JPH05184154A - Parallel operation controller for ac output converter - Google Patents

Abstract

PURPOSE:To divide a current quickly with good balance in a power supply system comprising a plurality of parallel connected instantaneous control type AC output converters which is operated in parallel with a common load. CONSTITUTION:A transversal current DELTAI1 flowing between converters is detected through a current detecting circuit 406 and delivered to a vertual impedance circuit 405 for limiting transversal current where a value ZXDELTAI1 is determined. A signal representing the value ZXDELTAI1 is then subtracted, by means of a subtractor 504, from a bus voltage command value V* to produce a signal V*1(=V*-ZXDELTAI1) which is employed as a command value for an instantaneous voltage control circuit 403. On the other hand, a converter 411 takes out components substantially dependent on the output phase difference between converters from the transversal current DELTAI1 and varies frequency reference signal outputted from a voltage controlled oscillator 412 so that the traversal current is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for controlling the current balance between converters in a power supply system in which a plurality of AC output converters such as inverters are connected in parallel and are operated in parallel for a common load. Is.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram showing a conventional parallel operation system of AC output converters shown in, for example, Japanese Patent Publication Nos. 53-36137 and 56-13101.

In the figure, the No. 1 inverter device 1 supplies electric power to the load 4 while operating in parallel through the No. 2 inverter device 2 and the output bus 3 having the same structure. The No. 1 inverter device 1 is an inverter body 100 and a filter reactor 10
1, the same capacitor 102 as a main component, DC power supply 5
Is converted into alternating current and is connected to the output bus bar 3 through the output switch 103a. In order for the inverter devices 1 and 2 to operate in parallel, the detection signal I _1a is obtained from the output current I ₁ of the No. 1 inverter device by the CT 200a, and the difference from the detection signal I _{2a also} obtained from the No. 2 inverter device 2, That is, the signal ΔI ₁ corresponding to the cross current is obtained by the cross current detection circuit 151.
Next, from the phase shifter 150, two orthogonal voltage vectors E _A
And make E _B, [Delta] I ₁ signal from the arithmetic circuit 152, 153 the active power corresponding component and the reactive power corresponding component ΔQ respectively by Δ
Get P. The inverter is a voltage setting circuit 7 and a voltage feedback circuit
Based on the signal of 300, the voltage control circuit 403 controls the internally generated voltage by performing pulse width modulation of the inverter main body 100 via a pulse width modulation circuit (hereinafter referred to as PWM circuit) 400.

The reactive current corresponding component .DELTA.Q is given to the voltage control circuit 403 as an auxiliary signal, and operates by adjusting .DELTA.Q to zero by adjusting the internally generated voltage of the inverter body 100 by several percent.

On the other hand, the active power corresponding component ΔP is the PLL
(Phase-locked loop) Amplifier 154 that constitutes the circuit
By finely adjusting the frequency of the reference oscillator 155, the phase of the internally generated voltage of the inverter main body 100 is controlled, and the operation is performed so that ΔP becomes zero.

In this way, since the voltage and phase are controlled so that both ΔQ and ΔP are zero, cross current between the two inverters is eliminated, and stable load sharing is performed.

[0007]

Since the conventional parallel operation system of converters is constructed as described above, there are the following three problems. The first problem is that it is difficult to improve the control response speed in order to balance the shared currents by controlling the phase of the internally generated voltage of the inverter and the average value of the voltage. This is something that cannot be done. The second problem is that the crossflow control cannot be performed at high speed because a filter is required when separately detecting the crossflow into the effective component and the ineffective component. Therefore, there is a limit to the application of high-speed voltage control systems such as instantaneous waveform control that keeps the output of the inverter a high-quality sine wave with less distortion. The third problem is
It is difficult to operate the converter and the other power source in parallel, and it is particularly difficult to control the cross current even when trying to operate the converter and the power system in parallel.

The present invention has been made to solve the above problems, and provides a parallel operation control device for an AC output converter that balances shared currents at high speed.

