JP2003037938A - Power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support to the operation that a voltage on the system side or the load side becomes almost zero. SOLUTION: When a system voltage is lost while power is supplied from the power system 12 to the load 14 through a breaker 20 and a series transformer 24, the breaker 20 is opened, a shorting switch 22 is turned on, primary windings of phases of the series transformer 24 are mutually shorted, energy charged in an energy charging element 30 is supplied to the load 14 through a series power converter 28 and the series transformer 24 used as a delta-star connection transformer, and power to the load 14 is prevented from being interrupted while the energy charging element 30 maintains the energy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion system, and more particularly to a power conversion system suitable for changing a voltage applied to a load as needed when AC power is supplied from a power system to the load. .

[0002]

2. Description of the Related Art Conventionally, when power is supplied from a power system to a load, a series transformer is inserted in a circuit (distribution line) connecting the power system and the load, and the primary winding of the transformer is directly connected to the power system. Connected to the load and the secondary winding to the series power converter, adjusting the voltage on the primary side of the series transformer according to the output of the series power converter and controlling the voltage applied to the load. A power conversion system is adopted. In this case, connect a DC energy storage element such as a capacitor to the DC output side of the series power converter, connect the DC output side of the parallel power converter, and connect the AC input side of the parallel power converter to the parallel transformer. A configuration is adopted in which the power converter is connected in parallel to the power grid via the power converter and the power converter controller controls the power conversion operation of each power converter based on the load voltage command value. For example,
The series power converter gives a voltage drop through the series transformer by generating a voltage in the same phase as the load voltage, and performs control to reduce the voltage applied to the load. In this case, if the load is a passive load, the load voltage is reduced, so that the load current is reduced and the power consumption is reduced. This reduced power flows through the series power converter that causes a voltage drop to the DC output side of the power converter, and this power is converted to AC power by the parallel power converter and regenerated in the power grid. , DC voltage is kept constant.

In the power conversion system configured as described above, the power consumed by the load in the electric power system is reduced by the amount regenerated from the series power converter through the parallel power converter. In addition, the voltage of the electric power system varies from high to low depending on the time of day, and is not constant. In particular, when the load is a passive load, if the voltage rises, extra power is consumed correspondingly, so that the voltage of the power system rises. At that time, the power applied to the load is reduced by suppressing the voltage applied to the load by the power conversion system.

On the other hand, if the voltage generated from the series power converter has a phase opposite to that of the load voltage, the load voltage can be increased via the series transformer. In this case, the flow of power in the DC circuit between the series power converter and the parallel power converter is reversed, and power is supplied from the parallel power converter to the load via the series power converter.

From the above, in the power conversion system,
The voltage of the load can be freely controlled up and down within a range determined by the upper limit of the voltage that can be generated by the series power converter and the power that the series power converter and the parallel power converter can handle. Note that, as a system related to this type of system, there is, for example, JP-A-9-74678.

[0006]

The power conversion system in the prior art has been used as a system for reducing the load voltage to save power. However, since the load voltage can be freely controlled, the power conversion system is expected to be applied as a system having a function different from that of the related art, and two application examples will be described below.

[0007] One is an application relating to reduction of a starting voltage of an induction motor or the like. At the time of starting a large capacity induction motor, the starting rush current is large, so normally it is not started by direct insertion, but by some method, the applied voltage at the time of starting is started and the rotation speed is increased. According to the control, the applied voltage is increased by continuous or stepwise switching. When performing such control, the AC / DC power converter is
Connected in series, connecting the AC output side of one power converter to the AC system and using it as a so-called forward converter, the other power converter as a so-called reverse converter, and the voltage and frequency of the reverse converter side A configuration is adopted in which the start is made variable. In this case, the forward converter and the inverse converter each require the same capacity as the target induction motor. Further, unless the circuit is switched, the induction motor is connected to the motor even after the engine is started and the operation is performed at the normal voltage. On the other hand, when the speed of the induction motor to be controlled is controlled, the constant connection is useful because the frequency of the inverse converter is changed and realized.

