A method for building an electromagnetic transient equivalent model of a fan embodying energy balance transmission

Abstract

A method for constructing an equivalent electromagnetic transient model of a wind turbine that reflects energy balance transfer includes: a controlled current source module considering the energy balance transfer between the impeller and rotor sides, used to describe the transient steady-state energy transfer process of wind energy captured by the wind turbine impeller through the mechanical transmission shaft system, generator, and to the unit-side converter; a controlled voltage source module considering the energy balance transfer between the DC bus side and the grid-side converter, used to describe the energy transfer process between the wind turbine's DC bus side and the grid through the grid-side converter; determining the fundamental frequency amplitude of the controlled voltage source according to the wind turbine control strategy; determining the harmonic amplitude based on the equivalent switching devices; and a controlled power interaction module, where the controlled current source is connected to the grid in parallel with the controlled voltage source via an uncontrolled rectifier bridge to realize the interaction between the controlled current source and the controlled voltage source. This invention can accurately reflect the energy balance transfer process from wind energy captured by the wind turbine to electrical energy, improving simulation efficiency while ensuring the accuracy of the model's transient steady-state simulation.

Description

Technical Field

[0001] This invention belongs to the field of power system simulation modeling technology, and more specifically, relates to a method for building an equivalent electromagnetic transient model of a wind turbine that reflects energy balance transfer. Background Technology

[0002] Vigorously developing renewable energy sources, primarily wind and solar power, is the only way to achieve sustainable energy development. The power system, as the energy hub, is transforming and developing into a new type of power system dominated by new energy sources. A significant characteristic of the construction and operation control of this new power system is the high proportion of new energy grid connection and the high proportion of power electronic equipment. Its rapid dynamic response and large system scale present new challenges and urgent improvement needs for power system simulation technology and its applications.

[0003] New power systems, including massive amounts of new energy power generation components such as wind and solar power, as well as power electronic equipment, have complex topologies and diverse dynamic behaviors. In electromagnetic transient simulations, due to the high switching frequencies and the high frequencies of high-frequency transformers in the converter stages, extremely small simulation step sizes are required. While maintaining rapid dynamic response characteristics, the simulation scale increases dramatically, leading to a sharp increase in computational load. Solving ultra-high-order network matrices with massive numbers of nodes and the enormous computational load resulting from small step sizes make the simulation speed of such networks extremely slow, making it difficult to meet the needs of scientific research and engineering testing. Therefore, in order to balance simulation accuracy and efficiency, in the modeling of new energy power plants, the entire station topology is generally simplified by appropriate equivalence before modeling to reduce computational load and improve simulation efficiency.

[0004] Common equivalent modeling methods include single-unit equivalent and multi-unit equivalent based on unit grouping. Equivalent methods for new energy power plants, especially wind turbines, have become a hot research topic in related fields in recent years. Existing single-unit equivalent methods often use controlled voltage sources to simulate the voltage regulation process of the converter's bridge arm switching module, and connect controlled current sources in parallel across the DC capacitor to simulate the dynamic interaction between AC and DC during faults, which can significantly improve the model's operating efficiency. However, existing equivalent methods, based on the principle of instantaneous power conservation, directly equalize the active power output of the three-phase controlled voltage sources with the active power on the DC side. After model equivalence, the controlled sources on the AC and DC sides are independent of each other, ignoring the transient and steady-state energy losses during energy transfer. This fails to reasonably reflect the energy balance transfer characteristics between the AC / DC sides of the wind turbine and the converters on both the turbine and grid sides. Furthermore, the energy consumption of the leakage circuit caused by the absence of the DC side and mechanical transmission parts in the wind turbine equivalent model is still not reflected. Furthermore, the equivalent method is mainly applied to the modeling of new energy power plants in AC protection adaptability research. The key research point is the fault transient characteristics of AC systems, mainly focusing on power frequency application scenarios. However, the harmonic frequencies accompanying the switching frequency are complex and diverse. Therefore, while equivaling the switching link to a controlled voltage source, the high-frequency harmonic characteristics in the system simulation process are lost.

[0005] Secondly, existing multi-machine equivalent methods generally equate power generation units with the same control system to equivalent models of similar new energy sources. This model equivalence ensures simulation accuracy while improving simulation efficiency. In existing technologies, researchers typically use a method of establishing a single detailed unit model and then amplifying it through a power amplification module to achieve equivalence for new energy power plants, i.e., 'single-unit multiplication'. While this method can accurately describe the transient characteristics of a single new energy power plant, it still requires constructing multiple detailed unit models or equivalent power plants when characterizing application scenarios such as fault coupling relationships between units within a power plant and between different power plants. The problem of low computational efficiency in digital simulation models remains unresolved.

[0006] Therefore, establishing a method for constructing an equivalent electromagnetic transient model of a wind turbine that reflects energy balance transfer, while also characterizing the harmonic features of power electronic components during switching, is a technically urgent and increasingly pressing need. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for constructing an equivalent electromagnetic transient model of a wind turbine that reflects energy balance transfer. This method solves the problem that when performing equivalent processing on wind turbines, the simulation speed and accuracy cannot be simultaneously balanced, and the characteristics of energy transfer on the AC / DC side and harmonic characteristics during the simulation process cannot be accurately represented. It is applicable to the equivalent processing of wind power simulation models, reflecting the interaction of controlled AC / DC power supplies, the transient steady-state losses of energy balance transfer on the AC / DC side, and the harmonic characteristics accompanying the switching circuit. This method further ensures the accuracy of the equivalent model while improving simulation efficiency.

