JPH0667198B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a power converter including a DC voltage source that receives power from an AC power source and a load device for the DC voltage source.

[Technical background of the invention]

As a load device using a DC voltage source as a power source, there is a pulse width modulation control (PWM) inverter + induction motor, or a DC chipper device + DC motor. As a DC voltage source, there is not much problem when using batteries,
In recent years, when a direct current voltage is obtained from a commercial power source via an AC / DC power converter (converter), reactive power and harmonics generated on the commercial power source side have become a problem.

In order to solve this problem, a method has been proposed in which a pulse width modulation control (PWM) converter is inserted between a commercial power source and a DC voltage source (capacitor) as an AC / DC power converter.

FIG. 6 shows a configuration diagram of a conventional power converter using a PWM converter as an AC / DC power converter.

In the figure, SUP is a single-phase AC power supply, L _s is an AC reactor, CO
NV is an AC / DC power converter (converter), C _d is a DC smoothing capacitor, and LOAD is a load device. The converter CONV is composed of elements (for example, gate turn-off thyristors) S _{1 to} S _{4 having} self-extinguishing ability, wheeling diodes D _{1 to} D ₄ and DC reactors L ₁ and L ₂ and the elements S _{1 to} S ₄ are In order to control the value of the AC side voltage V ₀ , known pulse width modulation control is performed. That is, the converter CONV becomes a pulse width modulation control (PWM) inverter when viewed from the DC voltage source C _d , and in that case, the AC power supply SUP side can be regarded as a kind of load.

The conventional power conversion apparatus controls a current I _s to voltage V _d of the DC voltage source C _d is supplied from the AC power source to be substantially constant, 4 depending on the power demand from the load device LOAD Be capable of quadrant movement.

The input current I _s should always be controlled to be in phase with the power supply voltage V _s so that the input power factor becomes 1.

Also, the input current I _s is controlled in a sinusoidal manner, so that the harmonics are extremely small.

Is a feature.

The control operation of this device will be briefly described below.

The following are prepared as the control circuit. CT ₀ is an AC current detector, R ₁ and R ₂ are voltage dividing resistors for detecting a DC voltage, ISO is an isolation amplifier, VR is a DC voltage setter, C ₁
~ C ₃ is a comparator, G _V (S) is a voltage control compensation circuit, ML is a multiplier, OA is an inverting operational amplifier, G _I (S) is a current control compensation circuit, TRG is a carrier wave (triangular wave) generator, GC Is a gate control circuit.

First, the DC voltage V _d detected through the isolation amplifier ISO
And the voltage command value V _d ^* from the voltage setting device VR are input to the comparator C ₁ to obtain the deviation ε _v = V _d ^* -V _d . The deviation ε _v is input to the control compensating circuit G _v (S) and integrated or proportionally amplified to become the peak value command I _m of the input current I _s .

The peak value command I _m is input to a multiplier ML, is multiplied by the other input sin .omega.t. The input signal sinωt is a unit sine wave synchronized with the power supply voltage V _s = V _m · sinωt, and is obtained by detecting the power supply voltage V _s and multiplying it by a constant (1 / V _m times).

The output signal I _s ^* of the multiplier ML gives the command value of the current to be supplied from the power source, and is given by the following equation.

I _s ^* = I _m · sin ωt (1) The input current command value I _s ^* is inverted by the inverting amplifier OA,
AC current I _c supplied from converter CONV to power supply SUP
Command value I _c ^* of. Hereinafter, I _c ^* is referred to as a converter output current command value.

The converter output current I _c is detected by the alternating current detector CT _c and input to the comparator C ₂ . The command value I _c ^* is compared by the comparator C ₂ and the deviation ε _I = I _c ^* −I _c is obtained. The deviation ε _I is input to the next control compensation circuit G _I (S),
Control input signal for proportionally amplified pulse width modulation control
e _i .

