Method and device for determining current limiting value of static VAR generator

Abstract

The present invention provides a method and device for determining the current limiting value of a static VAR generator, which can be used in the field of power electronics technology. The method includes: determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator; determining the real-time junction temperature of each power device in the power submodule according to the average power loss of each power device in the power frequency cycle and the electrothermal model of the power submodule of the static VAR generator; if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limiting value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule. The method and device for determining the current limiting value of a static VAR generator provided by the present invention can dynamically and real-time set the current limiting value of the static VAR generator.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a method and a device for determining a current limiting value of a static VAR generator. Background Art

[0002] With the high proportion of access to renewable energy power plants, long-distance power transmission, the increase of nonlinear loads and system failures, the voltage stability in the renewable energy gathering area is easily reduced. SVG (static VAR generator) is a device that generates and absorbs reactive power in flexible AC transmission systems. When the voltage drops, SVG emits reactive power, which increases the reactive power at the voltage drop. It can also achieve power factor control and improve grid stability. Traditional SVG is limited by its topological structure and is difficult to promote to high-voltage and large-capacity applications. The modular multi-level converter based on the H-bridge cascade structure has the advantages of good scalability and small output harmonics. Its application in high-voltage reactive power compensation has become a research hotspot in recent years.

[0003] The basic working principle of H-bridge cascade SVG is to convert DC side power into AC power through cascaded inverters, and connect it to the power grid system through reactors or transformers. Unlike ordinary inverters, as a dynamic continuous compensation device, it is equivalent to a voltage source with the same frequency as the power grid and controllable output voltage amplitude and phase, which is connected to the power grid in parallel through a connected reactor. The system parameters are controlled by the voltage outer loop to output the reactive current command value, and then the output reactive current is controlled by the current inner loop. Figure 1 It is a typical three-phase full-bridge star-connected H-bridge cascade SVG topology. The three bridge arms are connected in a star shape and connected to the grid in parallel through a connecting reactor. Each bridge arm consists of multiple sub-modules connected in series. Each sub-module consists of 4 IGBTs, 4 freewheeling diodes and a capacitor. The working state of the SVG is controlled by controlling the switch of the IGBT.

[0004] With the development of AC and DC motor drives, various power supply technologies and power electronics, inverter circuits are widely used in the fields of industry and power equipment, among which the damage rate of power devices is the highest. As the power density of power electronic devices continues to increase, the safety issues of power devices are becoming more prominent, and most of their damage is induced by temperature. Therefore, most projects will limit the current of power devices, and the most commonly used method is the static current limiting method. This method simply sets the maximum current to a static limit value:

[0005]

[0006] In the formula, I CN is the rated current of the power device;

[0007] The parameter 1.5 is the overflow coefficient;

[0008] The fixed parameter 1.4 is the temperature coefficient.

[0009] In this current limiting method, in order to improve the reliability of avoiding overheating of power devices, the static current limit is usually set under harsh working conditions such as high ambient temperature and low convection wind speed, which is highly conservative; therefore, when the inverter circuit is not operating under harsh working conditions, the static limiting method will underestimate the current output capacity of the circuit, and the design of the current limit value will mostly have a large redundancy, affecting the electrical performance of the circuit; in addition, traditional current limiting methods are mostly considered in the design to protect the circuit from overload and overcurrent, and once overcurrent occurs, the current is limited immediately, but in fact it can withstand short-term overload conditions, and it is inevitable that there will be a "big horse pulling a small cart" phenomenon. The current source characteristics of the SVG control strategy limit the reactive capacity that the SVG can output, and also lead to the deterioration of the transient performance of the system when the voltage fluctuates. Summary of the invention

[0010] In view of the problems in the prior art, an embodiment of the present invention provides a method and device for determining a current limiting value of a static VAR generator, which can at least partially solve the problems in the prior art.

[0011] On the one hand, the present invention proposes a method for determining a current limiting value of a static VAR generator, comprising: determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator; determining the real-time junction temperature of each power device in the power submodule according to the average power loss of each power device in the power frequency cycle and the electrothermal model of the power submodule of the static VAR generator; if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limiting value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule.

[0012] Optionally, determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the operating characteristics of each power device in the static VAR generator includes:

[0013] Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator;

[0014] According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

[0015] Optionally, determining the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator includes:

[0016] Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor;

[0017] Determining the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator includes:

[0018] The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

[0019] Optionally, determining the average power loss of the insulated gate bipolar transistor within the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator includes:

[0020] Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator;

[0021] Determining the average power loss of the insulated gate transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate transistor;

[0022] Determining the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator includes:

[0023] Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator;

[0024] The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

[0025] Optionally, determining the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule includes:

[0026] Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator;

[0027] The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

[0028] Optionally, if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limit value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule includes:

[0029] If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule;

[0030] A current limiting value of the static VAR generator is determined according to the maximum allowable power loss of the power device.

