by a compensating circuit 13. Then, the ignition angle command signal and ignition angle conversion value are added to each other, and ignition angle command signal alpha is created and applied to the other converting means.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching control method for a forward/reverse power converter that can smoothly switch the operating mode of a motor operating in an intermittent current state.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional example of a forward/reverse power converter for switching the operating mode of an electric motor.

In FIG. 3, a forward converter 3 made up of a thyristor and a reverse converter 4 made of Thyrisk are connected in antiparallel to a DC motor 5 to create a forward/reverse power conversion device. By supplying AC power from the AC power supply 2 to this and operating the forward converter 3, the DC motor 5 is operated in power. Also, by switching the active forward converter 3 to the reverse converter 4 during power running, the DC motor 5 converts its kinetic energy into electrical energy and regenerates it to the AC power source 2, thereby rapidly This results in braking operation that reduces the speed.

In this way, the forward direction converter 3 and the reverse direction converter 4 are switched in order to switch the operation mode of the DC motor 5 from powering operation to braking operation or from braking operation to powering operation, but in this switching, Determining torque polarity,
A series of controls such as converter pulse shifting and converter switching after confirming zero current are performed by the control circuit 10.
For this purpose, the speed detection signal N from the speed transmitter 6 coupled to the DC motor 5, the current detection signal 1 from the current transformer 7, and the speed command signal N9 from the speed setter 8 are used as the control circuit FtPt1.
However, since the operation of this control circuit 10 has no direct relation to the present invention, its explanation will be omitted.

When switching from one converter to the other in response to a change in the operating mode of the DC motor 5, the ignition command signal given to this new converter changes depending on the motor speed at that time. It is necessary that the phases correspond to each other, and for this purpose, a back electromotive force calculation circuit 11 is provided, which calculates the back electromotive force corresponding to the motor speed at the time of switching, and calculates the arc cosine value of the calculated value. By calculating in the command generation circuit 12, an appropriate firing phase signal α is obtained.

Fig. 4 is a graph showing the characteristics of the back electromotive force calculation circuit used in the conventional circuit shown in Fig. 3, where the horizontal axis shows the motor speed and the vertical axis shows the back electromotive force. .

As is clear from FIG. 4, the back electromotive force increases in proportion to the increase in speed, reaches the rated voltage at a base speed of N, and remains constant in the speed range above this. Therefore, by utilizing this characteristic, if the motor speed N is detected, the back electromotive force at that time can be easily calculated.

(Problem to be Solved by the Invention) By the way, when the DC motor 5 is controlled by the forward or reverse converter 3 or 4 as shown in FIG. 3, the current flowing through the DC motor 5 is not continuous. It may become intermittent. This current interruption tends to occur frequently when the load current is small or when the circuit inductance value is small, but recently there is a trend to reduce the circuit inductance value in order to improve the coordination of the motor. The range of load currents in which the current becomes intermittent has been expanded.

The disadvantage of this current intermittent state is that the motor becomes uncontrolled during the period of current interruption. Therefore,
For example, by switching forward converter 3 to reverse converter 4,
When switching the DC motor 5 from the power operation mode to the control operation mode, conventionally, the firing phase angle given to the reverse direction converter 4 is determined by the load voltage at that time (that is, the back electromotive force obtained with the characteristics shown in FIG. 4). Because it was determined only by
If this switching operation is performed while the current is in an intermittent state, the current value immediately after switching will become excessive, and then an undershoot will occur to suppress this excessive current, resulting in a long settling time until the current stabilizes. It has some drawbacks.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to shorten the current settling time at the time of switching even if the load current is in an intermittent state, when switching the operating mode of a motor is achieved by switching the forward direction conversion means and the reverse direction conversion means. The idea is to make it a guest house.

[Means for Solving the Problems] In order to achieve the above object, the switching control method of the present invention provides a forward direction conversion means and a reverse direction conversion means between the power source and the electric motor, and When the converting means switches the electric motor to the other converting means during power running or braking operation, the counter electromotive force corresponding to the motor speed at that time is converted into an ignition command signal and applied to the other converting means. In a switching control method for a forward/reverse power converter,
The voltage correction amount corresponding to the motor current at the time of switching the conversion means is converted into a firing angle, and this firing angle conversion value is added to the firing command signal.

[Effect]

Conventionally, even though the relationship between current and voltage when the motor current is in an intermittent state changes to a different correlation than when the current is continuous, the ignition phase angle has been calculated by ignoring this change. However, in the present invention, it is possible to determine whether the current is in an intermittent state or not from the load current command value. The firing phase angle is shifted by the intermittent compensation bone corresponding to this current command value.
This is intended to prevent excessive current from occurring immediately after switching the conversion means.

