Main circuit topological structure of doubly-fed wind generating set

Abstract

The invention relates to the field of power electronics and power transmission, in particular to a main circuit topological structure of a doubly-fed wind generating set. According to the topological structure, optimized topological structures such as a cascade H-bridge multi-level converter, a modular multi-level converter and an active neutral-point-clamped three-level converter are integrated, and miniaturization, light weight, greenization and intelligentization of equipment can be achieved. On the basis of the functions of voltage conversion, electrical isolation, energy transmission and the like of a traditional transformer, the targets of electric energy quality adjustment, reactive compensation, harmonic suppression, new energy grid connection and the like are also achieved. Aiming at large voltage difference among a stator side, a rotor side and electric equipment, a dual-active full-bridge DC-DC converter topological structure based on high-frequency isolation is adopted, and functional requirements of different DC bus voltage grades are considered. According to the circuit topological structure, the targets of electric energy quality adjustment, reactive compensation, harmonic suppression, new energy grid connection and the like are generally achieved.

Description

Technical Field

[0001] This invention relates to the field of power electronics and electric transmission, specifically to a doubly-fed wind turbine generator main circuit topology. Background Technology

[0002] High-power doubly-fed induction generator (DFIG) wind turbines can achieve bidirectional energy transmission between the grid-connected side and the stator side. Specifically, the AC output from the generator stator is stepped up by a transformer and fed into the grid-connected AC side. Simultaneously, the grid-connected AC power supplies the generator rotor, stator, and internal electrical equipment via an AC-DC-AC converter and transformer. This power supply system involves four voltage levels: stator-side rated voltage, rotor-side rated operating voltage, rated voltage of internal auxiliary equipment, and grid-connected voltage. Addressing the problems of high leakage flux loss, low operating efficiency, electromagnetic interference, and localized overheating in traditional three-winding transformer power supply systems, power electronic transformers utilize high-frequency switching devices (such as IGBTs and MOSFETs) to ensure high-frequency operation, reducing transformer size and weight, while also lowering iron and copper losses. Furthermore, PWM (Pulse Width Modulation) technology can effectively suppress harmonics and improve the output voltage waveform. With its advantages of high efficiency, flexible voltage and frequency control, high power density, harmonic control, and intelligent control, power electronic transformers are gradually becoming important equipment in power systems.

[0003] Among existing methods, a doubly-fed wind power generation system and method (CN111245020B) proposes a wind power generation system based on a traditional transformer. It improves the wind turbine utilization rate by adding a step-up transformer, but it still relies on a traditional three-winding transformer to form the doubly-fed wind turbine power supply system. A method and system for offshore wind power conversion based on modular solid-state transformers (CN113708409B) solves the problem of excessively low AC cable voltage in wind turbine generators, which leads to high costs and large size, through solid-state transformer technology. Summary of the Invention

[0004] In order to solve the problems of large leakage flux loss, low operating efficiency, electromagnetic interference, and local overheating in traditional three-winding transformer power supply systems, this invention proposes a doubly-fed wind turbine generator main circuit topology based on power electronic transformer technology.

[0005] The present invention is achieved by the following technical solution: a main circuit topology of a doubly fed wind turbine generator set, comprising: a high-voltage module, a high-frequency transformer, a low-voltage module, an intermediate DC module, a modular multilevel converter module, and an active neutral-point clamping three-level converter module;

[0006] The high-voltage module is connected to the high-voltage power grid via a reactor. It is responsible for completing the bidirectional AC / DC and DC / AC conversion of electrical energy, converting low-frequency high-voltage sinusoidal AC power into high-frequency high-voltage pulse AC power. Through the connection of this port, it realizes energy extraction from the grid and power generation feeding back to the grid. The output port of the high-voltage module is connected to the input port of the high-frequency transformer.

