Method for building electromagnetic transient equivalent model of fan capable of reflecting energy balance transfer

Abstract

A fan electromagnetic transient equivalent model building method capable of reflecting energy balance transfer comprises the steps that a controlled current source module considering impeller and rotor side energy balance transfer is used for describing the transient steady state energy transfer process of wind energy captured by a fan impeller to a unit side converter through a mechanical transmission shaft system and a generator; the controlled voltage source module is used for describing an energy transfer process between the direct current bus side of the fan and the power grid through the grid-side converter and considering energy balance transfer between the direct current bus side and the grid-side converter; determining the fundamental frequency amplitude of the controlled voltage source according to the fan control strategy; determining a harmonic amplitude according to the equivalence of the switching device; according to the controlled power supply power interaction module, a controlled current source is connected with a controlled voltage source in parallel through an uncontrolled rectifier bridge and then connected into a power grid, and interaction between the controlled current source and the controlled voltage source is achieved. According to the method, the energy balance transfer process from wind energy captured by the wind turbine to electric energy can be accurately reflected, and the simulation efficiency is improved on the basis of ensuring the transient and steady state simulation precision of the model.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system simulation modeling, and more specifically, relates to a method for building an electromagnetic transient equivalent model of a wind turbine that embodies energy balance transfer. Background Art

[0002] Vigorously developing renewable energy, mainly wind power and photovoltaic power generation, is the only way to achieve sustainable energy development. As an energy hub, the power system is transforming and developing into a new power system with new energy as the main body. The significant features of the construction and operation control of the new power system are a high proportion of new energy grid-connected operation and a high proportion of power electronic equipment. Its fast dynamic response characteristics and large system scale have brought new challenges and urgent improvement needs to the power system simulation technology and application trends.

[0003] The new power system, which contains a large number of new energy power generation links such as wind power and photovoltaic power generation and power electronic equipment, has a complex topological structure and diverse dynamic behaviors. In electromagnetic transient simulation, due to the high switching frequency and the high-frequency transformer frequency in the conversion link, a very small simulation step is required. While having fast dynamic response characteristics, the simulation scale increases sharply, resulting in a sharp increase in the amount of calculation. The ultra-high-order network matrix solution containing a large number of nodes and the large amount of calculation brought by the small step size make the simulation speed of such networks extremely slow, which is difficult to meet the needs of scientific research and engineering testing. Therefore, in order to take into account both simulation accuracy and efficiency, in the modeling of new energy stations, the entire station topology is generally appropriately simplified and then modeled to reduce the amount of calculation and improve the efficiency of simulation calculations.

[0004] Common equivalent modeling methods include single-machine equivalent and multi-machine equivalent based on unit grouping. The equivalent method of new energy stations, especially wind turbines, has become one of the hot issues in related research in recent years. In the existing single-machine equivalent method, a controlled voltage source is often used to simulate the voltage regulation process of the bridge arm switch module of the converter, and a controlled current source is connected in parallel at both ends of the DC capacitor to simulate the dynamic interaction process between AC and DC during the fault, which can greatly improve the operation efficiency of the model. However, based on the principle of instantaneous power conservation, the active power output by the three-phase controlled voltage source is directly equal to the active power on the DC side in the existing equivalent method. After the model is equivalent, the controlled sources on the AC and DC sides are independent of each other, ignoring the transient and steady-state energy loss parts in the energy transfer process, and cannot reasonably reflect the characteristics of energy balance transfer between the AC and DC sides of the wind turbine and the machine-side grid-side converter. At the same time, the energy consumption of the energy dissipation circuit caused by the absence of the DC side and the mechanical transmission part in the wind turbine equivalent model is still not reflected. In addition, the equivalent method is mainly used in the modeling of new energy stations for the adaptability research of AC protection. The key to the corresponding research is the transient characteristics of the fault of the AC system, which mainly focuses on the power frequency application scenario. However, the harmonic frequencies accompanying the switching frequency are complex and diverse. Therefore, when the switching link is equivalent to a controlled voltage source, the high-frequency harmonic characteristics in the system simulation process are lost.

