CN115411761A - Multi-port direct-current boost converter and wind power full-direct-current extra-high voltage power transmission system - Google Patents

Abstract

The invention relates to the technical field of power transmission and transformation, and relates to a multi-port DC boost converter and a wind power full DC UHV power transmission system, wherein the multi-port DC boost converter includes at least one boost conversion module, and the boost conversion module includes n The low-voltage side of each phase unit forms a low-voltage side port, and the high-voltage sides of all phase units are connected in parallel to form a high-voltage side port; the wind power full DC UHV transmission system includes DC wind farms, DC booster stations, high-voltage The DC transmission line, the receiving-end converter station, the transformer station and the AC power grid, and the DC step-up station are provided with the above-mentioned multi-port DC step-up converter. The multi-port DC boost converter of the present invention has the characteristics of bidirectional flow of energy, high boost ratio, and high flexibility, and can collect the electric energy of multiple wind farms; the wind power full DC UHV transmission system can reduce the DC boost The step-up ratio of the converter has large capacity and high reliability.

Description

Multi-port DC boost converter and wind power full DC UHV transmission system

technical field

The invention relates to the technical field of power transmission and transformation, and relates to a multi-port DC boost converter and a wind power all-DC UHV power transmission system.

Background technique

At this stage, my country's wind energy resources and load centers are generally distributed in reverse, and the abundant wind energy resources in the "Three North Regions" are transmitted on a large scale and over long distances through the UHV DC transmission system. Existing UHVDC transmission technology can be divided into two types: thyristor-based traditional DC transmission technology (LCC-HVDC) and voltage source converter-based flexible DC transmission technology (VSC-HVDC). These two schemes are to convert the AC power output from the wind farm into UHV DC power through the converter after being boosted by the transformer, so as to carry out long-distance high-voltage transmission. After the power is sent to the receiving end converter, the UHV DC power After the energy is converted into AC power, the voltage level is adjusted to an appropriate level by the transformer and then connected to the power grid.

For LCC-HVDC technology, this technology uses a thyristor-based converter. The converter consumes a lot of reactive power, and needs to be equipped with a large number of reactive power compensation devices and filters; it can only work in the active inverter state, and cannot be connected to the passive system; interference in the AC system is prone to commutation failure, resulting in wind power The field power cannot be sent; the system does not have black start capability and other deficiencies.

For VSC-HVDC technology, there are disadvantages such as high construction cost, large loss of converter station; fault current on the DC side of the system is difficult to suppress, and corresponding DC circuit breakers need to be developed.

At the same time, the sending ends of these two schemes both use AC wind farms, and the output voltage level of the wind farms is low, which needs to be boosted by multi-stage transformers, which increases system losses and reduces transmission efficiency; in addition, with the wind farm capacity and With the increase of scale, the problem of reactive charging current and overvoltage caused by the collection of electric energy by AC cables inside the wind farm is becoming more and more serious.

Contents of the invention

The present invention provides a multi-port DC boost converter and wind power full DC UHV power transmission system, which overcomes the above-mentioned deficiencies in the prior art, and can effectively solve the problem of high system loss and The problem of low transmission efficiency.

One of the technical solutions of the present invention is achieved by the following measures: a multi-port DC boost converter includes at least one boost conversion module, and the boost conversion module includes n phase units, where n is an integer and n ≥1; the low-voltage side of each phase unit forms a low-voltage side port, and the high-voltage sides of all phase units are connected in parallel to form a high-voltage side port;

Each phase unit includes m bridge arm units, a thyristor valve T _Li connected to the low-voltage side port, a diode valve D _Hi connected to the high-voltage side port, and a thyristor valve T _Hi connected to the high-voltage side port, where m is an integer and m≥1, i is an integer and 1≤i≤n;

Each bridge arm unit includes a half-bridge sub-module bridge arm, a full-bridge sub-module bridge arm, a diode valve D _ik and a thyristor valve T _ik , where k is an integer and 0≤k≤m;

