JPH06233537A - Controller of neutral point clamp system converter - Google Patents

Abstract

PURPOSE:To control the total DC output voltage to be constant and to equalize impressed voltages onto two smoothing capacitors by controlling pulse width modulation according to the sum of output signal from an input current control circuit which controls input current by output signal from a sum voltage control circuit and that from a differential voltage control circuit. CONSTITUTION:A sum voltage control circuit AVR1 amplifies a deviation between sum voltage command value Vd*' and sum voltage detected value Vd to produce peak value command Im*, and then a multiplier ML multiplies it unit sinusoidal wave sinwt synchronous with source voltage Vs to produce input current command value Is*. An input current control circuit ACR amplifies a deviation between it and input current command value Is by inversion to produce voltage command values ea, eb. A differential control circuit AVR2 amplifies a deviation between differential voltage command value V0*=0 and differential voltage detected value V0 to produce compensation voltage DELTAe, and further a code switcher AS switches its polarity to produce DELTAe', and adder/subtracters A3, A4 add it to the voltage command values ea, eb to serve as the voltage command value to a PWM control circuit PWMC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width modulation control (PWM control) neutral point clamp type converter control device for converting single-phase or multi-phase AC power into DC power.

[0002]

2. Description of the Related Art FIG. 16 shows a main circuit configuration of a single-phase neutral point clamp type converter.

In the figure, SUP is a single-phase AC power supply, LS is an AC reactor, CNV is a neutral point clamp type converter (hereinafter referred to as NPC converter) main body, Cd1 and Cd2 are DC smoothing capacitors, and LOAD is Is a load.

The NPC converter has a self-extinguishing element S11 ...
S14, S21 to S24, Freewheeling diode D11
~ D14, D21 ~ D24, and clamp diode D15,
It is composed of D16, D25 and D26. The AC side terminal voltage VC of this converter is the voltage Va at point a and the voltage V at point b.
It is represented by the difference voltage of b, and VC = Va-Vb is established.

The voltage Va at the point a changes as follows by turning on and off the four elements S11 to S14.
However, the DC voltage of the two smoothing capacitors is Vd1, Vd
2. Vd1 = Vd2 = Vd, where Vd is the total DC voltage
/ 2. That is, when S11 and S12 are on, Va = + Vd / 2 When S12 and S13 are on, Va = 0 When S13 and S14 are on, Va = -Vd / 2 and three levels of voltage are generated. Similarly, the voltage Vb at the point b changes as follows by turning on and off the elements S21 to S24. When S21 and S22 are on, Vb = + Vd / 2 When S22 and S23 are on, Vb = 0 When S23 and S24 are on, Vb = -Vd / 2. As a result, the terminal voltage VC of the converter is + V
Five-level voltages of d, + Vd / 2,0, -Vd / 2, -Vd are generated. FIG. 17 is a time chart for explaining the pulse width modulation control (PWM control) operation of the NPC converter of FIG.

In the figure, X1, X2, Y1 and Y2 are carrier waves for PWM control, and ea and eb = -ea are PWM control input signals (voltage command values). Where X1 and X2 are 0 to + E
It is a triangular wave that varies between max and X2 is 180 ° out of phase with X1. Also, Y1 and Y2 are -Emax to 0.
Between the triangular waves X1 and X1, respectively.
It is an inverted value of 2. Input signal ea and triangular wave X1,
Y1 is compared and gate signals g11, g of the elements S11 to S14 are compared.
Make twelve. That is, when ea> X1, g11 = 1, S11 is turned on, S13 is turned off ea ≦ X1, g11 = 0, S11 is turned off, S13 is turned on ea <Y1, g12 = 1, S14 Is turned on and S12 is turned off. When ea ≧ Y1, g12 = 0, S14 is turned off and S12 is turned on. Also, the input signal eb = -ea and the triangular waves X2, Y2
And gate signals g21 and g22 of the elements S21 to S24 are produced. That is, when eb> X2, g21 = 1, S21 is turned on, S23 is turned off. Eb ≦ X2, g21 = 0, S21 is turned off, S23 is turned on. Eb <Y2, g22 = 1, S24. Is turned on and S22 is turned off. When eb ≧ Y2, when g22 = 0, S24 is turned off and S22 is turned on.

As a result, the voltage Va at the point a of the NPC converter CNV, the voltage Vb at the point b and the difference voltage Vc = Va.
-Vb has a waveform as shown, and its average value Vc (m) has a value proportional to the voltage command value ea-eb = 2.ea.

As described above, in the neutral point clamp type converter, the AC side terminal voltage Vc is 5 levels (+ Vd,
Voltages of + Vd / 2,0, -Vd / 2, -Vd) are obtained, and the voltage waveform has few harmonic components. As a result, there is an advantage that the current ripple supplied from the AC power supply becomes small. Further, as can be seen from the gate signals g11 to g22, the switching operation is stopped during the half cycle period of the output frequency, and the switching loss and snubber loss of the element are reduced as compared with the normal bridge inverter. There are advantages.

A differential voltage VL = Vs-Vc between the voltage Vs of the AC power supply SUP and the generated voltage Vc of the converter CNV is applied to the AC reactor Ls, and the input current Is is controlled by adjusting the difference voltage VL. To do.

That is, the voltage Vc is adjusted by performing pulse width modulation control (PWM control) on the NPC converter, and the input current Is is controlled so that the DC voltage Vd becomes substantially constant regardless of the size of the load LOAD. To do. At this time, the input current Is is controlled to be a sine wave having the same phase (power running operation) or reverse phase (regenerative operation) as the power supply voltage Vs. In other words, the NPC converter seen from the AC power supply has an input power factor of 1 and is an ideal load with few harmonics.

[0011]

However, the conventional neutral point clamp type converter control device has the following problems.

That is, the smoothing capacitors Cd1 and Cd2 connected to the DC side of the converter CNV are selected to have the same capacity in terms of design value, but in reality there are variations.
Either of them will get bigger.

On the other hand, the connecting points of the clamping diodes D15 and D16 and the connecting points of D25 and D26 of the NPC converter are connected to the connecting points (neutral point) of the smoothing capacitors Cd1 and Cd2, and the current flowing in and out between them. The voltage Vo at the DC neutral point is determined by Io. NPC with full bridge connection
In the converter, the neutral point current I regardless of power running or regenerative operation
The period t (+) flowing in the positive direction of o and the period t flowing in the negative direction
If (-) becomes equal and the capacitances of the smoothing capacitors Cd1 and Cd2 are equal, Vd1 = Vd2 can be maintained. However, when Cd1> Cd2, the capacitor Cd2 is used during power running.
Is charged faster and Vd1 <Vd2. Further, during regenerative operation, the capacitor Cd2 is discharged faster, and Vd1>
It becomes Vd2. If Cd1 <Cd2, the opposite is true.

