JPS62268323A - Parallel driving controller of ac output converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a power supply system in which a plurality of AC output converters are serially operated in 6ri rows for a common load. The present invention relates to a parallel operation control device for an AC output converter that controls balance.

[Conventional technology]

FIG. 8 is a block diagram showing the circuit configuration of a conventional parallel operation control device disclosed in, for example, Japanese Patent Publication No. 53-361-:37 and Japanese Patent Publication No. 56-13101. 2 is the inverter of the second unit, 3 is the output bus, and 4 is the load.

The inverter 1 of the first unit has an inverter main body 100, an output transformer 101, a filter reactor 102, and a capacitor 103 as its main components, converts the power of a DC power supply 5 to AC, and converts the power of the DC power supply 5 to AC, and outputs the output switch 1. 04 to the output bus 3.

Although the inverter 2 of the second machine is not shown, it has the same configuration as the inverter 1 of the first machine, and is operated in parallel through the inverter 1 of the first machine and the output bus 3 while
It supplies electricity to.

In order for inverter 1 of No. 1 and inverter 2 of No. 2 to operate in parallel, the output current of inverter 1 of No. 1 must be
A detection signal LA is obtained from the current transformer CT106. The difference from the detection signal 1zA obtained from the inverter 2 of the second unit, that is, the ΔI multiplied signal corresponding to the galvanic current detection 8li
Obtained by +107.

Next, the phase shifter 108 generates two orthogonal voltage vectors E.
Create A and E8, and use the arithmetic circuits 109 and 110 from the 1 signal.
A reactive power corresponding component ΔQ and an active power corresponding component ΔP are obtained respectively.

In the inverter 1 of the first unit, the voltage control circuit 113 is set to I based on the signals from the voltage setting circuit 111 and the voltage feedback circuit 112.
'Through the WM circuit 114, pulse width modulation of the inverter main body 100 is performed to control the internally generated voltage.

On the other hand, the above-mentioned reactive current corresponding component ΔQ is the voltage control circuit 11
By adjusting the internally generated voltage of the inverter main body 100 by several percent, the reactive current corresponding component ΔQ is brought to zero.

On the other hand, the aforementioned active power corresponding component ΔP passes through an amplifier 115 constituting a PLL circuit, and finely adjusts the frequency of the reference oscillator 105, thereby controlling the phase of the internally generated voltage of the inverter main body 100. It operates to make the active power corresponding component ΔP zero.

In this way, by controlling the voltage and phase, both the reactive current component ΔQ and the active power component ΔP are brought to zero, thereby eliminating cross current between the two inverters 1 and 2, resulting in a stable load. Allotment will be done.

[Problem that the invention seeks to solve]

Since the conventional parallel operation control device for an AC output converter has the above configuration, there are two major problems as explained below.

The first problem is that it is difficult to test and adjust parallel operation. That is, it is often necessary to test and inspect whether an inverter system to which such a parallel operation method is applied operates normally as scheduled.

However, in the system shown in Fig. 8, whether or not it operates normally is determined by connecting inverters 1 and 2 to the output bus 3.
11゜However, as is well known, the overcurrent withstand capacity of a general inverter is only about 150%, so while actually operating the system shown in Figure 8, there is no problem with the control circuit. It is very difficult to investigate this and adjust the responsiveness of the control.

In reality, each element of the control circuit shown in Figure 8 has been completely tested and adjusted, and after confirming that there are no wiring errors between elements, the entire system shown in Figure 8 must be tested for operation. can be done.

As described above, even if parallel operation is performed after careful confirmation, an excessive cross current will flow due to an unexpected failure, and the inverter will often fail due to commutation failure and be damaged.

This means that it is extremely difficult to investigate when a failure occurs (particularly failures such as contact failures that occasionally occur with poor reproducibility) and to conduct periodic inspections.

The second problem is uncontrollable phenomena due to harmonic cross currents. That is, due to the unexpected harmonic cross current contained in the output current of each inverter, the detected cross current signal Δ
(2) contains a large proportion of harmonics, which causes an error in the detection of the orthogonal component of the current, resulting in an uncontrollable phenomenon.

Capacitor 10 of output filter of each inverter
3 is directly connected to the output bus 3, the capacitors of other machines and the capacitor of the own machine form a resonant circuit through the inductance of the wiring of the output bus 3.

Although the resonant frequency of this resonant circuit depends on the length of the cable wiring, it often has a relatively high-order resonant frequency higher than the 7th tone. The harmonics generated by any of the inverters connected in parallel resonate with this resonant circuit, producing a very large harmonic cross current.

