JP3299718B2 - Self-excited semiconductor power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited semiconductor power converter, and more particularly, to a method in which AC voltages of a plurality of voltage-type self-excited converters are connected in series by an AC winding of a transformer for the converter and added. Self-excited semiconductor power converter multiplexed by

[0002]

2. Description of the Related Art Generally, in a self-excited semiconductor power converter of a multiplex configuration, a plurality of converters are connected in series on the AC side and in parallel on the series side. However, in some applications, it is necessary to connect the DC side in series to increase the DC voltage. In this case, the degree of modulation (amplitude) and the power factor angle of each converter are described as described in "Series connection of voltage-type self-excited converters" in the 2007 National Electrotechnical Industry Conference No. I-51. By changing the (control angle), it is possible to correct and adjust the AC voltage to perform voltage sharing control. For the sake of simplicity, consider the case where two converters are connected in series as shown in FIG. The entire device is controlled by a signal Vc from the control device 200. The pulse control of each converter normally uses PWM (pulse width modulation) control. That is, Vc is input to the PWM pulse generators 21 and 22 of each converter, where ON / OFF pulses of the converters are generated, and the converters 41 and 42 operate accordingly. As a result, the converters 41 and 42 apply the AC voltage V to the DC windings of the converter transformers 51 and 52, respectively.
generate _c1 and _Vc2 . The DC voltage of each converter is E _d1 ,
_Assuming that E _d2 and the conversion power of each converter are P ₁ and P ₂ , the DC current of each converter is

[0003]

I _d1 = P ₁ / E _d1 , I _d2 = P ₂ / E _d2 (1) The AC voltage of each converter is as shown in FIG.

[0004]

V _c1 = K · E _d1 · a ₁ , V _c2 = K · E _d2 · a ₂ (2) K is a proportionality constant (0.612 in sub-harmonic modulation)
), A ₁ and a ₂ are modulation degrees of each converter. Since the AC side of the converter transformer is connected in series, the AC current I _c
Are common

[0005]

P ₁ = √3V _c1 · I _c · cos φ ₁ = √3K · E _d1 · I _c · a ₁ · cos φ ₁ P ₂ = √3V _c2 · I _c · cos φ ₂ = √3K · E _d2 · I _c・ a ₂・ cosφ ₂ (3) Here, φ ₁ and φ ₂ are power factor angles of the respective converters.

[0006] Substituting this into equation (1)

[0007]

[Expression 4] I _d1 = √3K · I _c · a ₁ · cos φ ₁ I _d2 = √3K · I _c · a ₂ · cos φ ₂ (4) When a cos φ of each converter is corrected to this value by ± Δm in the same direction as the alternating current.

[0008]

## _EQU5 ## I _d1 = I _d + △ I _d I _d2 = I _d − △ I _d (5)

[0009]

DC current of each converter can be controlled regulated voltage shared by Equation 6] _{I d = √3K · I c ·} a · cosφ △ I d = √3K · I c · △ m ... (6) Therefore the method .

[0010] Here, phi is the resultant vector and the AC current I _c and forms power factor angle of the transducer 1 and the converter 2.

A method of realizing DC voltage multiplexing is described in
No. 949, "DC voltage balance control in self-excited HVDC DC cascade connection system". This system can generate seven types of voltage vectors as shown in FIG. 4, and in the case of four multiplexing, the converter generates 61 types of output voltage vectors in response to a voltage command. As shown in FIG. 5, a synthesized voltage vector closest to the voltage command vector is selected from the set of output possible vectors. The selected combined voltage vector is a voltage vector Va and V that form an angle of 60 ° with each other and output from the unit converter.
b, and the switching operation of the unit converter is determined by allocating these voltage vectors to each unit converter. In this method, since each unit converter is connected in series in the converter transformer on the AC side, the AC current is common to each unit converter. When a phase is selected such that active power is supplied from the converter to the system as the voltage vector Va, the DC voltage decreases and the voltage vector V
When a phase is assigned as b to inject active power from the system, the DC voltage increases. Therefore, by detecting the DC voltage of each unit converter and allocating a voltage vector in a direction for compensating the deviation from the target value, the DC voltage can be made uniform between stages. However, this method can output only 19 types of output voltage vectors in the case of a two-multiplex converter, so that it is necessary to increase the number of multiplexes in order to perform accurate control. Increasing the number of multiplexes increases the number of transformers for the conversion device, which causes problems such as an increase in cost.