[0031] Optionally, the method further includes: if the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, determining the current limiting value of the static VAR generator according to the rated current value of the power devices.

[0032] On the other hand, the present invention provides a device for determining a current limiting value of a static VAR generator, comprising:

[0033] A first determination module is used to determine the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator;

[0034] A second determination module is used to determine the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule;

[0035] The third determination module is used to determine the current limiting value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule if the real-time junction temperature of the power device is greater than the temperature limit value of the power device.

[0036] Optionally, the first determining module is specifically configured to:

[0037] Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator;

[0038] According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

[0039] Optionally, the first determining module determines the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator, including:

[0040] Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor;

[0041] The first determining module determines the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator, including:

[0042] The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

[0043] Optionally, the first determining module determines the average power loss of the insulated gate bipolar transistor within the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator, including:

[0044] Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator;

[0045] Determining the average power loss of the insulated gate transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate transistor;

[0046] The first determination module determines the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, including:

[0047] Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator;

[0048] The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

[0049] Optionally, the second determining module is specifically configured to:

[0050] Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator;

[0051] The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

[0052] Optionally, the third determining module is specifically used to:

[0053] If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule;

[0054] A current limiting value of the static VAR generator is determined according to the maximum allowable power loss of the power device.

[0055] Optionally, the device further comprises:

[0056] The fourth determination module is used to determine the current limiting value of the static VAR generator according to the rated current value of the power device if the real-time junction temperature of all the power devices is less than the temperature limit value of the power device.

[0057] On the other hand, the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for determining the current limiting value of a static VAR generator described in any of the above embodiments are implemented.

[0058] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for determining a current limiting value of a static VAR generator as described in any of the above embodiments.

[0059] The method, device and electronic device for determining the current limiting value of a static VAR generator provided by the embodiment of the present invention can accurately estimate the junction temperature of the power device in real time by establishing a reasonable electrothermal model using the relevant characteristic parameters of the power device; the temperature change caused by the power device loss is used to analyze the over-temperature and over-current relationship based on the junction temperature estimation, so as to dynamically and real-time set the current limiting value of the SVG system. The SVG dynamic current limiting strategy based on real-time junction temperature estimation can make full use of the device selection margin and the remaining temperature rise space during short-term overcurrent, so that the SVG has a certain short-term overcurrent capacity, instead of limiting the current to a fixed value and causing redundancy in the SVG output reactive capacity. After dynamic current limiting, the SVG system can maintain the maximum operating current value that does not cause device overheating, so that the SVG can work safely within the maximum available junction temperature range, while avoiding over-temperature operation of the power device, maximizing the operating performance limit, improving the power density and reliability of the system, obtaining a greater output capacity, and taking into account the reliability and economy of circuit operation, which is of great significance for large-capacity power grid compensation. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0061] Figure 1 This is a typical three-phase full-bridge star-connected H-bridge cascade SVG topology diagram.

[0062] Figure 2 It is a flow chart of a method for determining a current limiting value of a static VAR generator provided in one embodiment of the present invention.

[0063] Figure 3 It is a block diagram of an SVG electrothermal coupling model provided by an embodiment of the present invention.

[0064] Figure 4 Schematic diagram of the actual voltage and current waveforms of the device and the fitting curve.

[0065] Figure 5 This is a typical structural cross-section diagram of the SVG power submodule.

[0066] Figure 6It is a schematic diagram of an electrothermal model of an SVG power submodule provided in an embodiment of the present invention.

[0067] Figure 7 It is a flow chart of an SVG current limiting strategy provided by an embodiment of the present invention.

[0068] Figure 8 It is a schematic diagram of a current limiting controller provided in one embodiment of the present invention.

[0069] Fig. 9 The block diagram of a feedforward decoupling control strategy including dynamic current limiting is provided in one embodiment of the present invention.

[0070] Fig.10 It is a structural schematic diagram of a device for determining a current limiting value of a static VAR generator provided by an embodiment of the present invention.

[0071] Fig.11 It is a structural schematic diagram of a device for determining a current limiting value of a static VAR generator provided by another embodiment of the present invention.

[0072] Fig.12 It is a schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily.

[0074] In order to facilitate understanding of the technical solution provided by this application, the research background of the technical solution of this application is briefly described below.