[0005] Secondly, the multi-machine equivalence method in the prior art generally equates the power generation units of the same control system to the equivalent models of the same new energy. Through such model equivalence, the simulation accuracy is guaranteed while the simulation efficiency is improved. In the prior art, researchers usually adopt the method of establishing a single detailed unit model and passing it through a power amplification module to achieve the equivalence of a new energy station, that is, "single machine multiplication". Although this method can be prepared to describe the transient characteristics of a single new energy station, when characterizing application scenarios such as fault coupling relationships between units within a station and between different stations, it is also necessary to build multiple detailed unit models or equivalent stations, and the problem of low computational efficiency of digital simulation models has not been solved.

[0006] Therefore, it is urgent to establish a method for building an electromagnetic transient equivalent model of a wind turbine that reflects the energy balance transfer and can characterize the harmonic characteristics of the switching process of power electronic components. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a method for building an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer, which solves the problem that when performing equivalent processing on the wind turbine, the model simulation operation speed and accuracy cannot be taken into account, and the characteristics of energy transfer on the AC and DC sides and the harmonic characteristics in the simulation process cannot be reflected. It is suitable for the equivalence of wind power simulation models, the interaction of controlled power sources on the AC and DC sides, reflecting the transient steady-state losses of energy balance transfer on the AC and DC sides and the harmonic characteristics associated with the switching links, and further ensuring the accuracy of the equivalent model on the basis of improving the simulation efficiency.

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

[0009] A controlled current source module that takes into account the energy balance transfer between the impeller and the rotor side is established to describe the transient steady-state energy transfer process of the wind energy captured by the wind turbine impeller through the mechanical transmission shaft system and the generator to the unit-side converter;

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

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

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

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

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

[0015] Preferably, the transient steady-state energy transfer process of the wind energy captured by the fan impeller through the mechanical transmission shaft system and the generator to the unit-side converter includes:

[0016] Steady-state transfer meter and mechanical transmission loss, generator and machine-side converter efficiency loss;

[0017] Transient transfer includes the energy consumption of the rotor-side AC energy dissipation circuit and the DC-side energy dissipation circuit of the generator-side converter;

[0018] The energy transferred to the DC side is determined based on the energy 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, which is expressed by the following formula:

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

[0021] Where:

[0022] Z ref_DC is the energy transferred to the DC side,

[0023] E AC_win d is the wind energy captured by the wind turbine,

[0024] Z loss is the loss in the steady-state transmission process,

[0025] E AC_crow b ar and E DC_c h opper Energy consumption of AC and DC side energy dissipation circuit in 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 amplitude of the fundamental frequency part of the controlled current source can be expressed as follows:

[0027]

[0028] Where:

[0029] I ref_DC is the amplitude of the fundamental frequency part of the controlled current source,

[0030] V DC is a DC voltage.

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

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

[0033] The harmonic link caused by the switching process of the equivalent grid-side converter 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 part of the controlled voltage source obtained by multiplying the reference voltage of the grid-side converter by the control coefficient is expressed as follows:

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

[0036] Where:

[0037] k ctl is the control coefficient,

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

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

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

[0041]

[0042] Where:

[0043] k hmn is the harmonic content characterization coefficient, which is used to quantify the converter modulation mode;

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

[0045] V abc_ref_hmn is the input voltage amplitude of the harmonic part of the second three-phase controlled voltage source,

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

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

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

[0049] Where:

[0050] k hmm_PWM is the harmonic content characterization coefficient when PWM modulation is adopted;

[0051] k hmm_SPWM is the harmonic content characterization coefficient when SPWM modulation is adopted;

[0052] k hmm_SVPWM It is the harmonic content characterization coefficient when using SVPWM modulation.

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

[0054] By adjusting the energy transfer loss on the AC and DC sides, the equivalent current input amplitude of the wind turbine converter in different transient processes is obtained, and 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 fan control module and the converter switching frequency, the fundamental frequency and harmonic equivalent voltage input amplitude corresponding to different control strategies are obtained, and the controlled voltage source is connected to the grid in parallel with the controlled current source through the uncontrolled rectifier bridge.

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

[0057] E loss =f IGBT ×E on_off (12)

[0058] Where:

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

[0060] E loss is the steady-state loss of the switching element,

[0061] E on_off is the unit loss of the switching process.