[0012]

As described above, in the above-described control system, it is necessary to apply a voltage sharing adjustment correction voltage in the same direction as the output AC current. However, in the case of a current source converter, the AC voltage is a system voltage and is almost constant and serves as a reference for the phase. In addition, it is necessary to perform voltage sharing control, and there are the following problems.

It is necessary to control the phase of the correction voltage to be in phase with the AC current to be controlled.

Since the DC current of each converter is proportional to the AC current, the effective correction amount varies depending on the magnitude of the AC current. When the current becomes 0, control becomes impossible.

An object of the present invention is to solve this problem.

[0016]

In order to solve the above-mentioned problems, in a self-excited power converter according to the present invention, a voltage difference between a DC voltage of each converter and an average value of DC voltages of all converters is calculated. Generate a correction signal for correcting the AC voltage of each converter,
This correction signal is added to the control signal of the converter, and the AC voltage of each converter is corrected by the addition to adjust the DC voltage, thereby performing control for making the DC voltage equal to the average value. .

Further, in the self-excited power converter of the present invention,
Configured to generate the correction signal from the AC current set value,
The magnitude of the correction voltage vector is made to be inversely proportional to the magnitude of the alternating current.

Further, in the self-excited power converter of the present invention,
A limiter is provided in a control circuit that generates a correction signal from a difference voltage from the average value of the DC voltages of all converters, and the limiter is set so that the correction amount does not become excessive when the AC current is near zero. is there.

As described above, according to the present invention, in a converter in which the DC side of a voltage source self-excited converter for controlling power between AC systems is connected in series and multiplexed, the voltage is controlled so that the phase becomes the same as that of the AC current. Voltage sharing control is performed by generating a sharing control correction voltage and adding it to the AC voltage. The control block is configured to linearize the correction amount in inverse proportion to the magnitude of the current. Furthermore, a control block is configured so that voltage correction is always applied in a region where the current is close to 0, and a voltage correction amount for suppressing fluctuations in DC voltage to a level at which there is no problem because voltage sharing cannot be performed even when control is not applied. Is configured to be applied.

[0020]

FIG. 1 shows an embodiment of the present invention.
This embodiment is a case where the number of converters is two. In FIG. 1, converters 41 and 42, DC capacitors 61 and 62, converter transformers 51 and 52, AC system power supply (hereinafter referred to as system) 10, current transformer 30, voltage detection transformer 20, active power reference A setter 80A and a reactive power reference setter 81B. The other blocks are control blocks necessary for operating this converter normally. The operation will be described in detail below. The instantaneous value of the system voltage is detected from the voltage detecting transformer 20, and the instantaneous value of the system current is detected from the current transformer 30, and the instantaneous P and Q are calculated by the P and Q calculation circuit 16. The instants P and Q are subtracted by the subtracters 31C and 31I from the output P _dp of the active power reference setter 80A and the output Q _{dp of} the reactive power reference setter 80B, respectively, and the deviation is calculated by the APR circuit 110 and the AQR circuit 120. Becomes an active current command I _pk and a reactive current command I _qk that control so as to become 0. Effective current command I
_pk is applied to the lower limiter of the DC voltage control circuit 17. The DC voltage E _d2 of the DC voltage E _d1 transducer 42 of the transducer 41 is detected by DC voltage detector 71 and 72, obtains a DC voltage E _d the converter used in the power conversion by adder 31A taking the difference in the subtracter 31D and the output E _dp DC voltage reference value setter 80C, DC voltage control circuit 17
And of the input signal △ E _d. The DC voltage control circuit 17 works to make the difference ΔE _d zero, and the DC voltage E _d
Make it equal to _dp . Thus, the output I _dk of the DC voltage control circuit 17 is an effective current command value necessary for making the entire voltage equal to the reference voltage. The instantaneous value of the system current detected by the current transformer 30 is calculated by the three-phase / two-phase conversion circuit
After the two-phase conversion, the d / q axis conversion circuit 15 detects the current I _{dh as} the active current axis component and the current I _qh as the reactive current axis component. To perform this detection correctly, a synchronization signal generating circuit 13 for detecting the phase of the system voltage is provided. When the difference between the effective current command I _dk and the effective current axis component I _dh is obtained by the subtractor 31E and applied to the current control circuit 18A, the current control circuit 18A operates to make this difference zero, and as a result, the average DC voltage _Ed
Becomes equal to the average DC voltage reference value _Edp . As the current control circuit 18A, a circuit that performs a proportional-plus-integral operation is often used, but not limited thereto, a circuit that performs various operations is used. Similarly reactive power command I _qk is added to the reactive current axis taken the components I _qh and differential current control circuit 18B by the subtracter 31J. Since the current control circuit 18B operates to make this difference zero, the converter generates reactive power equal to the reactive power reference set value.