[0008] The present invention adopts the following technical solution. The present invention proposes a method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer, comprising:

[0009] A controlled current source module considering the energy balance transfer between the impeller and rotor sides is established to describe the transient steady-state energy transfer process of wind energy captured by the wind turbine impeller through the mechanical transmission shaft system, generator, and converter on the unit side.

[0010] A controlled voltage source module that takes into account the energy balance transfer between the DC bus side and the grid side converter is established to describe the energy transfer process between the wind turbine DC bus side and the grid through the grid side converter.

[0011] A controlled power source interaction module is established to connect the controlled current source module and the controlled voltage source module in parallel via an uncontrolled rectifier bridge to the power grid, thereby realizing the interaction between the controlled current source and the controlled voltage source and completing the construction of the electromagnetic transient equivalent model of the wind turbine that reflects the energy balance transfer.

[0012] Preferably, the method for building the electromagnetic transient equivalent model of the wind turbine further includes:

[0013] Establish a wind turbine model, including: rotor and mechanical transmission unit, generator unit and power electronic converter unit;

[0014] The impeller and mechanical transmission unit is used to convert the captured wind energy into mechanical energy input to the generator; the generator unit is used to convert the input mechanical energy into AC electrical energy; the power electronic converter unit includes: a machine-side converter and a grid-side converter and their auxiliary equipment; the machine-side converter is used to convert AC electrical energy into DC electrical energy, and the grid-side converter is used to convert DC electrical energy into AC electrical energy.

[0015] Preferably, the transient steady-state energy transfer process from the wind turbine rotor to the generator-side converter via the mechanical transmission shaft system and generator includes:

[0016] Steady-state transmission losses and mechanical transmission losses, efficiency losses of generators and generator-side converters;

[0017] Energy consumption of transient transfer meter and rotor-side AC energy dissipation circuit, and machine-side converter DC-side energy dissipation circuit;

[0018] The energy transferred to the DC side is determined based on the energy level, in order to calculate the current amplitude of the controlled current source module.

[0019] Preferably, the energy transferred from the impeller to the DC side via the machine-side converter is the captured wind energy minus the transient steady-state energy loss during the energy transfer process, expressed by the following formula:

[0020] Z ref_DC =E AC_wind -Z loss -E DC_chopper -E AC_crowbar (7)

[0021] In the formula:

[0022] Z ref_DC To transfer energy to the DC side,

[0023] E AC_win d represents the wind energy captured by the wind turbine.

[0024] Z loss This refers to the losses during the steady-state transmission process.

[0025] E AC_crow b ar and E DC_c h opper Energy consumption of the AC / DC side energy dissipation circuit during transient transfer process;

[0026] The energy transferred to the DC side is equal to the product of the DC voltage and the DC current. The fundamental frequency amplitude of the controlled current source can be expressed by the following formula:

[0027]

[0028] In the formula:

[0029] I ref_DC This represents the amplitude of the fundamental frequency portion of the controlled current source.

[0030] V DC It is a DC voltage.

[0031] Preferably, the energy transfer process between the wind turbine DC bus side and the grid via the grid-side converter includes:

[0032] The control process of the equivalent grid-side converter is to obtain the fundamental frequency input voltage amplitude of the three-phase controlled voltage source based on the grid-side converter control parameters;

[0033] Harmonic elements caused by the switching process of the equivalent grid-side converter are identified, and the harmonic amplitude of the controlled voltage source is determined based on the parameters of the power electronic components of the grid-side converter.

[0034] Preferably, the voltage amplitude of the base frequency input portion of the controlled voltage source, obtained by multiplying the reference voltage of the grid-side converter by the control coefficient, is expressed by the following formula:

[0035] V abc_ ref_ fund =k ctl ×V abc_ref (9)

[0036] In the formula:

[0037] k ctl For control coefficients,

[0038] V a b c_ref_fun d represents the amplitude of the fundamental frequency input voltage of the first three-phase controlled voltage source.

[0039] V a b c_ref This is the reference voltage output by the fan control module.

[0040] Preferably, a harmonic content characterization coefficient is set, and the voltage amplitude of the high-frequency harmonic component in the three-phase controlled voltage source is expressed by the following formula:

[0041]

[0042] In the formula:

[0043] k hmn The harmonic content characterization coefficient is used to quantify the converter modulation method;

[0044] f IGBT For the switching frequency of power electronic components,

[0045] V abc_ref_hmn The input voltage amplitude for the harmonic component of the second and third phase controlled voltage sources.

[0046] V abc_ref This is the reference voltage output by the fan control module.

[0047] Preferably, the harmonic content characterization coefficient when using PWM modulation is greater than that when using SPWM modulation, and is also greater than that when using SVPWM modulation, as expressed by the following formula:

[0048] k hmn_PWM >k hmn_SPWM >k hmn_SVPWM (11)

[0049] In the formula:

[0050] k hmm_PWM The harmonic content characterization coefficient is used when PWM modulation is employed.

[0051] k hmm_SPWM These are the harmonic content characterization coefficients when using SPWM modulation;

[0052] k hmm_SVPWM The harmonic content characterization coefficient is used when SVPWM modulation is employed.

[0053] Preferably, the controlled power supply interaction module enables interaction between the controlled current source and the controlled voltage source by including:

[0054] By adjusting the energy transfer loss on the AC and DC sides, the equivalent current input amplitude of the wind turbine converter is obtained during different transient processes. The controlled current source is connected in parallel with the three-phase uncontrolled rectifier bridge and then connected to the DC grid.

