JP5217477B2 - Control device for voltage type PWM inverter - Google Patents

Description

  The present invention relates to a voltage-type PWM inverter that drives a motor at a variable speed, and more particularly to a PWM inverter control device that switches a PWM carrier frequency in accordance with a speed command.

FIG. 3 shows an example of a variable speed driving device using a voltage type PWM inverter. The PWM control generates three-phase sine wave signals Vu ^* , Vv ^* , and Vw ^* that are proportional to the amplitude V of the output voltage and shifted by 120 degrees at the same frequency F as the output frequency. The carrier signal fc is compared with a comparator to determine the switching timing of the power device IGBT or the like constituting the main circuit of the inverter.

  The carrier frequency fc in the PWM inverter is an element that determines the switching frequency of the main circuit element, and greatly affects the switching loss and the element life. On the other hand, there is a technique that provides added value by switching the carrier frequency. For example, as a method for reducing the switching loss of the IGBT, there are a method of simply lowering the carrier frequency and a method of resting switching of one of the three arms of the IGBT of the main circuit (two-arm control). (For example, refer to Patent Document 1).

A dead time is provided in order to prevent the upper and lower arms from being short-circuited at the time of switching, but there is also a method of lowering the carrier frequency in order to suppress a reduction in voltage control accuracy due to the influence of the dead time.
JP-A-5-316744

  When a voltage type PWM inverter is applied to a servo motor drive device, a servo driver differs from a general inverter in that it mainly has the following operation pattern.

(A) Acceleration / deceleration operation for a short time with high torque (large current) (b) High torque control (stopping and holding pressure) while stopped
In particular, in the application (b), current concentrates on some main circuit elements, which leads to destruction of the main circuit elements due to heat concentration and a reduction in life.

  The following methods can be considered as countermeasures in these operation patterns.

  (1) A main circuit element having a larger frame (current rating) than usual is selected based on the current withstand capability in a stopped state.

  (2) Apply by lowering the carrier frequency.

  However, (1) has a problem that the cost increases. Also, (2) is not applied because lowering the carrier frequency leads to lower control responsiveness, and particularly in the servo system, torque responsiveness during acceleration / deceleration is important.

  As a third countermeasure, a method of lowering the carrier only at the time of high torque control in the stopped state can be considered, but the carrier frequency does not change instantaneously at the time of acceleration from the stopped state (because it is necessary to determine acceleration start) This will cause a problem in the acceleration characteristics from the stop state.

  An object of the present invention is to provide a control apparatus for a voltage-type PWM inverter that eliminates the need for a main circuit element having a large current capacity and enhances the response during acceleration / deceleration.

  In order to solve the above-mentioned problem, the present invention performs carrier frequency switching control for lowering the carrier frequency as necessary after completion of deceleration of the frequency command (speed command) and returning the carrier frequency to the original state before starting the acceleration. The control is provided with scheduling means for obtaining a torque response necessary for the acceleration / deceleration period determined by the operation pattern, and has the following configuration.

(1) A control device for a PWM inverter that performs speed control of an electric motor based on a predetermined operation pattern and can perform switching control of a PWM carrier frequency,
In the PWM carrier frequency switching control, after completion of deceleration of the speed command, the carrier frequency is lowered during the period when high torque control in the stopped state is necessary, and the carrier frequency is restored to the original state before starting acceleration from the stopped state. Switch,
There is provided scheduling means for obtaining a torque response necessary for an acceleration / deceleration period determined by a time according to the operation pattern or a rotational position of the electric motor.

  (2) The scheduling means sets the switching control of the PWM carrier frequency from the amount of heat generated by the switching loss of the main circuit element of the inverter and the torque necessary for the acceleration / deceleration of the electric motor.

  As described above, according to the present invention, after the completion of the deceleration of the frequency command (speed command), the carrier frequency is lowered as necessary, and the carrier frequency switching control for returning the carrier frequency before starting the acceleration is performed. Since the scheduling means for obtaining the torque response required during the acceleration / deceleration period determined by the operation pattern is provided, control with improved response during acceleration / deceleration can be performed.

  Specifically, in servo drivers that require acceleration / deceleration operation for a short time with high torque (large current) and high torque control in a stopped state, destruction of the main circuit elements due to heat concentration and reduction of life are prevented. As a countermeasure for this, it becomes unnecessary to select a main circuit element having a larger frame (current rating) than usual, which leads to cost reduction. Further, it is possible to prevent the acceleration / deceleration performance from being lowered by applying the carrier frequency at a low level.

FIG. 1 is a configuration diagram of a voltage type PWM inverter showing an embodiment of the present invention. In this configuration, as in FIG. 3, the V / F control unit 1 obtains αβ-axis voltages Vα ^* and Vβ ^* proportional to the frequency command F, and the phase detection unit 2 obtains the phase θ by integration of the frequency command F. The two-phase / three-phase converter 3 generates three-phase sine wave signals Vu ^* , Vv ^* , Vw ^* from the voltages Vα ^* , Vβ ^* and the phase θ.

