JP3249307B2 - 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 for converting a DC voltage having a neutral point potential into an AC voltage, and more particularly to an NPC inverter for suppressing a change in DC voltage due to a change in load power.

[0002]

2. Description of the Related Art When power is supplied to a load using a voltage-type inverter, the DC voltage temporarily fluctuates due to a sudden change in load power or the like, and this fluctuation may adversely affect the control performance of the system. .

When a neutral point clamped (NPC) inverter is used as a voltage source inverter, the DC voltage is divided into a positive side and a negative side, and the neutral point potential fluctuates. The effect is even more pronounced.

[0004] In order to suppress the fluctuation of the DC voltage due to such a sudden change in load power, a conventional NPC inverter employs a measure shown in FIG. Figure things 4, the positive DC voltage V _d is applied from the DC power supply 1 current voltage V ₁ and connected in series two pairs of capacitors 2 to obtain a neutral point potential N divided into negative DC voltage V _2, 3, the DC voltage V _d and the neutral point potential N is applied AC voltage reference ^{_{V u *, V v *,}} V w *
The inverter 4 converts the DC voltage _Vd into a three-phase AC voltage and supplies the AC voltage to the load 5 in accordance with
When detecting a positive side DC voltage V ₁ and the negative side DC voltage V ₂ through a 21, the AC voltage reference V a difference voltage detected value V _1f and V _2f
u ^*, V _v ^*, is obtained so as to suppress the fluctuation of the DC voltage by correcting the AC voltage reference is added respectively to V _w ^*.

According to this method, when the positive side DC voltage V ₁ is higher than the negative side DC voltage V ₂ , the positive side DC power consumption is increased by adding a positive bias to the voltage reference. Therefore, the fact that the positive DC voltage is reduced is used.

Reference numeral 7 denotes a carrier generator for outputting a triangular wave signal for pulse width modulation, and 8 denotes an inverter which compares the corrected AC voltage references V _u2 ^* , V _v2 ^* , V _w2 ^* with the triangular wave signal. 4 is a comparator that outputs a gate pulse for pulse width modulation control, 9 is an inverter output current I _u , I _v ,
From the detected value of I _w, the reactive component current I _df and the active component current I _qf
The coordinate converters 10 and 11 detect the reactive component current reference I.
_dr and effective component current reference I _qr and the I _df and I _qf compares each current controller for outputting a reactive component voltage reference E _dr and active ingredient voltage reference E _qr, 12 from the E _dr and E _qr 3
Phase of the AC voltage reference V _u ^*, V _v ^*, a coordinate converter that outputs a V _w ^*, a description thereof will be omitted for these effects not directly related to the present invention.

When the speed of an AC motor is controlled by using a normal voltage type inverter that outputs a DC voltage by a converter, the torque (effective component current) of the inverter is controlled.
An inverter output power P is calculated from a product of a reference and a speed feedback (or a speed reference), and is added to a voltage control output of the converter to suppress a DC voltage fluctuation.

[0008]

In the conventional device shown in FIG. 4 described above, the difference between the positive DC voltage feedback and the negative DC voltage feedback is added to the voltage reference of the inverter to suppress the DC voltage fluctuation. There is a problem that the effect of suppressing DC voltage fluctuation is not sufficient due to detection delay due to feedback.

Further, a method of calculating the output power of the inverter from the product of the torque reference of the inverter and the speed feedback (or the speed reference) and adding the calculated output power to the voltage control output of the converter to suppress the DC voltage fluctuation is disclosed in Japanese Patent Application Publication No. NPC divided into positive converter and negative converter
Inverters cannot be implemented because the sum of the power output from each converter matches the output power of the inverter.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a method of dividing the output power of an inverter into a positive side and a negative side. Provided are a device that suppresses fluctuations in DC voltage by reflecting power on a voltage reference of an inverter, and an NPC inverter that suppresses fluctuations in DC voltage by reflecting positive power and negative power on a voltage control output of a converter. It is in.

