CN115498862A - Cascaded bidirectional variable-current direct-current side short-circuit current suppression system and method - Google Patents

Abstract

The invention provides a cascade bidirectional variable-current direct-current side short-circuit current suppression system and a method, which belong to the technical field of power electronic control and comprise the following steps: the device comprises a cascade type bidirectional converter device, an isolation transformer, a short-circuit protection module and a current detection module; the short-circuit protection module is used for: a: if the real-time value of the direct current is greater than or equal to the I-level preset direct-current side short-circuit protection value, the cascade type bidirectional converter device operates in a low-power mode, and the IGBT modulation degree of a power unit of the bidirectional converter device is reduced to protect the power unit; b: and after the step a is executed, if the real-time value of the direct current is still greater than or equal to the II-level preset direct-current side short-circuit protection value, controlling the cascade type bidirectional converter to stop running, and turning off the IGBT output signal of the power unit of the bidirectional converter. The invention reasonably selects the protective measures according with the short-circuit fault condition, and avoids the damage of the short-circuit current to the IGBT components in the power module of the cascade bidirectional converter.

Description

A system and method for suppressing short-circuit current on the DC side of a cascaded bidirectional converter

technical field

The invention belongs to the technical field of power electronic control, and in particular relates to a cascading type bidirectional variable current DC side short-circuit current suppression system and method.

Background technique

For example, the cascaded bidirectional converter with publication number CN115051541A, based on the cascaded bidirectional converter, when a short-circuit fault or overload operation occurs in the power grid, the IGBT antiparallel diodes in the power unit of the bidirectional converter will be damaged in a short period of time. The impact of the large freewheeling current directly causes damage to the IGBT in the power unit, affecting the normal operation of the cascaded bidirectional converter. However, the usual protection method directly blocks the pulse signal of the IGBT regardless of the magnitude of the current, which will inevitably affect the normal operation of the system and cannot achieve reliable short-circuit protection of the bidirectional converter.

Contents of the invention

Aiming at the above-mentioned shortcomings of the prior art, the present invention provides a cascade-type bidirectional converter DC side short-circuit current suppression system and method to solve the above-mentioned technical problems.

In the first aspect, the present invention provides a cascaded bidirectional converter DC side short-circuit current suppression system, including: a cascaded bidirectional converter device, an isolation transformer, a short-circuit protection module, and a current detection module;

The high-voltage side of the isolation transformer is connected to the AC power grid, the low-voltage side of the isolation transformer is connected to the power unit of the cascaded bidirectional converter; the output terminal of the short-circuit protection module is connected to the low-voltage side of the isolation transformer; The input end of the short-circuit protection module is connected to the DC side of the cascaded bidirectional converter device;

The current detection module is used to obtain the real-time value of the DC side current of the cascaded bidirectional converter device and send it to the short circuit protection module; the short circuit protection module is used for:

a: If the real-time value of the DC current is greater than or equal to the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates in a weak power mode, reducing the IGBT turn-on time of the power unit of the bidirectional converter to protect the power unit;

b: After executing a, if the real-time value of the DC current is still greater than or equal to the level II preset DC side short-circuit protection value, control the cascaded bidirectional converter to stop running, and turn off the output signal of the power unit IGBT of the bidirectional converter;

c: After performing operations a and b, if the real-time value of the DC current is still greater than or equal to the level III preset DC side short-circuit protection value, disconnect the AC-side circuit breaker and DC-side contactor of the bidirectional converter device, and discharge the short-circuit current to the low voltage side of the isolation transformer.

Among them, the preset DC side short-circuit protection value of level III > the preset DC side short-circuit protection value of level II > the preset DC side short-circuit protection value of level I.

Further, the short-circuit protection module includes a rectifying bridge circuit composed of diodes and a reactor, and the rectifying bridge circuit and the reactor form a low-impedance topological circuit, which is used to suppress the cascaded bidirectional converter power unit and the reactor. High-frequency circulating current between AC grids and short-circuit current generated during short-circuit;

If the real-time value of the DC current is less than the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates normally, and the withstand current and high-frequency circulating current suppression module continues to suppress the power unit of the cascaded bidirectional converter and the AC grid between high-frequency circulation.

