JPS59185188A - Controlling method and device of pwm inverter - Google Patents

Abstract

PURPOSE:To reduce the noise generated from an AC motor by detecting the neutral voltage of a driven polyphase motor, and pulse-width-modulating to increase the effective value of the voltage in response to the magnitude of the neutral point voltage signal. CONSTITUTION:An AC power source AC is rectified by a rectifier 1 and smoothed by a smoothing unit 2, and applied to a PWm inverter 3. An induction motor 4 is connected to the output terminal of the inverter 3. A speed detector 5 is mechanically coupled directly to the motor 4, and the primary currents of the phases U and V of the motor 4 are detected by current detectors 8U, 8V. A speed detector 6 compares the signal of the detector 5 with the signal of a speed instructing circuit 14, and outputs a current command pattern signal to comparators 11U-11W. The signals detected by the detectors 8U, 8V are inputted to the comparators 11U-11W. A neutral point voltage detector 13 outputs a signal eN proportional to the neutral point voltage of the motor 4, and the signal eN is added to the output of the detector 6. In this manner, the inverter 3 is pulse-width-modulated, thereby reducing the noise of the motor 4.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides a method for controlling a PWM inverter that reduces magnetic noise by reducing harmonic components included in the output current of a PWM inverter that drives an AC motor. and regarding equipment.

[Background of the invention]

There are two types of control methods for PWM inverters: an instantaneous value control method and an average value control method. The instantaneous value control method uses a means for comparing the current deviation between the current command pattern signal (sine wave signal) and the output current detection signal of the inverter with hysteresis characteristics, and also compares the magnitude and polarity of the current deviation obtained from this comparison means. The ignition control of the PWM inverter is performed using a pulse width modulated pulse modulated based on the relationship.

The instantaneous value control method has the advantage of better current control responsiveness than the average value control method, which uses the current command pattern signal as the modulation wave signal and compares the carrier wave signal (triangular wave signal →) to generate a pulse width modulated pulse. .

In recent years, PWM has been developed using the instantaneous value control method, which has such advantages.
The practical application of controlling inverters has been studied and has already been put into practical use in some cases.

By the way, when an AC motor is driven by a PWM inverter, magnetic sound (noise) is generated from the motor.

The reason why magnetic noise occurs is that the output current of the inverter contains harmonic components. In particular, PWM inverters can be controlled using instantaneous value control. In the case of I control, an unpleasant magnetic sound is generated when the electric motor is operated at low speed.

On the other hand, AC motors are now being installed not only in high-noise locations but also in low-noise locations. Further, even when an AC electric generator is installed in a place with high noise levels, the unpleasant noise is not desirable from the viewpoint of the working environment. Therefore, it is strongly desired to reduce the magnetic noise of AC motors driven by PWM inverters.

Conventionally, methods for reducing the magnetic noise generated by an induction motor driven by a PWM inverter include a method of weakening the magnetic flux of the induction motor during light load or no-load conditions, or an instantaneous value control method and an average value control method depending on the rotational speed of the motor. ft1J
A method has been proposed in which the control methods are switched and used in combination.

However, although the former method can reduce noise when there is no load (@load), it has the disadvantage that noise cannot be reduced when the load is rated because the magnetic flux reaches the rated value. Furthermore, the latter has the drawback that the responsiveness of current control is reduced in the operating speed range (during low speed operation) based on the average value control method, and torque fluctuations occur during switching.

[Purpose of the invention]

The present invention has been made in response to the above-mentioned problems, and its purpose is to reduce the noise generated by an AC motor regardless of the load condition without causing a decrease in current control responsiveness or torque fluctuation. An object of the present invention is to provide a method and apparatus for controlling a PWM inverter.

[Summary of the invention]

The feature of the present invention is that the current deviation is determined by comparing the current command turn signal and the current detection signal, and when outputting a pulse width modulated pulse that is modulated based on the relationship between the magnitude and polarity of this current deviation. , the neutral point voltage of the AC motor is detected, and pulse width modulation is performed so that the effective value of the neutral point voltage increases according to the magnitude of the neutral point voltage signal.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention.

In the diagram g1, a diode rectifier circuit 1 converts an AC voltage applied from an AC power source A (3) into a DC voltage.

