JP3182322B2 - PWM control device for NPC inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an NPC inverter (Neutral Point Clamped Inverter), that is, a PWM device of a neutral point clamp type inverter.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a configuration of a main part of a conventional apparatus. In this figure, a three-phase voltage command calculation unit 11
Is the voltage command Vu Ref, Vv Ref, Vw of each phase of U, V, W
Output Ref. The triangular wave phase generator 15 receives the triangular wave frequency fsw as input and outputs a triangular wave phase θp. The positive triangular wave generator 16 and the negative triangular wave generator 17 output a positive triangular wave TRIp and a negative triangular wave TRIn based on the input of the triangular wave phase θp. The triangular wave comparing section 13 outputs PWM voltage commands Vu PWM, Vv PWM, Vw PWM of each phase based on a magnitude comparison between the three-phase voltage commands Vu Ref, Vv Ref, Vw Ref and these positive and negative triangular waves TRIp, TRIn. .

[0003]

However, the NPC
GTO used as switching element of inverter
(Gate turn-off thyristor) has a minimum on-pulse width time that cannot be turned off for a fixed time once turned on. Therefore, the voltage command is small, and the pulse width must be narrower than the minimum on-pulse width.
In the case of the WM voltage, in an operation region in which the command value is not followed, a current waveform distortion due to a difference in pulse width from the command value is caused, thereby causing problems of instability of a current control system and torque ripple.

The present invention has been made in view of the above circumstances, and provides a PWM control apparatus for an NPC inverter that can output a PWM voltage that can follow a small voltage command while securing a minimum on-pulse width. It is intended to provide.

[0005]

Means for Solving the Problems As means for solving the above-mentioned problems, the invention according to claim 1 is a three-phase voltage command calculation unit for calculating and outputting a three-phase voltage command, and a triangular wave frequency as an input. A triangular wave phase generator for outputting a sawtooth wave having an input frequency of 2π as a triangular wave phase, a triangular wave phase output from the triangular wave phase generator as an input, synchronizing with the input triangular wave phase, A positive triangular wave generator for calculating a triangular wave having an amplitude of half of the DC link voltage and outputting the triangular wave as a positive triangular wave, a positive / negative triangular wave phase difference setting unit for outputting a value π as a positive / negative triangular wave phase difference setting unit, and the triangular wave The added value of the triangular wave phase output from the phase generator and the positive / negative triangular wave phase output from the positive / negative triangular wave phase difference setting unit is input, and the DC of the inverter is synchronized with the input phase. A negative triangular wave generator that calculates a triangular wave having an amplitude of half the link voltage and outputs the triangular wave as a negative triangular wave, and a triangular wave phase output from the triangular wave phase generator as an input and a square synchronized with the input triangular wave phase A DC bias voltage generator that outputs a wave as a DC bias voltage; a three-phase voltage command output from the three-phase voltage command calculator; and a DC bias voltage output from the DC bias voltage generator. A DC bias voltage adding unit that adds a DC bias voltage to the phase voltage command and outputs a new three-phase voltage command; a three-phase voltage command output from the DC bias voltage adding unit; The positive triangular wave output from the unit and the negative triangular wave output from the negative triangular wave generating unit as inputs,
A triangular wave comparison unit that outputs a three-phase PWM voltage command by comparing the magnitude of the three-phase voltage command with the positive triangular wave and the negative triangular wave.

According to a second aspect of the present invention, in the first aspect of the present invention, a PW is input in accordance with the modulation rate and a modulation rate is input.
A PWM mode switching unit that outputs an M mode, wherein the positive / negative triangular wave phase difference setting unit receives the PWM mode output from the PWM mode switching unit as an input, and
The DC bias voltage generation unit selects either the value π or 0 according to the mode and outputs the selected value as a positive / negative triangular wave phase difference. The DC bias voltage generation unit includes a PWM mode output from the PWM mode switching unit and the triangular wave phase generation unit. Input the triangular wave phase output from the
When the M mode indicates the normal mode, a value of 0 is output as a DC bias voltage, and when the PWM mode indicates a DC bias mode, a square wave synchronized with the input triangular wave phase is output as a DC bias voltage.

According to a third aspect of the present invention, in the first aspect of the present invention, the DC bias voltage generator receives a modulation factor and a triangular wave phase output from the triangular wave phase generator as inputs. Synchronously with the phase of the triangular wave, a square wave having a different amplitude according to the input modulation factor is output as a DC bais voltage.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the DC bias voltage generating section includes: a triangular wave phase output from the triangular wave phase generating section; a DC link section positive side voltage; The negative triangular sine wave phase is input according to the positive and negative of the difference between the DC link positive voltage and the negative DC link voltage and the positive and negative of the load power factor with the negative load voltage and the load power factor as inputs. The DC bias is determined for each cycle, and a DC bias voltage is output according to the determined DC bias.