This harmonic cross current generates the following signal, taking as an example a case where synchronous rectifier circuits are applied as the arithmetic circuits 109 and 110.

FIGS. 9(b) and 9(c) show active power corresponding component ΔP and reactive power corresponding component ΔQ obtained by synchronously rectifying the fundamental wave cross current signal (a). Now, as an example, there is no delta signal for the basic liquid acid,
∆■ times signal due to 5th harmonic component, 9th harmonic component as harmonic galvanization
Let us consider the case where there is such a case as shown in figure (d).

When this is synchronously rectified, a signal shown in the figure (e) as the active power corresponding component ΔP and a signal shown in the same figure (f) as the reactive power corresponding component ΔQ are generated.

In this case, the average value of the reactive power corresponding component ΔQ in FIG. 9(f) becomes 0, but the average value of the reactive power corresponding component ΔQ in FIG.
The hatched part remains as a positive signal. A positive signal of this active power corresponding component ΔP means that the active power share of the inverter is too large, so the PLL circuit using the amplifier 115 temporarily lowers the frequency of the oscillator and delays the phase of inverter 1. works.

Furthermore, with respect to the inverter 2, since the harmonic cross current shown in FIG.
5 operates to advance the phase of inverter 2.

However, in reality, the fundamental wave component is
, 2, and the situation does not require phase difference adjustment.The operation of the PPL circuit due to the active power corresponding component ΔP described above is a malfunction, and as a result, the crossflow of the fundamental wave increases, and parallel operation is not possible. becomes impossible.

In the examples shown in FIGS. 9(d) to (f), the phase relationship between the fifth harmonic and the fundamental wave is set as shown, but when the phase relationship changes, active power corresponding component ΔP, reactive power corresponding component ΔQ Both can take on a variety of positive and negative values. Therefore, not only phase control but also voltage control abnormality occurs due to abnormality in reactive power corresponding component ΔQ.

Note that although the example in FIG. 9 shows the fifth harmonic for simplicity, it is possible that abnormal signals will occur in the active power corresponding component ΔP and the reactive power corresponding component ΔQ in the same way for other nth harmonics. it is obvious.

Generally, the nth harmonic causes a gain effect of 1/n as a result of synchronous rectification, making the parallel operation control system as shown in FIG. 8 unstable.

To solve such problems, the arithmetic circuit 109.1
As 10, use a multiplier and multiply the signal by Δ■ times E^+
It is known that a positive rJi wave may be used as En(N).

However, multipliers are generally complex, have a high failure rate, and are expensive. Therefore, a simple and highly reliable synchronous rectifier circuit is preferable for application to the device shown in FIG. 8.

This invention was made in order to solve the above-mentioned problems, and it makes it possible to test and adjust parallel operation control using only the control circuit without actually operating the main circuits in parallel. The purpose of this invention is to obtain a new parallel operation control device for an AC output converter that enables stable parallel operation load sharing even in the presence of wave cross currents.

[Means for solving problems]

A parallel operation control device for AC output conversion devices according to the present invention includes a plurality of AC output conversion devices to be operated in parallel, provided with a simulation conversion device for parallel operation control, and a parallel operation control device for controlling parallel operation from the output end of the simulation conversion device through an impedance element. The impedance element is connected to the simulated bus in iM/columns, and is equipped with a load sharing control means for controlling the current flowing through the impedance element to a predetermined value.

[Effect]

The simulating converter according to the present invention enables test adjustment of parallel operation of AC output converters by controlling parallel operation, and allows stable load sharing in parallel operation even in the presence of harmonic cross current between the AC output converters. is possible.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 8 are given the same reference numerals.

In FIG. 1, 119 is a simulated inverter driven by a PWM circuit 114 common to the inverter main body 100;
120 is a transformer that transforms the output of the simulated inverter 119, 121 is an actuator connected to the output end of the transformer 120, and 7 is a reactor 121 through the switch 1-22.
This is a simulated bus connected to the Note that the phase shifter 108 in the figure
, arithmetic circuits 109, 110, PLL amplifier 115, etc. constitute a load sharing control means.

Isolated amplifier 1 is used for the DC input of the simulated inverter 119.
18 is connected, one purpose is to isolate it from the DC power supply 5 of the main circuit by the isolation amplifier 118 and to obtain a DC voltage Ec proportional to the voltage ED of the DC power supply 5.

