Method and system for improving transient overcurrent capability of grid-type high-voltage direct-mounted energy storage system

Abstract

The present invention provides a method and system for improving the transient overcurrent capability of a grid-type high-voltage direct-mounted energy storage system, including: a high-voltage direct-mounted battery energy storage system, a grid-type control module, a junction temperature estimation module, a dynamic current limiting module based on a maximum junction temperature closed loop, a current inner loop control module, and a junction temperature optimization strategy execution module; the actual temperature of the reference point is collected, and a signal is formed with the aforementioned modules, and transmitted to an actuator through a transmission system to achieve transient overcurrent tolerance; signal transmission is performed between the dynamic current limiting module based on the maximum junction temperature closed loop and the junction temperature estimation module, signal transmission is performed between the current inner loop control module and the dynamic current limiting module based on the maximum junction temperature closed loop, and signal transmission is performed between the junction temperature optimization strategy execution module and the current inner loop control module. The present invention realizes the rapid response of the system to high and low voltage faults and the precise and limited utilization control of transient currents through the transmission of control signals between modules, thereby improving the transient current tolerance capability.

Description

Technical Field

[0001] The present invention relates to the field of electrical automation equipment technology, and in particular to a technology and system for improving the transient overcurrent capability of a grid-forming high-voltage direct-mounted energy storage system, and in particular to a transient current limiting utilization control strategy for a grid-forming high-voltage direct-mounted battery energy storage system and a transient current improving method for a high-voltage direct-mounted battery energy storage system. Background Art

[0002] The grid-connected high-voltage direct-mounted battery energy storage system is benchmarked against the grid-connected technical parameters of synchronous generators, with autonomous inertia response and primary frequency regulation capabilities, and can provide transient current support in the event of a grid failure; it has the ability to conduct stable grid-connected operations with load and islanding; it can independently establish voltage, has a black start function, can start from zero with the main transformer and line, and supply power to the outside; it is reflected in the voltage source characteristics, which can reach or approach the electrical characteristics of a synchronous generator.

[0003] Articles 3.6 and 3.7 of GB26860-2011 Electric Power Safety Work Regulations (Electrical Parts of Power Plants and Substations) define high and low voltage. Low voltage: voltage levels of 1000V and below in AC systems used for power distribution; high voltage: (1) usually refers to voltage levels exceeding low voltage. (2) Under specific circumstances, it refers to the voltage level for power transmission in the power system. It can be seen that the dividing line between high and low voltage electrical appliances is 1000 volts AC voltage. AC voltages above 1000 volts are called high voltage, while those below 1000 volts are called low voltage. In some cases, 35 kilovolts and below are called medium voltage.

[0004] The black start function refers to the process of starting the power system or microgrid without the help of the external network after the power system or microgrid stops operating due to a fault. The power supply or micro source with self-starting capability in the system is started, and the power supply or micro source without self-starting capability is gradually driven, and finally the recovery process of the entire system or microgrid is realized. The realization of black start depends on the power supply or micro source with self-starting capability in the system. These power supplies or micro sources can be started first when the system is completely black, providing initial power support for system recovery.

[0005] In the field of automation control, wire transmission signals can realize the transmission of control signals. Control signals can be transmitted in wires and controlled through corresponding interfaces, thereby realizing the control of equipment, robots, etc. The principle of wire transmission signals is to use the propagation properties of electrical signals in conductors. Electrical signals can be transmitted in conductors, and can also be converted through specific interfaces when transmitted between different conductors.

[0006] The high-voltage direct-mounted battery energy storage system has the ability to operate in four quadrants for active power and reactive power, while the traditional synchronous machine has only two-quadrant operation capabilities. Compared with the traditional synchronous machine, the performance advantages of the four-quadrant grid-type high-voltage direct-mounted battery energy storage system are mainly manifested in: ① It can absorb and emit active power at full capacity. Traditional synchronous machines cannot absorb active power, and the power direction is single; in addition, when participating in a frequency regulation, the active residual capacity of the traditional synchronous machine is adjusted according to the speed regulator's adjustment rate, and cannot be fully adjusted when the frequency drops slightly, while the grid-type high-voltage direct-mounted battery energy storage system does not have this problem and can be fully adjusted; ② It can emit and absorb reactive power at equal capacity. When the traditional synchronous machine absorbs reactive power, it is called phase-leading operation, and its amount is limited by the phase-leading depth, generally about 20% of the total capacity, while the grid-type high-voltage direct-mounted battery energy storage system has no such restrictions; ③ The throughput response speed of active and reactive power is faster than that of traditional synchronous machines. Whether it is the active throughput response speed or the reactive throughput response speed, it is generally within the s level, which is one order of magnitude faster than the traditional synchronous machine.

[0007] Restricted by the thermal stress of power devices, the grid-connected high-voltage direct-mounted battery energy storage system has limited transient current tolerance and cannot further support the transient voltage of the power grid. It is necessary to study the electro-thermal transient modeling method of the power devices of the high-voltage direct-mounted energy storage converter and the mechanism analysis of the limited transient current capacity of the converter output. From the perspective of improved PWM modulation of the converter and optimized control of the junction temperature of the power device, the theoretical proposition of "how should the grid-connected converter be controlled to tolerate larger transient currents" is answered. Under different transient current amplitudes and phase conditions, it is necessary to analyze and compare the temperature rise characteristics of power devices under different modulation modes, with the goal of significantly reducing the switching loss and conduction loss of power devices and significantly reducing the harmonic content of the grid-connected current at low switching frequencies. The minimum loss PWM modulation strategy of the high-voltage direct-mounted electrochemical static synchronous machine, the adaptive adjustment method of the switching frequency under transient faults, and the optimization control method of the grid-connected current harmonics at low switching frequencies are studied. The active thermal control modulation strategy and control method of the grid-connected high-voltage direct-mounted energy storage converter with transient current output capability are proposed and formed.