The pulse width modulation control is a known method, and the carrier wave generator TR is used.
This control is performed by G, the comparator C _3, and the gate control circuit GC.

That is, the carrier wave generator TRG has a triangular wave with a frequency of about 1 kHz.
e _T , the comparator C ₃ outputs the triangular wave e _T and the input signal e _i
And the ON / OFF signals are given from the gate control circuit GC to the gate turn-off thyristors S _{1 to} S ₄ according to the deviation ε _T = e _i −e _T.

When e _i > e _T , that is, when the deviation ε _T is positive, the thyristor S
₁ and S ₄ are turned on (at this time, S ₂ and S ₃ are turned off), and the AC output voltage V _c of the converter becomes + V _d .

Further, when e _i <e _T , that is, when the deviation ε _T is negative, the thyristors S ₂ and S ₃ are turned on (at this time, S ₁ and S ₄ are turned off), and V _c = −V _d .

Moreover, if e _i is a positive value and is large, the on period of S ₁ and S ₄ is long, the on period of S ₂ and S ₃ is short, and the average value of V _c is proportional to the input signal e _i . It has a positive value in voltage. Conversely e _i
When is a negative value, the on period of S ₂ and S ₃ is longer than the on period of S ₁ and S ₄ , and the average value of the converter output voltage V _c is a value proportional to the input signal e _i. Becomes the value of.

That is, the converter output voltage V _c is controlled to a value proportional to the input signal e _i .

Converter output current I _c (input current supplied from the power supply
The inverted value of I _s ) is controlled by adjusting the output voltage V _{c of the} converter.

A voltage difference V _L = V _s −V _c between the power supply voltage V _s and the output voltage V _{c of the} converter is applied to the AC reactor L _s .

When V _s > V _c , the power supply current I _s increases in the direction of the arrow in the figure. In other words, the converter output current I _c works so as to decrease in the direction of the arrow in the figure. Conversely, when V _s <V _c , the converter output current I _c works to increase in the direction of the arrow in the figure.

For the converter output current command value I _c ^* , the actual current I _c is
_{When c} ^* > I _c , the deviation ε _I = I _c ^* −I _c becomes a positive value and the PWM control input signal e via the control compensating circuit G _I (S) e
increase _i . Therefore, the converter output voltage V _c also increases in proportion to the input signal e _i , V _c > V _s , and the converter output current I _c increases in the direction of the arrow in the figure. Conversely, I _c ^* <I _c
, The deviation ε _I becomes a negative value and e _i, that is, V _c
Is reduced to V _c <V _s , and the output current I _c is reduced. Therefore, the output current I _{c of the} converter is controlled so as to match its command value I _c ^* . If the command value I _c ^* is changed in a sine wave shape, the actual current I _c is also controlled in a sine wave shape in accordance with the change.

The output current I _c of the converter is the inverted value of the input current I _s from the power supply, and the converter output current command value I _c ^* is the inverted value of the command value I _s ^* of the input current from the power supply. Therefore,
The input current I _s will be controlled following the command value I _s ^* .

Next, the control operation of the voltage V _d of the DC capacitor C _d will be described.

The comparator C ₁ compares the DC voltage detection value V _d with its command value V _d ^* . When V _d ^* > V _d , the deviation ε _v has a positive value, and the input current peak value Im is increased via the control compensation circuit G _v (S). The input current command value I _s ^* is given in the form of a sine wave having the same phase as the power supply voltage, as shown in equation (1). Therefore, _assuming that the actual input current I _s is controlled to I _s = I _s ^* as described above, when the peak value I _m is a positive value, the active power P _s shown by the following equation is simple. It is supplied from the phase power supply SUP to the DC capacitor C _d via the converter CONV.

P _s = V _s × I _s = V _m · I _m (sinωt) ² = V _m · I _m · (1-cos2ωt) / 2 ……
(2) sub connexion, energy -P _S · t is the DC capacitor C _d As a result, the DC voltage V _d rises.

