JPH02276494A - Controller for synchronous motor - Google Patents

Abstract

PURPOSE:To effect the variable speed driving of a synchronous motor equipped with field coils stably without providing any position detector by a method wherein the voltage of an inverter is controlled so that a reactive current for the motor becomes a predetermined value while a converter for a field is controlled so that the voltage becomes a voltage from a voltage setter. CONSTITUTION:The output phase of an inverter is obtained by a operating a driving angle frequency omega from an angular frequency reference omega* and integrating the operated values by an integrator 7. The voltage of an armature is outputted as a value, proportional to the driving angle frequency omega and obtained through a counter 13, and a value outputted from an amplifier 12 so that the value of a reactive current becomes equal to a reference value based on a difference between a reactive current reference value Id* and a reactive current operated value Id. On the other hand, the voltage reference V* of a motor is operated by the input of the driving angle frequency omega through a voltage setter 16. A difference between the value and the percentage modulating of the inverter is obtained and is amplified by another amplifier 18 to give the magnitude of a field voltage.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a method for controlling a synchronous motor having a field winding at variable speed by controlling the voltage and frequency of a voltage source inverter and the field voltage. The present invention relates to a control device for a synchronous motor to be driven.

(Prior Art) A so-called brushless motor that drives a synchronous motor having a permanent magnet rotor at variable speed is often used for small-capacity applications. When driving a pump, blower, etc., the control response does not need to be very fast. For this reason, a control method is often used in which the ratio of voltage to frequency (V/F) is maintained at a substantially constant value. Furthermore, brushless motors are usually equipped with a position detector, and the current and voltage are controlled according to this position. In order to simplify the device or for applications where a position detector cannot be provided, there are also known methods that do not require a position detector;
The method disclosed in Publication No. 7 is fortune-telling.

Figure 4 shows its configuration diagram, where 1 is a DC power supply, 2
is a smoothing capacitor, 3 is an inverter, 4 is a permanent magnet synchronous motor, 5 is a frequency calculator, 7 is an integrator, 8 is a PWM
Control circuit, 9 is a current detector, 1O is a reactive current calculator, 1
1.14 is an adder, 12 is an amplifier, and 13 is a coefficient multiplier.

Based on the angular frequency reference ω* of the electric motor, a frequency calculator 5 suppresses the rate of change to a predetermined value or less to obtain an angular frequency ω, which is integrated by an integrator 7 to provide an inverter voltage phase θ. The current detection value from the current detector 9 is combined with θ to calculate the reactive current 1d.

This value is compared with 16 reference values, and the amplifier 12 calculates a value corresponding to the deviation. This value and ω obtained by the coefficient unit 13
The modulation rate M of the inverter is determined by adding a value proportional to . The PWM control circuit 8 outputs pulses from θ and M, and provides on/off signals to the elements of the inverter 3.

The operation in the above configuration will be explained. FIG. 2 shows a vector diagram when the motor is in a driving state, where (a) shows the characteristics in a no-load state and (b) shows the characteristics in a state where a load is applied. e is the back electromotive force of the motor, ■ is the terminal voltage, and ■ is the current. In the same figure (a), the current ■ is 90% with respect to the reverse starting force e.
Suppose that the vehicle is being driven with a certain degree of lag. At this time, the terminal voltage V increases in the same direction as e by a value proportional to the magnitude of the current due to the leakage reactance of the armature. Even when the load shown in FIG. 6(e) is applied, the amount of increase in the component of the terminal voltage V in the same direction as e becomes a value proportional to the amount of current that lags e by 90 degrees.

The configuration shown in Figure 4 provides the characteristics shown in this vector diagram, but since a reactive current is caused to flow in advance and the voltage is made slightly higher than when there is no load, there is a possibility that the motor will go out of synchronization. I don't have much to worry about.

(Problems to be Solved by the Invention) Permanent magnet synchronous motors have a relatively small capacity, but as the capacity increases, many have field windings.

In a motor with a field winding, the field current must be varied according to the size of the load in order to keep the voltage at a nearly constant value while keeping the rotational speed constant. For this reason,
In addition to controlling the voltage and frequency of the motor's armature, it is also necessary to control the field winding.

An object of the present invention is to stably drive a synchronous motor with a field winding, which does not have a position detector, at variable speed.

(Structure of the Invention) (Means for Solving the Problem) In order to achieve this object, the present invention provides a current detector for detecting the current of the motor, a reactive current calculation means for calculating the reactive current of the motor, and a reactive current setting. Variable voltage, variable, in which the control circuit is equipped with voltage calculation means that determines the magnitude of the armature voltage from the value and the calculated value, and voltage setting means that applies voltage to the field winding so that the armature voltage becomes a predetermined value. It consists of a frequency control device.

