JPH04344174A - Control circuit for preventing uneven magnetization of inverter transformer - Google Patents

Abstract

PURPOSE:To obtain a circuit which can prevent uneven magnetization of an inverter transformer without impressing an excessive product of an applied voltage and time upon the transformer against disturbance caused when a load varies or a circuit breaker is put in or released. CONSTITUTION:An inverter control section is provided with a voltage detector 15 which detects the DC voltage of an inverter 4 and a control section 2A which calculates an alpha-limiting value so that the limiting value of the pulse width controlling angle alpha of the inverter 4 can become the product of an applied voltage and time which is lower than the overexcitation withstanding amount of an inverter transformer 6.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention prevents saturation due to DC bias magnetization of an inverter transformer used in a grid-connected inverter system using an inverter configured with a plurality of gate turn-off thyristors (hereinafter referred to as GTO). The present invention relates to an unbalanced magnetization prevention control circuit for an inverter transformer.

0002

2. Description of the Related Art In recent years, there has been a tendency for power demand to fluctuate widely over a day or a week. Therefore, it is necessary to take measures for power storage and peak loads in the power system. Under these circumstances, grid interconnection systems have been proposed that supply power from a DC power source 1 such as a solar cell, storage battery, fuel cell, new type battery, etc. to an AC commercial power system when necessary. FIG. 5 is a single line diagram showing a schematic configuration of an inverter system for grid connection using a self-cooling inverter made of self-extinguishing semiconductor elements such as GTO.

[0003] DC power output from a DC power source 1 such as the above-mentioned new type of battery is input to an inverter 4 via a DC reactor 3 and a DC filter capacitor 5. The inverter 4 is driven by the inverter control unit 2 and converts input DC power into AC power. The AC power output from the inverter 4 is inputted to one end of the circuit breaker 9 for grid connection/disconnection via the inverter transformer 6, harmonic filter 7, and grid connection reactor 8 for AC grid connection. An AC system 10 is connected to the other end of the circuit breaker 9 for grid connection/disconnection. Further, an AC load 12 is connected to the other end of the breaker 9 for grid connection/disconnection via a breaker 13 for grid separation/connection and a transformer 11 .

[0004] Therefore, under normal conditions, the circuit breaker 9 is closed, and the AC load 12 is supplied with AC power only from the AC system 10. When electricity demand peaks,
The circuit breaker 9 becomes conductive, and the AC power output from the inverter 4 is also supplied in parallel.

The harmonic filter 7 has a function of removing high frequency components contained in AC power, and as shown in the figure, is composed of a contactor 7a, a harmonic suppression reactor 7b, and a harmonic filter capacitor 7c.

The inverter control unit 2 also includes a current detector 2a attached to the output voltage circuit of the inverter 4.
and the current value and voltage value detected by the voltage detector 2b,
In other words, reactive power feedback value QFBK and active power feedback value P
FBK is input.

The inverter 4 and inverter transformer 6 are constructed as shown in FIG. 6, for example. As shown in the figure, input direct current (DC) power is input to three unit inverters 4U, 4V, and 4W. Each unit inverter 4U, 4V, 4W is composed of four GTOs 41 to 44, 45 to 48, and 49 to 52 connected in a bridge, respectively, and the output voltage VU, which is output from each unit inverter 4U, 4V, 4W, is VV and VW are the following Δ
The voltage is applied to each of the primary windings 6U1, 6V1, and 6W1 of the inverter transformer 6 which is connected and wound.

[0008]Thus, three-phase AC power is output from each terminal of the secondary windings 6U2, 6V2, and 6W2 of the inverter transformer 6. In addition, each unit inverter 4U, 4V
, 4W GTOs 41 to 52 are connected in parallel with feedback diodes of opposite polarity.

[0009] Each unit inverter 4U, 4V, 4
Each GTO 41 to 52 constituting W is an inverter control unit 2
It is controlled on/off by the conductive signal from FIG. 7 is a block diagram showing a schematic configuration of the inverter control section 2. As shown in FIG. Active power standard PR set by the active power standard setter 21
EF is differentially amplified with the active power feedback value PFBK detected by the voltage detector 2b, and then sent to the φ, α calculation circuit 2.
7. The φ, α calculation circuit 27 performs control calculations on the input differential signal to obtain a phase control signal φ, and sends it to the next φ limiter circuit 28 . The phase control signal φ output from the φ limiter circuit 28 is distributed by the gate control circuit 30 as a gate signal to each GTO in the first conduction cycle shown in FIG. 8 in each unit inverter 4U, 4V, 4W.