[0011]

Means for Solving the Problems As a first aspect of the present invention,
A DC voltage is applied and divided into a positive DC voltage and a negative DC voltage to obtain a neutral point potential.Two sets of capacitors connected in series are provided with the DC voltage and the neutral point potential. An inverter that converts the DC voltage to an AC voltage and outputs the converted voltage, and a power detection unit that separates positive power and negative power from the detected value of the AC voltage reference and the AC current reference or the detected value of the inverter output current and outputs the separated power. The AC voltage reference is corrected based on a difference value between the positive power and the negative power.

According to a second aspect of the present invention, a positive DC voltage and a negative DC voltage are output in accordance with the outputs of a positive voltage controller and a negative voltage controller, respectively. Two sets of converters connected in series so that the voltages are added, and an inverter that receives the positive DC voltage and the negative DC voltage as inputs and outputs an AC voltage according to an AC voltage reference; Power detection means for separating and detecting the positive side power and the negative side power from the reference value and the AC current reference or the detected value of the inverter output current; and providing the positive side DC voltage and the negative side DC voltage by the positive side power and the negative side power. Correct the voltage.

According to a third aspect of the present invention, the power detecting means further comprises positive / negative separating means for separating the AC voltage reference into a positive AC voltage reference and a negative AC voltage and outputting the separated AC voltage reference. The reference power and the negative power are detected by multiplying the reference and the negative AC voltage references by the detected values of the AC current reference and the inverter output current, respectively.

According to a fourth aspect of the present invention, in the first aspect, the AC voltage reference is corrected by subtracting a difference value obtained by subtracting the negative power from the positive power from the AC voltage reference.

According to a fifth aspect of the present invention, when the AC voltage reference is multi-phase, the correction is performed by subtracting the difference value from the AC voltage references of all phases. According to a sixth aspect of the present invention, in the second aspect, the correction of the positive DC voltage is performed by adding the positive power to the output of the positive voltage controller, and correcting the negative DC voltage. The correction is performed by adding the negative power to the output of the negative voltage controller.

[0016]

In the first and fourth aspects of the present invention, the power detection means separates and detects the positive power and the negative power from the AC voltage reference and the AC current reference or the detected value of the inverter output current. The difference between the power and the negative power is subtracted from the AC voltage reference and corrected.

In the invention according to claim 2 and claim 6, the power detection means separates and detects the positive power and the negative power from the AC voltage reference and the AC current reference or the detected value of the inverter output current. The output of the voltage controller is corrected by adding positive power, and the output of the negative voltage controller is corrected by adding negative power.

In the invention according to claim 3, the positive / negative separating means of the power detecting means divides the AC voltage reference into a positive side and a negative side, and separates and outputs the positive side AC voltage reference and the negative side AC voltage reference. Positive power is detected by multiplying the positive AC voltage reference by the AC current reference or the detected value of the inverter output current, and negative power is detected by multiplying the negative AC voltage reference by the AC current reference or the detected value of the inverter output current. I do.

In the invention of claim 5, in the case of an inverter that outputs a multi-phase AC voltage, the power detection means divides the AC voltage reference of all phases into positive and negative sides, respectively, and The AC voltage reference and the negative AC voltage reference are separated and output, and the positive AC voltage reference and the negative AC voltage reference of each phase are multiplied by the AC current reference or the detected value of the inverter output current to obtain the positive side of each phase. The power and the negative power are obtained, the positive power and the negative power are added, the positive power and the negative power of the inverter output are detected, and the difference between the positive power and the negative power is calculated from the AC voltage reference. To correct the AC voltage reference.

[0020]

FIG. 1 is a block diagram of an embodiment corresponding to claims 1, 3, 4, and 5 of the present invention. In FIG. 1, a DC voltage V _d supplied from a DC power supply 1 is divided into a positive DC voltage and a negative DC voltage by a smoothing capacitor 2 and a smoothing capacitor 3, and input to an NPC inverter 4. NPC
Inverter 4, the gate pulse output from the comparator 8, supplied to the load 5 converts the DC voltage V _d to the pulse width modulation on three-phase AC voltage.