[0007] The high-frequency transformer realizes the electrical isolation and level conversion functions of high and low voltage, converting high-frequency high-voltage pulse AC power into high-frequency low-voltage pulse AC power. The input port of the high-frequency transformer is connected to the output port of each high-voltage module, and the output port is connected to the input port of the low-voltage module.

[0008] The low-voltage module realizes AC / DC conversion of electrical energy. The input port of the low-voltage module is connected to the output port of the high-frequency transformer, and the output port of the low-voltage module is connected to the intermediate DC module.

[0009] The intermediate DC module converts medium-voltage DC power to low-voltage DC power, realizing DC / DC conversion of electrical energy. The output port is connected to the input port of the active midpoint clamping three-level converter module.

[0010] Modular multilevel converter modules convert medium-voltage DC to medium-voltage AC, achieving high-voltage, high-power power conversion. This topology is beneficial for improving output voltage quality and allows the use of power electronic devices with lower voltage ratings to achieve high-voltage power conversion. At the same time, the modular design concept is beneficial for expansion and maintenance.

[0011] The active neutral-point clamping three-level converter module achieves three-level output by controlling the on / off state of the switching devices, converting low-voltage DC power into two low-voltage AC voltage levels to meet the rated operating voltage of the doubly-fed motor rotor and the rated voltage of the internal auxiliary electrical equipment, respectively.

[0012] In the above-mentioned doubly fed wind turbine generator main circuit topology, the AC / DC conversion in the high-voltage module adopts a cascaded H-bridge multilevel converter. Each of the three phases ABC is composed of n1 cascaded H-bridge units. The DC / AC conversion adopts an H-full-bridge unit structure. The output of the H-full-bridge unit structure is connected to the input port of the high-frequency transformer.

[0013] The above-mentioned doubly fed wind turbine generator main circuit topology consists of m1 low-voltage units connected in series in a single low-voltage module. Each low-voltage unit uses an H-bridge unit to convert high-frequency low-voltage pulse AC power into low-voltage DC power, realizing AC / DC conversion of electrical energy. The input port of the low-voltage unit is connected to the output port of the high-frequency transformer. The output ports of each low-voltage module are connected to the input port of the intermediate DC module in parallel with other low-voltage modules using m2 low-voltage modules.

[0014] In the above-mentioned doubly fed wind turbine generator main circuit topology, the intermediate DC module uses a dual active full-bridge DC-DC converter to convert medium-voltage DC power into low-voltage DC power, realizing DC / DC conversion of electrical energy; the capacitors at the output ports of each intermediate DC module are connected to the input ports of the active midpoint clamped three-level converter module in a series connection of m3 and parallel connection of m4.

[0015] The above-mentioned doubly fed wind turbine generator main circuit topology consists of a modular multilevel converter module composed of n2 half-bridge sub-modules connected in series at the top and bottom, which converts medium-voltage DC power into medium-voltage AC power.

[0016] In the above-mentioned doubly fed wind turbine generator main circuit topology, a high-voltage module output H full bridge, a high-frequency transformer, and a low-voltage module H full bridge form a resonant circuit.

[0017] The aforementioned doubly-fed wind turbine generator main circuit topology enables the output of medium and low voltage DC power and medium, high and low voltage AC power, meeting the power needs of different loads.

[0018] The aforementioned doubly fed wind turbine generator main circuit topology conditions the voltage and current sampling signals in the circuit, and generates control signals based on the conditioned sampling signals and the target values ​​set by the system to adjust the switching state of the switching devices.

[0019] This invention integrates optimized topologies such as a cascaded H-bridge multilevel converter (CHB), a modular multilevel converter (MMC), and an active neutral-point clamped three-level ANPC converter, enabling miniaturization, lightweighting, environmental friendliness, and intelligence of the equipment. Building upon traditional transformer functions such as voltage conversion, electrical isolation, and energy transmission, it also achieves goals including power quality regulation, reactive power compensation, harmonic mitigation, and grid connection of new energy sources. Addressing the significant voltage differences between the stator side, rotor side, and electrical equipment, a dual active full-bridge DC-DC converter (DAB) topology based on high-frequency isolation is adopted, accommodating the functional requirements of different DC bus voltage levels.

