JP2644853B2 - Control method of voltage source inverter - Google Patents

Description

The present invention relates to a method for controlling an output voltage of a pulse width modulation inverter (hereinafter referred to as a PWM inverter).

[Conventional technology]

In the PWM inverter, the output voltage is PWM-controlled by alternately conducting the positive and negative switching elements constituting the inverter. However, since the switching element has a switching delay due to the turn-off time, a short-circuit prevention period (hereinafter referred to as on-delay) is provided so that the positive side and the negative side do not conduct simultaneously. For this reason, there is a problem that waveform distortion occurs in the output voltage of the inverter due to the influence of the on-delay.

Therefore, conventionally, as described in JP-A-62-135289, a method of compensating for a decrease in output voltage due to on-delay is to convert an output voltage drop due to on-delay into a three-phase output voltage command based on the polarity of a three-phase AC current command. A method of adding and compensating has been proposed. Further, Japanese Patent Publication No. Sho 59-8152 describes a feedback system in which an instantaneous value of an output current is detected and a compensation signal corresponding to the polarity is added to a three-phase output voltage command for compensation.

[Problems to be solved by the invention]

However, the prior art described above has a problem that a coordinate conversion operation is required to obtain a three-phase AC current command, and when digital control is performed, the calculation processing time increases and the load on the microprocessor increases. Also, in the feedback system in which the instantaneous value of the output current is detected and compensated according to the polarity, the polarity cannot be detected correctly due to a DC component in the detected current or distortion of the output current waveform, and compensation cannot be performed well. Was.

A first object of the present invention is to compensate for an output voltage drop due to on-delay based on the direction of the output current vector of the inverter (the phase angle of the output current) to make the output current waveform of the inverter a sine wave. It is an object of the present invention to provide a compensating means for shortening the arithmetic processing time in digital control.

[Means for solving the problem]

An object of the present invention is to provide an inverter for converting DC into three-phase alternating current, wherein an on-delay period for preventing a DC short circuit of a positive side switching element and a negative side switching element constituting the inverter is obtained by PWM obtained by pulse width modulation control. On the signal,
In a control method of a voltage source inverter for controlling an AC output voltage by the PWM signal, a detection value of two orthogonal components of a rotating magnetic field coordinate system or a command value (id, jq) of the AC output current of the inverter; Based on the output frequency command value ω ₁ * for controlling the output frequency of the inverter, the phase angle (∫ω ₁ * dt + tan ⁻¹ (i
q / id)), the polarity of each phase output current is determined based on the phase angle, the PWM signal controlling the output voltage of the inverter is corrected based on the determination result, and the output during the on-delay period is corrected. This is achieved by compensating for the voltage drop.

[Action]

As shown in FIG. 2, the output voltage drop due to the on-delay with respect to the magnitude of the output current of the PWM inverter is substantially constant and changes according to the polarity of the output current. Therefore, the on-delay output voltage drop due to the AC output current has a rectangular waveform related to the polarity of the output current. FIG. 3 (a),
(B) and (c) are waveforms of the output current of each phase of the inverter and the output voltage drop due to on-delay. Thus, in the present invention, as shown in FIG.
Divide into equal A, B,…, F sections and correct the pulse width of each arm of the inverter based on the current polarity of each phase in each section to compensate for the output voltage drop due to on-delay. You can get closer to the waves. Also, by selecting one of the sections A, B,... F according to the direction of the output current vector obtained by combining the three phases of the inverter output current, the polarities of the three phases can be determined collectively. Processing time can be reduced.

〔Example〕

 One embodiment of the present invention is shown in FIG.