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

[0063] The method proposed in the present invention simplifies the problem of rapid changes in circuit state caused by frequent switching actions and frequent updates of the circuit matrix by the solver, so that the dynamic complexity of the circuit is reduced while retaining the principle of the wind turbine control strategy, and the amount of simulation calculation is greatly reduced. By using the control process of the three-phase controlled voltage source equivalent to the grid-side converter, the output target of the wind turbine control strategy is directly used as the input of the controlled voltage source, without considering the parameter state of the bridge arm device and the complex iterative operation, which can essentially solve the problem of low simulation speed caused by power electronic switch operation.

[0064] While replacing the detailed switch module of the wind power converter with a controlled voltage source equivalent module, and replacing the DC side part of the wind power converter with a controlled current source equivalent module, the energy interaction process of the AC and DC controlled power sources is considered at the same time; in the process of calculating the controlled source input reference value, the transient steady-state loss existing in the energy transfer process between the wind energy captured by the wind turbine impeller and the unit-side converter is taken into account, so that the energy consumption of the AC and DC side energy dissipation circuit is reflected in the equivalent model, which solves the problem of directly considering the AC and DC side energies to be equal and causing loss of accuracy.

[0065] The method proposed in the present invention takes into account the problem that the equivalent model of the wind turbine generator set cannot reflect the harmonic characteristics of the converter due to the absence of a switching module. By setting the harmonic content characterization coefficient, the harmonic coefficient, the switching frequency of the power electronic component and the converter modulation method are used to characterize the high-frequency harmonic part in the grid-side controlled voltage source; and the harmonic part is superimposed on the fundamental frequency energy transfer part to determine the input voltage of the controlled voltage source.

[0066] The method proposed in the present invention is significantly different from the conventional simulation model equivalent means that regards the AC and DC sides as unrelated and does not contain any harmonic components. It can flexibly set the control coefficient, harmonic coefficient, switching frequency and modulation mode of the module according to the actual application scenario to adjust the output characteristics of the simulation model. It is suitable for the equivalence of different types of wind power simulation models such as double-fed wind turbines and full-power wind turbines, and associates the controlled sources on the AC and DC sides to reflect the transient process of energy transfer on the AC and DC sides and the harmonic characteristics associated with the switching links, and further ensure the accuracy of the equivalent model on the basis of improving the simulation efficiency.

[0067] The present invention focuses on the equivalent modeling of a single wind turbine unit in the entire new energy station, and is also capable of building simulation models for a single unit collection line or a new energy station transmission line. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a topological diagram of energy balance transfer between the impeller and the rotor side of the fan equivalent model in an embodiment of the present invention;

[0069] Figure 2 It is a topological diagram of energy transfer between the grid side and the DC side of the wind turbine equivalent model in an embodiment of the present invention;

[0070] Figure 3 It is the output voltage waveform of the wind turbine grid connection point obtained by the wind power equivalent model reflecting energy transfer;

[0071] Figure 4 It is the output voltage waveform diagram of the wind turbine generator grid connection point outlet obtained by the equivalent model of the prior art;

[0072] Figure 5 It is the output power waveform of the wind turbine grid connection point obtained by the wind power equivalent model reflecting energy transfer;

[0073] Figure 6 It is a waveform diagram of the output power at the outlet of the wind turbine generator grid connection point obtained by the equivalent model of the prior art. DETAILED DESCRIPTION

[0074] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present 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 that takes into account the energy balance transfer between the impeller and the rotor side is established to describe the transient steady-state energy transfer process of the wind energy captured by the wind turbine impeller through the mechanical transmission shaft system and the generator to the unit-side converter.

[0077] Among them, steady-state transfer takes into account mechanical transmission loss, efficiency loss of generator and machine-side converter; transient transfer takes into account the energy consumption of rotor-side AC energy dissipation circuit and DC-side energy dissipation circuit of machine-side converter; the energy transferred 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 taking 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 DC bus side of the wind turbine and the grid via the grid-side converter.

[0079] Among them, the fundamental frequency amplitude of the controlled voltage source is determined according to the calculation result of the fan control module; and the harmonic amplitude of the controlled voltage source is determined according to the equivalent situation of the switching device model.