[0020] This invention proposes a doubly fed wind turbine generator topology based on power electronic transformer technology. It adopts a modular design approach, which can achieve equipment miniaturization, high redundancy, and convenient maintenance. The proposed main circuit topology uses all power switching devices to meet the requirements of green, intelligent, and high-efficiency equipment. Overall, it achieves the goals of power quality regulation, reactive power compensation, harmonic control, and grid connection of new energy sources. Attached Figure Description

[0021] Figure 1 This is the main circuit topology diagram of a doubly fed wind turbine generator set.

[0022] Figure 2This is a circuit topology diagram of a high-voltage module.

[0023] Figure 3 This is the circuit topology diagram for the low-voltage module.

[0024] Figure 4 This is the circuit topology diagram of the intermediate DC module.

[0025] Figure 5 This is the topology diagram of a midpoint clamped three-level ANPC converter circuit.

[0026] Figure 6 This is a topology diagram of a modular multilevel MMC converter circuit.

[0027] Figure 7 This is the main circuit topology diagram of a 6MW doubly fed wind turbine generator set. Detailed Implementation

[0028] like Figure 1 As shown, the main circuit topology of the doubly fed wind turbine generator proposed in this invention includes modules such as a high-voltage module, a high-frequency transformer, a low-voltage module, an intermediate DC module, a modular multilevel converter module, and an active neutral-point clamping three-level converter, which realizes AC and DC port outputs of various voltage levels.

[0029] High-voltage module: Connected to the high-voltage power grid (A1kV) via a reactor, it is responsible for bidirectional AC / DC and DC / AC conversion, converting low-frequency high-voltage sinusoidal AC power into high-frequency high-voltage pulse AC power. This port enables power extraction from the grid and power generation for grid feeding. The A1kV AC port has a reactor at its inlet. The AC / DC conversion uses a cascaded H-bridge multilevel converter (CHB), with each of the three phases (A, B, and C) consisting of n1 cascaded H-bridge units. The DC / AC conversion uses a full-bridge H-unit structure. The output ports of each high-voltage module are connected to the input ports of the high-frequency transformer.

[0030] High-frequency transformer: Provides electrical isolation and level conversion between high and low voltage, converting high-frequency, high-voltage pulsed AC power into high-frequency, low-voltage pulsed AC power. The input port of the high-frequency transformer connects to the output ports of each high-voltage module, and the output port connects to the input port of the low-voltage module.

[0031] Low-voltage module: A single low-voltage module consists of m1 low-voltage units connected in series. Each low-voltage unit uses an H-bridge unit to convert high-frequency low-voltage pulse AC power into low-voltage DC power, achieving AC / DC conversion. The input port of each low-voltage unit is connected to the output port of the high-frequency transformer. The output ports of each low-voltage module are connected to the input port of the intermediate DC module in parallel with other low-voltage modules using m2 low-voltage modules, achieving the ±D1kV DC bus voltage level requirement.

[0032] Intermediate DC module: Employs a dual active full-bridge DC-DC converter to convert medium-voltage DC (D1kV) to low-voltage DC (D2V), achieving DC / DC conversion of electrical energy. The capacitors at the output ports of each intermediate DC module are connected to the input ports of the active neutral-point clamped three-level converter module in a series connection of m3 and parallel connection of m4.

[0033] Resonant circuit: The electrical circuit consisting of a high-voltage module's output H-bridge, a high-frequency transformer, and a low-voltage module's H-bridge is collectively referred to as a resonant circuit.

[0034] Modular Multilevel Converter (MMC): Composed of n2 half-bridge sub-modules connected in series, it converts medium-voltage DC D1kV to medium-voltage AC A2kV, realizing high-voltage, high-power power conversion. This topology is beneficial for improving output voltage quality and can use power electronic devices with low withstand voltage ratings to achieve high-voltage power conversion. At the same time, the modular design concept is beneficial for expansion and maintenance.