[0008] In the prior art, the following converter methods have been proposed:

[0009] The invention patent with the publication number CN117639463A provides a DPWM modulation method for improving the short-circuit current capability of the ANPC topology. The DPWM modulation method for improving the short-circuit current capability of the ANPC topology is disclosed. In view of the problem that the junction temperature distribution of the device is unbalanced when the converter provides short-circuit current to the power grid when the converter has a voltage drop fault in the power grid, the junction temperature distribution of the device under three types of commutation modes when the converter provides short-circuit current is calculated, and the commutation mode with the lowest junction temperature of the "hottest" device is selected as the basic commutation mode. This method improves the short-circuit current capability of the ANPC topology under the voltage drop of the power grid by balancing the junction temperature of the device, and does not further improve the transient current output capability of the converter from the perspective of maximizing the utilization of the junction temperature.

[0010] The invention patent with publication number CN115149573A discloses a system and method for improving the short-circuit current tolerance of a self-synchronous voltage source wind turbine, including: a machine-side converter control module, a grid-side converter control module, a short-circuit current improvement control module, and a fault logic and unloading circuit control module. The invention realizes the real-time calculation and comparison of the junction temperature and loss of the power device of the self-synchronous voltage source wind turbine, and changes the switching frequency in real time according to the temperature and loss information, and selects the modulation strategy with the minimum loss to reduce the heating of the power device under large short-circuit current. However, this patent is only applicable to wind power converters, and the topological structure of wind power converters is simple and is not suitable for high-voltage direct-hanging topology. The modular characteristics of high-voltage direct-hanging battery energy storage systems make the transient current tolerance of the system determined by the weakest module of the converter, and the junction temperature information of each sub-module needs to be extracted and uniformly controlled. Therefore, the improvement of the short-circuit current tolerance of high-voltage direct-hanging battery energy storage systems urgently needs further research. Summary of the invention

[0011] In view of the defects in the prior art that the maximum transient current and grid voltage support cannot be provided during grid faults, and the transient current tolerance improvement capability of various loss reduction methods cannot be evaluated, the present invention provides a method and system for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system.

[0012] According to a method and system for improving the transient overcurrent capability of a grid-type high-voltage direct-mounted energy storage system provided by the present invention, the scheme is as follows:

[0013] In a first aspect, a system for improving transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system is provided, the system comprising:

[0014] High-voltage direct-mounted battery energy storage system, main controller, sub-controller, grid-type control module, junction temperature estimation module, dynamic current limiting module based on maximum junction temperature closed loop, current inner loop control module, junction temperature optimization strategy execution module; collect the actual temperature of the reference point, form a signal with the above modules, and transmit it to the actuator through the transmission system to achieve transient overcurrent tolerance;

[0015] The network control module, the dynamic current limiting module based on the maximum junction temperature closed loop, the current inner loop control module, and the junction temperature optimization strategy execution module run in the main controller, and the junction temperature estimation module runs in the sub-controller;

[0016] The high-voltage direct-mounted battery energy storage system distributes the battery modules to the DC bus of each H-bridge circuit to form energy storage sub-modules. The energy storage sub-modules are cascaded on the AC side and then connected to the medium and high voltage power grid in a conductive state through a filter inductor.

[0017] The grid-forming control module calculates and outputs the power angle and internal potential amplitude of the high-voltage direct-mounted battery energy storage system, and calculates the output current reference value through the generated power angle and internal potential amplitude;

[0018] The junction temperature estimation module is implemented in the sub-controller of each energy storage sub-module, estimates the junction temperature of the power device of each sub-module by collecting the actual temperature of the reference point, and transmits the extracted junction temperature data to the main controller;

[0019] The dynamic current limiting module based on the maximum junction temperature closed loop receives the junction temperature data of all sub-controllers, performs closed-loop control on the junction temperature of the energy storage sub-module with the highest temperature, outputs the current limit value, and then limits the current reference value through the current limiter, and outputs the given value of the current inner loop control module;

[0020] The current inner loop control module controls the grid-connected point current to follow the given value, implements closed-loop control of the current inner loop, and outputs a modulated voltage waveform;

[0021] The junction temperature optimization strategy execution module converts the modulated voltage waveform into a pulse width modulation signal, executes the junction temperature management strategy, and improves the transient overcurrent tolerance capability of the high-voltage direct-mounted battery energy storage system;

[0022] Signal transmission is performed between the dynamic current limiting module based on the maximum junction temperature closed loop and the junction temperature estimation module, signal transmission is performed between the current inner loop control module and the dynamic current limiting module based on the maximum junction temperature closed loop, and signal transmission is performed between the junction temperature optimization strategy execution module and the current inner loop control module.

[0023] Preferably, the networking control module includes:

[0024] Active power-frequency characteristic control module outputs the power angle of the system through the primary frequency modulation link, virtual inertia link and damping control link;

[0025] The reactive power-voltage characteristic control module outputs the internal potential amplitude through the reactive voltage droop link and the internal potential adjustment link;

[0026] A virtual admittance control module converts the power angle and internal potential amplitude into an output current reference value instruction by simulating line impedance characteristics;

[0027] The power angle and the internal potential amplitude are used to calculate the output current reference value through a virtual admittance control module.

[0028] Preferably, the junction temperature estimation module collects the actual temperature of the reference point to extract junction temperature data, and transmits the data to the junction temperature optimization strategy execution module through a signal to execute junction temperature management.