The PWM control unit 4 compares the sine wave signals Vu ^* , Vv ^* , and Vw ^* with a carrier signal fc such as a triangular wave to generate a comparator 4A that generates a sine wave PWM signal for each UVW phase, and generates a carrier signal fc. A signal generator 4B for generating a signal, a dead time circuit 4C for forming a dead time between the sine wave PWM signals, and a drive signal for a power device (IGBT or the like) of the main circuit section 5 of the inverter using the sine wave PWM signal to be output The generated drive circuit 4D is configured.

  In this apparatus configuration, in this embodiment, a table processing unit 6 that generates a frequency command Fn and a carrier frequency command Fcn for each time Tn that defines a preset operation pattern is added.

  Here, when driving the injection molding machine or the servomotor for the saucer pan with the PWM inverter, the operation pattern for determining the output of the table processing unit 6 is (a) short time, high torque (large current) ) Acceleration / deceleration operation, and (b) high torque control (stopping and holding pressure) in a stopped state. However, in these applications, the operation pattern is determined depending on the machine or the manufactured product, and basically the operation is repeated. Once the operation pattern is determined, it can be said that there is almost no change later.

  In repetitive operation (frequency / voltage control) based on this operation pattern, PWM carrier frequency switching control is performed in addition to control for sequentially switching the frequency command F according to the time according to the operation pattern. Switch before entering.

  FIG. 2 shows an example of an operation pattern based on a frequency and carrier frequency table mounted on the table processing unit 6. In the operation pattern in which the frequencies F1 to F8 and the carrier frequencies Fc1 to Fc8 are switched in one cycle of the pattern, the period indicated by the hatched portion in the torque waveform is a portion where “high torque control in a stopped state” is necessary. As described above, since current concentrates on the main circuit element, it leads to destruction of the main circuit element and reduction of life due to heat concentration.

  Therefore, if the carrier frequency is lowered only during the current concentration period, the switching loss of the main circuit element can be reduced. However, if the carrier frequency is kept lowered during acceleration / deceleration, the acceleration / deceleration characteristics will be deteriorated. Therefore, the table processing unit 6 schedules the carrier frequency switching timing in the PWM inverter that is repeatedly controlled with the same operation pattern, and under conditions where the main circuit element is burdened, the carrier frequency is lowered to reduce the element destruction or the lifespan. While preventing acceleration / deceleration, the carrier frequency is restored to "original" in advance to prevent deterioration of acceleration / deceleration performance.

  In the example of FIG. 2, the torque frequency necessary for rapid deceleration is secured by keeping the carrier frequency high during the deceleration period F4 where the speed is decreased from F3 to F5, and the carrier frequency is decreased during the low speed period of the speed F5. The switching loss is reduced, and the torque current necessary for the rapid acceleration is secured by returning the carrier frequency to the original acceleration period F6 from the speed F5 to F7. Note that control for lowering the carrier frequency is not performed during the deceleration period of the speed F2. Since this is the initial operation pattern during the deceleration period, the heat setting due to the switching loss of the main circuit element is still set low, and is determined by the operation pattern.

  Although the embodiment shows a case where the present invention is applied to a V / F control type PWM inverter, it can be applied to a vector control type variable speed PWM inverter or the like to obtain the same effect. Further, instead of switching the frequency command and the carrier frequency according to the time, the table processing unit 6 can also switch according to the position when the operation pattern is determined by the rotation amount (position) of the electric motor.

The block diagram of the voltage type | mold PWM inverter which shows embodiment of this invention. Example of driving pattern. An example of a variable speed drive.

Explanation of symbols

1 V / F control unit 2 Phase detection unit 3 2-phase / 3-phase converter 4 PWM control unit 5 Inverter main circuit unit 6 Table processing unit

Claims (2)

A control device for a PWM inverter that performs speed control of an electric motor based on a predetermined operation pattern, and that can switch and control a PWM carrier frequency,
In the PWM carrier frequency switching control, after completion of deceleration of the speed command, the carrier frequency is lowered during the period when high torque control in the stopped state is necessary, and the carrier frequency is restored to the original state before starting acceleration from the stopped state. Switch,
A voltage-type PWM inverter control device comprising scheduling means for obtaining a torque response necessary for an acceleration / deceleration period determined by a time according to the operation pattern or a rotational position of an electric motor.   2. The voltage type PWM according to claim 1, wherein the scheduling means sets PWM carrier frequency switching control based on a heat generation amount due to switching loss of a main circuit element of an inverter and a torque required for acceleration / deceleration of an electric motor. Inverter control device.

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