In FIG. 1, an inverter 1 converts a DC voltage into an AC voltage and supplies a three-phase AC voltage to the induction motor 2.
The switching elements constituting the inverter 1 are turned on by the PWM pulse calculator 6 operated by the microprocessor 3 by comparing the output voltage commands ν _u *, ν _v *, ν _w * with the carrier signal. An off pulse is given. The pulse signal as described later positive side and a DC short-circuit prevention period of the negative side switching-element (hereinafter, Onderei abbreviated) t _d and,
The pulse is changed by the time _Td for compensating the output voltage drop due to the on-delay. Reference numeral 7 denotes an output current vector phase calculator. The integrator 9 calculates a coordinate conversion reference signal w ₁ * t from the primary angular frequency command signal w ₁ * of the induction motor 2 and outputs the coordinate conversion reference signal w ₁ * t to the coordinate conversion calculator 5 and the adder 12. Exciting current command signal of the induction motor 2 of the voltage command calculator 4 rotating field coordinate system I _d *, the torque current command signal I _q * and primary angular frequency command signal w ₁ * voltage command signal of the rotating magnetic field coordinate system based on the
V _d *, v _q * are calculated and output to the coordinate transformation calculator 5. The coordinate conversion calculator 5 converts the voltage command signals V _d *, V _q * into three-phase voltage command signals ν _u *, ν _v *, ν _w * based on the coordinate conversion reference signal w ₁ * t. The signal is converted and output to the PWM pulse calculator 6. The divider 10 calculates the ratio between the current command signals I _d * and I _q * in the rotating magnetic field coordinate system and outputs the ratio to the arctangent calculator 11. The adder 12 calculates the phase angle of the output current vector by adding the output signal θ * of the arctangent calculator 11 and the coordinate transformation reference signal w ₁ * t, and outputs the result to the polarity discriminator 8. The polarity discriminator 8 discriminates the output current polarity of each phase based on the phase angle of the output current vector, and outputs polarity signals SgnU, SgnV, SgnW to the PWM pulse calculator 6.

 Next, the operation will be described.

The control method shown in FIG. 1 is a vector control method using a PWM inverter, and a voltage command calculator 4 calculates a rotating magnetic field from an exciting current command signal I _d * and a torque current command signal I _q * in a rotating magnetic field coordinate system of the induction motor 2. Coordinate system voltage command signal _Vd *, _Vq
* Is calculated. This voltage command signal is a coordinate conversion reference signal w ₁ * t obtained by the coordinate conversion calculator 5 and calculated by the integrator 9.
, The AC voltage command signal ν _u *, ν _{v in} the stator coordinate system
*, Ν _w *.

The PWM pulse calculator compares the AC voltage command signal with the carrier signal to generate a PWM signal. The inverter 1 controls the output voltage of each phase according to the PWM signal. The calculation in the voltage command calculator 4 can be represented by the following equation.

Here, r ₁ : primary resistance I ₁ , I ₂ ′: primary and secondary leakage inductance M: excitation inductance Further, the calculation in the coordinate conversion calculator 5 can be expressed by the following equation.

Next, the operation for compensating the output voltage drop due to the on-delay according to the present invention will be described with reference to FIGS. 2, 3, and 4. FIG. The size x of the output voltage drop v _f due Onderei respect to the magnitude of the output current i of the PWM inverter, as shown in FIG. 2, polarity changes in the output voltage drop depending on the polarity of the substantially constant and the output current i . Accordingly, the output voltage drop due to the on-delay with respect to the AC output current has a rectangular waveform corresponding to the polarity of the output current. FIG. 3 (a),
(B) and (c) are waveforms of the output current of each phase and the voltage required to compensate for the output voltage drop due to on-delay. On the other hand, focusing on the polarity of the output current of each phase, FIG.
As shown in FIG. 7, the area changes according to the six areas A, B,... Therefore, in the present invention, the current command signals I _d *, I
_q * and the primary angular frequency command signal w ₁ *
Means for calculating the direction of the output current vector of the inverter and determining in which of the six areas A, B,... F the output current vector of the inverter is provided, based on the polarity signal of each phase corresponding to each area. Thus, the PWM pulse output signal of each phase is corrected. FIG. 4 shows the polarity of each phase with respect to the areas A, B,... F in FIG.

