JP2007014114A - PWM signal correction means - Google Patents

Abstract

The present invention provides a PWM signal correcting means for reducing PWM signal patterns that are difficult to detect current without increasing electromagnetic noise caused by current ripple.
A current detection unit 3 for detecting a current of a DC power source 2, an inverter unit 4 connected to the DC power source 2 and composed of a plurality of switching elements, and a DC current detected by the current detection unit 3 and given arbitrarily A voltage command calculation unit 5 that calculates a voltage command V vector from the torque current command Iq and the excitation current command Id, a PWM signal creation unit 6 that generates a PWM signal from the voltage command V vector, and an excitation current command from the voltage command V vector An excitation current command creation unit 7 for creating Id, and the excitation current command creation unit 7 calculates the motor current by changing the excitation current command Id according to the magnitude of the voltage command V vector to increase the output voltage. The frequency of PWM signal patterns that cannot be reduced is reduced.
[Selection] Figure 1

Description

  The present invention relates to a signal correction for improving a PWM signal pattern in which it is difficult to calculate a motor current from an inverter input current in a motor driving apparatus including an inverter unit that drives a motor by PWM driving.

  Conventionally, in order to drive a motor, it is common to provide current detection means in two phases of the motor line.

  However, in recent years, a motor drive device has been proposed that can detect two-phase currents of a motor line with a single current detection means (see, for example, Patent Document 1).

  That is, one current detection means connected between the DC power supply and the inverter main circuit for detecting an instantaneous current, and a PWM signal for ON / OFF control of a plurality of switching elements based on the detected instantaneous current This is a detection method that includes a PWM signal generating means for generating the motor current and detects at least two instantaneous currents during one carrier period of the PWM signal to detect any two-phase motor current.

In this method, the on / off period of the switching element of each phase is very short, that is, in the case of a PWM signal pattern in which the duty of one phase and another phase is very close, current detection is very difficult. This problem is avoided by correcting the duty in the first half and the second half of the PWM signal.
JP 2002-95263 A

  However, in the correction method described above, the output voltage is changed steeply in one carrier cycle, so that there is a problem that electromagnetic noise caused by current ripple due to correction increases.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object of the present invention is to provide a PWM signal correcting means for reducing PWM signal patterns that are difficult to detect current without increasing electromagnetic noise caused by current ripple.

  In order to solve the above-described problems, the present invention provides a current detection unit that detects a current of a DC power source, an inverter unit that is connected to the DC power source and includes a plurality of switching elements, a DC current detected by the current detection unit, and A voltage command calculation unit that calculates a voltage command from an arbitrary torque current command and excitation current command, a PWM signal generation unit that generates a PWM signal from the voltage command, and an excitation current command generation that generates an excitation current command from the voltage command The excitation current command creation unit changes the excitation current command according to the output voltage to increase the output voltage, thereby reducing the frequency of the PWM signal pattern in which the motor current cannot be calculated.

  By generating a PWM signal that increases the output voltage of the inverter circuit, it is possible to reduce PWM signal patterns that are difficult to detect current, and to suppress an increase in electromagnetic noise due to current ripple.

  A current detection unit for detecting a current of the DC power source, an inverter unit connected to the DC power source and including a plurality of switching elements, a DC current detected by the current detection unit, and a torque current command and an excitation current command which are arbitrarily given A voltage command calculation unit that calculates a voltage command from the voltage command, a PWM signal generation unit that generates a PWM signal from the voltage command, and an excitation current command generation unit that generates an excitation current command from the voltage command, from the voltage command to the motor An exciting current command creating unit that creates an exciting current command generates a PWM signal that increases the output voltage by changing the exciting current to reduce the frequency of the PWM signal pattern that is difficult to detect current.

  Example 1 of the present invention will be described with reference to the drawings. However, in the present embodiment, in order to simplify the explanation, the driven motor is an SPM motor.

  FIG. 1 is a configuration diagram of a main part of a motor driving device according to the present invention. In FIG. 1, a DC power supply 2 supplies DC power to an inverter unit 4. In the inverter unit 4, the switching element is turned on / off based on the PWM signal, and the motor 1 is driven by converting DC power into AC power. The current detector 3 detects a direct current and transmits it to the voltage command calculator 5. The voltage command calculation unit 5 calculates a voltage command from the DC current given from the current detection unit 3, the arbitrarily given torque current command, and the excitation current command given from the excitation current command creation unit 7. This is transmitted to the PWM signal creation unit 6. The PWM signal generation unit 6 generates a PWM signal from the voltage command and transmits it to the inverter unit 4. The excitation current command generator 7 changes the excitation current as shown in FIG. 4 according to the magnitude of the output voltage.

  Here, the voltage vector diagram and the output voltage diagram when the exciting current of the present invention is added are compared with the normal operation, and the effect will be described.

  First, FIG. 5 shows a vector diagram of a voltage command when the excitation current that is normally performed is set to 0, and the voltage command by the voltage command calculation is a V0 vector with respect to the torque current command Iq. FIG. 6 shows the duty of the PWM signal generated from the V0 vector. To simplify the comparison, the duty amplitude at this time is 25%, and the duty difference difficult to detect current is 5% or less. Then, the region where current detection cannot be performed is 80 degrees per 360 degrees per cycle.

  On the other hand, the voltage command V1 vector when the excitation current command is given as a positive value by the excitation current command generator 7 of the present invention is shown in FIG. 2, and compared with the V0 vector of FIG. It can be seen that the V1 vector is larger than the V0 vector by the amount of the voltage vector Vid with respect to the current command Iq, and a high voltage command can be obtained. FIG. 3 shows the duty of the PWM signal generated from the V1 vector. When the increase in voltage command by the voltage vector Vid is 5% and the duty amplitude is 30%, the region where current detection cannot be performed is one cycle 360. An area where the current cannot be detected is reduced to 68 degrees per degree.

  The PWM signal correction means of the present invention is useful for a motor drive device that calculates an inverter output current from a current of a DC power supply.

Main part configuration diagram of motor drive device Voltage vector diagram when excitation current command in the present invention is a positive value Output voltage diagram when excitation current command is positive in the present invention Relationship diagram between output voltage and excitation current in excitation current command generator Voltage vector diagram when excitation current command is 0 Output voltage diagram when excitation current command is 0

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 2 DC power supply 3 Current detection part 4 Inverter part 5 Voltage command calculating part 6 PWM signal generation part 7 Excitation current command preparation part

Claims (1)

In a motor drive device including an inverter circuit for PWM driving a motor, a current detection unit that detects a current of a DC power source, an inverter unit that is connected to the DC power source and includes a plurality of switching elements, and is detected by the current detection unit. A voltage command calculation unit that calculates a voltage command from the DC current and an arbitrarily given torque current command and excitation current command, a PWM signal creation unit that generates a PWM signal from the voltage command, and an excitation current command from the voltage command An excitation current command generator, which increases the output voltage by changing the excitation current command in accordance with the output voltage, thereby reducing the frequency of PWM signal patterns that cannot be used to calculate the motor current. PWM signal correction means characterized by:

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