JPS6377382A - Controller for inverter - Google Patents

Abstract

PURPOSE:To decrease switching frequency, and to reduce a higher harmonic component by turning a switch having proper phase ON-OFF from the phase of a current command and the magnitude of the current deviation of each phase. CONSTITUTION:In a controller according to a system of comparing instantaneous valves of current set speed omega and the detecting speed omegafb of a motor 2 are compared and a torque current command it is obtained by a speed control amplifier 3 and a coefficient multiplier 4, a primary current command value i1 is acquired by a vector computing element 5 from the torque current command it and the command value j0 of an exciting current section, the current command values ia, ib, ic of a, b, c each phase are obtained by a three-phase converter 6 from the primary current command value i1, a current deviation II is acquired by comparing the current command values and the output current detecting signals iaf, ibf, icf of a main circuit 1, and the gate signal of the main circuit 1 is generated selectively by a gate selecting circuit 7 from the current deviation II, thus determining ON-OFF of each switch for the main circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an inverter control device using an instantaneous current value comparison method.

B6 Summary of the Invention The present invention provides an inverter that controls a rust conduction motor using an instantaneous current value comparison method. This improves waveform distortion etc. during frequency operation.

BACKGROUND OF THE INVENTION One of the variable speed control methods for alternating current machines is called the current instantaneous value comparison method, which controls the voltage so that the current approaches a sine wave. As shown in FIG. 4, this device is a main circuit switch U of an inverter.

For on/off control of V, W r A pulse voltage is generated that brings the output current closer to the command value, respectively. In this inverter, the smaller the hysteresis width vH, the more the output current matches the command value.

D8 Problems to be Solved by the Invention Inverters using the instantaneous current value comparison method tend to have a large number of switching operations in the low frequency range. On the other hand, due to the responsiveness of main circuit switches such as transistors, there is a limit to the number of times the switch can be switched, and in order to limit the number of times the switch can be switched, it is necessary to widen the hysteresis width vH. However, if the hysteresis width is widened, the distortion of the output current waveform becomes severe and harmonic components increase, causing problems such as noise.

In addition, the magnetic flux of the electric motor serving as the load changes slightly, resulting in an increase in iron loss.

E9 Means and operation for solving problems The present invention has been made in view of the above-mentioned problems, and in an inverter using an instantaneous current value comparison method, the deviation between the current command of each phase and the detected current is determined, The gate pulse of the inverter main circuit switch is determined based on the phase with the large deviation within the voltage vector region corresponding to the phase of the current command, and the state of the three-phase current is determined in a scolding manner. Obtain gate pulses so that the output current and voltage match the current command.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, which is applied to a speed control device for an induction motor.

When the induction motor 2 is driven by the inverter main circuit 1, the control device using the current instantaneous value comparison method has a set speed ω
* and the detected speed ωfb of the electric motor 2 are compared to obtain the torque current command it* by the speed control amplifier 3 and the coefficient unit 4, and from this, the primary current command value 11 is determined by the vector calculator 5 from 10 command values for the excitation current. *, and from this, the three-phase converter 6 calculates the current command value ia* of each phase of a, b, and c.
, ib", ic*, and calculate this current command value and the output current detection signals of main circuit 1 iaf, ibf, i
The current deviation ΔH (Δia, Δib
, Δic), and a gate signal for the main circuit 1 is selectively generated by the gate selection circuit 7 from this current deviation ΔH.

Here, the gate selection circuit 7 comprehensively determines the current deviation ΔH, that is, the individual states of the three-phase currents, and determines on/off of each switch in the main circuit.

In the control device configured as described above, the gate selection circuit 7
The gate control will be explained in detail below.

When the electric motor 2 is operated at a low frequency, the induced voltage of the electric motor 2 can be ignored, so that the current deviation ΔH and the voltage vector Vn can be associated on a one-to-one basis. Therefore, the gate selection circuit 7
Then, the gate blade is obtained by selecting an appropriate voltage vector by comparing the currents from the current deviation ΔH. To explain this in detail, the output turn of main circuit 1 consists of six switches U to Z.
(Refer to Figure 4).If the state in which the upper arm switches U, V, and W are on is 111, and the state in which the lower arm switches x, y, and z are on is log, then Eight voltage vectors vn (=
vo, v1. ..., v7). Since the integral of the voltage corresponds to the magnetic flux, if the locus of the integral of the voltage is controlled to draw a circle, changes in the magnetic flux can be eliminated.

Therefore, during busy operation in the low frequency range, the voltage vectors that can be selected according to the phase of the command current from the correspondence between the current deviation and the voltage vector are divided into six regions Φ to ■ shown in Fig. 3, taking into account the circular locus. To select a voltage vector within each region, the first display shows decision table data according to the phase with the largest deviation based on the results of comparing the deviations Δia, Δib, Δic with the upper limit value IMAX and lower limit value IMIN for each phase. Choose from.

(Left below) Table 1 Note that in the gate selection mentioned above, two
CIMAX-"MIN" is reached.
When this happens, it can be handled by switching to conventional instantaneous value control.

This gate selection selects a voltage vector that matches the phase of the stain flow command, in other words turns the main circuit switch on and off, significantly reduces distortion (harmonic components) in the current output, and also reduces the switching frequency. (In experiments, approximately % reduction with the same hysteresis width) is obtained, and furthermore, the return of magnetic flux to the trajectory of magnetic flux is reduced, leading to a reduction in iron loss, etc.

G0 In addition to the effects of the invention, according to the present invention, the phase of the current command and the current deviation of each phase can be reduced, compared to the conventional method of determining the on/off of the switch of the phase by comparing the current independently for each phase. Since the appropriate phase switches are turned on and off based on the size, the switching frequency can be reduced, harmonic components can be reduced, and iron loss can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a voltage vector diagram, Fig. 3 is a correspondence diagram between current phase and voltage vector, Fig. 4 is a main circuit diagram of the inverter, and Fig. 5 is FIG. 3 is a waveform diagram of instantaneous current value control. 1--Main circuit, 2--Induction motor, 3--Speed control amplifier, 6--3-phase converter, 7--Gate selection circuit. Figure 2 Voltage Pect A/Figure 3 Figure 3 Hole Koshikihayagin I Star II Cape Nri Gray Map

Claims (1)

[Claims] In an inverter using the current instantaneous value comparison method, the deviation between the current command and the detected current for each phase is determined, and the inverter main circuit switch is determined based on the phase with the large deviation within the voltage vector region associated with the phase of the current command. An inverter control device that determines a gate pulse.