Further, the low-voltage side of the isolation transformer includes a first-level winding and a second-level winding; the first-level winding and the first-level power unit of the cascaded bidirectional converter device and the withstand current and high-frequency The output end of the circulation suppression module is connected; the second-level winding is connected with the second-stage power unit of the cascaded bidirectional converter and the output end of the withstand current and high-frequency circulation suppression module.

Further, the AC end of the rectifier bridge circuit is connected to the first-stage winding and the second-stage winding of the isolation transformer; the DC end of the rectifier bridge circuit is connected to the reactor; the reactor is connected to the cascaded The DC side of the type bidirectional converter device is connected.

Further, the current detection module includes a sampling circuit and a shunt; the shunt is connected to the negative bus bar of the DC side of the cascaded bidirectional converter device, and is used to collect the current value of the DC side; the sampling circuit and the shunt Connect to the short circuit protection module.

Further, the short-circuit protection module is also used for: when the real-time value of the DC current decreases to less than the level I preset DC-side short-circuit protection value, the pulse signal of the power limit and the closed IGBT is automatically released, so that the cascaded bidirectional transformer The streaming device resumes normal operation.

In the second aspect, the present invention provides a method for suppressing the short-circuit current on the DC side of the cascaded bidirectional converter, including:

Detect the real-time value of the DC side current of the cascaded bidirectional converter device, and compare it with the preset DC side short-circuit protection value of Class I, II, and III, among which, the preset DC side short-circuit protection value of Class III > the preset DC side short-circuit protection value > level I preset DC side short-circuit protection value;

a: If the real-time value of the DC current is greater than or equal to the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates in a weak power mode, reducing the IGBT turn-on time of the power unit of the bidirectional converter to protect the power unit;

b: After executing a, if the real-time value of the DC current is still greater than or equal to the level II preset DC side short-circuit protection value, the cascaded bidirectional converter device is controlled to stop running, and the power unit IGBT of the bidirectional converter device turns off the output signal;

c: After performing operations a and b, if the real-time value of the DC current is still greater than or equal to the level III preset DC side short-circuit protection value, disconnect the AC-side circuit breaker and DC-side contactor of the bidirectional converter device, and discharge the short-circuit current to the low voltage side of the isolation transformer.

Further, it also includes: after performing any one of operations a, b, and c, if the real-time value of the DC current is less than the level I preset DC side short-circuit protection value, then release the pulse signal to the power limit and turn off the IGBT, so that the bidirectional inverter The streaming device resumes operation.

Further, it also includes: when the bidirectional converter is in normal operation, when the bus voltage of the power supply grid rises to be greater than the sum of the peak voltages of the two sets of AC sides of the cascaded bidirectional converter, the power of the DC traction grid side will not be transmitted to the AC grid side.

The beneficial effect of the present invention is that the system and method provided by the present invention can reasonably select protection measures that meet the short-circuit fault situation according to the real-time value of the DC side current, so as to avoid the impact of the short-circuit current on the IGBT components in the power module of the cascaded bidirectional converter device. damage. In addition, the design principle of the present invention is reliable, the structure is simple, and has very wide application prospects.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, In other words, other drawings can also be obtained from these drawings on the premise of not paying creative work.

Fig. 1 is a schematic structural diagram of a cascaded bidirectional converter DC side short-circuit current suppression system according to an embodiment of the present invention.

detailed description

In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

An embodiment of the present invention provides a cascaded bidirectional converter DC side short-circuit current suppression system, as shown in Figure 1, which provides a topology diagram of the system provided by the present invention, including: cascaded bidirectional converter device, A transformer, a short-circuit protection module, and a current detection module; the high-voltage side of the isolation transformer is connected to the AC grid, and the low-voltage side of the isolation transformer is connected to the power unit of the cascaded bidirectional converter; the output terminal of the short-circuit protection module is connected to the The low-voltage side of the isolation transformer is connected; the input end of the short-circuit protection module is connected to the DC side of the cascaded bidirectional converter.