The bridge arm of the half-bridge sub-module includes N half-bridge sub-modules and a bridge arm reactor, and the N half-bridge sub-modules and a bridge arm reactor are connected in series; the bridge arm of the full-bridge sub-module includes N full-bridge sub-modules and a bridge arm A bridge arm reactor, N full bridge sub-modules and a bridge arm reactor are connected in series; where N is an integer and N≥1;

The half-bridge sub-module includes a capacitor, two IGBTs and two diodes, each IGBT is connected in antiparallel with a diode, the two IGBTs are connected in series, and the capacitor is connected in parallel with the series branch formed by the two IGBTs in series;

The full-bridge sub-module includes a capacitor, four IGBTs and four diodes, each IGBT is connected in antiparallel with a diode, two IGBTs are connected in series to form the first series branch, and the other two IGBTs are connected in series to form the second series branch circuit, the capacitor, the first series branch and the second series branch are connected in parallel;

The diode valve includes several diodes connected in series, and the thyristor valve includes several thyristors connected in series.

The following is a further optimization or/and improvement to one of the technical solutions of the above invention:

The number of the above-mentioned step-up conversion modules may be one, forming a unipolar multi-port DC step-up converter.

Each of the above-mentioned phase units can also include a full-bridge arm at the low-voltage side, and the full-bridge arm at the low-voltage side includes N full-bridge sub-modules and a bridge arm reactor, and the N full-bridge sub-modules and a bridge arm reactor are interconnected in series.

There may be two boost conversion modules to form a bipolar multi-port DC boost converter, and the common connection line of the two boost conversion modules is grounded.

The second technical solution of the present invention is achieved through the following measures: a wind power full direct current UHV power transmission system, including a direct current wind farm, a direct current booster station, a high voltage direct current transmission line, a receiving end converter station, a transformer station and The AC power grid, the DC step-up station is equipped with the above-mentioned multi-port DC step-up converter;

Each DC wind farm includes a certain number of DC wind turbines, and the DC wind turbines are connected in series. The positive pole of the output terminal of the first DC wind turbine in each DC wind farm is connected to the multi-port DC booster in the DC booster station. The positive pole of the input terminal corresponding to the converter is electrically connected, and the negative pole of the output terminal of the last DC wind turbine in each DC wind farm is electrically connected to the negative pole of the input terminal of the unipolar multi-port DC boost converter in the DC boost station;

The high-voltage direct current transmission line includes DC+ direct current transmission line and DC-direct current transmission line. Negative electrical connection of the output terminal of the high voltage side of the boost converter;

The receiving-end converter station is equipped with a modular multi-level converter. The positive pole of the input terminal of the modular multi-level converter in the receiving-end converter station is electrically connected to the DC+DC transmission line. The modular multi-level converter in the receiving-end converter station The negative pole of the input end of the flat converter is electrically connected to the DC-direct current transmission line;

An AC transformer is installed in the transformer station, the input end of the AC transformer is electrically connected to the output end of the modular multilevel converter in the receiving end converter station, and the output end of the AC transformer is electrically connected to the AC power grid.

The following is a further optimization or/and improvement to the second technical solution of the above invention:

A multi-port DC boost converter can be installed in the above-mentioned DC boost station, a modular multilevel converter can be installed in the receiving end converter station, and an AC transformer can be installed in the transformer station to form a unipolar wind power plant. Full DC UHV transmission system.

The above-mentioned DC booster station can be equipped with two multi-port DC boost converters, the receiving end converter station can be equipped with two modular multilevel converters, and the transformer station can be equipped with two AC transformers to form a double Polar wind power full DC UHV transmission system; the common connection line of two multi-port DC boost converters is grounded, and the common connection line of two modular multilevel converters is grounded.

