JPH06105560A - Method for controlling output voltage of voltage type inverter - Google Patents

Abstract

PURPOSE:To reduce in size and cost an inverter by reducing the number of current detectors required for controlling to correct an output voltage of a three-phase voltage type inverter according to output current. CONSTITUTION:A single-phase current detector 4 is provided in an arbitrary one phase of three phase outputs of a three-phase voltage type inverter 2 to detect its output current, and positive/negative polarity of the detected current is detected by a current polarity detector 5. With respect to other two-phase output currents, both the currents are disposed in a vector manner by a phase difference of 120 degrees with the detected current, and the sum of the three vectors becomes zero. Thus, positive and negative polarity relationship of the two-phase output currents is operated to be estimated based on the positive/negative polarity relationship of the detected currents by a three-phase current polarity operator 6, and a predetermined correction amount is output by deciding an adding/subtracting direction in a predetermined phase to an output voltage target value of corresponding phase according to the positive/negative polarity relationship of the three-phase output currents by a three-phase voltage correction signal output circuit 7, thereby obtaining a new voltage target value with respect to the three-phase output voltages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output voltage control method for a three-phase voltage source inverter for driving an induction motor, which controls the output voltage target value according to the positive / negative polarity of the output current.

[0002]

2. Description of the Related Art In a conventional output voltage control method for a three-phase voltage source inverter of this type, in detecting the output current of each phase required for correcting the output voltage, there is a hole in each of the output three phases of the inverter. It is known that a current detector using an element or the like is provided to individually detect the output current of each of the three phases.

[0003]

As described above, in the conventional output voltage control method for a three-phase voltage source inverter, three sets of current detectors are required for detecting the output current of each of the three phases. In general, the variable range of the output frequency of an induction motor variable speed drive inverter is quite wide, and it is a magnetic field due to the iron core of a normal winding type current transformer or Hall current transformer using Hall elements. In a current detector having a path, a variable frequency one is larger and more expensive than a constant frequency one, and therefore an inverter device using such a current detector is also large and expensive. It had to be something.

In view of the above, the present invention provides a method of controlling the output voltage of a three-phase voltage source inverter for an induction motor variable speed drive for reducing the size and cost of the inverter device by reducing the required number of current detectors. It is intended.

[0005]

In order to achieve the above object, an output voltage control method for a voltage source inverter according to the present invention is an induction motor variable speed control for correcting the output voltage target value according to the positive / negative polarity of the output current. In an output voltage control method for a driving three-phase voltage source inverter, the output current in any one phase of the three-phase output of the inverter is detected, the positive / negative polarity of the detected current is detected, and the polarity detection result is determined according to the polarity detection result. Detecting the phase difference between the detected output current and the target value of the output voltage that changes with the same frequency as the required inverter output voltage in the same phase as the detected current, and further detects the current detection phase. And electrical angle of 120 degrees or 24
Regarding the inverter output currents in the other two phases having the phase difference of 0 degree, the positive and negative polarities are inverted with the same phase difference as the value in the detection current with respect to the target value of the corresponding output voltage. Assuming that each positive and negative polarity fluctuation pattern is estimated by calculation and the positive and negative polarities and current values of the three-phase output current of each of the three phases of the inverter determined as described above are designated, and the timing and polarity and magnitude of the adjustment are specified. The output voltage correction amount is added to the target value of the output voltage of each phase in the same phase as the output current of each phase, and the output voltage correction control is performed.

[0006]

The output voltage control method for a three-phase voltage source inverter for driving an induction motor according to the present invention relates to a sine wave conversion of the output current by correcting the output voltage target value according to the polarity of the output current of the inverter. For the purpose of improvement, correction control as shown in the correction operation waveform diagram of FIG. 3 is performed on various output amounts of the inverter shown in the vector diagram of FIG.

First, in FIG. 2, E _u , E _v , and E _w are vector representations of target output voltage values in the U, V, and W output phases of the inverter, respectively, and a phase difference of 120 degrees from each other in electrical angle. Is arranged. The output voltage of each phase according to each target value can be regarded as being in the same vector state as the target value in its normal value.

I _u , I _v , and I _w are vector representations of the inverter output currents energized by the phase output voltages according to the output voltage target values E _u , E _v , and E _w , respectively.
It has phase differences α _u , α _v , and α _w between the corresponding voltage vectors E _u , E _v , and E _w , respectively. Here, the input impedance of each of the three phases of the induction motor, which is the load of the inverter, is the same, and the output voltage target values E _u , E _v , and E _w have the same magnitude, and are 120 degrees relative to each other. Therefore, if the equivalent negative phase component in each phase output current is negligibly small with respect to the positive phase component, the phase output currents I _u , I _v and I _w also have the same magnitude and have a phase difference of 120 degrees from each other, and therefore the phase difference α _u between the voltage vectors E _u , E _v , and E _w ,
α _v and α _w also have the same size.

The vector sum of the output currents I _u , I _v , and I _{w of} each phase in the vector state as described above becomes zero. Therefore, by detecting the value of any one of the three, the other It is possible to specify them by calculating the magnitude and phase of each of the two. That is, as in the present invention, it is not necessary to install a current detector for each of the three phases for specifying the output current of each of the three phases, and it is possible to install a set of current detectors in any one phase. You're done.