Further, the simulated inverter 119 may be as small as several tens of VA even if the capacity of the inverter main body 100 is several tens of KVA or more. Since the output voltage can be arbitrarily selected depending on the DC voltage Ec and the transformer 120, it is selected to be, for example, 100 cm.

In addition, depending on the rated current of the inverter,
If the rated current equivalent current of 21 is O and LA, and if the combined impedance of the reactor 102 and transformer 101 of the inverter main body 100 is 10%, then the impedance of the reactor]-21 is set to 100Ω.

It is also desirable to match the impedance angles of both as much as possible.

With this setting, the circuit connected to the simulated bus 7 in FIG. 1 constitutes a model in which the load 4 and the filter capacitor are excluded from the main circuit that operates in parallel. That is, the equivalent circuit of the main circuit is shown in FIG. 2(a), but the model is the equivalent circuit shown in FIG. 2(b).

In the case of Fig. 2(a), the current i□ includes both the load current and the cross current, but in the case of Fig. 2(b), it includes only the cross current, so the conventional parallel operation control shown in Fig. 8 above Cross current ΔI can be detected without providing the cross current detection circuit 107 required in the circuit.
Since the current Izo in FIG. 1 corresponding to can be obtained, for example, O, lA10. The cross current signal ΔI can be converted into LA, and thereafter the same control operation as explained with reference to FIG. 8 can be performed.

FIG. 3 shows another embodiment of the invention. For simplicity,
The same parts as in FIG. 1 are omitted, and only the circuit diagram for detecting the cross current corresponding signal is shown. Here, the u, V, and W phase conversion balls 134. ．． A conversion ball 137 corresponding to the U-phase conversion ball 134 out of 1'35° 136 is used as a simulated inverter 119.

The primary of the transformer 120 is connected between the conversion ball 137 and the midpoint N of the DC power supply made by the capacitors 132 and 133, and the U phase is taken as the representative phase.

In FIG. 3, the same numbers as those in FIG. 8 represent the same functions, so explanations will be omitted. In FIG. There is. Further, in order to prevent resonance with the same capacitor of the inverter 2 of the second machine, a damping resistor 126 is provided in series with the capacitor 125.

This damping resistor 126 can also be provided in series with the switch 22, like the resistor 124 shown.

In addition, if necessary, by providing a resonant filter glue 1:SO and a capacitor 131 that are not included in the circuit, harmonics can be removed even more sufficiently and a control signal that is not affected by harmonics can be obtained. It's easy.

As described above, the configuration shown in FIG. 3 has the first feature that when testing and adjusting the control circuit, only the switch 122 is closed without closing the outlet switch 104, and a preliminary test of parallel operation is performed through the simulated bus 7. Therefore, it is possible to realize the great advantage that test adjustment and inspection are easy. In addition, in normal parallel operation, the output switch 104 and the switch 122 are opened and closed in conjunction with each other as shown in the illustrated example.

Moreover, as a second feature, since it is possible to detect a signal that is not affected by harmonic cross current flowing between the filter capacitors 103 of the main circuit of the inverter, it is easy to design a stable control system.

In the above embodiment, the main circuit of the inverter is three-phase, but the simulated bus circuit is single-phase. This is because normally the inverter does not control the three phases separately, but controls them all at once.
This is because load balancing only needs to be performed for one representative phase.

In addition, if the circuit shown in FIG. 3 is provided for all three phases, it is possible to perform load balancing with excellent rapid dissolution.

4, 5, 6, and 7 show other embodiments of this invention. For simplicity, the same parts as in FIG. 1 are omitted.

First, in FIG. 4, a DC/DC converter 117 is provided as an insulating means between the main circuit of the inverter main body 100 and the simulated inverter 119.
, 7 insulate the DC power supply 5 from the simulated inverter 119, so the transformer on the output side of the simulated inverter is omitted.

The DC/DC converter 117 may be an isolated amplifier, etc.
Any device that can input a DC voltage, output a DC voltage at an appropriate level proportional to the input DC voltage, and have an insulation function may be used.

In FIG. 5, a simulated inverter 119 is provided with a plurality of phases, operated with an appropriate phase difference (for example, 6o°), and the output is combined with the secondary winding of a transformer 120 to output to the simulated bus 7. The present invention is characterized by reducing harmonics contained in the voltage, particularly low-order harmonics, and as a result, reducing harmonics contained in the cross current detection signal ΔI.