When a neutral point clamp type inverter or the like is connected to the load LOAD, a current flows in and out of the neutral point of the DC capacitor according to the load condition, and the DC voltage Vd1 and Vd2 are balanced. It is also the cause of breaking down.

When the balance of the DC voltage becomes unbalanced in this way, the voltage applied to each element forming the converter increases or decreases, and the breakdown voltage of the element is threatened.

The present invention has been made in view of the above points, and is a neutral point clamp type converter in which the entire DC voltage is controlled to be substantially constant and the voltages applied to the two smoothing capacitors are equalized. -The purpose is to provide a control device.

[0017]

In order to achieve the above-mentioned object, a control device of the present invention comprises a single-phase AC power source and a neutral point clamp for full bridge connection which is connected to the single-phase AC power source via a reactor. Formula converter (NPC converter),
First and second DC smoothing capacitors connected to the output terminals of the NPC converter, a load using the DC smoothing capacitor as a DC power source, and a sum voltage of the two DC smoothing capacitors is detected to obtain a sum voltage. A sum voltage control circuit for controlling so as to match the command, an input current control circuit for controlling an input current supplied from the AC power supply by an output signal of the sum voltage control circuit, and a differential voltage between the two DC smoothing capacitors And a pulse width modulation of the NPC converter according to the sum of the output signal of the differential voltage control circuit and the output signal of the input current control circuit. It has a control circuit.

Further, with respect to a polyphase (N-phase) AC power supply, the device of the present invention has a power transformer for insulating the polyphase AC power supply for each phase and a secondary winding of the transformer via a reactor. N full bridge connection type neutral point clamp type converters (NPC converters) to be connected, and the NPC converters.
The output terminals of the DC / DC converter are connected in parallel, and the first and second DC smoothing capacitors connected in series are connected to the output terminal;
A load using one DC smoothing capacitor as a DC power source, a sum voltage control circuit that detects a sum voltage of the two DC smoothing capacitors, and controls so as to match the sum voltage command, and an output signal of the sum voltage control circuit. An input current control circuit for controlling an input current supplied from the AC power source, a differential voltage control circuit for detecting a differential voltage between the two DC smoothing capacitors, and controlling so as to match the differential voltage command value, and the differential voltage control circuit. A circuit for pulse width modulation controlling the NPC converter according to the sum of the output signal of the voltage control circuit and the output signal of the input current control circuit is provided.

[0019]

[Function] Applied voltage Vd of DC smoothing capacitors Cd1 and Cd2
1, Vd2 is detected and the sum voltage Vd = Vd1 + Vd2 and the difference voltage V
Determine o = Vd1-Vd2.

The sum voltage control circuit must be output by the converter.
DC voltage value to sum voltage command value Vd^* And the sum voltage detection
Deviation εd = Vd compared with the output value Vd^* Find -Vd,
The deviation is amplified and the input current peak value command Im^* Made
It This peak value command Im^* Is synchronized with the power supply voltage Vs
Input sine wave sin ωt, input current command value Is^* =
Im^* ・ Make sinωt.

The input current control circuit uses the input current command value Is.
^* And the input current detection value Is are compared, and the deviation εI =
Is ^* -Is is inverted and amplified to give voltage command values ea and eb = -ea to the next PWM control circuit.

The NPC converter uses the voltage command value ea
A voltage Vc proportional to -eb = 2.ea is generated. Is
^* When> Is, the deviation εI has a positive value, which decreases the voltage Vc and increases the input current value Is. Conversely, Is ^* <
In the case of Is, the deviation εI has a negative value, which increases the voltage Vc and decreases the input current value Is. As a result, Is = I
s ^* Is controlled so that

Also, Vd^* Deviation εI when> Vd
Becomes a positive value and the current peak value command Im^* Increase the power supply
Input current in phase with pressure Vs Is = Is^* To increase. This
As a result, the effective power Ps = Vs.multidot.Is = Vm.multidot.Im (1-cos.omega.t) / 2 supplied from the AC power source increases, and the DC voltage Vd increases. Conversely, Vd^* <
When it becomes Vd, the deviation εd becomes a negative value and the current peak value
Command Im^* The input current in phase with the power supply voltage Vs
Is = Is^* To reduce. As a result, the AC power supply
The supplied active power Ps also decreases and the DC voltage Vd decreases.
Let Therefore, Vd = Vd^* Is controlled so that

The differential voltage control circuit has a differential voltage command value Vo ^*. =
0 and the difference voltage detection value Vo = Vd1-Vd2 are compared, and the deviation .epsilon.o = Vo ^* -Determine Vo. The deviation ε o is amplified to create the compensation voltage Δe, and the input signal e of the PWM control circuit is generated.
Add to a and eb. That is, ea '= ea + Δe eb' = eb + Δe = -ea + Δe. At this time, the point a voltage Va and the point b voltage Vb of the converter are voltages proportional to the input signals ea 'and eb', respectively, and the difference voltage Vc = Va-Vb is the compensation voltage .DELTA.
Not affected by e. Input power Pc of NPC converter
= VIs is positive (power running mode), if the compensation voltage Δe is set to a positive value, the voltage V of the DC capacitor Cd1 is increased.
It is possible to increase d1 and decrease the voltage Vd2 of the smoothing capacitor Cd2. For example, if Pc> 0, Is> 0
Then Vc> 0, Va> 0, Vb <0. At this time, when the compensation voltage Δe is added, the voltage Va at the point a
Is increased, the period during which the current Is supplied from the AC power source flows to the DC capacitor Cd1 via the point a is increased, and the voltage V
Increase d1. Further, the voltage Vb at the point b is a negative value, its absolute value decreases, the period during which the input current Is flows to the DC capacitor Cd2 via the point b is shortened, and the voltage Vd2 is decreased. Therefore, the difference voltage Vo = Vd1-Vd2 increases. When Pc is positive and Δe is set to a negative value, the voltage Vd1 of the DC smoothing capacitor Cd1 is decreased and the smoothing capacitor Cd1 is reduced.
The voltage Vd2 of d2 can be increased. Input power Pc
Is negative (regenerative operation mode), the sign of the compensating voltage .DELTA.e is reversed to similarly obtain the difference voltage Vo = Vd1-V.
d2 can be controlled.

