JPH031918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic flux control method when an induction motor is driven from a power source whose voltage, such as a battery, fluctuates.

[Technical background of the invention]

Conventionally, methods for variable speed operation of induction motors have been widely used, mainly using frequency converters. Among these devices, devices using vector control that can control torque and speed with responsiveness are making their way into fields where only DC motors have traditionally been applied. As is well known, vector control of an induction motor is a method in which the primary current is treated as a vector quantity, and the torque component and magnetic flux component are separated and controlled independently. If the speed range of the induction motor is wide, field-weakening control is also possible in the same way as with a DC motor. For example, field weakening control in vector control is
This is already a known technique as disclosed in Japanese Patent No. 38116.

Although a cycloconverter, a current source inverter, a voltage source inverter, etc. can be considered as a frequency conversion device that performs such control, the voltage source inverter will be discussed here. A voltage source inverter generally rectifies a commercial AC power supply, converts it to a nearly constant voltage, and then performs pulse width modulation (PWM) control to control the current of an induction motor. In such a control method, the commercial power supply is usually more powerful than the load capacity, so even if the load fluctuates greatly, the DC voltage does not change much. Therefore, when performing field-weakening control, it is common to start the field weakening control when the speed of the induction motor exceeds a certain value. In this case, the amount of information for performing field weakening may be focused on the speed of the induction motor.

[Problems with background technology]

However, when a direct current power source is used, such as a battery, where the voltage changes greatly depending on the size of the load and the state of charge, the following problems occur. That is, since the maximum value of the output voltage of a PWM-controlled inverter is proportional to the DC voltage, when the DC voltage decreases, the maximum value of the output voltage also decreases accordingly. Therefore, when driving the induction motor to high speed while the DC voltage is greatly reduced, the magnetic flux begins to rotate at a rotation speed lower than the rotation speed at which field weakening starts at the original DC voltage.

That is, as shown in FIG. 1, the rotational speeds N ₀ and N ₁ at which field weakening is started differ by two times when the DC voltage V is V ₀ and when it is V ₀ /2.
Therefore, if we start field weakening from the rotation speed N ₀ as in the conventional method, when the DC voltage is halved, the magnetic flux will start to decrease from the rotation speed N ₁ , and the rotation speed and induction motor current will also decrease. In the vector control method, the set magnetic flux and the actual magnetic flux become significantly different at a rotation speed of N ₁ or higher, making it impossible to achieve good vector control.

[Purpose of the invention]

The present invention has been made to improve the above-mentioned drawbacks, and an object of the present invention is to provide a magnetic flux control method for an induction motor that detects the DC voltage of an inverter and automatically performs magnetic flux control in consideration of speed.

[Summary of the invention]

In order to achieve this object, the present invention provides a voltage detector that detects the voltage of the DC power supply and a speed detector that detects the speed of the induction motor, divides the voltage signal by the speed symbol, and obtains a predetermined value. If the magnetic flux is less than the value, the primary current of the induction motor is controlled so that the magnetic flux corresponds to the signal obtained by division.

[Embodiments of the invention]

FIG. 2 is a configuration diagram showing an embodiment of the present invention, in which 1 is a battery, 2 is a transistor inverter, 3 is an induction motor, 4 is a speed detector, 5 is a voltage detector, 7 is a divider, 8 is a limiter, 9 is a vector calculation circuit, 10 is a base drive circuit, 61, 6
2, 63 are current detectors, 101, 102, 103
is an adder. The main circuit configuration is a system in which an induction motor is driven by a voltage source inverter. The vector calculation circuit 9 calculates magnetic east command value φ ^* , torque command value Τ,
The rotor speed ω _r from the speed detector 4 is input, and each phase current command value i _u , i ^* _v , i ^* _w of the induction motor 3 is output. Each of these command values and the actual current values i _u , i _v , i _w are compared in adders 101 to 103, and the base drive circuit 10 shapes and amplifies the waveform of these comparison outputs and sends them to each base of the transistor inverter 2. Sends continuity control signal.

The gist of the present invention is the part that gives the magnetic flux command value φ ^* , including the divider 7 that divides the signal from the voltage detector 5 by the aforementioned ω _r , and the divider 7 that divides the signal from the voltage detector 5 by the above-mentioned ω r. It consists of a limiter 8 that outputs. In other words, if the battery voltage is V, calculate K・V/ω _r , and when this value is greater than or equal to φ ^*0 , φ ^* = φ ₀ ^* , and when it is less than or equal to φ ₀ ^* , φ ^* = K・V /
The value of ω _r is output to the vector calculation circuit 9. However, K is a calculation constant, and φ ₀ ^* is a magnetic flux command value when field weakening is not performed.

FIG. 3 is a block diagram showing another embodiment of the present invention, showing only the portion for calculating the magnetic flux command value φ ^* .
In FIG. 3, 104 is an adder, 105 is a coefficient unit, and the same numbers as in FIG. 2 indicate the same elements. In this embodiment, the torque command value T ^* is calculated from the voltage detection signal V.
We are calculating a quantity proportional to . This is done in consideration of the fact that the magnetic flux of the induction motor is proportional to the voltage divided by the primary frequency, and in the embodiment described above, the voltage was divided by the rotational angular frequency. In other words, this takes into consideration that the slip angular frequency ω _s changes depending on the torque command even at the same rotation speed, and is effective in equipment with a large field weakening region and small capacity machines. Further, in these embodiments, dividers and limiters are mainly used, but they may be processed collectively by a microprocessor.

〔Effect of the invention〕

As described above, according to the present invention, when an induction motor is driven by vector control using a voltage source inverter from a power source where the DC voltage fluctuates greatly, the magnetic flux command value is automatically set according to the magnitude of the DC voltage and the rotation speed. This makes it possible to obtain good drive characteristics over a wide DC voltage range.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram of the rotation speed and magnetic flux of an induction motor according to a conventional control method, Fig. 2 is a configuration diagram showing one embodiment of the present invention, and Fig. 3 is a magnetic flux command showing another embodiment of the present invention. FIG. 3 is a configuration diagram of a value calculation section. 1... Battery, 2... Transistor inverter, 3... Induction motor, 4... Speed detector, 5...
...voltage detector, 7...divider, 8...limiter,
9... Vector calculation circuit, 10... Base drive circuit, 61, 62, 63... Current detector, 101,
102, 103, 104...adder, 105...
Coefficient machine.

Claims (1)

[Claims] 1. In an induction motor drive device that has a main circuit configuration of a DC power source, an inverter, and an induction motor, and provides a speed detector and a current detector for the induction motor, and performs vector control using these as main detection signals, the voltage of the DC power source is An arithmetic unit is provided which inputs the detection signal of the voltage detector that detects the voltage and the speed detection signal and divides the voltage detection signal by the speed detection signal, and the output of the arithmetic unit is the magnetic flux command when field weakening is not performed. A magnetic flux control method for an induction motor, comprising controlling the primary current of the induction motor so that the magnetic flux corresponds to a calculation unit output when the magnetic flux is less than a value.