According to the present invention, when the voltage command is small, the DC bias voltage is added to each phase voltage command, and the phase voltage command value is limited to the minimum on-pulse width while keeping the line voltage as the command value. The minimum on-pulse width is secured by changing the size so that it does not overlap.
The line voltage is controlled so as to be equal to the command value, the positive triangular wave and the negative triangular wave are set so as to have opposite phases, and the DC bias voltage is applied alternately to the positive and negative. This makes it possible to balance the flow of each switching element without increasing the number of times of switching.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment. The PWM control device according to this embodiment includes a three-phase voltage command calculating unit 11 and a DC bias voltage adding unit 12
, A triangular wave comparison unit 13 and a DC bias voltage generation unit 14
, A triangular wave phase generating unit 15, a positive / negative triangular wave phase difference setting unit 16, a positive triangular wave generating unit 17, and a negative triangular wave generating unit 1.
8 is provided.

The triangular wave phase generator 15 has a triangular wave frequency f
With the sw as an input, a sawtooth wave having an amplitude of 2π (π: pi) and a frequency of fsw is output as a triangular wave phase θp.
FIG. 3 shows the waveform of the triangular wave phase θp.

[0012]

(Equation 1) The positive-side triangular wave generator 17 receives the triangular wave phase θp output from the triangular wave phase generator 15 as an input, and in synchronization with θp, the triangular wave TRIp whose amplitude is half of the DC link voltage Vdc.
Is calculated by the following equation and output.

[0013]

(Equation 2) The positive / negative triangular wave phase difference setting unit 16 outputs π as the positive / negative triangular wave phase difference phase δ.

The negative triangular wave generator 18 includes a triangular wave phase θp output from the triangular wave phase generator 15 and a positive / negative triangular wave phase difference phase δ output from the positive / negative triangular wave phase difference setting unit 16.
And outputs the triangular wave TRIn whose amplitude is half of the DC link voltage Vdc in accordance with the following equation in synchronization with θn.

[0015]

(Equation 3) The three-phase voltage command calculator 11 outputs voltage commands Vu Ref, Vv Ref, and Vw Ref for each of the U, V, and W phases.

The DC bias voltage generator 14 receives the triangular wave phase θp output from the triangular wave phase generator 15 as an input, and outputs a DC bias voltage Vbias by the following calculation according to the triangular wave phase θp as shown in FIG. . When θp = 0, Vbias (N) = − Vbias (N−1) (N is an integer) The magnitude | Vbias | of the DC bias voltage Vbias is set to, for example, １ ／ of the DC link voltage Vdc. | Vbias | = 1/4 · Vdc The DC bias adding section 12 is a DC bias voltage adding section 1
4 and the three-phase voltage commands Vu Ref, Vv Ref, Vw R output from the three-phase voltage command calculation unit 11.
ef, and a new three-phase voltage command Vu is obtained by the following calculation.
, Vv, Vw. Vu = Vu Ref + Vbias Vv = Vv Ref + Vbias Vw = Vv Ref + Vbias The triangular wave comparator 13 outputs the three-phase voltage commands Vu, Vv, Vw output from the DC bias voltage adder 12 and the positive output from the positive triangular wave generator 17. Side triangular wave TRIp and negative side triangular wave TRIn output from negative side triangular wave generator 18.
, And each phase PWM voltage command Vu PWM, Vv PW is obtained by comparing the magnitude of each phase voltage command with a positive / negative triangular wave.
M and Vw PWM are obtained and output.

Regarding the U-phase: When Vu ≧ TRIp: VuPWM = + Vdc / 2 When Vu ≦ TRIn: VuPWM = −Vdc / 2 When TRIn <Vu <TRIp: VvPWM = 0 Also for the V-phase W phase Similarly, for the V phase: When Vv ≧ TRIp: Vv PWM = + Vdc / 2 When Vv ≦ TRIn: Vv PWM = −Vdc / 2 TRIn <Vv <For TRIp: Vv PWM = 0 For the W phase: Vw ≧ In the case of TRIp: Vw PWM = + Vdc / 2 When Vw ≦ TRIn: Vw PWM = −Vdc / 2 In the case of TRIn <Vw <TRIp: Vw PWM = 0 FIG. Voltage command Vu PWM, positive triangular wave TRIp, negative triangular wave TRI
FIG. 6 is a waveform diagram showing the mutual relationship of n. U-phase voltage command V
By adding the DC bias voltage Vbias to u Ref to obtain a new U-phase voltage command Vu, the U-phase PWM voltage command Vu is obtained.
The minimum on-pulse width can be ensured even for the pulse having the smallest width among the u PWM pulses. Since the phases of the positive triangular wave TRIp and the negative triangular wave TRIn are shifted by π and the polarity of the DC bias voltage Vbias is alternately changed in accordance with the cycle of the triangular wave phase θp, the switching is performed without increasing the number of switching operations. It is possible to balance the flow of the elements.
That is, by using the PWM control device having the configuration shown in FIG. 1, even if the voltage command value is small, it is possible to output a voltage according to the command value regardless of the minimum on-pulse width limitation of the switching element.