(Function) The magnitude of the armature voltage is controlled so that the reactive current of the motor becomes a predetermined value, and the field voltage is adjusted so that the value of this voltage becomes a value proportional to the drive frequency.

(Embodiment) Fig. 1 is a configuration diagram showing an embodiment of the present invention, in which 15 is a synchronous motor with a field winding, 1B is a voltage setting device, 17 is an adder, 18 is an amplifier, and 19 is for the field. 4, in which the same numbers correspond to the same elements as shown in FIG.

The output phase of the inverter is determined by calculating the driving angular frequency ω from the angular frequency reference ω* using a frequency calculator 5, and integrating this using an integrator 7 to obtain the output phase θ. The magnitude of the armature voltage is determined by the amplifier 12 from the value proportional to ω via the coefficient unit 13 and the deviation between the reactive current reference value Id* and the reactive current calculation value 1d.
outputs a value that makes the reactive current equal to the reference value. The sum of these values becomes the modulation rate M of the inverter.

On the other hand, using ω as an input, the voltage setter IB calculates seven voltage standards for the motor. The deviation between this value and M is taken and amplified by an amplifier 18 to provide the magnitude of the field voltage.

As explained above, in this embodiment, the voltage of the motor is adjusted so that the reactive current becomes a predetermined value, and the field voltage is also adjusted so that this motor voltage is proportional to the drive angular frequency.

With the above configuration and operation, the present embodiment operates with the reactive current maintained at a predetermined value, so that unstable phenomena such as tax adjustment do not occur. Further, even at the same driving frequency, the field voltage is adjusted according to the size of the load, so that the voltage does not change much even when the load changes.

FIG. 3 is a block diagram showing another embodiment of the present invention, with 20
is a step-down chopper, 21 is a transistor, 22 is a diode, 23 is a reactor, and 24 is a coefficient multiplier. Elements with other numbers correspond to the same elements as those in FIGS. 1 and 4.

This is an example in which the input voltage of the inverter is changed by a step-down chopper. Based on the angular frequency ω of the inverter, a coefficient multiplier 24 controls the conduction width of the transistor 21 using a signal proportional to ω, thereby providing an inverter DC input voltage proportional to ω. On the other hand, the modulation factor M of the inverter is given by giving a constant amount K and combining it with a value calculated by the amplifier 12 so that the reactive current becomes a predetermined value. For example, vO may be zero.

Further, field control is performed so that the output of the amplifier 12 becomes a predetermined value vO. Therefore, the modulation factor M of the inverter
is a constant value even if the drive frequency is different, and the motor voltage is proportional to the voltage controlled by the step-down chopper.

Since the modulation rate M is almost constant, the PWM control circuit 8
By calculating a pulse pattern in which harmonics are reduced in , a waveform with fewer harmonics can be given to the motor.

【Effect of the invention〕

As explained above, in the present invention, stable operation is possible because the reactive current of the synchronous motor with field winding is controlled to a predetermined value, and the field voltage is also equal to the armature voltage proportional to the driving frequency. Therefore, it is possible to realize a good control device with little voltage fluctuation.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
3 is a vector diagram of the synchronous motor shown in the figure, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 4 is a conventional block diagram. 1... DC power supply 3... Inverter 5... Frequency calculator 7... Integrator 9... Current detector 11, 14. 17... Adder 12, 18... Amplifier 13. 24... Coefficient unit 15... Synchronous motor with field winding 1B... Voltage setting device 19... Field converter 2
0...Step-down chopper 21...Transistor 22
...Diode 23...Reactor 2...
Smoothing capacitor 4...Permanent magnet synchronous machine 6...Voltage generator 8...PWM control circuit 1O...Reactive current calculator Representative Patent attorney Noriyuki Chika Ken Yudo Daishimaru Ken Figure 1 ) Figure Figure

Claims (1)

[Claims] In a control device for a synchronous motor consisting of a voltage source inverter that supplies alternating current power with variable voltage and frequency control, a synchronous motor having a field winding, and a field converter that supplies direct current power to the field winding. , a current detector that detects the armature current of the synchronous motor, a calculation means that calculates the reactive current of the synchronous motor based on the voltage phase of the voltage source inverter and a signal from the current detector, a reactive current setting device, and a voltage calculator that determines the magnitude of the voltage of the inverter according to the set value of and the calculated reactive current value; a voltage setting device that determines the magnitude of the voltage of the motor according to the output frequency; A control means is provided to determine the voltage of the field converter in accordance with the signal from the voltage calculator, and the voltage of the inverter is controlled so that the reactive current to the motor becomes a predetermined value, and the voltage is controlled by the voltage from the voltage setting device. A control device for a synchronous motor, characterized in that it controls a field converter so that the voltage becomes constant.