JPH04156292A - Equipment for controlling permanent magnet type motor - Google Patents

Abstract

PURPOSE:To remove an error of a difference between DC currents, which is caused by the change of the frequency of an applied voltage, by correcting the error of changing quantity of the DC current, which is caused by the discrepancy of the timing of sensing the current, and by making the condition of sensing the current constant, and further, by controlling an inverter so that a computed power factor comes about one. CONSTITUTION:The difference between DC currents at two time points in each frequency comes into A in the case of a waveshape A, and 6 B in the case of a waveshape B. In the case of driving a motor under a fixed condition, when the frequency is changed, errors are generated in the differences A, B between the DC currents. When A and B are changed, the output value of a circuit 36 for computing a power factor comes erroneous and it is brought impossible to drive the motor so that the power factor comes about one. Therefore, the output of the circuit 36 for computing the power factor is made to be inputted to a correction circuit 37. There, the errors are removed, and A and B are so corrected that they come into identical values respectively. Then, the corrected values are inputted to a V/F computing circuit 38, and a control is so performed that the power factor comes about one.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a control device for controlling an electric motor having a permanent magnet rotor.

(Prior Art) As a conventional electric motor equipped with a permanent magnet type rotor, there is a permanent magnet type brushless motor. So 5
Here, we will discuss the control device that controls the permanent magnet brushless motor.

First, in brushless motors, the relative position between the stator winding and the permanent magnet rotor is determined by using the terminal voltage, including the induced voltage, generated in the stator winding, without using a 1st-order detection element such as a Hall element. Increasingly, detection methods are being adopted.

This conventional example is shown in FIG. 3, where 1 is a DC power source, and 2 is a fixed pre-winding 1.3 U of a brushless motor 3.

Inverter circuit for energizing 3v and 3W, 4.5
and 6 are filter circuits that phase shift the terminal voltages uv, vv, wv including the induced voltages generated in the stator windings 3U, 3V, and 3W by 90°; 7 is a neutral point from the output signals of these filter circuits 4 to 6; A detection circuit for obtaining the voltage NV; 8.9 and 10 are comparators that respectively compare the output signals of the filter circuits 4 to 6, which are first-order delay elements, with the neutral point voltage NV; and 11 is a control circuit.

FIG. 4 is a time chart showing the operation of the conventional example, and now, referring to this chart, let us consider the U phase. The terminal voltage UV generated in the stator winding 3U (see Fig. 4(a)) is as follows:
It includes a spike-like voltage component caused by conduction of the pair of arm freewheeling diodes during commutation in the inverter circuit 2. In order to eliminate the influence of this spike-like voltage component,
The phase of the terminal voltage UV is shifted by 90° by the filter circuit 4 to obtain a phase-shifted voltage DU■ as shown in FIG. 4(b). Thereafter, this phase shift voltage DUV and the neutral point voltage NV shown in FIG. 4(b) are compared by the comparator 8,
A position detection signal PSU is obtained as shown in C). The same goes for the other V and W phases, and based on the terminal voltages VV and WV, comparators 9 and 10 convert
The position detection signals PSv and PSW are obtained as shown in FIG. These position detection signals PSU, PSV and psw are 180
The energization signal becomes a signal with a phase difference of 120 degrees, and these signals are given to the control circuit 11.

The control circuit 11 outputs six commutation signals to be applied to the bases of transistors serving as switching elements of the inverter circuit 2.

However, in the apparatus for controlling the brushless motor, filter circuits 4 to 6 having a 90° delayed phase characteristic are provided in order to remove spike-like voltage components contained in the terminal voltages UV, VV, and Wv. The time constants of the filter circuits 4 to 6 are large, so there is a problem that rapid acceleration/deceleration cannot be followed, and there is also a problem that position detection in a low speed region is difficult. Furthermore, the terminal voltage UV
.

The magnitude of the spike-like voltage components included in Vv and WV changes depending on the t current of the stator windings 3U, 3V, and 3W and the magnitude of the load, so if the load fluctuation is large, filter circuits 4 to 6 and onwards This results in a phase error in the signal waveform, which poses a stability problem.

Therefore, it becomes difficult to stably drive the inverter during low speed operation.

Therefore, a commonly considered method is to detect the DC current flowing through the DC link of the inverter section using a current detection means, and to control the current to be applied to the windings of the brushless motor based on the detected current. According to this method, since the induced voltage is not used, the stability problem caused by the -order lag filter is solved, and the current detection means can be used as a t-current detector for the purpose of overcurrent protection of switching elements. Since the present invention can also be applied, there are many advantages such as eliminating the need to separately provide a detector for overcurrent protection.