However, if it is necessary only at the start,
Both the forward converter and the inverse converter have a capacity equivalent to that of the induction motor, and the equipment is idle, resulting in a waste. Further, when starting a plurality of induction motors at a time, frequency control is difficult in consideration of the case where the rotation speeds of the plurality of motors do not increase uniformly. Furthermore, if the rotation speed control is not necessary and the induction motor of the load is always connected to the power converter, the power loss of the forward converter and the reverse converter itself will always occur, which is uneconomical.

Since the power conversion system in the prior art has a structure in which the voltage can be freely changed under the rated frequency, its application has been studied as an alternative to the forward-inverse converter.

However, in the conventional configuration, the load voltage is determined by the difference between the system voltage and the voltage drop of the series transformer, but the voltage drop in the series transformer is equal to the magnitude of the exciting current due to the output of the series power converter. It is determined by the phase, and normally this current is extremely small with respect to the rated current, so accurate control is difficult. Further, since the system voltage always fluctuates slightly, it is difficult to accurately determine the load voltage determined by the vector difference from the system voltage.

On the other hand, another application example is an application relating to maintaining a load voltage by compensating for a short time (several 10 ms) drop or loss of the system voltage. In this application, the forward-reverse power converter described above is used, and the capacity of the DC circuit between the power converters is particularly large, that is, the capacity of the capacitor is large, or the battery is used.
It can be used as a so-called uninterruptible power supply. Even when the uninterruptible power supply is configured, the forward-reverse power converter is always connected in series between the load and the power system, so that there is a problem of loss due to the constant connection.

Since the power conversion system in the prior art has a structure in which the voltage can be freely changed under the rated frequency, its application as an alternative to the above-mentioned forward / reverse power converter has been studied.

However, the conventional structure has the following problems.

(1) Among the system voltage losses, when the system voltage loss occurs in the form of opening the circuit, the system side circuit of the series transformer is opened, so that a three-phase circuit is generated. It will not close and the load current will not flow in the open phase.

(2) When the system voltage is lost due to the short circuit of the system voltage, the voltage output from the series power converter is divided between the load and the short-circuit impedance, and The load current flows through the short circuit point. Therefore, the power generated by the series power converter is supplied to both the load and the short-circuit impedance, and the fault point cannot be removed in order to maintain the load current.

An object of the present invention is to provide a power conversion system capable of coping with the operation when the voltage on either the grid side or the load side is close to zero.

[0017]

In order to solve the above problems, the present invention relates to a parallel transformer connected in parallel to a power system, and a parallel power converter connected to the parallel transformer for converting electric power. A series transformer that is inserted in a circuit that connects the power system and a load and that is connected in series to the power system; a series power converter that is connected to the series transformer and converts power; and a parallel power converter. And an energy storage element that stores DC energy on the DC output side of the series power converter, a circuit breaker that is inserted into a circuit connecting the power system and the series transformer to open and close the circuit, and the series transformer. And a short-circuit switch for short-circuiting the power system side of each phase of the primary side winding connected to the power system among the three-phase windings.

According to the above means, when the system side is short-circuited or the system voltage is lost, the circuit breaker is opened, the short-circuit switch is turned on, the output voltage of the parallel power converter is increased, and the load voltage is kept constant. The output of the series power converter based on the energy stored in the energy storage element is supplied to the load through the short-circuit switch, and the power failure of the load can be prevented while the energy of the energy storage element is maintained. . This makes it possible to cope with the operation when the voltage on either the system side or the load side is close to zero.

In constructing the power conversion system, the following elements can be added.

(1) The series transformer is configured as an open delta transformer and functions as a delta-star connection transformer when the primary winding of each phase is short-circuited by the short-circuit switch. Become.

When the series transformer is composed of an open delta transformer, the series winding functions as a delta-star connection transformer because the primary winding of each phase is short-circuited by the short-circuit switch. The energy stored in the energy storage element can be supplied to the load via the short-circuiting switch even when the side is short-circuited.

(2) An auxiliary short-circuit switch for opening and closing a circuit connecting the power system and the load by bypassing the circuit breaker and the series transformer, a system voltage detector for detecting a voltage of the power system, and A load voltage detector that detects the voltage of the load, the auxiliary short-circuit switch in synchronization with the voltage of the power system based on the detection output of the system voltage detector and the detection voltage of the load voltage detector when the system is restored. And a switch closing control means for turning on.