Another object of the present invention is to provide means that can be applied to not only inverters but also parallel operation of other instantaneous control type AC output converters.

[0010]

A parallel operation control device for an AC output converter according to the present invention provides a voltage control circuit for an instantaneous control type AC output converter, which outputs a signal corresponding to a cross current component of a current flowing between the converters. And to change the oscillation frequency of the voltage reference oscillator of the converter.

[0011]

In the parallel operation system of the AC output converter by the parallel operation control device according to the present invention, the voltage control circuit operates so as to reduce the cross current between the converters or between the converter and another power supply. Further, the oscillation frequency of the voltage reference oscillator is changed so that a cross current due to the output voltage phase difference between the converters or between the converter and another power supply does not flow.

[0012]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, No. 1 inverter device 1
Supplies electric power to the load 4 while operating in parallel through the output busbar 3 and the No. 2 inverter device 2 of the same configuration which is simplified in the drawing. Reference numeral 5 is a DC power source connected to the No. 1 inverter device 1, and 6 is a DC power source connected to the No. 2 inverter device 2. In addition, although the same numbers are given to the functions corresponding to those in FIG. 10 described above, while FIG. 10 shows an inverter device of the type that controls the average value of the output voltage, FIG. Since it is an inverter device of the type that controls the average value, circuits with the same number do not necessarily have the same function.

Numbers from 100 onward are constituent elements of the inverter device. Numbers without suffixes and numbers with suffix a are constituent elements of the inverter device 1 and suffixes with number b are inverters 2. It is a component of the device 2.

Reference numeral 100 denotes an inverter body, which is composed of, for example, a self-extinguishing element such as a transistor or a MOSFET capable of high-frequency switching, and is a three-phase bridge inverter as shown in FIG. 2A or as shown in FIG. Each single-phase bridge inverter arm has an output frequency (eg 60
It switches at a high frequency of 10 times to several hundred times of (Hz), and converts a DC voltage to a rectangular high-frequency AC voltage containing a sinusoidal fundamental wave. Reference numerals 101 and 102 denote a reactor and a capacitor that form a low-pass filter, which remove harmonics from the rectangular-wave-shaped high-frequency AC voltage generated by the inverter body 100 to obtain a sine-wave output voltage and output the output switch 103a. It is connected to the output bus bar 3.

200a is the output current I _{1 of the} No. 1 inverter device.
201 is a current sensor for detecting the output current I _A1 of the inverter main body 100. Reference numeral 300 is a voltage sensor that detects the voltage of the capacitor 102 (it becomes the output bus voltage during parallel operation).

Reference numeral 400 denotes a PWM circuit that determines the switching timing of the inverter main body 100. For example, a triangular wave comparison type PWM that switches the inverter main body 100 at the intersection of the voltage command signal for the fundamental wave to be output by the inverter main body 100 and the triangular wave carrier. Circuit. 401 is an instantaneous current control circuit for controlling the output current I _A1 of the inverter body 100. Reference numeral 402 is a limiter circuit that limits the output current command value of the inverter main body 100. 403 is the capacitor 102
It is an instantaneous voltage control circuit for controlling the voltage of. Reference numeral 404 is a capacitor current reference generation circuit that outputs a current value to be passed through the capacitor 102 to generate a desired output voltage. 40
Reference numeral 5 denotes a cross current limiting virtual impedance circuit for virtually inserting the impedance Z between the No. 1 inverter device 1 and the No. 2 inverter device 2 to operate so as to limit the cross current. Reference numeral 406 is a current detection circuit for detecting a cross current output from the No. 1 inverter device 1 and a load current value to be shared.