[0029] Preferably, the junction temperature estimation module estimates the junction temperature of each submodule power device according to the junction temperature extraction technology, and extracts the junction temperature data;

[0030] The junction temperature extraction technology includes a junction temperature estimation algorithm and a loss estimation algorithm. The loss generated by the device is calculated according to the currently estimated junction temperature, and then a new junction temperature is re-estimated according to the calculated loss. The junction temperature is accurately estimated by iterating until the junction temperature error between the previous and next two times is within a preset range.

[0031] The junction temperature estimation algorithm includes a thermal network model, a numerical model or an analytical model;

[0032] The loss estimation algorithm includes loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet or loss calculation based on mathematical model.

[0033] Preferably, the dynamic current limiting module based on the maximum junction temperature closed loop performs closed loop control by collecting the junction temperature information of all sub-controller power devices, and the output current limit value is

[0034]

[0035] in, I max is the output current limit value, K P1 is the proportional parameter of the junction temperature closed-loop PI controller, K I1 is the integral parameter of the junction temperature closed-loop PI controller, s is the differential operator, T jmax * is the maximum operating junction temperature, T jmax is the maximum junction temperature of all sub-controller power devices; is the rated current of the switching device;

[0036] The current reference value is limited by the current limiter, and the given value of the output current inner loop control module is

[0037]

[0038] in, i dq,cmd is the given value of the dq axis current inner loop control module, i dq,ref is the dq axis current reference value.

[0039] Preferably, the junction temperature optimization strategy execution module converts the modulation voltage into a pulse width modulation signal while executing various junction temperature management strategies;

[0040] The junction temperature management strategy includes adjusting the switching frequency, changing the modulation strategy, adjusting the DC bus voltage, designing an intelligent gate drive, dynamically distributing power, and adjusting the power factor angle and reactive power.

[0041] In a second aspect, a method for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system is provided, the method comprising:

[0042] Step S1: Establish the loss model and circuit model of the submodule, and design the junction temperature extraction algorithm;

[0043] Step S2: construct two major indicators: loss balance between submodules and loss reduction of the energy storage submodule with the highest temperature, and evaluate the contribution rate and feasibility of each loss reduction method to the improvement of transient overcurrent tolerance capability;

[0044] Step S3: quantitatively analyzing various factors affecting the junction temperature, comprehensively considering the adjustment capability, applicable working conditions and mutual influencing factors of each control method, and coordinating various junction temperature management methods;

[0045] Step S4: Further evaluate the junction temperature control and efficiency optimization methods for reducing converter losses, and achieve junction temperature control and optimization by means of dynamic current limiting.

[0046] Preferably, the step S1 comprises:

[0047] Step S1.1: Establish loss models for switch components and batteries in the submodule, including loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet, and loss calculation based on mathematical model;

[0048] Step S1.2: Establishing a circuit model of the switch components and the battery in the submodule, and obtaining the loss value of the switch components and the battery at the current temperature by analyzing the heat generation behavior of each component;

[0049] Step S1.3: Design a temperature extraction algorithm for the switch components and the battery in the submodule, and obtain the temperature update values ​​of the switch components and the battery by constructing a thermal network model, a numerical model or an analytical model;

[0050] Step S1.4: Iterate to step S1.2 through temperature, calculate the loss value of the switch components and the battery under the temperature update value, and continue to execute step S1.3;

[0051] Step S1.5: Iterate until the junction temperature errors between the previous and subsequent times are within a set range, and output an accurate estimate of the junction temperature.

[0052] Preferably, the junction temperature management method in step S3 includes:

[0053] Decompose the modulation voltage vector so that the submodules can operate at a power factor angle that can withstand the maximum short-circuit current without affecting the external power factor of the system;

[0054] Reduce the switching frequency of the switch submodule to further reduce the switching loss of the submodule;

[0055] Adopting a gate drive strategy that can reduce device switching and conduction losses, freeing up device margin without reducing lifespan.

[0056] In a third aspect, a computer-readable storage medium storing a computer program is provided, and when the computer program is executed by a processor, the steps of the method for improving the transient overcurrent capability of the grid-connected high-voltage direct-mounted energy storage system are implemented.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. The present invention controls the transient current of the system through the transmission of control signals between modules, realizes the autonomous and rapid response of the grid-type high-voltage direct-mounted battery energy storage system to high and low voltage faults and the precise and limited utilization control of transient current, and improves the transient current tolerance capability;

[0059] 2. The present invention provides the maximum possible transient current and grid voltage support for the grid-connected high-voltage direct-mounted battery energy storage system when a grid failure occurs without increasing the original hardware configuration and cost;

[0060] 3. The present invention constructs two major indicators, namely, the loss balance between submodules and the loss reduction of the energy storage submodule with the highest temperature, to evaluate the contribution rate and feasibility of each loss reduction method to the improvement of transient current tolerance capability;

[0061] 4. The modular characteristics of the present invention make the transient current tolerance capability of the system determined by the weakest module of the converter. The proposed method accurately obtains the junction temperature information of the power device, and then conducts quantitative analysis on various factors affecting the junction temperature, evaluates the contribution rate and feasibility of each loss reduction method to the improvement of transient current tolerance capability, and obtains a control method for improving transient current tolerance capability.

