JP2544509B2 - Power converter, control method thereof, and variable speed system of AC motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power converter that prevents generation of torque ripple and deterioration of control characteristics of an AC motor drive device that uses a pulse width modulation inverter, and a control method thereof. The present invention relates to a variable speed system of an AC motor.

[Conventional technology]

Vector controllers that control AC motors with high-speed response and high accuracy using pulse width modulation (PWM) inverters have been applied to drive rolling mills and machine tools.

In the PWM inverter, a method is adopted in which the positive side and the negative side switching elements forming the inverter are alternately conductively controlled to control the output voltage by PWM. When performing such a control method, since there is a delay in switching due to the turn-off time of the switching element, the ON delay time (DC short circuit prevention After the period), the other is turned on later. Due to the effect of this on-delay, there is a problem that output voltage fluctuation and waveform distortion occur especially when the inverter output frequency is low.

Therefore, in the PWM inverter, the output voltage may not be accurately controlled, and even if the vector control is applied, high-speed response and high-precision control cannot be satisfactorily performed. Further, since the output voltage fluctuation includes harmonic components, torque ripple occurs.

Conventionally, as a countermeasure against this, as disclosed in Japanese Patent Laid-Open No. 60-82066, a method has been proposed in which the output voltage of the inverter is detected and the pulse width is corrected. Further, as described in JP-A-62-135289, the output voltage drop due to the on-delay of the inverter is calculated based on the output current command signal, and the calculated value is added to the output voltage command of the inverter to calculate the on-delay. There has been proposed a method of compensating for the output voltage drop due to.

Further, as described in JP-A-62-152392, a bias voltage synchronized with the PWM cycle is added to the output voltage command of the inverter to prevent the modulation width from becoming smaller than the on-delay period. , A method of improving the waveform distortion near the zero current by reducing the effect of on-delay has been proposed.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional technique, the correction timing is delayed due to the detection delay and the dead time due to the arithmetic processing, and particularly when the current at which the polarity of the output current of the inverter is reversed is near zero, an on-delay compensation error occurs and the output current is It may continue to vibrate at a specific frequency. Furthermore, in the method of giving the same bias voltage to the output voltage command of each phase as in the third conventional example, this bias voltage becomes a zero phase component, and the line voltage of the inverter output does not appear to be offset. Therefore, the inverter output current is not affected by the bias voltage at all, and the output current waveform distortion is not improved.

Further, due to the vibration of the output current, torque ripple is generated in the AC motor, and mechanical vibration between the AC motor and the load device mechanically coupled to the AC motor may be generated, resulting in high-speed response and high-precision control. There is a problem that cannot be satisfied.

An object of the present invention is to make the average value of the on-delay voltage drop and the compensation voltage equivalently zero when the inverter output current is near zero, and prevent the oscillation of the current caused by the compensation voltage error and compensation delay due to the on-delay compensation. Another object of the present invention is to provide a power conversion device that suppresses resonance between a load device mechanically connected to an AC motor, a control method thereof, and a variable speed system of the AC motor.

[Means for solving the problem]

In order to achieve the above object, the present invention, as a first control method, changes to a positive or negative value at a predetermined cycle longer than a cycle of a carrier wave in PWM modulation and shorter than a winding time constant of an AC motor, and a predetermined amplitude value. The signal having is added to the phase value of the output current of the power converter, the on-delay compensation signal is calculated based on this added signal, and the on-delay compensation is performed by adding it to the voltage command signal. The polarity of the on-delay compensation signal is repeatedly inverted between positive and negative polarities over a predetermined period before and after the polarity transition.

As a second control method, on the side related to torque generation of the output voltage vector component command of the rotating coordinate system of the AC motor,
The output of the power conversion device is controlled by adding a dither signal of a predetermined magnitude that is inverted in a predetermined cycle to positive and negative polarities.

[Action]

The output voltage drop due to the on-delay period of the switching element forming the power conversion device changes according to the output current polarity of each phase because the current during the on-delay period flows through the diode connected in antiparallel to the switching element. On the other hand, the compensation signal that compensates for the output voltage drop due to on-delay is
A delay occurs in the compensation timing with respect to the output current polarity of each phase. As a result, a compensation error occurs, the polarity cannot be smoothly reversed in the vicinity of zero in the output current, and the compensation error continues oscillatingly. This becomes torque ripple of the AC motor and vibrates the mechanical system.