On the contrary, when V _d ^* <V _d , the deviation ε _v becomes a negative value, and the peak value I _m is decreased via the control compensation circuit G _v (S) until I _m <0. Therefore, the active power P _s also has a negative value,
This time, the energy P _s t is regenerated to the power supply from the DC capacitor C _d. As a result, the DC voltage V _d drops and finally
V _d = V _d ^{* is} controlled.

The load device LOAD is, for example, a known PWM inverter drive induction motor or the like, and exchanges electric power with a DC capacitor C _d that is a DC voltage source. When the load device LOAD consumes power, the DC voltage V _d drops, but the above-described control allows the active power P _s to be supplied from the power supply to constantly control V _d ≈V _d ^* . Conversely, when power is regenerated from the load device LOAD (when the induction motor is regeneratively operated), V _d rises once,
By regenerating the active power P _s to the power supply SUP accordingly,
After all, V _d ≈ V _d ^* . That is, the power P _s supplied from the power supply SUP is automatically adjusted according to the power consumption or power regeneration of the load device LOAD.

At this time, the input current I _s is controlled to be a sine wave having the same phase or opposite phase (during regeneration) with the power supply voltage.
At 1, the harmonic component has an extremely small value.

FIG. 7 is a configuration diagram showing another example of a conventional power conversion device.

In the figure, SUP is a single-phase AC power supply, TR is a power transformer, L
_s1 and L _s2 are AC reactors, CONV1 and CONV2 are pulse width modulation control converters, C _d is a DC smoothing capacitor, INV is a pulse width modulation control inverter that converts a DC voltage into a three-phase voltage of a variable voltage variable frequency, and IM is 3 It is a phase induction motor.

The PWM inverter INV and the induction motor IM are DC voltage sources
It becomes a load device of C _d . The control operation of the load device will be briefly described as follows.

The rotation speed N of the induction motor IM is detected by the speed detector PG, the detected value N is compared with the speed command value N ^* , and the speed control circuit SPC controls so that N≈N ^* . SP
The output signal I _L ^* of C gives the command value of the three-phase current I _L supplied to the induction motor IM. Current command value I _L ^* and actual current I _L
Are compared, and I _L ≈I _L ^* by the load current control circuit ALC ^.
Control so that. Inverter side PWM control circuit PW
M _I PWM-controls the inverter INV according to the output signal from the load current control circuit ALC.

On the other hand, the converters CONV1 and CONV2 control the current I _s supplied from the power supply SUP so that the DC voltage V _d of the smoothing capacitor C _d becomes substantially constant, as described in the device of FIG.

That is, the DC voltage command value V _d ^* is compared with the DC voltage detection value V _d , and the voltage control circuit AVC controls so that V _d ≈V _d ^* . The output signal I _s ^* of AVC is the power supply SUP
The current I _s supplied from and the command value are given. The current command value I _s ^* is compared with the input current detection value I _s, and control is performed by the input current control circuit ASC so that I _s ≈I _s ^* . The converter-side PWM control circuit PWM _c controls the converters CONV1 and CONV2 according to the output signal of the input current control circuit ASC.

Here, the converters CONV1 and CONV2 are connected in parallel in order to increase the converter capacity, which is a general method.

In this case, the AC reactors L _S1 and L _S2 serve to balance the currents of both converters and to suppress the pulsation of the input currents I _S1 and I _S2 .

[Problems of background technology]

Such a conventional power conversion device has the following problems.

That is, the pulse width modulation control converter needs to perform a switching operation at the modulation frequency (several kilohertz), and normally a GTO (gate turn off) thyristor or the like must be used. Compared with general thyristors, GTO thyristors have a smaller maximum rated value of withstand voltage or allowable current, so that it is difficult to increase the capacity of the converter.

Therefore, as shown in FIG. 7, a method of increasing the capacity by connecting converters in parallel is adopted. However, since the capacity of each converter is limited, the larger the capacity,
The number of GTO thyristors will increase. Therefore, it goes without saying that the size and shape of the device are large, and the cost of the device is high.