[0062] Other beneficial effects of the present invention will be explained in the specific implementation manner through the introduction of specific technical features and technical solutions. Through the introduction of these technical features and technical solutions, those skilled in the art should be able to understand the beneficial technical effects brought about by the technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0064] Figure 1 This is a control block diagram for transient current limiting utilization of high-voltage direct-mounted battery energy storage system;

[0065] Figure 2 Schematic diagram of the electric-thermal field-circuit coupling model and junction temperature extraction algorithm for high-voltage direct-mounted battery energy storage system;

[0066] Figure 3 This is a classification diagram of transient current boosting methods for high-voltage direct-mounted battery energy storage systems;

[0067] Figure 4 Schematic diagram of modulation voltage vector decomposition to improve transient current capability. DETAILED DESCRIPTION

[0068] The present invention is 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 are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0069] Embodiment 1:

[0070] The embodiment of the present invention provides a system for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system. Figure 1-4 The meanings of the parameters appearing in are as follows: Indicates the filter inductance value; Represents the parasitic resistance of the filter inductor; Indicates device case loss; Represents the junction loss of the device; Indicates the total DC voltage of the first group of submodules; Indicates the total DC voltage of the second group of submodules; Indicates the AC voltage amplitude of the first group of submodules; Indicates the AC voltage amplitude of the second group of submodules; is the grid voltage amplitude.

[0071] Specifically, the system solution refers to Figure 1As shown, it includes the following contents: high-voltage direct-mounted battery energy storage system, main controller, sub-controller, grid-type control module, junction temperature estimation module, dynamic current limiting module based on maximum junction temperature closed loop, current inner loop control module, junction temperature optimization strategy execution module; collect the actual temperature of the reference point, form a signal with the above modules, and transmit it to the actuator through the transmission system to achieve transient overcurrent tolerance;

[0072] The network control module, the dynamic current limiting module based on the maximum junction temperature closed loop, the current inner loop control module, and the junction temperature optimization strategy execution module run in the main controller, and the junction temperature estimation module runs in the sub-controller;

[0073] The high-voltage direct-mounted battery energy storage system distributes the battery modules to the DC bus of each H-bridge circuit to form energy storage sub-modules. The energy storage sub-modules are cascaded on the AC side and then connected to the medium and high voltage power grid in a conductive state through a filter inductor.

[0074] The grid-forming control module calculates and outputs the power angle and internal potential amplitude of the high-voltage direct-mounted battery energy storage system, and calculates the output current reference value through the generated power angle and internal potential amplitude.

[0075] The network control module includes:

[0076] The active power-frequency characteristic control module outputs the power angle of the system through the primary frequency modulation link, the virtual inertia link and the damping control link; specifically, the active power-frequency characteristic control module produces the command value of the active power through the primary frequency modulation link:

[0077]

[0078] in, ω n is the rated angular frequency, ω g is the grid angular frequency, D p is the primary frequency modulation droop coefficient, P set is the active power setting value of the grid connection point, P ref is the actual active power reference value, P max The maximum active power of the high-voltage direct-mounted battery energy storage system;

[0079] Then the power angle of the system is output through the virtual inertia link and the damping control link:

[0080]

[0081] in, J is the virtual inertia coefficient, s is the differential operator, Dd is the damping coefficient, P PCC It is the actual value of active power at the grid connection point.

[0082] The reactive power-voltage characteristic control module outputs the internal potential amplitude through the reactive voltage droop link and the internal potential adjustment link; the internal potential amplitude calculation method is:

[0083]

[0084] in, E is the internal potential amplitude, ω n is the rated angular frequency, K is the internal potential adjustment coefficient, s is the differential operator, D q is the reactive voltage droop coefficient, V N is the grid connection point voltage rating, V PCC is the actual value of the grid connection point voltage, Q set is the reactive power setting value of the grid connection point, Q PCC It is the actual value of reactive power at the grid connection point.

[0085] The virtual admittance control module converts the power angle and internal potential amplitude into an output current reference value instruction by simulating the line impedance characteristics; the circuit equation for realizing the virtual admittance is:

[0086]

[0087] in, R v is a virtual resistor, L v is the virtual inductor, v * d is the d-axis voltage command, v * q is the q-axis voltage command, i * d is the d-axis current command, i * q is the q-axis current command, v d is the d-axis voltage feedback value, v q is the q-axis voltage feedback value;

[0088] Among them, the power angle and the internal potential amplitude are used to calculate the output current reference value through the virtual admittance control module.

[0089] The junction temperature estimation module is implemented in the sub-controller of each energy storage sub-module. It estimates the junction temperature of the power device of each sub-module by collecting the actual temperature of the reference point, and transmits the extracted junction temperature data to the main controller.

[0090] The dynamic current limiting module based on the maximum junction temperature closed loop receives the junction temperature data of all sub-controllers, performs closed-loop control on the junction temperature of the energy storage sub-module with the highest temperature, outputs the current limit value, and then limits the current reference value through the current limiter to output the given value of the current inner loop control module;

[0091] The current inner loop control module controls the grid-connected point current to follow the given value, realizes the closed-loop control of the current inner loop, and outputs a modulated voltage waveform;

[0092] A junction temperature optimization strategy execution module converts the modulated voltage waveform into a pulse width modulation signal, executes a junction temperature management strategy, and improves the transient overcurrent tolerance capability of the high-voltage direct-mounted battery energy storage system;

[0093] Signal transmission is performed between the dynamic current limiting module based on the maximum junction temperature closed loop and the junction temperature estimation module, signal transmission is performed between the current inner loop control module and the dynamic current limiting module based on the maximum junction temperature closed loop, and signal transmission is performed between the junction temperature optimization strategy execution module and the current inner loop control module.

[0094] Among them, the junction temperature estimation module collects the actual temperature of the reference point to extract the junction temperature data, and transmits it to the junction temperature optimization strategy execution module through a signal to perform junction temperature management.

[0095] The junction temperature estimation module estimates the junction temperature of each submodule power device according to the junction temperature extraction technology, and extracts the junction temperature data;

[0096] The junction temperature extraction technology includes a junction temperature estimation algorithm and a loss estimation algorithm. The loss generated by the device is calculated based on the current estimated junction temperature, and then a new junction temperature is re-estimated based on the calculated loss. The junction temperature is accurately estimated by iterating until the junction temperature error between the previous and subsequent times is within a preset range.