[0035] Active neutral-point clamping three-level converter module: It achieves three-level output by controlling the on and off of switching devices, converting low-voltage DC D2V into low-voltage AC A3V and A4V voltage levels, which respectively meet the rated operating voltage of the doubly-fed motor rotor and the rated voltage of the internal auxiliary electrical equipment. This helps to reduce the voltage stress and switching loss of the switching devices, reduce harmonic content, and ensure good waveform quality of AC output by adopting appropriate control strategies.

[0036] Cascaded H-bridge circuit: All high-voltage modules are electrically connected in series at their input terminals via a full H-bridge circuit. This electrical circuit is collectively referred to as a cascaded H-bridge circuit.

[0037] Multiple voltage level output ports: This power electronic transformer realizes medium and low voltage DC power output ports as well as medium and high voltage AC power output ports, which can meet the power needs of different loads.

[0038] Drive control module: This module conditions the voltage, current, and other sampled signals from the power electronic transformer. Based on the conditioned sampled signals and the system's set target values, it generates control signals to adjust the switching states of the switching devices. It employs appropriate pulse modulation technology to generate drive signals that control the switching time of the switching devices, achieving precise regulation of the output voltage or current. This enables power quality regulation, reactive power compensation, harmonic control, and grid connection of new energy sources.

[0039] Example

[0040] As can be seen from the above, the main circuit topology of the doubly-fed wind turbine generator proposed in this invention includes a high-voltage module, a low-voltage module, an intermediate DC module, an active neutral-point clamped three-level converter module (ANPC), and a modular multilevel converter module (MMC). The invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0041] A single high-voltage module circuit topology is as follows Figure 2 As shown, the two H-bridges, mainly composed of power switching devices, require a total of eight switching devices. The output ports are connected to the corresponding high-frequency transformer input ports to convert mains frequency AC power into DC power and high-frequency AC power. A single high-voltage module requires eight drive pulses, namely... , , , , , , and .

[0042] Low-voltage module circuit topology as follows Figure 3 As shown, it consists of m1 low-voltage units connected in series, with each low-voltage unit requiring 4m1 switching devices. A single low-voltage unit is composed of an H-bridge consisting of power switching devices, requiring a total of 4 drive pulses, namely... , , and (with low-voltage unit M) l1 (For example). A single low-voltage module is connected to the output terminals of other low-voltage modules in parallel as m² low-voltage modules, providing a suitable DC voltage level for the high-voltage AC port. It is important to note that a single low-voltage module is not limited to m¹ H-bridges connected in series; it can also be composed of n (n>1) H-bridges connected in series. It is only necessary to ensure that the output H-bridge of the high-voltage module corresponds to one H-bridge in the low-voltage module in terms of electrical connection. The output and input ports of both are electrically connected through a high-frequency transformer, serving the purpose of high-low voltage isolation and level conversion.

[0043] The intermediate DC module circuit topology is as follows: Figure 4 As shown, the module consists of two H-bridge power switches and a high-frequency transformer, requiring a total of 8 switching devices. Both the input and output terminals are connected to supporting capacitors. This module requires a total of 8 drive pulses, namely... , , , , , , and The output of the H-bridge is connected to the output support capacitor C. z2The output terminals of other intermediate DC modules are connected in series with m3 and in parallel with m4 to provide a suitable DC voltage level for the conversion of low-voltage AC power.

[0044] The AC power used by the doubly-fed generator rotor and the auxiliary electrical equipment inside the wind turbine generator set is provided by... Figure 5 The active midpoint clamped three-level converter module shown is implemented using ANPC and includes 18 switching devices and voltage divider capacitor C. t1 and C t2 The components require a total of 18 drive pulses, namely... , , , , , , , , , , , , , , , , and The ANPC active neutral-point clamping three-level converter module with A3V output is directly connected to the generator rotor; the ANPC active neutral-point clamping three-level converter module with A4V output is connected to the Dyn power frequency transformer to supply power to the internal auxiliary equipment.

