HK1087251B - Power converter - Google Patents

Description

Power converter

Technical Field

The present invention relates to a power converter connected in series to a system such as an electric power system, a power distribution system, and a single-phase ac overhead line, and more particularly to a power converter capable of continuing operation even in the event of a failure.

Background

Fig. 8 is a circuit diagram showing a configuration of a conventional power converter shown in, for example, U.S. patent No. 5646511. The power converter includes a series transformer in which a 2-stage primary coil is connected in series with a single-phase ac overhead line (hereinafter, simply referred to as a system) for a power system, a power distribution system, an electric subway, or the like, and a multi-stage multiple transformer (multi-arm transformers) on the secondary side thereof, and connects an ac-dc converter unit to the system. The power converter has the function of the power flow control means of the system. In the figure, a primary winding 201 of a series transformer 200 is connected between a power source side 1 of the system and a power source side (or a load side) 2 of the system. The secondary winding 202 of the series transformer 200 is connected in series with the primary windings 411 to 441 of the multi-stage multiplex transformers 410 to 440 (4-stage multiplex case is shown). The secondary windings 412 to 442 of the multilevel multiplex transformers 410 to 440 are connected to AC sides of the AC-DC converter units 510 to 540, respectively, and DC sides of 4 AC-DC converter units 510 to 540 are connected to a common DC circuit 511.

With the conventional power converter configured as described above, even if one of the ac-dc converter units 510 to 540 fails, the dc voltage of the dc circuit 511 cannot be maintained, and thus all the ac-dc converter units cannot operate, and the power converter must be stopped. There is also a problem that the power converter should be stopped until the repair or the periodic maintenance is completed, so that the operation rate of the system is lowered.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a power converter that can continue to operate with respect to a system even if 1 of a plurality of ac-dc converter units fails or stops operating during regular maintenance.

Disclosure of Invention

The power converter of the present invention includes:

a series transformer having a primary winding connected in series to a system, a multistage compound transformer comprising a plurality of transformers connected in series to a secondary winding of the series transformer, normally closed switches connected in series to both ends of the primary winding of each transformer of the multistage compound transformer, normally open shunt devices connected in parallel to a series body formed by the primary winding of each transformer of the multistage compound transformer and the switches connected to both ends thereof, ac-dc converter units each having a secondary winding of each transformer of the multistage compound transformer connected to an ac side thereof, and dc circuits connected to dc sides of the ac-dc converter units and independent of each other, wherein the shunt devices of the primary winding of a specific transformer of the multistage compound transformer are turned off and the switches connected to both ends of the primary winding are turned on, a particular transformer of the multi-stage compound transformer and the ac-dc converter unit connected thereto may be isolated from other transformers of the multi-stage compound transformer.

Therefore, the operation rate of the whole device is improved, the reliability is improved, and the capacity of the device is increased due to convenient capacity expansion.

Further, a power converter according to the present invention includes:

a multistage compound transformer comprising a plurality of transformers each having a primary winding connected in series with a system, normally closed switches connected in series to both ends of the primary winding of each transformer of the multistage compound transformer, normally open type 1 st shunt devices connected in parallel to a series body formed by the primary winding of each transformer of the multistage compound transformer and the switches connected to both ends thereof, an ac-dc converter unit having an ac side connected to a secondary winding of each transformer of the multistage compound transformer, dc circuits connected to respective dc sides of the ac-dc converter units and independent of each other, and normally open type 2 nd shunt devices connected in parallel to all the transformers of the multistage compound transformer connected in series, wherein the 1 st shunt device of the primary winding of a specific transformer of the multistage compound transformer is turned off and the switches connected to both ends of the primary winding are turned on, a particular transformer of the multi-stage compound transformer and the ac-dc converter unit connected thereto may be isolated from other transformers of the multi-stage compound transformer.

Therefore, the operation rate of the whole device is improved, the reliability is improved, and the capacity of the device is increased due to convenient capacity expansion.