[0055] By adjusting the switching frequency of the wind turbine control module and the converter, the equivalent voltage input amplitude of the fundamental frequency and harmonics corresponding to different control strategies is obtained. The controlled voltage source is connected to the power grid after being connected in parallel with the controlled current source through an uncontrolled rectifier bridge.

[0056] Preferably, the steady-state energy transfer loss and the switching losses of the power electronic components in the converter are expressed by the following formula:

[0057] E loss =f IGBT ×E on_off (12)

[0058] In the formula:

[0059] f IGBT For the switching frequency of power electronic components,

[0060] E loss For the steady-state losses of switching elements,

[0061] E on_off This represents the unit loss during the switching process.

[0062] Compared with the prior art, the beneficial technical effects of the present invention include at least the following:

[0063] The method proposed in this invention simplifies the problems of rapid circuit state changes and frequent circuit matrix updates caused by frequent switching operations. While retaining the wind turbine control strategy, it reduces the dynamic complexity of the circuit and significantly lowers the simulation computation load. By using a three-phase controlled voltage source to represent the control process of the grid-side converter, the output target of the wind turbine control strategy is directly used as the input of the controlled voltage source. This eliminates the need to consider the parameter states of the bridge arm devices and complex iterative calculations, fundamentally solving the problem of low simulation speed caused by power electronic switching operations.

[0064] By replacing the detailed switching module of the wind power converter with the equivalent module of the controlled voltage source, and replacing the DC side of the wind power converter with the equivalent module of the controlled current source, the energy interaction process of the AC and DC controlled power sources is considered. In the process of calculating the input reference value of the controlled source, the transient steady-state loss existing in the energy transfer process between the wind energy captured by the wind turbine rotor and the energy of the unit-side converter is taken into account. This realizes the energy consumption of the AC and DC side energy leakage circuit in the equivalent model, and solves the problem of accuracy loss caused by directly treating the AC and DC side energy as equal.

[0065] The method proposed in this invention addresses the problem that the equivalent model of a wind turbine cannot reflect the harmonic characteristics of the converter due to the absence of a switching module. By setting a harmonic content characterization coefficient, the high-frequency harmonic component in the grid-side controlled voltage source is characterized using the harmonic coefficient, the switching frequency of the power electronic components, and the converter modulation method. The harmonic component is then superimposed with the fundamental frequency energy transfer component to determine the input voltage of the controlled voltage source.

[0066] The method proposed in this invention differs significantly from conventional simulation models that treat the AC and DC sides as unrelated and devoid of any harmonic components. It allows for flexible adjustment of the simulation model's output characteristics by setting the module's control coefficients, harmonic coefficients, switching frequencies, and modulation methods according to the actual application scenario. It is applicable to the equivalent simulation models of different types of wind power, such as doubly-fed induction generators (DFIGs) and full-power wind turbines. It correlates the controlled sources on both the AC and DC sides, reflecting the transient processes of energy transfer on both sides and the harmonic characteristics accompanying the switching process, thereby improving simulation efficiency while further ensuring the accuracy of the equivalent model.

[0067] This invention focuses on the equivalent modeling of a single wind turbine unit in the entire new energy power station, and is also capable of meeting the requirements for building simulation models of single unit collection lines or new energy power station outgoing connection lines. Attached Figure Description

[0068] Figure 1 This is a topology diagram of energy balance transfer between the impeller and rotor sides of the equivalent model of the wind turbine in this embodiment of the invention;

[0069] Figure 2 This is a diagram of the energy transfer topology on the grid side and DC side of the wind turbine equivalent model in this embodiment of the invention;

[0070] Figure 3 It is a waveform diagram of the output voltage at the grid connection point of the wind turbine obtained from the wind power equivalent model that reflects energy transfer;

[0071] Figure 4 This is a waveform diagram of the output voltage at the grid connection point of the wind turbine obtained from an equivalent model of existing technology.

[0072] Figure 5 It is a waveform diagram of the output power at the grid connection point of the wind turbine obtained from the wind power equivalent model that reflects energy transfer;

[0073] Figure 6 The waveform diagram of the output power at the grid connection point of the wind turbine is obtained from the equivalent model of the existing technology. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0075] Embodiment 1 of the present invention provides a method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer, comprising:

[0076] A controlled current source module considering the energy balance transfer between the impeller and rotor sides is established to describe the transient steady-state energy transfer process of wind energy captured by the wind turbine impeller through the mechanical transmission shaft system, generator, and converter on the unit side.

[0077] Among them, steady-state transmission considers mechanical transmission losses and efficiency losses of generators and machine-side converters; transient transmission considers the energy consumption of rotor-side AC energy dissipation circuit and machine-side converter DC energy dissipation circuit; the energy transmitted to the DC side is determined based on the energy to calculate the amplitude of the controlled current source.

[0078] A controlled voltage source module is established to consider the energy balance transfer between the DC bus side and the grid side converter, which is used to describe the energy transfer process between the wind turbine DC bus side and the grid through the grid side converter.

[0079] Specifically, the fundamental frequency amplitude of the controlled voltage source is determined based on the calculation results of the wind turbine control module; and the harmonic amplitude of the controlled voltage source is determined based on the equivalent situation of the switching device model.

[0080] A controlled power source power interaction module is established. The controlled current source module is connected to the power grid after being connected in parallel with the controlled voltage source module through an uncontrolled rectifier bridge, so as to realize the interaction between the controlled current source and the controlled voltage source and complete the construction of the electromagnetic transient equivalent model of the wind turbine that reflects the energy balance transfer.