In this case, when the load voltage is raised from 0 to the system voltage equivalent or when the voltage of the system that has been out of power is restored, the system voltage and the load voltage are detected, and the voltage of the system voltage is detected based on the detected voltage. The reclosing operation can be smoothly performed by turning on the auxiliary short-circuiting switch in synchronization with.

(3) A system voltage detector for detecting the voltage of the power system, and a system voltage detector for the parallel power converter when the system voltage detector detects that the voltage of the power system is lower than a set voltage. A power converter control means for stopping the power conversion operation, and then restarting the parallel power converter when the system voltage detector detects that the voltage of the power system has recovered to a set voltage. Become.

In this case, when the system voltage is lost, the parallel power converter is temporarily stopped, and when the system voltage is recovered to the set voltage thereafter, the parallel power converter is restarted to maintain the DC voltage. . As a result, the power conversion system responds to the operation when the voltage on either the system side or the load side is close to 0, and restores the normal state, especially when the system voltage is lost due to a short circuit. can do.

(4) A plurality of energy storage elements are provided, and a switching circuit for connecting the plurality of energy storage elements in series or in parallel is provided.

In this case, the operation of the parallel power converter is stopped due to the loss of the system voltage, and even if a high voltage is required when the load voltage is maintained by the output voltage of the series power converter, a plurality of power converters are required. A high voltage can be supplied by connecting the individual energy storage elements in series.

The present invention also provides, as a system for compensating for system voltage loss or for starting an induction motor, a parallel transformer connected in parallel to a power system and a parallel power converter connected to the parallel transformer for converting power. Power converter, a series power converter connected to a load connected in series to the power system to convert power, and an energy storage that stores DC energy at the DC output side of the parallel power converter and the series power converter An element, an auxiliary short-circuit switch that opens and closes a circuit that connects the power system and the load, a system voltage detector that detects the voltage of the power system, a load voltage detector that detects the voltage of the load, and the load The auxiliary short-circuit switch is turned on at the time of power supply to, and when the voltage loss of the power system is detected by the system voltage detector, the auxiliary short-circuit switch is opened, Power comprising switch closing control means for closing the auxiliary short-circuiting switch in synchronism with the voltage of the power system based on the detection output of the system voltage detector and the detection voltage of the load voltage detector during power restoration and restoration. It is a configuration of the conversion system.

According to the above-mentioned means, the power can be supplied to the load by turning on the auxiliary short-circuit switch in the normal state, and the load voltage can be maintained by opening the auxiliary short-circuit switch when the system voltage is lost. . Further, when the system voltage is restored, the normal state can be restored by turning on the auxiliary short-circuit switch.

The present invention also provides, as a system voltage loss compensation system, an auxiliary short-circuit switch for opening and closing a circuit connecting a power system and a load, and a load connected in series to the power system via the auxiliary short-circuit switch. Connected to the series power converter for converting power, an energy storage element for storing DC energy on the DC output side of the series power converter, a system voltage detector for detecting the voltage of the power system, and the load A power conversion system comprising: a switch closing control means for opening the auxiliary short-circuit switch when the system voltage detector detects a voltage loss in the power system when power is supplied to the auxiliary short-circuit switch. It is composed.

According to the above-mentioned means, power is normally supplied to the load by turning on the auxiliary short-circuit switch.
When the system voltage is lost, the energy stored in the energy storage element can be supplied to the load by opening the auxiliary short-circuit switch.

As a result, in a power conversion system which can be operated when the voltage on either the system side or the load side is close to 0 and which is restored to the normal state, especially when the system voltage is lost due to a short circuit. But you can continue driving.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a power conversion system showing an embodiment of the present invention. In FIG.
The power conversion system 10 includes a three-phase power system 12 and a load 1.
This power conversion system 10 is disposed between the power conversion system 10 and
Is a parallel transformer 16, a parallel power converter 18, a circuit breaker 2
0, short-circuit switch 22, series transformer 24, instrument transformer 26, series power converter 28, energy storage element 30,
The control device 32, the load voltage command setting device 34, and the instrument transformer 36 are provided.