[0097] The junction temperature estimation algorithm includes thermal network models, numerical models or analytical models;

[0098] The loss estimation algorithms include definition-based loss calculation, physical model-based loss calculation, data sheet-based loss calculation, or mathematical model-based loss calculation.

[0099] The dynamic current limiting module based on the maximum junction temperature closed loop collects the junction temperature information of all sub-controller power devices for closed loop control. The output current limit value is

[0100]

[0101] in, I max is the output current limit value, K P1 is the proportional parameter of the junction temperature closed-loop PI controller, K I1 is the integral parameter of the junction temperature closed-loop PI controller, s is the differential operator, T jmax * is the maximum operating junction temperature, T jmax is the maximum junction temperature of all sub-controller power devices; is the rated current of the switching device;

[0102] The current reference value is limited by the current limiter, and the given value of the output current inner loop control module is

[0103]

[0104] in, i dq,cmd is the given value of the dq axis current inner loop control module, i dq,ref is the dq axis current reference value.

[0105] The junction temperature optimization strategy execution module converts the modulation voltage into a pulse width modulation signal while executing various junction temperature management strategies;

[0106] Junction temperature management strategies include adjusting switching frequency, changing modulation strategy, adjusting DC bus voltage, designing intelligent gate drive, dynamic power distribution, adjusting power factor angle and reactive power.

[0107] The present invention also provides a method for improving the transient overcurrent capability of a grid-type high-voltage direct-mounted energy storage system, the method comprising:

[0108] Step S1: Establish the loss model and circuit model of the submodule, and design the junction temperature extraction algorithm;

[0109] The step S1 comprises:

[0110] Step S1.1: Establish loss models for switch components and batteries in the submodule, including loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet, and loss calculation based on mathematical model;

[0111] Step S1.2: Establishing a circuit model of the switch components and the battery in the submodule, and obtaining the loss value of the switch components and the battery at the current temperature by analyzing the heat generation behavior of each component;

[0112] Step S1.3: Design a temperature extraction algorithm for the switch components and the battery in the submodule, and obtain the temperature update values ​​of the switch components and the battery by constructing a thermal network model, a numerical model or an analytical model;

[0113] Step S1.4: Iterate to step S1.2 through temperature, calculate the loss value of the switch components and the battery under the temperature update value, and continue to execute step S1.3;

[0114] Step S1.5: Iterate until the junction temperature errors between the previous and subsequent times are within a set range, and output an accurate estimate of the junction temperature.

[0115] Step S2: construct two major indicators: loss balance between sub-modules and loss reduction of the energy storage sub-module with the highest temperature, and evaluate the contribution rate and feasibility of each loss reduction method to the improvement of transient overcurrent tolerance capability.

[0116] The uneven distribution of thermal stress in the submodules leads to limited transient current in the system. Balancing the heat load between the submodules is beneficial to breaking through the weakest link in thermal stress. Balancing the junction temperature of the IGBT and anti-parallel diode in the submodule is beneficial to improving the module's tolerance to larger transient currents. On the basis of achieving loss balancing, the junction temperature control and efficiency optimization methods are evaluated to further reduce the converter loss.

[0117] Step S3: Quantitatively analyze the various factors that affect the junction temperature, comprehensively consider the adjustment capability of each control method, the applicable working conditions and the influencing factors between each other, and coordinate the various junction temperature management methods. Among them, the various factors that affect the junction temperature include switching frequency, gate drive strategy, power factor angle, etc.;

[0118] In this step, each junction temperature management method includes:

[0119] Decompose the modulation voltage vector so that the submodules can operate at a power factor angle that can withstand the maximum short-circuit current without affecting the external power factor of the system;

[0120] Reduce the switching frequency of the switch submodule to further reduce the switching loss of the submodule;

[0121] Adopting a gate drive strategy that can reduce device switching and conduction losses, freeing up device margin without reducing lifespan.

[0122] Step S4: Further evaluate the junction temperature control and efficiency optimization methods for reducing converter losses, and achieve junction temperature control and optimization by means of dynamic current limiting.

[0123] Embodiment 2:

[0124] This embodiment describes the present invention in more detail based on the above-mentioned embodiment.

[0125] The present invention provides a transient overcurrent capability improvement system for a grid-type high-voltage direct-mounted energy storage system, the system comprising: a high-voltage direct-mounted battery energy storage system, a main controller, a sub-controller, a grid-type control module, a junction temperature estimation module, a dynamic current limiting module based on a maximum junction temperature closed loop, a current inner loop control module, and a junction temperature optimization strategy execution module;

[0126] The network control module, the dynamic current limiting module based on the maximum junction temperature closed loop, the current inner loop control module, and the junction temperature optimization strategy execution module run in the main controller, and the junction temperature estimation module runs in the sub-controller;

[0127] The high-voltage direct-mounted battery energy storage system is to disperse the battery modules to the DC bus of each H-bridge circuit. The H-bridge circuit is cascaded on the AC side and then connected to the medium and high voltage grid through the filter inductor.

[0128] The network control module includes:

[0129] Active power-frequency characteristic control module outputs the power angle of the system through the differential equation composed of primary frequency modulation link, virtual inertia link and damping control link θ :

[0130]

[0131] in, P ref is the active power reference value, P is the instantaneous active power, D p is the active power-frequency droop coefficient, J is the inertia coefficient of the active power loop, ω is the angular frequency generated by the active power loop.