The multi-port DC boost converter in the present invention has the characteristics of bidirectional flow of energy, high boost ratio and high flexibility, and can be divided into two types: unipolar and bipolar. The bipolar multi-port DC boost converter is suitable for systems with large system capacity and high reliability requirements. The wind farm at the sending end adopts DC wind turbines and conducts DC collection of electric energy to solve the problem of reactive charging current and overvoltage caused by AC cables inside the wind farm. The DC wind turbines are connected in series to increase the output voltage level of the wind farm, reduce the step-up link, reduce the step-up loss, and improve the transmission efficiency. The multi-port DC boost converter can collect the electric energy of multiple wind farms, and the output voltage levels of different wind farms can be different, which improves the flexibility and capacity of the system. In the unipolar wind power full DC UHV transmission system, the DC wind turbines in the DC wind farm are connected in series to increase the output voltage level of the DC wind farm, thereby reducing the boost ratio of the DC boost converter. The bipolar wind power all-DC UHV transmission system has large capacity and high reliability. When a single pole fault occurs in the system, the non-faulty pole can still operate normally.

Description of drawings

Accompanying drawing 1 is the topological structure diagram of unipolar multi-port DC boost converter.

Accompanying drawing 2 is the structural diagram of the half-bridge sub-module of the multi-port DC boost converter.

Accompanying drawing 3 is the structure diagram of the full-bridge sub-module of the multi-port DC boost converter.

Accompanying drawing 4 is the structural diagram of the thyristor valve of the multi-port DC boost converter.

Accompanying drawing 5 is the structural schematic diagram of the diode valve of the multi-port DC boost converter.

Figure 6 is a schematic diagram of the energy circuit when the unipolar multi-port DC boost converter is in the starting state.

Figure 7 is a schematic diagram of the energy circuit when the unipolar multi-port DC boost converter is in the parallel charging state.

Figure 8 is a schematic diagram of the energy circuit when the unipolar multi-port DC boost converter is in a series discharge state.

Figure 9 is a schematic structural diagram of a unipolar wind power all-DC UHV transmission system.

Figure 10 is a schematic diagram of the topology of a bipolar multi-port DC boost converter.

Figure 11 is a schematic structural diagram of a bipolar wind power all-DC UHV transmission system.

Figure 12 is a schematic diagram of a derivative topology of a unipolar multi-port DC boost converter.

Figure 13 is a schematic diagram of the energy circuit when the derivative topology of the unipolar multi-port DC boost converter is in the starting state.

Figure 14 is a schematic diagram of the energy circuit when the derivative topology of the unipolar multi-port DC boost converter is in the parallel charging state.

Figure 15 is a schematic diagram of the energy circuit when the derived topology of the unipolar multi-port DC boost converter is in a series discharge state.

Fig. 16 is a schematic diagram of a derivative topology of a bipolar multi-port DC boost converter.

Detailed ways

The present invention is not limited by the following examples, and specific implementation methods can be determined according to the technical solutions of the present invention and actual conditions.

In the present invention, for the convenience of description, the description of the relative positional relationship of each component is described according to the layout of the drawings in the specification, such as: the positional relationship of front, rear, upper, lower, left, right, etc. is It is determined according to the layout direction of the attached drawings.

Below in conjunction with embodiment and accompanying drawing, the present invention will be further described:

Embodiment 1: As shown in Figures 1-8, the multi-port DC boost converter includes at least one boost conversion module, and the boost conversion module includes n phase units with the same structure, where n is an integer and n≥ 1. The low-pressure side of each phase unit forms a low-pressure side port, and the high-voltage sides of all phase units are connected in parallel to form a high-pressure side port; each phase unit includes m bridge arm units and a thyristor valve connected to the low-voltage side port T _Li , a diode valve D _Hi connected to the high-voltage side port, and a thyristor valve T _Hi connected to the high-voltage side port, where m is an integer and m≥1, i is an integer and 1≤i≤n; each bridge The arm unit includes a half-bridge sub-module bridge arm, a full-bridge sub-module bridge arm, a diode valve D _ik and a thyristor valve T _ik , where k is an integer and 0≤k≤m; the half-bridge sub-module bridge arm includes N half-bridge sub-modules and a bridge arm reactor, N half-bridge sub-modules and a bridge arm reactor are connected in series; the bridge arm of the full-bridge sub-module includes N full-bridge sub-modules and a bridge arm reactor, N The full-bridge sub-module and a bridge arm reactor are connected in series; where N is an integer and N≥1; the half-bridge sub-module includes a capacitor, two IGBTs and two diodes, each IGBT is connected in antiparallel with a diode, and the two Two IGBTs are connected in series, and the capacitor is connected in parallel with the series branch formed by two IGBTs in series; the full-bridge sub-module includes a capacitor, four IGBTs and four diodes, each IGBT is connected in antiparallel with a diode, and two IGBTs The series connection forms the first series branch, and the other two IGBTs are connected in series to form the second series branch, and the capacitor, the first series branch and the second series branch are connected in parallel; the diode valve includes several diodes connected in series, and the thyristor valve It consists of several thyristors connected in series.