[0081] This invention can accurately reflect the energy balance transfer process from wind energy captured by the wind turbine to electrical energy, and improves simulation efficiency while ensuring the accuracy of the model's transient steady-state simulation.

[0082] Embodiment 2 of the present invention provides a method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer, including:

[0083] Step 1: Establish a wind turbine model, including but not limited to: impeller and mechanical transmission, generator and power electronic converter, etc.; it can be understood that the wind turbine model can include different types such as doubly fed wind turbines and full-power wind turbines.

[0084] Preferably, but not limitingly, the impeller and mechanical transmission unit is used to convert the captured wind energy into mechanical energy input to the generator, including but not limited to: blades, hubs, gearboxes, drive shafts and other components; the generator unit is used to convert the input mechanical energy into AC electrical energy, including but not limited to: motor stator, rotor and their auxiliary equipment; the power electronic converter unit includes but is not limited to: machine-side converter for converting AC electrical energy into DC electrical energy and grid-side converter for converting DC electrical energy into AC electrical energy and their auxiliary equipment.

[0085] Step 2: Based on the wind turbine model obtained in Step 1, establish a controlled current source module that takes into account the energy balance transfer between the impeller and rotor sides.

[0086] The electromagnetic transient equivalent simulation model of the energy balance transfer of the wind turbine is based on the energy transfer process from the mechanical module to the machine-side converter using a controlled current source. Preferably, but not restrictively, a controlled current source is connected in parallel across the DC capacitor to simulate the dynamic interaction process between the AC and DC sides during the fault transient. The energy transferred to the DC side is calculated using the wind energy captured by the impeller and mechanical transmission parts, as well as the transient steady-state energy loss during the AC and DC side energy transfer process. The fundamental frequency amplitude of the input current of the controlled current source is determined in combination with the DC voltage.

[0087] The controlled current source module describes the transient steady-state energy balance transfer process between the impeller and the rotor side; further preferably, but not restrictively, the steady-state transfer process considers mechanical transmission losses, efficiency losses of the generator and the machine-side converter; the transient transfer process considers the energy consumption of the rotor-side AC energy dissipation circuit and the machine-side converter DC energy dissipation circuit.

[0088] Based on the principle of energy balance transfer, the energy transferred from the impeller to the DC side via the turbine-side converter is the captured wind energy minus the transient steady-state energy loss during the energy transfer process; thus, the energy transferred to the DC side can be obtained, expressed by the following formula (13):

[0089] Z ref_DC =E AC_wind -Z loss -E DC_chopper -E AC_crowbar (13)

[0090] In the formula:

[0091] Z ref_DC To transfer energy to the DC side,

[0092] E AC_wind represents the wind energy captured by the wind turbine.

[0093] Z loss This refers to the losses during the steady-state transmission process.

[0094] E AC_crow b ar and E DC_c h opper This refers to the energy consumption of the AC / DC side energy leakage circuit during the transient transmission process.

[0095] Further preferred but not restrictive, the steady-state energy transfer loss, considering the switching losses of the power electronic components in the converter, is directly proportional to the switching frequency. Therefore, the switching power loss per unit time is equal to the unit loss of a single switching process multiplied by the switching frequency per unit time, expressed by the following formula (14):

[0096] E loss =f IGBT ×E on_off (14)

[0097] In the formula:

[0098] f IGBT For the switching frequency of power electronic components,

[0099] E loss For the steady-state losses of switching elements,

[0100] E on_off This represents the unit loss during the switching process.

[0101] The energy transferred to the DC side is equal to the product of the DC voltage and the DC current. The fundamental frequency amplitude of the controlled current source can be expressed by the following formula (15):

[0102]

[0103] In the formula:

[0104] I ref_DC This represents the amplitude of the fundamental frequency portion of the controlled current source.

[0105] V DC It is a DC voltage.

[0106] Step 3: Based on the wind turbine model obtained in Step 1, establish a three-phase controlled voltage source module, including: a fundamental frequency part of the controlled voltage source and a harmonic part of the controlled voltage source. These two parts are superimposed in parallel to form an equivalent grid-side converter. The fundamental frequency part of the controlled voltage source represents the control process of the grid-side converter, and the harmonic part represents the harmonic components caused by the switching process of the grid-side converter. Preferably, but not limitingly, Step 3 specifically includes:

[0107] Step 3.1: Based on the wind turbine model obtained in Step 1, establish the base frequency part of the controlled voltage source of the control process of the equivalent grid-side converter.

[0108] The electromagnetic transient equivalent simulation model of the energy balance transfer of the wind turbine is based on the control process of the grid-side converter equivalent to the three-phase controlled voltage source. The fundamental frequency input voltage amplitude of the three-phase controlled voltage source is obtained by using the reference voltage of the converter control system and the set control coefficient.

[0109] The controlled voltage source module describes the energy balance transfer process between the grid side and the DC side, that is, the energy balance transfer process between the DC bus side and the grid side converter. The energy transfer between the wind turbine modulation module and the grid side converter is reflected in the base frequency input part. The input voltage of the three-phase controlled voltage source is obtained by multiplying the reference voltage of the converter control system by the control coefficient. The voltage amplitude of the base frequency input part of the controlled voltage source can be expressed by the following formula (16):

[0110] V abc_ ref_ fund =k ctl ×V abc_ref (16)

[0111] In the formula:

[0112] k ctl For control coefficients,

[0113] V a b c_ref_fun d represents the amplitude of the fundamental frequency input voltage of the three-phase controlled voltage source.