The parallel transformer 16 is connected in parallel with the power system 12, the primary winding is connected to the power system 12, and the secondary winding is connected to the AC input side of the parallel power converter 18. . The parallel power converter 18 is, for example, as shown in FIG. 2, a switching element Tr1 such as a thyristor or a GTO.
To Tr6 and diodes D1 to D6, the AC / DC conversion operation is performed in accordance with a control signal from the converter control device 32, and AC power is converted to DC power or DC power is converted to AC power. The output side is connected to the energy storage element 30.

The energy storage element 30 is composed of, for example, a capacitor or a battery, and is configured to store DC energy at the DC output sides of the parallel power converter 18 and the series power converter 28.

On the other hand, the circuit breaker 20 is inserted in a circuit (distribution line) that connects the power system 12 and the load 14, and opens and closes the circuit according to a command from the control device 32.

The series transformer 24 includes the power system 12 and the load 1
It is inserted in the circuit connecting 4 and. This series transformer 24
3, an open delta circuit configuration is adopted, the primary winding is connected to the power system 12 and the load 14, and the secondary winding is the AC side of the series power converter 28. It is connected to the.

The short-circuit switch 22 is installed between the circuit breaker 20 and the series transformer 24 and short-circuits the primary windings of each phase of the series transformer 24 to each other in response to a closing command from the controller 32. Is configured to. During this short circuit,
The series transformer 24 functions as a delta-star connection transformer.

The series power converter 28 is the parallel power converter 1
Similar to 8, it is configured to include transistors Tr1 to Tr6 and diodes D1 to D6, performs a power conversion operation according to a control signal from the control device 32, and converts AC power into DC power or DC power into AC power. Is configured to convert to.

The control device 32 controls the output voltage of the transformer 26 as a load voltage detector for detecting the voltage of the load 14, the output voltage of the transformer 36 as a system voltage detector for detecting the system voltage, and the load voltage. The load voltage command by the setting of the command setting device 34 is respectively taken in, the control signal for controlling the switching element of each power converter 18, 28 is generated based on each output voltage and the load voltage command, and the generated control signal is generated. It outputs to each power converter 18, 28, each power converter 18,
It is configured as power converter control means for controlling the power conversion operation of the switch 28, and is also configured as switch closing control means for controlling the opening / closing operation of the circuit breaker 20 and the short-circuit switch 22.

In the above structure, when the short circuit switch 22 is in the open state and the circuit breaker 20 is turned on, the AC power from the power system 12 is supplied to the load 14 via the circuit breaker 20 and the series transformer 24. It At this time, when the power conversion operation by the parallel power converter 18 and the series power converter 28 is performed according to the control signal from the control device 32, the series transformer 24 is generated according to the magnitude and phase of the exciting current by the output of the series power converter 28. The voltage drop due to is determined. At this time, when a voltage in phase with the load voltage is generated from the series power converter 28, the voltage applied to the load 14 decreases, and if the load 14 is a passive load, the load current decreases as the load voltage decreases, and the power consumption decreases. Is reduced. The reduced power flows to the energy storage element 30 side via the series power converter 28, is regenerated to the power system 12 via the parallel power converter 18 and the parallel transformer 16, and the DC voltage is maintained constant. .

On the other hand, when the voltage generated from the DC power converter 28 has a reverse phase with respect to the load voltage, a voltage rise is given through the series transformer 24, and the voltage rises between the parallel power converter 18 and the series power converter 28. The flow of electric power in the DC circuit is reversed, and electric power is supplied from the parallel electric power converter 18 to the load 14 via the serial electric power converter 28. In this way, the power conversion system 10 can freely control the voltage applied to the load 14 up and down.

Here, when performing the operation of controlling the load voltage to around 0, as shown in FIG. 4, the breaker 20 is opened, the short-circuit switch 22 is turned on, and each of the series transformers 24 is turned on before starting. Phase primary windings are short-circuited to each other and series transformer 2
4 is used as a transformer with a delta-star connection. When a voltage is generated from the series power converter 28 when the load voltage is controlled to around 0 by the activation of the series power converter 28, this voltage is supplied to the load 14 via the series transformer 24. This supply energy is temporarily the energy of the energy storage element 30. At this time, power system 1
When there is a system voltage at 2, the parallel power converter 18 can be operated to replenish the consumed energy and maintain a constant DC voltage.