There is one step-up conversion module, which constitutes a unipolar multi-port DC step-up converter. According to the direction of energy transmission, the operating state of the unipolar multi-port DC boost converter can be divided into the start-up state where the energy is transferred from the high-voltage side to the low-voltage side and the working state where the energy is transferred from the low-voltage side to the high-voltage side. According to the charge and discharge state of the bridge arm, it can be divided into a parallel charge state and a series discharge state. The voltage of the bridge arm is controlled by controlling the input quantity of the bridge arm sub-module, and the bidirectional flow of energy is realized by using the reverse characteristic of the bridge arm voltage of the full-bridge sub-module, thereby realizing the bridge arm of the half-bridge sub-module and the full-bridge sub-module in the bridge arm unit The bridge arm is connected in parallel and connected in series, so as to realize the conversion of the charging and discharging state of the converter.

The energy circuit of the unipolar multi-port DC boost converter is shown in Figure 6 when it is in the starting state. At this time, energy is transmitted from the high-voltage side to the low-voltage side, and electric energy flows in from the positive port of the high-voltage side, and energy is transmitted to each phase unit at the same time. Electric energy passes through the high-voltage side thyristors of each phase unit, m full-bridge sub-modules and m bridge-arm half-bridge sub-module bridge arms, and then collects at the negative terminal. At this time, the m full-bridge sub-module bridge arms and m half-bridge sub-modules The bridge arms of the modules are connected in series, and each low-voltage side port is connected in parallel with the half-bridge sub-module bridge arm in the first bridge arm unit of the phase unit through the low-voltage side thyristor valve of the corresponding phase unit, so as to realize the acquisition of electric energy.

The energy circuit when the unipolar multi-port DC boost converter is in the parallel charging state is shown in Figure 7 (taking the first phase unit as an example). The positive port on the low-voltage side flows in, and then flows through m diode valves, m half-bridge sub-module bridge arms, m full-bridge sub-module bridge arms, and m thyristor valves, and then flows to the low-voltage side negative port. At this time, the low-voltage side port It is connected in parallel with m half-bridge sub-module bridge arms and m full-bridge sub-module bridge arms, and the voltage of the bridge arm is slightly lower than the voltage of the low-voltage side port, so as to realize the charging of the low-voltage side port to the phase unit.

The energy circuit of the unipolar multi-port DC boost converter in the series discharge state is shown in Figure 8 (taking the first phase unit as an example). At this time, the electric energy is discharged from the phase unit to the high-voltage side, and the electric energy flows through m Half-bridge sub-module bridge arms, m full-bridge sub-module bridge arms, and high-voltage side diode valve TH1 flow to the high-voltage side port. At this time, m half-bridge sub-module bridge arms are connected in series with m full-bridge sub-module bridge arms. , the sum of the voltages of all bridge arms is slightly greater than the high-voltage side voltage, realizing the discharge of the phase unit to the high-voltage side port.

The unipolar multi-port DC boost converter has n phase units, the n phase units correspond to n low-voltage side ports, and the n low-voltage side ports correspond to n DC wind farms, since the bridge arm voltage of each phase unit can be independently Therefore, the voltage of each low-voltage side port of the multi-port DC boost converter can be different, so the output voltage of each DC wind farm connected to the multi-port DC boost converter can also be different, so as to realize DC wind power with different output voltage levels The collection of field output electric energy improves the flexibility and capacity of the system.