Next, the operation of the present invention will be specifically described. Fifth
The figure shows the calculation contents of the PWM pulse for one phase using waveforms. By comparing the output voltage command signal v * with the carrier signal as shown in FIG. 5 (a) and calculating the intersection, the switching elements on the positive side and the negative side as shown in (b) and (c) are obtained. Are determined as pulse widths. Further, by setting the Onderei period t _d of positive and negative as shown, the pulse of the portion subjected to Hatsuchingu is given to each switching-element. as a result,
As shown in (d) and (e), when the output current is positive (i> 0) and negative (i <0), the output voltage is generated as shown by the solid line. Incidentally, the voltage originally desired to be output is the output voltage indicated by the broken line. Therefore, in the present invention, the arithmetic processing as shown in FIG. 6 is performed by the PWM pulse calculator 6 based on the output signals SgnU, SgnV, SgnW of the polarity discriminator 8. Note that the U-phase, V-phase and W-phase are the same operation except that ν _u * and SgnU are different, so the U-phase 61U will be described with reference to FIG. In FIG. 6, a block 62U calculates a positive-side pulse width _T1U corresponding to a voltage originally desired to be output. The arithmetic expression is represented as the following expression.

Here, T _s : calculation cycle (carrier wave cycle) V _max : maximum output voltage The block 63U calculates the off timing T _1PU on the positive side. T _1PU is determined by the sign of the current polarity signal SgnU in FIG.
It changes as follows. That is, if SgnU is positive, T _1PU
Is increased from T _1U by T _d / 2, and conversely, if SgnU is negative, T
The so as to decrease from T _1U only T _d / 2 _1PU. Block 64
U calculates the positive-side ON timing _T2PU . _{T2PU is} also the seventh
As shown in FIG. 7B, the value varies depending on the sign of SgnU.

That is, when SgnU is positive, the T _2PU than T ₂ It increased by, on the contrary, when SgnU is negative than T ₂ to T _2PU is Just to increase. Block _65U calculates the negative-side ON timing _T1NU . T _1NU is positive off timing
Obtained by adding the Onderei period t _d to T _1PU. Block 66
U calculates the negative-side off timing T _2NU . T _2NU is _obtained by subtracting the on-delay period t _d from the positive-side ON timing T _2PU . Each is shown in FIG. 7 (c). As a result, an output voltage equivalent to the voltage originally desired to be output can be output as shown in FIGS. 7 (d) and 7 (e) regardless of the polarity of the output current.

As described above, according to the present invention, the direction of the output current vector is determined to be in any of the six regions A, B,... F shown in FIG. 3, and from the correspondence shown in FIG. Since the pulse width is determined by the arithmetic processing shown in FIG. 6, the output voltage drop due to on-delay is compensated for by simple arithmetic processing, and the output voltage is determined by the command value. Can be controlled. As described above, in this embodiment, in addition to preventing the waveform distortion of the inverter output voltage,
This has the effect that highly accurate control can be realized in a short time.

FIG. 8 shows another embodiment of the present invention. The difference from FIG. 6 of the first embodiment is that the on-delay period is T _{s in} the first embodiment.
Whereas _Td / 2 is compensated equally for the pulse widths on both sides centering on / 2, the present embodiment is divided into arbitrary widths to compensate. .

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

FIG. 9 shows another embodiment of the present invention. The difference from FIG. 6 of the first embodiment is that in the first embodiment, the on-delay period is compensated by T _d / 2 with respect to the pulse width on both sides centering on T _s / 2. On the other hand, in the present embodiment, one pulse width is compensated for by _Td . Ninth
In the drawing, when the polarity signal SgnU of the block 67U is positive, the operation of the block 68U is performed, and when the polarity signal SgnU is negative, the operation of the block 69U is branched. The block 68U calculates the positive-side ON and OFF timings T _1PU and T _2PU when SgnU is positive. Block 69U calculates the positive-side ON and OFF timings T _1PU and T _2PU when SgnU is negative. The result is the tenth
It is shown in FIG. Block 70U calculates the negative side ON and OFF timings _T1NU and _T2NU . The result is shown in FIG. 10 (c). According to the present embodiment, FIG.
As shown in (e), it is possible to output an output voltage that matches the voltage originally desired to be output. Further, the same effect as in the first embodiment can be obtained.

Although the above embodiment has been described using the current command signal in the rotating magnetic field coordinate system, it is apparent that the present invention can be applied even using the detected actual value.