Reference numeral 407 is a multiplier that creates an instantaneous voltage command value of the voltage to be output from the No. 1 inverter device 1. An average voltage control circuit 408 controls the average value of the output voltage of the No. 1 inverter 1. Reference numeral 409 is a voltage setting device that gives an average command value to the voltage control circuit. 410 is the voltage detector 300
Is an average value circuit for deriving an average value of the voltage of the capacitor 102 from the output of. Reference numeral 411 is a converter that detects a component due to the voltage phase difference of the cross current detected by the current detection circuit 406. 412 is a voltage controlled oscillator whose oscillation frequency changes according to the detection signal of 411.

Reference numerals 500, 501, 502, 503, 504 and 505 are adder / subtractors.

The No. 2 inverter device 2 has the same structure as the No. 1 inverter device 1, and the output is connected in parallel with the No. 1 inverter device 1 through the output bus bar 3, and 103b is the output switch of the No. 2 inverter device 2. , 200b are current sensors for detecting the output current I ₂ of the No. 2 inverter device 2.

FIG. 3 is a block diagram showing the details of the current detection circuit 406. 406s and 406t are adder / subtractors, and 406u is an amplifier circuit having a gain of 1 / n where n is the number of parallel inverter devices. Adder output current I ₁ of the No. 1 inverter device 1 and adding the No.2 inverter device 2 of the output current I ₂ in search of the load current I _L at 406S, amplifying circuit 406u this signal
To the load current I _L in parallel with n (in this case n
= 2), the value I _L / n is calculated, and this is output as the load current I _L1 ^* to be shared by the No. 1 inverter device 1. Further, the subtracter 406t, 1 No. inverter device 1 of the output current I ₁ and the current I _L1 ^* difference to be shared, i.e., the cross current _{ΔI 1 (= I 1 -I L1} *) to the operation output.

Next, the operation will be described.

This inverter device is provided with a current minor loop, and the instantaneous current control circuit 401 is connected to the inverter body 10 fed back by the current sensor 201.
The output current I _{A1 of} 0 is the current command I from the limiter circuit 402.
The command value of the voltage to be applied to the reactor 101 is output so as to match _A1 ^* . Since the output bus 3 has a voltage from the capacitor 102 and the No. 2 inverter device 2, in order to apply a desired voltage to the reactor 101,
It is necessary that 100 generate the sum of the voltage of the output bus 3 and the voltage to be applied to the reactor 101. Therefore, the voltage detector
Voltage and current control circuit 40 of capacitor 102 detected by 300
The output of 1 is added by the adder 500, and this signal is given to the triangular wave comparison type PWM circuit 400 as a voltage command.

The capacitor current reference generation circuit 404 generates a sine wave current reference 90 degrees in phase ahead of the voltage command V ₁ ^* of the capacitor 102 according to the capacity of the capacitor 102, as a current to flow through the capacitor. It will be described later that the voltage command V ₁ ^* of the capacitor 102 is obtained from the output of the subtractor 504. The instantaneous voltage control circuit 403 uses the voltage command V ₁ ^* of the capacitor 102 and the capacitor detected by the voltage detector 300.
The signal calculated by the subtractor 503 of the deviation from the voltage of 102 is input, and in order to reduce this deviation, the inverter main unit 10
0 outputs the correction current signal that should be output.

Output current command value I _{A1 of the} inverter body 100
^{* Indicates} the output of the capacitor current reference generation circuit 404 and the instantaneous voltage control circuit 403, and the load current sharing command value I _L1 ^* of the first inverter device 1 output by the current detection circuit 406 to the adder 50.
The signal is calculated by 2 and the result is limited by the limiter circuit 402. Therefore, in the no-load state, the inverter main body 100 supplies the current that should flow to the capacitor 102 to establish the no-load voltage. In this case, the instantaneous voltage control circuit 403 controls the current control error and the capacitor 102
The excess or deficiency of the output of the capacitor current reference generation circuit 404 caused by the error between the design value and the actual value of the capacitance of is corrected.
Next, when the load 4 is turned on, a command (I _L1 ^* ) is given from the current detection circuit 406 to the current minor loop so as to share 1/2 of the load current I _L , and each inverter outputs the load current. It will be divided into halves. Here, the limiter circuit 402 limits the command value to the current control circuit 401 to a current allowable value of the inverter body 100 or less so that the inverter body 100 does not supply an overcurrent such as a rush current at the time of starting the load.