On the other hand, in order to perform the DC voltage sharing control of each converter, the following configuration is required. Shared voltage correction amount ΔV shown in FIG. 6, a relationship of the following between the AC voltage V _c1, V _c2 of -ΔV and each transducer and the resultant voltage V _c.

[0022]

(Equation 7)

Here, .DELTA.V is selected to have the same phase as that of the alternating current. Therefore, if K is a proportional coefficient having a resistance dimension, the following relational expression is obtained.

[0024]

(Equation 8)

Where I _d : active current component, I _q : reactive current component, and the AC voltages V _c1 , V _c2 , and ΔV of each converter are expressed by active current and reactive current components.

[0026]

V _P1 = V _d + ΔV _d , V _Q1 = V _q + ΔV _q , V _P2 = V _d −ΔV _d , V _Q2 = V _q −ΔV _q ... (9) From this, the power P ₁ generated in the converter ₁ is

[0027]

[Number 10] _{P 1 ≒ (V d + ΔV} d) · I d + (V q + ΔV q) · I q ≒ (V d I d + V q I q) + (ΔV d I d + ΔV q I q) = P + ΔP .. (10) where P is the power that each converter accommodates and ΔP is the converter 1
Is the power required to share the voltage. Where ΔV
_{d = A · I d / (} I 2 d + I 2 q), ΔV q = A · I q / (I 2 d +
If I ² _q ), the second term in equation (10) is A, which is the same as the power ΔP for DC voltage sharing. That is, in order to perform the DC voltage sharing control, A may be used as an operation amount.
From this, the manipulated variable A is a signal obtained by converting the DC voltage error signal of each converter by the PI block.

In order to stably perform the DC voltage sharing control, the DC voltage detectors 71 and 72 detect the DC voltage E _d1 of the converter 41 and the DC voltage E _d2 of the converter 42, and subtract the difference by a subtractor 31B. Find the DC voltage difference between each inverter,
The voltage is applied to the DC voltage control circuit 11 and the voltage sharing difference voltage ΔE _d1
Get. However, since the voltage sharing control does not work when the output does not flow the system current, the DC voltage control circuit 11 is provided with a limiter for reducing the unbalance of the DC voltage to a predetermined amount or less. In addition, since the voltage sharing is performed by operating the power stored in the DC capacitor of each converter as described above, the operation command is the sum of squares of the active current command value I _dk and the reactive current command value I _qk . , A command value △ E _dp for voltage sharing is created by the square sum circuit 22. Thereafter, in addition to the limiter circuit 19B for setting the current command value shown in FIG. 7 to a fixed value when the current command value is less than the predetermined amount, the voltage sharing voltage difference ΔE _d1 is divided by the divider circuit 23. Effective current command value I _dk ,
Limiter circuit 19 for _setting reactive current command value I _qk to a fixed value
A, signals 25A and 25B passing through 19C and the multiplication circuit 22
A and 22B are multiplied to generate d-axis and q-axis voltage correction signals D _dv and Q _dv . The voltage correction signals D _dv and Q _dv obtained in this way are used by an adder 31F to provide an impedance circuit 21B for performing a voltage drop correction by the output of the d-axis current control circuit and the impedance of the transformer for the converter, and the q-axis current command value I _qk . The feedforward voltage V _{dh of the} d-axis is added from the multiplied output signal and the system voltage by the code shown in FIG.
Then, d-axis voltage command value of three-phase PWM the transducer 41 to adder 31G the D _dv is obtained in this 31F output. Similarly, the q-axis voltage command value is also added by the adder 31K to the impedance circuit 21 for correcting the voltage drop by the output of the q-axis current control circuit and the impedance of the transformer for the converter.
The output signal obtained by multiplying the A and the d-axis current command value I _dk can be obtained by adding the q-axis feedforward voltage V _qh from the system voltage with the sign shown in the figure by the adder 31L. On the other hand, the d-axis voltage command value and the q-axis voltage command value of the converter 42 are inversely calculated by subtracting the voltage correction signals D _dv and Q _dv from the sum of the feedforward voltages V _dh and V _qh and the output of the impedance correction circuit. Gain by doing. In this way, by adding the voltage correction signals in the converter 41 and the converter 42 in reverse, it is possible to prevent the influence of the DC voltage correction on the converter output as a whole.