Drawings

Fig. 1 is a circuit diagram of a power converter that does not show the configuration of embodiment 1 of the present invention.

Fig. 2 is a circuit diagram showing the composition of a power converter of embodiment 2.

Fig. 3 is a circuit diagram showing the composition of a general single-phase ac-dc converter.

Fig. 4 is a circuit diagram showing the composition of a power converter according to embodiment 3.

Fig. 5 is a circuit diagram showing the configuration of a power converter according to embodiment 4.

Fig. 6 is a circuit diagram showing the composition of a power converter of embodiment 5.

Fig. 7 is a circuit diagram showing the composition of a power converter of embodiment 6.

Fig. 8 is a circuit diagram showing a configuration of a conventional power converter.

Detailed Description

Embodiment mode 1

Fig. 1 is a circuit diagram showing a power converter according to embodiment 1 of the present invention. In the drawings, the same reference numerals are used for the same or corresponding portions, and the same is true hereinafter. In fig. 1, a primary winding 201 of a series transformer 200 is connected in series between a power source side 1 of a system and a power source side or a load side 2 of the system. The secondary winding 202 of the series transformer 200 is connected in series with the primary windings 411 to 441 of the multi-stage multiplex transformers 410 to 440 (4-stage multiplex case is shown). The secondary windings 412-442 of the multi-stage multiplexing transformers 410-440 are connected to the AC side of the AC-DC converter units 510-540, respectively, and the DC side of the 4 AC-DC converters 510-540 are connected to the DC circuits 511-541 independent of each other.

The power converter of the invention has such a composition that the DC circuits of the AC-DC converter units 510-540 are independent from each other and are not connected with the DC circuits of other AC-DC converter units. Normally closed switches (current interrupters, circuit breakers or semiconductor switches) 311 to 341 and 312 to 342 are arranged (connected) to both ends of each of primary coils 411 to 441 of the multistage compound transformers 410 to 440, respectively, and normally open shunt devices (current interrupters, circuit breakers or semiconductor switches) 310 to 340 are arranged (connected) in parallel on a series connection body of the primary coils 411 to 441 of the multistage compound transformers 410 to 440 and the switches 311 to 341 and 312 to 342 at both ends thereof. Thus, a particular multi-stage multiplexing transformer is isolated from the system when its shunt device is taken to conduct its primary winding and the switches across its primary winding are blocked.

Switches (circuit breakers, and semiconductor switches) 101 and 102 are arranged (connected) in series at both ends of a primary coil 201 of the series transformer 200, respectively, and shunt devices (circuit breakers, and semiconductor switches) 103 are arranged (connected) in parallel in a series body of 2 switches 101 and 102 of the primary coil 201 of the series transformer 200.

Short-circuiting devices (current interrupters, circuit breakers and semiconductor switches) 300 for short-circuiting the secondary winding 202 of the series transformer 200 are also provided to form a short-circuiting current when a system fails, so that the components can protect the ac-dc converter units 510 to 540 and the multistage compound transformers 410 to 440 together. Due to the shunt devices 310-340, the shorting device 300 may also be omitted in some cases. These devices can be selected according to design concepts of cost, installation space, and redundancy.

In embodiment 1, the coil structure of the secondary coil 202 of the series transformer 200 can be applied to Δ (delta) connection, Y (star) connection, or single-phase connection. The coil structure of the secondary coils 412-441 of the multi-stage compound transformers 410-440 can also be applied in delta (delta) connection, Y (star) connection or single phase connection.