[0045] Modular Multilevel Converter (MMC) Topology Figure 6 As shown, the upper and lower parts are each composed of n² sub-modules and one reactor connected in series. Each part requires 4n² switching devices and 4n² drive pulses. , , , , , , and Each submodule contains an IGBT module, a support capacitor, and sensors, among other components. The output of the three-phase modular multilevel converter (MMC) is directly connected to the generator stator.

[0046] The following example illustrates a 6MW doubly-fed wind power converter system. The grid-connected voltage of the wind turbine is 35kV, the rated voltage on the generator stator side is 6.6kV, the rated voltage on the rotor side is 0.69kV, and the rated voltage of the auxiliary equipment inside the unit is 0.4kV. Considering both economy and efficiency, the following method is determined according to the present invention... Figure 7The main circuit topology of the 6MW doubly fed wind turbine generator shown has four AC ports: 35kV, 6.6kV, 690V and 400V.

[0047] There is a reactor at the 35kV AC port inlet. A cascaded H-bridge multilevel converter (CHB) is used. Each of the three phases (A, B, and C) is composed of 48 cascaded H-bridge units. The DC bus voltage of each unit is 750V. The switching device uses 1200V / 150A IGBTs.

[0048] The 6.6kV AC port uses a modular multilevel converter (MMC). The upper and lower parts of the ABC three-phase bridge arm are composed of 8 half-bridge units and 1 reactor, respectively. The DC bus voltage of each half-bridge unit is 750V, and the switching device uses 1200V / 650A IGBTs.

[0049] The 690V AC port uses an active neutral-point clamped three-level converter (ANPC), with both positive and negative DC bus voltages at 750V, and 1200V / 1500A IGBTs as the switching devices. The 400V AC port uses an active neutral-point clamped three-level converter (ANPC), with both positive and negative DC bus voltages at 50V, and 1200V / 100A IGBTs as the switching devices.

[0050] The main circuit of a doubly fed wind turbine generator set has two DC bus voltages, namely 12kV and 1500V.

[0051] The 12kV DC bus provides DC power to the 6.6kV AC port, consisting of 144 low-voltage unit output DC capacitors arranged in a 16-series, 9-parallel configuration, with each capacitor having a voltage of 750V. These low-voltage unit output capacitors are isolated from the high-voltage module output terminal on the 35kV AC side by a high-frequency transformer, operating at a frequency of 10kHz, and using 1200V / 150A IGBTs as switching devices.

[0052] The 1500V DC bus provides DC power to the 690V and 400V AC ports. The input consists of 16 DC capacitors connected in series, and the output consists of 16 DC capacitors arranged in a 2-series-8-parallel configuration, with each capacitor operating at 750V. These capacitors are connected to the 12kV DC bus capacitors via a dual active full-bridge DC-DC converter (DAB). The DAB uses high-frequency transformer isolation, operates at 10kHz, and uses 1200V / 300A IGBTs as switching devices.

[0053] This invention employs power electronic transformer technology to replace the power frequency transformer in traditional generator sets. Through high-frequency conversion, semiconductorization, and digitalization, it reconstructs the power conversion topology, achieving a significant breakthrough in flexibility, controllability, and integration. With the decreasing cost of new semiconductor devices and optimized topology, this technology is expected to gradually replace traditional transformers in grids with high penetration rates of new energy sources and in high-end industrial applications, becoming a core node of the future energy internet.