FIG. 4 is a block diagram showing the configuration of the second embodiment. The PWM control device according to this embodiment includes a three-phase voltage command calculating unit 11 and a DC bias voltage adding unit 12
, A triangular wave comparator 13 and a DC bias voltage adder 14
, A triangular wave phase generating unit 15, a positive / negative triangular wave phase difference setting unit 16, a positive triangular wave generating unit 17, and a negative triangular wave generating unit 1.
8 and a PWM mode switching unit 19.

The PWM mode switching unit 19 determines the modulation factor α of the three-phase output voltage (α is defined as follows. If the amplitude of the three-phase voltage command is | V |, α = 2 × | V | Vdc, Vdc is the DC link voltage) and PW
The M mode PWM mode is output. That is, the PWM mode switching modulation rate αCHG and the input modulation rate α are compared in magnitude, and when α> αCHG: PWMmode = 1 (1 represents the normal mode) When α ≦ αCHG: PWMmode = 0 (0 is “1” or “0” is output as shown in FIG.

Here, the PWM mode switching modulation rate αCHG
Must satisfy the following conditions. 0 <αCHG <0.5 αCHG is set to, for example, 0.3.

The DC bias voltage generating section 14 is adapted to output the PWM mode PWMmode output from the PWM mode switching section 19.
And the triangle wave phase θ output from the triangle wave phase generator 15
When p is input and the PWM mode value is 0, as shown in FIG. 3, according to the triangular wave phase θp,
The DC bias voltage Vbias is output by the following calculation, and PW
When the value of the M mode PWMmode is 1, 0 is output as the DC bias voltage Vbias. When PWMmode = 0 (DC bias mode): When θp = 0, Vbias (N) = − Vbias (N−1) (N is an integer) The magnitude | Vbias | of the DC bias voltage Vbias is, for example, DC Set to 1/4 of the link voltage Vdc. | Vbias | =＝ · Vdc When PWMmode = 1 (in the normal mode): Vbias = 0 The positive / negative triangular wave phase difference setting unit 16 sets the PWM mode switching unit 1
9, the PWM mode output from the PWM mode 9 is input, and the positive and negative triangular wave phase difference phase δ is switched and output in accordance with the PWM mode. When PWMmode = 0 (in DC bias mode): δ = π When PWMmode = 1 (in normal mode): δ = 0 Since the operation of the other components is the same as in the first embodiment, Description is omitted.

Next, a third embodiment will be described with reference to FIG. This is such that the DC bias voltage is changed by the modulation factor α in the first embodiment. That is, the DC bias voltage generator 14 of this embodiment receives the modulation rate α and the triangular wave phase θp output from the triangular wave phase generator 15 and outputs the DC bias voltage Vbias stored in advance according to the input. . Then, as shown in FIG. 3, the DC bias voltage Vbias is output by the following calculation according to the triangular wave phase θp. When θp = 0, Vbias (N) = Vbias (N−1) (N is an integer) The magnitude | Vbias | of the DC bias voltage Vbias is set as follows by the modulation factor α, for example. | Vbias | = Vdc × α / 2 The operation of the other components is the same as that of the first embodiment, and thus the description is omitted.

Next, a fourth embodiment will be described with reference to FIG. This is a modification of the first embodiment in which control is performed to suppress the fluctuation of the DC link voltage neutral point potential of the NPC inverter. The DC bias voltage generation unit 14 in this embodiment includes a DC link positive voltage VdcP and a DC link negative voltage VdcM, a load power factor cos φ obtained from a phase difference φ between the inverter output voltage and current, and a triangular wave phase generation. With the triangular wave phase θp output from the unit 15 as an input,
The DC bias voltage Vbias is obtained and output in the following procedure.

That is, first, the DC link section positive side voltage V
The difference between dcP and the DC link section negative voltage VdeM is calculated as the DC link section voltage difference ΔVdc, and the sign is determined to determine the DC link voltage difference sign PMdc. The sign of the input load power factor cos φ is determined, and the load power factor sign PML is obtained. The magnitude | Vbias | of the DC link voltage is, for example, Vdc / 4.
And The DC bias voltage command VbiasRef is obtained by the following calculation. VbiasRef = PML × PMdc × | Vbias | The DC bias voltage command VbiasRef when the input triangular wave phase θp is θp = 0 is output as the DC bias voltage Vbias, and the DC bias voltage Vbias until the value is changed next.
bias is kept at that value. The operation of the other components is the same as in the first embodiment, and a description thereof will not be repeated.