That is, Vo during power running^* > Vo
In this case, the deviation εo is a positive value and the compensation voltage Δe is also a positive value.
Becomes Therefore, the differential voltage Vo increases and Vo = Vo^* Tona
To be controlled. On the contrary, Vo^* <When it becomes Vo
The deviation ε o is a negative value, and the compensation voltage Δe is also a negative value.
Become. Therefore, the difference voltage Vo decreases and Vo = Vo^* Becomes
Controlled as. Also, the compensation voltage Δe is
By reversing, Vo = Vo^* So that
Can be controlled.

In this way, the control device for the NPC converter of the present invention controls the DC voltage of the whole to be substantially constant and the voltage applied to the two smoothing capacitors regardless of the power running operation and the regenerative operation. It can be controlled to be equal.
At this time, the input current is controlled to have a sine wave in phase with the power supply voltage, and an AC / DC power converter with an input power factor of 1 and few harmonics can be obtained.

In the case of a multi-phase (N-phase) power source, N full-bridge NPC converters are prepared and the sum of the voltages Vd1 and Vd2 applied to the DC smoothing capacitors Cd1 and Cd2 is Vd =
The input current of each phase converter is controlled so that Vd1 + Vd2 becomes almost constant, and the compensating voltage Δe is applied so that the difference voltage Vo = Vd1-Vd2 becomes zero, and the input current of each phase of the NPC converter is generated. The sign of the product of the voltage is detected for each phase, and the sign of the compensation voltage Δe is switched according to the sign to perform the above control for each phase converter. As a result, the problem of uncontrollability at the zero crossing point of the input current generated in the single-phase power supply is eliminated, and continuous differential voltage control is possible.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a neutral point clamp type converter of the present invention.
FIG. 3 is a main circuit configuration diagram and a control circuit block diagram showing an embodiment of a computer control device.

In the figure, SUP is a single-phase AC power source, LS is an AC reactor, CNV is a neutral point clamp type converter (hereinafter referred to as NPC converter) main body, Cd1 and Cd2 are DC smoothing capacitors, and LOAD is Is a load.

As a control device for the NPC converter,
Input current detector CTS, AC voltage detector PTS, DC voltage detectors PT1 and PT2, adder / subtractors A1 to A4, sum voltage control circuit AVR1, input current control circuit ACR, difference voltage control circuit AVR2, multipliers ML1 and ML2, Code switch A
S and a pulse width modulation control circuit PWMC are prepared.
The NPC converter has self-extinguishing elements S11 to S14, S21.
~ S24, Freewheeling diode D11 ~ D14, D
21 to D24 and clamp diodes D15, D16, D2
It is composed of 5, D26. The AC side terminal voltage VC of this converter is represented by the difference voltage between the voltage Va at the point a and the voltage Vb at the point b, and VC = Va-Vb.

The voltage Va at point a changes as follows by turning on and off the four elements S11 to S14.
However, the DC voltage of the two smoothing capacitors is Vd1, Vd
2. Vd1 = Vd2 = Vd, where Vd is the total DC voltage
/ 2. That is, when S11 and S12 are on, Va = + Vd / 2 When S12 and S13 are on, Va = 0 When S13 and S14 are on, Va = -Vd / 2 and three levels of voltage are generated. Similarly, the voltage Vb at the point b changes as follows by turning on and off the elements S21 to S24. When S21 and S22 are on, Vb = + Vd / 2 When S22 and S23 are on, Vb = 0 When S23 and S24 are on, Vb = -Vd / 2. As a result, the AC side terminal voltage VC of the converter
Is (+ Vd, + Vd / 2, 0, -Vd / 2, -Vd)
5 level voltage is generated.

The voltage detectors PT1 and PT2 detect the DC voltages Vd1 and Vd2 of the smoothing capacitors Cd1 and Cd2, respectively. The adder / subtractor A1 calculates the sum of the voltage detection values Vd1 and Vd2 and inputs Vd = Vd1 + Vd2 to the sum voltage control circuit AVR1. Further, the adder / subtractor A2 is provided with the voltage detection values Vd1 and Vd2.
Difference is calculated, and Vo = Vd1-Vd2 is calculated as the difference voltage control circuit AV
Enter in R2. The current detector CTS detects the input current Is supplied from the power supply SUP and inputs it to the current control circuit ACR and the multiplier ML2. Also, the voltage detector PTS is N
The AC side terminal voltage Vc of the PC converter is detected and input to the multiplier ML2.

The sum voltage control circuit must be output by the converter.
DC voltage value to sum voltage command value Vd^* And the sum voltage detection
Deviation εd = Vd compared with the output value Vd^* Find -Vd,
The deviation is amplified and the peak value command Im of the input current is input.^* Made
It

Next, the current peak value command Im ^{* is} applied by the multiplier ML1 ^. Unit sine wave s synchronized with the power supply voltage Vs
Multiply by inωt, input current command value Is ^* = Im ^* ・ Si
Make nωt.

The input current control circuit ACR has an input current command value Is ^*. And the input current detection value Is are compared, and the deviation ε
I = Is ^* -Is is inverted and amplified to obtain voltage command values ea, e
b = -ea is given to the adder / subtractors A3 and A4.

The differential voltage control circuit AVR2 has a differential voltage command value Vo ^*. = 0 and the differential voltage detection value Vo = Vd1-Vd2 are compared, and the deviation .epsilon.o = Vo ^* -Vo is amplified to compensate voltage Δ
e is generated and is input to the sign switch AS. Code changer AS
Switches the sign of the compensation voltage .DELTA.e according to the sign of the input power Pc = Vc.multidot.Is of the NPC converter. That is, when Pc ≧ 0, Δe ′ = Δe When Pc <0, Δe ′ = − Δe. This compensating voltage Δe 'is added to the adder / subtractor A3, A4.
To enter. The adder / subtractors A3 and A4 are provided with the voltage command value e
, Eb by adding the compensation voltage Δe ′ to the PWM control circuit PW
New voltage command values ea 'and eb' are given to MC. That is, ea '= ea + Δe' eb '= eb + Δe' =-ea + Δe '. FIG. 2 is a time chart for explaining the pulse width modulation control (PWM control) operation of the NPC converter of FIG.