Therefore, by estimating a predetermined period before and after the timing at which the polarity of the output current reverses, and inverting the polarity of the on-delay compensation signal at a predetermined period during this period, the output current is forced to be positive or negative. Let the sex continue. as a result,
In the above-mentioned predetermined period, the output voltage drop due to on-delay oscillates positively and negatively, and the average value becomes zero, and the compensation voltage also oscillates positively and negatively, so the average value becomes zero, and the values are equal. The error can be eliminated.

In addition, the output current of each phase of the power converter is controlled by adding a dither signal of a predetermined magnitude that inverts positively and negatively in a predetermined cycle to the output voltage vector component of the rotating coordinate system to control the output voltage. Near zero, the output current is positive,
It is possible to oscillate in a negative polarity in a predetermined short cycle and make the average value of the voltage drop due to the on-delay zero. In this case, the average value of the on-delay compensation signal also becomes zero.

Therefore, the oscillation of the output current near zero is eliminated,
As a result, the torque ripple of the AC motor is eliminated,
Resonance with a load device mechanically connected to the AC motor is eliminated, and the speed control system can be stabilized, so that high-speed response and highly accurate control can be performed.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an induction motor 2 with a roll 1 of a rolling mill as a load.
1 shows a system configuration in which a power converter drives variable speeds. The inverter 4 is a switching element such as a transistor
Arms consisting of TrP and TrN are provided by the number corresponding to the number of phases of the induction motor, and the transistor is turned on and off based on the pulse signal obtained by pulse width modulation (called PWM) described later, and the size of the pulse width is increased. The DC voltage input Vdc of the inverter is converted into an AC voltage by controlling. This type of inverter is called a voltage-type PWM control inverter. Further, there is a vector control described below as a control method of the electric motor.

The control configuration will be described below. The rotation speed of the induction motor 2 is detected by the speed detector 3, the adder 5 subtracts the speed detection signal ωr from the speed command ωr *, and the torque current is supplied from the speed controller (ASR) 6 so that the deviation becomes zero. Directive I
Output q *. One of the torque current commands Iq * is input to the slip angular frequency calculator 7 and is multiplied by the slip coefficient Ks to calculate the slip angular frequency command ωs *. The adder 8 adds the speed detection signal ωr and the slip angular frequency command ωs * to generate a primary angular frequency command ω ₁ *. The integrator 9 time-integrates the primary angular frequency command ω ₁ * and coordinates reference phase signal 0 * (=
It is converted to ω ₁ * t) and supplied to the coordinate converters 10 and 11.

The coordinate converter 10 is configured as a first coordinate converter, and is a current detector 12 that detects the output current of the inverter 4.
The detection signals iu and iw from u and 12w are converted into an exciting current component Id and a torque current component Iq in the rotating coordinate system of the induction motor 2 according to the coordinate reference phase signal θ *. Then, the converted excitation current detection signal Id is sent to the adder 13 and the torque current detection signal Iq.
Are input to the adder 14, and the adder 13 subtracts the exciting current detection signal Id from the exciting current command Id *.
Then, the torque current detection signal Iq is subtracted from the torque current command Iq *, and the output of each adder 13, 14 is the current regulator (AC
R) Input to 15,16. Each of the current regulators 15 and 16 generates the output voltage vector component commands Vd * and Vq * in the rotating coordinate system so that the input value becomes zero and inputs them to the coordinate converter 11.
Here, the coordinate converter 11 outputs the output voltage vector component commands Vd * and Vq * according to the coordinate reference phase signal θ * to the three-phase AC output voltage commands Vu * and Vv in the stator coordinate system of the induction motor 2.
It is configured as a second coordinate converter for converting to *, Vw *.

