CN-121984354-A - Direct current conversion device for series connection type offshore wind power direct current collection and working method thereof

CN121984354ACN 121984354 ACN121984354 ACN 121984354ACN-121984354-A

Abstract

The invention discloses a direct current conversion device for tandem type offshore wind power direct current collection and a working method thereof, wherein the direct current conversion device comprises a plurality of submodules, input ports of the submodules are mutually independent and are connected with output ports of a direct current fan, the output ports are connected in cascade connection on a high-voltage direct current side, a power balance branch is connected between midpoints of secondary full-bridge circuits of two adjacent submodules, a fault isolation unit is connected in series on the high-voltage direct current side between the two adjacent submodules, the submodules comprise a primary full-bridge circuit, a secondary full-bridge circuit and a high-frequency transformer connected between the primary full-bridge circuit and the secondary full-bridge circuit, an input capacitor is connected between the primary full-bridge circuit and the input ports, an output capacitor is connected between the secondary full-bridge circuit and the output ports, and the input ports are connected in parallel with an unloading branch. The invention realizes unbalanced power treatment, on-line switching and fault isolation in the marine direct current fan series collection.

Inventors

WANG ZHE
CHEN ZHE
ZHOU XINGXING
HUANG RUANMING
LIU FEI

Assignees

武汉大学
国网上海市电力公司

Dates

Publication Date: 20260505
Application Date: 20251110

Claims (10)

1. The direct current conversion device for series connection type offshore wind power direct current collection is characterized by comprising a plurality of sub-modules, wherein the input ports of the sub-modules are mutually independent and are connected with the output port of a direct current fan, and the output ports are cascaded at a high-voltage direct current side; the submodule comprises a primary full-bridge circuit, a secondary full-bridge circuit and a high-frequency transformer connected between the primary full-bridge circuit and the secondary full-bridge circuit, wherein an input capacitor is connected between the primary full-bridge circuit and an input port, an output capacitor is connected between the secondary full-bridge circuit and an output port, and the input port is connected with an unloading branch in parallel.
2. The direct current conversion device for tandem type offshore wind power direct current collection according to claim 1, wherein the direct current conversion device realizes direct current fan power transmission and submodule output capacitance voltage equalizing through power device multiplexing, and in a power device multiplexing equivalent structure, a submodule secondary full bridge circuit and a power balancing branch circuit share two switches on a third bridge arm and a fourth bridge arm and a fault isolation unit switch of a submodule i+1 in a submodule i secondary full bridge circuit.
3. The direct current conversion device for tandem type offshore wind power direct current collection according to claim 1, wherein the fault isolation unit comprises a fault isolation unit switch and a diode.
4. The direct current conversion device for tandem type offshore wind power direct current collection according to claim 1, wherein the power balance branch circuit is formed by connecting an inductor and a capacitor in series.
5. The direct current conversion device for tandem type offshore wind power direct current collection according to claim 1, wherein the unloading branch is formed by connecting an unloading resistor and an unloading switch in series.
6. A tandem type offshore wind power direct current collection system, characterized in that a direct current conversion device for tandem type offshore wind power direct current collection according to any one of claims 1 to 5 is provided.
7. A method of operating a dc conversion arrangement for tandem offshore wind power dc collection according to any one of claims 1 to 5, comprising: During steady-state operation of the direct-current conversion device, a fault isolation unit switch is turned on, a diode is clamped reversely, an unloading branch switch is kept off, and a submodule adopts a single-phase pulse width modulation strategy to realize power transmission of a fan and power balance among the submodules; The driving signal of the third bridge arm switch of the sub-module i secondary full-bridge circuit is used as a reference signal of a single phase-shifting pulse width modulation strategy, and driving signals of the third bridge arm switch of the sub-module i primary full-bridge circuit and the driving signal of the third bridge arm switch of the sub-module i+1 secondary full-bridge circuit are obtained through phase shifting; According to the phase shift duty ratio between the driving signal of the third bridge arm switch of the primary full bridge circuit of the submodule i and the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i, regulating the power transmission of the submodule; And according to the phase shift duty ratio between the driving signal of the third bridge arm switch of the secondary full-bridge circuit of the sub-module i and the driving signal of the third bridge arm switch of the secondary full-bridge circuit of the sub-module i+1, unbalanced power transmission among the sub-modules is regulated.
8. The method of operating a dc conversion device for tandem offshore wind power dc collection of claim 7, wherein regulating sub-module power transfer further comprises: When the phase shift duty ratio between the driving signal of the third bridge arm switch of the primary full bridge circuit of the submodule i and the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i meets the positive value threshold range, the power of the direct current fan is transmitted to the output port of the submodule; And when the phase shift duty ratio between the driving signal of the third bridge arm switch of the primary side full bridge circuit of the submodule i and the driving signal of the third bridge arm switch of the secondary side full bridge circuit of the submodule i meets a negative value threshold range, power is reversely transmitted.
9. The method of operating a dc conversion device for tandem offshore wind power dc collection of claim 7, wherein the adjusting the unbalanced power transfer between the sub-modules further comprises: When the phase shift duty ratio between the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i and the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i+1 meets a positive value threshold range, unbalanced power is transmitted from the submodule i to the submodule i+1; When the phase shift duty ratio between the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i and the driving signal of the third bridge arm switch of the secondary full bridge circuit of the submodule i+1 meets a negative threshold range, unbalanced power is transmitted to the submodule i by the submodule i+1.
10. A fault control method based on the series-type offshore wind power direct current collection system as claimed in claim 6, comprising: When the low-voltage side of the direct-current conversion device fails, all switches of a primary full-bridge circuit of a sub-module i corresponding to the failed direct-current fan are blocked, a first bridge arm switch and a second bridge arm switch of a secondary full-bridge circuit are blocked, a third bridge arm switch and a fourth bridge arm switch of the secondary full-bridge circuit work normally, the failed direct-current fan is re-cut off from a direct-current collecting system, and an output capacitor of the sub-module i is reserved in a main circuit; When the high-voltage side of the direct-current conversion device fails, the full-bridge circuit switch of the submodule of the direct-current conversion device is turned off, the switch of the fault isolation unit is turned off, the diode is turned on, the output capacitor and the discharge loop of the fault point are cut off, and during the fault period, the fault crossing is realized by adopting a direct-current fan rotor overspeed and direct-current conversion device unloading branch coordinated control mode.