With the above arrangement, even if the voltage command value is small, the voltage according to the command value is output without being limited by the minimum on-pulse width of the switching element, while suppressing the fluctuation of the neutral point potential of the DC link voltage. It becomes possible to do.

[0026]

As described above, according to the present invention, when the voltage command is small, the DC bias voltage is applied to each phase voltage command, and the line voltage is maintained as the command value, and each phase voltage command value is set to the minimum on-pulse. Since the width is changed so as not to limit the width, it is possible to control the line voltage to be equal to the command value while securing the minimum on-pulse width. In this case, since the positive triangular wave and the negative triangular wave are set to have the opposite phases, and the DC bias voltage is applied alternately to the positive and negative, the switching of each switching element is performed without increasing the number of switching. The flow can be balanced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining triangular wave comparison in the first embodiment.

FIG. 3 is a waveform chart for explaining the operation of the DC bias voltage generator in the first embodiment.

FIG. 4 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating a DC bias voltage generator according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a DC bias voltage generator according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 11 Three-phase voltage command calculator 12 DC bias voltage adder 13 Triangular wave comparator 14 DC bias voltage generator 15 Triangular wave phase generator 16 Positive / negative triangular wave phase difference setting unit 17 Positive triangular wave generator 18 Negative triangular wave generator 19 PWM mode Switching unit

Claims (4)

(57) [Claims] 1. A three-phase voltage command calculation unit for calculating and outputting a three-phase voltage command, a triangular wave frequency as an input, and an amplitude 2 at the input frequency.
a triangular wave phase generator that outputs a sawtooth wave of π as a triangular wave phase, and a triangular wave phase output from the triangular wave phase generator as an input, and synchronizes the half of the DC link voltage of the inverter with the input triangular wave phase. A positive triangular wave generating unit that calculates the triangular wave with the output as a positive triangular wave, a positive / negative triangular wave phase difference setting unit that outputs a value π as a positive / negative triangular wave phase difference setting unit, and an output from the triangular wave phase generating unit The sum of the triangular wave phase and the positive / negative triangular wave phase output from the positive / negative triangular wave phase difference setting unit is input, and in synchronization with the input phase, a triangular wave having an amplitude equal to half the DC link voltage of the inverter is calculated. A negative triangular wave generator that outputs a negative triangular wave, a triangular wave phase output from the triangular wave phase generator is input, and a square wave synchronized with the input triangular wave phase is directly converted to a triangular wave. A DC bias voltage generator that outputs a bias voltage, a three-phase voltage command output from the three-phase voltage command calculator, and a three-phase voltage command that receives the DC bias voltage output from the DC bias voltage generator as an input. And a DC bias voltage adding unit that outputs a new three-phase voltage command, a three-phase voltage command output from the DC bias voltage adding unit, and an output from the positive triangular wave generating unit. And outputs a three-phase voltage command and a three-phase PWM voltage command by comparing the magnitude of the three-phase voltage command with the positive and negative triangular waves. A PWM control device for an NPC inverter, comprising: 2. The PWM of the NPC inverter according to claim 1.
The control device further includes a PWM mode switching unit that receives a modulation rate and outputs a PWM mode in accordance with the modulation rate, wherein the positive / negative triangular wave phase difference setting unit receives the PWM mode output from the PWM mode switching unit as an input, The DC bias voltage generation unit selects either the value π or 0 according to the set PWM mode and outputs the selected value as a positive / negative triangular wave phase difference. The PWM mode switching unit outputs the PWM mode and the triangular wave. According to the PWM mode, a value of 0 is input when the PWM mode indicates the normal mode, and a square wave synchronized with the input triangular wave phase is input when the PWM mode indicates the DC bias mode. The PW of the NPC inverter is output as a DC bias voltage. The control device. 3. The PWM of the NPC inverter according to claim 1.
In the control device, the DC bias voltage generation unit receives a modulation rate and a triangular wave phase output from the triangular wave phase generation unit as inputs, and synchronizes with the input triangular wave phase to generate an amplitude according to the input modulation rate. A PWM control device for an NPC inverter, which outputs different square waves as a DC bais voltage. 4. The PWM of the NPC inverter according to claim 1.
In the control device, the DC bias voltage generation unit receives a triangular wave phase output from the triangular wave phase generation unit, a DC link unit positive side voltage, a DC link unit negative side voltage, and a load power factor, and In accordance with the sign of the difference between the link part positive side voltage and the DC link part negative side voltage and the load power factor sign, the polarity of the DC bias is determined for each cycle of the input triangular wave sine wave phase, and the determined DC is determined. A PWM controller for an NPC inverter, which outputs a DC bias voltage according to the positive or negative of a bias.