With this configuration, the inverter is protected against overcurrent by its own current minor loop, and the output voltage is always sinusoidal by quickly following the distortion or sudden change of the load current. You can keep on the waves. The characteristic of this method is that such control is performed each time the high frequency PWM switching of the inverter is performed.
The response is very fast. For example, when a switching frequency of 10 kHz is used, control is performed every 100 μsec, so transient phenomena due to disturbances such as sudden changes in load are approximately
Completed in about 10 times 100 μsec, and excellent control performance can be obtained.

When the response and accuracy of the voltage control system of the No. 1 inverter device 1 and that of the No. 2 inverter device 2 are exactly the same, the cross current does not flow in the above control system configuration, but in reality the accuracy and control of the components are controlled. Due to variations in gain, main circuit constants, etc., stable parallel operation with less cross current is difficult if left unchanged. For example, the voltage sensors of the first inverter device 1 and the second inverter device 2 are -0.5% and + 0.5%, respectively.
If the wiring impedance between the inverters is 1% or less, the cross current will flow 100% or more.

The present invention suppresses the cross current by configuring the control circuit so that the impedance exists only for the cross current flowing between the inverters as follows. The virtual impedance circuit 405 for limiting the cross current is Δ
I ₁ × Z (ΔI ₁ is a cross current: I ₁ −I _L1 ^* , Z is a virtual impedance transfer function) is calculated, and this signal is output by the subtractor 504 from the multiplier 407 to output voltage command value V ^* Subtract this from voltage command V ₁ ^* of capacitor 102
And The voltage of the capacitor 102 instantaneously follows the voltage command V ₁ ^* by the voltage control system described above.

Now, with reference to FIG. 4, it will be described that the virtual impedance circuit 405 for limiting the cross current causes the inverter to have an output impedance of Z only for the cross current and operate as a low impedance voltage source for the current components other than the cross current. .. FIG. 4 is a simplified block diagram of the instantaneous cross current control unit of FIG. 1. In the figure, 700a and 700b are derived from the voltage command values V ₁ ^* and V ₂ ^{* of the} _first inverter device 1 and the second inverter device 2, respectively. Shows the transfer function up to the output voltage,
Reference numerals 701a and 701b show blocks of a portion for creating the output voltage reference V ^* of the first inverter device 1 and the second inverter device 2, respectively. The other numbers have already been described in FIG. 1 described above, and the same numbers are given to the same functions. Some symbols have already been used, but the following symbols will be defined again. V _B : Output bus voltage V ^* : Output voltage command value V ₁ ^* : No. 1 inverter capacitor voltage command value V ₂ ^* : No. 2 inverter capacitor voltage command value _IL : Load current I ₁ : No. 1 inverter output current I ₂ : No. 2 inverter output current ΔI ₁ : No. 1 inverter cross current (= I ₁ −I _L / 2) ΔI ₂ : No. 2 inverter cross current (= I ₂ −I _L / 2) G ₁ : No. 1 inverter voltage control system transmission Function G ₂ : No. 2 inverter voltage control system transfer function Z: Cross current limiting virtual impedance value Using these symbols, a relational expression showing the effect of the cross current limiting virtual impedance is derived next.