[0132] Reactive power-voltage characteristic control module outputs the internal potential amplitude through the differential equation composed of reactive voltage droop link and internal potential regulation link E :

[0133]

[0134] in, Q ref and V ref is the reference value of reactive power and grid connection point voltage, Q and V is the instantaneous reactive power and grid-connected point voltage, Dq are the reactive power-voltage droop coefficients, K is the integral coefficient of the reactive power loop.

[0135] The generated power angle and internal potential amplitude are then output as current reference values ​​through the virtual admittance control module. v d * = E , v q * =0, the circuit equation for realizing virtual admittance on the dq axis is:

[0136]

[0137] in, R v and L v are virtual resistance and virtual inductance, v d * and v q * is the voltage command value on the dq axis, v d and v q is the actual value of the voltage on the dq axis, i dref and i qref is the current command value on the dq axis.

[0138] The junction temperature estimation module is implemented in the sub-controller of each energy storage sub-module. It collects the actual temperature of the reference point and estimates the junction temperature of the power device of each sub-module based on the junction temperature extraction technology, and transmits the extracted junction temperature data to the main controller.

[0139] The junction temperature extraction technology includes a junction temperature estimation algorithm and a loss estimation algorithm. The loss generated by the device is calculated based on the current estimated junction temperature, and then a new junction temperature is re-estimated based on the calculated loss. The junction temperature error between the two iterations is within a certain range, which can be considered as an accurate estimate of the junction temperature.

[0140] Junction temperature estimation algorithms include but are not limited to thermal network models, numerical models, and analytical models;

[0141] Taking the thermal network model as an example, the steady-state junction temperatures of the switch tube and the diode are calculated as follows:

[0142]

[0143]

[0144] in, and are the steady-state junction temperatures of the switch tube and the diode, respectively. and are the losses of the switch tube and the diode respectively, and are the thermal resistances from the switch tube and diode chip to the package shell, are the thermal resistance from package to environment. The loss estimation algorithm includes but is not limited to loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet (data sheet of switching device), loss calculation based on mathematical model, etc.

[0145] Taking the loss calculation based on the data sheet as an example, the switch loss is calculated as

[0146]

[0147]

[0148] in, and are the loss of the switch tube and the switching loss respectively. and are the current and voltage drop flowing through the switch tube, They are the voltage and current when the switch is turned on and off, Indicates the number of times it is opened in an exchange cycle; Indicates the number of shutdowns in one AC cycle; Represents the junction temperature of the device.

[0149] The dynamic current limiting module based on the maximum junction temperature closed loop receives the junction temperature data of all sub-controllers, performs closed-loop control on the junction temperature of the energy storage sub-module with the highest temperature, outputs the current limit value, and then limits the current reference value through the current limiter to output the given value of the current inner loop control module.

[0150] The dynamic current limiting module based on the maximum junction temperature closed loop collects the junction temperature information of all sub-controller power devices for closed loop control. The output current limit value is

[0151]

[0152] in, I max is the output current limit value, K P1 is the proportional parameter of the junction temperature closed-loop PI controller, K I1 is the integral parameter of the junction temperature closed-loop PI controller, sis the differential operator, T jmax * is the maximum operating junction temperature, T jmax is the maximum junction temperature of all sub-controller power devices;

[0153] The current reference value is limited by the current limiter, and the given value of the output current inner loop control module is

[0154]

[0155] in, i dq,cmd is the given value of the dq axis current inner loop control module, i dq,ref is the dq axis current reference value.

[0156] The current inner loop control module controls the grid-connected point current to follow the given value of the current inner loop control module, realizing the closed-loop control of the current inner loop. The output modulation voltage waveforms vd and vq are as follows:

[0157]

[0158] In the formula, K iP , K iI It is the proportional adjustment gain and integral adjustment gain of the current inner loop; Indicates the actual value of the d-axis current in the stationary coordinate system; Indicates the d-axis current command value of the stationary coordinate system. Indicates the actual value of the q-axis current in the stationary coordinate system; Indicates the q-axis current command value of the stationary coordinate system; Indicates the filter inductance value; Indicates the actual value of the d-axis grid voltage in the stationary coordinate system; It represents the actual value of the q-axis grid voltage in the stationary coordinate system.

[0159] The junction temperature optimization strategy execution module converts the modulated voltage into a pulse width modulation signal while executing various junction temperature management strategies that can reduce losses, thereby improving the transient overcurrent tolerance capability of the grid-type high-voltage direct-mounted battery energy storage system.

[0160] The junction temperature management strategy includes but is not limited to adjusting the switching frequency, changing the modulation strategy, adjusting the DC bus voltage, designing intelligent gate drive, dynamic power distribution, adjusting the power factor angle and reactive power, etc. For an example of adjusting the power factor angle, refer to Figure 4, decompose the modulated voltage vector so that the submodules can work at a power factor angle that can withstand the maximum short-circuit current and does not affect the system's external power factor. In order to achieve two modulation voltages, the energy storage submodules of each phase need to be divided into two groups. Since the voltage amplitudes of the two groups of modulation may differ greatly, the number of energy storage submodules contained in each group needs to be determined when grouping to prevent over-modulation. The number of energy storage submodules contained in each group is allocated according to the ratio of the voltage amplitudes of the two groups of modulation:

[0161]

[0162]

[0163] In the formula, and They are submodules allocated to realize two groups of modulation voltages respectively; N represents the total number of bridge arm submodules.

[0164] The present invention provides a method for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system, which specifically includes:

[0165] Step S1: Establish an accurate electrothermal field-circuit coupling model (including loss model, circuit model, and thermal circuit model) of the power device of the energy storage submodule, and design a junction temperature extraction algorithm.