Next, when the output voltage of the transformer 36 drops below the set voltage and the system voltage is lost, for example, the system voltage becomes
When it becomes 0 V for 0 ms, as shown in FIG.
Simultaneously with the loss of system voltage, the circuit breaker 20 is opened and the short-circuit switch 22 is turned on. At this time, the series power converter 2
8 is operated to increase the output voltage so as to maintain the load voltage at a constant level, the energy stored in the energy storage element 30 is supplied to the load 14, and the energy of the energy storage element 30 continues for the duration of the load. It is possible to prevent 14 blackouts.

As described above, according to this embodiment, it is possible to supply power to the load 14 even when the voltage on either the system side or the load side is close to zero.

Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, an auxiliary short-circuit switch 38 that opens and closes a circuit that bypasses the circuit breaker 20 and the series transformer 24 and connects the power system 12 and the load 14 is provided in parallel with the circuit breaker 20 and the series transformer 24. The opening / closing operation of the switch 38 is controlled by the control device 32, and other configurations are similar to those of FIG.

The control device 32 takes in the output voltage of the instrument transformer 36 and the output voltage of the instrument transformer 26 and restores the system voltage when the load voltage is raised from 0 to the system voltage or when the system voltage is interrupted. If so, each transformer 36, 2
It is configured as a switch closing control means for closing the auxiliary short-circuit switch 28 in synchronization with the system voltage based on the output voltage of 6, for example, in synchronization with the zero cross point.

The circuit breaker 20 is opened and the short circuit switch 22 is opened.
Considering the case where the load voltage is raised from 0 to the system voltage equivalent or the system voltage which has been out of power is restored in a state where the power is supplied to the load 14 from the series power converter 28, In either case, it is necessary to re-parallel to the grid and restore the normal state in which power is directly supplied from the grid.

In such a case, as shown in FIG. 7, first, the magnitude and phase of the output voltage of the series power converter 28 are adjusted, and the auxiliary short-circuit switch 38 is turned on to reclose the circuit. At this time, the auxiliary short-circuit switch 38 is turned on in synchronization with the system voltage. Next, the short-circuit switch 22 is opened to set the current supplied from the series power converter 28 to the load 14 via the series transformer 24 to 0, and the power feeding path is completely shifted to the system side. At this time, the series power converter 28 temporarily stops its operation after opening the short circuit switch 22. After that, the circuit breaker 20 is turned on to restore the circuit to the normal state.
In this state, by restarting the series power converter 28 again and opening the auxiliary short-circuit switch 38, normal load voltage control can be performed thereafter.

According to the present embodiment, it is possible to realize an electric power conversion system which can be operated in the case where the voltage on either the system side or the load side is close to 0 and which can be restored to the normal state. The operation can be performed smoothly.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, as one element of the power converter control means, an undervoltage relay 40 is provided between the transformer 36 and the control device 32, and the voltage of the power system is lower than the set voltage. When it is detected that the system voltage has been lost due to the short circuit, the parallel power converter 1
The power conversion operation of No. 8 is stopped, and then the parallel power converter 18 is restarted when the voltage of the power system is restored to the set voltage, that is, when the system voltage is restored.

Specifically, when the loss of system voltage occurs due to a system short circuit, an overcurrent may flow from the parallel power converter 18 to the short circuit point via the parallel transformer 16. In this case, a short circuit may (1) shut down the system to protect the device from overcurrent,
(2) There are two possibilities that the overcurrent of the short circuit may discharge the energy of the DC circuit. In either case, the system will be stopped due to a problem on the side of the parallel power converter 18, and as it is, power cannot be supplied to the load 14 during a power failure.

In order to avoid this, in the present embodiment, when the loss of the system voltage is detected by the undervoltage relay 40, the power conversion operation of the parallel power converter 18 is temporarily stopped by a command from the control device 32. Let After that, after the system voltage is restored to a normal voltage, the parallel power converter 18 is restarted by a command from the control device 32, and control is performed to maintain the DC voltage constant.

According to the present embodiment, the operation when the voltage on either the system side or the load side is close to 0 is dealt with,
In addition, in the power conversion system that returns to the normal state, the operation can be continued especially when the system voltage is lost due to a short circuit.