Using the d-axis voltage command value and the q-axis voltage command value thus obtained, the PWM pulse generation circuits 21 and 22 generate ON / OFF pulses for the converters 41 and 42 to perform DC voltage sharing control. Converter control can be performed. Here, in the present embodiment, the DC voltage sharing control is performed based on the difference voltage of the DC voltage. However, even if the control is performed based on the difference voltage between the DC voltage and the average voltage for each converter, the gain is reduced to one half. Except for this, it is the same as above.

FIG. 2 is a control block diagram of a voltage source self-excited multiplex converter according to a second embodiment of the present invention. In this embodiment,
The DC circuits 41 and 42 of the converter are connected in parallel.
Two circuits are connected in series. Also, converters 41 and 42
The correction signal is generated from the difference voltage between the DC voltage and the average voltage. The other configuration is the same as the configuration of FIG. 1 described above. The DC power supply 70 simulates a converter on the REC side, and supplies power to the converter on the INV side. Even with such an apparatus configuration, it is possible to obtain the same effect as that of the above-described embodiment.

[0031]

According to the present embodiment, since the voltage sharing between the converters connected in series is controlled, the voltage sharing can be equalized. As a result, the converters can be easily connected in series, and there is an effect that a converter in which the DC voltage is increased by the series connection can be easily provided.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment of the present invention.

FIG. 2 is a configuration diagram of a voltage source self-excited multiplex converter according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating another conventional semiconductor power converter.

FIG. 4 is an output vector diagram of a unit converter.

FIG. 5 illustrates the principle of approximation vector output.

FIG. 6 is a voltage sharing control method.

FIG. 7 shows a limiter characteristic for sum of squares.

FIG. 8 shows limiter characteristics.

[Explanation of symbols]

10: AC system, 20: Transformer for voltage detection, 21, 22
... Pulse generator, 30 ... Current transformer, 41,42,43,
44: converter, 51, 52, 53, 54: transformer for converter, 61, 62: DC capacitor, 200: controller.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoichiro Furuseki 3-1-1, Komachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Inside the Hitachi Plant (72) Inventor Toshiyuki Hayashi 2--11, Iwatokita, Komae-shi, Tokyo No. 1 Inside the Central Research Institute of Electric Power Industry Komae Research Center (72) Inventor Masahiro Takasaki 2-1-1, Iwatokita, Komae City, Tokyo, Japan Inside the Komae Research Center Central Electricity Research Institute (56) References JP 9 -37553 (JP, A) JP-A-9-172783 (JP, A) JP-A-7-288197 (JP, A) JP-A-6-233537 (JP, A) (58) Fields investigated (Int. . ^7, DB name) H02M 7/19 H02M 7/155

Claims (3)

(57) [Claims] 1. A self-excited semiconductor power converter in which AC voltages of a plurality of converters are serially connected and multiplexed on an AC winding side of a converter transformer, and DC circuits of the respective converters are connected in series. In the device, a correction signal for correcting the AC voltage of each converter is generated from a difference voltage between the DC voltage of each converter and the average value of the DC voltages of all converters, and the correction signal is used as a control signal of the converter. A self-excited semiconductor power converter, wherein the DC voltage is adjusted by correcting the AC voltage of each converter by the addition, and the DC voltage is adjusted to an average value. 2. The self-excited semiconductor power converter according to claim 1, wherein a correction signal is generated from an AC current set value, and the magnitude of said correction voltage vector is made inversely proportional to the magnitude of the AC current. A self-excited semiconductor power converter, wherein the inversely proportional processing is not performed so that the correction amount does not become excessive when the AC current is near zero. 3. A self-excited semiconductor power converter according to claim 1, wherein a limiter is provided in a control circuit for generating a correction signal from a difference voltage between a DC voltage and an average value of all converters. A self-excited semiconductor power conversion device characterized in that the correction amount is set so as not to become excessive near 0.