[0075] The switching devices of the SVG submodule are IGBT and FWD. Overcurrent damage is one of the main causes of damage to IGBT and FWD. The mechanism of overcurrent damage is that a large current passes through in a short period of time, causing the conduction loss and switching loss to rise rapidly, so that the heat accumulation cannot be dissipated in time, causing the device to exceed the safe working junction temperature and burn out. Therefore, the junction temperature can be used as the basis for dynamic current limiting. Accurately estimating the real-time junction temperature of the power device is the key to fully utilizing the thermal capacity of the device. The traditional junction temperature measurement method can only measure the average junction temperature of the power device over a period of time, and cannot accurately estimate the real-time junction temperature.

[0076] Figure 2 FIG. 1 is a flow chart of a method for determining a current limiting value of a static VAR generator provided by an embodiment of the present invention. Figure 2 As shown, the method for determining the current limiting value of a static VAR generator provided by an embodiment of the present invention includes:

[0077] S101, determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator;

[0078] In this step, the modulation strategy (PWM modulation) of the static VAR generator refers to the analog control mode of the static VAR generator, specifically, the bias of the transistor base or the MOS tube gate is modulated according to the change of the corresponding load to achieve the change of the transistor or MOS tube conduction time, thereby achieving the change of the output of the switching regulated power supply. The power devices in the static VAR generator may include insulated gate bipolar transistors and diodes; the operating characteristics of each of the power devices can be derived according to the relevant data in the data manual of the power device.

[0079] After the operating characteristics of each power device in the static VAR generator are obtained, the average power loss of each power device in the static VAR generator during the power frequency cycle can be determined in combination with the modulation strategy of the static VAR generator.

[0080] S102, determining the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule;

[0081] This step, such as Figure 1 As shown, the STATCOM power submodule includes a DC side capacitor, four diodes, and four switching devices IGBT (insulated gate bipolar transistors); the electrothermal model of the power submodule can be constructed according to the topological structure of the power submodule.

[0082] When SVG is working, the heat generated by the power device loss will cause the junction temperature of the SVG device to rise. Therefore, the real-time junction temperature of each power device is related to the average power loss of the power device during the power frequency cycle. Therefore, the real-time junction temperature of each power device in the power sub-module can be determined based on the real-time power loss of each power device in the SVG power sub-module and the electrothermal model of the power sub-module.

[0083] S103: If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determine the current limit value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule.

[0084] In this step, the temperature limit value of each power device can be the maximum temperature T of the device specified in the technical manual of the power device. lim, the real-time junction temperature of the power device does not exceed the maximum withstand temperature T of the power device lim When the real-time junction temperature of the power device is greater than the temperature limit value of the power device, the current of the static VAR generator is limited. Specifically, the current limit value of the static VAR generator can be determined according to the real-time junction temperature of the power device and the electrothermal model of the power submodule.

[0085] The method for determining the current limiting value of the static VAR generator provided by the embodiment of the present invention can accurately estimate the junction temperature of the power device in real time by establishing a reasonable electrothermal model using the relevant characteristic parameters of the power device; the temperature change caused by the power device loss is used to analyze the over-temperature and over-current relationship based on the junction temperature estimation, so as to dynamically and real-time set the current limiting value of the SVG system. The SVG dynamic current limiting strategy based on real-time junction temperature estimation can make full use of the device selection margin and the remaining temperature rise space during short-term overcurrent, so that the SVG has a certain short-term overcurrent capacity, instead of limiting the current to a fixed value and causing redundancy in the SVG output reactive capacity. After dynamic current limiting, the SVG system can maintain the maximum operating current value that does not cause device overheating, so that the SVG can work safely within the maximum available junction temperature range, while avoiding over-temperature operation of the power device, maximizing the operating performance limit, improving the power density and reliability of the system, obtaining a greater output capacity, and taking into account the reliability and economy of circuit operation, which is of great significance for large-capacity power grid compensation.

[0086] Optionally, determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the operating characteristics of each power device in the static VAR generator may include:

[0087] Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator;

[0088] According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

[0089] In this embodiment, the instantaneous power loss of the insulated gate bipolar transistor can be derived in combination with the working characteristics of the insulated gate bipolar transistor recorded in the relevant data in the device data manual; because the current flowing through the insulated gate bipolar transistor changes with the modulation strategy of the static VAR generator within a modulation wave cycle of the static VAR generator, the average power loss of the insulated gate bipolar transistor within the power frequency cycle can be determined in combination with the modulation strategy of the static VAR generator and the derived instantaneous power loss of the insulated gate bipolar transistor.

[0090] Similarly, the instantaneous power loss of the diode can be derived by combining the working characteristics of the diode recorded in the relevant data in the device data manual; since the current flowing through the diode changes with the modulation strategy of the static VAR generator within a modulation wave cycle of the static VAR generator, the average power loss of the diode within the power frequency cycle can be determined by combining the modulation strategy of the static VAR generator and the derived instantaneous power loss of the diode.