In the figure, X1, X2, Y1 and Y2 are carrier waves for PWM control, and ea 'and eb' are PWM control input signals (voltage command values). Where X1 and X2 are 0 to + Emax
Is a triangular wave that varies between X2 and X2 has a phase of 1 relative to X1.
80 ° off. Further, Y1 and Y2 are triangular waves which vary between -Emax and 0, and are inverted values of the triangular waves X1 and X2, respectively. Input signal ea 'and triangular wave X1, Y
1 is compared with the gate signals g11 and g12 of the elements S11 to S14.
make. That is, when ea '> X1, g11 = 1, S11 is on, S13 is off ea'≤X1, g11 = 0, S11 is off, S13 is on ea'<Y1, g12 = 1 Then, S14 is turned on and S12 is turned off. When ea '≧ Y1, g12 = 0, S14 is turned off and S12 is turned on. Further, the input signal eb 'is compared with the triangular waves X2 and Y2 to generate gate signals g21 and g22 of the elements S21 to S24.
That is, when eb '> X2, g21 = 1, S21 is turned on, S23 is turned off. Eb'≤X2, g21 = 0, S21 is turned off, S23 is turned on. Eb'<Y2, g22 = 1. Then, S24 is turned on and S22 is turned off. When eb '≧ Y2, when g22 = 0, S24 is turned off and S22 is turned on.

As a result, the voltage Va at the point a and the voltage Vb at the point b of the NPC converter CNV have the waveforms shown in the figure. That is, the average value of the voltage Va is proportional to the voltage command value ea ', and the average value of the voltage Vb is proportional to the voltage command value eb'. In addition, the AC side voltage V of the NPC converter CNV
c is the difference between the voltage Va at point a and the voltage Vb at point b,
An average value VC (m) of Vc = Va-Vb (shown by a broken line) is a value proportional to the voltage command value ea'-eb '= ea-eb = 2.ea. First, the operation of the sum voltage control will be described.
Between the NPC converter CNV AC side terminals, the voltage command values ea-eb are irrespective of the value of the compensation voltage Δe as described above.
A voltage Vc proportional to = 2 · ea is generated.

A differential voltage VL = Vs-Vc between the voltage Vs of the AC power supply SUP and the generated voltage Vc of the converter CNV is applied to the AC reactor Ls, and the input current Is is adjusted by adjusting the difference voltage VL. Control.

Is ^* When> Is, the deviation εI has a positive value, which decreases the voltage Vc and increases the input current Is. Conversely, Is ^* When <Is, the deviation εI has a negative value, which increases the voltage Vc and decreases the input current Is.
As a result, Is = Is ^* Is controlled so that

Also, Vd ^* When> Vd, the deviation εd becomes a positive value, and the current peak value command Im ^* Input current Is = Is ^{* in} phase with the power supply voltage Vs. To increase. As a result, the effective power Ps = Vs.multidot.Is = Vm.multidot.Im (1-cos2.omega.t) / 2 supplied from the AC power supply increases, and the DC voltage Vd increases. Conversely, Vd ^* <
When it becomes Vd, the deviation εd becomes a negative value, and the current peak value command Im ^* Input current Is = Is ^{* in} phase with the power supply voltage Vs. To reduce. As a result, the effective power Ps supplied from the AC power supply is also reduced and the DC voltage Vd is reduced. Therefore, Vd = Vd ^* Is controlled so that Next, the differential voltage control operation will be described. By the multiplier ML2,
The input current Is is multiplied by the AC side voltage Vc of the NPC converter to obtain the instantaneous input power Pc = Vc.multidot.Is.

FIG. 3 shows a voltage / current vector diagram during power running. When the input current Is is controlled to be in phase with the power supply voltage Vs, the voltage applied to the AC reactor Ls is VL = jω.multidot. Ls · Is. Here, ω is the angular frequency of the AC power supply. As a result, the voltage Vc generated by the converter becomes a vector whose phase is delayed by θ from the power supply voltage Vs.

FIG. 4 shows the voltage and current waveforms during the powering operation. The converter voltage Vc is plotted against the input current Is.
Are delayed by the phase angle θ. At this time, the input power of the converter Pc = Vc.Is is equal to the power frequency of 2 as shown in the figure.
It changes by a factor of 2. The sign switch AS switches the sign of the compensation voltage .DELTA.e from the differential voltage control according to the sign of the instantaneous input power Pc obtained by the multiplier ML2 as follows. That is, when Pc ≧ 0, Δe ′ = Δe When Pc <0, Δe ′ = − Δe. Here, when Is> 0 and Vc> 0, that is, P
A case of c> 0 will be described as an example. First, the compensation voltage Δ
The case of e = 0 will be described.

When Vc> 0, the voltage at point a of the converter V
When a> 0, the voltage at point b is Vb <0. Point a voltage V
a> 0 means that elements S11 and S12 are on and Va = +
PWM control is performed by either Vd1 or by turning on the elements S12 and S13 and Va = 0. Also, the voltage at point b Vb
<0 means that the elements S23 and S24 are on and Vb =
Either -Vd2 or element S22 and element S23 are on and Vb = 0, whichever is present, and PWM control is performed.

FIG. 5 shows that when Is> 0, Va = + Vd1, Vb.
A current path when = 0 is shown. The input current Is is the power source S
UP → Ls → D12 → D11 → Cd1 → D25 → S22 → Power SU
It flows in the path of P and increases the voltage Vd1 of the capacitor Cd1.

FIG. 6 shows that when Is> 0, Va = 0 and Vb = 0.
The current path in the case of is shown. Input current Is is the power supply SUP
->Ls->S13->D16->D25->S22-> Power source SUP, which is not related to the voltages Vd1 and Vd2 of the capacitors Cd1 and Cd2.

In FIG. 7, Is> 0, Va = 0, Vb =-
The current path for Vd2 is shown. The input current Is is the power source S
UP → Ls → S13 → D16 → Cd2 → D24 → D23 → Power SU
It flows in the path of P and increases the voltage Vd2 of the capacitor Cd2.

Similarly, when Is> 0, Va = + Vd1, Vb
= -Vd2, the input current Is is equal to the power supply SUP → Ls →
D12->D11->Cd1->Cd2->D24->D23-> Power supply SUP, and increases both the voltages Vd1 and Vd2 of the capacitors Cd1 and Cd2. That is, when Is> 0 and Vc> 0, 2
The voltages Vd1 and Vd2 of the two capacitors Cd1 and Cd2 both operate in the increasing direction.