The current detection module acquires the real-time value of the current on the DC1500V input side and sends it to the short-circuit protection module, which is used to take short-circuit protection measures to protect the For the IGBT in the power unit, the short-circuit protection measures are divided into three levels a, b, and c, corresponding to different degrees of real-time current values, specifically including:

a: If the real-time value of the DC current is greater than or equal to the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates in a weak power mode, reducing the IGBT turn-on time of the power unit of the bidirectional converter to protect the power unit;

b: After executing a, if the real-time value of the DC current is still greater than or equal to the level II preset DC side short-circuit protection value, control the cascaded bidirectional converter to stop running, and turn off the output signal of the power unit IGBT of the bidirectional converter;

c: After performing operations a and b, if the real-time value of the DC current is still greater than or equal to the level III preset DC side short-circuit protection value, disconnect the AC-side circuit breaker and DC-side contactor of the bidirectional converter device, and discharge the short-circuit current to the low voltage side of the isolation transformer;

Through three types of operations a, b, and c, the internal IGBT of the traction power supply cascaded bidirectional converter device can be protected from damage, and at the same time, the bidirectional converter device can still resume normal operation after the fault is removed, effectively avoiding short-circuit current damage to the device influences.

Among them, the preset DC side short-circuit protection value of level III > the preset DC side short-circuit protection value of level II > the preset DC side short-circuit protection value of level I.

The impact of the three levels of protection measures a, b, and c on the two-way converter device is a < b < c, and the operation with less impact is preferred.

The above is the case of overcurrent, when a short-circuit fault occurs in the power grid, compare it with the preset short-circuit protection value of the DC side to determine whether there is a short-circuit fault on the DC side. If there is no fault, the pulse signal of the power unit will be maintained, and the device will continue to run. At the same time, the short-circuit protection module will suppress the high-frequency circulating current between the power unit of the cascaded bidirectional converter system and the AC grid, and realize the short-circuit protection described in this part of the function. The module includes a rectifier bridge circuit composed of diodes and a reactor. The rectifier bridge circuit and the reactor form a low-impedance topological circuit, which is used to suppress the high-frequency circulating current between the power unit of the cascaded bidirectional converter and the AC grid and The short-circuit current generated during short-circuit; when the bus voltage of the power supply grid rises to be greater than the sum of the peak voltages of the two sets of AC sides of the cascaded bidirectional converter, the withstand current and the voltage of the DC side of the high-frequency circulating current suppression module are greater than the voltage of the AC side Voltage, the bridge rectifier circuit composed of diodes and the DC side of the reactor will not transmit the electric energy of the AC side to the DC traction network side.

If the real-time value of the DC current is less than the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates normally, and the withstand current and high-frequency circulating current suppression module continues to suppress the power unit of the cascaded bidirectional converter and the AC grid between high-frequency circulation.

Optionally, as an embodiment of the present invention, it is characterized in that the low-voltage side of the isolation transformer includes a first-level winding and a second-level winding; the first-level winding and the cascaded bidirectional converter I The first-stage power unit is connected to the output end of the withstand current and high-frequency circulation suppression module; the second-stage winding is connected to the second-stage power unit of the cascaded bidirectional converter device and the above-mentioned withstand current and high-frequency circulation suppression module output connection.

Optionally, as an embodiment of the present invention, the AC end of the rectification bridge circuit is connected to the first-stage winding and the second-stage winding of the isolation transformer; the DC end of the rectification bridge circuit is connected to the reactor ; The reactor is connected to the DC side of the cascaded bidirectional converter.

In this embodiment, the isolation transformer is mainly a 35kV transformer on the AC side. The transformer is dry-type, indoor, self-cooling, and cast with epoxy resin. The connection mode is Dy11/y11. The high-voltage side is connected to the 35kV AC power grid, and the low-voltage side is divided into two stages. Winding, the first level winding is connected to the output of the withstand current and high-frequency circulating current suppression module and the AC circuit breaker of the first-level bidirectional conversion module of the cascaded bidirectional conversion system, and the second level winding is connected to the withstand current and high-frequency circulating current suppression module The AC circuit breaker of the output and cascade type bidirectional converter system II level bidirectional converter module, the voltage is the AC rated voltage of the traction power supply bidirectional converter device, and when the DC side is short-circuited, the withstand current and the high-frequency circulating current suppression module will be The short-circuit current is discharged to the low-voltage side winding of the transformer.

Optionally, as an embodiment of the present invention, the current detection module includes a sampling circuit and a shunt; the shunt is connected to the negative bus bar of the DC side of the cascaded bidirectional converter, and is used to collect the current value of the DC side; The sampling circuit is connected with the shunt and the short circuit protection module. The embodiment of the present application configures the real-time value of the DC current at the DC1500V input side of the current detection module.

Optionally, as an embodiment of the present invention, the short-circuit protection module is also used for: when the real-time value of the DC current drops to less than the level I preset DC-side short-circuit protection value, then automatically release the power limit and turn off the IGBT pulse signal, so that the cascaded bidirectional converter can resume normal operation. In this embodiment, after the fault is removed, the bidirectional converter device can be controlled to automatically resume normal operation, effectively avoiding the influence of the short-circuit current on the device.

In the second aspect, the embodiment of the present invention provides a cascaded bidirectional converter DC side short-circuit current suppression method, which includes: detecting the real-time value of the DC side current of the cascaded bidirectional converter device, and communicating with I, II, and III pre-set Set the short-circuit protection value of the DC side for comparison, among which, the preset short-circuit protection value of the DC side at level III > the preset short-circuit protection value of the DC side at level II > the preset short-circuit protection value of the DC side at level I;

a: If the real-time value of the DC current is greater than or equal to the level I preset DC side short-circuit protection value, the cascaded bidirectional converter operates in a weak power mode, reducing the IGBT turn-on time of the power unit of the bidirectional converter to protect the power unit;

b: After executing a, if the real-time value of the DC current is still greater than or equal to the level II preset DC side short-circuit protection value, the cascaded bidirectional converter device is controlled to stop running, and the power unit IGBT of the bidirectional converter device turns off the output signal;

c: After performing operations a and b, if the real-time value of the DC current is still greater than or equal to the level III preset DC side short-circuit protection value, disconnect the AC-side circuit breaker and DC-side contactor of the bidirectional converter device, and discharge the short-circuit current to the low voltage side of the isolation transformer.

Optionally, as an embodiment of the present invention, after performing any one of operations a, b, and c, if the real-time value of the DC current is less than the level I preset DC side short-circuit protection value, the power limit is released and the IGBT is turned off The pulse signal of the two-way converter device resumes operation.

Optionally, as an embodiment of the present invention, the method for suppressing the high-frequency circulating current between the power unit of the cascaded bidirectional converter system and the AC grid is as follows: when the bidirectional converter device operates normally, when the bus voltage of the power supply grid increases When it is greater than the sum of the peak voltages of the two sets of AC sides of the cascaded bidirectional converter device, the power from the DC traction grid side will not be transmitted to the AC grid side.

Although the present invention has been described in detail in conjunction with preferred embodiments with reference to the accompanying drawings, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those skilled in the art can make various equivalent modifications or replacements to the embodiments of the present invention, and these modifications or replacements should be within the scope of the present invention. Those skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention, and all should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (9)

1. A cascaded bidirectional variable-current direct-current side short-circuit current suppression system is characterized by comprising: the device comprises a cascade type bidirectional converter device, an isolation transformer, a short-circuit protection module and a current detection module;

the high-voltage side of the isolation transformer is connected with an alternating current power grid, and the low-voltage side of the isolation transformer is connected with a power unit of the cascade type bidirectional converter; the output end of the short-circuit protection module is connected with the low-voltage side of the isolation transformer; the input end of the short-circuit protection module is connected with the direct current side of the cascade bidirectional converter;

the current detection module is used for acquiring a direct-current side current real-time value of the cascade bidirectional converter and sending the direct-current side current real-time value to the short-circuit protection module; the short-circuit protection module is used for:

a: if the real-time value of the direct current is greater than or equal to the I-level preset direct-current side short-circuit protection value, the cascade type bidirectional converter device operates in a low-power mode, and the IGBT turn-on time of a power unit of the bidirectional converter device is reduced to protect the power unit;

b: after a is executed, if the real-time value of the direct current is still larger than or equal to the II-level preset direct-current side short-circuit protection value, controlling the cascade type bidirectional converter to stop running, and closing a power unit IGBT output signal of the bidirectional converter;

c: after the operation a and the operation b are executed, if the real-time value of the direct current is still larger than or equal to the III-level preset direct-current side short-circuit protection value, the alternating-current side circuit breaker and the direct-current side contactor of the bidirectional converter are switched off, and the short-circuit current is discharged to the low-voltage side of the isolation transformer to be wound;

wherein, the III-level preset direct current side short-circuit protection value is larger than the II-level preset direct current side short-circuit protection value is larger than the I-level preset direct current side short-circuit protection value.