The PWM pulse calculator 17 compares the voltage command signals Vu *, Vv *, Vw * (modulation wave) from the coordinate converter 11 with the carrier signal,
A pulse width modulation signal (PWM signal) corresponding to the comparison result is generated. The PWM signal is input to the on-delay compensator 20,
Process the PWM signal according to the current polarity signals Su, Sv, Sw.
Here, the voltage drop due to on-delay is corrected by correcting the PWM pulse width, and a detailed description thereof will be given later.
Further, the PWM signal from the on-delay compensator is input to the on-delay setting device 18, and a delay time Td (on-delay period) is provided at the rising edge of the on-pulse of the PWM signal. This is to prevent a short circuit due to the switching elements of the positive side TrP and the negative side TrN of the arm forming the inverter being turned on at the same time. Then, the PWM signal processed by the on-delay setting unit 18 is input to the driver 19, and the switching element of each arm of the inverter is turned on and off based on the firing pulse signal from the driver.

The part A surrounded by a broken line in the figure is a current polarity calculation part for creating the input signals Su, Sv, Sw of the on-delay compensator 20, which is the excitation current command Id *, the torque current command Iq * and the coordinate reference. The current phase calculator 21, the adder 22, the current polarity discriminator 23, the dither signal generator 24, the changeover switch 25, and the changeover command device 26, which use the phase signal θ * and the speed command ωr * as input signals.
It is composed of

In the above-mentioned structure, the present invention resides in the current polarity calculating section A and the on-delay compensator 20 which operates based on the output signal thereof. Next, a detailed description of each part will be given.

FIG. 2 shows a specific configuration of the current polarity calculator A. The current phase calculator 21 inputs the exciting current command Id * (or the exciting current detection value Id) and the torque current command Iq * (or the detected torque current value Iq) to the arctangent calculator 210,
The current phase angle ψ is calculated from the equation (1), and the current phase angle ψ and the coordinate reference signal θ * are added by the adder 211 to calculate the current phase signal θi.

Further, the adder 22 adds the signal θz from the dither signal generator 24 to the current phase signal θi, and the current polarity discriminator 23
To enter. In the current polarity discriminator 23, the current phase signals θiu, θiv, θiw of each phase in the stator coordinate system are converted into the following (2)
Calculate with an expression. Here, the adders 230 and 231 are (2)
It constitutes the arithmetic part of the expression.

Then, the current phase signals θiu, θiv, and θiw of each phase are input to the cosine functions 232, 233, and 234, respectively, and the comparator 23
Polarity signals Su, Sv, Sw of each phase output current depending on 5, 236, 237
Is output. The respective polarity signals are applied to the on-delay compensator 20.
Is input to

The dither signal θz (amplitude ± θz, a rectangular wave signal having a period Tz) added to the current phase signal θi is supplied from the dither signal generator 24 through the switch (SW1) 25. Whether to add θz to the current phase signal θi is determined based on the magnitude of the speed command signal ωr *. That is, the switch (SW1) 25 is turned on and off in accordance with the signal from the switching command device 26, and the switch is turned on in the low speed range, and θz is added to θi.

FIG. 3 is an explanatory diagram of a specific configuration of the on-delay compensator 20 and shows only the U phase. The PWM pulse signal Up obtained by the PWM pulse calculator 17 is input to the pulse correction circuits 200 and 201, respectively. The pulse correction circuit 200 lengthens the pulse-on time by Td time, and the pulse correction circuit 201, on the other hand, corrects the pulse width so as to shorten the pulse-on time by Td time. One of the outputs of the pulse correction circuits 200 and 201 is selected by the change-over switch (SW2) 202. If the current polarity signal Su has a positive polarity, SW2 closes the A side, and if it has a negative polarity, the B side switch closes. PW modified according to signal
Outputs M pulse signal Us.

Next, the operation of the present invention will be described. In the control system shown in FIG. 1, as shown in FIGS. 4 (a) and 4 (b),
The reference axis (d-axis) of the rotating coordinate system is set in the magnetic flux direction. Also,
The d-axis has a phase θ with respect to the U-phase axis of the stator winding. Therefore, the phase relationship among the voltage, the current, and the magnetic flux is shown as in FIG. 4 (a), and the phase θi of the current i _{1 has} the phase angle ψ with respect to the magnetic flux φd. The instantaneous value of the current can be expressed by a cosine function of the current phase, as shown in Fig. 4 (b).