Next, the operation thereof will be described. The power converter in series with the system is characterized by: the AC-DC converter units 510-540 cannot control the current flowing through the units themselves, and only the magnitude and phase of the voltage output by the units 510-540 are controlled. The reason why the power converter can indirectly control the current of the system is that the vector sum of the output voltages of the ac-dc converter units 510-540 is mediated by the multi-stage multiplex transformers 410-440, a voltage is generated in the primary winding 201 of the series transformer 200, and the injected voltage (injectivevoltage) generates a voltage of a certain magnitude between the system 1 and the system 2 at a certain phase, so that all the voltage sources and current sources on the system network can change the current passing through the power converter in all the system impedance states. This means that the power converter has the function of the power flow control means of the system. Therefore, the ac-dc Converter units 510 to 540 of the power Converter employ voltage source converters (VoltageSourced converters) as voltage sources. Due to this working principle, it is not necessary for each ac-dc converter unit to generate the same voltage, and even if 1 ac-dc converter unit is stopped, the power converter has no problem and can continue to operate.

In the power converter of embodiment 1, the shunt device 103 is in the blocking state, the switches 101 and 102 are in the conducting state, the short-circuit device 300 is in the blocking state, the shunt devices 310 to 340 are in the blocking state, and the switches 311 to 341 and 312 to 342 are in the conducting state at ordinary times.

Assume now that the ac-dc converter unit 510 is out of the system due to a fault. At this time, the shunt device 310 is turned on, and the switches 311 and 312 are turned off, so that the dc circuit 511 is also electrically isolated from the dc circuits 521 to 541 of the other ac-dc converter units in embodiment 1. Therefore, the operation of the power converter can be continued. In the conventional power converter, the ac-dc converter units cannot be operated if a part of the ac-dc converter units are disconnected, because neither the ac side nor the dc side of the ac-dc converter units is independent.

The AC-DC converter cell groups 510-540 are required to generate a voltage difference specified as a whole for the primary winding 201 of the series transformer 200. In embodiment 1, since the ac-dc converter unit groups 510 to 540 are independently configured, even if 1 or more ac-dc converter units are disconnected, the power converter can operate as a power converter.

When the number (N) of AC-DC converter units meets the specification required by the power converter, if 1 or more (N) of redundant (N + N) AC-DC converter units are added, even if the N AC-DC converter units are failed, the rated value of the system is not damaged, and the system can continue to operate. Therefore, if the ac-dc converter unit is provided as a redundant unit, the power converter can be operated at a rated value of 100% as it is without the redundant ac-dc converter unit.

When the maximum current flowing through the AC-DC converter units 510-540 is larger than the rated current of the AC-DC converter units 510-540 under the condition of system failure and the like, the maximum current of the AC-DC converter units 510-540 can be reduced by increasing the number of the multiple connection stages of the multi-stage multiple connection transformer and the AC-DC converter units through the selected composition. This is achieved according to the nature of the power converter in series with the system. When the product of the voltage Vs injected to the primary winding of the series transformer 200 and the maximum current Is of the system Is defined as the rated value of the power converter, the number of stages N can be obtained by dividing the rated value (Vs × Is) of the power converter by the product (Vc × Ic) of the rated voltage Vc and the rated current Ic of the 1-stage part of the multi-stage multiplexing transformer and the ac-dc converter unit. The maximum current of the ac-dc converter voltage exceeds the rated current even in the case of a system failure or the like by the number of stages N1 obtained from the rated current of the system at ordinary times, and therefore, the rated current Ic2 of the ac-dc converter unit can be used in consideration of the maximum current Is2 at system failure so as to reduce the rated value to be smaller than the maximum rated value at ordinary times by using the rated values of the ac-dc converter unit and the multi-stage compound transformer at ordinary times. This is equivalent to reducing the voltage of the primary windings 411 to 441 of the multi-stage multiplexing transformers 410 to 440, so that the number of multiplexing stages N is increased.

Embodiment 1 utilizes the above-described property of the power converter connected in series to the system, and adds a multistage multiplex transformer and an ac-dc converter unit in a series state after the power converter is installed, thereby expanding the capacity of the power converter. This feature is only possible due to the independent dc circuit composition of the ac-dc converter unit.