Here, when the compensation voltage Δe '= Δe is added, as shown in FIG. 8, when Is> 0 Vc> 0, a
The voltage at the point becomes Va ′ = Va + Kc · Δe, and increases at a positive value. Also, the voltage at point b Vb '= Vb + Kc.Δe
= −Va + Kc · Δe, which is a negative value and its absolute value decreases.

When the point a voltage Va 'is positive and its value is large, the period shown in FIG. 5 is increased, the voltage Vd1 of the capacitor Cd1 is increased, and when the point b voltage Vb' is negative and its value is small, The period shown in FIG. 7 is reduced and the voltage Vd2 of the capacitor Cd2 is reduced. That is, when Is> 0 and Vc> 0, Vo = V by adding the compensation voltage Δe> 0.
d1-Vd2 can be increased. Similarly, Is
When <0 and Vc <0 (when Pc> 0), the compensation voltage Δ
Vo = Vd1−Vd2 can be increased by adding e> 0. Further, when Pc> 0, by making Δe a negative value, Vo = Vd1−Vd2 can be reduced. Next, the case of Pc <0 will be described.

The direction of the input current Is is reversed and Is <0,
When Vc> 0, that is, Pc <0, FIGS.
Then, consider the case where the direction of the current Is is reversed. That is, when Is <0 and Va = + Vd1 and Vb = 0, the input current Is is equal to the power supply SUP → S23 → D26 → Cd1.
->S11->S12->Ls-> The power supply SUP flows to decrease the voltage Vd1 of the capacitor Cd1.

When Is <0 and Va = 0 and Vb = 0,
The input current Is is the power supply SUP → S23 → D26 → D15 → S12
→ Ls → flows through the path of the power supply SUP and is not related to the voltages Vd1 and Vd2 of the capacitors Cd1 and Cd2.

When Is <0 and Va = 0 and Vb = -Vd2, the input current Is is as follows: power supply SUP → S23 → S24 → Cd2 →
D15➝S12➝Ls➝power supply SUP to reduce the voltage Vd2 of the capacitor Cd2.

Similarly, when Is <0, Va = + Vd1, Vb
= -Vd2, the input current Is is equal to the power supply SUP → S23 →
S24->Cd2->Cd1->S11->S12->Ls-> The power supply SUP flows to reduce the voltages Vd1 and Vd2 of the capacitors Cd1 and Cd2.

Here, when the compensation voltage Δe '=-Δe is added (where Δe is a positive value), the voltage at the point a becomes Va' = Va-KcΔe and has a positive value. Get smaller. The voltage at point b is Vb '= Vb-Kc. [Delta] e
= -Va-Kc. [Delta] e, which is a negative value and its absolute value increases.

When the point a voltage Va 'is positive and its value becomes small, the period of (Is <0, Va = + Vd1, Vb = 0) increases, the voltage Vd1 of the capacitor Cd1 increases, and the point b voltage Vb increases. 'Is negative and its value becomes small (Is <0,
The period of Va = 0, Vb = -Vd2) decreases, and the voltage Vd2 of the capacitor Cd2 decreases. That is, Is <0, Vc>
When 0 (when Pc <0), the compensation voltage Δe ′ = − Δe
Vo = Vd1-Vd2 can be increased by adding

Similarly, when Is> 0 and Vc <0 (when Pc <0), Vo = Vd1−Vd2 can be increased by adding the compensation voltage Δe ′ = − Δe. Further, when Pc <0, by making .DELTA.e a negative value, the difference voltage Vo = Vd1-Vd2 can be reduced.

That is, in the powering mode (Pc> 0), V
o ^* When> Vo, the deviation εo has a positive value, and the compensation voltage Δe also has a positive value. Therefore, the difference voltage Vo increases and Vo = Vo ^* Is controlled so that On the contrary, Vo
^* When <Vo, the deviation εo has a negative value and the compensation voltage Δe also has a negative value. Therefore, the difference voltage Vo decreases,
After all, Vo = Vo ^* Is controlled so that In the regenerative mode, by inverting the compensation voltage Δe,
Similarly, Vo = Vo ^* Can be controlled to be

As described above, the input current Is of the converter is
Is used to control the difference voltage Vo between the DC voltages Vd1 and Vd2, the control response depends on the magnitude of the input current Is. Normally, the input current Is for controlling the power supply power factor to 1
Is controlled in the same phase as the power supply voltage Vs, and the input current Is is large during heavy load operation and is small during light load operation.
As a result, the control response of the differential voltage Vo deteriorates during light load operation with a small Is, and it becomes impossible to control Vo in the extreme case of Is = 0.

FIG. 9 is a control block showing another embodiment of the present invention. In the figure, C1 to C3 are comparators, Gv (s) is a sum voltage control compensation circuit, G1 (s) is an input current control compensation circuit, and
o (s) is a differential voltage control compensation circuit, ML1 to ML4 are multipliers,
AD1 to AD4 are adders, IV is an inverting circuit, ROM is a memory table, VRQ is a reactive current setting device, SH is a Schmitt circuit, and PWMC1 and PWMC2 pulse width modulation control circuits.

First, the comparator C1 outputs the sum voltage command value Vd.
^* And the sum voltage detection value Vd = Vd1 + Vd2 are compared, and the deviation .epsilon.d = Vd ^* Find -Vd. Sum voltage control compensation circuit Gv
The deviation εd is amplified by (s) and the effective current peak value command IPm ^*
Is input to the multiplier ML1. In addition, the reactive current peak value command IQm ^{* is} set by the reactive current setting device VRQ ^. Is input to the multiplier ML2. The memory table ROM is a unit sine wave sinωt synchronized with the detected voltage Vs of the power supply voltage.
And a unit cosine wave cosωt with a phase difference of 90 ° from the voltage
Which are input to the multipliers ML1 and ML2, respectively. That is, the active current command IP ^* is given by the multiplier ML1 ^.
= IPm ^* * Sin ωt is obtained, and the reactive current command IQ ^* is calculated by the multiplier ML2 ^. = IQM ^* ・ Calculate cosωt. Furthermore,
The adder AD1 calculates the sum of the valid and reactive current commands, and the input current command value Is ^* = IP ^* ＋ IQ ^* And The current command value Is ^{* is} output by the comparator C2 ^. And input current detection value I
s and compare the deviation εI = Is ^* -Is is inverted and amplified by the current control compensation circuit G1 (s). The adder AD2 is a signal es ^* for compensating the output signal of the current control compensation circuit GI (s) and the power supply voltage ^. In addition, the AC side generated voltage command value ec ^{* of the} converter And Voltage command value ec ^* Is the voltage command value ea ^{* at} point a via the adder AD3 Pulse width modulation control circuit P
Input to WMC1. Also, the voltage command value ec ^* Is inverted by the inverting circuit IV, and the voltage command value eb ^{* at} point b is added via the adder AD4 ^. Is input to the pulse width modulation control circuit PWMC2. As explained before, the NPC converter a
The voltage Va at the point is the voltage command value ea ^{* at the} point a ^. PWM control is performed so as to be in proportion to the voltage Vb at the point b, and the voltage command value eb ^{* at the} point b ^. PWM control is performed so as to be proportional to. Therefore,
The generated voltage of the converter Vc = Va-Vb is ea ^* -Eb
^* = 2ec ^* The voltage is proportional to.