Embodiment 2: As shown in Figures 12, 13, 14, and 15, each phase unit of the multi-port DC boost converter also includes a low-voltage side full-bridge bridge arm, and the low-voltage side full-bridge bridge arm includes N pieces A full-bridge sub-module and a bridge-arm reactor, and N full-bridge sub-modules and a bridge-arm reactor are connected in series.

The derived topology of the unipolar multi-port DC boost converter is shown in Figure 12. It is mainly composed of n phase units with similar structures. The low-voltage side of each phase unit forms a low-voltage side port. The high-voltage side of all phase units The parallel connections together form a high-voltage side port. Each phase unit consists of 1 low-voltage side full-bridge bridge arm, m (1≤m) bridge arm units, a thyristor valve T Li (1≤i≤n) connected to the negative port of the low-voltage side, and a thyristor valve T _Li (1≤i≤n) connected to the high-voltage side port A connected diode valve D _Hi and a thyristor valve T _Hi connected to the high-voltage side port; each bridge arm unit consists of a half-bridge sub-module bridge arm, a full-bridge sub-module bridge arm, and a diode valve D _ik ( 0≤k≤m) and a thyristor valve T _ik ; among them, the bridge arm of the half-bridge sub-module is composed of N (1≤N) half-bridge sub-modules and a bridge arm reactor connected in series, and the bridge arm of the full-bridge sub-module is composed of N full-bridge sub-modules and a bridge arm reactor are connected in series; among them, the half-bridge sub-module is composed of a capacitor, two IGBTs and their anti-parallel diodes, and the full-bridge sub-module is composed of a capacitor and four IGBTs and their anti-parallel diodes. Diodes connected in parallel; wherein, the diode valve is composed of a group of diodes connected in series, and the thyristor valve is composed of a group of thyristors connected in series.

According to the direction of energy transmission, the operating state of the derived topology of the unipolar multi-port DC boost converter can be divided into the start-up state where the energy is transferred from the high-voltage side to the low-voltage side and the working state where the energy is transferred from the low-voltage side to the high-voltage side. The working state can be divided into a parallel charging state and a series discharging state according to the charging and discharging state of the bridge arm.

The energy circuit of the unipolar multi-port DC boost converter derived topology is shown in Figure 13. At this time, the energy is transmitted from the high-voltage side to the low-voltage side, and the electric energy flows in from the positive port of the high-voltage side, and is transmitted to each phase unit at the same time. energy. The electric energy passes through the high-voltage side thyristors of each phase unit, (m+1) full-bridge sub-modules, m-arm half-bridge sub-module bridge arms and low-voltage ports, and then collects at the negative port. At this time, each phase (m+ 1) Bridge arms of full-bridge sub-modules, m bridge arms of half-bridge sub-modules, and low-voltage side ports are connected in series to directly obtain electric energy.

The energy circuit of the derived topology of the unipolar multi-port DC boost converter is shown in Figure 14 (taking the first phase unit as an example) when the derived topology of the unipolar multi-port DC boost converter is in the parallel charging state. At this time, the electric energy is charged from the low-voltage side port to the phase unit. It flows in from the positive port on the low-voltage side, and then flows through m diode valves, m half-bridge sub-module bridge arms, (m+1) full-bridge sub-module bridge arms, m thyristor valves, and low-voltage side thyristor valve T _L1 At this time, the low-voltage side port is connected in parallel with m half-bridge sub-module bridge arms and (m+1) full-bridge sub-module bridge arms, and the bridge arm voltage is slightly lower than the low-voltage side port voltage to achieve low-voltage Charging from the side port to the bridge arm.

The energy circuit of the unipolar multi-port DC boost converter derived topology is shown in Figure 15 (taking the first phase unit as an example) when the derived topology of the unipolar multi-port DC boost converter is in the state of series discharge. Discharge, the electric energy flows through the low-voltage side port, m half-bridge sub-module bridge arms, (m+1) full-bridge sub-module bridge arms, high-voltage side diode valve T _H1 , and then flows to the high-voltage side port. At this time, the low-voltage side port It is connected in series with m half-bridge sub-module bridge arms and (m+1) full-bridge sub-module bridge arms. The sum of the voltage of the low-voltage side port and all bridge arms is slightly greater than the voltage of the high-voltage side to realize discharge to the high-voltage side port.