In parallel operation for increasing the capacity of the converters, it is necessary to balance the input currents of the converters. Therefore, it is necessary to insert as many AC reactors as the number of converters on the secondary side of the power transformer. At this time, the AC reactor absorbs the harmonic component contained in the AC-side output voltage accompanying the switching operation of the PWM converter, and serves to suppress the pulsation of the input current supplied from the power supply. However, since the switching frequency (modulation frequency) of each converter is at most several kilohertz, it is necessary to prepare a considerably large inductance value for the AC reactor. That is, in the conventional device, an AC reactor having a considerably large capacity was indispensable for each converter operated in parallel. For this reason, there is a drawback in that the device cannot be made compact and lightweight, and it cannot be applied to applications where the installation location is restricted.

[Object of the Invention]

The present invention has been made in view of the above, facilitates increasing the capacity of the device, and reduces the capacity of the AC reactor,
It is an object of the present invention to provide a power conversion device that is compact, lightweight, and inexpensive.

[Outline of Invention]

According to the present invention, this object is connected to an AC power supply, a plurality of power supply transformers in which primary windings are connected in series to the AC power supply via an AC reactor, and to a secondary winding of the power supply transformer. A plurality of self-exciting converters, a common smoothing capacitor connected to the DC side of the self-exciting converter, and a load device using the smoothing capacitor as a DC voltage source. Only one unit is a pulse width modulation control converter, and the other self-exciting converters are control means for generating an AC rectangular wave voltage including a zero voltage on the AC side during one cycle period of the frequency of the AC power supply; This can be achieved by using a control means for generating a desired AC side output voltage in the entire excitation converter.

Example of Invention

FIG. 1 is a configuration diagram showing an embodiment of the power conversion device of the present invention.

In the figure, SUP is a single-phase AC power supply, L _s is an AC reactor, TR
₁ and TR ₂ are power transformers, CONV1 and CONV2 are self-exciting converters,
C _d is a DC smoothing capacitor, and LOAD is a load device. Here, a pulse width modulation control inverter INV and an induction motor IM are prepared as the load device LOAD.

Two self-excited converter CONV1, CONV2 are connected in parallel at the DC side, AC side is by connexion insulated power transformer TR _1, TR _2. The primary windings of the power supply transformers TR ₁ and TR ₂ are connected in series and are connected to the AC power supply SUP via the AC reactor L _s .

The control of the load device LOAD is the same as that described with reference to the device of FIG. 7, and since it is not the object of the present invention, its description is omitted.

Below, the self-exciting converter CONV1 including the smoothing capacitor C _d
The control operation of CONV2 will be described.

As constituting a control circuit, the power supply current current transformer for detecting the I _s CT _s, the DC voltage setting device VR, comparator C ₁ -C _3,
Voltage control compensation circuit G _v (S), multiplier ML, current control compensation circuit G
_I (S), adder AD, level detector SH, operational amplifier OA
K, a carrier wave generator TRG, and gate control circuits GC ₁ and GC ₂ are prepared.

First, the DC voltage _Vd of the smoothing capacitor _Cd is detected and the comparator
Type in C ₁ . The comparator C ₁ compares the voltage command value V _d ^* from the DC voltage setting device VR with the above detection value V _d , and the deviation ε _v = V _d ^* -V
Output _d . The deviation ε _v is the voltage control compensation circuit G
_It is input to _v (S) and proportionally or integrally amplified, and becomes the peak value command I _m of the input current I _s from the power supply.

The peak value command I _m is input to the multiplier ML and is multiplied by the other input sin ωt. The input signal sinωt is a unit sine wave synchronized with the power supply voltage V _s = V _m · sinωt, and the voltage V _s
Is detected and is multiplied by a constant (1 / V _m times).