Description

Direct current conversion device for series connection type offshore wind power direct current collection and working method thereof Technical Field The invention relates to the technical field of new energy power systems, in particular to a direct current conversion device for series-type offshore wind power direct current collection and a working method thereof. Background The offshore wind power generation has been widely concerned because of the advantages of abundant offshore wind resources, high number of hours for power generation and utilization, no occupation of land and the like. The method for collecting and sending the direct current of the offshore wind power comprises the steps of collecting energy through a direct current intranet by using a direct current wind turbine generator and sending the energy by using a high-voltage direct current line. Compared with alternating current collection and direct current transmission, the method has the advantages of reducing construction cost and improving transmission efficiency. In the offshore wind power series direct current collection structure, a direct current fan is connected in series through a DC/DC conversion device to be connected into a high-voltage direct current transmission line. The series boosting structure omits a direct current transformer and an offshore converter station, simplifies the structure of an offshore direct current collecting system, and reduces the power transmission loss and the cost. However, in the serial direct current collection structure, serial port voltages are mutually coupled, power fluctuation caused by wind speed change of the fan is directly reflected as serial port voltage fluctuation, and the fan with higher wind speed has higher serial port voltage. Meanwhile, the offshore direct current collection system has fault isolation and fault crossing capacity due to higher maintenance cost of the offshore wind power system. When the DC blower is cut off due to a low side fault (low voltage fault, LVF), the output power of the corresponding serial port is 0. At the moment, other normal fans in the serial collection system can work normally, and the situation that individual fault fans influence the whole fan serial cluster is avoided. When a high-voltage side short-circuit fault (high voltage fault, HVF) occurs at the HVDC port, the direct current collection system should be capable of rapidly isolating the fault and avoiding the overcurrent damage of the power device. Therefore, how to realize unbalanced power treatment, on-line switching and fault isolation in the series collection of the offshore wind turbine is a technical problem to be solved in the application of offshore wind power direct current collection and delivery. Disclosure of Invention The invention aims to provide a direct current conversion device for series connection type offshore wind power direct current collection and a working method thereof, so as to realize unbalanced power treatment, on-line switching and fault isolation in the series connection collection of offshore direct current fans. According to one aspect of the specification, the invention provides a direct current conversion device for tandem type offshore wind power direct current collection, which comprises a plurality of sub-modules, wherein the input ports of the sub-modules are mutually independent and are connected with the output port of a direct current fan, and the output ports are cascaded at a high-voltage direct current side; the submodule comprises a primary full-bridge circuit, a secondary full-bridge circuit and a high-frequency transformer connected between the primary full-bridge circuit and the secondary full-bridge circuit, wherein an input capacitor is connected between the primary full-bridge circuit and an input port, an output capacitor is connected between the secondary full-bridge circuit and an output port, and the input port is connected with an unloading branch in parallel. As a further technical scheme, the direct current conversion device realizes direct current fan power transmission and submodule output capacitance voltage equalizing through power device multiplexing, and in a power device multiplexing equivalent structure, a submodule secondary full-bridge circuit and a power balancing branch share two switches on a third bridge arm and a fourth bridge arm in a submodule i secondary full-bridge circuit and a fault isolation unit switch of a submodule i+1. As a further technical solution, the fault isolation unit includes a fault isolation unit switch and a diode. As a further technical scheme, the power balance branch circuit is formed by serially connecting an inductor and a capacitor. As a further technical scheme, the unloading branch is formed by serially connecting an unloading resistor and an unloading switch. According to an aspect of the present invention, there is provided a series-type offshore wind power direct current collection syst