Claims

1. A main circuit topology for a doubly-fed wind turbine generator set, characterized in that: include: High-voltage modules, high-frequency transformers, low-voltage modules, intermediate DC modules, modular multilevel converter modules, and active neutral-point clamping three-level converter modules; The high-voltage module is connected to the high-voltage power grid via a reactor. It is responsible for completing the bidirectional AC / DC and DC / AC conversion of electrical energy, converting low-frequency high-voltage sinusoidal AC power into high-frequency high-voltage pulse AC power. Through the connection of this port, it realizes energy extraction from the grid and power generation feeding back to the grid. The output port of the high-voltage module is connected to the input port of the high-frequency transformer. The high-frequency transformer realizes the electrical isolation and level conversion functions of high and low voltage, converting high-frequency high-voltage pulse AC power into high-frequency low-voltage pulse AC power. The input port of the high-frequency transformer is connected to the output port of each high-voltage module, and the output port is connected to the input port of the low-voltage module. The low-voltage module realizes AC / DC conversion of electrical energy. The input port of the low-voltage module is connected to the output port of the high-frequency transformer, and the output port of the low-voltage module is connected to the intermediate DC module. The intermediate DC module converts medium-voltage DC power to low-voltage DC power, realizing DC / DC conversion of electrical energy. The output port is connected to the input port of the active midpoint clamping three-level converter module. The modular multilevel converter module converts medium-voltage DC power to medium-voltage AC power; The active neutral-point clamping three-level converter module achieves three-level output by controlling the on / off state of the switching devices, converting low-voltage DC power into two voltage levels of low-voltage AC power, which respectively meet the rated operating voltage of the doubly-fed motor rotor and the rated voltage of the internal auxiliary electrical equipment.

2. The main circuit topology of a doubly-fed wind turbine generator according to claim 1, characterized in that: In the high-voltage module, the AC / DC conversion adopts a cascaded H-bridge multilevel converter. Each of the three phases ABC is composed of n1 cascaded H-bridge units. The DC / AC conversion adopts an H-full-bridge unit structure. The output of the H-full-bridge unit structure is connected to the input port of the high-frequency transformer.

3. The main circuit topology of a doubly-fed wind turbine generator set according to claim 2, characterized in that: A single low-voltage module consists of m1 low-voltage units connected in series. Each low-voltage unit uses an H-bridge unit to convert high-frequency low-voltage pulse AC power into low-voltage DC power, realizing AC / DC conversion of electrical energy. The input port of the low-voltage unit is connected to the output port of the high-frequency transformer. The output ports of each low-voltage module are connected to the input port of the intermediate DC module in parallel with other low-voltage modules using m2 low-voltage modules.

4. The main circuit topology of a doubly-fed wind turbine generator set according to claim 3, characterized in that: The intermediate DC module uses a dual active full-bridge DC-DC converter to convert medium-voltage DC to low-voltage DC, realizing DC / DC conversion of electrical energy; the capacitors at the output ports of each intermediate DC module are connected to the input ports of the active midpoint clamping three-level converter module in a series connection of m3 and parallel connection of m4.

5. The main circuit topology of a doubly-fed wind turbine generator set according to claim 4, characterized in that: The modular multilevel converter module consists of n2 half-bridge sub-modules connected in series at the top and bottom to convert medium-voltage DC power into medium-voltage AC power.

6. The main circuit topology of a doubly-fed wind turbine generator according to claim 2, 3, 4, or 5, characterized in that: A high-voltage module's output H-bridge, a high-frequency transformer, and a low-voltage module's H-bridge form a resonant circuit.

7. The main circuit topology of a doubly-fed wind turbine generator set according to claim 2, 3, 4, or 5, characterized in that: It enables the output of medium and low voltage DC power ports as well as medium, high and low voltage AC power ports to meet the power needs of different loads.

8. The main circuit topology of a doubly-fed wind turbine generator set according to claim 2, 3, 4, or 5, characterized in that: The voltage and current sampling signals in the circuit are conditioned, and control signals are generated based on the conditioned sampling signals and the target values ​​set by the system to adjust the switching state of the switching devices.

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