[0114] V a b c_ref This is the reference voltage output by the fan control module.

[0115] It is worth noting that, as one of the outstanding substantive features of this invention, the control process of the grid-side converter is equivalent to that of a three-phase controlled voltage source. The output target of the wind turbine control strategy is directly used as the input of the controlled voltage source. There is no need to consider the parameter state of the bridge arm device and complex iterative calculations. This can fundamentally solve the problem of low simulation speed caused by power electronic switching operations.

[0116] Step 3.2: Based on the wind turbine model obtained in Step 1, establish the controlled voltage source harmonic component of the harmonic link caused by the switching process of the equivalent grid-side converter.

[0117] The electromagnetic transient equivalent simulation model of the energy balance transfer of the wind turbine is based on the three-phase controlled voltage source as the harmonic link caused by the switching process of the grid-side converter. The harmonic content characterization coefficient is set, and the high-frequency harmonic input voltage amplitude in the three-phase controlled voltage source is characterized by the harmonic coefficient, the switching frequency of the power electronic components and the modulation method of the converter.

[0118] The controlled voltage source module describes the equivalent process of the grid-side switching process, that is, the energy balance transfer process between the grid side and the DC side, which is reflected in the harmonic input part; the harmonic content characterization coefficient is set, where the harmonic content is related to the switching frequency of the power electronic components and the modulation method of the converter, and the higher the switching frequency and the more complex the modulation method, the smaller the corresponding harmonic content. Therefore, the voltage amplitude of the high-frequency harmonic part in the three-phase controlled voltage source can be expressed by the following formula (17):

[0119]

[0120] In the formula:

[0121] k hmn The harmonic content characterization coefficient is used to quantify the converter modulation method;

[0122] f IGBT For the switching frequency of power electronic components,

[0123] V abc_ref_hmn The input voltage amplitude for the harmonic component of the three-phase controlled voltage source.

[0124] V abc_ref This is the reference voltage output by the fan control module.

[0125] Further, but not restrictively, for the three main forms of power electronic converter modulation—PWM modulation, SPWM modulation, and SVPWM modulation—there is an inverse relationship between harmonic content and the accuracy of the modulation method. Therefore, a harmonic coefficient is set to measure the complexity and accuracy of the modulation method. It should satisfy the following condition: the harmonic content characterization coefficient for PWM modulation is greater than that for SPWM modulation, and also greater than that for SVPWM modulation, as expressed by the following formula:

[0126]

[0127] In the formula:

[0128] k hmm_PWM The harmonic content characterization coefficient is used when PWM modulation is employed.

[0129] k hmm_SPWM These are the harmonic content characterization coefficients when using SPWM modulation;

[0130] k hmm_SVPWM The harmonic content characterization coefficient is used when SVPWM modulation is employed.

[0131] It is worth noting that, as one of the outstanding substantive features of this invention, considering the problem that the equivalent model of the wind turbine cannot reflect the harmonic characteristics of the converter due to the absence of a switching module, a harmonic content characterization coefficient is set, and the high-frequency harmonic part in the grid-side controlled voltage source is characterized by the harmonic coefficient, the switching frequency of the power electronic components and the modulation method of the converter; and the input voltage of the controlled voltage source is determined by superimposing the harmonic part with the fundamental frequency energy transfer part.

[0132] Furthermore, this approach differs significantly from conventional simulation models that treat the AC and DC sides as unrelated and devoid of any harmonic components. It allows for flexible adjustment of the simulation model's output characteristics by setting the module's control coefficients, harmonic coefficients, switching frequencies, and modulation methods according to the actual application scenario. It is applicable to the equivalence of different types of wind power simulation models, such as doubly-fed induction generators (DFIGs) and full-power wind turbines. It correlates the controlled sources on both the AC and DC sides, reflecting the transient processes of energy transfer on both sides and the harmonic characteristics accompanying the switching circuitry. This improves simulation efficiency while further ensuring the accuracy of the equivalent model.

[0133] Step 4: Establish a controlled power supply power interaction module, which is used to connect the controlled current source module that takes into account the energy balance transfer between the impeller and rotor sides and the controlled voltage source module that takes into account the energy balance transfer between the DC bus side and the grid side converter to the grid, so as to obtain the equivalent electromagnetic transient model of the wind turbine that reflects the energy balance transfer.

[0134] Preferably, but not limitingly, the controlled power supply interaction module for energy balance transfer is characterized by obtaining the equivalent current input amplitude of the wind turbine converter during different transient processes by adjusting the energy transfer loss on the AC / DC side. The controlled current source is connected to the DC grid after being connected in parallel with the three-phase uncontrolled rectifier bridge. By adjusting the switching frequency of the wind turbine control module and the converter, the equivalent voltage input amplitude of the fundamental frequency and harmonics corresponding to different control strategies is obtained. The controlled voltage source module is connected to the grid after being connected in parallel with the controlled current source through the uncontrolled rectifier bridge, thereby obtaining the equivalent electromagnetic transient model of the wind turbine that reflects energy balance transfer.

[0135] It is worth noting that, as one of the outstanding substantive features of this invention, while replacing the detailed switching module of the wind power converter with the equivalent module of the controlled voltage source and the DC side of the wind power converter with the equivalent module of the controlled current source, the energy interaction process of the AC and DC controlled power sources is considered. In the process of calculating the input reference value of the controlled source, the transient steady-state loss existing in the energy transfer process between the wind energy captured by the wind turbine rotor and the energy of the unit-side converter is taken into account, so as to realize the energy consumption of the AC and DC side energy leakage circuit in the equivalent model, and solve the problem of accuracy loss caused by directly treating the AC and DC side energy as equal.