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

[0081] The present invention can accurately reflect the energy balance transfer process from wind energy captured by the wind turbine to electrical energy, and improve the simulation efficiency on the basis of ensuring the transient steady-state simulation accuracy of the model.

[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, comprising:

[0083] Step 1: Establish a wind turbine model, including but not limited to: impeller and mechanical transmission, generator and power electronic converter and other units; it is understandable that the wind turbine model can include different types such as double-fed wind turbine and full-power wind turbine.

[0084] Preferably but not restrictively, the impeller and mechanical transmission unit are used to convert the captured wind energy into mechanical energy input into 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 stators, rotors and their ancillary equipment; the power electronic converter unit includes but is not limited to: a machine-side converter for converting AC electrical energy into DC electrical energy and a grid-side converter for converting DC electrical energy into AC electrical energy and its ancillary equipment.

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

[0086] The electromagnetic transient equivalent simulation model of the wind turbine with energy balance transfer is an energy transfer process from a controlled current source equivalent mechanical module to a machine-side converter; preferably but not restrictively, a controlled current source is connected in parallel across the DC capacitor to simulate the dynamic interaction process of the AC and DC sides during a fault transient, and the energy transferred to the DC side is calculated by utilizing the wind energy captured by the impeller and the mechanical transmission part and the transient energy loss in the energy transfer process on the AC and DC sides, and 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 and steady-state energy balance transfer process between the impeller and the rotor side; further preferably but not restrictively, the steady-state transfer process takes into account the mechanical transmission loss, the efficiency loss of the generator and the machine-side converter; the transient transfer process takes into account the energy consumption of the rotor-side AC energy dissipation circuit and the DC-side energy dissipation circuit of the machine-side converter.

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

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

[0090] Where:

[0091] Z ref_DC is the energy transferred to the DC side,

[0092] E AC_wind is the wind energy captured by the wind turbine,

[0093] Z loss is the loss in the steady-state transmission process,

[0094] E AC_crow b ar and E DC_c h opper It is the energy consumption of the AC and DC side energy dissipation circuit during the transient transfer process.

[0095] Further preferably but not restrictively, the steady-state transfer energy loss considers the switching loss of the power electronic components in the converter, which is proportional to the switching frequency. It can be obtained that the switching loss power per unit time is equal to the unit loss of a switching process multiplied by the switching frequency per unit time, which is expressed by the following formula (14):

[0096] E loss =f IGBT ×E on_off (14)

[0097] Where:

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

[0099] E loss is the steady-state loss of the switching element,

[0100] E on_off is the unit loss of 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 amplitude of the fundamental frequency part of the controlled current source can be expressed as follows:

[0102]

[0103] Where:

[0104] I ref_DC is the amplitude of the fundamental frequency part of the controlled current source,

[0105] V DC is a DC voltage.

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

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

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

[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, in which the energy transfer between the wind turbine modulation module and the grid side converter is reflected as the base frequency input part; the reference voltage of the converter control system is multiplied by the control coefficient to obtain the input voltage of the three-phase controlled voltage source; the voltage amplitude of the base frequency input part of the controlled voltage source can be expressed as follows:

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

[0111] Where:

[0112] k ctl is the control coefficient,

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

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

[0115] It is worth noting that, as one of the outstanding substantial features of the present invention, the control process of the three-phase controlled voltage source equivalent to the grid-side converter is used, and 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 the complex iterative calculation, which can essentially solve the problem of low simulation speed caused by power electronic switch calculation.

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

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

[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 mode of the converter, and the higher the switching frequency and the more complex the modulation mode, the smaller the corresponding harmonic content. Therefore, it can be concluded that the voltage amplitude of the high-frequency harmonic part in the three-phase controlled voltage source is expressed by the following formula (17):

[0119]

[0120] Where:

[0121] k hmn is the harmonic content characterization coefficient, which is used to quantify the converter modulation mode;

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

[0123] V abc_ref_hmn is the input voltage amplitude of the harmonic part of the three-phase controlled voltage source,

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

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

[0126]

[0127] Where:

[0128] k hmm_PWM is the harmonic content characterization coefficient when PWM modulation is adopted;

[0129] k hmm_SPWM is the harmonic content characterization coefficient when SPWM modulation is adopted;

[0130] k hmm_SVPWM It is the harmonic content characterization coefficient when using SVPWM modulation.