From Kirchhoff's law, the following equation holds. I _L = I ₁ + I ₂ (1) From the formula (1), ΔI ₁ and ΔI ₂ are as follows. ΔI ₁ = I ₁ −I _L / 2 = (I ₁ −I ₂ ) / 2 (2) ΔI ₂ = I ₂ −I _L / 2 = (I ₂ −I ₁ ) / 2 (3) ΔI ₂ = − ΔI ₁ (4) From FIGS. 4 and (4), V ₁ ^* and V ₂ ^* are as follows. V ₁ ^* = V ^* −Z × ΔI ₁ (5) V ₂ ^* = V ^* −Z × ΔI ₂ = V ^* + Z × ΔI ₁ (6) From the definitions of G ₁ and G ₂ , the following formula is established. V _B = V ₁ ^* × G ₁ (7) V _B = V ₂ ^* × G ₂ (8) From the equations (5) to (8), the following equation is established. ^{_{V B = V * × G 1}} -Z × ΔI 1 × G 1 (9) V B = V * × G 2 + Z × ΔI 1 × G 2 (10) (9) - from (10), the [Delta] I ₁ The formula is as follows. When the equation (9) + (10) is obtained and divided by 2, the following equation is obtained.

From the equation (11), it is understood that the cross current can be suppressed by the virtual impedance value Z. That is, G ₁ , G ₂
Since the gain can be made approximately 1 at the output frequency by configuring the voltage control system with the instantaneous voltage control type as described above, equation (11) becomes the following equation. When the output voltage difference between the individual inverter devices in the case of the islanding operation is ΔV, the equation (13) becomes the following equation. For example, if ΔV is 1% and Z = 50% is selected, the cross current is ΔV / (2 × Z) = 1% / 100% = 1%.

Next, the second term on the right side of the equation (12) becomes the following equation when the equation (13) is substituted. Since ΔV is as small as about 1%, it can be considered that (ΔV) ² ≈0. Therefore, the equation (12) has only the first term on the right side and becomes the following equation. From the equation (16), the bus voltage V _B during parallel operation is the average value of the output voltage of each inverter device during independent operation, and the virtual impedance value Z has no effect.

Z may be any transfer function as long as it has an appropriate impedance value for limiting the cross current at the output frequency. For example, if this circuit is a proportional circuit, Z is a resistor, if it is a differentiating circuit, Z is a reactor, and if it is an integrating circuit, Z is a capacitor.
If it is a combination circuit of integration and differentiation, Z operates as a combination circuit of a resistor, a capacitor, and a reactor.
Further, Z is a circuit including a nonlinear element such as a positive / negative asymmetric limiter, which can stably limit the cross current as long as it has an appropriate impedance value for limiting the cross current at the output frequency.

In the above description, the current and the voltage are vector quantities for the sake of simplification, but the same relationship holds even for vector quantities.

If the No. 1 and No. 2 inverter devices are operated in parallel only by the virtual impedance Z, the voltage difference Δ between the two is as described above.
A cross current of ΔI = ΔV / (2 × Z) flows with respect to V. This active current component of the cross current is reversibly converted by the inverters. Therefore, for example, when two inverters are operating in parallel with no load, the DC power source of one inverter is changed to the DC power source of the other inverter. Active power will flow. When this active power cross current becomes larger than the loss of the inverter and the DC power supplies 5 and 6 cannot regenerate power like a thyristor rectifier, the inflow of this active power raises the DC voltage, resulting in overvoltage. There is a risk of becoming.

Next, in order to suppress such an inflow of active power and stably operate in parallel without a DC overvoltage,
The inverter frequency control by ΔI _1P will be described.

From equation (14), the cross current ΔI ₁ is Is. FIG. 5 shows a vector diagram when the absolute values of V ₁ ^* and V ₂ ^* are completely the same and the phase of V ₂ ^* lags the phase of V ₁ ^* by θ. Here, if the resistance component of the virtual impedance Z is R and the reactance component is X, it can be expressed as Z = R + jX, and its impedance angle α is α = argZ = tan ⁻¹ (X / R) (17) .. If Z has only reactance,
R = 0 and α = 90 °.

From FIG. 5, each of the cross current components ΔI ₁ and ΔI ₂
Among the components, the component due to the voltage phase difference between the voltage command values V ₁ ^* and V ₂ ^* is the cross current component ΔI based on the virtual voltage vector Er obtained by delaying the phase of the load bus voltage vector V _B by α. ₁ , invalid portion of ΔI ₂ (component perpendicular to Er)
It turns out to be equal to.