The output signal I _s ^* = I _m · sin ωt of the multiplier ML gives a command value of the current I _s to be supplied from the power source, and its inverted value I _s ^* is input to the comparator C ₂ . The comparator C ₂ compares the detected value I _s of the power supply current with the above command value I _s ^* to obtain the deviation ε _I = I _s -I _s ^*
To the next current control compensation circuit G _I (S). For simplicity of explanation, it is assumed here that G _I (S) is just a proportional amplifier.

_One output signal e ₁ of G _I (S) is input to the adder AD and the other is input to the level detector SH.

The level detector SH outputs a signal of "+1" when the input e ₁ is larger than the positive side set level value + e _b, and outputs a "-1" signal when the input e ₁ is smaller than the negative side set level value -e _b. It outputs and outputs a "0" signal in the area of -e _b <e ₁ <+ e _b .

The gate control circuit GC ₂ outputs the output signal e of the level detector SH.
Depending on ₂ , apply ON / OFF signals to the self-exciting converter CONV2. That is, the AC side output voltage V ₀₂ of the self-excited converter CONV ₂ has the following value due to the signal e ₂ .

When e ₂ = “+ 1”, V ₀₂ = + V _{d When} e ₂ = “0”, V ₀₂ = 0 When e ₂ = “− 1”, V ₀₂ = -V _d where 1 of power transformer TR ₂ When the secondary / secondary turns ratio is 2 to 1, the voltage on the primary side of TR ₂ is V ₀₂ ′ = 2 · V ₀₂ .

On the other hand, the output signal e ₂ of the level detector SH is the operational amplifier OA.
It is input to the adder AD via K. Operational amplifier OAK
Is to multiply the input e ₂ by K and output a signal e ₃ = K · e ₂ .

The adder AD adds the output signal e ₁ of the current control compensation circuit G _I (S) and the inverted value -e ₃ of the output signal e ₃ of the operational amplifier OAK, and the input signal e _i = for pulse width modulation control e ₁ -e ₃ is given.

The input signal e _i and the output signal (triangular wave with a frequency of about 1 kHz) e _T from the carrier wave generator TRG are compared by the comparator C ₃ .
In accordance with the deviation ε _T = e _i -e _T , the gate control circuit GC ₁ controls the pulse width modulation of the self-exciting converter CONV ₁ .

As described above, the AC side output voltage V _c1 of the self-excited converter CONV1 has a value proportional to the input signal e _i .

Here, when the primary / secondary turns ratio of the power transformer TR ₁ is 1: 1, the voltage V _c1 ′ on the primary side of TR ₁ is V _c1 ′ = V _c1 .

Accordance connexion, the AC inductor L _s, the power supply voltage V _s and two transformer TR _1, the sum of the primary voltage of the _{TR 2 V c1 '+ V c2} ' and Niyotsute, the voltage V _L represented by the following formula Is applied.

V _L = V _s − (V _c1 ′ + V _c2 ′) = V _s − (V _c1 + 2V _c2 ) When the input current I _s flows in the direction of the arrow in the figure, V _L > 0
By setting I _s , I _s can be increased in the direction of the arrow, and conversely, by setting V _L <0, I _s can be decreased.

Conversely, if the input current I _s was flowing opposite to the arrow direction of FIG. <With 0, it is possible to increase the I _s in the opposite direction to the arrow, V _L Conversely> V _L and 0 By doing
I _s can be reduced.

FIG. 2 shows a voltage-current vector diagram on the AC side of the apparatus of FIG. 1, and the power supply voltage _s is the vector sum of the reactor applied voltage _L and the sum _{c of the} converter output voltages. _s = _L + _c Input current _s and reactor applied voltage _L are orthogonal,
The following relationship holds. _L = jωL _{s s} ω = 2πf _s : The angular frequency of the power supply. In other words, in order to control the input current I _s , the sum of converter output voltage V _c = V _c1 ′ + V _c2 ′ is increased / decreased. It controls by changing V _L.