[Conventional technology]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In FIG. 1, a forward converter 3 and a reverse converter 4, both of which are composed of thyristors, are connected in antiparallel to each other to form a forward/reverse power converter. A power supply 2 is connected to the DC side, and a DC motor 5 is connected to the DC side so that the DC motor 5 can be operated in a power running mode or a braking mode. A control circuit 10 is provided to control the speed detection signal N from the speed transmitter 6 coupled to the DC motor 5, the current detection signal from the current transformer 7! , and the speed command signal N'' from the speed setter 8 are input to this control circuit 10, as in the case of the conventional example circuit already described in FIG.

Furthermore, a back electromotive force calculation circuit 11 that calculates the back electromotive force of the DC motor 5 from the aforementioned speed detection value N, and an ignition I command that calculates the inverse cosine of this back electromotive force and outputs an ignition command signal. It is the same as in the conventional circuit shown in FIG. 3 that a generating circuit 12 is provided to determine the ignition phase immediately after switching to the forward or reverse conversion circuit 3 or 4.

In the present invention, the current command signal I0 generated in the control circuit 10 is taken out, and this current command signal l* is inputted to the intermittent compensation circuit 13 to detect whether or not the motor current is in an intermittent state, When in an intermittent state, the inverse cosine of a predetermined voltage corresponding to the current at that time is calculated, and the result of this calculation is applied to the firing phase that is the output of the firing angle command generation circuit 12 mentioned above. By adding them, the ignition phase is shifted in the direction of delay and the generation of excessive current is prevented.

FIG. 2 is a graph showing the relationship between the current and voltage of the DC motor 5, with the horizontal axis representing the voltage and the vertical axis representing the current. Note that the two-dot chain line in FIG. 2 indicates the limit at which the current of the DC motor 5 is intermittent; below this intermittent limit line, the current is in an intermittent state, and above this intermittent limit line, the current is continuous.

As is clear from Figure 2, when the current decreases and changes from continuous to intermittent, the relationship between current and voltage changes. Because the ignition phase signal was output, an excessive current was caused to flow. However, in the present invention, the inverse cosine of the voltage change when the current is interrupted is calculated by the action of the intermittent compensation circuit 13, and the result of this calculation is By adding this to the output signal of the conventional firing command generation circuit 12, the firing phase angle is shifted. Therefore, even when the load current is intermittent, the power converter is fired at an appropriate firing phase, thereby preventing excessive current and providing quick switching operation.

A normal converter switching operation is performed in the following order: current command reversal → ignition phase angle shift → zero current detection → converter switching, but during the ignition phase angle shift and zero current detection, there is no control. A loop outside the current regulation loop, for example, a speed regulation loop, holds its output, but in the present invention, this holding is stopped, so the current command value output by the speed regulation loop changes from moment to moment. Intermittent current is predicted from the current command value, and compensation is performed accordingly.

〔Effect of the invention〕

According to this invention, when switching a forward converter to a reverse converter or vice versa in response to a change in the operating mode of the electric motor, which is a load, the magnitude of the current command value of the electric motor is , predicts whether or not the motor current is in an intermittent state, and when it is in an intermittent state, activates an intermittent compensation circuit that compensates for the load voltage corresponding to the current command value, and adjusts the firing phase angle at the time of converter switching. Since the current at the time of switching is prevented from becoming excessive by adjusting the current to be appropriate, it is possible to exhibit the effect of shortening the current settling time.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between voltage and current of a DC motor.
Figure 3 is a circuit diagram showing a conventional example of a forward/reverse power converter that switches the operating mode of a motor, and Figure 4 is a graph showing the characteristics of the back electromotive force calculation circuit used in the conventional example circuit in Figure 3. It is. 2... AC power supply, 3... Forward converter, 4... Reverse converter, 5... DC motor, 6... Speed transmitter, 7... Current transformer, 8... ...Speed setting device, 10...Control circuit, 11...Reverse''jA 1 Figure 2 Figure 1!, 4 Note 33 Mouth

Claims (1)

[Claims] 1) A forward direction conversion means and a reverse direction conversion means are provided between the power supply and the electric motor, and when switching the electric motor to the other conversion means during power running or control operation using either of the conversion means, In a switching control method for a forward/reverse power conversion device, in which a back electromotive force corresponding to a motor speed at a time point is converted into an ignition command signal and given to the other conversion means, a voltage corresponding to a motor current at a time point when the conversion means is switched. A switching control method for a forward/reverse power converter, comprising converting a correction amount into a firing angle, and adding the converted firing angle value to the firing command signal.