Returning to FIG. 1, the description will be continued. Reference numeral 411 is a converter that extracts a component ΔI _1P (DC signal) perpendicular to the virtual voltage vector Er from the cross current ΔI ₁ detected by the current detection circuit 406, and is composed of, for example, a synchronous rectification circuit or a multiplier and a smoothing filter.

On the other hand, the output voltage of the inverter device is subtracted from the reference voltage output from the voltage setting device 409 by the adder / subtractor 505 as a feedback voltage of the average value via the voltage detector 300 and the average value circuit 410.

The voltage controlled oscillator 412 generates a sine wave signal sinωt which serves as a phase reference of the output voltage. The oscillation frequency ωt changes according to ΔI _1P , and when the active power component of the cross current is positive, that is, when the active power is flowing out from the inverter, the frequency is lowered. Then, the output voltage phase of the inverter is relatively delayed, so that the outflow of active power is suppressed. On the contrary, when the active power component of the cross current is negative, that is, when the active power is flowing into the inverter, the frequency is raised to suppress the inflow of the active power.

The multiplier 407 receives the absolute value of the output voltage reference | V ^* | output from the average value voltage control circuit 408 and the sine wave signal sinωt output from the voltage controlled oscillator 412, and outputs the output voltage command. The value V ^* = | V ^* | .sinωt is output. This signal V ^* is input to the subtractor 504 as a command value.

As described above, the output frequency is controlled by the component ΔI _1P caused by the difference in absolute value of the voltage of the cross current ΔI ₁ between the inverters, and the cross current is controlled so as to be reduced. It should be noted that this control may be performed relatively slowly within the range where the cross flow is not harmful.

Although the control method of FIG. 1 described above is an example of a single-phase inverter, it can be applied to a three-phase inverter by providing a similar control circuit for each phase or for two phases.

In the above description, two inverters having the same capacity have been described for the sake of simplicity, but the present invention can be applied to parallel operation of n converters having different capacities. In this case, all converters may be configured to share the load in proportion to the capacity.

Example 2. Next, regarding the method that has a common oscillator and controls the frequency by individual frequency adjusters,
This will be described with reference to FIG.

In the figure, 413 is a voltage-frequency converter for converting the signal ΔI _1P output from the converter 411 into a frequency signal. The component ΔI _1P is a component of the current ΔI ₁ perpendicular to the voltage Er.

Reference numeral 420 denotes a common oscillator that serves as a reference for the output frequency of each inverter, and its output is sent to each inverter device. Reference numeral 411 is a frequency adder / subtractor, which adds or subtracts the output signal of the voltage-frequency converter 413 to the frequency signal of the oscillator 420 to create a sine wave signal sinωt serving as the phase reference of the output voltage. With this signal, the output voltage command value V ^* = | V ^* | .sin by the multiplier 407
The generation of ωt is the same as in the first embodiment.

Therefore, in the embodiment of FIG. 6, the output frequencies of the No. 1 inverter unit 1 and No. 2 inverter unit 2 are controlled by the common oscillator 420, and the adder / subtractor is used for controlling the cross current.
Since it is slightly changed by 414, the frequency difference between the parallel inverter devices can be maintained within a certain range and the accuracy of the output frequency can be improved. Note that this control may also be relatively slow.

Example 3. Next, an example in which the present invention is applied to a system in which a converter and another power supply system are operated in parallel will be described with reference to FIG.

FIG. 7 shows an inverter device 1 and an AC power supply system 8
6 is a block diagram showing a configuration in which and supply electric power to a load 4 while operating in parallel via an output busbar 3. FIG. It should be noted that parts of the inverter 1 that are substantially similar to those in FIG. 1 or 6 are simplified and shown.