〔The invention's effect〕

According to the present invention, by calculating the phase angle of the inverter output current in the rotating magnetic field coordinate system, even if the output current waveform is distorted, the phase angle of the output current with respect to the fundamental wave component can be accurately obtained. By compensating the output voltage drop due to the on-delay based on the phase angle, the output current can be made into a sine wave.

In the rotating magnetic field coordinate system, the calculated phase angle of the inverter output current is the direction of the vector obtained by combining the three phases of the output current, and to which of the angular ranges this direction divides 360 ° into six equal parts. Since the polarities of the output currents for the three phases can be determined according to the above, the operation can be simplified, and there is an effect that the operation processing time in digital control can be shortened.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the magnitude of output voltage drop due to on-delay of a PWM inverter, and FIG. 3 is inverter output current and output voltage drop due to on-delay. FIG. 4 is a table for giving the polarity signal of the output current of the present invention, FIG. 5 is a waveform diagram for explaining the operation contents of the PWM pulse signal, and FIG. 6 is a PWM diagram of the present invention. FIG. 7 is a waveform chart illustrating the compensation effect of the present invention. FIGS. 8 and 9 are flow charts illustrating the second and third embodiments of the present invention. FIG. FIG. 13 is a waveform diagram illustrating a compensation effect of the third embodiment. 1 ... Inverter 2 ... Induction motor 3 ... Microprocessor 4 ... Voltage calculator 5 ... Coordinate conversion calculator
6 ... PWM pulse calculator, 7 ... output current vector phase calculator, 8 ... polarity discriminator.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichi Takahashi 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Omika Plant, Hitachi, Ltd. (72) Inventor Shigeru Sugiyama 5-2-2, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Inside the Omika Plant of Hitachi, Ltd. (56) References JP-A-59-72991 (JP, A)

Claims (3)

(57) [Claims] 1. An inverter for converting DC to three-phase AC, wherein an on-delay period for preventing a DC short circuit between a positive side switching element and a negative side switching element constituting the inverter is provided.
Provided in a PWM signal obtained by pulse width modulation control,
A control method of a voltage source inverter for controlling an AC output voltage by a signal, comprising: a detection value of two orthogonal components of a rotating magnetic field coordinate system or a command value (id, jq) of an AC output current of the inverter; The phase angle (∫ω ₁ * dt + tan ^-1 (iq / id)) of the AC output current of the inverter is calculated based on the output frequency command value ω ₁ * for controlling the frequency, and each phase output is calculated based on the phase angle. Controlling the voltage-source inverter, wherein the polarity of the current is determined, the PWM signal for controlling the output voltage of the inverter is corrected based on the determination result, and the output voltage drop due to the on-delay period is compensated. Method. 2. The method according to claim 1, wherein the period of the carrier of the pulse width modulation is T _s , the output voltage designation signal is ν _u *, the maximum output voltage is V _max , the on-delay period is t _d , the compensation period is T _d , The polarity signal is S _gn U, the arbitrary constant is α (where 0 ≦ α ≦ 1),
And In this case, the off timing T _1PU and the on timing T _2PU of one of the pulse width signals on the positive side or the negative side of the inverter are _represented by T _1PU = T _1U + α · T _d · S _gn UT _2PU = T _s −T _1U + t _{d - (1-α) ·} T d · S gn control method of the voltage source inverter and controlling according to U. 3. The method according to claim 1, wherein the period of the carrier of the pulse width modulation is T _s , the output voltage designation signal is ν _u *, the maximum output voltage is V _max , the on-delay period is t _d , the compensation period is T _d , The polarity signal is S _gn U, the arbitrary constant is α (where 0 ≦ α ≦ 1),
And In this case, the off timing T _1PU and the on timing T _2PU of one of the pulse width signals on the positive side or the negative side of the inverter are controlled in accordance with T _1PU = T _1U T _2PU = T _s −T _1U −T _d + t _d. , the current polarity signal if S _gn U is _{negative, T 1PU = T 1U -T d} T 2PU = T s -T 1U + t control method of the voltage source inverter and controlling according to _d.