JPH05130779A - Controller for voltage type pwm inverted - Google Patents

Abstract

PURPOSE:To reduce electromagnetic noise without enlarging the device in case of controlling an induction motor by a voltage type PWM inverter. CONSTITUTION:The magnetic flux vector is brought closer to the locus of a circle thereby reducing electromagnetic noise than a conventional one by providing it with an integrator, which seeks the phase angle of an inverter by integrating an inverter frequency command, and a carrier frequency modulator 9, which modulates the frequency of a modulation signal to go up by a certain angle with every 60 deg. phase angle as center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage type PWM inverter for reducing noise when an induction motor (hereinafter, also simply referred to as an induction machine) is driven at a variable speed by a voltage type PWM inverter.
The present invention relates to an inverter control device.

[0002]

2. Description of the Related Art Recently, there has been an increasing tendency to drive an induction machine at a variable speed by using a voltage type PWM inverter, and nowadays it is also used for private facilities such as air conditioning equipment of buildings. In this way, when it starts to be used near people, the electromagnetic noise of the induction machine driven by the inverter comes to the fore. FIG. 5 shows the configuration of a general voltage type PWM inverter, and FIG. 6 shows the signal waveform of each part. Note that FIG.
In FIG. 1, 1 is a sine wave generator, 2 is a triangular wave generator, 3 is a comparator, 4 is an inverter, 5 is a base drive circuit, 6 is a voltage source inverter, and 7 is an induction machine (IM). That is, the sine wave generator 1 generates a sine wave control signal as shown in FIG. 6A from the inverter frequency command f _m and the voltage command V _m, and the triangular wave generator 2 generates the carrier frequency command f _c.
To output a triangular wave modulation signal S _m as shown in FIG.
The comparator 3 compares (binarizes) these signals and, based on the result, turns on and off the switching element of the voltage source inverter 6 via the base drive circuit 5, thereby obtaining an output as shown in FIG. The induction machine 7 is driven at a variable speed.

[0003]

As described above, the voltage source P
Since a pulsed voltage is applied to the induction machine from the WM inverter, a specific noise called electromagnetic noise is generated from the induction machine. By the way, it is known that carrier frequency components are dominant when frequency analysis of this noise is performed. Therefore, as a countermeasure, IGB
T (insulated gate bipolar mode transistor) and MO
By using a high-speed switching element such as SFET (MOS type field effect transistor) and increasing the switching frequency (or carrier frequency) of PWM,
The method of moving electromagnetic noise out of the audible range may be adopted. However, this causes a problem that not only the loss of the switching element increases with the increase of the switching frequency but also the cooling fin becomes large. In addition, there is also a problem that the field of application is limited because the cost increases. Therefore, an object of the present invention is to reduce electromagnetic noise without increasing the size of the device.

[0004]

In order to solve such a problem, according to the present invention, a signal generator for generating a sine wave control signal from a voltage command and a frequency command, and a sine wave control signal and a modulation signal are provided. In a controller of a voltage type PWM inverter for pulse width modulation (PWM) controlling a voltage type inverter for driving an induction motor based on the comparison result, an integrator for integrating the frequency command. And a modulator which modulates the control signal so as to raise the frequency of the modulation signal by a certain angle based on the output of the integrator at every 60 degrees of the phase angle of the control signal.

[0005]

The electromagnetic noise is reduced by increasing the frequency of the modulation signal for a certain angle around each 60 ° phase angle of the pulse width modulation control signal.

[0006]

FIG. 1 shows an embodiment of the present invention. This embodiment is constructed by adding an integrator 8 and a carrier frequency modulator 9 to the conventional example shown in FIG. Others are the same as in FIG. That is, the integrator 8 integrates the inverter frequency command f _m and converts it into the inverter phase angle θ _m , which is synchronized with the phase of the control signal. The carrier frequency modulator 9 receives the inverter phase angle θ _m ,
The carrier frequency is changed according to the phase angle. The output becomes the carrier frequency command f _c , and the operation thereafter is the same as that of FIG. As the carrier frequency modulator 9, for example 0 degrees as shown in FIG. 2, 60 °, the carrier frequency command f _c only between 120 ° ... ± alpha degrees around the every 60 degrees as a (alpha ≦ 30 °) Is set to a high value. Here, the constant value is set to be a continuous constant value during this period, but it may be discontinuous or may have a certain inclination.

