JPH07114553B2 - Switching control method for forward-reverse power converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching control method for a forward / reverse power conversion device capable of smoothly switching the operation mode of an electric 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 that switches the operation mode of an electric motor.

In FIG. 3, a forward converter 3 composed of a thyristor and a reverse converter 4 also composed of a thyristor are connected in antiparallel to a DC motor 5 to form a forward / reverse power converter. AC power is supplied from the AC power supply 2 to the power supply, and the forward converter 3 is operated to drive the DC motor 5 to perform power running. In addition, by switching the forward converter 3 in operation to the reverse converter 4 during the power running operation, the DC motor 5 converts its kinetic energy into electric energy and regenerates it into the AC power supply 2 to rapidly The braking operation reduces the speed.

Thus, in order to switch the operation mode of the DC motor 5 from the power running operation to the braking operation or from the braking operation to the power running operation, the forward direction converter 3 and the reverse direction switching device 4 are switched. Discrimination of torque polarity,
The control circuit 10 performs a series of control such as pulse shift of the converter and switching of the converter after confirmation of zero current. For that purpose, the speed detection signal N from the speed transmitter 6 connected to the DC motor 5 is used. The current detection signal I from the current transformer 7 and the speed command signal N ^* from the speed setter 8 are input to the control circuit 10, but the operation of this control circuit 10 is not directly related to the present invention. The description is omitted.

When one converter is switched to the other converter in response to a change in the operation mode of the DC motor 5, the ignition command signal given to this new converter corresponds to the motor speed at that time. The counter electromotive force calculation circuit 11 is provided for that purpose, the counter electromotive force corresponding to the motor speed at the time of switching is calculated, and the arc cosine value of the calculated value is set as the firing command. An appropriate firing phase signal α is obtained by calculating in the generation circuit 12.

FIG. 4 is a graph showing the characteristics of the counter electromotive force calculation circuit used in the conventional circuit of FIG. 3, in which the horizontal axis represents the motor speed and the vertical axis represents the counter electromotive force.
As is apparent from FIG. 4, the counter electromotive force increases in proportion to the increase in speed, reaches the rated voltage at the base speed of N ₀ , and the voltage is constant in the speed range higher than this. Therefore, by using this characteristic, if the motor speed N is detected, the back electromotive force at that time can be easily calculated.

[Problems to be Solved by the Invention]

By the way, as shown in FIG. 3, when the direct-current motor 5 is controlled by the forward or reverse converters 3 or 4, the current flowing through the direct-current motor 5 may not be continuous but may be in an intermittent state. This current interruption tends to occur frequently when the load current is small or the inductance value of the circuit is small, but recently, in order to improve the quick response of the electric motor, there is a tendency to decrease the circuit inductance value. The range of load current in which the current is intermittent has been expanded.

The disadvantage of this intermittent current state is that the motor is in an uncontrolled state during the period of current interruption. Therefore,
For example, switching the forward converter 3 to the reverse converter 4,
Conventionally, when the DC motor 5 is switched from the power running mode to the control mode, the ignition phase angle given to the reverse converter 4 is the load voltage at that time (that is, the counter electromotive force obtained by the characteristics shown in FIG. 4). Because it was decided only by
If this switching operation is performed while the current is intermittent, the current value immediately after switching becomes excessive, and undershoot occurs to suppress this excessive current.
It has a drawback that the settling time until the current stabilizes becomes long.

Therefore, an object of the present invention is to shorten the current settling time at the time of switching the operation mode of the electric motor, even when the load current is in the intermittent state, when the switching between the forward conversion means and the reverse conversion means is achieved. Is to let.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the switching control method of the present invention includes a forward conversion means and a reverse conversion means between the power source and the electric motor, and one of the conversion means drives the electric motor in the previous period. Alternatively, when switching to the other conversion means during the braking operation, the back electromotive force corresponding to the electric motor speed at that time is converted into a firing command signal and given to the other conversion means. In the method, the intermittent state of the electric motor current is predicted based on the electric current command value of the electric motor, and when the electric current is in the intermittent state, the voltage correction amount corresponding to the electric current command value is converted into a firing angle, and the firing angle is calculated. The converted value shall be added to the roll call command signal.