[0136] The method proposed in this invention simplifies the problem of rapid circuit state changes and frequent circuit matrix updates caused by frequent switching operations. This reduces the dynamic complexity of the circuit and significantly lowers the simulation computation load while preserving the wind turbine control strategy. This invention focuses on the equivalent modeling of a single wind turbine in the entire renewable energy power plant, and is also capable of building simulation models for single turbine feed lines or renewable energy power plant outgoing connection lines.

[0137] To more clearly illustrate the outstanding substantive features of this invention and the significant progress it brings to the prior art, an application example of implementing this invention is described below.

[0138] In this embodiment of the invention, 20 doubly-fed induction generator (DFIG) wind turbines with the same control strategy are used. Each DFIG wind turbine has a rated capacity of 3MW, a DC voltage reference value of 1200V, and a rated output voltage of 690V at the grid connection point. Figure 1 This is a topology diagram of a controlled current source module for balanced energy transfer between the impeller and rotor sides. Figure 2 The topology of the controlled voltage source module is shown in the diagram for balanced energy transfer between the grid side and the DC side.

[0139] like Figure 1 As shown, the wind turbine model includes modules such as impeller, mechanical transmission, generator, and power electronic converter, used to convert captured wind energy into mechanical energy input to the generator. The generator and power electronic converter simulation module includes the generator stator, rotor, and turbine-side and grid-side converters and their auxiliary equipment; the generator module converts the input mechanical energy into AC electrical energy; the turbine-side converter module converts AC electrical energy into DC electrical energy. This module describes the transient steady-state energy transfer process of wind energy captured by the wind turbine impeller through the mechanical transmission shaft system, generator, and to the turbine-side converter. The steady-state transfer considers mechanical transmission losses and efficiency losses of the generator and turbine-side converter; the transient transfer considers the energy consumption of the rotor-side AC energy dissipation circuit and the turbine-side converter's DC energy dissipation circuit. The energy transferred to the DC side is determined based on the energy input to calculate the amplitude of the controlled current source.

[0140] like Figure 2 As shown, V a_ref_fun d, V b_ref_fun d and V c_ref_fun d represents the amplitude of the fundamental frequency input voltage of the three-phase controlled voltage source, V. a_ref_ h mn V b_ref_hmn and V c_ref_ h mn The input voltage amplitude is the harmonic component of the three-phase controlled voltage source, and the control signal is the reference voltage V output by the fan control module. abc_ref I ref_DCThis module represents the fundamental frequency amplitude of the controlled current source. It describes the energy transfer process between the wind turbine DC bus side, the grid-side converter, and the power grid. Specifically, it determines the fundamental frequency amplitude of the controlled voltage source based on the calculation results from the wind turbine control module, and determines the harmonic amplitude of the controlled voltage source based on the equivalent characteristics of the switching device model.

[0141] A dynamic interaction circuit between AC and DC is established to simulate the dynamic interaction of AC and DC power. Specifically, the fundamental frequency portion I of the controlled current source connected in parallel on the DC side... ref_DC The control signals include: the active power P output by the controlled current source. ref_DC and DC voltage U DC .

[0142] The controlled current source module describes the transient steady-state energy balance transfer process between the impeller and rotor sides. The steady-state transfer process considers mechanical transmission losses, generator and generator-side converter efficiency losses. The transient transfer process considers the energy loss of the rotor-side AC energy dissipation circuit (Crowbar) and the energy consumption of the generator-side converter's DC-side energy dissipation circuit (Chopper). Based on the energy balance transfer principle, the energy transferred from the impeller to the DC side via the generator-side converter is the captured wind energy minus the transient steady-state energy loss during the energy transfer process. The energy transferred to the DC side satisfies the following relationship:

[0143] Z ref_DC =E AC_wind -Z loss -E DC_chopper -E AC_crowbar (19)

[0144] In this embodiment of the invention, the resistance of the energy dissipation circuit is always R. AC_crowbar =R DC_chopper =0.5Ω, the energy consumption of the AC / DC side energy dissipation circuit during the transient transfer process is taken as E AC_crow b ar =E DC_c h opper =0.6MW.

[0145] The energy Z transferred to the DC side ref_DC Equal to DC voltage U DC The product of the current and the DC current yields the following relationship for the fundamental frequency amplitude of the controlled current source:

[0146]

[0147] Among them, I ref_DC The fundamental frequency amplitude of the controlled current source is given by the DC voltage V. DC =1200V.

[0148] Controlled three-phase voltage source V raV rb and V rc The controlled signal is the reference voltage V output by the converter control system. ra_ref V rb_ref and V rc_ref With control coefficient k ctl The product of is shown in the following formula:

[0149] V a_ref_fund =k ctl ×V a_ref (twenty one)

[0150] V b_ref_fund =k ctl ×V b_ref (twenty two)

[0151] V c_ref_fund =k ctl ×V c_ref (twenty three)

[0152] Wherein, the control coefficient k ctl It is a parameter related to the control effect, and k is taken as... ctl =0.95.

[0153] The method proposed in this invention equates the power electronic switching process of the wind power converter to a three-phase controlled voltage source, and directly uses the output target value of the control strategy as the input of the three-phase controlled voltage source; it eliminates the need to consider the parameter states of the bridge arm devices and complex iterative calculations, thereby fundamentally solving the problem of low simulation speed caused by the frequent switching actions and iterative calculations of the power electronics.