The DC output voltage of the rectifier circuit 1 is smoothed by a smoothing capacitor 2 and then applied to the PWM inverter 3.
+ SvP ... Return blocking diodes DuP, DvP connected in antiparallel to SyN and each switching element.
・1], N. An induction motor 4 is connected to an AC output terminal of each phase U, V, and w of the impark 3. A speed detector 5 is mechanically directly connected to the induction motor 4. Primary ton current iu, i of U phase and V phase of induction motor 4
.

(Output current of inverter 3) is constant current generator 8 U +8
detected by v. Current detector 8U, 8V detection current 1. ! 7 is a comparator 11U.

11v with the polarities shown and both detection currents are added to the adder 9 with the polarities shown. Ka'74-. Vessel 9
The W-phase detection current of the induction motor 4 can be obtained from .

The speed control circuit 6 receives the speed command signal N* of the speed command circuit 14.
A current pattern command signal ii+in with an amplitude proportional to the speed deviation obtained by comparing the speed detection signal N of the speed detector 5 and a 120° phase difference whose frequency is proportional to the primary frequency command signal is output. The primary frequency command signal is given, for example, as the sum of a rotational frequency proportional to the speed detection signal N and a frequency proportional to the speed deviation. Current command pattern signal 'r,'F
are added to the neutral point voltage signal eN in the adder 10U and toy, respectively, and the comparator 11 with hysteresis characteristics
U, added to IIV.

Further, both current command patterns I u'' and j 1' are vector-added with the polarities shown in the figure by an adder. The adder 7 outputs a W-phase current command pattern signal 47. The current command pattern signal I- is added as a vector with the illustrated polarity. Neutral point voltage signal e at 10W
N and is added to the comparator 11W having hysteresis characteristics. Comparator 11U.

11V and IIW are adders 10U and 1(N', respectively).

10W output signal and current detection signal i. ,i,.

i-, all pulse width modulated pulses (PWM pulses) for turning on and off the switching elements SuP, SvP...S, N constituting the inverter 3 are generated. Gate circuit 12U, 12V, 12W is comparator 11U,
The PWM pulses output by IIV and IIW are given as gate signals to switching children S,, p, S, p...S+rN. The neutral point voltage detection circuit 13 adds the PWM pulses of the comparators 11U, IIV, and IIW with the illustrated polarities to obtain a neutral point voltage signal e. Output.

Next, its operation will be explained with reference to FIGS. 2 and 3.

First, in order to facilitate understanding of the present invention, a period 'r1 in which the neutral point voltage signal e6 is not applied from the neutral point voltage detection circuit 13 will be explained.

When the output currents iu, ia, and 1a of the inverter 3 are flowing in the direction of the arrow shown in the first figure, the polarity is positive. current iu
, iv, i are switching elements SuP, Svp
, Svp is turned on, it increases with positive polarity, and when the switching elements SIN and S y N I S wN are turned on, it increases with negative polarity. Also, the current I5゜1, l'9
When the switching element is turned off while flowing with positive polarity, the diode D u N + D v N + D v
When the switching element S, , N and S A N18vN are turned off, the diodes D u P and D V P I D w
It flows through P and decreases.

Switching elements S a P , S v P , S W
N on.

Off is PWM generated by comparators 11U, IIV, and IIW.
This is done by pulses. Figure 2(a) shows the current command pattern signal 1- applied to the comparator 11U and the current detection signal 1.
1 is shown. During the T1 period, the relationship between the current deviation Δiu of the current detection signal lu between the current command pattern signal i7 and the current detection signal i and the hysteresis width -Δ■ is IΔi, l
When >lΔII, the comparator 11U sets the P'WM pulse to the It1g3 level as shown in FIG. 2(d). The gate circuit 12U provides a gate signal to the switching element S uP when the PWM pulse (d) reaches the 11177 level. In this case, since the switching element SuP is turned on, the U-phase current l. increases as shown. When the U-phase current i7 increases and becomes larger than the hysteresis width +31 from the current command pattern signal 1゜*, the comparator 11U changes to PW.
Set M pulse (d) to (L-III level).

When the PWM pulse (d) reaches the °I, n level, a gate signal is given to the switching element S.sub.N, and the switching element S.sub.N. P is off. During the T1 period, the U-phase current 16 is flowing with positive polarity. When the switching element is turned off, the U-phase current 1 flows through the diode D u N and decreases. When the U-phase current lu decreases and becomes smaller by the current command pattern signal 1 - the hysteresis width - Δ■, the PWM pulse (d) of the comparator 11U becomes the tE11 level again, and the above-described operation is repeated. When the U-phase current 16 is flowing with negative polarity, the current 11 flows through the switching element S u )q and the diode D u p. In this way, the U-phase current i6 of the inverter 3 is controlled to follow the current command pattern signal 1. This kind of operation also generates comparators 11V and IIW for the V and W phases.