[0131] It is worth noting that, as one of the outstanding substantial features of the present 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, by setting the harmonic content characterization coefficient, the harmonic coefficient, the switching frequency of the power electronic components and the converter modulation method are used to characterize the high-frequency harmonic part in the grid-side controlled voltage source; and the harmonic part is superimposed on the fundamental frequency energy transfer part to determine the input voltage of the controlled voltage source.

[0132] Furthermore, it is significantly different from the conventional simulation model equivalent method that regards the AC and DC sides as unrelated and does not contain any harmonic components. According to the actual application scenario, the control coefficient, harmonic coefficient, switching frequency and modulation method of the module can be flexibly set to adjust the output characteristics of the simulation model. It is suitable for the equivalence of different types of wind power simulation models such as double-fed wind turbines and full-power wind turbines, and associates the controlled sources on the AC and DC sides to reflect the transient process of energy transfer on the AC and DC sides and the harmonic characteristics associated with the switching links, further ensuring the accuracy of the equivalent model on the basis of improving the simulation efficiency.

[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 the rotor side 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 power grid, and obtain the electromagnetic transient equivalent model of the wind turbine that reflects the energy balance transfer.

[0134] Preferably but not restrictively, the controlled power supply power interaction module of the energy balance transfer is manifested in that the equivalent current input amplitude of the wind turbine converter in different transient processes is obtained by adjusting the energy transfer loss on the AC and DC sides, and the controlled current source is connected to the DC power grid in parallel with the three-phase uncontrolled rectifier bridge; by adjusting the wind turbine control module and the converter switching frequency, the fundamental frequency and harmonic equivalent voltage input amplitude corresponding to different control strategies are obtained, and the controlled voltage source module is connected to the power grid in parallel with the controlled current source via the uncontrolled rectifier bridge to obtain the wind turbine electromagnetic transient equivalent model reflecting the energy balance transfer.

[0135] It is noteworthy that, as one of the outstanding substantial features of the present invention, while replacing the detailed switch module of the wind power converter with a controlled voltage source equivalent module, and replacing the DC side part of the wind power converter with a controlled current source equivalent module, the energy interaction process of the AC and DC controlled power sources is considered; in the process of calculating the controlled source input reference value, the transient steady-state losses existing in the energy transfer process between the wind energy captured by the wind turbine impeller and the unit-side converter are taken into account, so as to realize the energy consumption of the AC and DC side energy dissipation circuits in the equivalent model, thereby solving the problem of directly considering the AC and DC side energies to be equal and causing loss of accuracy.

[0136] The method proposed in the present invention simplifies the problem of rapid changes in circuit states caused by frequent switching actions and frequent updates of the circuit matrix by the solver, so that the dynamic complexity of the circuit is reduced while retaining the control strategy of the wind turbine set, and the amount of simulation calculation is greatly reduced. The present invention focuses on the equivalent modeling of a single wind turbine set in the entire new energy station, and is also competent for the simulation model construction requirements of a single unit collection line or a new energy station transmission line.

[0137] In order to more clearly introduce the outstanding essential features of the present invention and the significant progress it brings to the prior art, an application example of implementing the present invention is introduced below.

[0138] In the embodiment of the present invention, 20 doubly-fed wind turbines with the same control strategy are used, each doubly-fed wind turbine has a rated capacity of 3MW, a DC voltage reference value is set to 1200V, and a rated output voltage of 690V at the grid connection point outlet of the unit. Figure 1 The topology diagram of the controlled current source module for energy balance transfer between the impeller and the rotor side. Figure 2 Topology diagram of the controlled voltage source module for balanced energy transfer between the grid side and the DC side.

