JPS5914385A - Drive system for ac motor - Google Patents

Abstract

PURPOSE:To control to smoothly decelerate an AC motor without disorder of torque by stopping energization at a specific angle of an electric angle when the control of the motor is shifted from power drive motor to a regenerative motor. CONSTITUTION:A polarity discriminator 201 outputs a polarity change signal PCS to a microcomputer 112 and a monitor 202 when the polarity of a speed deviation signal epsilonr varies. The monitor 202 counts a resulting pulse Pt from the generating time of a signal PCS, and when the resultant pulses of N/2 pieces are generated, a timeover signal TOS is outputted to the microcomputer 112. The microcomputer 112 inhibits the sinusoidal output by the signal PCS, and outputs a counting direction inverting signal CPS to a counter 111. When a signal TOS representing that 1/2 period is elapsed is generated, the microcomputer 112 again outputs sinusoidal wave of 2-phase on the basis of the counter value of the counter 111. In this manner, when the AC motor is shifted in control from the power drive motor to the regenerative mode, it is stopped energization at 180 deg. of an electric angle, and can be smoothly controlled in deceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC motor drive system, and more particularly to an AC motor drive system suitable for application when transitioning an AC motor from power operation to regeneration operation or from regeneration operation to power operation. .

A so-called "vector control system" was developed that can control the primary current of an AC motor by instantaneous value and generate torque similar to that of a shunt-wound DC motor, and is now being put into practical use. There is.

□ Figure 1 is an equivalent circuit of an AC motor under vector control, where 1m is the excitation reactance, γ2 is the equivalent resistance, and S is the slip. Considering the equivalent circuit of such an AC motor, the generated torque A and RI are as follows. Note that ω is the angular frequency. In this case, if L & 8ω are proportional, the torque T is proportional to the secondary current I, and the motor has a torque generation mechanism similar to that of a DC motor. By the way, the first
From the figure, γ! ω・1m・■. =-・Eng.

Because the package is established, I! In order to make Sω proportional to the excitation current ■. must be kept constant. From the above, vector control is performed using the exciting current Io while maintaining the orthogonality between the exciting current Io and the secondary current, as shown in the vector diagram of FIG.
. This is a control method in which the secondary current I is maintained constant and only the secondary current I is changed in proportion to the load torque. In vector control, the deviation (speed difference) ER between the command speed and actual speed is regarded as the torque command, so the speed deviation ER
According to the primary electrician, 1, = I. Control is performed so that +j- becomes -ER(3).

By the way, in vector control, when the AC motor is in the running state, the secondary current ■, as shown by the solid line in Figure 3,
Although the phase is delayed by 90 degrees in electrical angle with respect to the excitation current ioK, when in the regenerative state, the excitation current ■ is as shown by the dotted line. It is necessary for the 0° phase to advance. It is necessary to transition from the running state to the regeneration state with a very quick response, but at this time, transient torque disturbances occur, in other words, the torque does not change smoothly, and this causes deceleration. There were times when it was not possible to do this smoothly.

In light of the above, an object of the present invention is to provide an AC motor drive system that can smoothly transition from a running state to a regenerative state, or from a regenerative state to a power running state.

Now, in the AC motor drive system, a slip pulse with a frequency corresponding to the speed deviation between the commanded speed and the actual speed and a speed pulse with a frequency proportional to the actual speed are combined, and the resulting synthesized pulse is counted by a counter with a predetermined capacity. Then, using the count value of the counter, a 52π 4π phase sine wave signal sinωt, 5in(ωt 10s ),
stn (ωt+T) (however, each sine wave is a composite pulse N
If the frequency of the composite pulse is f, then ω is ω-2πf), and a current amplitude of 2π 4π width is generated according to the speed deviation, and sinωt, 5in(ωt + )
+ sin (ωt + s) is multiplied by the 3-phase primary current, 11si + ωE + 113 + n (ω
10-), Il sin (ω10-)6 is generated.

FIG. 4 is a block diagram of an embodiment of the AC motor drive method. In the figure, 101 is an AC motor, 102 is a pulse generator, and they are 90 degrees to each other in proportion to the rotation speed.
Two phase-shifted pulses Pa and Pb are generated. 10
3 is a quadruple circuit, which quadruples the frequency of the two-phase pulses Pa and Pb. Moreover, the quadrupling circuit 103 outputs the pulse train P a +
Monitor the phase of P b, and if it is rotating in the normal direction, the line l,
A normal rotation pulse Pn is output to the line , and a reverse rotation pulse Pr is output to the lines / and when the rotation is reverse. 104 is a forward rotation or reverse rotation pulse P n + P r.