[0091] Optionally, in the above embodiment, determining the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator includes:

[0092] Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor;

[0093] Determining the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator includes:

[0094] The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

[0095] In this embodiment, the power loss of the SVG device is mainly the conduction loss and switching loss of the IGBT and the conduction loss and reverse recovery loss of the FWD (diode). Figure 3 The SVG electrothermal coupling model block diagram shown in FIG. 1 includes a power loss model. The power loss model is based on the SVG DC bus voltage V dc , bridge arm current i j And the power device junction temperature feedback value Tx Calculate IGBT conduction loss P on-I 、IGBT switching loss P on-F 、FWD conduction loss P sw-I 、FWD reverse recovery loss P sw-F When calculating the loss, the power device is assumed to be a pure resistive device, so the power factor generally takes two extremes, one is when PF = 1 (cosθ = 1), and the other is when PF = -1 (cosθ = -1).

[0096] (1) Calculation of on-state power loss

[0097] Figure 4 The actual voltage and current waveforms of the device and the fitting curve diagram (the output characteristic curve and fitting curve of IGBT, the forward deviation characteristic curve and fitting curve of FWD can be used Figure 4 express).

[0098] IGBT on-state voltage drop V T-I and current i j It is a nonlinear relationship, which is fitted into a linear relationship. T0-I is the fitting straight line and V T-I The intersection of the axes, r T-I is the approximate on-resistance of the IGBT.

[0099] On-state voltage drop: V T-I =V T0-I +i j × T-I

[0100] On-state power loss: P on-I =V T-I ×i j =V T0-I ×i j +i j 2 × T-I Formula (1);

[0101] Similarly, the on-state voltage drop of FWD is V T-F and current i j It is a nonlinear relationship, which is fitted into a linear relationship. T0-F is the fitting straight line and V T-F The intersection of the axes, r T-F is the approximate on-resistance of the IGBT.

[0102] On-state voltage drop: V T-F =V T0-F +i j × T-F

[0103] On-state power loss: Pon-F =V T-F ×i j =V T0-F ×i j +i j 2 × T-F Formula (2);

[0104] Where V T0-I 、V T0-F It is formed due to the PN junction and its relationship with the on-resistance r T-I 、r T-F will be affected by temperature and have an approximately linear relationship. When calculating conduction loss, 25°C given in the technical manual is generally selected as the reference temperature. T0-I-25℃ 、V T0-F-25℃ and r T-I-25℃ 、r T-I-25℃ They are the starting on-voltage and approximate on-resistance of IGBT and FWD at 25°, T x In order to provide real-time feedback of junction temperature, the correlation coefficient can be obtained by fitting the relationship curve between temperature, starting on-voltage and approximate on-resistance given in the technical manual of the selected device: K V-I , K V-F They are the on-state voltage coefficients of IGBT and FWD, and K r-I , K r-F They are the on-resistance coefficients of IGBT and FWD respectively.

[0105] V T0-I =V T0-I-25℃ +K V-I (T x -25℃) Formula (3);

[0106] r T-I =r T-I-25℃ +K r-I (T x -25℃) Formula (4);

[0107] V T0-F =V T0-F-25℃ +K V-F (T x -25℃) Formula (5);

[0108] r T-F =r T-F-25℃ +K r-F (T x -25℃) Formula (6).

[0109] (2) Calculation of switching power loss

[0110] According to the technical manual: IGBT turn-on loss E on、IGBT turn-off loss E off With voltage V T-I 、Current i j The change of is nonlinear; FWD reverse recovery loss E r With voltage V T-F 、Current i j The change of is also nonlinear, and it is affected by many factors such as temperature, which is difficult to accurately describe quantitatively with analytical expressions. Therefore, we should try to consider the influencing factors in the switching loss estimation to reduce the error. Experience shows that E on 、E off and E r With the DC bus voltage V dc And the current i j The change can be regarded as a proportional relationship, generally with the rated current i jr And the rated voltage V dcr Lower rated turn-on loss E onr , Rated turn-off loss E offr And the rated reverse recovery loss E rr As a reference value, the linear conversion can meet the needs of engineering calculations. In addition, considering the impact of temperature on device loss, according to the temperature provided in the technical manual, the switching loss is generally calculated under the condition of a junction temperature of 125°C. By fitting the relationship curves between temperature and switching loss and reverse recovery loss given in the technical manual of the selected device, the IGBT temperature coefficient K can be obtained respectively. T-I 、FWD temperature coefficient K T-F , based on which the IGBT switch loss power P can be obtained sw-I and FWD reverse recovery power loss P r-F :

[0111]

[0112]

[0113] In the formula, f s-I is the IGBT switching frequency, f s-F is the FWD switching frequency.