[0139] like Figure 1 As shown in the figure, the wind turbine model includes modules such as impeller, mechanical transmission, generator and power electronic converter, which are used to convert the captured wind energy into mechanical energy input to the generator. The generator and power electronic converter simulation module includes the generator stator, rotor, machine-side and grid-side converters and their ancillary equipment; the generator module is used to convert the input mechanical energy into AC power; the machine-side converter module is used to convert AC power into DC power. This module describes the transient and steady-state energy transfer process of the wind energy captured by the wind turbine impeller through the mechanical transmission shaft system and the generator to the unit-side converter; among them, the steady-state transfer considers the mechanical transmission loss, the efficiency loss of the generator and the machine-side converter; the transient transfer considers the energy consumption of the rotor-side AC energy dissipation circuit and the DC-side energy dissipation circuit of the machine-side converter; the energy transferred to the DC side is determined based on the energy 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 is the fundamental frequency input voltage amplitude of the three-phase controlled voltage source, V a_ref_ h mn 、V b_ref_hmn and V c_ref_ h mn is the input voltage amplitude of the harmonic part 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_DCis the amplitude of the fundamental frequency part of the controlled current source. This module describes the energy transfer process between the DC bus side of the wind turbine and the grid through the grid-side converter; among them, the fundamental frequency amplitude of the controlled voltage source is determined according to the calculation results of the wind turbine control module; and the harmonic amplitude of the controlled voltage source is determined according to the equivalent situation of the switching device model.

[0141] The dynamic interaction circuit between AC and DC is established to realize the dynamic interaction simulation of AC and DC power. ref_DC The control signal includes: 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 energy balance transfer process between the impeller and the rotor side. In the steady-state transfer process, mechanical transmission loss, generator and machine-side converter efficiency loss are considered. In the transient transfer process, the energy loss of the rotor-side AC energy dissipation circuit Crowbar and the energy consumption of the machine-side converter DC energy dissipation circuit Chopper are considered. Based on the energy balance transfer principle, the energy transferred from the impeller to the DC side through the machine-side converter is the captured wind energy minus the transient 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 the embodiment of the present invention, the resistance of the energy dissipation circuit is R AC_crowbar =R DC_chopper =0.5Ω, the energy consumption of the AC and DC side energy dissipation circuit in the transient transmission process is E AC_crow b ar =E DC_c h opper =0.6MW.

[0145] The energy transferred to the DC side is Z ref_DC Equal to DC voltage U DC By multiplying the product of the DC current, it can be concluded that the amplitude of the fundamental frequency part of the controlled current source satisfies the following relationship:

[0146]

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

[0148] Controlled three-phase voltage source V ra、V 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 and control coefficient k ctl The product of is shown below:

[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] Among them, the control coefficient k ctl is a parameter related to the control effect, k ctl =0.95.

[0153] The method proposed in the present 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; there is no need to consider the parameter state of the bridge arm device and the complex iterative calculation, which essentially solves the problem of low simulation speed caused by the frequent switching actions and iterative calculations of power electronics.

[0154] The controlled voltage source module describes the energy balance transfer process between the grid side and the DC side, in which the harmonic input part is reflected as the equivalent of the switching process; the harmonic content characterization coefficient k is set hmn , where the harmonic content is related to the switching frequency of the power electronic components and the modulation mode of the converter. Therefore, it can be concluded that the voltage amplitude of the high-frequency harmonic part in the three-phase controlled voltage source satisfies the following relationship:

[0155]

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

[0157] There are three main forms of modulation for power electronic converters, namely PWM modulation, SPWM modulation, and SVPWM modulation. There is an inverse relationship between the harmonic content and the accuracy of the modulation method. Therefore, the harmonic coefficient is set 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 grid-side controlled voltage source reference value is composed of the fundamental frequency part of the energy transfer through the AC and DC sides and the harmonic part caused by the power electronic switching link in parallel.

[0160] The present invention replaces the detailed switch module of the wind power converter with the equivalent module of the controlled voltage source in the prior art, and uses the energy transfer process of the mechanical module to the machine-side converter as the equivalent of the controlled current source, and uses the control process of the grid-side converter as the equivalent of the three-phase controlled voltage source and the harmonic link caused by the switching process, and considers the internal interaction process of AC and DC. In the process of calculating the input reference value of the controlled source, the transient steady-state loss caused by the AC and DC energy transfer process is considered, and the error caused by directly considering the AC and DC side energies as equal is solved. At the same time, considering the problem that the equivalent model of the wind turbine set cannot reflect the harmonic characteristics of the converter due to the absence of the switch module, the harmonic content characterization coefficient is set, and the high-frequency harmonic part in the controlled voltage source is characterized by using the harmonic coefficient, the switching frequency of the power electronic component and the converter modulation mode; and the harmonic part is superimposed with the fundamental frequency energy transfer part to determine the input voltage of the controlled voltage source.

[0161] The present invention focuses on the equivalent modeling of a single wind turbine in the entire new energy station, and is competent for the simulation model building requirements of a single turbine collection line or a new energy station transmission line. The wind turbine model described in the present invention includes different types such as double-fed wind turbines and full-power wind turbines. Specifically, in the controlled power interaction module, by adjusting the energy transfer loss on the AC and DC sides, the equivalent current input amplitude of the wind turbine converter in different transient processes is obtained, and the controlled current source is connected to the DC grid in parallel with the three-phase uncontrolled rectifier bridge; by adjusting the wind turbine control module and the converter switching frequency, the fundamental frequency and harmonic equivalent voltage input amplitude corresponding to different control strategies are obtained, and the controlled voltage source is connected to the grid in parallel with the controlled current source through the uncontrolled rectifier bridge to obtain a wind power equivalent simulation model. The invention can accurately reflect the energy balance transfer process of the wind turbine capturing wind energy to electrical energy, and improve the simulation efficiency on the basis of ensuring the transient and steady-state simulation accuracy of the model.

[0162] By using the method proposed in the present invention, the same parameters and working conditions are set in PSCAD V4.6.0 software, and the operating efficiency of the detailed and equivalent models of the system composed of 20 wind turbines is compared. The following conclusions are drawn: the simulation step size is fixed to 20us, the simulation time is 10s, the simulation time of the detailed model is 21.937s, and the simulation time of the equivalent model is 5.281s. The simulation rate can be increased by about 4 times.

[0163] Depend on Figure 4 It can be seen that the traditional model equivalent method cannot reflect the harmonic characteristics, the power quality will be very good, the waveform will be smooth, but the accuracy and authenticity will be poor; Figure 3 It can be seen that the output voltage curve of the wind power simulation model considering energy transfer in the present invention can reflect the harmonic components and more accurately reflect the actual situation. Figure 5 and Figure 6 The output power waveforms of wind turbine grid connection points obtained by the wind power simulation model considering energy transfer and the equivalent model of the prior art are respectively, with a step change to 0.5P at 4s. n , step to 0.75P in 6s n , the active power at 8s is P n When the wind speed is low, there is energy loss in the transient steady state, and the active power cannot follow the power command. However, the existing equivalent method directly regards the energy on the AC and DC sides as equal. When the wind speed is low, the controlled power supply still maintains a large value, which cannot reflect the conflict between the wind speed and the energy dissipation circuit. Therefore, the power always follows the command.

[0164] In combination with large-scale scenarios and limited hardware environments, the present invention associates the controlled sources on the AC and DC sides and considers energy balance transfer and harmonic characteristics. Therefore, this equivalent method has certain applicability in the study of power frequency transient characteristics and harmonic characteristics, and can reflect the connection between wind speed and transient steady-state energy loss in the energy transfer process to a certain extent, which is very meaningful for reducing the distortion of the equivalent process of the new energy model.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection 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 that takes into account the energy balance transfer between the impeller and the rotor side is established to describe the transient steady-state energy transfer process of the wind energy captured by the wind turbine impeller through the mechanical transmission shaft system and the generator to the unit-side converter; A controlled voltage source module is established that takes into account the energy balance transfer between the DC bus side and the grid-side converter to describe the energy transfer process between the DC bus side of the wind turbine and the grid via the grid-side converter. A controlled power interaction module is established to connect the controlled current source module to the power grid in parallel with the controlled voltage source module through an uncontrolled rectifier bridge, thereby realizing the interaction between the controlled current source and the controlled voltage source and completing the construction of an electromagnetic transient equivalent model of the wind turbine that reflects the energy balance transfer.

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

3. A method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer according to claim 1 or 2, characterized in that: The transient steady-state energy transfer process of wind energy captured by the fan impeller through the mechanical transmission shaft system and the generator to the unit-side converter includes: Steady-state transfer meter and mechanical transmission loss, generator and machine-side converter efficiency loss; Transient transfer includes the energy consumption of the rotor-side AC energy dissipation circuit and the DC-side energy dissipation circuit of the generator-side converter; The energy transferred to the DC side is determined based on the energy to calculate the current amplitude of the controlled current source module.

4. The method for constructing a wind turbine electromagnetic transient equivalent model reflecting energy balance transfer according to claim 3 is characterized in that: The energy transferred from the impeller to the DC side through the machine-side converter is the captured wind energy minus the transient energy loss during the energy transfer process, which is expressed by the following formula: With ref_DC =E AC_wind -Z loss -E DC_chopper -E AC_crowbar (1) Where: Z ref_DC is the energy transferred to the DC side, E AC_wind The wind energy captured by the wind turbine, Z loss is the loss in the steady-state transmission process, E AC_crowbar and E DC_chopper Energy consumption of AC and DC side energy dissipation circuit in transient transfer process; The energy transferred to the DC side is equal to the product of the DC voltage and the DC current. The amplitude of the fundamental frequency part of the controlled current source can be expressed as follows: Where: I ref_DC is the amplitude of the fundamental frequency part of the controlled current source, V DC is a DC voltage.

5. A method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer according to claim 1 or 2, characterized in that: The energy transfer process between the wind turbine DC bus side and the grid via the grid-side converter includes: The control process of the equivalent grid-side converter obtains the fundamental frequency input voltage amplitude of the three-phase controlled voltage source based on the control parameters of the grid-side converter; The harmonic link caused by the switching process of the equivalent grid-side converter is determined based on the parameters of the power electronic components of the grid-side converter.

6. The method for constructing a wind turbine electromagnetic transient equivalent model reflecting energy balance transfer according to claim 5 is characterized in that: The voltage amplitude of the fundamental frequency input part of the controlled voltage source is obtained by multiplying the reference voltage of the grid-side converter by the control coefficient and is expressed as follows: V abc_ref_fund =k ctl ×V abc_ref (3) Where: k ctl is the control coefficient, V abc_ref_fund is the fundamental frequency input voltage amplitude of the first three-phase controlled voltage source, V abc_ref It is the reference voltage output by the fan control module.

7. The method for constructing a wind turbine electromagnetic transient equivalent model reflecting energy balance transfer according to claim 5 is characterized in that: By setting the harmonic content characterization coefficient, the voltage amplitude of the high-frequency harmonic part in the three-phase controlled voltage source is expressed as follows: Where: k hmn is the harmonic content characterization coefficient, which is used to quantify the converter modulation mode; f IGBT is the switching frequency of power electronic components, V abc_ref_hmn is the input voltage amplitude of the harmonic part of the second three-phase controlled voltage source, V abc_ref It is the reference voltage output by the fan control module.

8. The method for constructing a wind turbine electromagnetic transient equivalent model reflecting energy balance transfer according to claim 7 is characterized in that: The harmonic content characterization coefficient when PWM modulation is used is greater than the harmonic content characterization coefficient when SPWM modulation is used, and is greater than the harmonic content characterization coefficient when SVPWM modulation is used, and is expressed by the following formula: k hmn_PWM >k hmn_SPWM >k hmn_SVPWM (5) Where: k hmm_PWM is the harmonic content characterization coefficient when PWM modulation is adopted; k hmm_SPWM is the harmonic content characterization coefficient when SPWM modulation is adopted; k hmm_SVPWM It is the harmonic content characterization coefficient when using SVPWM modulation.

9. A method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer according to claim 1 or 2, characterized in that: The controlled power source power interaction module realizes the 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 in different transient processes is obtained, and 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 fan control module and the converter switching frequency, the fundamental frequency and harmonic equivalent voltage input amplitude corresponding to different control strategies are obtained. The harmonic part of the controlled voltage source is connected to the grid in parallel with the controlled current source through an uncontrolled rectifier bridge.

10. A method for constructing an electromagnetic transient equivalent model of a wind turbine that reflects energy balance transfer according to claim 1 or 2, characterized in that: The steady-state transfer energy loss includes the switching loss of the power electronic components in the converter and is expressed as follows: E loss =f IGBT ×E on_off (6) Where: f IGBT is the switching frequency of power electronic components, E loss is the steady-state loss of the switching element, E on_off is the unit loss of the switching process.

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