Fig. 2 (a) is a vector diagram during power running, and AC power supply SU
In this state, power is being supplied from P to the load LOAD side.
_The phase of _L is ahead of the power supply voltage _s by 90 °, and as a result,
The input current _s has the same phase as the power supply voltage V _s . That is, the input power factor is 1.

FIG. 2 (b) is a vector diagram during the regenerative operation, and shows a mode in which electric power is regenerated from the load side to the power source side. _The phase of _L is delayed by 90 ° from _s , and as a result, the input current _s has a reverse phase with respect to the power supply voltage _s . Also in this case, the input power factor is 1
It is said.

That is, in order to always keep the input power factor at 1, it is necessary that the reactor applied voltage _L always keeps an orthogonal relationship with the power source voltage _s , and it is the AC side output voltage _c of the converter that controls it. .

Next, the control operation of the converter output voltage V _c of the device of the present invention will be described.

In the device of FIG. 1, when the maximum value of the output signal e _I of the current control compensation circuit G _I (S) is e _max , the set level value e _b of the level detector SH is And

Therefore, At this time, e ₂ = “+ 1”, and the output voltage V _c2 of the self-excited converter CONV2 becomes + V _d . At this time, the input signal e _i for controlling the pulse width modulation control (PWM) converter CONV1 becomes e _i = e ₁ -e ₃ = e ₁ -Ke ₂ as described above, and the voltage proportional to the control input signal e _i. V _c1 is generated on the AC side of converter CONV1. Here, the proportional constant K of the operational amplifier OAK is set to (2 /
3) If you select e _max , then e _i = e _1- (2/3) ・ e _max × e ₂ = e _1- (2/3) ・ e _max .

Similarly, Then, e ₂ = “-1” and e _i = e ₁ + (2/3) · e _max .

further, In the region of, e ₂ = “0” and e _i = e ₁ .

FIG. 3 shows a time chart showing the above relationship.

The PWM converter CONV1 has a voltage V proportional to e _i in FIG.
Generates _c1 . The maximum value of voltage V _c1 is DC smoothing capacitor C
_d is the voltage V _d of. Therefore, Then V _c1 = + V _d , Then V _c1 = -V _d . Input signal e _i The output voltage V _c1 of the converter CONV1 is e _i
Changes in proportion between -V _d and + V _d . Since the pulse width modulation control is known, it will be omitted.

The output voltage V _c2 of the self-exciting converter CONV2 is the input signal e ₂
Accordingly, when e ₂ = “1”, V _c2 = + V _d e ₂ = “0”, V _c2 = 0 When e ₂ = “− 1”, V _c2 = -V _d .

Therefore, the converter voltage V _c generated on the primary side of the power transformer is Next to Substituting the relation of Therefore, V _c has a value proportional to the output signal e ₁ of the current control compensation circuit G _I (S).

When the current command value I _s ^* is larger than the actual current I _s , e ₁ becomes a negative value, and V _c = V _c1 ′ + V _c2 ′ is set to a negative value, and the input current I _{s is changed.}
To increase.

Conversely, if I _s ^* <I _s , then e ₁ is a positive value and V _c
= V _c1 ′ + V _c2 ′ is made a positive value, and the current I _s is reduced. Eventually, I _s = I _s ^* and settle down.

If I _s ^* is changed in a sinusoidal manner, the actual current I _s is tracked accordingly.
Is also controlled in a sinusoidal manner.

Since the control of the DC voltage V _d is the same as that described above, the description thereof will be omitted.

FIG. 4 is a block diagram showing another embodiment of the device of the present invention.

It consists of three self-exciting converters CONV1 to CONV2,
The converter CONV1 is pulse width modulation controlled, and the other two converters generate a square wave voltage including zero voltage.

The transformer TR _{1 has} a primary / secondary turns ratio of 1: 1 and the transformers TR ₂ and TR _{3 have} a primary / secondary turns ratio of 2: 1.