In embodiment 1, when the voltage of the secondary winding is lowered, the maximum current of the secondary winding 202 is generally increased in the series transformer 200 in the case of a system failure or the like. Embodiment 1 may also adopt a method of boosting the secondary winding in the series transformer 200 in reverse to optimize the rated values of the semiconductor switch 300, the circuit breakers 310 to 340, and the circuit breakers 311 to 341, 312 to 342 when the maximum current of the secondary winding 202 exceeds the rated currents of the semiconductor switch (short-circuit device) 300, the circuit breakers (shunt device) 310 to 340, and the circuit breakers (switches) 311 to 341, 312 to 342.

Embodiment mode 2

In embodiment 1, the ac-dc converter units 510 to 540 are isolated one by one, but as shown in fig. 2, 2 ac-dc converter units 550 to 580 are connected to the secondary coils 452 and 462 of the multistage multiplex transformers 450 and 460, respectively. At this point, the pair of 2 DC circuits 551 and 552 become commoned, but independent of the other DC circuit pairs 561 and 562. This point is the same as embodiment 1.

When the number of ac-dc converter units is2 × N, the number of stages of the multistage compound transformer is only half of N as compared with embodiment 1, and therefore, the multistage compound transformer can be expected to be manufactured at low cost. However, in embodiment 2, the ac-dc converter unit is failed or periodically overhauled to stop 2 units, but if the desired operation rate of redundancy is not affected, a system without problems can be provided. In embodiment 2, 2 ac-dc converter units are controlled simultaneously, and a part of circuits called dc voltage control is shared among control units (not shown), so that 1 can be omitted and the cost can be reduced.

Fig. 3 is a circuit diagram showing the composition of a general single-phase ac-dc converter (single-phase converter). In the figure, the ac side terminal 901 is connected to the self arc extinguishing elements 911 and 912 and the flywheel diodes 921 and 922, and the ac side terminal 902 is connected to the self arc extinguishing elements 913 and 914 and the flywheel diodes 923 and 924. The dc square terminal is connected to the capacitor 930. Embodiment 2 can also be applied to a case where the ac-dc transformer unit constitutes a single-phase bridge circuit shown in fig. 3. In the case of a system of single-phase ac overhead lines of an electric subway, since a three-phase bridge ac-dc transformer unit cannot be employed, it is necessary to employ the single-phase bridge ac-dc converter unit of fig. 3.

Embodiment 3

In embodiment 1, the series transformer 200 is disposed between the system power source side 1 and the system power source side (or load side) 2 to constitute the multistage multiplex transformers 410 to 440 and the ac-dc converter units 510 to 540, but in embodiment 3 shown in fig. 4, the multistage multiplex transformers 410 to 440 may be directly connected in series between the system power source side 1 and the system power source side (or load side) 2. The primary coils 411 to 441 of the multistage multiplex transformers 410 to 440 are connected in parallel to a shunt device (a breaker, a circuit breaker, or a semiconductor switch) 300, and when a system fails, the primary coils 411 to 441 of the multistage multiplex transformers 410 to 440 are all bypassed together.

The circuit of fig. 4 can be used when the multi-stage compound transformer can be directly connected to the system, when the semiconductor switch can be directly connected, and when the multi-stage compound transformer can convert (generally step down) a system voltage which is considered to be higher into an ac voltage of the ac-dc transformer unit with 1 stage, and the like.

In embodiment 1, when the voltage of the secondary winding of the series transformer 200 is reduced, the current of the secondary winding 202 is generally increased. Therefore, when the maximum current flows through the secondary coil 202 too much in the event of a system failure or the like, the semiconductor switch 300 having a large rated current should be manufactured. When the semiconductor switch 300 having a high voltage and a small rated current is easy to manufacture compared with the semiconductor switch 300 having a low voltage and a large rated current, the series transformer 200 may be omitted and the configuration of embodiment 3 may be adopted.