103s is a switch on the AC power supply system side, 200s is a current sensor for detecting the current Is of the AC power supply system 8, 415 is a current sharing circuit for determining the current shared by the inverter device 1, 415s and 415t are adder / subtractors, 415u is a gain β that determines the current sharing ratio β (0 ≦ β ≦ 1) shared by the inverter device.
416 is a PLL circuit synchronized with the output bus 3
A (phase-locked loop) circuit, 417 is an oscillator that generates a sine wave signal sinωt based on the output of the PLL circuit.

The current sharing circuit 415 adds the output current I ₁ of the inverter device ₁ and the current Is of the AC power supply system 8 to the adder 41.
The load current I _L is calculated by adding for 5 s, and this signal is amplified.
415u is multiplied by β and output as a load current I _L1 ^* to be shared by the inverter device 1. The inverter device 1 operates to supply the command value I _L1 ^* output from the current sharing circuit 415, as in the embodiment of FIG. β may be determined from the ratio of the capacity of the inverter device to the capacity of the load, and if it is continuously changed by a command from the outside, the sharing of the load current between the inverter device and the AC power supply system can be moderated. It can also be transferred.

In this embodiment as well, the operation is performed so that there is no voltage difference or phase difference between the voltage of the inverter device and the voltage of the AC power supply system, so that the cross current ΔI ₁ becomes substantially zero and is controlled by the virtual impedance Z.

In the embodiment described above, the controllability is improved by giving the current minor loop command value the current value that should flow to the parallel capacitor 102 of the output filter of the inverter. The current reference generation circuit 404 may be omitted. This is because the voltage control circuit 403 operates so that the output voltage of the No. 1 inverter device 1 matches the output voltage reference V ₁ ^*, and as a result, generates a signal replacing the capacitor current reference signal, the control of the sine wave inverter is performed. This is because the system operates without any problems. In this case, the deviation of the voltage control becomes smaller when the amplification rate of the voltage control circuit 403 is sufficiently large.

Further, in the above description, the case where the control circuit is of the instantaneous voltage control type having the current minor loop has been described, but the voltage control capable of controlling the output voltage at high speed without the current minor loop. If it is a system, the AC output converters can be stably operated in parallel by adding a virtual impedance circuit for limiting the cross current.

Example 4. In the above description, the case where the present invention is used for parallel operation of inverters has been described. However, other converters may be used, for example, a high frequency inverter and a cycloconverter are combined as shown in FIG. The same principle can be applied to a converter capable of instantaneous voltage control, such as a high frequency link converter for converting to a low frequency sine wave.

In the converter shown in FIG. 8, the transistor Q1
To Q4, a rectangular wave as shown in FIG. 9A is obtained from the secondary side of the transformer TR. Next, as shown in FIG. 7B, a sawtooth wave synchronized with the switching of the inverter is created, and the intersection of the sawtooth wave and the output voltage command signal indicated by line X ₁ -X ₂ in the drawing is as shown in FIG. Ask for. Based on the polarity of this signal and the voltage RS of the inverter,
By selecting the switch of the cycloconverter as shown in FIG. 10, the voltage corresponding to the signals X ₁ -X ₂ can be obtained between the UNs of FIG. 8 as shown in FIG.

As is clear from the above description, the circuit of FIG. 8 can obtain a single-phase PWM voltage equivalent to that of FIG. Further, in the case of three-phase output, a three-phase high frequency link converter using three sets of circuits on the secondary side of the transformer TR in FIG. 8 may be used.

In order to realize the principle shown in FIGS. 1, 6, and 7, a discrete circuit using an analog operation amplifier or the like may be used, or software processing by digital control by a microprocessor or a digital signal processor may be performed. It can also be realized.

[0060]

As described above, the present invention provides a simple circuit configuration by applying a signal corresponding to the amount of cross current of the current flowing between the converters to the instantaneous voltage control circuit for controlling the instantaneous value of the output voltage. Therefore, there is an effect of promptly suppressing the cross current.

There is also an effect that it is possible to prevent the inverter DC side voltage from rising due to the cross flow of active power.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an example of a converter used in the present invention.