Embodiment 3: As shown in accompanying drawing 10, the quantity of the step-up transformation module of this multi-port DC boost converter is two, constitutes bipolar multi-port DC step-up converter, the public of two boost-transform modules The connecting wire is grounded. In its topology diagram, p represents the positive end and n represents the negative end. The capacity and reliability of the system can be improved by using a bipolar multi-port DC boost converter. When one pole of the system fails, the non-faulty pole can still operate normally.

Embodiment 4: As shown in Fig. 16 , Fig. 16 is a schematic diagram of a derivative topology of a bipolar multi-port DC boost converter. In the figure, p represents the positive pole and n represents the negative pole. The converter topology is mainly composed of two unipolar multi-port DC boost converter derived topologies, where the common connection line of the two unipolar multi-port DC boost converter derived topologies is grounded, each The structure and operating state of the derived topology of the port DC boost converter are consistent with those described in Embodiment 2. Both unipolar multi-port DC boost converter derived topologies and bipolar multi-port DC boost converter derived topologies can be used in unipolar wind power full DC UHV transmission system and bipolar wind power full DC UHV transmission system.

Embodiment 5: As shown in Figure 9, the wind power all-DC UHV power transmission system includes n DC wind farms, DC booster stations, HVDC transmission lines, receiving-end converter stations, transformer stations and AC grids, DC The above-mentioned multi-port DC boost converter is installed in the booster station; wherein, each DC wind farm includes a certain number of DC wind turbines, and the DC wind turbines are connected in series. The DC wind turbines in different DC wind farms The number and output voltage level can vary. Each DC wind farm corresponds to a low-voltage side input port of the multi-port DC boost converter in the DC boost station, and the positive pole of the output terminal of the first DC wind turbine in each DC wind farm is connected to the multi-port DC booster in the DC boost station. The positive pole of the input terminal corresponding to the voltage converter is electrically connected, and the negative pole of the output terminal of the last DC wind turbine in each DC wind farm is electrically connected to the negative pole of the input terminal of the unipolar multi-port DC boost converter in the DC boost station. The positive poles of the output terminals of the remaining DC wind turbines in the DC wind farm are electrically connected to the negative poles of the output terminal of the previous DC wind turbine, and the negative poles of the output terminals of the remaining DC wind turbines are electrically connected to the positive poles of the output terminal of the next DC wind turbine; , the high-voltage direct current transmission line includes a DC+ direct current transmission line and a DC-direct current transmission line, the DC+ direct current transmission line is electrically connected to the positive pole of the high-voltage side output terminal of the multi-port DC boost converter in the DC booster station, and the DC-direct current transmission line is connected to the multi-port The negative pole of the output terminal of the high-voltage side of the DC boost converter is electrically connected; among them, a modular multilevel converter (MMC) is installed in the receiving end converter station, and the input of the modular multilevel converter in the receiving end converter station The positive pole of the terminal is electrically connected to the DC+DC transmission line, and the negative pole of the input terminal of the modular multilevel converter in the converter station at the receiving end is electrically connected to the DC-DC transmission line; among them, there is an AC transformer in the transformer station, and the input of the AC transformer The terminal is electrically connected to the output terminal of the modular multilevel converter in the receiving terminal converter station, and the output terminal of the AC transformer is electrically connected to the AC power grid.

A multi-port DC boost converter is installed in the DC booster station, a modular multilevel converter is installed in the receiving end converter station, and an AC transformer is installed in the transformer station to form a unipolar wind power full DC UHV power transmission system. In the unipolar wind power full DC UHV transmission system, the DC wind turbines in the DC wind farm are connected in series to increase the output voltage level of the DC wind farm, thereby reducing the boost ratio of the DC boost converter. The unipolar multi-port DC boost converter in the DC boost station increases the output voltage level of multiple DC wind turbines to the UHV transmission level, and transmits electric energy through the high-voltage DC transmission line. The receiving-end converter station converts the DC power transmitted by HVDC into AC power, and transforms the AC power into an appropriate voltage level through the transformer in the substation, and then connects it to the AC power grid.