On the other hand, the reactive power standard QREF set by the reactive power standard setter 22 is
After being differentially amplified with the reactive power feedback value QFBK detected at points a and 2b, it is input to the φ, α calculating circuit 27. φ
, α calculation circuit 27 performs control calculations on the input differential signal to obtain a pulse width control angle signal α, and sends it to the next α limiter 29. The α limiter 29 provides maximum and minimum limits for the pulse width control angle of the output voltage. The gate control circuit 30 controls the GTO in the first conduction cycle to control the pulse width of the output voltage.
With a delay of ΔT time (phase angle α), the signal is distributed as a gate signal to each GTO in the second conduction cycle shown in FIG. 8 in each unit inverter 4U, 4V, 4W.

FIG. 8 shows each GTO 4 of the unit inverter 4U.
1 is a time chart showing the conduction timing and output voltage waveform of Nos. 1 to 43; As shown in the figure, inverter control section 2
The GTO 41 becomes conductive in the first half of the first conduction cycle set in , and the GTO 42 becomes conductive in the second half delayed by 180°. Further, in the first half of the second conduction cycle delayed by the pulse width control angle α from the first conduction cycle, the GTO 44 becomes conductive, and in the second half delayed by 180°, the GTO 43 becomes conductive. Therefore, the waveform of the output voltage VU is a pseudo sine waveform as shown in the figure, since each voltage waveform whose phase is delayed by α is superimposed.

The output voltages VV and VW of the other unit inverters 4V and 4W have almost the same waveforms, but the phases of the first and second conduction cycles are the same as those of the previous unit inverters 4U and 120.
Since the inputs are shifted by degrees, each output voltage VU, VV,
The VW waveforms are offset from each other by 120°. Therefore, three-phase AC power is output from this inverter 4. However, the grid-connected inverter systems shown in FIGS. 5 to 8 still have the following problems.

In the DC power supply 1 shown in FIG. 5, the DC voltage fluctuates over a wide range, and the equivalent circuit differs at the beginning, middle, and end of discharge, for example. FIG. 9(a) shows the V and I characteristics of the DC power supply 1 at the beginning, middle, and end of discharge, and FIG. 9(b) shows the equivalent circuit.
(c) shows a change in the voltage waveform applied to the primary winding of the inverter transformer 6. For example, the characteristics at the initial stage of discharge (A)
As shown in Fig. 9(c), the pulse width control angles are αA, αB, αC for grid-connected operation with the same power supply for mid-term characteristics (B) and final characteristics (C). It fluctuates. Due to such a wide range of DC voltage fluctuations,
The control system is disturbed by load fluctuations during interconnection and disconnection, and fluctuations in the pulse width control angle α exceed the overexcitation tolerance of the inverter transformer 6, causing the inverter transformer 6 to saturate due to DC bias, resulting in overcurrent. There is a problem that this may lead to serious failure and shutdown. For example, FIG. 9(d) shows an example of the voltage application waveform of the overexcitation tolerance of the inverter transformer 6. Δ
α, that is, a region where the inverter transformer becomes over-excited and becomes saturated when a voltage exceeding the voltage-time product of the shaded area is applied.

[0014]

[Problems to be Solved by the Invention] As described above, in the conventional grid-connected inverter system, the inverter transformer 6 becomes unbalanced due to fluctuations such as closing and opening of the circuit breaker or sudden changes in load, and due to overcurrent, There was a problem with it breaking down and stopping.

[0015] The present invention calculates the α control angle that gives the maximum limit value without biasing the voltage-time product applied to the primary winding of the inverter transformer in accordance with the fluctuation state of the DC voltage, and sets a limit on the α control angle to control the inverter. The object of the present invention is to provide an anti-biased magnetic control circuit that prevents saturation of a transformer.

[0016]

[Means for Solving the Problems] The present invention detects DC voltage, calculates the limit value of the α control angle from the applied voltage time product of the primary winding that gives the maximum limit value that does not saturate the inverter transformer, and The control system is configured to set a limit on the α control angle depending on the voltage fluctuation state.

[0017]

[Function] In the grid-connected inverter system configured as described above, it is possible to prevent the inverter transformer from becoming unbalanced and overcurrent due to fluctuations such as closing and opening of the circuit breaker or sudden changes in load, thereby reducing power demand. power can be supplied to the alternating current system in response to sudden changes in

[0018]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a control configuration of an embodiment of the present invention. Components that are the same as those in FIG. 7 are given the same reference numerals and their explanations will be omitted. The α limiter 29 constitutes a calculation means to set a limit on the α control angle according to the DC voltage Ed.