Embodiment 4

In embodiment 2, the series transformer 200 is disposed between the power source side 1 of the system and the power source side (or load side) 2 of the system to constitute the multistage multiplex transformers 450 to 460 and the ac-dc converter units 550 to 580, but in embodiment 4 shown in fig. 5, the multistage multiplex transformers 450 to 460 may be directly connected in series between the power source side 1 of the system and the power source side (or load side) 2 of the system. The secondary coils 451 to 461 of the multiplexers 450 to 460 are connected in parallel to a shunt device (a breaker, or a semiconductor switch) 300, and all the primary coils 451 to 461 of the multistage multiplexing transformers 450 to 460 are bypassed together in the event of a system failure or the like.

The circuit of fig. 5 can be used when the multi-stage compound transformer can be directly connected to the system, when the semiconductor switch can be directly connected, and when the multi-stage compound transformer can convert (generally step down) a system voltage which is considered to be higher into an ac voltage of the ac-dc transformer unit with 1 stage, and the like.

In embodiment 2, when the voltage of the secondary winding of the series transformer 200 is reduced, the current of the secondary winding 202 is generally increased. Therefore, when the maximum current flows through the secondary coil 202 too much in the event of a system failure or the like, the semiconductor switch 300 having a large rated current should be manufactured. When the semiconductor switch 300 having a high voltage and a small rated current is easy to manufacture compared with the semiconductor switch 300 having a low voltage and a large rated current, the series transformer 200 may be omitted and the configuration of embodiment 4 may be adopted.

Embodiment 5

In embodiment 1, each of the multistage compound transformers constitutes 1 set of switches 311 to 341 and 312 to 342 and shunt devices 310 to 340 for isolating the primary coils 411 to 441 of the multistage compound transformers 410 to 440 from each other, but in embodiment 5, as shown in fig. 6, a multistage compound transformer 801 is constituted by a plurality of transformers 810 and 820 connected in series. Also, the multistage compound transformer 802 is constituted by a plurality of transformers 830 and 840 connected in series. Normally closed switches 311 and 322 are connected in series at both ends of a series body of primary coils 811 and 821 of the plurality of transformers 810 and 820. Similarly, normally-closed switches 331 and 342 are connected in series at both ends of a series body of primary coils 831 and 841 of a plurality of transformers 830 and 840. The 1 normally-open shunt device 310 is connected in parallel to the series body of the switches 311 and 322 at both ends of the plurality of transformers 810 and 820. Also, 1 normally-open shunt device 330 is connected in parallel to the series body of the switches 331 and 342 at both ends of the plurality of transformers 830 and 840. The secondary coils 812, 822, 832, 842 of the transformers 810-840 are connected to the AC-DC converter units 510-540, respectively. With the composition structure of fig. 6, the cost can be reduced.

This configuration loses redundancy of the multi-stage multiplex transformer and the ac-dc converter unit, but can be adopted as long as there is no problem in redundancy of the power converter.

The method in which the structure is changed from embodiment 1 to embodiment 5 can also be applied to embodiment 2, embodiment 3, or embodiment 4.

Embodiment 6

In embodiment 1, each ac-dc converter unit is connected not only to the capacitor but also to other energy storage devices, so that the injection voltage output from the power converter can output both the voltage of the active component and the voltage of the reactive component in any phase of 360 degrees.

Examples of the energy storage device include a secondary battery typified by a battery, an energy storage device such as a large-capacity capacitor, and another ac-dc converter voltage in which a mechanical energy source such as a flywheel is connected through a generator which also serves as an engine.

The structure of embodiment 6 shown in fig. 7 may be understood as DVR (Dynamic Voltage Restorer) and UPFC (Unified Power Flow Controller). The AC-DC converters 513 to 543 are independently connected to the DC circuits 511 to 541 of the AC-DC converter units 510 to 540, and the AC-DC converters 513 to 543 are connected to the system through the transformers 610 to 640, the current breakers 611 to 641, the transformer 700, and the current breaker 701, so that independent energy can be obtained.