[0166] Reference Figure 2 , step S1 needs to be implemented by the following steps:

[0167] Step S1.1: Establish loss models of switch components and batteries in the submodule, including but not limited to loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet, loss calculation based on mathematical model, etc.;

[0168] Step S1.2: Establishing a circuit model of the switch components and the battery in the submodule, and obtaining the loss value of the switch components and the battery at the current temperature by analyzing the heat generation behavior of the components;

[0169] Step S1.3: Design a temperature extraction algorithm for the switch components and the battery in the submodule, including but not limited to a thermal network model, a numerical model, and an analytical model, etc., and obtain the temperature update values ​​of the switch components and the battery based on the model;

[0170] Step S1.4: Iterate to step S1.2 through temperature, calculate the loss value of the switch components and the battery under the temperature update value, and continue to execute step S1.3;

[0171] Step S1.5: Iterate until the junction temperature errors between the previous and subsequent times are within a certain range, and output an accurate estimate of the junction temperature.

[0172] Step S2: construct two major indicators, namely, the loss balance between sub-modules and the loss reduction of the energy storage sub-module with the highest temperature, to evaluate the contribution and feasibility of each loss reduction method to the improvement of transient current tolerance capability.

[0173] Reference Figure 3 In step S2: the uneven distribution of thermal stress in the submodules leads to the limitation of transient current in the system. Balancing the heat load between the submodules is conducive to breaking through the weakest link of thermal stress. The junction temperature of IGBT (Insulate-Gate Bipolar Transistor) and anti-parallel diode in the submodule is balanced, which is conducive to improving the module's tolerance to larger transient current. On the basis of achieving loss balancing, the junction temperature control and efficiency optimization methods for further reducing converter losses are evaluated.

[0174] Step S3: Quantitatively analyze various factors affecting junction temperature, comprehensively consider the adjustment capability, applicable working conditions and mutual influence of each control method, so as to coordinate various junction temperature management methods. Among them, the factors affecting junction temperature include switching frequency, gate drive strategy, power factor angle, etc.;

[0175] Specifically, in step S3, various junction temperature management methods include but are not limited to the following strategies:

[0176] Reference Figure 4 , decompose the modulation voltage vector so that the submodules can work at a power factor angle that can withstand the maximum short-circuit current without affecting the external power factor of the system;

[0177] Reduce the switching frequency of the switch submodule to further reduce the switching loss of the submodule;

[0178] A gate drive strategy that can reduce device switching and conduction losses is adopted to fully release device margin without reducing device life.

[0179] Step S4: Evaluate the junction temperature control and efficiency optimization methods to further reduce the converter loss, and realize the junction temperature control and optimization by means of dynamic current limiting;

[0180] The embodiment of the present invention provides a method and system for improving the transient overcurrent capability of a grid-type high-voltage direct-mounted energy storage system. Without increasing the original hardware configuration and cost, the grid-type high-voltage direct-mounted battery energy storage system can provide the maximum transient current and grid voltage support as much as possible when a grid fault occurs, and realize the autonomous and rapid response of the grid-type high-voltage direct-mounted battery energy storage system to high and low voltage faults and the precise and limited utilization control method of transient current, evaluate the contribution rate and feasibility of various loss reduction methods to the improvement of transient current tolerance capability, and obtain a control method for improving transient current tolerance capability.

[0181] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0182] The above describes the specific embodiments of the present invention. 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. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A transient overcurrent capability enhancement system for a grid-type high-voltage direct-mounted energy storage system, characterized in that: include: High-voltage direct-mounted battery energy storage system, main controller, sub-controller, grid-type control module, junction temperature estimation module, dynamic current limiting module based on maximum junction temperature closed loop, current inner loop control module, junction temperature optimization strategy execution module; collect the actual temperature of the reference point, form a signal with the above modules, and transmit it to the actuator through the transmission system to achieve transient overcurrent tolerance; Among them, the network control module, the dynamic current limiting module based on the maximum junction temperature closed loop, the current inner loop control module, and the junction temperature optimization strategy execution module run in the main controller, and the junction temperature estimation module runs in the sub-controller; The high-voltage direct-mounted battery energy storage system distributes the battery modules to the DC bus of each H-bridge circuit to form energy storage sub-modules. The energy storage sub-modules are cascaded on the AC side and then connected to the grid in a conductive state through a filter inductor. The grid-forming control module calculates and outputs the power angle and internal potential amplitude of the high-voltage direct-mounted battery energy storage system, and calculates the output current reference value through the generated power angle and internal potential amplitude; The junction temperature estimation module is implemented in the sub-controller of each energy storage sub-module, estimates the junction temperature of the power device of each sub-module by collecting the actual temperature of the reference point, and transmits the extracted junction temperature data to the main controller; The dynamic current limiting module based on the maximum junction temperature closed loop receives the junction temperature data of all sub-controllers, performs closed-loop control on the junction temperature of the energy storage sub-module with the highest temperature, outputs the current limit value, and then limits the current reference value through the current limiter, and outputs the given value of the current inner loop control module; The current inner loop control module controls the grid-connected point current to follow the given value, implements closed-loop control of the current inner loop, and outputs a modulated voltage waveform; The junction temperature optimization strategy execution module converts the modulated voltage waveform into a pulse width modulation signal, executes the junction temperature management strategy, and improves the transient overcurrent tolerance capability of the high-voltage direct-mounted battery energy storage system; Signal transmission is performed between the dynamic current limiting module based on the maximum junction temperature closed loop and the junction temperature estimation module, signal transmission is performed between the current inner loop control module and the dynamic current limiting module based on the maximum junction temperature closed loop, and signal transmission is performed between the junction temperature optimization strategy execution module and the current inner loop control module; The dynamic current limiting module based on the maximum junction temperature closed loop performs closed loop control by collecting the junction temperature information of all sub-controller power devices, and the output current limit value is in, I max is the output current limit value, K P1 is the proportional parameter of the junction temperature closed-loop PI controller, K I1 is the integral parameter of the junction temperature closed-loop PI controller, s is the differential operator, T jmax * is the maximum operating junction temperature, T jmax is the maximum junction temperature of all sub-controller power devices; is the rated current of the switching device; The current reference value is limited by the current limiter, and the given value of the output current inner loop control module is in, i dq,cmd is the given value of the dq axis current inner loop control module, i dq,ref is the dq axis current reference value; The current inner loop control module controls the grid-connected point current to follow the given value of the current inner loop control module, realizes the closed-loop control of the current inner loop, and outputs the modulated voltage waveforms vd and vq as follows: In the formula, K iP , K iI It is the proportional adjustment gain and integral adjustment gain of the current inner loop; Indicates the actual value of the d-axis current in the stationary coordinate system; Indicates the d-axis current command value of the stationary coordinate system; Indicates the actual value of the q-axis current in the stationary coordinate system; Indicates the q-axis current command value of the stationary coordinate system; Indicates the filter inductance value; Indicates the actual value of the d-axis grid voltage in the stationary coordinate system; Indicates the actual value of the q-axis grid voltage in the stationary coordinate system; The junction temperature optimization strategy execution module converts the modulation voltage into a pulse width modulation signal while executing various junction temperature management strategies; The junction temperature management strategy includes adjusting the switching frequency, changing the modulation strategy, adjusting the DC bus voltage, designing an intelligent gate drive, dynamically distributing power, and adjusting the power factor angle and reactive power.