Next, FIG. 3 shows a new voltage target value E by correcting the output voltage target value E _u according to the positive / negative polarity of the output current I _u of the U phase by taking the U phase in the three-phase output of the inverter as an example. _um
FIG. 7 is a correction operation waveform diagram showing a state in which the correction operation having the same relative relationship between the target value of the output voltage and the output current is performed in each of the other V and W phases. Figure 3 here
(B) shows a polarity detection waveform which is a rectangular wave shaped the waveform of the output current I _u and has positive and negative constant values I _u (+) and I _u (-) according to its positive and negative polarities.

[0011] In FIG. 3 (b) shows the U-phase output voltage target value E _u by the solid line, the new output voltage target value of the target value E _u obtained corrected by subtraction of the correction amount E _um is shown by a dotted line, and in the positive polarity section where the constant value I _u (+) of the output current I _u is taken as shown, a predetermined correction amount is added to the target value E _u , and the constant value is also the same. I
_{In the} negative polarity section where _u (-) is taken, a predetermined correction amount is subtracted to obtain the target value E _um . The predetermined correction amount is given by a process of previously determining an appropriate value according to the current value of the output current or the like.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the block circuit diagram of FIG. In FIG. 1, 1 is an AC power supply, 2 is a three-phase voltage type inverter, 3 is a three-phase induction motor, and 4 is a single-phase current for detecting an arbitrary one-phase output current in the three-phase output of the inverter. Detector 5 is a current polarity detection circuit for obtaining a positive / negative polarity detection signal of the detection current as shown in FIG. 3B from the detection signal of the current detector, 6 is a current related to the detection current from the current polarity detection circuit Based on the polarity detection result, a three-phase current polarity calculation circuit for estimating the positive / negative polarity of the output currents of the two phases other than the current detection phase according to the vector diagram of FIG. 2, 7 is an output of the three-phase current polarity calculation circuit A three-phase voltage correction signal output circuit that outputs a predetermined correction amount in a predetermined phase with respect to the output voltage target value E _u of the corresponding phase in a predetermined addition / subtraction direction according to the positive / negative polarity estimation result of the output current of each of the three phases. , The correction signal output circuit According correction signal applied to the inverter 2 becomes a three-phase instantaneous voltage target value or the the target value E _u like addition and subtraction of the output voltage final voltage command value or the new output voltage target value E _um like the To be done.

With the circuit configuration as described above, the output current detection for only one arbitrary phase in the three-phase output of the inverter is performed, and the correction control of the output voltage target value is performed according to the positive / negative polarity of the output current as shown in FIG. It becomes possible to control the output voltage of the three-phase voltage source inverter for driving the induction motor as shown. It should be noted that most of the above-mentioned various calculations can be performed by software in a calculation circuit such as a CPU.

[0014]

According to the present invention, in the output voltage control method of the three-phase voltage source inverter for induction motor variable speed drive, the output voltage target value is corrected according to the positive / negative polarity of the output current, the output voltage control method comprising: The output current in any one phase of the phase output is detected, the positive / negative polarity of the detected current is detected, and further 120 in electrical angle with the current detection phase.
For the inverter output currents in the other two phases having a phase difference of 240 degrees or 240 degrees, the vector sum of the output currents of the three phases is zero, and the output voltage and the output current level are different in each of the three phases. Since the phase differences are the same, a current detector is provided for each of the three phases for specifying the output current of each of the three phases by calculating and estimating each positive and negative polarity relationship based on the positive and negative polarity relationship regarding the detected current. Since it is not necessary to install a set of current detectors in any one phase, it is possible to reduce the size and cost of the inverter device by reducing the required number of current detectors.

[Brief description of drawings]

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

FIG. 2 is a vector diagram of output quantities of the inverter.

FIG. 3 is a waveform chart of a correction operation with respect to an inverter output voltage target value.

[Explanation of symbols]

 1 AC power supply 2 Three-phase voltage type inverter 3 Induction motor 4 Single-phase current detector 5 Current polarity detection circuit 6 Three-phase current polarity calculation circuit 7 Three-phase voltage correction signal output circuit

Claims (1)

[Claims] 1. An output voltage control method for a three-phase voltage source inverter for variable speed drive of an induction motor, wherein the output voltage target value is corrected and controlled according to the polarity of the output current. The output current in one phase is detected, the positive / negative polarity of the detection current is detected, and according to the polarity detection result, the detected current changes in the same phase as the required inverter output voltage in the same phase. The phase difference between the target value of the output voltage and the detected output current is detected, and further 12 in electrical angle with the current detection phase.
Regarding the inverter output currents in the other two phases having a phase difference of 0 degree or 240 degrees, the positive and negative polarities thereof have the same phase difference as the value in the detected current from the corresponding output voltage target values. Each positive and negative polarity fluctuation pattern is estimated by calculation as an inversion, and according to the positive and negative polarities and current values of the three-phase output current of each of the three phases of the inverter determined as above, the timing, polarity and magnitude of the adjustment The output voltage of the voltage source inverter is characterized in that the specified output voltage correction amount is added to the target value of the output voltage of each phase in the same phase as the output current of each phase to perform the correction control of the output voltage. Control method.