[0114] In summary, the instantaneous power loss of IGBT and FWD are:

[0115]

[0116] Optionally, in the above embodiment, determining the average power loss of the insulated gate bipolar transistor within the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator includes:

[0117] Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator;

[0118] Determining the average power loss of the insulated gate transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate transistor;

[0119] Determining the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator includes:

[0120] Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator;

[0121] The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

[0122] In this embodiment, for example, taking unipolar PWM modulation as an example, when unipolar PWM modulation is adopted, a group of IGBT and FWD combination duty cycle δ y for Where M is the modulation ratio, ω is the angular velocity of the modulation wave, is the phase difference between the modulation wave voltage and current. Within this range, the IGBT gate has a trigger signal; based on the trigger signal, in a current cycle (the same as the modulation wave cycle) 0~T, because a single IGBT module is only responsible for the positive half-cycle (or negative half-cycle) current flowing through, the conduction area is taken as 0~T / 2, and the FWD is turned on when the current is reversed. From equations (1) to (6), the average on-state power loss calculation formula of a group of IGBT and FWD combination devices in the power frequency cycle can be obtained:

[0123]

[0124]

[0125] The average switching loss power of the IGBT in the power frequency cycle is equal to the IGBT switching loss power P calculated in the above embodiment. sw-I Equal, so P can be used sw-I Represents the average switching power loss of IGBT during the power frequency cycle; the average power loss of IGBT during the power frequency cycle is equal to P on-Ix With P sw-I sum.

[0126] Similarly, the average switching loss power of FWD in the power frequency cycle is equal to the reverse recovery loss power P of FWD calculated in the above embodiment. r-FEqual, so P can be used r-F Represents the average switching power loss of FWD during the power frequency cycle; the average power loss of FWD during the power frequency cycle is equal to P on-Fx With P r-F sum.

[0127] Optionally, in any of the above embodiments, determining the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule includes:

[0128] Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator;

[0129] The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

[0130] In this embodiment, according to the heat transfer theory, there are three main ways of heat transfer: heat conduction, heat convection and heat radiation. The heat source of the device is the IGBT and FWD chip, which transfers heat to the external environment through the shell and the heat sink. There is heat conduction between the chip and the shell and the heat sink. There is heat convection and heat radiation between the outer surface of the device and the external environment. However, the submodule will be encapsulated with silicone grease, which has a good insulation effect, so heat convection and heat radiation can be ignored and only longitudinal heat conduction can be considered.

[0131] Figure 5 The typical structural cross-section of the SVG power submodule is shown in Figure 1. It is mainly composed of a chip, a housing and a heat sink, wherein the housing contains a DCB substrate, a bottom plate and a connecting welding layer, and the housing and the heat sink are connected with silicone grease.

[0132] Figure 6 is the electrothermal model of the SVG power submodule. From the device technical manual, we can get the transient thermal impedance Z from the P / N junction to the shell with respect to time t. thJC The curve is fitted using the following formula (7) to extract thermal resistance and thermal capacitance. It is generally believed that the 3-4 order thermal network has good accuracy, so 4 thermal resistances R can be established. i and heat capacity C i The Foster model is composed of RC circuits connected in parallel and in series. s is the thermal impedance from case to heat sink, Z h is the thermal impedance of the heat sink. The relevant parameters adopt the recommended values ​​provided by the device manufacturer.

[0133]

[0134] From the above model analysis and heat transfer formula, we can know the instantaneous junction temperature of a single power device:

[0135] T x-I =P I Z thJC-I +(P I +P F )(Z s +Z h )+T e

[0136] T x-F =P F Z thJC-F +(P I +P F )(Z s +Z h )+T e

[0137] Where, T x-I is the real-time junction temperature of the IGBT, T x-F is the real-time junction temperature of FWD, Z thJC-I is the IGBT thermal impedance, Z thJC-F is the FWD thermal impedance; T e For ambient temperature, the installation position of the ambient temperature sensor is relatively flexible, the ambient temperature measurement reliability is high, and the failure rate is small.

[0138] Optionally, in the above embodiment, if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limit value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule may include:

[0139] If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule;

[0140] A current limiting value of the static VAR generator is determined according to the maximum allowable power loss of the power device.

[0141] In this embodiment, the real-time junction temperature of all IGBTs can be compared in real time to select the maximum value T max-I And the real-time junction temperature of all FWDs is selected as the maximum value T max-F As long as the temperature does not exceed the maximum withstand temperature T specified in the technical manual lim The device will not be damaged, so the T lim as the temperature limit value of the device.