In this embodiment, the phase θi of the fundamental current is not directly obtained from the AC current output from the inverter, but the exciting current command value Id * (or the detected value Id) of the rotating coordinate system and the torque current command value Iq orthogonal thereto. The phase angle ψ with respect to the magnetic flux axis is calculated from * (or the detected value Iq) by the equation (1), and is calculated by addition with the magnetic flux phase (coordinate reference phase signal θ *). This is a fundamental current phase detection method that avoids the influence of harmonics as much as possible.

Here, for convenience of explanation, consider the case where the operation of the inverter is steady and the switch (SW1) 25 is first opened, that is, the case where the dither signal θz is not added to the current phase θi.
FIG. 5A shows the relationship between the current phase signal θi and the current polarity signal Su. The current phase signal θi changes from 0 to 2π by adding the phase angle ψ to the coordinate reference phase signal θ *. Since the magnitude Cu of the current changes with the cosine function of the current phase as described above, the current polarity Su matches the polarity of this cosine function.

Next, when the switch (SW1) 25 is closed, that is, the current phase θ
Consider the case where the dither signal θz is added to i. This will be described with reference to FIG. 5B, in comparison with the case where θz is not added. The u-phase current phase θiu has an amplitude ± θ of θi.
A rectangular dither original signal of z and period Tz is superposed, and therefore, a dither signal is superposed on the fundamental wave also on the magnitude Cu of the current. Therefore, the current polarity signal Su repeats the polarity reversal in the phase range of ± θz with the time Tz as a cycle in the current phases of 90 degrees and 270 degrees where the magnitude of the current is near zero. Here, if the magnitude of θz is adjusted, the range of the phase in which the polarity inversion is repeated can be adjusted.

The present invention manipulates on-delay compensation in the vicinity of zero of the inverter output current by skillfully using the current polarity inversion signal. Next, the operation including on-delay compensation will be described.

FIG. 6 shows an operation waveform for on-delay compensation by correcting the pulse width of the PWM modulation signal by the current polarity signal Su.
Here, the period Tz of the dither signal (square wave) is the carrier wave Vc.
It is set to twice the (triangular wave) cycle Tc. In the figure, Up is the PWM pulse waveform obtained by comparing the u-phase voltage command Vu * (modulation wave) and the carrier wave Vc, Up-N is the u-phase voltage waveform obtained by the Up pulse, and Us is the current polarity signal. The output waveform of the On-delay compensator 20 in which the pulse width of Up is modified based on the polarity of Su, and Usp-sN is the u-phase voltage waveform obtained by the pulse of Us. From this, the difference between Up-N and Usp-sN becomes the on-delay compensation voltage, and its voltage polarity is the current polarity signal.
It can be seen that the effect on the on-delay compensation voltage due to the addition of the dither signal θz to the current phase θi, which matches the polarity of Su, occurs when the magnitude of the inverter output current iu is near zero. That is, in the vicinity of zero of the output current, the on-delay compensation voltage changes according to the dither signal θz regardless of the polarity of the current phase θi, and the polarity inversion is repeated in a short cycle. Therefore, the average value of the on-delay compensation is zero in the vicinity of zero of the output current. Becomes Since the dither signal acts only near zero of the output current of each phase, this on-delay compensation voltage appears in the line voltage without being canceled by the line voltage.

FIG. 7 shows electric motor characteristics when the rolling mill is used as a load and the induction motor is driven at a variable speed in the inverter control system according to the present invention. The speed is changed stepwise during low speed operation in the low speed region of 0.3 Hz. The phenomenon waveforms of the actual motor speed ωr, the roll speed, the current components Id, Iq, and the on-delay compensation voltage when the frequency is increased by 0.1 Hz are shown. The figure (a) is the case where a dither signal is not added to the on-delay compensation, and the figure (b) is
Shows the case where a dither signal is added to the on-delay compensation.
From this, the output current polarity reversal (zero current) in FIG.
It can be seen that vibration is generated in the vicinity, and vibration is also generated at the actual motor speed ωr. The cause of this vibration is
Resonance occurs in the mechanical system with the load device connected to the electric motor due to the delay of the on-delay compensation timing due to the current detection delay, the dead time due to the arithmetic processing, and the torque ripple of the electric motor due to the current vibration. In particular, when the inverter output frequency is low, the on-delay compensation voltage becomes higher than the induced voltage of the electric motor, so that the above-mentioned vibration is remarkable when the output current is near zero.