An example of a device to which this method is applied is the one shown in FIG.

That is, the three-phase AC power supply 20 is connected to the rectifier 21 and the capacitor 2.
2 converts the DC power into DC power, and the inverter circuit 23 converts the DC power into AC power. Further, in the control unit, the current detector 24 detects the DC current flowing through the DC link of the inverter circuit 23, and the detected DC rjLt current signal Idc is expressed as 'SS
An outflow circuit 25 is provided. This Kl
The output I of the detection circuit 25 is sent to the power factor calculation circuit 26. This power factor calculation circuit 26 calculates the power factor and current change based on the DC current signal Idc, and provides the power factor signal ΔIdc and the t-current change amount ΔIdc- to the V/F calculation circuit 27 as output signals. The ■/F calculation circuit 27 calculates the voltage signal ■ and the frequency signal F based on the power factor signal ΔTdc, @flow change amount ΔIdc'' and the speed command value ω° given from a setting device (not shown). The signal V and the frequency signal F are given to the drive circuit 28.The drive circuit 28 generates pwM based on the voltage signal 2 and the frequency signal F.
IIItll six drive signals u, v, w.

X, Y, and Z are outputted and applied to the bases of the six transistors of the inverter circuit 23, so that the brushless motor 29 is rotated at the rotational speed indicated by the speed command value ω°. ing. Furthermore, in Figure 6,
The output waveform of the current detection circuit 25 is shown, that is, FIG.
shows the output waveform when the power factor lags, (b) shows the output waveform when the power factor becomes approximately 1, and (C) shows the output waveform when the power factor advances. , the waveform is repeated every 60 degrees in electrical angle of the output frequency. Therefore, this time point (0', 60°) every 60° electrical angle.

120°, 180', ...360°), and detect the difference (Ib - Ia) between the current value Ia at point A immediately before each point and the current value 1b at point B immediately after that point. However, by controlling so that this difference is zero, that is, the current values 1a and Ib are equal, changes in the DC current are treated as a power factor, and the power factor becomes approximately 1 as shown in Figure 6 (b). The brushless motor 29 can be operated.

(Problem to be Solved by the Invention) However, even in the above method, the difference in DC current between immediately before and after every 60 degrees of electrical angle is zero or the appointed value, regardless of the frequency of the applied voltage. Therefore, when configured with a discrete system using a microcomputer, there are constraints such as the current detection time and control response time of the microcomputer, and as shown in Figure 2, the applied voltage There is a problem in that the detection timing shifts depending on the frequency, current cannot be detected under the same conditions, and an error occurs in the difference in DC current, making it impossible to operate with a power factor of approximately 1.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a control device for a permanent magnet motor that eliminates the error in the difference in direct current caused by the frequency of the applied voltage.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides current detection means for detecting the amount of change in direct current of an inverter circuit, and a detection signal of the current detection means. Based on the first calculation means for calculating the power factor, and based on the output signal of the first calculation means, the error in the amount of change in the DC current due to the deviation in the current detection timing by the current detection means is calculated. a correction means for correcting;
a second calculation means for calculating the control amount of the permanent magnet motor based on at least the output signal of the correction means and the output signal of the first calculation means; The present invention is characterized by comprising an inverter control means for controlling the circuit.

(Function) The permanent magnet type electric motor of the present invention configured as described above has four functions! According to , when detecting the amount of change in the $ residue on the DC side of an inverter circuit and calculating the power factor based on the amount of change in the detected direct current, changes in the DC current due to a shift in current detection timing are detected. The inverter is controlled so that the calculated power factor is approximately 1 by correcting the quantity error and keeping the conditions for trX detection constant, so the power factor is always approximately 1 regardless of the frequency of the applied voltage. A permanent magnet motor can be controlled so that

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

First, the overall configuration will be described with reference to FIG.

A rectifier 31 converts the AC power from the three-phase AC power supply 30 into DC power, a capacitor 32 smoothes the DC power from the rectifier 31, and the smoothed DC power from the capacitor 32 is in charge! The main circuit includes an inverter circuit 33 that converts AC power to AC power having a frequency of . The control unit also includes a t-outflow circuit 34 that detects the DC current flowing in the DC link of the inverter circuit 33, and a t-outflow circuit 35 that processes the detected DC current signal 1dc by amplifying, sampling, holding, etc. , this t
The power factor and current change are calculated based on the output I from the outflow circuit 35, and the power factor signal ΔIdC and the current change amount ΔIdc are calculated.
A power factor calculation circuit 36 that outputs − and this power factor calculation circuit 3
a correction circuit 37 that removes an error in the output from the power factor calculation circuit 36 based on the power factor signal ΔIdc and the amount of change in ta ΔIdc- from 6 and the speed command value ω° given from a setting device not shown; ■/F calculation circuit 38 that calculates the voltage signal V and frequency signal F based on the output from 37
Based on this voltage signal ■ and frequency signal F, PWM
6 drive signals U, V, W, X, Y
, and a drive circuit 39 that generates Z.