Next, another embodiment of the energy element 30 will be described with reference to FIG. The energy element 30 according to the present embodiment includes a plurality of energy storage elements 30a and 30b including capacitors and batteries, and a switching circuit 42a for connecting the energy storage elements 30a and 30b directly or in parallel. 42b.

When the system voltage is lost, the power conversion operation of the parallel power converter 18 is stopped, and the load voltage is controlled by the output voltage of the series power converter 28. In this case, the voltage of the DC circuit may need to be higher than the output voltage of the series power converter 28 on the AC side. For example, when the series power converter 28 is configured using transistors as shown in FIG. 2, the AC output voltage of the series power converter 28 is output by switching the positive and negative voltages of the DC circuit using the transistors. Therefore, the maximum voltage that can be obtained depends on the DC voltage. Therefore, when a high voltage is required as the output voltage of the series power converter 28 such as when the system voltage is lost, the energy storage elements 30a and 30b are switched from the parallel connection to the series connection by switching the switching circuits 42a and 42b. And energy storage element 3
It is possible to supply a high voltage from 0 to the DC side of the series power converter 28.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, the power conversion system 1
In order to use 0 in the system for compensation of system voltage loss or for starting the induction motor, the power conversion system 1 shown in FIG.
From 0, circuit breaker 20, short-circuit switch 22, series transformer 2
4 is removed, the AC side of the series power converter 28 is directly connected to the load 14, and the auxiliary short-circuit switch 38 is turned on at normal times. Other configurations are similar to those of FIG.

The control device 32 in the present embodiment turns on the auxiliary short-circuit switch 38 when power is supplied to the load 14, and opens the auxiliary short-circuit switch 38 when the voltage of the power system is lost.
When the system is restored, it functions as a switch closing control means for closing the auxiliary short-circuit switch 38 in synchronization with the system voltage based on the system voltage and the load voltage. In addition, in the present embodiment, the output voltage of the series power converter 28 needs to be adjusted to correspond to the rated voltage of the load 14.

When the system voltage is lost, how quickly the short-circuit switch 22 is short-circuited or how the timing of the short-circuit and the timing of opening the circuit breaker 20 are matched. This difficulty is due to the series power converter 28 being connected to the load 14 via the series transformer 24.

In order to eliminate this difficulty, in the present embodiment, the series transformer 24 is omitted and the series power converter 28 is directly connected to the load 14, so that the power conversion system 10 loses the system voltage. It can be used for compensating or induction motor starting systems.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, a parallel transformer 16 and a parallel power converter 1 are added to the power conversion system 10 shown in FIG.
8, the circuit breaker 20, the short-circuit switch 22, and the series transformer 24 are removed, and the AC side of the series power converter 28 is directly connected to the load 14
, And the auxiliary short-circuit switch 38 is normally closed.

The control device 32 in the present embodiment turns on the auxiliary short-circuit switch 38 at the time of supplying power to the load 14, and opens the auxiliary short-circuit switch 38 when the loss of the system voltage is detected by the undervoltage relay 40. It will function as a means.

According to the present embodiment, if the system power loss compensation system is specialized, the energy storage element 30 may be used to store energy in the series power converter 28. Can be removed. In addition, since the load 14 is normally supplied with power via the auxiliary short-circuit switch 38, the series power converter 28 handles only the power to compensate for the loss of the energy storage element 30.

According to the present embodiment, the operation when the voltage of either the system side or the load side is close to 0 is dealt with,
In addition, in the power conversion system that returns to the normal state, in particular, the operation can be continued even when the system voltage is lost due to a short circuit.

[0065]

As described above, according to the present invention,
Even if the system side is short-circuited or the system voltage is lost, it is possible to handle the operation when the voltage on either the system side or the load side is close to 0, and the energy of the energy storage element continues. The load can be powered for a period of time.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a power conversion system showing a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a power converter.

FIG. 3 is a circuit configuration diagram of a series transformer.

FIG. 4 is a time chart for explaining the operation when the load voltage of the system shown in FIG. 1 is controlled to around 0.

5 is a time chart for explaining the operation of the system shown in FIG. 1 when the system voltage is lost.