On the other hand, in the same figure (b) according to the present invention, the above-mentioned vibration phenomenon does not occur in the motor current components Id and Iq,
It can be seen that the actual rotation speed ωr can be controlled according to the command value. This is because in the vicinity of zero of the motor current, the on-delay compensation voltage has positive and negative polarity inversion in the cycle of the dither signal, and the average value of the compensation voltage becomes zero in this range,
This is because the output current changes positively and negatively little by little in the cycle of the dither signal, and the average value of the on-delay voltage drop becomes zero.

According to the present invention, as described above, the unstable oscillation phenomenon of the output current can be prevented without being affected by the error due to the on-delay compensation or the resonance of the mechanical system even at the extremely low speed operation, and the stable speed control can be performed. There is an effect that can be. Further, in the on-delay compensator, even if there is some error in the correction amount of the pulse width for compensating the on-delay voltage and the compensation phase with respect to the actual output current phase (polarity), the control system can be easily designed.

By the way, in the embodiment of FIG. 1, the amplitude and period of the rectangular wave signal θz output from the dither signal generator 24 are fixed.
As shown in FIG. 8, the amplitude commander 27 and the cycle commander 28 are determined depending on the speed and the winding time constant of the motor.
Alternatively, the amplitude value θz of the dither signal generator 24 and the period Tz may be changed. This is because the current waveform distortion factor increases due to the effect of the voltage drop due to the on-delay in the low speed region.
Since the zero-crossing period becomes long as shown by the current waveform in the figure, an error is likely to occur in the determination of the fundamental wave current polarity. Therefore, the amplitude value θz of the dither signal is small in the high-speed range and increases as the speed decreases. I tried to be. Also, when the time constant of the motor winding is large, the rate of change of current is small.Therefore, the cycle Tz of the dither signal is the cycle Tc of the carrier wave Vc so that positive and negative changes in the current due to the dither signal occur reliably.
Is set to be larger than twice, and smaller than the period of the time constant of the motor winding and the natural frequency of the mechanical system.

According to the embodiment shown in FIG. 8 described above, in addition to the effect of the embodiment shown in FIG. 1, the range of dither is smoothly changed in accordance with the magnitude of speed, so that the transient current due to the turning on and off of the dither signal. The effect of eliminating fluctuation can be obtained.

In the first embodiment and the eighth embodiment described above, whether or not the dither signal is added to the current phase signal for operating the on-delay compensation is determined based on the magnitude of the speed. In the illustrated embodiment, it is determined whether to add a dither signal to the current phase signal based on the magnitudes of the harmonic ripple currents superimposed on the detected values Id and Iq of the exciting current and torque current in the rotating coordinate system. . This is because if the output current oscillates due to an on-delay compensation error or mechanical resonance, the detected values of Id and Iq will include ripples according to the vibrations. Whether or not it has occurred is judged by the judging devices 31 and 32. If the allowable value is exceeded, a signal is output from each judging device and the OR signal 33
Thus, the switch 25 is closed according to the sum of these signals, the dither signal θz is added to the current phase signal θi, the current polarity is discriminated by the phase signal θiu, and on-delay compensation is performed.

According to this embodiment, when the current vibration occurs, the dither signal is added to suppress the current vibration, so that the vibration can be prevented from being diverged due to mechanical resonance.

In the embodiment described above, the current phase signal θi is calculated from the detected current values Id and Iq converted into the rotating coordinate system, but it goes without saying that the phase may be obtained directly from the instantaneous alternating current value of the inverter output. .

In the embodiment shown in FIGS. 1, 8, and 9, the dither signal θz from the dither signal generator 24 is used as the current phase signal θ.
i was added and on-delay compensation was performed based on this signal. In the embodiment shown in FIG. 10, however, a rectangular wave dither signal ΔI having an amplitude value ± ΔI and a cycle Tz is added to the exciting current command Id *, and the addition is performed. The arc tangent function unit 20 calculates the current phase angle ψ ′ based on the value Id ** and the torque current command Iq *, and the added value of this ψ ′ and the coordinate reference signal θ * is added to the current polarity discriminator 23,
From this, the current polarity signals Su, Sv, Sw are obtained, and on-delay compensation is performed based on these signals.