Industrial applicability of the invention

In summary, the power converter of the present invention is suitable for use in a power flow control apparatus that can continue to operate even in the event of a partial failure.

Claims (4)

1. A power converter, comprising

A series transformer (200) with a primary coil (201) connected in series with the system,

A multi-stage multiplex transformer composed of a plurality of transformers (410-440) connected in series with the secondary coil (202) of the series transformer (200),

Normally closed switches (311-342) respectively connected in series to both ends of primary coils (411-441) of transformers (410-440) of the multi-stage compound transformer,

Normally open shunt devices (310-340) connected in parallel to a series body formed by primary coils (411-441) of transformers (410-440) of the multistage compound transformer and switches (311-342) at two ends of the primary coils,

AC-DC converter units (510-540) having secondary coils (412-442) of transformers (410-440) of the multi-stage compound transformer connected to the AC side, and

DC circuits 511 to 541 connected to DC sides of the AC-DC converter units 510 to 540 respectively and independent of each other,

the specific transformer (410) of the multi-stage compound transformer and the AC-DC converter unit (510) connected thereto can be isolated from the other transformers (420-440) of the multi-stage compound transformer by turning off the shunt device (310) of the primary coil (411) of the specific transformer (410) of the multi-stage compound transformer and turning on the switches (311, 312) at both ends of the primary coil (411).

2. The power converter as recited in claim 1 wherein,

there are a plurality of AC-DC converter units (550-580) connected on the AC side to each of the secondary coils (452, 462) of the transformers (450, 460) of the multi-stage compound transformer,

-providing a single dc circuit (551) commonly connected to the dc side of a plurality of ac-dc converter units (550, 570) of the secondary winding (452) of each transformer (450) of the multi-stage compound transformer, the single dc circuit (551) being independent of a single dc circuit (561) commonly connected to the dc side of a plurality of ac-dc converter units (560, 580) of the secondary winding (462) of each other transformer (460) of the multi-stage compound transformer.

3. A power converter, comprising

A multi-stage multiplex transformer composed of a plurality of transformers (410-440) in which primary coils (411-441) and a system are connected in series,

Normally closed switches (311-342) respectively connected in series to both ends of primary coils (411-441) of transformers (410-440) of the multi-stage compound transformer,

Normally open type 1 st shunt devices (310-340) connected in parallel to a series body formed by primary coils (411-441) of transformers (410-440) of the multistage compound transformer and switches (311-342) at two ends of the primary coils,

AC-DC converter units (510-540) having AC sides respectively connected to secondary coils (412-442) of transformers (410-440) of the multistage compound transformer,

DC circuits 511 to 541, which are connected to the respective DC sides of the AC-DC converter units 510 to 540 and are independent of each other, and

a normally open type 2 nd shunt device (300) connected in parallel to the transformers (410-440) of all the multi-stage compound transformers connected in series,

the specific transformer (410) of the multi-stage compound transformer and the AC-DC converter unit (510) connected with the specific transformer (410) can be isolated from other transformers (420-440) of the multi-stage compound transformer by turning off the 1 st shunt device (310) of the primary coil (411) of the specific transformer (410) of the multi-stage compound transformer and turning on the switches (311, 312) at both ends of the primary coil (411).

4. The power converter as recited in claim 3 wherein,

there are a plurality of AC-DC converter units (550-580) connected on the AC side to each of the secondary coils (452, 462) of the transformers (450, 460) of the multi-stage compound transformer,

-providing a single dc circuit (551) commonly connected to the dc side of a plurality of ac-dc converter units (550, 570) of the secondary winding (452) of each transformer (450) of the multi-stage compound transformer, the single dc circuit (551) being independent of a single dc circuit (561) commonly connected to the dc side of a plurality of ac-dc converter units (560, 580) of the secondary winding (462) of each other transformer (460) of the multi-stage compound transformer.