The same is done with a phase difference of 1200 by using PWM pulses. FIG. 2(b) shows the relationship between the V-phase current command pattern signal 1- and the V-phase current iv, and FIG. 2(e) shows the PWM pulse generated by the comparator 11'V. Similarly, FIG. 2(C) shows the current command pattern signals iJ and W of the W phase.
The relationship between the phase currents iW is shown, and the PWM pulse generated by the comparator 11W is shown in (f) of the figure.

As described above, the instantaneous value control of the PWM inverter 3 is carried out, but the output current! . ,i,,l.

The instantaneous value of is detected and the current command pattern signal 11* is generated.

The instantaneous value control that switches the PWM inverter 3 depending on the excess or deficiency of iV''1 j - allows current control to be performed with good responsiveness.

By the way, the PWM inverter 3 generates PWM pulses (d),
(e) and (f), so the output voltage (phase voltage) is controlled by PWM pulses (d) and (e
l.

It changes in synchronization with (f). Focusing on the relationship between the U-phase voltage (d) and the V-phase voltage (e) during the T1 period shown in Fig. 2, when the U-phase voltage (d) is exactly at the "1" level, the V-phase voltage (e) is Negative (“-1” level) or vice versa
When the phase voltage (d) is negative, there is a period in which the V-phase voltage (e) is positive. The difference between voltages (d) and (e) is the line voltage, W
Line voltage e, including phase voltage (f).

When e, , are shown, they become as shown in Fig. 3 (h), (su, and (j)).

Note that (d) to (j) in FIG. 3 show the PX'JM pulses in FIG. 2. The line-to-line voltage during the T1 period shown in (h) γ(j) in the third image contains many harmonic voltages with large amplitudes. Therefore, a large amount of harmonic current flows through the induction motor 4, increasing magnetic noise.

Next, according to the present invention, the neutral point voltage signal eN of the primary winding of the induction motor 4 is converted into a current command pattern signal i u*, i
The operation when the neutral point voltage signal eN is added to -, l, , 11 will be explained.

The T2 period in FIGS. 2 and 3 is an operating waveform when the neutral point voltage signal eH is applied.

Comparator 11U, 11V, 11WI7) PWM
Pulses (d), (e), and (f) are proportional to each phase voltage, and are detected from the neutral point voltage detection circuit 13 to the neutral point proportional to the neutral point voltage of the primary winding of the induction motor 4. voltage signal e
N is obtained. The neutral point voltage signal eN has a waveform as shown in FIG.

Current command pattern signal j W” at 10V, IOW
Hj II" J j J. At this time, the comparators 12U, 12V, 12Wid
i-i*≧ΔI + e N・Yu...When (1), change the PWM pulse from 1 #J level to "-1" level, i-i"≦-Δ■+eN...・・・
・In case (2), the PWM pulse is changed from I(, ?+ level to a
It will be t II + II le. This means that the hysteresis width of comparators 12U, 12V, and 12W is ±Δ
This means that I is changed by the neutral point voltage signal eN. Current command pattern signals i-, i, +k.

Since it would be complicated to illustrate the state in which the neutral point voltage signal eN is added to iW1', FIG. 2 shows the state in which the hysteresis width ±Δ■ is varied.

Current command pattern signal j ll*T , j II , j
A neutral operation is performed at 'II' to generate more PWM pulses as shown in Figure 2 (d) to (f). Figure 2 (d> to (f)
) The PWM inverter 3 is activated by the PWM pulse of the T2 period shown in
The line voltages e, v, ~v1 when ignition is controlled
ev-u is as shown in Figures 3v (h) to (j). The line voltage in the T2 period, which is the sum of the neutral point voltage signal e, decreases compared to the TI period. As a result, the harmonic voltage decreases, and the harmonic current flowing through the induction motor 4 also decreases, making it possible to reduce magnetic noise.

As described above, the current command pattern signal i, *, 4-9i/
The magnetic noise is reduced by adding the neutral point voltage signal eN to -, but the neutral point voltage signal eN is
g). As is clear from Figure 2 (g),
The effective value of the neutral point voltage in the T2 period is larger than that in the T1 period.This means that the neutral point voltage signal eN is added to the current command pattern signal so that the effective value of the neutral point voltage eN becomes larger. It turns out. In other words, pulse width modulation is performed so that the effective value of the neutral point voltage becomes large.

In the embodiment shown in FIG. 1, the neutral point voltage signal eN is added to the current command pattern signal i, but it is also possible to add the neutral point voltage signal eH to the current detection signal i with the same polarity. However, the same operation can be performed.

This is also clear from the relationship between equations (1) and (2+).

FIG. 4 shows another embodiment of the present invention, in which the comparator 11
The hysteresis widths of U, IIV, and IIW are directly changed by the neutral point voltage signal eN.

In FIG. 4, the same symbols as in FIG. 1 indicate equivalents, and the hysteresis width adjustment circuit 15 connects the comparators 11U and IIV according to the neutral point voltage signal eN.

Fully adjust the hysteresis width ±ΔI of 11W.

FIG. 5 shows a detailed circuit diagram of the hysteresis width adjustment circuit 15 and the comparator 11U.

A current deviation Δi obtained by comparing the current command pattern signal i- and the current detection signal i via input resistors 22 and 23 is input to the negative terminal of the comparator amplifier 21. Comparison amplifier 2
The output voltage divided by a resistor 24.25 is fed back to the positive polarity terminal of 1.

The output voltage of the comparison amplifier 21 is limited by the diodes 26 and 27, and the limiting value can be adjusted by the magnitude of the voltage applied to the resistors 28 and 29.

Diodes 26, 27 and resistors 28, 29 constitute a well-known limiter circuit. The comparator 11tJ is composed of the above comparison amplifier 21, the diodes 26.27, and the resistors 22 to 25°28.29. On the other hand, the hysteresis adjustment circuit 15 includes a reference width setting circuit 30 that sets a reference hysteresis width Δ■8, adders 31 and 32 that add the reference value ΔΔ8 and the neutral point voltage signal eH with the polarities shown, and It is composed of amplifiers 33 and 34 that amplify based on polarity.

Now, the amplifier 34 outputs a positive polarity voltage that is the sum of the set value Δ■8 and the neutral point voltage signal eN.

When comparator amplifier 21 produces a negative output that is greater than the positive voltage of amplifier 34, diode 7 becomes conductive. Therefore, the absolute value of the negative output voltage of the comparator amplifier 21 decreases and is limited to a value corresponding to the output voltage of the amplifier 34.

Similarly, the positive output voltage of the comparison amplifier 21 is
is limited depending on the magnitude of the negative polarity voltage. Amplifier 33
．． The output voltage of 34 is proportional to the sum or difference of the reference hysteresis width ΔI6 and the neutral point voltage signal eN,
In the end, the output voltage of the comparator amplifier 21 is limited by the set value ΔIIl and the neutral point voltage signal eN. Comparison amplifier 21
has hysteresis characteristics depending on the magnitude of the output voltage fed back to the positive terminal. The output voltage of the comparison amplifier 21 changes depending on the output signal of the hysteresis width adjustment circuit 14. Therefore, the hysteresis width ±Δ of the comparator 11U changes depending on the neutral point voltage signal eN.

The hysteresis widths of the comparators 11V and IIW are also adjusted by the hysteresis width adjustment circuit 14.

In this manner, the same control as in FIG. 1 is performed in the embodiment shown in FIG. 4 as well, making it possible to reduce harmonic current and reduce magnetic noise.

FIG. 6 shows another embodiment of the invention.

In the embodiment shown in FIG. 6, the neutral point voltage signal eN is directly applied to the positive terminal of the comparison amplifier 21.

In FIG. 6, the same symbols as in FIGS. 1 and 4 indicate equivalents. Adder 40U, 40V.

40W is the current deviation of each phase Δiu1Δl・, Δ from the current command pattern signals i-, i- and the current detection signal iu1 iv.
i, is output. Current deviation of each phase Δiu1Δlv, Δ
i is amplified by amplifiers 41U, 41, ;, 41W,
It is input to the negative polarity terminal of the comparator amplifier 21 of each phase. The positive terminals of the comparator amplifiers 21 of each phase are connected via resistors 42, respectively.

In this configuration, the voltage C' applied to the positive terminal of the comparator amplifier 21 can be expressed by the following equation.

(3) Here, R1: Resistance value of resistor 24 2: Resistance value of resistor 25 R3: Resistance value of resistor 42 e: Output voltage eN of comparison amplifier 21 of each phase: The first term in parentheses on the right side of the sum of the output signals of the comparator amplifier 21 of each phase (3) indicates the output signal of the comparator amplifier 21, and the second term indicates the neutral point voltage signal eH.

