JPS6031432Y2 - Primary frequency control device for induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a primary frequency control device for an induction motor using a voltage source inverter, and more particularly to a control device that achieves stable control by keeping the voltage-frequency ratio constant even in a transient state.

A conventional control system for primary frequency control of an induction motor using a voltage source inverter as a power source has a configuration shown in FIG.

The deviation between the speed setting value ωr* and the detected speed ωr of the motor is amplified by the speed controller 1 and used as a voltage control signal vr* and a frequency control signal Fr*.

The voltage control signal Vr* is amplified by the voltage controller 2 to amplify the deviation from the detected voltage Vr of the motor, and this output is the current control signal Ir.
* Then, the deviation from the motor's primary current detection value 1r is taken and amplified by the current controller 3, and is made into the output voltage control signal (■) of the voltage source inverter.

On the other hand, the frequency control signal Fr* is passed through the voltage-frequency converter 4, and the output frequency of the voltage source inverter is controlled as a frequency control signal F proportional to the voltage.

In this way, the conventional device has a current control loop as a minor loop of the voltage control loop, so when the current controller 3 is limited in overcurrent in a transient state such as sudden load fluctuation, the voltage It becomes impossible to keep the ratio constant, and stable control becomes impossible.

Furthermore, since the control device has three types of loops: a speed control loop, a voltage control loop, and a current control loop, the response is poor.

Furthermore, since only the voltage is manipulated to control the current, there is a risk that the slip frequency will exceed the maximum torque of the motor, causing a so-called stall phenomenon.

The present invention provides a control device that controls the output limit value of the speed controller according to the detected speed value, thereby omitting the current minor loop and controlling the voltage-frequency ratio to be constant even in a transient state. The purpose is to

FIG. 2 shows a main control circuit showing an embodiment of the present invention.

The deviation between the speed set value ωr* and the detected speed value ωr is amplified by a speed controller 5, and the output of this speed controller 5 is made into a voltage control signal Vr* and a frequency control signal Fr*.

The deviation of the signal Vr* from the detected voltage value Vr is passed through the voltage controller 2 and made into the output voltage control signal V of the voltage source inverter.

The time constant of the frequency control signal Fr* is matched with that of the voltage control system by the time constant adjustment circuit 6, and the frequency control signal Fr* is converted into a frequency signal by the voltage-frequency converter 4, and is made into the output frequency control signal F of the voltage source inverter.

Here, the speed controller 5 sets its output limit value to the detected speed value ω
It is controlled according to r.

In this way, the present invention does not provide a current minor loop for overcurrent limitation.

This is because the current is determined by the difference between the power supply frequency and the rotational speed, that is, the slip frequency, and the current is determined by the difference between the terminal voltage and the induced voltage. By setting the frequency so that the current exceeds the limit value, no current minor loop is created and the current does not exceed the limit value.

In order to be able to regulate the difference between the rotational speed and the output frequency within a certain range even in a transient state, the output limit value of the speed controller 5 is changed according to the detected vehicle speed value, and the voltage control signal V and frequency control are The time constant with the signal F is matched by a time constant adjustment circuit 6.

FIG. 3 shows another embodiment of the present invention, and the difference between this figure and FIG. 2 is that when direct speed detection is not performed, the frequency control signal F, the detection voltage ■, and the detection current I are used to control the slip frequency ω.
An arithmetic circuit 7 for calculating S is provided, and this slip frequency ωS
and the frequency control signal F is fed back as the detected speed value ωr.

In this configuration as well, as in the case of FIG. 2, the current minor loop is omitted and control can be performed in which the voltage-frequency ratio is always kept constant.

Note that the calculation of the slip frequency is based on, for example, the magazine IEEE, T
r.

VoJA llN0, 5 Sept 10ct 1975, pages 483-488.

As described above, according to the present invention, the voltage control system becomes a single loop with a current limiting function without the need for a current minor loop in the voltage control loop, and the time constant adjustment element is added to the frequency control system. By simply providing this, it is possible to match the time constants of the voltage control system and the frequency control system, control the voltage-frequency ratio to be constant even in a transient state, and achieve stable speed control.

Furthermore, since the current control loop can be omitted, the number of loops is reduced by one, and the responsiveness of the control system can be improved.

Furthermore, since both the voltage and frequency are controlled to suppress the current, there is no stall phenomenon that occurs when the torque exceeds the maximum point.

Furthermore, unlike the conventional seven-bag arrangement, the voltage control system of the present invention can be configured as an open loop, and in this case, the speed control system becomes a single loop, further improving the responsiveness of the control system.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional primary frequency control device for an induction motor, Fig. 2 is a block diagram of a control device showing one embodiment of the present invention, and Fig. 3 is a block diagram showing another embodiment of the present invention. be. 2... Voltage controller, 4... Voltage-frequency converter, 5... Speed controller, 6...
Time constant adjustment circuit, 7...Slip frequency calculation circuit.

Claims (1)

[Scope of utility model registration request] In a device that controls the speed of an induction motor by primary frequency control of the induction motor using a voltage source inverter, the control device amplifies the deviation between a speed setting value and a detected speed value, and controls a limit value according to the detected speed value. a speed controller; and control circuit means for making the output of the speed controller an output voltage control signal of a voltage source inverter and for making an output frequency control signal having a time constant and a constant ratio with the output voltage control signal. A primary frequency control device for an induction motor, characterized by comprising: