Transient current capability improvement control system and method of wind and light power generation system

Abstract

The invention provides a transient current capability improvement control system and method of a wind and light power generation system. The system comprises a self-synchronizing voltage source control module, a junction temperature prediction module, a transient current improvement control module, a current instruction calculation module and a transient current precise control module. According to the invention, online observation of the junction temperature of the wind-solar converter power device can be realized, the maximum short-circuit current which can be output can be accurately predicted, the DC bus voltage, the switching frequency and the modulation strategy are adjusted when the power grid has a fault, the junction temperature of the power device is reduced, and the transient current endurance capability of the power device is improved. And the transient current is accurately controlled to limit the utilization of the transient capability of the power device.

Description

Technical Field

[0001] The present invention relates to the technical field of control of new energy power generation systems, and specifically, to a control system and method for improving the transient current capacity of a wind-solar power generation system. Background Art

[0002] Grid-forming control is a key technology for building a new power system. It can make the new energy power generation system exhibit external characteristics similar to those of a synchronous generator, be able to synchronize with the power grid independently, have an inertia response characteristic to damp the frequency change of the power grid, and a transient voltage response to support the power grid voltage. However, the active support ability of a self-synchronizing voltage source new energy unit for the grid fault voltage is restricted by the transient current tolerance ability of the power device of the converter. Currently, the transient current output ability of a new energy converter is about 1.1 times the rated current, which can only ensure that the unit successfully crosses the fault under a grid fault, but cannot effectively support the power grid voltage. More seriously, with the gradual increase in the proportion of grid-forming control new energy power generation, the lack of transient current support ability will trigger the occurrence of system cascading failures, and then lead to the serious consequences of voltage and frequency collapse one after another.

[0003] Currently, the research on the transient current output and the improvement of the active support ability of grid-forming power generation units is still blank, and all are limited to restricting the output current of grid-forming power generation units under a grid fault to smoothly cross the fault, and cannot support the voltage stability of the new power system. Therefore, it is necessary to change the idea of restricting fault current to improving transient current. Through a three-dimensional dynamic adjustment mechanism of DC voltage, switching frequency, and modulation strategy, combined with real-time observation of the junction temperature of the power device, make full use of the transient tolerance ability of the power device as much as possible, accurately control the transient current output, and enable the new energy power generation unit to output more than 3 times the rated current within 625 ms at the lowest cost; at the same time, through the adaptive optimization control of the transient current phase, the support for the grid fault voltage is maximized.

[0004] Patent document CN116388264A discloses a control system and method for a DC self-synchronizing enhanced permanent magnet direct drive wind turbine. The control system includes a wind turbine generator, a machine-side converter, a DC capacitor, a grid-side converter, and a grid-side structure. The method includes: the machine-side converter controls the machine-side converter through a power control loop, a first current inner loop, a first Park converter, and a first space vector pulse width modulator, and the grid-side converter controls the grid-side converter through a synchronization loop, a reactive-voltage droop loop, a voltage outer loop, a second current inner loop, a second Park converter, and a second space vector pulse width modulator, and finally realizes the control of the wind turbine generator. However, this patent cannot completely solve the existing technical problems and cannot meet the requirements of the present invention. Summary of the Invention

[0005] Aiming at the defects in the prior art, the purpose of the present invention is to provide a control system and method for improving the transient current capacity of a wind-solar power generation system.

[0006] The control system for improving the transient current capacity of a wind-solar power generation system provided by the present invention includes:

[0007] A self-synchronous voltage source control module: performing voltage source control on the grid-side converter of the new energy unit;

[0008] A junction temperature prediction module: calculating the power device loss in real time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit, inputting the loss data to the heat flow correction link to update the loss data, and inputting the updated loss data to the thermal circuit model to calculate the current power device junction temperature;

[0009] A transient current boost control module: calculating the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and selecting according to the boundary values to predict the reduced loss value; or presetting the boundary values of the switching frequency, modulation voltage, and DC voltage, calculating the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit, combining the current transient current boost requirement, optimizing the required optimal switching frequency, modulation voltage, and DC voltage adjustment values, and using them as command outputs for adjustment;

[0010] A current command calculation module: calculating the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information;

[0011] A transient current precise control module: controlling the transient current amplitude to follow the junction temperature and the command value output by the transient current boost control module in real time.

[0012] Preferably, the self-synchronous voltage source control module includes:

[0013] An inertia synchronization control module: outputting the phase angle θ of the modulation voltage of the grid-side converter vsg , multiplying the deviation between the rated value u dcn of the DC voltage and the actual value u dc by a proportional coefficient K dc and then accumulating it to the rated angular frequency ω0 for integration, so as to realize the function of the DC voltage mirroring the grid frequency change and autonomous synchronization in real time. The expression is:

[0014]

[0015] A port voltage control module: including a reactive power controller, a damping enhancement controller, and a reference value U tn , generating the modulation voltage U t of the grid-side converter of the new energy power generation unit, and realizing the control of the reactive power output by the self-synchronous voltage source control unit. The expression is:

[0016]

[0017] Among them, K QP and K QI are the coefficients of the PI regulator corresponding to the reactive power, Q gef and Q g are the command and actual value corresponding to the reactive power, K D is the damping coefficient, and s is the corresponding differential operator;

[0018] Machine-side inertia transfer control module: decouples the dq-axis electrical quantities to achieve the power generation power control of the front-stage converter of the new energy generation unit, and at the same time introduces an inertia transfer control link to achieve inertia response without a frequency detection device. The expression is:

[0019]

[0020] Among them, P MPPT is the maximum wind power tracking module, which is used to output the current power according to the optimal tip speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to the active power; T m is the filtering time constant, which is used to filter out the high-frequency components contained in the DC voltage signal; P ref is the finally output power command, which is used as the input of the controller;

[0021] Vector control module: decouples the dq-axis electrical quantities to achieve the power generation power control of the front-stage converter of the new energy generation unit, and at the same time generates the current commands I sdref and I sqref , and the expression is:

[0022]

[0023] Among them, P m is the active power actually output by the machine-side converter, K po and K io are the proportional and integral coefficients of the power controller respectively.

[0024] Preferably, the junction temperature prediction module includes:

[0025] Loss calculation module: samples the amplitude of the current output phase voltage U cx , the amplitude of the phase current I cx , the DC voltage U dc , the switching frequency f sw and the junction temperature T jx , and calculates the conduction loss P T,Dcon of the IGBT anti-parallel diode in the converter within a power frequency cycle and the switching loss PT,Dsw , where the subscript x corresponds to the A, B, and C phase arms of the grid-side converter, and the calculation expressions for the conduction loss and switching loss are as follows:

[0026]

[0027] Among them, V x corresponds to the conduction voltage drop of the IGBT or the reverse conduction voltage drop of the diode; E x corresponds to the turn-on and turn-off energies of the IGBT or the reverse recovery energy of the diode; d x corresponds to the modulation degree of the IGBT or the diode; U ref is the switching loss test reference voltage of the IGBT or the diode; K sw is the calibration coefficient; T min and T max are the lower and upper limits of the junction temperature given in the data sheet;

[0028] Junction temperature calculation module: Calculate the junction temperatures T jx of the IGBT and its anti-parallel diode and the common module case temperature T c respectively, and use the output of the loss calculation module as the input of the thermal circuit model to obtain the temperature difference ΔT jx between the junction and the case of the IGBT or the diode. The expression is:

[0029] ΔT jx =(P T,Dcon +P T,Dsw )Z jh (s) (6)

[0030] Among them, Z jh (s) is the thermal impedance between the junction and the case of the IGBT or the diode, and s is the corresponding differential operator. The expression is:

[0031]

[0032] Among them, τ i is the time constant of each stage i of the thermal impedance. There are 4 stages between the junction and the case, which are given by the device data sheet;

[0033] The temperature difference ΔT c between the case of the IGBT and the diode and the radiator is obtained in the same form as formula (5). The expression is:

[0034] ΔT c =ΔP loss Z ch (8)

[0035] Among them, Z ch is the thermal impedance from the IGBT case to the radiator; ΔPloss is the sum of the IGBT and diode losses;

[0036] When the radiator temperature is set to T h , the junction temperature calculation formula is obtained according to formulas (6)-(8):

[0037] T jx =ΔT jx +ΔT c +T h (9).

[0038] Preferably, the transient current boost control module includes:

[0039] Switching frequency adjustment module: adjusts the switching frequency f of the new energy unit converter sw to change the switching losses of the power devices, and their corresponding relationship is:

[0040] f sw =K1f swn (10)

[0041] where f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient;

[0042] Global optimal modulation strategy module: realizes discontinuous modulation that minimizes the switching losses of power devices within the entire power factor range. The switching frequency adjustment coefficient K2 is used to select whether to turn off or turn on the global optimal discontinuous modulation function between 0 and 1, and the expression is:

[0043]

[0044] where SVWPM is space vector modulation and GDPWM is the global optimal modulation used in this module;

[0045] DC voltage adjustment module: adjusts the action threshold of the DC side Chopper circuit to adjust the switching losses of the power devices, and their corresponding relationship is:

[0046] U chop =K3f swn (12)

[0047] where U chop is the voltage of the DC side Chopper circuit, and K3 is the switching frequency adjustment coefficient;

[0048] Maximum transient current prediction module: sets the adjustment coefficients K1, K2, and K3 of the switching frequency - modulation strategy - DC voltage, and finally outputs the current command value I set ;

[0049] Optimize the K1, K2, and K3 coefficients in real time according to the currently allowed upper limit of the junction temperature and the loss value, and optimize and solve for the maximum short-circuit current amplitude I that does not exceed the junction temperature limit within the allowable operating range of the switching frequency and DC voltage. set And use I set As the input of the transient current precise control module.

[0050] Preferably, the transient current precise control module includes:

[0051] Virtual admittance module: Establish the relationship between the internal potential U tdq Of the grid-side converter of the self-synchronous voltage source new energy unit and the output current command I refdq The relationship is expressed as:

[0052]

[0053] Among them, U cdq Is the dq-axis voltage on the filter capacitor at the output port of the self-synchronous voltage source new energy unit, L v And R v Are the values of the virtual inductor and the virtual resistor, and the reciprocal of the sum of the two is the virtual admittance;

[0054] Circular current limiting module: Under the condition of keeping the output power component of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, limit its transient current amplitude not to exceed the set value, and at the same time generate the final dq-axis current command value I mrefdq The expression is:

[0055]

[0056] If the current amplitude I t Is less than the amplitude command I set Output by the maximum transient current prediction module, then use the output I refdq Of the virtual admittance link as the current command. If the current amplitude I t Is greater than the amplitude command I set Output by the maximum transient current prediction module, then scale down the dq-axis current command value in proportion to I set / I t ;

[0057] Transient current precise control link: According to the current command output by the circular current limiting module, control the transient current to the command value, and at the same time add a non-linear virtual resistor to suppress the impact current during the transient moment. The expression is:

[0058]

[0059] Among them, U stdis the finally generated modulation voltage; K ip and K iI are the proportional and integral coefficients of the grid-side converter current controller respectively, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop on the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage, and s is the corresponding differential operator;

[0060] The expression of the virtual resistance is:

[0061]

[0062] wherein, K v is the resistance value adjustment coefficient of the virtual resistance. Under the same current I t the R v increases with the increase of K v If I t exceeds I set , then the virtual resistance R v is put into use; if the peak value of I t has not exceeded the limit, then R v is not put into use.

[0063] According to the transient current capacity improvement control method of the wind-solar power generation system provided by the present invention, it includes:

[0064] Self-synchronous voltage source control step: performing voltage source control on the grid-side converter of the new energy unit;

[0065] Junction temperature prediction step: calculating the power device loss in real time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit, inputting the heat flux correction link to update the loss data, and inputting the updated loss data into the thermal circuit model to calculate the current power device junction temperature;

[0066] Transient current boost control step: calculating the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and selecting according to the boundary values to predict the reduced loss value; or presetting the boundary values of the switching frequency, modulation voltage, and DC voltage, calculating the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit, combining with the current transient current boost requirement, optimizing the required optimal switching frequency, modulation voltage, and DC voltage adjustment values, and using them as command outputs for adjustment;

[0067] Current command calculation step: calculating the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information;

[0068] Transient current precise control step: Control the transient current amplitude to follow the junction temperature and the command value output by the transient current boost control step in real time.

[0069] Preferably, the self-synchronous voltage source control step includes:

[0070] Inertial synchronization control step: Output the phase angle θ of the modulation voltage of the grid-side converter vsg , multiply the deviation between the rated value u of the DC voltage dcn and the actual value u dc by a proportionality coefficient K dc , and then accumulate it onto the rated angular frequency ω0 for integration, so as to realize the function of the DC voltage mirroring the grid frequency change and self-synchronization in real time. The expression is:

[0071]

[0072] Port voltage control step: Include a reactive power controller, a damping enhancement controller, and a reference value U tn , generate the modulation voltage U of the grid-side converter of the new energy power generation unit t , and realize the control of the reactive power output by the self-synchronous voltage source control unit. The expression is:

[0073]

[0074] Among them, K QP and K QI are the coefficients of the PI regulator for reactive power, Q gef and Q g are the command and actual value corresponding to reactive power, K D is the damping coefficient, and s is the corresponding differential operator;

[0075] Machine-side inertia transfer control step: Decouple the dq-axis electrical quantities, realize the power generation power control of the front-stage converter of the new energy power generation unit, and at the same time introduce an inertia transfer control link to realize the inertia response without a frequency detection device. The expression is:

[0076]

[0077] Among them, P MPPT is the maximum wind power tracking module, which is used to output the current power according to the optimal tip speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to active power; T m is the filtering time constant, which is used to filter out the high-frequency components contained in the DC voltage signal; P ref is the finally output power command, which is used as the input of the controller;

[0078] Vector control steps: Decouple the electrical quantities on the dq axes to achieve the power control of the front-stage converter of the new energy power generation unit, and simultaneously generate the current commands I sdref and I sqref , the expressions are:

[0079]

[0080] where P m is the active power actually output by the machine-side converter, and K po and K io are the proportional and integral coefficients of the power controller respectively.

[0081] Preferably, the junction temperature prediction steps include:

[0082] Loss calculation steps: Sample the current output phase voltage amplitude U cx , phase current amplitude I cx , DC voltage U dc , switching frequency f sw and junction temperature T jx , and calculate the conduction loss P T,Dcon of the anti-parallel diode of the IGBT in the converter within one power frequency cycle and the switching loss P T,Dsw , where the subscript x corresponds to the A, B, and C phase bridges of the grid-side converter, and the calculation expressions of the conduction loss and the switching loss are:

[0083]

[0084] where V x corresponds to the conduction voltage drop of the IGBT or the reverse conduction voltage drop of the diode; E x corresponds to the turn-on and turn-off energies of the IGBT or the reverse recovery energy of the diode; d x corresponds to the modulation degree of the IGBT or the diode; U ref is the switching loss test reference voltage of the IGBT or the diode; K sw is the calibration coefficient; T min and T max are the lower and upper limits of the junction temperature given in the data sheet;

[0085] Junction temperature calculation steps: Calculate the junction temperatures T jx of the IGBT and its anti-parallel diode and the common case temperature T c respectively, and use the output of the loss calculation steps as the input of the thermal circuit model to obtain the temperature difference ΔT jx between the junction and the case of the IGBT or the diode due to the loss, and the expression is:

[0086] ΔT jx =(PT,Dcon +P T,Dsw )Z jh (s) (22)

[0087] Among them, Z jh (s) is the thermal impedance from the junction to the case of the IGBT or diode, s is the corresponding differential operator, and the expression is:

[0088]

[0089] Among them, τ i is the time constant of each stage i of the thermal impedance. There are a total of 4 stages from the junction to the case, which are given by the device data sheet;

[0090] The temperature difference ΔT between the case of the IGBT and the diode and the radiator c is obtained in the same form as formula (5), and the expression is:

[0091] ΔT c =ΔP loss Z ch (24)

[0092] Among them, Z ch is the thermal impedance from the IGBT case to the radiator; ΔP loss is the sum of the losses of the IGBT and the diode;

[0093] When the radiator temperature is set to T h , according to formulas (6)-(8), the junction temperature calculation formula is obtained:

[0094] T jx =ΔT jx +ΔT c +T h (25).

[0095] Preferably, the transient current boost control step includes:

[0096] Switching frequency adjustment step: Adjust the switching frequency f of the new energy unit converter sw to change the switching loss of the power device, and the corresponding relationship is:

[0097] f sw =K1f swn (26)

[0098] Among them, f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient;

[0099] Global optimal modulation step: Discontinuous modulation that minimizes the switching losses of power devices across all power factor ranges. The switching frequency adjustment coefficient K2 is used to select whether to turn on or off the global optimal discontinuous modulation function between 0 and 1, and the expression is:

[0100]

[0101] Among them, SVWPM is space vector modulation, and GDPWM is the global optimal modulation used in this step;

[0102] DC voltage regulation step: Adjust the action threshold of the DC side Chopper circuit to adjust the switching losses of power devices, and their corresponding relationship is:

[0103] U chop =K3f swn (28)

[0104] Among them, U chop is the voltage of the DC side Chopper circuit, and K3 is the switching frequency adjustment coefficient;

[0105] Maximum transient current prediction step: Set the adjustment coefficients K1, K2, and K3 for the switching frequency - modulation strategy - DC voltage, and finally output the current command value I set ;

[0106] According to the currently allowed upper limit of the junction temperature and the loss value in real - time, optimize the K1, K2, and K3 coefficients, and optimize and solve for the maximum short - circuit current amplitude I set that does not exceed the junction temperature within the allowable operating range of the switching frequency and the DC voltage, and use I set as the input of the transient current precise control step.

[0107] Preferably, the transient current precise control step includes:

[0108] Virtual admittance step: Establish the relationship between the internal potential U tdq of the grid - side converter of the self - synchronous voltage source new energy unit and the output current command I refdq , and its relationship is expressed as:

[0109]

[0110] Among them, U cdq is the dq - axis voltage on the filter capacitor at the output port of the self - synchronous voltage source new energy unit, L v and R v are the values of the virtual inductor and the virtual resistor, and the reciprocal of the sum of the two is the virtual admittance;

[0111] Circular current limiting step: Under the condition of keeping the output power component of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, limit its transient current amplitude not to exceed the set value, and at the same time generate the final dq-axis current command value I mrefdq , the expression is:

[0112]

[0113] If the current amplitude I t is less than the amplitude command I set output by the maximum transient current prediction step, then use the output I refdq of the virtual admittance link as the current command. If the current amplitude I t is greater than the amplitude command I set output by the maximum transient current prediction step, then scale down the dq-axis current command value in proportion according to I set / I t ;

[0114] Transient current precise control link: According to the current command output by the circular current limiting step, control the transient current to the command value, and at the same time add a non-linear virtual resistance to suppress the impact current in the transient moment. The expression is:

[0115]

[0116] Among them, U std is the finally generated modulation voltage; K ip and K iI are the proportional and integral coefficients of the grid-side converter current controller respectively, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop of the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage, and s is the corresponding differential operator;

[0117] The expression of the virtual resistance is:

[0118]

[0119] Among them, K v is the resistance value adjustment coefficient of the virtual resistance. Under the same current I t , R v increases with the increase of K v . If I t exceeds I set , then the virtual resistance R v is put into use; if the peak value of I t has not exceeded the limit, then R v is not put into use.

[0120] Compared with the prior art, the present invention has the following beneficial effects:

[0121] (1) The present invention realizes real-time online observation of the junction temperature of the power devices in the new energy power generation converter;

[0122] (2) The present invention can give the upper limit of the current maximum allowable transient current amplitude based on the data-driven electro-thermal coupling model;

[0123] (3) The present invention dynamically regulates the power device losses of the converter through the three-dimensional model of switching frequency - modulation strategy - DC voltage, adaptively reduces the junction temperature, and improves the transient current tolerance ability, so as to realize the short-term tolerance of the new energy unit to 3 - 5 times the rated current value at the lowest cost;

[0124] (4) The present invention realizes precise control of the transient current through the virtual admittance and the circular current limiter, without impact and without over-limiting;

[0125] (5) The present invention can realize the adaptive adjustment of the transient current phase, and adjusts the phase angle according to the current fault scenario to maximize the support for the recovery of the fault voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0126] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious:

[0127] Figure 1 is the structural block diagram of the control system for improving the transient current tolerance ability of the self-synchronous voltage source new energy unit;

[0128] Figure 2 is the schematic diagram of the self-synchronous voltage source control module;

[0129] Figure 3 is the schematic diagram of the junction temperature prediction module;

[0130] Figure 4 is the schematic diagram of the module for improving the transient current tolerance ability;

[0131] Figure 5 is the flow chart of the maximum transient current prediction;

[0132] Figure 6 is the schematic diagram of the precise control module of the transient current. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0133] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0134] Embodiment 1

[0135] The present invention provides a control method for improving the transient current capacity of a wind-solar power generation system, including:

[0136] Self-synchronous voltage source control step: performing voltage source control on the grid-side converter of the new energy unit;

[0137] Junction temperature prediction step: calculating the power device loss in real time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit, inputting the loss data to the heat flux correction link to update the loss data, and inputting the updated loss data to the thermal circuit model to calculate the current power device junction temperature;

[0138] Transient current boost control step: calculating the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and selecting according to the boundary values to predict the reduced loss value; or presetting the boundary values of the switching frequency, modulation voltage, and DC voltage, calculating the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit, combining the current transient current boost demand, optimizing the required optimal switching frequency, modulation voltage, and DC voltage adjustment values, and using these as command outputs for adjustment;

[0139] Current command calculation step: calculating the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information;

[0140] Transient current precise control step: controlling the transient current amplitude to follow the junction temperature and the command value output by the transient current boost control step in real time.

[0141] The self-synchronous voltage source control step includes:

[0142] Inertial synchronization control step: outputting the phase angle θ of the modulation voltage of the grid-side converter vsg , multiplying the deviation between the rated value u dcn of the DC voltage and the actual value u dc by a proportionality coefficient K dc , and then integrating it with the rated angular frequency ω0 to achieve the function of real-time mirroring the grid frequency change and autonomous synchronization of the DC voltage. The expression is:

[0143]

[0144] Port voltage control steps: including a reactive power controller, a damping enhancement controller, and a reference value U tn , generate the modulation voltage U of the grid-side converter of the new energy power generation unit t , realize the control of the reactive power output by the self-synchronous voltage source control unit, and the expression is:

[0145]

[0146] Among them, K QP and K QI are the coefficients of the PI regulator corresponding to reactive power, Q gef and Q g are the command and actual value of reactive power respectively, K D is the damping coefficient, and s is the corresponding differential operator;

[0147] Machine-side inertia transfer control steps: decouple the dq-axis electrical quantities, realize the power generation power control of the front-stage converter of the new energy power generation unit, and at the same time introduce an inertia transfer control link to realize inertia response without a frequency detection device, and the expression is:

[0148]

[0149] Among them, P MPPT is the maximum wind power tracking module, which is used to output the current power according to the optimal tip speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to active power; T m is the filtering time constant, which is used to filter out the high-frequency components contained in the DC voltage signal; P ref is the finally output power command, which is used as the input of the controller;

[0150] Vector control steps: decouple the dq-axis electrical quantities, realize the power generation power control of the front-stage converter of the new energy power generation unit, and at the same time generate the current commands I sdref and I sqref , and the expression is:

[0151]

[0152] Among them, P m is the active power actually output by the machine-side converter, K po and K io are the proportional and integral coefficients of the power controller respectively.

[0153] The junction temperature prediction steps include:

[0154] Loss calculation steps: sample the current output phase voltage amplitude U cx of the grid-side converter, the phase current amplitude I cx, DC voltage U dc , switching frequency f sw and junction temperature T jx , calculate the conduction loss P T,Dcon and switching loss P T,Dsw of the IGBT anti-parallel diode in the converter within one power frequency cycle, where the subscript x corresponds to the A, B, and C phase arms of the grid-side converter, and the calculation expressions for the conduction loss and switching loss are as follows:

[0155]

[0156] where, V x corresponds to the conduction voltage drop of the IGBT or the reverse conduction voltage drop of the diode; E x corresponds to the turn-on and turn-off energy of the IGBT or the reverse recovery energy of the diode; d x corresponds to the modulation degree of the IGBT or diode; U ref is the switching loss test reference voltage of the IGBT or diode; K sw is the calibration coefficient; T min and T max are the lower and upper limits of the junction temperature given in the data sheet;

[0157] Junction temperature calculation steps: Calculate the junction temperature T jx of the IGBT and its anti-parallel diode respectively, and the common case temperature T c , use the output of the loss calculation step as the input of the thermal model, and thus obtain the temperature difference ΔT jx between the junction and the case of the IGBT or diode, and the expression is:

[0158] ΔT jx = (P T,Dcon + P T,Dsw ) Z jh (s) (38)

[0159] where, Z jh (s) is the thermal impedance between the junction and the case of the IGBT or diode, s is the corresponding differential operator, and the expression is:

[0160]

[0161] where, τ i is the time constant of each stage i of the thermal impedance. There are 4 stages between the junction and the case, which are given by the device data sheet;

[0162] The temperature difference ΔT c between the case of the IGBT and diode and the radiator is obtained in the same form as formula (5), and the expression is:

[0163] ΔTc = ΔP loss Z ch (40)

[0164] Among them, Z ch is the thermal impedance between the IGBT case and the radiator; ΔP loss is the sum of the IGBT and diode losses;

[0165] When the radiator temperature is set to T h , according to formulas (6)-(8), the junction temperature calculation formula is obtained:

[0166] T jx = ΔT jx + ΔT c + T h (41).

[0167] The transient current boost control steps include:

[0168] Switching frequency adjustment step: Adjust the switching frequency f of the new energy unit converter sw to change the switching losses of the power devices, and their corresponding relationship is:

[0169] f sw = K1f swn (42)

[0170] Among them, f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient;

[0171] Global optimal modulation step: Implement discontinuous modulation to minimize the switching losses of the power devices within the entire power factor range. The switching frequency adjustment coefficient K2 is used to select whether to turn off or turn on the global optimal discontinuous modulation function, and the expression is:

[0172]

[0173] Among them, SVWPM is space vector modulation, and GDPWM is the global optimal modulation used in this step;

[0174] DC voltage adjustment step: Adjust the action threshold of the DC side Chopper circuit to adjust the switching losses of the power devices, and their corresponding relationship is:

[0175] U chop = K3f swn (44)

[0176] Among them, U chop is the voltage of the DC side Chopper circuit, and K3 is the switching frequency adjustment coefficient;

[0177] Maximum transient current prediction step: Set the adjustment coefficients K1, K2, and K3 for the switching frequency, modulation strategy, and DC voltage, and finally output the current command value I set ;

[0178] According to the currently allowed upper limit of the junction temperature and the loss value in real time, optimize the K1, K2, and K3 coefficients, and optimize and solve within the allowable action range of the switching frequency and DC voltage to obtain the maximum short-circuit current amplitude I that does not exceed the junction temperature limit set , and use I set as the input of the transient current precise control step

[0179] The transient current precise control step includes:

[0180] Virtual admittance step: Establish the relationship between the internal potential U tdq of the grid-side converter of the self-synchronous voltage source new energy unit and the output current command I refdq , and its relationship is expressed as:

[0181]

[0182] where U cdq is the dq-axis voltage on the filter capacitor at the output port of the self-synchronous voltage source new energy unit, L v and R v are the values of the virtual inductor and virtual resistor, and the reciprocal of the sum of the two is the virtual admittance;

[0183] Circular current limiting step: Under the condition of keeping the output power component of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, limit its transient current amplitude not to exceed the set value, and at the same time generate the final dq-axis current command value I mrefdq , and the expression is:

[0184]

[0185] If the current amplitude I t is less than the amplitude command I set output by the maximum transient current prediction step, then use the output I refdq of the virtual admittance link as the current command. If the current amplitude I t is greater than the amplitude command I set output by the maximum transient current prediction step, then scale down the dq-axis current command value in proportion according to I set / I t ;

[0186] Transient current precise control link: According to the current command output by the circular current limiting step, control the transient current to the command value, and at the same time add a non-linear virtual resistor to suppress the impact current during the transient moment, and the expression is:

[0187]

[0188] Among them, U std is the finally generated modulation voltage; K ip and K iI are the proportional and integral coefficients of the grid-side converter current controller respectively, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop on the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage, and s is the corresponding differential operator;

[0189] The expression of the virtual resistance is:

[0190]

[0191] Among them, K v is the resistance value adjustment coefficient of the virtual resistance. Under the same current I t , R v increases with the increase of K v . If I t exceeds I set , then the virtual resistance R v is put into use; if the peak value of I t has not exceeded the limit, then R v is not put into use.

[0192] Embodiment 2

[0193] The present invention also provides a transient current capacity improvement control system for a wind-solar power generation system. The transient current capacity improvement control system for the wind-solar power generation system can be realized by executing the process steps of the transient current capacity improvement control method for the wind-solar power generation system. That is, those skilled in the art can understand the transient current capacity improvement control method for the wind-solar power generation system as the preferred implementation manner of the transient current capacity improvement control system for the wind-solar power generation system.

[0194] The present invention provides a transient current capacity improvement control system for a wind-solar power generation system. The overall structural block diagram of this system is as Figure 1 shown, and it includes the following modules:

[0195] Self-synchronous voltage source control module: used to implement the voltage source control of the grid-side converter of the new energy unit, so that the unit can synchronize with the power grid independently without a phase-locked loop and has the ability to actively support the transient frequency and voltage.

[0196] Junction temperature prediction module: used to calculate the power device losses in real time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit, and at the same time input to the heat flux correction link to update the loss data, and input the updated loss data into the thermal circuit model to calculate the current junction temperature of the power device.

[0197] Transient current boost control module: Method 1: Calculate the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and select according to the boundary values to predict the reduced loss value.

[0198] Method 2: Preset the boundary values of the switching frequency, modulation voltage, and DC voltage, calculate the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit, consider the current transient current boost requirement, optimize the required optimal switching frequency, modulation voltage, and DC voltage adjustment values, and use them as command outputs for adjustment.

[0199] Current command calculation module: Calculate the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information.

[0200] Transient current precise control module: used to control the transient current amplitude to follow the junction temperature and the command value output by the transient current boost control module in real time, and at the same time ensure the dynamic performance and accuracy of the control.

[0201] Among them, the self-synchronous voltage source control module is as Figure 2 shown, including the following modules:

[0202] Inertial synchronization control module. This module is used to output the phase angle θ of the modulation voltage of the grid-side converter vsg , used to multiply the deviation between the rated value u dcn of the DC voltage and the actual value u dc by a proportional coefficient K dc and then accumulate it to the rated angular frequency ω n for integration, so as to realize the function of real-time mirroring the grid frequency change and autonomous synchronization of the DC voltage. Its principle can be expressed by formula (1):

[0203]

[0204] Port voltage control module. This module is used to generate the modulation voltage U t of the grid-side converter of the new energy power generation unit. It includes a reactive power controller, a damping enhancement controller, and a reference value U tn , and its principle can be expressed as formula (2), where K QP and K QI are the coefficients of the PI regulator corresponding to reactive power, Q gef and Q g are the command and actual values corresponding to reactive power, KD is the damping coefficient, and s is the corresponding differential operator;

[0205]

[0206] This module can control the reactive power output of the self - synchronous voltage source controlled unit, and at the same time enhance the damping of the system, making the unit more stable.

[0207] The machine - side inertia transfer control module. This module is used to achieve inertia response without a frequency detection device. Its principle is to add a variable related to the DC voltage, which can be expressed as formula (3):

[0208]

[0209] where P MPPT is the optimal power output by the maximum wind power tracking module, which is used to output the current power according to the optimal tip - speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to active power; T m is the filtering time constant, which is used to filter out the high - frequency components contained in the DC voltage signal; P ref is the finally output power command, which is used as the input of the controller.

[0210] The vector control module. This module is used to decouple the dq - axis electrical quantities, realize the power control of the front - stage converter of the new - energy power generation unit, and at the same time generate the dq - axis current commands I sdref and I sqref :

[0211]

[0212] where P m is the active power actually output by the machine - side converter, and K po and K io are the proportional and integral coefficients of the power controller respectively.

[0213] Among them, the junction - temperature prediction module is as shown in Figure 3 and includes the following modules:

[0214] The loss calculation module. This module is used to sample the amplitude of the current output phase voltage U cx , the amplitude of the phase current I cx , the DC voltage u dc and the switching frequency f sw , and the junction temperature T jx , and is used to calculate the conduction loss P T,Dcon of the IGBT anti - parallel diode in the converter within one power - frequency cycle and the switching loss P T,DswAmong them, the subscript x corresponds to the A, B, and C phase arms of the grid-side converter, and the calculation methods of conduction loss and switching loss can be expressed by formula (4):

[0215]

[0216] Among them, U cx is regarded as the conduction voltage drop of the IGBT or the reverse conduction voltage drop of the diode, and E x corresponds to the turn-on and turn-off energies of the IGBT or the reverse recovery energy of the diode, d x corresponds to the modulation degree of the IGBT or the diode, u ref is the reference DC voltage for the switching loss test of the IGBT or the diode, K sw is the switching loss calibration coefficient, and T min and T max are the lower and upper limits of the junction temperature given in the data sheet.

[0217] Junction temperature calculation module. This module is used to calculate the junction temperatures T jx of the IGBT and its anti-parallel diode respectively, as well as the common module case temperature T c . Taking the output of the loss calculation module as the input of the thermal circuit model, the temperature difference ΔT jx between the junction and the case of the IGBT or the diode due to the loss is obtained:

[0218] ΔT jx =(P T,Dcon +P T,Dsw )Z jh (s) (54)

[0219] Among them, Z jh (s) is the thermal impedance between the junction and the case of the IGBT or the diode:

[0220]

[0221] Among them, τ i is the time constant of each stage of the thermal impedance. There are 4 stages between the junction and the case, which are given by the device data sheet. R i corresponds to the thermal resistance value in the thermal circuit of the power device.

[0222] The temperature difference ΔT c between the case of the IGBT and the diode and the radiator is obtained in the same form as formula (5):

[0223] ΔT c =ΔP loss Z ch (56)

[0224] Among them, Z chis the thermal impedance between the IGBT case and the radiator, ΔP loss is the sum of the IGBT and diode losses.

[0225] When the radiator temperature is set to T h , according to formulas (6)-(8), the junction temperature calculation formula can be obtained:

[0226] T j,x = ΔT j,x + ΔT c + T h (57)

[0227] Among them, the transient current tolerance improvement module is as Figure 4 shown and includes the following modules:

[0228] Switching frequency adjustment module. This module is used to adjust the switching frequency f sw of the converter of the new energy unit to change the switching losses of the power devices, and their corresponding relationship can be expressed as:

[0229] f sw = K1f swn (58)

[0230] where f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient.

[0231] Global optimal modulation strategy module. This module is used to implement discontinuous modulation that minimizes the switching losses of power devices within the entire power factor range. K2 is used to select whether to turn off or turn on the global optimal discontinuous modulation function between "0" and "1".

[0232]

[0233] where SVWPM is space vector modulation and GDPWM is the global optimal modulation used in this module.

[0234] DC voltage adjustment module. This module is used to adjust the action threshold of the DC-side Chopper circuit to adjust the switching losses of the power devices, and their corresponding relationship can be expressed as:

[0235] U chop = K3f swn (60)

[0236] Maximum transient current prediction module. This module is used to set the adjustment coefficients of the switching frequency - modulation strategy - DC voltage, namely K1, K2, K3, and finally output the current command value I set , as Figure 5 shown.

[0237] Optimize the K1-K3 coefficients in real time according to the current allowable upper limit of the junction temperature and the loss value, and optimize and solve for the maximum short-circuit current amplitude I that can keep the junction temperature within the limit within the allowable operating range of the switching frequency and the DC voltage. set I set As the input of the accurate transient current control link.

[0238] Among them, the accurate transient current control module is as Figure 6 shown, including the following modules:

[0239] Virtual admittance module. This module is used to establish the internal potential U of the grid-side converter of the self-synchronous voltage source new energy unit tdq and the output current command I refdq The relationship between them can be expressed as:

[0240]

[0241] Among them, U cdq is the dq-axis voltage on the filter capacitor at the output port of the self-synchronous voltage source new energy unit, L v and R v are the values of the virtual inductor and the virtual resistor, and the reciprocal of the sum of the two is the virtual admittance.

[0242] Circular current limiting module. This module is used to limit the transient current amplitude not to exceed the set value while keeping the output power component of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, and at the same time generate the final dq-axis current command value I mrefdq . Its principle can be expressed by formula (14):

[0243]

[0244] That is, when the current amplitude I t is less than the amplitude command I set output by the maximum transient current prediction module, then use the output I refdq of the virtual admittance link as the current command. When the current amplitude I t is greater than the amplitude command I set output by the maximum transient current prediction module, then scale down the dq-axis current command value in proportion to I set / I t .

[0245] Accurate transient current control link. This link is used to control the transient current to the command value according to the current command output by the circular current limiting module, and at the same time add a non-linear virtual resistor to suppress the impact current during the transient moment. Its principle can be expressed by formula (15):

[0246]

[0247] Among them, U std is the finally generated modulation voltage, K ip and K iI are respectively the proportional and integral coefficients of the grid-side converter current controller, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop in the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage.

[0248] Meanwhile, the expression of the virtual resistance R v is as follows:

[0249]

[0250] Among them, K v is the resistance value adjustment coefficient of the virtual resistance. Under the same current I t , R v increases with the increase of K v . That is, when I t exceeds I set , the virtual resistance R v is put into use. If the peak value of I t has not exceeded the limit, then R v is not put into use. .

[0251] Those skilled in the art know that in addition to implementing the systems, devices and their various modules provided by the present invention in the form of pure computer-readable program codes, the method steps can be logically programmed to enable the systems, devices and their various modules provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. to achieve the same program. Therefore, the systems, devices and their various modules provided by the present invention can be regarded as a kind of hardware component, and the modules included therein for implementing various programs can also be regarded as the structures within the hardware component; the modules for implementing various functions can also be regarded as either software programs for implementing the methods or the structures within the hardware component.

[0252] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A transient current capacity improvement control system for a wind-solar power generation system, characterized in that, Including: Self - synchronous voltage source control module: Conduct voltage source control on the grid - side converter of the new energy unit; Junction temperature prediction module: Calculate the power device losses in real - time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit. At the same time, input the heat - flow correction link to update the loss data, and input the updated loss data into the thermal circuit model to calculate the current junction temperature of the power device; Transient current boost control module: Calculate the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and select according to the boundary values to predict the reduced loss value; Or preset the boundary values of the switching frequency, modulation voltage, and DC voltage, calculate the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit, combine the current transient current boost demand, optimize the required optimal adjustment values of the switching frequency, modulation voltage, and DC voltage, and use them as command outputs for adjustment; Current command calculation module: Calculate the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information; Transient current precise control module: Control the transient current amplitude to follow the command value output by the junction temperature and the transient current boost control module in real - time.

2. The transient current capacity improvement control system of the wind-solar power generation system according to claim 1, wherein The self - synchronous voltage source control module includes: Inertial synchronization control module: Output the phase angle θ of the modulation voltage of the grid-side converter vsg , multiply the deviation between the rated value u dcn of the DC voltage and the actual value u dc by a proportionality coefficient K dc , and then accumulate it onto the rated angular frequency ω0 for integration, so as to realize the function of the DC voltage mirroring the grid frequency change in real time and autonomous synchronization. The expression is as follows: Port voltage control module: includes a reactive power controller, a damping enhancement controller, and a reference value U tn , generating the modulation voltage U of the grid-side converter of the new energy power generation unit t , realizing the control of the reactive power output of the self-synchronous voltage source controlled unit. The expression is: Among them, K QP and K QI are the coefficients of the PI regulator corresponding to the reactive power, Q gef and Q g are the command and the actual value corresponding to the reactive power, K D is the damping coefficient, and s is the corresponding differential operator; Machine - side inertia transfer control module: Decouple the dq - axis electrical quantities, realize the power generation power control of the front - stage converter of the new energy power generation unit, and at the same time introduce the inertia transfer control link to realize the inertia response without a frequency detection device. The expression is: Among them, P MPPT is the maximum wind power tracking module, which is used to output the current power according to the optimal tip speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to active power; T m is the filtering time constant, which is used to filter out the high-frequency components contained in the DC voltage signal; P ref is the finally output power command and serves as the input of the controller; Vector control module: decouples the electrical quantities on the dq axes, realizes the power control of the front-stage converter of the new energy power generation unit, and simultaneously generates the current commands I sdref and I sqref for the dq axes of the machine-side converter. The expression is as follows: Among them, P m is the active power actually output by the machine-side converter, and K po and K io are the proportional and integral coefficients of the power controller respectively.

3. The transient current capacity improvement control system of the wind-solar power generation system according to claim 1, wherein The junction temperature prediction module includes: Loss calculation module: sample the current output phase voltage amplitude U of the grid-side converter cx , the phase current amplitude I cx , the DC voltage U dc , the switching frequency f sw and the junction temperature T jx , and calculate the conduction loss P of the anti-parallel diode of the IGBT in the converter within one power frequency cycle T,Dcon and the switching loss P T,Dsw , where the subscript x corresponds to the A, B, and C phase bridges of the grid-side converter, and the calculation expressions for the conduction loss and the switching loss are as follows: Among them, V x corresponds to the on-state voltage drop of the IGBT or the reverse on-state voltage drop of the diode; E x corresponds to the turn-on and turn-off energies of the IGBT or the reverse recovery energy of the diode; d x corresponds to the modulation degree of the IGBT or the diode; U ref is the switching loss test reference voltage of the IGBT or the diode; K sw is the calibration coefficient; T min and T max are the lower and upper limits of the junction temperature given in the data sheet; Junction temperature calculation module: calculate the junction temperatures T of the IGBT and its anti-parallel diode respectively jx and the common module case temperature T c , take the output of the loss calculation module as the input of the thermal circuit model, and thus obtain the temperature difference ΔT between the junction and the case of the IGBT or diode due to the loss jx , and the expression is: ΔT jx =(P T,Dcon +P T,Dsw )Z jh (s) (70) Among them, Z jh (s) is the thermal impedance between the junction and the case of the IGBT or diode, s is the corresponding differential operator, and the expression is: where τ i is the time constant of each stage i of the thermal impedance. There are a total of 4 stages from the junction to the case, which are given in the device data sheet; The temperature difference ΔT between the case of the IGBT and the diode and the heat sink c Obtained in the same form as formula (5), the expression is: ΔT c = ΔP loss Z ch (72) Among them, Z ch is the thermal impedance between the IGBT case and the heat sink; ΔP loss is the sum of the IGBT and diode losses; When the radiator temperature is set to T h , the junction temperature calculation formula is obtained according to formulas (6)-(8): T jx = ΔT jx + ΔT c + T h (73).

4. The transient current capacity improvement control system of the wind-solar power generation system according to claim 1, characterized in that, The transient current boost control module includes: Switching frequency adjustment module: Adjust the switching frequency f of the converter of the new energy unit sw to change the switching losses of the power devices, and their corresponding relationship is as follows: f sw = K1f swn (74) Among them, f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient; Global optimal modulation strategy module: Realize the discontinuous modulation that minimizes the switching losses of power devices within the entire power factor range. The switching frequency adjustment coefficient K2 is used to select whether to turn off or turn on the global optimal discontinuous modulation function between 0 and 1. The expression is: Where, SVWPM is space vector modulation, and GDPWM is the global optimal modulation used in this module; DC voltage regulation module: Adjust the action threshold of the DC - side Chopper circuit to adjust the switching losses of power devices. The corresponding relationship is: U chop = K3f swn (76) Among them, U chop is the voltage of the DC-side Chopper circuit, and K3 is the switching frequency adjustment coefficient; Maximum transient current prediction module: Set the adjustment coefficients K1, K2, and K3 for the switching frequency, modulation strategy, and DC voltage, and finally output the current command value I set ; Optimize the K1, K2, and K3 coefficients in real time according to the currently allowed upper limit of the junction temperature and the loss value, and optimize and solve for the maximum short-circuit current amplitude I that does not exceed the junction temperature limit within the allowable operating range of the switching frequency and the DC voltage. set And use I set as the input of the transient current precise control module.

5. The transient current capacity improvement control system of the wind-solar power generation system according to claim 1, characterized in that The transient current precise control module includes: Virtual admittance module: Establish the internal electromotive force U of the grid-side converter of the self-synchronized voltage source new energy unit tdq and the output current command I refdq The relationship between them is expressed as: Among them, U cdq is the dq-axis voltage on the filter capacitor at the output port of the self-synchronous voltage source new energy unit, L v and R v are the values of the virtual inductor and the virtual resistor, and the reciprocal of the sum of the two is the virtual admittance; Circular current limiting module: Under the condition of keeping the output power components of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, it limits the transient current amplitude not to exceed the set value, and at the same time generates the final dq-axis current command value I mrefdq , and the expression is: If the current amplitude I t is less than the amplitude command I output by the maximum transient current prediction module set , then use the output I of the virtual admittance link refdq as the current command. If the current amplitude I t is greater than the amplitude command I output by the maximum transient current prediction module set , then scale down the dq-axis current command values in proportion to I set / I t ; Transient current precise control link: According to the current command output by the circular current limiting module, control the transient current to the command value, and at the same time add a non - linear virtual resistor to suppress the impact current during the transient moment. The expression is: Among them, U std is the finally generated modulation voltage; K ip and K iI are the proportional and integral coefficients of the grid-side converter current controller respectively, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop in the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage, and s is the corresponding differential operator; The expression of the virtual resistor is: Among them, K v is the resistance adjustment coefficient of the virtual resistor. Under the same current I t , R v increases with the increase of K v . If I t exceeds I set , then the virtual resistor R v is put into use; if the peak value of I t has not exceeded the limit, then R v is not put into use.

6. A transient current capacity improvement control method for a wind-solar power generation system, characterized in that, Including: Self - synchronous voltage source control step: Conduct voltage source control on the grid - side converter of the new energy unit; Junction temperature prediction step: Calculate the power device losses in real - time according to the current switching frequency, DC voltage, AC voltage, and power factor of the new energy unit. At the same time, input the heat - flow correction link to update the loss data, and input the updated loss data into the thermal circuit model to calculate the current junction temperature of the power device; Transient current boost control step: Calculate the value boundaries of the current switching frequency, modulation voltage, and DC voltage, and select according to the boundary values to predict the reduced loss value; Or the boundary values of the preset switching frequency, modulation voltage, and DC voltage. Calculate the distribution of the junction temperature participation factor according to the current operating state of the new energy power generation unit. Combine the current transient current increase requirement to optimize the required optimal switching frequency, modulation voltage, and DC voltage adjustment values, and use these as command outputs for adjustment; Current command calculation steps: Calculate the corresponding maximum transient current command value according to the current junction temperature and the reduced loss information; Transient current precise control steps: Control the transient current amplitude to follow the command value output by the junction temperature and the transient current increase control steps in real time.

7. The transient current capacity improvement control method of the wind-solar power generation system according to claim 6, wherein The self-synchronous voltage source control steps include: Inertial synchronization control steps: output the phase angle θ of the grid-side converter modulation voltage vsg , multiply the deviation between the rated value u dcn of the DC voltage and the actual value u dc by a proportionality coefficient K dc and then accumulate it onto the rated angular frequency ω0 for integration, so as to achieve the function of the DC voltage mirroring the grid frequency change in real time and autonomous synchronization. The expression is as follows: Port voltage control steps: including a reactive power controller, a damping enhancement controller, and a reference value U tn , generating a modulation voltage U of the grid-side converter of the new energy power generation unit t , realizing the control of the reactive power output of the self-synchronous voltage source controlled unit. The expression is: Among them, K QP The coefficient of the PI regulator corresponding to the reactive power of K QI Q is gef The instruction and the actual value corresponding to the reactive power of Q g K is D the damping coefficient, s is the corresponding differential operator; Machine-side inertia transfer control steps: Decouple the dq-axis electrical quantities to achieve the power generation power control of the front-stage converter of the new energy power generation unit. At the same time, introduce an inertia transfer control link to achieve inertia response without a frequency detection device. The expression is: Among them, P MPPT is the maximum wind power tracking module, which is used to output the current power according to the optimal tip speed ratio; K c is the inertia transfer coefficient, which is used to control the magnitude of the unit's response to active power; T m is the filtering time constant, which is used to filter out the high-frequency components contained in the DC voltage signal; P ref is the finally output power command and serves as the input of the controller. Vector control steps: decouple the electrical quantities on the dq axes to achieve the power control of the front-stage converter of the new energy power generation unit, and at the same time generate the current commands I sdref and I sqref , and the expression is: Among them, P m is the active power actually output by the machine-side converter, and K po and K io are the proportional and integral coefficients of the power controller, respectively.

8. The transient current capacity improvement control method for the wind-solar power generation system according to claim 6, wherein The junction temperature prediction steps include: Loss calculation steps: Sample the current output phase voltage amplitude U of the grid-side converter cx , the phase current amplitude I cx , the DC voltage U dc , the switching frequency f sw and the junction temperature T jx , and calculate the conduction loss P of the IGBT anti-parallel diode in the converter within one power frequency cycle T,Dcon and the switching loss P T,Dsw , where the subscript x corresponds to the A, B, and C phase bridges of the grid-side converter, and the calculation expressions for the conduction loss and the switching loss are as follows: Among them, V x corresponds to the on-state voltage drop of the IGBT or the reverse on-state voltage drop of the diode; E x corresponds to the turn-on and turn-off energies of the IGBT or the reverse recovery energy of the diode; d x corresponds to the modulation degree of the IGBT or the diode; U ref is the switching loss test reference voltage of the IGBT or the diode; K sw is the calibration coefficient; T min and T max are the lower and upper limits of the junction temperature given in the data sheet; Junction temperature calculation steps: Calculate the junction temperatures T of the IGBT and its anti-parallel diode respectively jx and the common case temperature T c , take the output from the loss calculation step as the input of the thermal circuit model, and thus obtain the temperature difference ΔT between the junction and the case of the IGBT or diode due to the loss jx , and the expression is: ΔT jx =(P T,Dcon +P T,Dsw )Z jh (s) (86) Among them, Z jh (s) is the thermal impedance between the junction and the case of the IGBT or diode, s is the corresponding differential operator, and the expression is: where τ i is the time constant of each stage i of the thermal impedance. There are a total of 4 stages from the junction to the case, which are given in the device data sheet; The temperature difference ΔT between the case of the IGBT and the diode and the heat sink c Obtained in the same form as formula (5), the expression is: ΔT c = ΔP loss Z ch (88) Among them, Z ch is the thermal impedance between the IGBT case and the heat sink; ΔP loss is the sum of the IGBT and diode losses; When the radiator temperature is set to T h , the junction temperature calculation formula can be obtained according to formulas (6)-(8): T jx = ΔT jx + ΔT c + T h (89).

9. The transient current capacity improvement control method of the wind-solar power generation system according to claim 6, characterized in that The transient current increase control steps include: Switching frequency adjustment steps: Adjust the switching frequency f of the converter of the new energy unit sw to change the switching losses of the power devices, and their corresponding relationship is as follows: f sw = K1f swn (90) where f swn is the rated switching frequency corresponding to the converter, and K1 is the switching frequency adjustment coefficient; Global optimal modulation steps: Implement discontinuous modulation that minimizes the switching loss of power devices within the entire power factor range. The switching frequency adjustment coefficient K2 is used to select whether to turn off or turn on the global optimal discontinuous modulation function between 0 and 1. The expression is: Among them, SVWPM is space vector modulation, and GDPWM is the global optimal modulation used in this step; DC voltage regulation steps: Adjust the action threshold of the DC-side Chopper circuit to adjust the switching loss of the power device. The corresponding relationship is: U chop = K3f swn (92) Among them, U chop is the voltage of the DC-side Chopper circuit, and K3 is the switching frequency adjustment coefficient; Maximum transient current prediction step: Set the adjustment coefficients K1, K2, and K3 for the switching frequency, modulation strategy, and DC voltage, and finally output the current command value I set ; Optimize the K1, K2, and K3 coefficients in real time according to the currently allowed upper limit of the junction temperature and the loss value, and optimize and solve for the maximum short-circuit current amplitude I that does not exceed the junction temperature limit within the allowable operating range of the switching frequency and the DC voltage. set , and use I set as the input for the transient current precise control step.

10. The transient current capacity improvement control method for the wind-solar power generation system according to claim 6, characterized in that, The transient current precise control steps include: Virtual admittance step: Establish the internal potential U of the grid-side converter of the self-synchronous voltage source new energy unit tdq and the output current command I refdq The relationship between them is expressed as: Among them, U cdq is the dq-axis voltage on the filtering capacitor at the output port of the self-synchronous voltage source new energy unit, L v and R v are the values of the virtual inductor and the virtual resistor, and the reciprocal of the sum of the two is the virtual admittance; Circular current limiting step: Under the condition of keeping the output power component of the grid-side converter of the self-synchronous voltage source new energy unit unchanged, limit its transient current amplitude not to exceed the set value, and at the same time generate the final dq-axis current command value I mrefdq , and the expression is: If the current amplitude I t is less than the amplitude command I output by the maximum transient current prediction step set , then use the output I of the virtual admittance link refdq as the current command. If the current amplitude I t is greater than the amplitude command I output by the maximum transient current prediction step set , then scale down the dq-axis current command values in proportion to I set / I t ; Transient current precise control link: According to the current command output by the circular current limiting step, control the transient current to the command value, and at the same time add a non-linear virtual resistor to suppress the impact current during the transient moment. The expression is: Among them, U std is the finally generated modulation voltage; K ip and K iI are the proportional and integral coefficients of the grid-side converter current controller respectively, I tdq is the actual value of the transient current output by the grid-side converter, ΔU ωdq is the dq-axis current decoupling term, ΔU Rvdq is the virtual resistance voltage drop in the dq-axis, U cdq is the dq-axis component of the actual grid connection point voltage, and s is the corresponding differential operator; The expression of the virtual resistor is: Among them, K v is the resistance adjustment coefficient of the virtual resistor. Under the same current I t , R v increases with the increase of K v . If I t exceeds I set , then the virtual resistor R v is put into use; if I t has not exceeded the peak value, then R v is not put into use.

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