Fig. 6 is applicable to cases where the DC power supply 5 of the inverter main body 1oo is common, and a constant voltage DC power supply 116 independent of the DC power supply 5 of the main circuit is provided as an input to the simulated inverter 119. . As the DC power source 116, for example, a constant voltage power source such as a control power source for the device can be used. In addition,
A constant voltage DC power source 116 may be generated from the DC power source 5 using a DC/DC converter.

FIG. 7 shows the cross current detection signal Δ
A filter circuit 140 is provided in the path (2) to reduce harmonics, and since the signal is at the control signal level, it has the advantage of being extremely small and inexpensive.

The filter circuit 140 may consist of a resistor and a capacitor, or may include an active element such as an amplifier. The embodiment shown in FIG. 7 can also be applied to the above-mentioned FIGS. 3 to 6.

In the above explanation, a voltage source inverter with constant voltage, constant frequency, and sine wave output of the same rating was used as an example, but the principle of this invention applies to current source inverters, cycloconverters, etc.
It is equally applicable to other types of AC output conversion devices. It goes without saying that it can also be applied not only to constant frequency/constant voltage but also to variable frequency/variable voltage rectangular wave output inverters, and also to AC output converters of different capacities16 [Invention [Effect] As described above, according to the present invention, the AC output converter is provided with a simulated converter for parallel operation control, and the output end of the simulated converter is connected in parallel to the simulated bus line via an impedance element, Since the load sharing control means is configured to control the current flowing through the impedance element to a predetermined value, the parallel operation control circuit can be tested and adjusted without connecting the AC output converters in parallel. In addition, a control circuit that is not affected by harmonic cross current between the AC output converters described in 111I can be configured by a synchronous rectifier circuit without using a multiplier, which makes the control circuit more economical. This has the effect of realizing high reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a parallel operation control device for an AC output converter according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram for explaining the principle of FIG. 1, and FIGS. 3 to 7 8 is a block diagram of a main part showing another embodiment of the present invention, FIG. 8 is a block diagram showing a conventional parallel operation control device for an AC output converter, and FIG. 9 is a block diagram of an arithmetic circuit for detecting orthogonal components of a cross current. It is a figure explaining a principle. 1.2 is an AC output converter (inverter), 3 is an output bus, 4 is a load, 7 is a simulated bus, and 119 is a simulated inverter. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Patent applicant: Mitsubishi Electric Corporation Figure 2 (a) (b)

Claims (8)

[Claims] (1) In a parallel operation control device for operating a plurality of controllable voltage and controllable frequency AC output converters in parallel for a common load, each AC output converter has a simulation for parallel operation control. A converter is provided, and each of the simulated converters is connected in parallel from the output end to a commonly provided simulated bus bar via an impedance element, and each of the alternating currents is connected in parallel to the simulated bus bar provided in common through an impedance element, so that the current flowing through the impedance element becomes a predetermined value. 1. A parallel operation control device for an AC output converter, characterized by comprising load sharing control means for controlling the voltage and frequency of the output converter and the simulating converter. (2) Claim (1) characterized in that each AC output converter and the simulation converter are controlled so that the current flowing through the impedance element becomes zero.
Parallel operation control device for the AC output conversion device described in 2. (3) The current flowing through the impedance element is decomposed into two components, one that changes mainly depending on the voltage and the other that changes mainly depending on the phase, and each component is balanced with the same component in other AC output converters and simulation converters. A parallel operation control device for an AC output converter according to claim (1), characterized in that the parallel operation control device controls the AC output converter according to claim (1). (4) Parallel operation of the AC output converter according to claim (1), wherein the DC input voltage of the simulating converter is a voltage proportional to the DC input voltage of the main AC output converter. Control device. (5) The AC output converter according to claim (1), wherein the DC input voltage of the simulating converter is a constant voltage regardless of the DC input voltage of the main AC output converter. parallel operation control device. (6) The AC output according to claim (1), wherein each of the simulated conversion devices is connected to the simulated bus bar in an insulated manner using an isolation transformer and a reactor as the impedance element. Parallel operation control device for conversion equipment. (7) The current proportional to the output current of the AC output converter is C
The alternating current output converter according to claim 1, characterized in that a current source is applied to the simulated bus by T, and a load corresponding current that changes according to an increase or decrease in the actual load is applied to the simulated bus. Parallel operation control device. (8) A harmonic filter consisting of a capacitor and, if necessary, a reactor is provided on the simulated bus, and in order to prevent resonance between the capacitor of this harmonic filter and the same capacitor of another simulated conversion device, a harmonic filter is installed between the two capacitors. A parallel operation control device for an AC output converter according to claim 1, characterized in that a damping resistor is provided in series with the AC output converter.