A frequency voltage converter (referred to as an F/V converter) 105 converts frequency into voltage, and 105 is a difference ε between a speed command voltage VCMD commanded from a speed command circuit (not shown) and an actual speed voltage TSA.
Arithmetic circuit for calculating r (hereinafter referred to as speed deviation), 106
is an error amplifier that performs a PI operation, and a 107 voltage frequency converter (referred to as a V/F converter) which outputs a pulse Pe with a frequency fe proportional to the output value ER of the error amplifier 106. 108 is a slip counter, and as shown in FIG. 5, a constant value is preset when the actual speed is below the base speed Nb, and a value inversely proportional to the actual speed (rotational speed) is set when the actual speed is above the base speed Nb. As a result, voltage frequency converter 107
The pulse Pe of the frequency fe generated from the pulse is divided by the value Sn set in the slip counter 108, becomes a slip pulse Ps, and is input to the subsequent microcomputer.

Now, below the base speed Nb, a constant value is set in the slip counter 108, and above the base speed Nb, a value inversely proportional to the speed is set, so the frequency of the slip pulse Ps (slip frequency) fs is as shown in FIG. base velocity N
It remains a constant value up to b, and increases in proportion to the actual speed above the base speed. Note that, considering that there is a relationship between the slip frequency f8 and the actual speed f as fs+=s−f (s is slip) (4), the slip becomes constant above the base speed.

From the above, by presetting the numerical value in the slip counter 108 in the manner described above, so-called 1-vector control in which the slip frequency is constant below the base speed is performed, and above Nb, the slip frequency is increased in proportion to the actual speed. So-called”
"Slip frequency control" is performed. 109 is a synthesis circuit, which controls the slip frequency fs (ω3=2πfs).
frequency fn (ωn=2πf
n) pulses (Pn or Pr) are synthesized to output a synthesized pulse pt with a frequency ft. 110 is a counter that counts pulses P8 generated in a certain period of time, 111 is a counter with a capacity N that counts composite pulses pt, and 112 is a microcomputer. The microcomputer 112 includes a processing device 112a and a control program memory 1.
12b and a data memory 112C. Data memo IJ112 (! indicates torque versus amplitude characteristic (T-I, characteristic), torque versus phase characteristic (T-ψ characteristic), counter 111
The count values versus signature pattern characteristics are digitally stored as a function table.

The processing device 112a regards the count value M of the counter 110 as the torque T, and calculates and outputs T-■ from the characteristics.

Note that this current amplitude is expressed as being equal to the amplitude of the primary current shown in equation (3). Further, the processing device 1123 calculates the phase difference ψ from the T-ψ characteristic, and calculates the phase difference ψ from the counter 111.
gin (ωnt+ωst+ψ)(5)sin (ωn
t+ωst+ψ+2π/3) (6) is output digitally. 11.5, 114 is a multiplication type DA converter, ■,
11 sin (ωnt+ω8t+ψ)(7)I, obtained by multiplying equation (5), ■, and equation (6),
・sin (ωn to 1ωs t-19++2 π15
) (Converts + to analog and outputs U-phase and V-phase analog current commands 1u and iv. 11
5 is i u + i y - + i w
Perform the addition operation in (9) and set the W phase N sweat command 1 w
Current transformer that detects the phase currents iua and iva flowing through the U phase of the AC motor, 116 and 117, and 118 is iua+iva-+iwa
The phase current i flowing through the W phase after performing the QO addition operation
Arithmetic circuit that outputs wa, 119U, 120V, 121
W is provided for each phase, and the current difference (iuiua)
, rlv 1va).

Current control circuit that calculates and amplifies (iw iwa), 1
22 is a pulse width modulation circuit, and three pulse width modulation circuits 122U and 122V are provided for each phase.

122W, and pulse width modulation is performed on each of the current differences.

125 is an inverter circuit made of transistors, 124
is a rectifier that converts three-phase alternating current to direct current.

Now, when the AC motor is rotating in the CCW direction, the count value n of the counter 111 (assuming the capacity is 2'?=512)
The relationship between the sine wave UPP and the one-phase sine wave UPP is as shown by the solid line in FIG. That is, the counter 111 is preset to 512 when rotating in the CCW direction, counts down every time a composite pulse pt is generated, and thereafter is preset to 512 every time 512 composite pulses pt are generated. Then, the digital value corresponding to the count value n is output to the microcomputer 112.
A sine wave UPP is read out from the sine pattern stored in the data memory 112CK.

On the other hand, when the AC motor is rotating in the CW direction, the seventh
As shown in the figure, the counter 111 changes from zero to the composite pulse p.
t is counted (counted up), and its contents are made zero again every time 512 composite pulses pt are generated. and,
A sine wave UPP corresponding to the count value n is output from the microcomputer 112.