Embodiment 6: As shown in Figure 11, the wind power all-DC UHV power transmission system includes n DC wind farms, DC booster stations, HVDC transmission lines, receiving-end converter stations, transformer stations and AC grids, DC The above-mentioned multi-port DC boost converter is arranged in the booster station. There are two multi-port DC boost converters in the DC booster station, two modular multilevel converters in the receiving end converter station, and two AC transformers in the transformer station, forming a bipolar wind power plant. DC UHV power transmission system; the common connection line of two multi-port DC boost converters is grounded, and the common connection line of two modular multilevel converters is grounded.

Specifically, each DC wind farm includes a certain number of DC wind turbines, and the DC wind turbines are connected in series. The number and output voltage level of DC wind turbines in different DC wind farms can be different. Each DC wind farm corresponds to A low-voltage side input port of the unipolar multi-port DC boost converter in the DC boost station, and the positive pole of the output terminal of the first DC wind turbine in each DC wind farm is connected to the unipolar multi-port DC booster in the DC boost station. The positive pole of the input terminal corresponding to the voltage converter is electrically connected, and the negative pole of the output terminal of the last DC wind turbine in each DC wind farm is electrically connected to the negative pole of the input terminal of the unipolar multi-port DC boost converter in the DC boost station. The positive poles of the output terminals of the remaining DC wind turbines in the DC wind farm are electrically connected to the negative poles of the output terminal of the previous DC wind turbine, and the negative poles of the output terminals of the remaining DC wind turbines are electrically connected to the positive poles of the output terminal of the next DC wind turbine; The common connecting line of the two DC wind turbines is grounded. Among them, the DC boost station is equipped with a bipolar multi-port DC boost converter, which is composed of two unipolar multi-port DC boost converters, and the two unipolar multi-port DC boost converters The common connection wire is grounded. Among them, the high-voltage direct current transmission line includes DC+ direct current transmission line and DC-direct current transmission line. The line is electrically connected to the negative pole of the output end of the high-voltage side of the bipolar multi-port DC boost converter. Among them, there are two modular multilevel converters (MMC) in the receiving end converter station, and the common connection line of the two modular multilevel converters is grounded, and the modular multilevel converter in the receiving end converter station The positive pole of the input terminal of the converter is electrically connected to the DC+direct current transmission line, and the negative pole of the input terminal of the modular multilevel converter in the receiving end converter station is electrically connected to the DC-direct current transmission line. Among them, there are two AC transformers in the substation, and the input terminals of the two AC transformers in the substation are respectively electrically connected with the output terminals of the two modular multilevel converters in the converter station at the receiving end. The output ends of the transformers are collected and then electrically connected to the AC power grid.

Compared with the unipolar wind power full DC UHV transmission system, the bipolar wind power full DC UHV transmission system has large capacity and high reliability. When a single pole fault occurs in the system, the non-faulty pole can still operate normally.

The above technical features constitute the embodiment of the present invention, which has strong adaptability and implementation effect, and non-essential technical features can be increased or decreased according to actual needs to meet the needs of different situations.

Claims (8)