Therefore, the AC side output voltage V _c of the converter is V _c = V _c1 ′ + V _c2 ′ + V _c3 ′ = V _c1 + 2V _c2 + 2V ₃ .

When the maximum value of the output signal e ₁ of the current control compensation circuit G _I (S) is e _max , the set level value e _b1 of the level detector SH ₁ is (1/5) e
_max, and the set level value of the level detector SH ₂ is (3/5) e _max
And

Self-excited converter CONV2 is Yotsute the input signal e _2, the next voltage V
_c2 is generated on the AC side.

When e ₁ > (1/5) e _max , e ₂ = “1” and V _c2 = + V _d .

When e ₁ <-(1/5) e _max , e ₂ = “− 1” and V _c2 = −V _d .

-(1/5) e _{max When} e ₁ (1/5) e _max , e ₂ = “0” and V _c2 = 0.

Also, the self-excited converter CONV3 occurs to the AC side a voltage V _c3 yo connexion next to the input signal e _4.

When e ₁ > (3/5) e _max , e ₄ = “1” and V _c3 = + V _d .

When e ₁ <-(3/5) e _max , e ₄ = “− 1” and V _c3 = −V _d .

-(3/5) e _{max When} e ₁ (3/5) e _max , e ₄ = “0”, V
_c3 = 0.

The control input signal e _i of the PWM converter CONV1 has a relationship of e _i = e ₁ -e ₃ = e ₁ -K (e ₂ + e ₄ ), and the proportional constant K of the operational amplifier OAK is K = (2
/ 5) ・ Set to e _max .

FIG. 5 shows the control input signals e ₁ , e ₂ , e ₄ and e _i of the device of FIG.
It represents the relationship of. That is, the PWM control input signal e _i is controlled within a range of ± (1/5) e _max with respect to the maximum value e _max of the entire input signal e ₁ .

Here, the transformer primary side voltage V _c of the entire converter of the apparatus of FIG. 6 is obtained as follows.

Therefore, it can be seen that V _c is a voltage proportional to e ₁ .

The control of the DC voltage V _{d and} the control of the input current I _s are the same as those described above.

Although the single-phase power source has been described with reference to FIGS. 1 and 4, it goes without saying that a three-phase power source or another multi-phase power source can be similarly used.

Further, in the above-described embodiment, the primary / secondary turns ratio of the power transformer TR1 on the pulse width modulation control converter side is set to 1: 1 and the power transformer TR2 on the rectangular wave output converter side is set to 1: 1.
Although the description has been made assuming that the secondary / secondary turns ratio is 2: 1, the present invention does not particularly limit the primary / secondary turns ratio of the power transformers TR1 and TR2.

The present invention makes it possible to control the electric power more than the capacity of the pulse width modulation control converter by appropriately sharing the electric power between the pulse width modulation control converter and the rectangular wave output converter. If the ratio is selected as described above, the output voltage waveform of the pulse width modulation control converter has the same peak value of the positive side voltage and the negative side voltage, as can be seen from e _{i in} FIGS. 3 and 5, In other cases, if one peak value decreases (increases), the other peak value increases (decreases) and becomes unequal, and the capacity that the pulse width modulation control converter bears increases with respect to the total capacity. However, both converters share the power.

〔The invention's effect〕

As described above in detail, according to the present invention, only one self-exciting converter is controlled by pulse width modulation, and the other self-exciting converters are AC rectangular wave voltage including zero voltage in one cycle period of the power supply frequency. It may be controlled so that is generated only once.

Therefore, it is necessary to use a GTO thyristor for the pulse width modulation control self-exciting converter, but for other self-exciting converters, for example, a thyristor converter having a forced commutation circuit can be sufficiently controlled. Therefore, the capacity can be easily increased, and the switching loss can be reduced.