According to this embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained.

In the embodiment shown in FIG. 10, the dither signal generator is used.
The same effect can be obtained by adding the dither signal ΔI from 24 'to the torque current command Iq * instead of the exciting current command Id *.

Further, in the embodiment of FIG. 1, the method of performing the on-delay compensation by changing the PWM pulse width is shown.
In the illustrated embodiment, instead of changing the pulse width, the on-delay compensation voltage is added to the three-phase AC voltage command signals Vu *, Vv *, Vw *. That is, the on-delay compensation voltage calculator 39 changes the polarity comparators 235 to 237 in the current polarity discriminator 23 shown in FIG. 2 into function units 238 to 240, and in each function unit, the cosine function calculators 232 to 234 Positive and negative voltage signals ΔVu, ΔVv, and ΔVw are output for each current phase, and this on-delay compensation voltage signal is output from the coordinate converter 11 as output signals Vu *, Vv *,
Add to Vw * and add three-phase AC voltage command signal Vu **, Vv **,
Vw ** is generated and PWM control is performed based on this signal.

According to this embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained, and further, as shown in FIG.
To change the magnitude of the on-delay compensation voltage for each current phase from the cosine function calculators 232 to 234. That is, by reducing the on-delay compensation voltage at a small current, it is possible to suppress the current variation at the boundary between the inside and the outside of the polarity change range of the compensation signal due to the dither signal θz as shown in FIG. can get.

The embodiments described above are all methods of performing on-delay compensation with reference to the output current phase θi. However, the present invention is not limited to the current phase and can be implemented based on the magnitude of the output current.

FIG. 13 shows another embodiment of the essential part A of the present invention shown in FIG. Detect the magnitude of each phase current of the inverter output current (note that iv may be obtained by adding iu and iw),
A rectangular wave signal having an amplitude value ± ΔI and a period Tz output from the dither signal generator 24 'is added to each of the phase current detection values iu to iw, and the current signal having the added value is added to the comparators 235 to 237. After inputting, the polarity signals Su, Sv, Sw of each phase output current are obtained, and on-delay compensation is performed based on this. here,
By changing the amplitude value ΔI of the dither signal, it is possible to adjust the range in which the on-delay compensation voltage repeats positive and negative polarity inversion in the vicinity of zero of the output current.

According to this embodiment, the same effect as that of the embodiment shown in FIG. 1 can be obtained, and the calculation of the current polarity calculator A can be reduced.

Further, FIG. 14 shows another embodiment of the present invention. 1 is different from the embodiment shown in FIG. 1 in that the on-delay compensation voltage is inverted between positive and negative polarities for a predetermined period to interrupt the output current, whereas in the embodiment shown in FIG. The amplitude voltage ± ΔV output from the dither signal generator 24 ″ and the rectangular wave signal ΔV with the period Tz are added to the output voltage vector component command Vq * of the controller 16. Here, the on-delay compensation is the dither signal. This is performed based on the current phase signal that is not added, whereby the q-axis output current ((ΔV) is generated by the dither signal ± ΔV of the output voltage vector component command Vq ** (= Vq * ± ΔV) of the rotating coordinate system to which the dither signal is added. Torque current)
Is intermittent at the cycle Tz of the dither signal. Here, the range in which the output current is interrupted near zero can be adjusted by the magnitude of the amplitude value ΔV of the dither signal.

As a result, according to the present embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained, and the gain of the unstable loop of the on-delay compensation system, which is the positive feedback, can be reduced and stable operation can be performed.

FIG. 15 shows another embodiment of the present invention. The difference from the control configuration of the embodiment shown in FIG. 1 is that the coordinate converter 11 'converts the exciting current command Id * and the torque current command Iq * of two current vector component commands orthogonal to each other in the rotating coordinate system into three phases of the fixed coordinate system. Converted to AC current command signals iu *, iv *, iw * and output voltage command signal Vu corresponding to the deviation between the AC current command signal and the inverter output current by AC current regulators 40u, 40v, 40w for each phase. *, Vv *, Vw * are generated, and the output voltage of the inverter is controlled by this voltage command signal.