2. The transient overcurrent capability enhancement system of the grid-type high-voltage direct-mounted energy storage system according to claim 1 is characterized in that: The networking control module includes: Active power-frequency characteristic control module outputs the power angle of the system through the primary frequency modulation link, virtual inertia link and damping control link; The reactive power-voltage characteristic control module outputs the internal potential amplitude through the reactive voltage droop link and the internal potential adjustment link; A virtual admittance control module converts the power angle and internal potential amplitude into an output current reference value instruction by simulating line impedance characteristics; The power angle and the internal potential amplitude are used to calculate the output current reference value through a virtual admittance control module.

3. The transient overcurrent capability enhancement system of the grid-type high-voltage direct-mounted energy storage system according to claim 1 is characterized in that: The junction temperature estimation module collects the actual temperature of the reference point to extract junction temperature data, and transmits the data to the junction temperature optimization strategy execution module through a signal to execute junction temperature management.

4. The transient overcurrent capability enhancement system of the grid-type high-voltage direct-mounted energy storage system according to claim 1 is characterized in that: The junction temperature estimation module estimates the junction temperature of each submodule power device according to the junction temperature extraction technology, and extracts the junction temperature data; The junction temperature extraction technology includes a junction temperature estimation algorithm and a loss estimation algorithm. The loss generated by the device is calculated according to the currently estimated junction temperature, and then a new junction temperature is re-estimated according to the calculated loss. The junction temperature is accurately estimated by iterating until the junction temperature error between the previous and next two times is within a preset range. The junction temperature estimation algorithm includes a thermal network model, a numerical model or an analytical model; The loss estimation algorithm includes loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet or loss calculation based on mathematical model.

5. A method for improving the transient overcurrent capability of a grid-type high-voltage direct-mounted energy storage system, based on the transient overcurrent capability improvement system of a grid-type high-voltage direct-mounted energy storage system according to any one of claims 1 to 4, characterized in that: include: Step S1: Establish the loss model and circuit model of the submodule, and design the junction temperature extraction algorithm; Step S2: construct two major indicators: loss balance between submodules and loss reduction of the energy storage submodule with the highest temperature, and evaluate the contribution rate and feasibility of each loss reduction method to the improvement of transient overcurrent tolerance capability; Step S3: quantitatively analyzing various factors affecting the junction temperature, comprehensively considering the adjustment capability, applicable working conditions and mutual influencing factors of each control method, and coordinating various junction temperature management methods; Step S4: Further evaluate the junction temperature control and efficiency optimization methods for reducing converter losses, and achieve junction temperature control and optimization by means of dynamic current limiting.

6. The method for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system according to claim 5 is characterized in that: The step S1 comprises: Step S1.1: Establish loss models for switch components and batteries in the submodule, including loss calculation based on definition, loss calculation based on physical model, loss calculation based on data sheet, and loss calculation based on mathematical model; Step S1.2: Establishing a circuit model of the switch components and the battery in the submodule, and obtaining the loss value of the switch components and the battery at the current temperature by analyzing the heat generation behavior of each component; Step S1.3: Design a temperature extraction algorithm for the switch components and the battery in the submodule, and obtain the temperature update values ​​of the switch components and the battery by constructing a thermal network model, a numerical model or an analytical model; Step S1.4: Iterate to step S1.2 through temperature, calculate the loss value of the switch components and the battery under the temperature update value, and continue to execute step S1.3; Step S1.5: Iterate until the junction temperature errors between the previous and subsequent times are within a set range, and output an accurate estimate of the junction temperature.

7. The method for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system according to claim 5 is characterized in that: The junction temperature management method in step S3 includes: Decompose the modulation voltage vector so that the submodules can operate at a power factor angle that can withstand the maximum short-circuit current without affecting the external power factor of the system; Reduce the switching frequency of the switch submodule to further reduce the switching loss of the submodule; Adopting a gate drive strategy that can reduce device switching and conduction losses, freeing up device margin without reducing lifespan.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for improving the transient overcurrent capability of a grid-connected high-voltage direct-mounted energy storage system described in any one of claims 5 to 7 are implemented.

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