[0154] The controlled voltage source module describes the energy balance transfer process between the grid side and the DC side, where the harmonic input part is represented by the equivalent switching process; a harmonic content characterization coefficient k is set. hmn The harmonic content is related to the switching frequency of the power electronic components and the modulation method of the converter. Therefore, the voltage amplitude of the high-frequency harmonic component in the three-phase controlled voltage source satisfies the following relationship:

[0155]

[0156] In the formula, k hmn f is a harmonic content characterization coefficient used to quantify the converter modulation method. IGBT V is the switching frequency of power electronic components. a b c_ref_ h mn The input voltage amplitude of the harmonic component of the three-phase controlled voltage source, V a b c_ref This is the reference voltage output by the fan control module.

[0157] There are three main forms of modulation in power electronic converters: PWM modulation, SPWM modulation, and SVPWM modulation. There is an inverse relationship between harmonic content and the accuracy of the modulation method. Therefore, the harmonic coefficient is used to measure the complexity and accuracy of the modulation method and should meet the following requirements:

[0158] k hmn_PWM >k hmn_SPWM >k hmn_SVPWM (25)

[0159] The reference value of the grid-side controlled voltage source consists of the fundamental frequency component transferred through the AC / DC side and the harmonic component caused by the power electronic switching circuit in parallel.

[0160] This invention replaces the detailed switching modules of wind turbine converters with equivalent modules of controlled voltage sources in existing technologies. It also uses a controlled current source to represent the energy transfer process from the mechanical module to the generator-side converter, and a three-phase controlled voltage source to represent the harmonic components caused by the control and switching processes of the grid-side converter. Considering the internal AC / DC interaction process, it takes into account the transient steady-state losses caused by AC / DC energy transfer during the calculation of the controlled source input reference value, thus solving the error caused by directly treating AC / DC energy as equal. Furthermore, considering the problem that the equivalent model of the wind turbine cannot reflect the harmonic characteristics of the converter due to the absence of a switching module, it sets harmonic content characterization coefficients and uses harmonic coefficients, power electronic component switching frequencies, and converter modulation methods to characterize the high-frequency harmonic components in the controlled voltage source. Finally, it superimposes the harmonic components with the fundamental frequency energy transfer components to determine the input voltage of the controlled voltage source.

[0161] This invention focuses on the equivalent modeling of a single wind turbine unit within the entire renewable energy power plant. It also meets the requirements for building simulation models of single-unit collection lines or renewable energy power plant transmission lines. The wind turbine models described in this invention include different types such as doubly-fed induction generators (DFIGs) and full-power turbines. Specifically, in the controlled power supply interaction module, the equivalent current input amplitude of the wind turbine converter during different transient processes is obtained by adjusting the energy transfer losses on the AC / DC side. The controlled current source is connected to the DC grid after being connected in parallel with the three-phase uncontrolled rectifier bridge. By adjusting the wind turbine control module and the converter switching frequency, the equivalent voltage input amplitudes of the fundamental frequency and harmonics corresponding to different control strategies are obtained. The controlled voltage source is connected to the grid after being connected in parallel with the controlled current source via the uncontrolled rectifier bridge, thus obtaining the equivalent simulation model of wind power. This invention can accurately reflect the energy balance transfer process from wind energy capture to electrical energy, improving simulation efficiency while ensuring the accuracy of the model's transient steady-state simulation.

[0162] Using the method proposed in this invention, and with the same parameters and operating conditions set in PSCAD V4.6.0 software, the running efficiency of detailed and equivalent models of a system consisting of 20 wind turbines was compared. The following conclusions were drawn: with a fixed simulation step size of 20µs and a simulation duration of 10s, the detailed model simulation took 21.937s, while the equivalent model simulation took 5.281s. This can increase the simulation speed by approximately four times.

[0163] Depend on Figure 4 It can be seen that traditional model equivalence methods cannot reflect harmonic characteristics, resulting in good power quality and smooth waveforms, but with poor accuracy and realism; while... Figure 3 It can be seen that the output voltage curve of the wind power simulation model considering energy transfer in this invention can reflect harmonic components and more accurately reflect the actual situation. Figure 5 and Figure 6 The images show the output power waveforms at the grid connection point of the wind turbine, obtained from a wind power simulation model considering energy transfer and an equivalent model based on existing technology. The power waveforms step up to 0.5P at 4 seconds. n The speed jumped to 0.75P in 6 seconds. n The active power at 8s is P n Because of energy loss in the transient steady state at low wind speeds, the active power cannot follow the power command. However, the existing equivalent method directly treats the AC and DC side energy as equal. At low wind speeds, the controlled power supply still maintains a large value, which cannot reflect the conflict between wind speed and energy leakage circuit. Therefore, the power always follows the command.