Here, the on-delay compensation voltages ΔVu, ΔVv, and ΔVw are added to the three-phase AC voltage command signals Vu *, Vv *, and Vw *. The on-delay compensation voltage is calculated in the same manner as in the embodiment shown in FIG. That is, the excitation current command Id * and the torque current command Iq *
And the phase θi of the fundamental wave of the inverter output current from the coordinate reference phase signal θ *, and the current phase signal θ
The phase signal θz of the dither signal generator 24 is added to i, and the on-delay compensation voltage calculator is based on the added signal θiu.
Calculated by 39.

According to this embodiment, the same effect as that of the embodiment of FIG. 1 is obtained, and the on-delay voltage drop is compensated in a feedforward manner, so that the lack of response of the AC current regulator in the low current region is eliminated and stabilization is achieved. There is an effect that it can be achieved.

Although the on-delay compensation in the embodiment of FIG. 15 is performed on the voltage command side, it goes without saying that the same effect can be obtained even if the PWM pulse is modified as in the embodiment of FIG.

In the embodiments described above, the control configuration is shown as an image of hardware, but it goes without saying that it is also possible to realize the present invention by software by applying a microcomputer, and at the same time, the present invention can be implemented by changing the AC power supply voltage to DC. It is also possible to stabilize the on-delay compensation system by applying it to converter control for conversion.

〔The invention's effect〕

As described above, according to the present invention, when the inverter output current is near zero, it is possible to prevent the current from vibrating due to a voltage error in on-delay compensation, a correction delay, or the like.
Further, as a result, torque ripple of the electric motor can be prevented, resonance with the mechanically coupled load device is eliminated, the control system is stabilized, and high-speed response and highly accurate speed control can be achieved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, and FIG.
A concrete configuration diagram of the current polarity calculation unit of FIG. A part, FIG.
The specific configuration diagram of the on-delay compensator in the figure, FIGS. 4, 5, and 6 are diagrams for explaining the operation of the present invention, and FIG. 7 is a characteristic diagram of an induction motor driven by the control system according to the present invention,
8 to 11 are block diagrams of another embodiment of the present invention.
FIG. 12 is a function curve diagram of the function unit in the embodiment shown in FIG.
FIG. 14, FIG. 14 and FIG. 15 are configuration diagrams of another embodiment of the present invention. 4 ... Inverter, 10, 11 ... Coordinate converter, 15, 16 ...
Current regulator, 17 ... PWM pulse calculator, 18 ... ON delay setting device, 20 ... ON delay compensator, 21 ... Current phase calculator, 23 ... Current polarity discriminator, 24 ... Dither signal generator, 26 ... Switching command device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Takahashi 5-2-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Omika factory (72) Inventor Takashi Salmon River 2-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd. Omika factory

Claims (12)