The three-phase output currents I _u , I _v ,
I _w is detected by the current detector 6 and the coordinate conversion unit 9
Is input to The coordinate converter 9 converts the detected values (I _uf , I _vf , I _wf ) of the inverter output current into an ineffective component I _df and an effective component I _qf of the power supplied to the load 5.

The current control units 10 and 11 _perform proportional / integral amplification of the difference between the reactive component current reference I _dr and the reactive component current I _df and the difference between the active component current reference I _qr and the active component current I _qf. Thus, an invalid component voltage reference E _dr and an effective component voltage reference E _qr are output.

The voltage references E _dr and E _qr are converted by the coordinate converter 12 into three-phase AC voltage references (V _u ^* , V _v ^* , V _w ^* ). On the other hand, the current references I _dr and I _qr are
The three-phase AC current reference ( _Iu ^* , _Iv ^* , _Iw)
^* ).

The power detector 14 calculates and outputs the positive-side power P _P and the negative power P _N of the AC power output from the inverter 4 from the AC voltage reference and an AC current reference of the three phases.
FIG. 2 shows a specific example of the power detector 14, which is provided with positive / negative separating means (51, 52) for dividing the AC voltage reference into a positive side and a negative side for each phase. That is, the U-phase positive-side separating means 51 limits the lower limit of the AC voltage reference _Vu ^* to 0, and outputs only the positive-side AC voltage reference as _Vup ^* . on the other hand,
The negative side separation means 52 limits the upper limit of the AC voltage reference _Vu ^* to 0, and outputs only the negative AC voltage reference as V _UN ^* . AC voltage references V _UP ^* and V _UN separated into positive and negative sides
^* Is multiplied by the AC current reference I _u ^* in multipliers 53 and 54,
U-phase positive power and negative power are determined. V-phase, W-phase positive-side power and negative power are determined in the same manner also, the positive power of each phase positive power and negative power are added by the adder 55 and 56 P _P and the negative power P Output _N. Subtractor 15 in FIG.
The positive side power P _P of the value obtained by subtracting the negative power P _N from output as the correction signal V _C, the AC voltage reference of each phase by the subtracter 16 output from the power detector 14 V _u ^*, V _v ^* , _Vw ^*, and the correction signal V _C is subtracted from the corrected AC voltage reference V _u2 ^* ,
By obtaining V _v2 ^* and V _w2 ^* and inputting the corrected AC voltage reference to the comparator 8, the object of the present invention is achieved.

That is, when the positive power output from the inverter 4 is larger than the negative power, the voltage of the positive DC smoothing capacitor 2 tends to be lower than the voltage of the negative DC smoothing capacitor 3. Subtract the difference between the positive and negative power from the inverter's AC voltage reference (bias)
Then, the amount of voltage drop of the positive DC smoothing capacitor 2 decreases. That is, the bias component corresponds to the positive / negative power difference, so that the DC voltage fluctuation can be suppressed.

FIG. 3 is a block diagram of an embodiment corresponding to the second, third and sixth aspects of the present invention. This embodiment, with each outputting a positive side DC voltage V ₁ and the negative side DC voltage V ₂ in accordance with the output of the positive voltage controller 23 and the negative voltage controller 24, a positive-side DC voltages V ₁ Two sets of converters 33 and 34 connected in series so that the negative DC voltage V ₂ is added, the positive DC voltage V ₁ and the negative DC voltage V ₂ are input, and an AC voltage reference V _u ^* , V _v ^*, it can be applied to those having an inverter 4 which outputs an AC voltage corresponding to V _w ^*.