[0164] In large-scale scenarios with limited hardware, this invention associates controlled sources on both the AC and DC sides, considering energy balance transfer and harmonic characteristics. Therefore, this equivalent approach is applicable to both power frequency transient characteristics and harmonic characteristics studies. It can reflect the relationship between wind speed and transient steady-state energy loss during energy transfer to a certain extent, which is very meaningful for reducing the distortion of the equivalent process of new energy models.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer, characterized in that, include: A controlled current source module is established to consider the energy balance transfer between the impeller and rotor sides. This module describes the transient steady-state energy transfer process of wind energy captured by the wind turbine impeller through the mechanical transmission shaft system, generator, and generator to the unit-side converter. This includes: steady-state transfer measurement of mechanical transmission losses, efficiency losses of the generator and generator-side converter; transient transfer measurement of the AC energy dissipation circuit on the rotor side, and energy consumption of the DC energy dissipation circuit on the generator-side converter; and determination of the energy transferred to the DC side based on the energy to calculate the current amplitude of the controlled current source module. A controlled voltage source module considering the energy balance transfer between the DC bus side and the grid side converter is established to describe the energy transfer process between the wind turbine DC bus side and the grid via the grid side converter. This includes: the control process of the equivalent grid side converter, obtaining the fundamental frequency input voltage amplitude of the three-phase controlled voltage source based on the grid side converter control parameters; and the harmonic elements caused by the switching process of the equivalent grid side converter, determining the harmonic amplitude of the controlled voltage source based on the power electronic component parameters of the grid side converter. A controlled power source interaction module is established to connect the controlled current source module and the controlled voltage source module in parallel via an uncontrolled rectifier bridge to the power grid, thereby realizing the interaction between the controlled current source and the controlled voltage source and completing the construction of the electromagnetic transient equivalent model of the wind turbine that reflects the energy balance transfer.

2. The method for constructing an equivalent electromagnetic transient model of a wind turbine reflecting energy balance transfer according to claim 1, characterized in that: The method for constructing the electromagnetic transient equivalent model of the wind turbine also includes: Establish a wind turbine model, including: rotor and mechanical transmission unit, generator unit and power electronic converter unit; The impeller and mechanical transmission unit is used to convert the captured wind energy into mechanical energy input to the generator; the generator unit is used to convert the input mechanical energy into AC electrical energy; the power electronic converter unit includes: a machine-side converter and a grid-side converter and their auxiliary equipment; the machine-side converter is used to convert AC electrical energy into DC electrical energy, and the grid-side converter is used to convert DC electrical energy into AC electrical energy.

3. A method for constructing an equivalent electromagnetic transient model of a wind turbine reflecting energy balance transfer, as described in claim 1 or 2, characterized in that: The energy transferred from the impeller to the DC side via the turbine-side converter is the captured wind energy minus the transient steady-state energy loss during the energy transfer process, expressed by the following formula: In the formula: Z ref_DC To transfer energy to the DC side, E AC_wind Wind energy captured by the wind turbine Z loss This refers to the losses during the steady-state transmission process. E AC_crowbar and E DC_chopper Energy consumption of the AC / DC side energy dissipation circuit during transient transfer process; The energy transferred to the DC side is equal to the product of the DC voltage and the DC current. The fundamental frequency amplitude of the controlled current source can be expressed by the following formula: In the formula: I ref_DC This represents the amplitude of the fundamental frequency portion of the controlled current source. V DC It is a DC voltage.

4. A method for constructing an electromagnetic transient equivalent model of a wind turbine reflecting energy balance transfer, as described in claim 1 or 2, characterized in that: The voltage amplitude of the base frequency input portion of the controlled voltage source, obtained by multiplying the reference voltage of the grid-side converter by the control coefficient, is expressed by the following formula: In the formula: k ctl For control coefficients, V abc_ref_fund The amplitude of the fundamental frequency input voltage of the first three-phase controlled voltage source. V abc_ref This is the reference voltage output by the fan control module.

5. The method for constructing an equivalent electromagnetic transient model of a wind turbine reflecting energy balance transfer according to claim 1, characterized in that: By setting the harmonic content characterization coefficient, the voltage amplitude of the high-frequency harmonic component in the three-phase controlled voltage source is expressed by the following formula (4): In the formula: k hmn The harmonic content characterization coefficient is used to quantify the converter modulation method; f IGBT For the switching frequency of power electronic components, V abc_ref_hmn The input voltage amplitude for the harmonic component of the second and third phase controlled voltage sources. V abc_ref This is the reference voltage output by the fan control module.

6. The method for constructing an equivalent electromagnetic transient model of a wind turbine reflecting energy balance transfer according to claim 5, characterized in that: use PWM The harmonic content characterization coefficient during modulation is greater than that used SPWM The harmonic content characterization coefficient during modulation is greater than that used SVPWM The harmonic content characterization coefficient during modulation is expressed by the following formula: In the formula: k hmm_PWM To adopt PWM Harmonic content characterization coefficients during modulation; k hmm_SPWM To adopt SPWM Harmonic content characterization coefficients during modulation; k hmm_SVPWM To adopt SVPWM Harmonic content characterization coefficient during modulation.

7. A method for constructing an electromagnetic transient equivalent model of a wind turbine reflecting energy balance transfer, as described in claim 1 or 2, characterized in that: The controlled power supply interaction module enables interaction between the controlled current source and the controlled voltage source, including: By adjusting the energy transfer loss on the AC and DC sides, the equivalent current input amplitude of the wind turbine converter is obtained during different transient processes. The base frequency part of the controlled current source is connected in parallel with the three-phase uncontrolled rectifier bridge and then connected to the DC grid. By adjusting the switching frequency of the wind turbine control module and the converter, the equivalent voltage input amplitude of the fundamental frequency and harmonics corresponding to different control strategies is obtained. The harmonic part of the controlled voltage source is connected to the power grid after being connected in parallel with the controlled current source through an uncontrolled rectifier bridge.

8. A method for constructing an electromagnetic transient equivalent model of a wind turbine reflecting energy balance transfer according to claim 1 or 2, characterized in that: The steady-state energy transfer loss and the switching losses of power electronic components in the converter are expressed by the following formula: In the formula: f IGBT For the switching frequency of power electronic components, E loss For the steady-state losses of switching elements, E on_off This represents the unit loss during the switching process.

Images