[0142] like Figure 7As shown, when T max-I <T lim And T max-F <T lim When the short-time overcurrent is limited to not exceed the device rated current 2I N When T max-I ≥T lim or T max-F ≥T lim When the current is limited, it is necessary to control the current. Figure 8 It is a current limiting controller.

[0143] From equations (8) and (9), the maximum allowable power loss of IGBT and FWD can be obtained:

[0144]

[0145]

[0146] Among them C I , C F , τ I , τ F , R I , R F They are respectively the thermal capacitance corresponding to the maximum thermal resistance in the fourth-order Foster thermal network of IGBT and FWD, the time constant of the current limiting closed-loop control system (the value needs to balance the response speed and stability of the control system), and the device thermal resistance.

[0147] Specifically, through the formula of the aforementioned "power loss model", the real-time collected phase current is first set as the maximum operating current of each phase to be determined, and then the original power loss to be determined is set as the known maximum allowable power loss. Finally, the current required quantity, that is, the maximum operating current of each phase of the two devices, can be reversely solved, and the minimum value is compared and selected as the maximum operating phase current amplitude i of the entire SVG system. lim , which is the vector sum of active current and reactive current. Ensuring the stability of the SVG DC side voltage is the premise of all system control and normal operation. Therefore, the active current demand must be met first, and the remaining current margin is used to meet the SVG's external reactive compensation. Therefore, the active current reference value The limit value is i lim , The limit value of the active current reference value and reactive current reference value output after limiting:

[0148]

[0149] In this way, the active and reactive currents are limited and distributed by taking full account of the control requirements of SVG on active and reactive power.

[0150] Optionally, the method may further include: if the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, determining the current limit value of the static VAR generator according to the rated current value of the power devices.

[0151] In this embodiment, as long as the temperature does not exceed the maximum withstand temperature T specified in the technical manual, lim The device will not be damaged. Due to the current carrying capacity of the device itself, the current cannot exceed the rated current of the device 2I N Therefore, when the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, the current limit value of the static VAR generator can be determined as 2I N .

[0152] Fig. 9 This is a block diagram of a feedforward decoupling control strategy including dynamic current limiting formulated based on the method for determining the current limiting value of a static VAR generator provided in the above embodiments. Fig. 9 As shown in the figure, the collected value of the grid voltage is compared with the rated value as the reactive current reference value output by the voltage outer loop; in addition, due to the active power loss in the system, in order to stabilize the DC bus voltage, an active current reference value is output by a voltage outer loop. The current reference value and the current sampling value are input into the current inner loop for calculation to obtain the modulation wave, which is modulated to output the control signal of the IGBT.

[0153] Fig.10 FIG. 1 is a schematic diagram of a structure of a device for determining a current limiting value of a static VAR generator provided by an embodiment of the present invention. Fig.10 As shown, the device for determining the current limiting value of a static VAR generator provided by an embodiment of the present invention includes:

[0154] A first determination module 21 is used to determine the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator;

[0155] A second determination module 22 is used to determine the real-time junction temperature of each power device in the power submodule according to the average power loss of each power device in the power frequency cycle and the electrothermal model of the static VAR generator power submodule;

[0156] The third determination module 23 is used to determine the current limiting value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule if the real-time junction temperature of the power device is greater than the temperature limit value of the power device.

[0157] The device for determining the current limiting value of a static VAR generator provided by the embodiment of the present invention can accurately estimate the junction temperature of the power device in real time by establishing a reasonable electrothermal model using the relevant characteristic parameters of the power device; and analyze the over-temperature and over-current relationship based on the junction temperature estimation by using the temperature change caused by the power device loss, so as to dynamically and real-time set the current limiting value of the SVG system. The SVG dynamic current limiting strategy based on real-time junction temperature estimation can make full use of the device selection margin and the remaining temperature rise space during short-term overcurrent, so that the SVG has a certain short-term overcurrent capacity, instead of limiting the current to a fixed value and causing redundancy in the SVG output reactive capacity. After dynamic current limiting, the SVG system can maintain the maximum operating current value that does not cause device overheating, so that the SVG can work safely within the maximum available junction temperature range, while avoiding over-temperature operation of the power device, maximizing the operating performance limit, improving the power density and reliability of the system, obtaining a greater output capacity, and taking into account the reliability and economy of circuit operation, which is of great significance for large-capacity power grid compensation.