A differential voltage VL = Vs-Vc between the voltage Vs of the AC power supply SUP and the generated voltage Vc of the converter CNV is applied to the AC reactor Ls, and the input current Is is controlled by adjusting the difference voltage VL. To do.

Is ^* When> Is, the deviation εI has a positive value, which decreases the voltage Vc and increases the input current Is. Conversely, Is ^* When <Is, the deviation εI has a negative value, which increases the voltage Vc and decreases the input current Is.
As a result, Is = Is ^* Is controlled so that

Reactive current command value IQm^* = 0, I
s^* = IP^* And the input current Is is the same as the power supply voltage Vs.
Controlled by a phase sine wave. IQm for simplicity
^* The sum voltage control operation will be briefly described assuming that = 0. Vd^*
> Vd, the deviation εd becomes a positive value,
Effective current peak value command IPm^* To increase. As a result, exchange
Active power supplied from the power source Ps = Vs.Is = Vm.IPm (1-cos2.omega.t) / 2 increases, and the DC voltage Vd increases. Conversely, Vd^* <
When it becomes Vd, the deviation εd becomes a negative value and the active current
Crest value command IPm^* To reduce. As a result, is the AC power supply
The active power Ps supplied from it also decreases and the DC voltage Vd decreases.
Reduce. Therefore, Vd = Vd^* Is controlled to be
It On the other hand, the input current command value Is^* And voltage command ec^* Squared
Input to the calculator ML3, Pc^* = Is^* ・ Ec^* Seeking
It Is = Is^* , Vc = K · ec^* Considering above,
Pc^* Is a value proportional to the instantaneous input power Pc of the converter
Become. This Pc^* Is input to the Schmitt circuit SH,
To determine. That is, Pc^* When ≧ 0, +1 is output,
Pc^* When <0, -1 is output. This schmitt times
Output signal sgn (Pc^* ) Is input to the multiplier ML4
I will be forced.

Further, the differential voltage command value Vo is output by the comparator C3.
^* And the difference voltage detection value Vo = Vd1-Vd2 are compared, and the deviation .epsilon.o = Vo ^* The -Vo is amplified by the differential voltage control compensating circuit Go (s) to obtain the compensation voltage Δe. The compensation voltage Δe is input to the multiplier ML4, and the output signal sgn (Pc ^{* of the} Schmot circuit SH is output ^. ). That is, Pc ^* When ≧ 0, Δe ′ = + Δe Pc ^* When <0, .DELTA.e '=-. DELTA.e, which is input to the adders AD3 and AD4. The differential voltage control operation has been described in detail above, and will be omitted.

Reactive current command value IQm ^* When = 0, the input current Is has a small value under light load or no load. Therefore, even if the compensating voltage Δe for the differential voltage control is given, the current does not easily flow into the DC smoothing capacitor Cd1 or Cd2, and the control response becomes very poor.

FIG. 10 shows the active current command IPm ^*. = 0, reactive current command IQm ^* The voltage-current vector diagram when ≠ 0 is given and input current Is is controlled is shown. When the current Is is applied to lead the power supply voltage Vs, the voltage drop due to the reactor Ls becomes jωLs Is, and the NPC converter is Vs.
And a voltage Vc having the same phase as that of Vc is generated.

FIG. 11 shows the voltage-current waveform in the vector relation of FIG. 10, and the voltage Vc has a phase of 9 with respect to the current Is.
0 degrees ahead. Also, the instantaneous input power Pc of the converter
Is the product of the voltage Vc and the current Is, and its average value is zero.

The above-mentioned compensation voltage Δe 'is the instantaneous power Pc.
The polarity is inverted according to the sign of. Thus, the reactive current I
By flowing Q, the input current Is is secured, and the differential voltage control becomes possible again. However, when the reactive current IQ is passed, the power factor of the power supply deteriorates, so in order to improve the defect, the reactive current command value IQM ^* May be given only during light load operation. 12 is a main circuit configuration diagram showing still another embodiment of the neutral point clamp type converter control device of the present invention.
3 is a control circuit configuration diagram thereof.

In FIG. 12, R, S, T are power receiving terminals of a three-phase AC power source, Tr is a power transformer, LSR, LSS, LST.
Is an AC reactor, CNVR, CNVS, and CNVT are neutral-point clamp type converters (hereinafter referred to as NPC converters) that are single-phase full-bridge connected, Cd1 and Cd2 are DC smoothing capacitors, and LOAD is a load. .

In FIG. 13, C1 to C5 are comparators, Gv (s) is a sum voltage control compensating circuit, GR (s), GS (s), G.
T (s) is an input current control compensation circuit, Go (s) is a differential voltage control compensation circuit, ML1 to ML9 are multipliers, A1 to A6 are adders / subtractors, SH1 to SH3 are Schmitt circuits, and US is a unit sine wave generation circuit. , PWMR, PWMS, and PWMT are pulse width modulation control circuits for converters CNVR, CNVS, and CNVT, respectively.

The R-phase converter CNVR has the same structure as the single-phase NPC converter shown in FIG. The S-phase and T-phase converters are similarly constructed. The primary side of the power transformer Tr is Y-connected, and the secondary winding is separated into two terminals for each phase. The secondary windings of the transformer Tr are connected to the converters CNVR, CNVS, CNVT via AC reactors LSR, LSS, LST, respectively.
Three NPC converters CNVR, CNVS, CNVT
Is the voltage Vd applied to the DC smoothing capacitors Cd1 and Cd2
Three-phase input current IR so that the sum of 1 and Vd2 is almost constant
, IS, IT, and Vd1 = Vd2.