Next, the characteristic of the carrier frequency modulator is set to 0.
± α degrees (α ≦ 30 degrees) centering around degrees, 60 degrees, 120 degrees, etc.
The rationale for increasing the carrier frequency command f _c only during the period will be described below. Now, when the voltage obtained by the PWM pattern is taken as a space vector,
There are a total of 8 types of 6 types of voltage vectors and 2 types of zero vectors. When this is expressed by a mathematical expression, the number 1 is obtained. However, bold letters indicate vector amounts, and the same applies hereinafter.

[Equation 1] On the other hand, the change in the magnetic flux vector is expressed as in Equation 2.

[Equation 2]

Further, since the magnetic flux vector is delayed by 90 degrees with respect to the voltage vector, focusing on the locus of the magnetic flux vector created by the voltage vector, these vectors are represented as shown in FIG. The voltage vector used in each zone is shown in Table 1.

[Table 1]

By the way, it has been pointed out that as the locus of the magnetic flux vector shown in FIG. 3 becomes a circle, the drive becomes closer to the commercial drive and the noise can be reduced. Therefore, when a part of FIG. 3 is enlarged as shown in FIG. 4 and the dispersion of the magnetic flux vector locus and the circular locus during PWM control is examined, it is ½ of each zone at every 60 degrees.
It can be seen that the difference between the two is the smallest near the equiangular angle (here, 30 degrees), and is the largest at the points of 0 degree and 60 degrees. This is because there is a voltage vector in the tangential direction of the circle that is the traveling direction of the magnetic flux vector near 30 degrees,
This is because in the vicinity of 0 degree and 60 degrees, the magnetic flux vector is rotated by the two voltage vectors and the zero vector forming an angle of 60 degrees with the magnetic flux vector. This relationship is the same for each zone of 60 degrees such as 0 to 60 degrees, 60 to 120 degrees. Therefore, generally, by increasing the carrier frequency in the range of θ = n · π / 3 to n · π / 3 ± π / 6 (n = 0, 1, ... 5), the locus of the magnetic flux vector becomes more circular. It is possible to get closer to the trajectory.

[0010]

According to the present invention, the induction machine is a voltage source PW.
When controlled by the M inverter, the carrier frequency is increased by a certain angle around every 60 degrees where the magnetic flux vector deviates from the circular locus, so that the magnetic flux vector locus can be made closer to the circular locus. as a result,
High speed switching elements such as IGBT and MOSFET
It is possible to easily and inexpensively reduce the electromagnetic noise without using the above or increasing the size of the cooling fin.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining a characteristic example of a carrier frequency modulator.

FIG. 3 is an explanatory diagram for explaining a relationship between a voltage vector and a magnetic flux vector.

FIG. 4 is an explanatory diagram for explaining the principle of the present invention.

FIG. 5 is a configuration diagram showing a general example of a voltage-type PWM inverter.

FIG. 6 is a waveform diagram showing waveforms at various points in FIG.

[Explanation of symbols]

1 ... Sine wave generator, 2 ... Triangle wave generator, 3 ... Comparator, 4 ... Inverter, 5 ... Base drive circuit, 6 ... PWM inverter, 7 ... Induction motor (IM), 8 ... Integrator, 9 ... Carrier frequency Modulator

Claims (1)

[Claims] 1. At least a signal generator for generating a sine wave control signal from a voltage command and a frequency command, and a comparator for comparing the sine wave control signal with a modulation signal, and induction based on the comparison result. In a control device of a voltage type PWM inverter that controls a pulse width modulation (PWM) of a voltage type inverter that drives an electric motor, an integrator that integrates the frequency command, and a phase angle of the control signal every 60 degrees based on the integrator output. And a modulator for performing modulation so as to raise the frequency of the modulation signal for a certain angle with respect to the center.