The output signal e of the comparator amplifier 21 is a bipolar signal having both positive and negative polarities, and by being applied to the positive terminal, the comparator amplifier 21 is given a hysteresis characteristic. Furthermore, since the neutral point voltage signal eN is applied, the same operation as in the above-described embodiment is performed and the same effect can be obtained.

Further, the same effect can be obtained even when the resistance value of the resistor 21 is zero, that is, when the positive polarity inputs of each comparator are directly connected. In that case, the positive Kugata voltage e' is expressed by the following equation.

The voltage e' in equation (4) is only the voltage at the neutral point, and does not include the output signal e of each comparison amplifier 21 alone. Therefore, the hysteresis characteristic given in relation to the voltage e disappears, but even in this case, the comparator operates without any problem and generates the required PWM pulse. In this way, a satisfactory effect can be obtained without increasing the number of parts.

FIG. 7 shows experimental results according to the present invention.

Characteristic a in FIG. 7 is background noise, and characteristic A is the characteristic when no neutral point voltage signal is applied. ! Characteristic C is a characteristic in the embodiment of FIG. 1 or FIG. 4, and characteristic d is a characteristic in the embodiment of FIG. 6. As is clear from the characteristics c and d, according to the invention, the overall noise level is lowered, and especially at low speed rotation, it is found that the noise level 1//< can be significantly reduced.

〔Effect of the invention〕

As explained above, the present invention simply detects the neutral point voltage of the AC motor and performs pulse width modulation so that the effective value of the neutral point voltage increases according to the magnitude of this neutral point voltage. And PW
The noise generated by the AC motor driven by the M inverter can be reduced.

Particularly in the present invention, remarkable effects can be achieved when the AC motor rotates at low speed.

In addition, in the above embodiment, the neutral point voltage signal is obtained by calculating the sum of PWM pulses of each phase.
Of course, it may be the sum of the output voltage detection signals of each phase of the M inverters or the neutral point voltage detection signal of the motor primary winding.

In addition, although the above-mentioned embodiment shows an analog configuration,
Of course, the present invention can also be adopted when performing digital control using a microprocessor or the like.

Furthermore, according to the present invention, it is also possible to apply the neutral point voltage only during low speed rotation where magnetic noise is a problem.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Fig. 2, Fig. 3
Figure 4 is a waveform diagram for explaining its operation, Figure 4 is a configuration diagram showing another embodiment of the present invention, and Figure 5 is a detailed circuit diagram showing an example of the hysteresis width adjustment circuit and comparator in Figure 4. , FIG. 6 is a block diagram showing another embodiment of the present invention, and FIG. 7 is a characteristic diagram showing the actual results of the present invention. 3... PWM inverter, 4... induction motor, 11
... Comparator, 13... Neutral point voltage detection circuit. Agent: Patent Attorney Akio Takahashi, 1゛lV,,,,,
. 1st rod 2nd day 3rd 4th [21 foil 5' eye Atsushi 6th eye rotation speed (?shallow,)

Claims (1)

[Claims] 1. A device for driving a multi-phase AC motor, in which a current command pattern signal and a current detection signal are compared for each phase to obtain a current deviation, and the relationship between the magnitude and polarity of this current deviation is determined. PWM controlled by pulse width modulated pulses modulated based on
The inverter detects the neutral point voltage of the multiphase AC motor, and performs pulse width modulation so that the effective value of the neutral point voltage increases according to the magnitude of the neutral point voltage signal. A method for controlling a PWM computer, characterized by the following. 2. The method of controlling a PWM inverter according to claim 1, wherein the neutral point voltage is obtained by adding pulse width modulated pulses of each phase. 3. A PWM controller that drives a polyphase AC motor;
A speed control circuit that outputs a current command pattern signal that commands the output current of the PWM inverter, a current detection means that detects the output current of the PWM inverter, and a magnitude of a current deviation between the current command pattern signal and the current detection signal. The pulse width modulating means generates a pulse width modulated pulse based on the polarity, and the neutral point voltage detecting means generates a neutral point voltage of the multiphase AC motor. A PW characterized by inputting a voltage signal and performing pulse width modulation so that the effective value of the neutral point voltage becomes large.
M inverter control device. 4. A control device for a PWM inverter according to claim 3, wherein the neutral point voltage detection means detects the neutral point voltage by adding pulse width modulated pulses of each phase.