[0158] Optionally, the first determining module is specifically configured to:

[0159] Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator;

[0160] According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

[0161] Optionally, the first determining module determines the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator, including:

[0162] Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor;

[0163] The first determining module determines the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator, including:

[0164] The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

[0165] Optionally, the first determining module determines the average power loss of the insulated gate bipolar transistor within the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator, including:

[0166] Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator;

[0167] Determining the average power loss of the insulated gate transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate transistor;

[0168] The first determination module determines the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, including:

[0169] Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator;

[0170] The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

[0171] Optionally, the second determining module is specifically configured to:

[0172] Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator;

[0173] The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

[0174] Optionally, the third determining module is specifically used to:

[0175] If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule;

[0176] A current limiting value of the static VAR generator is determined according to the maximum allowable power loss of the power device.

[0177] like Fig.11 As shown, optionally, the device may further include:

[0178] The fourth determination module 24 is configured to determine the current limiting value of the static VAR generator according to the rated current value of the power device if the real-time junction temperature of all the power devices is less than the temperature limit value of the power device.

[0179] The embodiments of the device provided by the present invention can be specifically used to execute the processing flow of the above-mentioned method embodiments. Its functions are not described in detail here, and reference can be made to the detailed description of the above-mentioned method embodiments.

[0180] Fig.12 A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention is shown in FIG. Fig.12 As shown, the electronic device may include: a processor 301, a communication interface 302, a memory 303 and a communication bus 304, wherein the processor 301, the communication interface 302 and the memory 303 communicate with each other through the communication bus 304. The processor 301 may call the logic instructions in the memory 303 to execute the method described in any of the above embodiments.

[0181] In addition, the logic instructions in the above-mentioned memory 303 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0182] This embodiment discloses a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided by the above-mentioned method embodiments.

[0183] This embodiment provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program enables the computer to execute the methods provided by the above-mentioned method embodiments.

[0184] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0185] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0186] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0187] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0188] In the description of this specification, the description with reference to the terms "one embodiment", "a specific embodiment", "some embodiments", "for example", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0189] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for determining a current limiting value of a static VAR generator, characterized in that: include: Determine the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator, wherein the power devices include insulated gate bipolar transistors and diodes; Determining the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule; If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limit value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule; If the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, determining the current limit value of the static VAR generator according to the rated current value of the power devices; If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the current limit value of the static VAR generator according to the real-time junction temperature of the power device and the electrothermal model of the power submodule includes: if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule; determining the current limit value of the static VAR generator according to the maximum allowable power loss of the power device; If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule, including: If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, the maximum allowable power loss of the power device is calculated according to the following maximum allowable power loss calculation formula: Among them, P lim-I Indicates the maximum allowable power loss of an insulated gate bipolar transistor; P lim-F Indicates the maximum allowable power loss of the diode; C I , C F , τ I , τ F , R I , R F They represent the thermal capacitance corresponding to the maximum thermal resistance in the fourth-order electrothermal model of the insulated gate bipolar transistor and the diode, the time constant of the current limiting closed-loop control system, and the device thermal resistance respectively; Determining the current limiting value of the static VAR generator according to the maximum allowable power loss of the power device includes: Determining a maximum operating current per phase of the insulated gate bipolar transistor according to a maximum allowable power loss of the insulated gate bipolar transistor; Determining the maximum operating current per phase of the diode according to the maximum allowable power loss of the diode; The smaller value of the maximum operating current per phase of the insulated gate bipolar transistor and the maximum operating current per phase of the diode is used as the maximum operating phase current amplitude of the static VAR generator; If the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, determining the current limit value of the static VAR generator according to the rated current value of the power devices, comprises: If the real-time junction temperatures of all the power devices are less than the temperature limit value of the power devices, the current limit value of the static VAR generator is determined to be twice the rated current value of the power devices.

2. The method according to claim 1, characterized in that Determining the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator includes: Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator; According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

3. The method according to claim 2, characterized in that Determining the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator comprises: Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching power loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor; Determining the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator includes: The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

4. The method according to claim 2, characterized in that: Determining the average power loss of the insulated gate bipolar transistor within the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator includes: Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator; Determining the average power loss of the insulated gate bipolar transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate bipolar transistor; Determining the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator includes: Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator; The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

5. The method according to claim 1, characterized in that Determining the real-time junction temperature of each power device in the power submodule according to the average power loss of each power device in the power frequency cycle and the electrothermal model of the static VAR generator power submodule includes: Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator; The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