The load LOAD is a DC smoothing capacitor Cd.
1, Cd2 is used as a DC voltage source, and is composed of, for example, a three-phase output NPC inverter INV and an AC motor M. The three-phase NPC inverter INV converts a DC voltage into AC power with a variable voltage and a variable frequency.
To drive. Here, the control operation of the inverter INV is omitted. Next, the control operation of the apparatus shown in FIGS. 12 and 13 will be described.

In FIG. 13, first, the comparator C1 outputs the sum voltage command value Vd ^*. And the sum voltage detection value Vd = Vd1 + Vd2 are compared, and the deviation .epsilon.d = Vd ^* Find -Vd. The deviation εd is amplified by the sum voltage control compensation circuit Gv (S), and the input current peak value command Im ^* To the multipliers ML1 to ML3. Further, the unit sine wave generator US allows three unit sine waves sinω synchronized with the three-phase power supply voltages VR, VS, and VT.
t, sin (ωt−2π / 3), sin (ωt + 2π /
3) is created and input to the multipliers ML1 to ML3, and a three-phase input current command value as shown by the following equation is obtained. That is, IR ^* = Im ^* ・ Sinωt IS ^* = Im ^* ・ Sin (ωt-2π / 3) IT ^* = Im ^* -Sin (ωt + 2π / 3).

The R-phase input current control is performed as follows. That is, the comparator C2 causes the R-phase current command value IR ^*
And R-phase current detection value IR are compared, and the deviation εR = IR
^* -IR is inverted and amplified by the current control compensation circuit GR (S). Output signal eR ^{* of} current control compensation circuit GR (S) Is the adder / subtractor A1
, A2 to become the PWM control input signal of the R-phase converter. The R-phase converter CNVR has the above voltage command value eR ^{* at the} AC side terminal ^. A voltage VCR proportional to is generated to control the R-phase input current IR.

The AC reactor LSR has a difference voltage VLR = V between the power supply voltage VR and the generated voltage VCR of the converter CNVR.
R-VCR is added, and the input current IR is controlled by adjusting the difference voltage VLR.

IR^* > IR, the deviation εR is a positive value
, The voltage VCR is decreased and the input current IR is increased.
It On the contrary, IR^* <IR, the deviation εR is a negative value.
Increase the voltage VCR and decrease the input current IR.
As a result, IR = IR^* Is controlled so that S phase
Also, the input current control of the T phase is performed in the same manner. Also, Waden
Pressure control is performed as follows. Vd^* > When Vd
Deviation εd becomes a positive value, the input current peak value command Im^* To
increase. As a result, the effective power supplied from the AC power source PI = VR.multidot.IR + VS.multidot.IS + VT.multidot.IT = 3.multidot.Vm.multidot.Im / 2 increases to increase the direct current voltage Vd. Conversely, Vd^* <
When it becomes Vd, the deviation εd becomes a negative value and the input current peak
Value command Im^* To reduce. As a result, power is supplied from the AC power supply.
The active power PI to be reduced also decreases the DC voltage Vd.
It Therefore, Vd = Vd^* Is controlled so that one
, The input current command value IR^* , IS^* , IT^* And voltage
Command eR^* , ES^* eT^* To the multipliers ML4 to ML6
Enter each, PCR^* = IR^* ・ ER^*  PCS^* = Is^* ・ ES^*  PCT^* = IT^* ・ ET^*  Ask for. Where IR = IR^* , IS = IS^* , IT
= IT^* Controlled, and VCR = K · eR^* , VCS = K
・ ES^* , VCT = K · eT^* Considering the above, the above PC
R^* , PCS^* , PCT^* Is the input power PC of each phase converter
The value is proportional to R, PCS, PCT. This PCR^* , PCS^*
, PCT^* Is input to the Schmitt circuits SH1 to SH3,
Determine whether it is positive or negative. That is, to explain the R phase, PCR
^* When ≧ 0, +1 is output and PCR^* <0, -1
Is output. The same applies to the S phase and the T phase. This schmidt
Output signals sgn (PCR of circuits SH1 to SH3^* ), Sg
n (PCS^* ), Sgn (PCT^* ) Is the multiplier ML7
 ~ Input to ML9. In addition, the comparator C5
Pressure command value Vo^* And the difference voltage detection value Vo = Vd1-Vd2
And the deviation εo = Vo^* -Vo is a differential voltage control compensation circuit
The compensation voltage Δe is obtained by amplifying with Go (S). Compensation voltage Δ
e is input to the multipliers ML7 to ML9, and
Output signals sgn (PCR of the output circuits SH1 to SH3^* ),
sgn (PCS^* ), Sgn (PCT^* ).
That is, PCR^* When ≧ 0, ΔeR = + Δe PCR^* When <0, .DELTA.eR =-. DELTA.e, which is input to the adder / subtractors A1 and A2, and PCS^* When ≧ 0, ΔeS = + Δe PCS^* When <0, .DELTA.eS =-. DELTA.e, which is input to the adder / subtractor A3, A4, PCT^* When ≧ 0, ΔeT = + Δe PCT^* When <0, .DELTA.eT =-. DELTA.e, which is input to the adder / subtractors A5 and A6. Figure 1
4 is for explaining the control operation of the apparatus of FIGS. 12 and 13.
It is a time chart of. During power running, each phase
The generated voltages VCR, VCS and VCT of the barter are input currents IR and IS.
 , IT, the phase advances by θ.

As described above, the code sgn (PCR ^* of the instantaneous active power of the converter ), Sgn (PCS ^* ), Sgn (P
CT ^* ), The compensating voltage ΔeR, ΔeS of each phase converter
, ΔeT, the difference voltage Vo of the DC voltage
Can be controlled as described in the apparatus of FIG.

However, there are the following differences between single-phase operation and three-phase operation. That is, in the single-phase operation, since the input current IS is an alternating current, when the zero crosses and IS = 0, the difference voltage Vo cannot be controlled even if the compensation voltage .DELTA.e is changed. On the other hand, in the three-phase operation, the input current I of each phase is
Similarly, R, IS, and IT also cross the zero point, but they are out of phase, so that when IR = 0, for example, the differential voltage Vo can be controlled by the S phase and the T phase. That is, the difference voltage Vo is controlled by the absolute value of the input current IS in the single-phase operation, whereas the difference voltage Vo is controlled by the sum of the absolute values of the three-phase input currents in the three-phase operation.