Now, time t. When a deceleration command is generated to cause the AC motor to shift from the running state to the regeneration state, according to the conventional method, the composite pulse pt is immediately output by the counter 111.
As the counting direction changes (from countdown to countup), the sine wave UPP changes as shown by the dotted line in FIG.

However, if the phases of the U-phase, ■-phase, and W-phase are suddenly changed in this way, the torque is disturbed and smooth deceleration cannot be performed.

Therefore, the present invention provides an electrical angle of 1 after the deceleration command is generated.
80 degrees, in other words, ten cycles (if the generation of N pulses corresponds to one cycle, then N/2 composite pulses are generated), the primary current command is applied to the AC motor. I am trying not to apply it. Then, after ten cycles, U, V, W
A six-phase primary current with reversed phases is generated and applied to the AC motor. That is, according to the present invention, the current is controlled as shown by the one-dot chain line in FIG.

FIG. 8 is a flow diagram of an embodiment of the present invention. The differences from Fig. 4 are: (a) A polarity determination circuit 201 for speed deviation εr is provided. (b) When it is detected that the polarity has changed and a deceleration command has been generated, the time elapsed over ten cycles is monitored. (Actually, a monitoring circuit 202 was provided to monitor whether or not P composite pulses pt were generated.) (c) Until ten cycles elapsed (5), (6) The difference is that the two-phase sine wave signal shown in the formula is not output, and (2) the direction of counting of the composite pulses by the counter 11 (count up, count down) is changed by changing the polarity.

Now, when deceleration is commanded and the polarity of the speed deviation signal εr changes, the polarity determining circuit 201 immediately determines this and outputs a polarity change signal PC8 to the microcomputer 112 and the monitoring circuit 202. Monitoring circuit 202 polarity change signal PC
The time-over signal TO8 is output to the microcomputer 112 when M2 composite pulses are generated. - On the other hand, the microcomputer 112 receives the polarity change signal PC
8, the output of the two-phase sine wave shown in equations (5) and (6) is prohibited, and a counting direction inversion signal CDS is output to the counter 111. Thereby, the counter 111 updates its contents in the opposite direction every time the composite pulse pt is generated. After that, if the time-over signal TO8 indicating that % period has passed is generated, the microcomputer 11
2 again outputs a two-phase sine wave whose phase is inverted based on the count value of the counter 111. Thereafter, five-phase primary current commands 1u+i, 1w are generated in the same manner as in FIG. 4 to drive and control the AC motor 101.

As described above, according to the present invention, AC is switched from power mode to regeneration mode.
When the control of the motor is transferred, the excitation is stopped by 180 degrees in terms of electrical angle, and there is no torque disturbance, and deceleration control can be performed easily.

In addition, although the case of power running → regeneration has been described above, the present invention is not limited to this and can of course be applied to regeneration → power running.

[Brief explanation of drawings]

Figure 1 shows the equivalent circuit of an AC motor in vector control.
Fig. 2 is a vector diagram, Fig. 5 is a vector diagram during power operation and regeneration operation, and Fig. 4 is a block diagram of a conventional AC motor drive circuit. Figure 5 is a diagram of the relationship between the number of revolutions and the preset value for the slip counter, Figure 6 is a diagram of the relationship between the number of revolutions and the ten-period frequency, Figure WC7 is a waveform diagram to explain the Kien υ month, and Figure 8 is a diagram of the relationship between the number of rotations and the preset value for the slip counter. 1 is a block diagram of an AC motor drive circuit of the present invention. FIG. 101...AC motor, 102...pulse generator, 104...f converter, 106...error amplifier, 107...V/P conversion R'? r, 108...Slip counter, 109...Synthesizing circuit, 110...Counter, 111...Counter, 112...Microcombiner, 201...Polarity discrimination circuit, 202...
・Surveillance circuit patent applicant: Fanariku Co., Ltd. Representative Patent Attorney: Mangai Tsuji (1 person)

Claims (2)

[Claims] (1) Using the speed difference between the commanded speed and the actual speed,
In an AC motor drive system that outputs a secondary current command and drives an AC motor based on the primary current command, an electrical angle of 180 An AC motor drive system characterized by stopping excitation for a period corresponding to . (2) A counter with a predetermined capacity counts the synthesized pulse obtained by combining a slip pulse with a frequency corresponding to the speed deviation value between the commanded speed and the actual speed and a speed pulse with a frequency proportional to the actual speed. In an AC motor drive system that generates one cycle of three-phase primary current commands with 78 composite pulses using the count value of a counter, when transitioning from power action to regenerative action or from regenerative action to power action, An AC motor drive system characterized by stopping excitation of the AC motor until N/2 composite pulses are generated.