2. The system according to claim 1, wherein the short-circuit protection module comprises a rectifier bridge circuit and a reactor which are composed of diodes, the rectifier bridge circuit and the reactor form a low-impedance topological circuit, and the low-impedance topological circuit is used for inhibiting high-frequency ring current between the power unit of the cascade type bidirectional converter and the alternating current network and short-circuit current generated in short circuit;

if the real-time value of the direct current is smaller than the I-level preset direct-current side short-circuit protection value, the cascade type bidirectional converter device normally operates, and the high-frequency circulating current between the power unit of the cascade type bidirectional converter device and the alternating current network is continuously restrained by the current-tolerant and high-frequency circulating current restraining module.

3. The system of claim 1, wherein the low voltage side of the isolation transformer comprises a first stage winding, a second stage winding; the first-stage winding is connected with a first-stage power unit of the cascade type bidirectional converter and the output end of the withstand current and high-frequency circulating current suppression module; and the second-stage winding is connected with the II-stage power unit of the cascade type bidirectional converter and the output end of the withstand current and high-frequency circulating current suppression module.

4. The system of claim 1, wherein an ac terminal of a rectifier bridge circuit is connected to the primary winding and the secondary winding of the isolation transformer; the direct current end of the rectifier bridge circuit is connected with the reactor; the reactor is connected with the direct current side of the cascade bidirectional converter.

5. The system of claim 1, wherein the current detection module comprises a sampling circuit and a current divider; the current divider is connected with a negative bus on the direct current side of the cascade bidirectional converter and is used for collecting the current value on the direct current side; the sampling circuit is connected with the shunt and the short-circuit protection module.

6. The system of claim 1, wherein the short-circuit protection module is further configured to: when the real-time value of the direct current is reduced to be smaller than the I-level preset direct-current side short-circuit protection value, the pulse signal of the module for limiting and closing the power is automatically removed, and the cascade bidirectional converter is enabled to recover normal operation.

7. A method for restraining short-circuit current on a cascade bidirectional variable-current direct-current side is characterized by comprising the following steps:

detecting a direct current side current real-time value of the cascade bidirectional converter device, and comparing the direct current side current real-time value with I, II and III-level preset direct current side short-circuit protection values, wherein the III-level preset direct current side short-circuit protection value is larger than the II-level preset direct current side short-circuit protection value is larger than the I-level preset direct current side short-circuit protection value;

a: if the real-time value of the direct current is greater than or equal to the I-level preset direct-current side short-circuit protection value, the cascade type bidirectional converter device operates in a low-power mode, and the IGBT (insulated gate bipolar translator) turn-on time of a power unit of the bidirectional converter device is reduced to protect the power unit;

b: after a is executed, if the real-time value of the direct current is still larger than or equal to the II-level preset direct-current side short-circuit protection value, controlling the cascade type bidirectional converter to stop running, and turning off an output signal by a power unit IGBT of the bidirectional converter;

c: and c, after the operation a and the operation b are executed, if the real-time value of the direct current is still larger than or equal to the III-level preset direct-current side short-circuit protection value, the alternating-current side circuit breaker and the direct-current side contactor of the bidirectional converter are switched off, and the short-circuit current is discharged to the low-voltage side of the isolation transformer to be wound.

8. A method for suppressing short-circuit current at a cascade bidirectional variable DC side is characterized by further comprising the following steps: after any operation of a, b and c is executed, if the real-time value of the direct current is smaller than the I-level preset direct-current side short-circuit protection value, the pulse signal of the module for limiting and closing the power is removed, and the bidirectional converter is enabled to recover the operation.

9. A method for suppressing short-circuit current at a cascade bidirectional variable DC side is characterized by further comprising the following steps: when the bidirectional converter device normally operates, when the bus voltage of a power supply grid is increased to be larger than the sum of peak voltages of two groups of alternating current sides of the cascade bidirectional converter device, electric energy of a direct current traction grid side cannot be transmitted to the alternating current grid side.

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