That is, in FIG.
AC voltage supplied by the gate pulse G _1, G ₂ outputted from the phase control unit 27, 28 by the positive side converter 33 and a negative converter 34, to the positive DC voltage V ₁ and the negative side DC voltage V ₂ from Is converted. These DC voltages are
The signal is smoothed by the smoothing capacitor 2 and the smoothing capacitor 3 and input to the NPC inverter 4. The NPC inverter 4 converts the DC voltages V ₁ and V ₂ into three-phase AC voltages and supplies them to the load 5 by the gate pulse G ₃ output from the comparator 8.

The positive voltage controller 23 and the negative voltage controller 24
_Are the positive voltage reference V _1r and the negative voltage reference V _2r , the output voltage feedback V _1f of the positive converter 33 detected via the voltage detector 20 and the negative voltage detected via the voltage detector 21. The output voltage feedback V _2f of the converter 34 is compared with each other, and the difference is proportionally integrated and amplified to output a positive current reference I _1r and a negative current reference I _2r . The current controllers 25 and 26 are connected to the current references I _1r and I _2r and the positive-side converter 33 detected through the current detectors 35 and 36, respectively.
Output current feedback I _1f , I _{2f of} negative side converter 34
, And control signals C ₁ and C ₂ are output so as to reduce the difference value, and the phase controllers 27 and 28 output gate pulses G ₁ and G ₂ having phases corresponding to the control signals C ₁ and C ₂ , respectively. Is output, and the positive converter 33 and the negative converter 34 are controlled as described above, and the positive DC voltage V ₁ and the negative DC voltage V ₂
Is controlled to a value corresponding to the positive voltage reference V _1r and the negative voltage reference V _2r .

The alternating current I _u of the three-phase output from the inverter 4, I _v, I _w is, I _uf via the current detector 6, I
_These are detected as _vf and _Iwf , and are converted by the coordinate conversion unit 9 into an inactive component current _Idf and an active component current _Iqf . Current controller
10 and 11 are the reactive component current reference I _dr and the active component current reference I _qr, and the reactive component current I _df and the active component current reference I _{q
and qf} , respectively, and the difference is proportionally integrated and amplified to output an invalid component voltage reference _Edr and an effective component voltage reference _Eqr . Coordinate conversion unit 12, the AC voltage of the reactive component voltage reference E _dr and enable component voltage reference E _qr 3-phase reference ^{_{V u *, V v *,}} V
_w ^* , and the comparator 8 calculates the AC voltage reference _Vu ^* ,
V _v ^*, by comparing the triangular wave output from the V _w ^* and the carrier generator 7, and outputs a gate pulse G ₃ which is pulse width modulated AC voltage of three-phase output from the inverter 4, 3-phase of the AC voltage reference V _u ^*, V _v ^*, is controlled to a value corresponding to V _w ^*.

The coordinate converter 13 converts the reactive component current reference _Idr and the active component current reference _Iqr into three-phase AC current references _Iu ^* and _Iu ^* .
_v ^* , _Iw ^* . Power detection unit 14, in the same manner as described above in to three-phase AC voltage reference ^{_{V u *, V v *,}} V w * and 3
The positive power _PP and the negative power _PN are detected from the phase AC current references _Iu ^* , _Iv ^* , _Iw ^* . Detected positive power P
_P and the negative power _PN are output from the positive voltage control unit 23 and the negative voltage control unit 24 (positive current reference I
_1r and the negative current reference I _2r ) achieve the object of the invention.

That is, when the positive power and the negative power output from the inverter 4 instantaneously increase or decrease, the positive power P _P is applied to the positive current reference I _1r and the negative current reference I _{2r accordingly.}
Negative power P _N is added as a bias amount and, since the power supplied from the primary converter 33 and the negative-side converter 34 increases or decreases, suppressing a variation of the positive-side DC voltage V ₁ and the negative side DC voltage V ₂ be able to.

As described above, by obtaining the positive power and the negative power from the AC voltage reference and the AC current reference of the inverter 4 and compensating, the voltage fluctuation can be suppressed more quickly, and the DC voltage of the conventional system can be reduced. Even better results are obtained compared to compensating with feedback.