(57) [Claims] 1. A method of controlling a power conversion device for converting a DC voltage of a DC power supply into an AC voltage by turning on / off a switching element based on a pulse width modulation signal, the fundamental wave of an output current of the power conversion device. A dither signal having a predetermined magnitude that is positively and negatively inverted in a predetermined cycle over a predetermined period before and after the timing when the polarity of the pulse is inverted is added to the modulated wave when the pulse width modulated signal is produced, or Alternatively, the output voltage is controlled by changing the pulse width of the pulse width modulation signal with the dither signal. 2. A switching element is turned on and off based on a pulse width modulation signal to convert a direct current voltage of a direct current power source into a multi-phase alternating current voltage, and each is output in accordance with a deviation between an output current of each phase and a current command value. In a control method of a power converter that controls a phase output voltage, a predetermined positive and negative polarity inversion is performed in a predetermined cycle over a predetermined period before and after the polarity of the fundamental wave of the output current of the power conversion device is inverted. A dither signal having a magnitude of 1 is added to the modulated wave when the pulse width modulated signal is produced, or the pulse width of the pulse width modulated signal is changed by the dither signal to control the output voltage. A method for controlling a power conversion device having a characteristic feature. 3. In claim 1 or claim 2,
The dither signal is calculated based on a phase signal obtained by adding a phase signal of a fundamental wave of an output current vector of the power converter with a signal having a predetermined magnitude of positive / negative inversion at a predetermined cycle. A method for controlling a power conversion device, comprising: 4. In claim 1 or claim 2,
The dither signal is positive with respect to a signal relating to the magnitude of the fundamental wave component of the output current of the power converter at a predetermined cycle,
A method of controlling a power conversion device, comprising: operating on the basis of a signal obtained by adding signals having a predetermined amplitude value that is inverted to a negative polarity. 5. In claim 1 or claim 2,
The dither signal includes two output current vector components orthogonal to each other in the rotating coordinate system of the power conversion device, a signal having a predetermined magnitude that is positively and negatively inverted in a predetermined cycle, and coordinates of the rotating coordinate system. A control method for a power conversion device, characterized in that calculation is performed based on a reference phase signal. 6. A pulse width modulation signal obtained by comparing a modulated wave of a voltage command signal with a carrier in a power converter for controlling a DC pulse of a DC power source into an AC voltage by controlling an ignition pulse of a switching element. Means for controlling the ignition pulse width of the switching element, and a predetermined positive and negative polarity reversal at a predetermined period for a predetermined period before and after the timing when the polarity of the fundamental wave of the output current of the power converter is reversed. Means for generating a dither signal having a magnitude of, and adding the dither signal to a modulated wave when the pulse width modulated signal is made, or changing the pulse width of the pulse width modulated signal by the dither signal An electric power conversion device comprising: 7. A power converter that controls a firing pulse of a switching element to convert a DC voltage of a DC power supply into a multi-phase AC voltage, wherein a deviation between an output current of each phase of the power converter and a current command value. Means for generating an output voltage command signal for each phase according to the above, and a pulse width modulation signal obtained by comparing a modulated wave of the output voltage command signal for each phase with a carrier wave, to control the ignition pulse width of the switching element. And a means for generating a dither signal having a predetermined magnitude that is positively and negatively inverted in a predetermined cycle for a predetermined period before and after the polarity of the fundamental wave of the output current of the power converter is inverted. And a means for adding the dither signal to a modulated wave when the pulse width modulated signal is made, or for changing the pulse width of the pulse width modulated signal by the dither signal. An electric power conversion device characterized by being provided. 8. A power conversion device for converting a DC voltage of a DC power supply into an AC voltage by controlling an ignition pulse of a switching element, wherein two output voltage vector component commands orthogonal to each other in a rotating coordinate system of the power conversion device. At least one of a means for calculating a signal, a means for generating a dither signal having a predetermined magnitude that is inverted in a positive or negative polarity at a predetermined cycle, and two output voltage vector component command signals orthogonal to each other in the rotating coordinate system. To
Means for adding the dither signal, means for converting the output voltage vector component command signal into an output voltage command signal of a stator coordinate system, and pulse width modulation obtained by comparing a modulated wave of the voltage command signal with a carrier wave. And a means for controlling the ignition pulse width of the switching element by a signal. 9. A variable speed system for an AC motor, comprising: the power converter according to any one of claims 6 to 8; and an AC motor driven by the power converter. . 10. When driving the AC motor by the power converter according to any one of claims 6 to 8, the cycle of positive and negative polarity inversion of the dither signal is:
Power that is longer than the cycle of the carrier wave in the pulse width modulation and shorter than the cycle of the winding time constant of the AC motor and the natural frequency between the AC motor and the load device mechanically connected to the AC motor. Converter. 11. When driving an AC electric motor by the electric power converter according to any one of claims 6 to 8, the magnitude of the dither signal in the electric power converter has a magnitude of the AC electric motor. The power conversion device is characterized in that it is changed according to the rotation speed of, and is small when the rotation speed is high, and is increased when the rotation speed is low. 12. When driving an AC electric motor with the power converter according to any one of claims 6 to 8, two output current vector components orthogonal to each other in the rotational coordinate system of the AC electric motor. The dither signal is added to the modulated wave when the pulse width modulated signal is generated, or the dither signal is generated only when the detected value vibrates with a predetermined magnitude or when the number of vibrations exceeds a predetermined value. The power converter is characterized in that the pulse width of the pulse width modulation signal is changed by or is added to at least one of the two output voltage vector component command signals orthogonal to each other in the rotating coordinate system.