Next, the main effect of this embodiment will be explained using the current waveform shown in FIG. 2. Waveform A in FIG. It is a direct current waveform. The current value at T1 of waveform A is A I , the current value at T2 is A2 , and T of waveform B
, the current value at T is B1, and the current value at T is B, then the difference in DC current at each frequency is A in the case of waveform A.

-AI (=ΔA), for waveform B, Bx-B
, (=ΔB).

If the frequency increases when the motor is operated under the same conditions, an error will occur in the DC current differences ΔA and ΔB. If ΔA and ΔB are different, the output of the power factor arithmetic circuit 36 will be a value containing an error, making it impossible to operate with a power factor of approximately 1.

Therefore, the output of the power factor calculation circuit 36 is input to the correction circuit 37, where the above-mentioned error is removed and correction is made so that ΔA and ΔB become the same value.
8 and performs control such that the power factor becomes approximately 1.

Furthermore, the operation of the correction circuit 37 will be explained in detail.

Using the output of the power factor calculation circuit 36 and the speed command value ω° given from a setting device (not shown) as input signals, the above error is removed by an arbitrary function such as the following equation (1).

PFouy = F (Ill, IA, PF, ω”)
......(1) (However, PFOUT: Output of the correction circuit 37, F: Any function, PF: Output of the power factor calculation circuit 36.

■A: The current value just before the negative 60゜, 1. (current value immediately after 60 degrees of force, ω0: speed command value) For example, in the case of Fig. 2, if we consider that the changes between T and T2 for both waveforms A and B are linear, the waveform The frequency command value of A is ωa,
Assuming that the frequency command value of waveform B is ωb, the current difference (denoted as ΔB′) of waveform B can be calculated using the following equation (2).

ΔB−=ΔBX(ωa/ωb) (2) As a result, ΔA=ΔB”, and the difference in DC current can be considered as a power factor regardless of the frequency of the applied voltage.

Note that if the calculation is complex, a table may be created and an arbitrary value may be added to the output of the power factor calculation circuit 36 for the frequency of the applied voltage.

Therefore, in the correction circuit 37, the current value for every 60" electrical angle,
Using a function F related to the output of the power factor calculation circuit 36 and the speed command value ω0 given from a setting device (not shown),
Calculate the power factor independent of the frequency of the applied voltage, and calculate V
/F is output to the summer circuit 38. Based on the power factor, the V/F calculation circuit 38 calculates l so that the power factor becomes approximately 1.
II control is executed.

Note that the above embodiments can be implemented using either hardware or software.

[Effects of the Invention] As described above, according to the present invention, since the error in current detection is corrected by the correction means, the power factor is always approximately 1 regardless of the frequency of the applied voltage. The permanent magnet layer motor can be controlled so that

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing one embodiment of the present invention, Fig. 2 is a DC current waveform diagram showing errors in current detection depending on the frequency of the applied voltage, and Fig. 3 is a conventional permanent magnet. Control system for layer motor! 4 is a time chart showing the operation of the control device for the permanent magnet layer motor shown in FIG. 3. FIG. 5 is an overall configuration diagram of the conventional control device for the permanent magnet layer motor. FIG. 6 is a time chart showing the operation of the control device for the permanent magnet layer motor shown in FIG. 33... Inverter circuit, 34... Current exhibition. 35... Current detection circuit, 36... Power factor calculation circuit. 37... Correction circuit, 38... V/F calculation circuit. 39... Drive circuit. 40...Brushless motor

Claims (1)

[Claims] An inverter means that converts the output from a DC power supply into AC power having an arbitrary frequency, a current detection means that detects the amount of change in the DC current of this inverter means, and a power factor is determined based on the detection signal of this current detection means. and a correction means for correcting an error in the amount of change in the direct current caused by a difference in current detection timing by the current detection means, based on the output signal of the first calculation means. , a second calculation means for calculating the control amount of the permanent magnet electric motor based on at least the output signal of the correction means and the output signal of the first calculation means, and based on the second calculation means, 1. A control device for a permanent magnet motor, comprising: inverter control means for controlling an inverter means.