FIG. 2 is a block diagram showing a schematic configuration of the entire grid-connected inverter system according to the embodiment. The AC power output from the inverter 4 is inputted to one end of a circuit breaker 9 for grid connection/disconnection via an inverter transformer 6, a harmonic filter, and a grid connection reactor 8 for AC grid connection. An AC system 10 is connected to the other end of the circuit breaker 9 for grid connection/disconnection. In addition, at the other end of the circuit breaker 9 for grid connection/disconnection, a circuit breaker 13 for grid separation/grid connection, and a transformer 1
An AC load 12 is connected via 1. The inverter 4 is driven by the control unit 2A and converts input DC power into AC power. The DC power output from the DC power supply 1 is transferred to a DC reactor 3 and a DC filter capacitor 5.
The signal is input to the inverter 4 via the inverter 4. In this embodiment, for the conventional control unit 2, depending on the DC voltage Ed,
Calculation means for calculating the limit value of the α control angle is added.

FIGS. 3 and 4 show the α limiter 29 in FIG.
3 is a flowchart showing a control sequence of FIG. When the flowchart of FIG. 3 is started, in S (step) 1, the power standard PRE
F, QREF and power feedback values PFBK, QFBK
, the phase control angle φ and the pulse width control angle α are calculated from the DC voltage Ed, and the process proceeds to S50, where the DC bias prevention limit value calculation process shown in FIG. 4 is executed. When the process in FIG. 4 is started,
In S52, the instantaneous value of the DC voltage Ed is detected, and the process proceeds to S53, where the transformer overexcitation withstand voltage-time product VSM,
By substituting the DC voltage Ed, the α limit value αMAX is calculated. Proceed to S54, set an α limit to the obtained αMAX, return to the flowchart of FIG. 3, and proceed to S2, where the pulse width control angle α is compared to see if it is less than or equal to αMAX, and if it is less than or equal to αMAX, proceed to S3 and set α=αMAX. The limit is set, and the process proceeds to S4, where pulse width control operation is performed using the calculated α and φ.

[0021] With the grid-connected inverter system configured as described above, even if the power grid suddenly changes, the inverter transformer can be controlled without being biased. Therefore, stable operation is possible. In addition, since the control is suppressed below the overexcitation tolerance of the transformer, it is also useful for protecting the transformer.

It should be noted that the present invention is not limited to the embodiments described above. In the embodiment, the inverter 4 is
Although the three-phase inverter configuration is made by combining the unit inverters 4U, 4V, and 4W, an inverter with an arbitrary phase configuration can be configured by changing the number of unit inverters combined.

[0023]

[Effects of the Invention] As explained above, according to the present invention, a means is provided for calculating the limit of the pulse width control angle α according to fluctuations in the DC voltage. It is possible to provide an unbalanced magnetization prevention control circuit for an inverter transformer that prevents unbalanced magnetization without applying an excessive voltage-time product to the inverter transformer in response to disturbances.

[Brief explanation of drawings]

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

FIG. 2 is an overall system diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing a control sequence of the present invention.

FIG. 4 is a flowchart showing a method for calculating an α limit according to the present invention.

FIG. 5 is a diagram of a conventional overall system.

FIG. 6 is a detailed configuration diagram of the inverter circuit in FIG. 5;

FIG. 7 is a conventional control block diagram.

FIG. 8 is a time chart of each part explaining the operation of the inverter in FIG. 6;

FIG. 9 is a diagram illustrating battery characteristics and the waveform of the transformer primary winding voltage.

[Explanation of symbols]

1...DC power supply such as new type batteries, 3...DC reactor, 4...
Inverter, 5... Capacitor, 6... Inverter transformer, 7... Harmonic filter, 8... Connection reactor, 9... Circuit breaker, 10... AC system, 11... Transformer, 12... Load, 1
3... Breaker, 2,2A... Control unit, 41-52... GTO,
21...Active power standard setter, 22...Reactive power standard setter, 27...φ, α calculation means, 28...φ limiter, 29...α
Limiter, 30...gate control means.

Claims (1)

[Claims] [Claim 1] Multiple GTOs (gate turn-off
It consists of an inverter that converts DC power input from the DC system into AC power, and a function to detect the active power and reactive power of the output power of this inverter. an inverter control unit that controls on/off timing of each of the GTOs so that the power meets specified active power standards and reactive power standards; and an inverter control unit that transforms the output voltage of the inverter with an inverter transformer, and In an inverter system for grid connection that includes a harmonic filter that removes harmonic components of electric power and a grid interconnection reactor for connecting to an AC system, the inverter control unit is configured to detect a DC voltage of the inverter. The detection means and the limit value of the pulse width control angle α of the inverter are
Unbalanced magnetization prevention control for an inverter transformer, comprising means for calculating an α limit value according to the detected DC voltage value so that the applied voltage time product is less than or equal to the overexcitation tolerance of the inverter transformer. circuit.