Further, according to the device of the present invention, the primary side of the power transformer is connected in series, and is connected to the power source via the AC reactor L _s . Therefore, only one AC reactor L _s is required, and the sum of the output voltages of the other self-excited converters including the PWM converter is applied, so that the voltage ripple is reduced and the capacitance of the AC reactor L _s is reduced. Can be reduced.

Further, in the device of the present invention, if the primary / secondary turns ratio of the power transformer of the PWM converter is n: 1 and the primary / secondary turns ratio of the other self-excited converter is 2n: 1, the PWM
The peak value on the positive side and the peak value on the negative side of the output voltage of the converter become equal. For example, in the device of FIG. 1, the capacity of the PWM converter is 1/3 of the total capacity, and
In the device of FIG. 4, it is sufficient to prepare a PWM converter having a capacity of 1/5 of the total capacity. In this case, the capacity of the PWM converter with respect to the total capacity is minimized. That is, one of the N self-exciting converters is PW
If it is an M converter, its capacity is 1 / (2N- of the total capacity.
1) will be enough. Therefore, it is possible to reduce the proportion of the PWM converter whose capacity is difficult to increase, and accordingly reduce the switching loss, so that an efficient power conversion device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the power converter of the present invention, FIG. 2 is a voltage-current vector diagram for explaining the operation of FIG. 1, and FIG. 3 is a control operation of FIG. FIG. 4 is a block diagram showing another embodiment of the device of the present invention, FIG. 5 is a time chart for explaining the control operation of FIG. 4, FIG. 6 and FIG. FIG. 4 is a configuration diagram showing a conventional power conversion device. SUP… AC power supply L _s … AC reactor TR ₁ , TR ₂ , TR ₃ … Power transformer CONV1, CONV2, CONV3… Self-exciting converter C _d … DC smoothing capacitor LOAD… Load VR… DC voltage setter C _{1 to} C ₃ … Comparator AD… Adder G _v (S)… Voltage control compensation circuit G _I (S)… Current control compensation circuit ML… Multiplier SH, SH ₁ , SH ₂ … Level detector OAK… Operational amplifier TRG… Carrier wave generator GC1, GC2, GC3 ... Gate control circuit

Claims (2)

[Claims] 1. An AC power supply, one first power supply transformer and one or more second power supply transformers in which primary windings are connected in series to the AC power supply via an AC reactor, and A first self-exciting converter for pulse width modulation control in which an AC side terminal is connected to the secondary winding of the first power transformer, and an AC in which an AC side terminal is connected to the secondary winding of the second power transformer. One or more second self-exciting converters that generate a rectangular wave voltage, a common smoothing capacitor connected between the DC side terminals of the self-exciting converters, a load device that uses the smoothing capacitor as a DC power source, and the smoothing device. A voltage control compensation circuit to which a deviation signal between the set value of the capacitor voltage and the detected value of the smoothing capacitor voltage is applied, and an output signal of the voltage control compensation circuit is multiplied by a unit sine wave signal synchronized with the AC power supply voltage. The AC power supply A multiplier for outputting an alternating current reference signal of the flowing alternating current; and a difference signal between the alternating current reference signal and a detected value of the alternating current flowing in the alternating current power source, applied between the primary winding terminals connected in series. A current control compensating circuit for outputting a command value of the AC output voltage synthesized by the both self-exciting converters, and having a zero voltage period in synchronization with the AC output voltage command value to which the AC output voltage command value is applied. Control means for calculating one or more rectangular wave signals and generating an AC rectangular wave voltage proportional to the rectangular wave signal on the AC side of the second self-exciting converter; the AC output voltage command value; A power conversion device comprising control means for performing pulse width modulation control of the first self-excited converter using a signal having a difference in signal proportional to one or more rectangular wave signals as a pulse width modulation input signal. 2. A primary / secondary winding ratio of the first power transformer is set to n: 1, and a primary / 2 of the second power transformer is set.
The power conversion device according to claim 1, wherein the next turns ratio is set to 2n: 1.