FIG. 3 is a block diagram of the current detection circuit of FIG.

FIG. 4 is a simplified block diagram of FIG.

FIG. 5 is a vector diagram for explaining the present invention.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a converter according to a fourth embodiment of the present invention.

FIG. 9 is an operation explanatory diagram of the converter according to the fourth embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a conventional system.

[Explanation of symbols]

 1 Inverter device 1 2 Inverter device 2 Output bus 4 Load 5, 6 DC power supply 8 AC power supply system 403 Instantaneous voltage control circuit 404 Capacitor current reference signal generation circuit 405 Cross-current limiting virtual impedance circuit 406 Current detection circuit 408 Average value Voltage control circuit 411 Converter 412 Voltage control oscillator 413 Voltage-frequency converter 414 Frequency adder / subtractor 415 Current sharing circuit 416 PLL circuit 417, 420 Oscillator

Claims (4)

[Claims] 1. A parallel converter system in which outputs of a plurality of AC output converters are connected to a common bus bar and which operates in parallel while sharing a load current, wherein each of the converters constitutes a converter. The phase arm is an instantaneous voltage control type converter that controls the instantaneous value of the output voltage by performing switching a plurality of times during one cycle. Each of the converters has an independent voltage reference oscillator, and By detecting the cross current of the current flowing between the converters, by this detection signal, while changing the output of the instantaneous voltage control circuit, by changing the oscillation frequency of the oscillator,
A parallel operation control device for an AC output converter, wherein an output voltage of the converter is controlled so as to suppress a cross current of a current flowing between the converters. 2. In a parallel converter system in which outputs of a plurality of AC output converters are connected to a common busbar and are operated in parallel while sharing a load current, each of the converters constitutes a converter. The phase arm is an instantaneous voltage control type converter that controls the instantaneous value of the output voltage by performing switching a plurality of times during one cycle. Each of the converters has an independent voltage reference oscillator, and The cross current component of the current flowing between the converters is detected, the output of the instantaneous voltage control circuit is changed by this detection signal, and the component of the cross current component mainly due to the phase difference between the converters is detected. By controlling the oscillation frequency of the oscillator by the detection signal, the output voltage of the converter is controlled so that the cross current of the current flowing between the converters is suppressed. A parallel operation control device for AC output converters. 3. A parallel converter system in which outputs of a plurality of AC output converters are connected to a common busbar and which operates in parallel while sharing a load current, wherein each of the converters constitutes a converter. The phase arm is an instantaneous voltage control type converter that controls the instantaneous value of the output voltage by switching a plurality of times during one cycle. Each of the above converters is synchronized by a common signal and It has a frequency regulator for the corresponding synchronization signal, detects the cross current component of the current flowing between each of the converters, and by this detection signal,
By changing the output of the instantaneous voltage control circuit, detecting the component of the cross current mainly due to the phase difference between the converters, and changing the adjustment amount of the frequency adjuster by this detection signal, A parallel operation control device for an AC output converter, characterized in that the output voltage of the converter is controlled so that the cross current of the current flowing between the converters is suppressed. 4. A parallel converter system in which the output of one or a plurality of AC output converters and another power supply system are connected to a common bus bar and which operates in parallel while sharing a load current,
The above-mentioned converter is an instantaneous voltage control type converter that controls the instantaneous value of the output voltage by switching the arms of each phase constituting the converter a plurality of times during one cycle.
The converter is constructed so as to be able to slightly change the frequency while operating in synchronization with the frequency of the power supply system, and detects the cross current component of the current flowing between the converters and between the converters and the power supply system. Then, the output of the instantaneous voltage control circuit is changed by this detection signal, and the output frequency of the converter is changed by the component caused by the phase difference between the converters of the cross current or between the converters and the power supply system. By doing so, the parallel operation control of the AC output converters is characterized in that the output voltage of the converters is controlled so that the cross current of the currents flowing between the converters and between the converters and the power supply system is suppressed. apparatus.