The waveform of the sum of the absolute values of the three-phase input currents is shown at the bottom of FIG. That is, it can be seen that the differential voltage control can be continuously performed, although it varies between 1.5 Im and 1.73 Im with respect to the input current peak value Im. However, when the input current peak value Im itself is zero, the differential voltage Vo cannot be controlled as described above.

FIG. 15 shows a time chart when only the reactive current is passed during the three-phase converter operation. Also in this case, the differential voltage Vo is controlled by the sum of the absolute values of the three-phase input currents, and the differential voltage control can be continuously performed.
Although the three-phase power supply has been described above, it is needless to say that the same can be applied to power supplies having two or more phases.

[0082]

As described above, according to the neutral point clamp type converter control device of the present invention, the sum voltage of two DC smoothing capacitors connected in series is controlled to be substantially constant. It is possible to control the voltages of the two capacitors to be the same. As a result, it is possible to provide a neutral point clamp type converter control device that can tolerate a certain amount of variation in the smoothing capacitor capacity and that serves as a stable DC voltage source against sudden changes in load.

[Brief description of drawings]

FIG. 1 is a main circuit configuration diagram showing an embodiment of a controller for a neutral point clamp type power converter of the present invention and a block diagram of the controller.

FIG. 2 is a time chart for explaining the PWM control operation of the control device of FIG.

3 is a voltage for explaining the operation of the device of FIG. 1,
Current vector diagram.

FIG. 4 is a time chart for explaining the operation of the apparatus shown in FIG.

FIG. 5 is an operation mode diagram for explaining the operation of the apparatus shown in FIG.

FIG. 6 is an operation mode diagram for explaining the operation of the apparatus shown in FIG.

FIG. 7 is an operation mode diagram for explaining the operation of the apparatus shown in FIG.

FIG. 8 is a time chart for explaining the operation of the apparatus shown in FIG.

FIG. 9 is a control circuit configuration diagram showing another embodiment of the NPC converter control device of the present invention.

FIG. 10 is a voltage / current vector diagram for explaining the operation of the device in FIG. 9;

FIG. 11 is a time chart for explaining the operation of the apparatus shown in FIG.

FIG. 12 is a main circuit configuration diagram showing still another embodiment of the NPC converter control device of the present invention.

13 is a configuration diagram of a control circuit for controlling the main circuit of FIG.

FIG. 14 is a time chart for explaining the operation of the apparatus shown in FIGS. 12 and 13.

FIG. 15 is a time chart for explaining the operation of the apparatus of FIGS. 12 and 13.

FIG. 16 is a main circuit configuration diagram of a conventional NPC converter.

FIG. 17 is a time chart for explaining the PWM control operation of the device shown in FIG.

[Explanation of symbols]

SUP: Single-phase AC power supply, LS: AC reactor, CNV: Neutral point clamp type converter body, Cd1, Cd2: DC smoothing capacitor, LOAD: Load, CTS: Input current detector, PTS ...... AC voltage detector, PT1, PT2 ...... DC voltage detector, A1 to A4 …… Adder / subtractor, AVR1 …… sum voltage control circuit, ACR …… input current control circuit, AVR2 …… differential voltage control circuit, ML1 , ML2 ・ ・ ・ Multiplier, AS ・ ・ ・ Sign switcher, PWMC ・ ・ ・ Pulse width modulation control circuit, S11 to S14, S21 to S24, ・ ・ ・ Self-extinguishing element, D11 to D14, D21 to D24, ・ ・ ・ Free Wheeling diode D15, D16, D25, D26, ... Clamping diode

Claims (6)

[Claims] 1. A single-phase AC power source, a neutral point clamp type converter connected to the single-phase AC power source via a reactor, and an output terminal of the neutral point clamp type converter. A first and a second DC smoothing capacitor connected to the load, a load using the DC smoothing capacitor as a DC power source, and a sum voltage of the two DC smoothing capacitors,
A sum voltage control circuit for controlling so as to match the sum voltage command, and an input current control circuit for controlling an input current supplied from the AC power supply by an output signal of the sum voltage control circuit,
A differential voltage control circuit that detects the differential voltage between the two DC smoothing capacitors and controls the voltage to match the differential voltage command value;
A neutral point clamp type converter comprising a circuit for pulse width modulation controlling the neutral point clamp type converter according to the sum of the output signal of the differential voltage control circuit and the output signal of the input current control circuit. Control device. 2. The differential voltage control circuit comprises an input current supplied from the AC power supply and the neutral point clamp type converter.
A means for detecting the sign of the product of the AC voltage generated by the switch, and the sign of the output signal of the differential voltage control circuit is switched according to the signal from the sign detecting means. The control device for the neutral point clamp type converter according to 1. 3. The active current command value provided based on the output signal of the sum voltage control circuit, the input current control circuit,
The neutral point clamp type converter according to claim 1 or 2, wherein the input current supplied from the AC power supply is controlled by the sum of the reactive current command values set separately. Control device 4. A multi-phase (N-phase) AC power supply, a power supply transformer that insulates the multi-phase AC power supply for each phase, and two of the transformers.
N full bridge connection type neutral point converters connected to the next winding via a reactor and the output terminals of the neutral point clamp type converters are connected in parallel and connected to the output terminals. The first and second direct-current smoothing capacitors connected in series, the load using the two direct-current smoothing capacitors as a direct-current power source, and the sum voltage of the two direct-current smoothing capacitors are detected so as to match the sum voltage command. To control the input voltage supplied from the AC power supply by the output signal of the sum voltage control circuit, and the difference voltage between the two DC smoothing capacitors, A differential voltage control circuit that controls the voltage to match the voltage command value; Neutral point clamped converter comprising comprises a circuit for controlling tone - other control devices. 5. The sign of the product of the input current of each phase supplied from the multi-phase AC power source and the AC voltage of each phase generated by the neutral point clamp converter is defined by the differential voltage control circuit. The means for detecting for each phase is provided, and the sign of the output signal of the differential voltage control circuit is switched for each phase according to the signal from the sign detecting means. Control unit for neutral point clamp type converter. 6. The input current supplied from the AC power supply by the sum of an active current command value given based on an output signal of the sum voltage control circuit and a reactive current command value set separately, in the input current control circuit. The control device for the neutral point clamp type converter according to claim 4 or 5, wherein