FIG. 6 is a block configuration diagram of a power conversion system showing a second embodiment of the present invention.

FIG. 7 is a time chart for explaining the operation of the system shown in FIG.

FIG. 8 is a block configuration diagram of a power conversion system showing a third embodiment of the present invention.

FIG. 9 is a circuit configuration diagram showing another embodiment of the energy storage element.

FIG. 10 is a block configuration diagram of a power conversion system showing a fourth embodiment of the present invention.

FIG. 11 is a block configuration diagram of a power conversion system showing a fifth embodiment of the present invention.

[Explanation of symbols]

10 Power conversion system 12 power system 14 load 16 parallel transformer 18 Parallel power converter 20 circuit breaker 22 Short-circuit switch 24 series transformer 26 Instrument transformers 28 Series power converter 30 energy storage elements 32 control device 34 Load voltage command setter 36 Meter Transformer 38 Auxiliary short-circuit switch 40 Undervoltage relay

Claims (7)

[Claims] 1. A parallel transformer connected in parallel to an electric power system, a parallel power converter connected to the parallel transformer to convert electric power, and inserted into a circuit connecting the electric power system and a load to supply the electric power. A series transformer connected in series to the grid, a series power converter connected to the series transformer to convert electric power, and a DC energy storage at the DC output side of the parallel power converter and the series power converter. An energy storage element, a circuit breaker that is inserted into a circuit connecting the power system and the series transformer to open and close the circuit, and a primary side of the three-phase winding of the series transformer that is connected to the power system. A power conversion system, comprising: a short-circuit switch that short-circuits each phase of the windings on the power system side. 2. The power conversion system according to claim 1, wherein the series transformer is configured as an open delta transformer, and when the primary winding of each phase is short-circuited by the short-circuit switch, -A power conversion system characterized by functioning as a star-connected transformer. 3. The power conversion system according to claim 1, wherein an auxiliary short-circuit switch that opens / closes a circuit that bypasses the circuit breaker and the series transformer and connects the power system and the load, and the power system. A system voltage detector that detects the voltage of, and a load voltage detector that detects the voltage of the load,
And a switch closing control means for closing the auxiliary short-circuiting switch in synchronization with the voltage of the power system based on the detection output of the system voltage detector and the detection voltage of the load voltage detector when the system is restored. Power conversion system characterized by. 4. Any one of claims 1, 2 and 3
In the power conversion system according to the item, a system voltage detector that detects the voltage of the power system, and the parallel power when the system voltage detector detects that the voltage of the power system is lower than a set voltage. A power converter control means for stopping the power conversion operation of the converter, and then restarting the parallel power converter when the system voltage detector detects that the voltage of the power system has recovered to a set voltage. An electric power conversion system comprising: 5. The power conversion system according to claim 1, wherein the power conversion system includes a plurality of the energy storage elements, and the plurality of energy storage elements are connected in series or An electric power conversion system comprising a switching circuit connected in parallel. 6. A parallel transformer connected in parallel to a power system, a parallel power converter connected to the parallel transformer to convert power, and a power connected to a load connected in series to the power system. , A parallel power converter, an energy storage element that stores DC energy on the DC output side of the parallel power converter and the series power converter, and an auxiliary short circuit that opens and closes a circuit that connects the power system and the load. A switch, a system voltage detector that detects the voltage of the power system, a load voltage detector that detects the voltage of the load, and the auxiliary short-circuit switch is turned on when power is supplied to the load. When a voltage loss in the power system is detected, the auxiliary short-circuit switch is opened, and based on the detection output of the system voltage detector and the detection voltage of the load voltage detector when the system is restored. A power conversion system comprising: switch-on control means for switching on the auxiliary short-circuit switch in synchronization with the voltage of the power system. 7. An auxiliary short-circuit switch that opens and closes a circuit that connects a power system and a load, and a series power converter that is connected to a load connected in series to the power system via the auxiliary short-circuit switch to convert power. An energy storage element that stores DC energy on the DC output side of the series power converter, a system voltage detector that detects the voltage of the power system, and the auxiliary short-circuit switch is turned on when power is supplied to the load, A power conversion system comprising switch-on control means for opening the auxiliary short-circuit switch when the system voltage detector detects a voltage loss in the power system.