In the above description, the positive power and the negative power are obtained from the AC voltage reference and the AC current reference of the inverter. However, the detected value of the inverter output current is used instead of the AC current reference. Can be similarly implemented.
In addition, although the example in which the inverter 4 outputs a three-phase alternating current is shown, the present invention can also be applied to a case where a single-phase or a multi-phase other than the three-phase alternating current is output.

[0034]

According to the present invention, in an NPC inverter that converts a DC voltage having a neutral point potential into an AC voltage and outputs the AC voltage, it is possible to effectively suppress a change in the DC voltage due to a change in load power. NP with improved control performance
A C inverter can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claims 1, 3, 4, and 5 of the present invention.

FIG. 2 is a detailed configuration diagram showing a specific example of a power detection unit 14 used in the present invention.

FIG. 3 is a configuration diagram of an embodiment according to claims 2, 3, and 6 of the present invention.

FIG. 4 is a configuration diagram of a conventional apparatus.

[Description of Signs] 1 ... DC power supply 2, 3 ... Smoothing capacitor 4 ... Inverter 5 ... Load 6 ... Current detector 7 ... Carrier generator 8 ... Comparator 9 ... Coordinate converter 10 and 11 ... Current controller 12 and 13 ... Coordinate converter 14 ... Power detector 15,16 ... Subtractor 20,21 ... Voltage detector 23,24 ... Voltage controller 25,26 ... Current controller 27,28 ... Phase controller 29,30 ... Adder 31 , 32 ... AC power supply 33,34 ... Converter 35,36 ... Current detector

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-261550 (JP, A) JP-A-6-54547 (JP, A) JP-A-6-30564 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02M 7/48 H02M 7/5387

Claims (6)

(57) [Claims] 1. A series connection of two capacitors to which a DC voltage is applied and which is divided into a positive DC voltage and a negative DC voltage to obtain a neutral point potential, and wherein the DC voltage and the neutral point potential are provided. An inverter that converts the DC voltage into an AC voltage and outputs the AC voltage according to the AC voltage reference, and separates the positive power and the negative power from the detected value of the AC voltage reference and the AC current reference or the inverter output current to output An NPC inverter, wherein the AC voltage reference is corrected based on a difference value between the positive power and the negative power. 2. A positive DC voltage and a negative DC voltage are respectively output according to outputs of a positive voltage controller and a negative voltage controller, and the positive DC voltage and the negative DC voltage are added. And two inverters connected in series as described above, and an inverter that receives the positive DC voltage and the negative DC voltage as input and outputs an AC voltage according to the AC voltage reference, and the AC voltage reference and the AC current reference. Alternatively, power detection means for separating and detecting the positive power and the negative power from the detected value of the inverter output current is provided, and the positive DC voltage and the negative DC voltage are corrected by the positive power and the negative power. N characterized by
PC inverter. 3. The NPC inverter according to claim 1, wherein said power detection means separates said AC voltage reference into a positive AC voltage reference and a negative AC voltage and outputs the separated AC voltage reference. An NPC inverter comprising a separating unit, wherein the positive power and the negative power are detected by multiplying the positive AC voltage reference and the negative AC voltage reference by the detected values of the AC current reference and the inverter output current, respectively. . 4. The NPC inverter according to claim 1, wherein the correction of the AC voltage reference is performed by subtracting a difference value obtained by subtracting the negative power from the positive power from the AC voltage reference. NPC inverter. 5. The NPC inverter according to claim 4, wherein when the AC voltage reference is multi-phase, the difference is subtracted from the AC voltage references of all phases to correct the difference. 6. The NPC inverter according to claim 2, wherein the correction of the positive DC voltage is performed by adding the positive power to the output of the positive voltage controller to correct the negative DC voltage. Wherein the NPC inverter corrects the output of the negative voltage controller by adding the negative power.