6. A device for determining a current limiting value of a static VAR generator, characterized in that: include: A first determination module is used to determine the average power loss of each power device in the power frequency cycle according to the modulation strategy of the static VAR generator and the working characteristics of each power device in the static VAR generator; A second determination module is used to determine the real-time junction temperature of each of the power devices in the power submodule according to the average power loss of each of the power devices in the power frequency cycle and the electrothermal model of the static VAR generator power submodule; a third determination module, configured to determine a current limiting value of the static VAR generator according to the real-time junction temperature of the power device and an electrothermal model of the power submodule if the real-time junction temperature of the power device is greater than a temperature limit value of the power device; A fourth determination module, configured to determine a current limit value of the static VAR generator according to a rated current value of the power device if the real-time junction temperature of all the power devices is less than a temperature limit value of the power device; The third determination module is specifically used to: if the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determine the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule; determine the current limiting value of the static VAR generator according to the maximum allowable power loss of the power device; If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, determining the maximum allowable power loss of the power device according to the real-time junction temperature of the power device and the electrothermal model of the power submodule includes: If the real-time junction temperature of the power device is greater than the temperature limit value of the power device, the maximum allowable power loss of the power device is calculated according to the following maximum allowable power loss calculation formula: Among them, P lim-I Indicates the maximum allowable power loss of an insulated gate bipolar transistor; P lim-F Indicates the maximum allowable power loss of the diode; C I , C F , τ I , τ F , R I , R F They represent the thermal capacitance corresponding to the maximum thermal resistance in the fourth-order electrothermal model of the insulated gate bipolar transistor and the diode, the time constant of the current limiting closed-loop control system, and the device thermal resistance respectively; Determining the current limiting value of the static VAR generator according to the maximum allowable power loss of the power device includes: Determining a maximum operating current per phase of the insulated gate bipolar transistor according to a maximum allowable power loss of the insulated gate bipolar transistor; Determining the maximum operating current per phase of the diode according to the maximum allowable power loss of the diode; The smaller value of the maximum operating current per phase of the insulated gate bipolar transistor and the maximum operating current per phase of the diode is used as the maximum operating phase current amplitude of the static VAR generator; If the real-time junction temperature of all the power devices is less than the temperature limit value of the power devices, determining the current limit value of the static VAR generator according to the rated current value of the power devices, comprises: If the real-time junction temperatures of all the power devices are less than the temperature limit value of the power devices, the current limit value of the static VAR generator is determined to be twice the rated current value of the power devices.

7. The device according to claim 6, characterized in that The first determining module is specifically used for: Determine the instantaneous power loss of the insulated gate bipolar transistor according to the working characteristics of the insulated gate bipolar transistor in the static VAR generator; determine the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator; According to the working characteristics of the diode in the static VAR generator, the instantaneous power loss of the diode is determined; according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, the average power loss of the diode within the power frequency cycle is determined.

8. The device according to claim 7, characterized in that The first determining module determines the instantaneous power loss of the insulated gate bipolar transistor according to the operating characteristics of the insulated gate bipolar transistor in the static VAR generator, including: Determine the on-state power loss of the insulated gate bipolar transistor according to the output characteristic curve of the insulated gate bipolar transistor; determine the switching power loss of the insulated gate bipolar transistor according to the switching loss curve of the insulated gate bipolar transistor; determine the instantaneous power loss of the insulated gate bipolar transistor according to the on-state power loss and switching power loss of the insulated gate bipolar transistor; The first determining module determines the instantaneous power loss of the diode according to the working characteristics of the diode in the static VAR generator, including: The on-state power loss of the diode is determined according to the forward deviation characteristic curve of the diode; the reverse recovery power loss of the diode is determined according to the reverse recovery loss curve of the diode; and the instantaneous power loss of the diode is determined according to the on-state power loss and reverse recovery power loss of the diode.

9. The device according to claim 7, characterized in that The first determining module determines the average power loss of the insulated gate bipolar transistor in the power frequency cycle according to the instantaneous power loss of the insulated gate bipolar transistor and the modulation strategy of the static VAR generator, including: Determining the conduction time of the insulated gate bipolar transistor in any switching cycle according to the modulation strategy of the static VAR generator; Determining the average power loss of the insulated gate bipolar transistor in a power frequency cycle according to the on-time of the insulated gate bipolar transistor in any switching cycle and the instantaneous power loss of the insulated gate bipolar transistor; The first determination module determines the average power loss of the diode within the power frequency cycle according to the instantaneous power loss of the diode and the modulation strategy of the static VAR generator, including: Determining the conduction time of the diode in any switching cycle according to the modulation strategy of the static VAR generator; The average power loss of the diode in the power frequency cycle is determined according to the conduction time of the diode in any switching cycle and the instantaneous power loss of the diode.

10. The device according to claim 6, characterized in that The second determining module is specifically used for: Establishing an electrothermal model of the power submodule according to a transient thermal impedance curve of a power device in the power submodule of the static VAR generator; The real-time junction temperature of each power device in the power submodule is determined according to the electrothermal model of the power submodule and the average power loss of each power device in the power submodule during an operating frequency cycle.

11. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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