1. A multi-port DC boost converter, characterized in that it comprises at least one boost conversion module, and the boost conversion module includes n phase units, wherein n is an integer and n≥1; the low voltage side of each phase unit Each forms a low-voltage side port, and the high-voltage sides of all phase units are connected in parallel to form a high-voltage side port; Each phase unit includes m bridge arm units, a thyristor valve T _Li connected to the low-voltage side port, a diode valve D _Hi connected to the high-voltage side port, and a thyristor valve T _Hi connected to the high-voltage side port, where m is an integer and m≥1, i is an integer and 1≤i≤n; Each bridge arm unit includes a half-bridge sub-module bridge arm, a full-bridge sub-module bridge arm, a diode valve D _ik and a thyristor valve T _ik , where k is an integer and 0≤k≤m; The bridge arm of the half-bridge sub-module includes N half-bridge sub-modules and a bridge arm reactor, and the N half-bridge sub-modules and a bridge arm reactor are connected in series; the bridge arm of the full-bridge sub-module includes N full-bridge sub-modules and a bridge arm A bridge arm reactor, N full bridge sub-modules and a bridge arm reactor are connected in series; where N is an integer and N≥1; The half-bridge sub-module includes a capacitor, two IGBTs and two diodes, each IGBT is connected in antiparallel with a diode, the two IGBTs are connected in series, and the capacitor is connected in parallel with the series branch formed by the two IGBTs in series; The full-bridge sub-module includes a capacitor, four IGBTs and four diodes, each IGBT is connected in antiparallel with a diode, two IGBTs are connected in series to form the first series branch, and the other two IGBTs are connected in series to form the second series branch circuit, the capacitor, the first series branch and the second series branch are connected in parallel; The diode valve includes several diodes connected in series, and the thyristor valve includes several thyristors connected in series. 2. The multi-port DC boost converter according to claim 1, characterized in that the number of boost conversion modules is one, constituting a unipolar multi-port DC boost converter. 3. The multi-port DC boost converter according to claim 1 or 2, wherein each phase unit also includes a full-bridge bridge arm on the low-voltage side, and the full-bridge bridge arm on the low-voltage side includes N full-bridge sub-modules and a bridge arm reactor, N full bridge sub-modules and a bridge arm reactor are connected in series. 4. multi-port direct current step-up converter according to claim 1, it is characterized in that the quantity of step-up conversion module is two, constitutes bipolar multi-port direct-current step-up converter, the public of two step-up conversion modules The connecting wire is grounded. 5. The multi-port DC boost converter according to claim 4, wherein each phase unit also includes a low-voltage side full-bridge bridge arm, and the low-voltage side full-bridge bridge arm includes N full-bridge sub-modules and a A bridge arm reactor, N full bridge sub-modules and a bridge arm reactor are connected in series. 6. A wind power full DC UHV power transmission system, characterized in that it includes a DC wind farm, a DC booster station, a high-voltage DC transmission line, a receiving end converter station, a transformer station and an AC power grid, and the DC booster station is equipped with such The multi-port DC boost converter described in any one of requirements 1-5; Each DC wind farm includes a certain number of DC wind turbines, and the DC wind turbines are connected in series. The positive pole of the output terminal of the first DC wind turbine in each DC wind farm is connected to the multi-port DC booster in the DC booster station. The positive pole of the input terminal corresponding to the converter is electrically connected, and the negative pole of the output terminal of the last DC wind turbine in each DC wind farm is electrically connected to the negative pole of the input terminal of the unipolar multi-port DC boost converter in the DC boost station; The high-voltage direct current transmission line includes DC+ direct current transmission line and DC-direct current transmission line. Negative electrical connection of the output terminal of the high voltage side of the boost converter; The receiving-end converter station is equipped with a modular multi-level converter. The positive pole of the input terminal of the modular multi-level converter in the receiving-end converter station is electrically connected to the DC+DC transmission line. The modular multi-level converter in the receiving-end converter station The negative pole of the input end of the flat converter is electrically connected to the DC-direct current transmission line; An AC transformer is installed in the transformer station, the input end of the AC transformer is electrically connected to the output end of the modular multilevel converter in the receiving end converter station, and the output end of the AC transformer is electrically connected to the AC power grid. 7. The wind power full DC UHV power transmission system according to claim 6, characterized in that a multi-port DC boost converter is installed in the DC booster station, and a modular multi-level converter is installed in the receiving end converter station There is an AC transformer in the substation to form a full DC UHV transmission system for unipolar wind power. 8. The wind power full DC UHV power transmission system according to claim 6, characterized in that two multi-port DC boost converters are installed in the DC boost station, and two modular multi-level converters are installed in the receiving end converter station Converter, two AC transformers are installed in the substation to form a full DC UHV transmission system for bipolar wind power; the common connection line of the two multi-port DC boost converters is grounded, and the two modular multilevel converters The common connection wire of the device is grounded.

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