[Action]

Conventionally, although the relationship between the current and the voltage when the motor current is in the intermittent state changes to a correlation different from that in the continuous current state, the ignition phase angle that ignores this change Was applied to the conversion means immediately after switching, and therefore an excessive current was required, so that it took a long time to settle the current.In the present invention, whether the current is intermittent or not from the load current command value. Whether or not it is estimated, the ignition phase angle is shifted by the intermittent compensation corresponding to the current command value, and an excessive current is prevented from being generated immediately after the conversion means is switched.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, a forward converter 3 composed of a thyristor.
And a reverse converter 4 are connected in reverse parallel to each other to form a forward-reverse power converter, and an AC power source 2 is connected to the AC side of the forward-reverse power converter and a DC motor 5 is connected to the DC side of the forward-reverse power converter. The DC motor 5 is designed to be operated in a power running mode or a braking mode, but a control circuit is provided for controlling the DC motor 5 such as switching of the operation mode.
10 is provided and controls 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 setting device 8. Input to the circuit 10 is the same as in the case of the conventional circuit described in FIG.

Further, a back electromotive force calculation circuit 11 that calculates the back electromotive force of the DC motor 5 from the speed detection value N described above, and a firing command generation circuit that calculates the reverse cosine of this back electromotive force and outputs a firing command signal.
It is also the same as in the case of the conventional example circuit of FIG. 3 in that the ignition phase is determined by providing 12 and 12 and immediately after switching to the forward or reverse conversion circuit or 4.

In the present invention, the current command signal I ^* generated in the control circuit 10 is taken out, and this current command signal I ^* is input to the intermittent compensation circuit 13 to detect whether or not the motor current is in the intermittent state. , In the intermittent state, the arc cosine of the voltage determined in advance corresponding to the current at that time is calculated, and this calculation result is used as the firing angle command generation circuit 12 described above.
Is added to the ignition phase, which is the output of, to shift the ignition phase in the delay direction and prevent the generation of excessive current.

FIG. 2 is a graph showing the relationship between the current and voltage of the DC motor 5, where the horizontal axis represents voltage and the vertical axis represents current. The double-dashed line in FIG. 2 represents the limit at which the current of the DC motor 5 is interrupted. Below the interrupt limit line, the current is in an interrupted state, and above it is continuous. As is apparent from FIG. 2, when the current decreases and changes to a continuous interrupted state, the relationship between the current and the voltage changes, but conventionally, even in the current interrupted state,
Since an ignition phase signal corresponding to the voltage at that time was output, an excessive current flowed.However, in the present invention, the action of the intermittent compensation circuit 13 causes the inverse cosine of the voltage change during intermittent current. Is calculated and the result of this calculation is added to the output signal of the conventional ignition command generating circuit 12 to shift the ignition phase angle. Therefore, even when the load current is intermittent, the power converter is ignited in a firing phase commensurate with it, so that an overcurrent is prevented and a quick switching operation is performed.

Normal converter switching operation is performed by the procedure of current command reversal → ignition phase angle shift → current zero detection → converter switching, but there is no control during ignition phase angle shift and current zero detection. The loop outside the current control loop, for example, the speed control loop holds its output, but in the present invention, since this hold is stopped, the current command value output by the speed control loop changes from moment to moment. Current interruption is predicted from the current command value, and compensation is performed accordingly.

〔The invention's effect〕

According to the present invention, when the forward converter is switched to the reverse converter or vice versa in response to the change in the operation mode of the electric motor which is the load, the magnitude of the electric current command value of the electric motor is changed. , Predicting whether or not the motor current is in the intermittent state, and in the intermittent state, activates the intermittent compensation circuit that compensates the load voltage corresponding to the current command value, and the ignition phase angle at the time of switching the converter is Since the current is appropriately controlled to prevent the switching current from becoming excessive, the effect of shortening the current settling time can be exhibited.

[Brief description of drawings]

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.
FIG. 3 is a circuit diagram showing a conventional example of a forward / reverse power converter that switches the operation mode of the electric motor, and FIG. 4 is a graph showing the characteristics of the counter electromotive force calculation circuit used in the conventional example circuit of FIG. Is. 2 ... AC power supply, 3 ... Forward converter, 4 ... Reverse converter, 5 ... DC motor, 6 ... Speed transmitter, 7 ... Current transformer, 8 ... Speed setter, 10 ...... Control circuit, 11 ・ ・ ・ Counter electromotive force calculation circuit, 12 ・ ・ ・ Ignition command generation circuit, 13 ・ ・ ・ Interruption compensation circuit

Claims (1)

[Claims] 1. A forward conversion means and a reverse conversion means are provided between a power source and an electric motor, and when either one of the conversion means switches the electric motor to the other conversion means during a power running operation or a braking operation. In the switching control method of the forward-reverse power converter, the counter electromotive force corresponding to the motor speed at that time is converted into a firing command signal and given to the other conversion means, based on the current command value of the motor. The intermittent state of the electric motor current is predicted, and when it is in the intermittent state, the voltage correction amount corresponding to the current command value is converted into a firing angle, and this firing angle conversion value is added to the firing command signal. A method for controlling switching of a forward-reverse power converter, comprising: