A method for active support of transient voltage of a converter based on protection demand

Abstract

The application discloses a kind of based on protection demand's converter transient voltage active support method, belong to power electronics technical field, it includes obtaining converter instantaneous electric stress parameter, obtains real-time thermal stress state in combination with the thermal response relationship of power semiconductor device;Fusion electric stress parameter and thermal stress state, and generate dynamic safety operating boundary in combination with safety operating area characteristic data;While detecting power grid transient information, generate ideal transient support instruction according to support guide;According to boundary, instruction is constrained and restructured, through intelligent adjustment its amplitude or change rate, generate adaptive transient support instruction.The application generates safety operating boundary dynamically by real-time sensing the electric-thermal stress state of power semiconductor device, and according to the boundary, the ideal support instruction following the guide of power grid is intelligently constrained and restructured, can maximize the transient support capability of converter, while ensuring the operation safety and reliability of equipment itself.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a converter transient voltage active support method based on protection requirements. BACKGROUND

[0002] As a kind of key power electronic device, converter plays a vital role in modern power system, and is widely used in new energy grid-connected, flexible DC transmission, power quality management and other fields. Its core function is to realize the conversion and control of electric energy form. With the increasing penetration rate of power electronic equipment in power grid, the converter not only needs to complete the basic electric energy transmission task, but also is required to actively provide transient voltage support when the power grid fails or is disturbed, so as to enhance the stability and resilience of the power grid.

[0003] In the prior art, in order to ensure the safe operation of the converter in the transient process, a protection strategy based on fixed threshold is usually adopted. One or more static current limits are preset in the control system, which are usually determined according to the rated parameters of power semiconductor devices under the worst working condition and with a large margin. When the power grid transient event triggers the support requirement, the support current instruction calculated by the controller will exceed the preset limit value, and the protection logic will act immediately, usually by forcing the current instruction to be clamped at the limit value, or in more serious cases, directly blocking the pulse output of the converter, so that it is disconnected from the power grid.

[0004] The prior art has obvious technical defects. First of all, the fixed protection threshold set based on the worst working condition is too conservative, resulting in that the actual bearing potential of the converter is seriously wasted in most non-limit working conditions, and the transient support capability provided by the converter is also greatly reduced. Secondly, this protection strategy lacks the perception of the real running state of the power semiconductor device, and cannot distinguish between short-time and bearable current pulse and continuous overcurrent that may cause thermal damage, so the protection action is relatively rough. Simple current clamping method may lead to unsatisfactory support effect, and direct disconnection from the grid will exacerbate the power imbalance of the grid, which is contrary to the original intention of providing transient support. SUMMARY

[0005] To solve the above problems, the present application provides a converter transient voltage active support method based on protection requirements, which adopts real-time sensing of the electrical and thermal stress state of the power semiconductor device to dynamically generate a safe working boundary, and intelligently constrains and reconstructs the ideal support instruction according to the grid code based on the boundary, so as to maximize the transient support capability of the converter while ensuring the safe and reliable operation of the device itself.

[0006] The above object can be achieved by the following scheme:

[0007] The application discloses a converter transient voltage active support method based on protection requirements, and relates to the technical field of power electronic equipment.

[0008] Optionally, obtaining the real-time thermal stress state comprises: monitoring the instantaneous current flowing through the power semiconductor device and the DC side voltage of the converter in real time to obtain the instantaneous electrical stress parameter; and calculating the real-time junction temperature and the corresponding thermal stress quantitative index based on the instantaneous electrical stress parameter and in combination with the thermal response relationship of the power semiconductor device to obtain the real-time thermal stress state.

[0009] Optionally, calculating the real-time junction temperature and the corresponding thermal stress quantitative index comprises: obtaining the thermal characteristic data of the power semiconductor device under different working conditions through offline experiments or simulation; fitting and calibrating the thermal response relationship structure parameters based on the thermal characteristic data; and performing discrete recursive calculation according to the thermal response relationship structure parameters to obtain the real-time junction temperature and the thermal stress quantitative index.

[0010] Optionally, dynamically calculating and adaptively generating the dynamic safety working boundary comprises: extracting the real-time junction temperature in the real-time thermal stress state and the DC side voltage in the instantaneous electrical stress parameter to generate a combined state parameter; calculating the maximum allowable pulse current and the maximum allowable continuous current in the next control period by using the safety working area characteristic data corresponding to the power semiconductor device and in combination with the combined state parameter; and combining the maximum allowable pulse current and the maximum allowable continuous current to dynamically calculate and adaptively generate the dynamic safety working boundary.

[0011] Optionally, the method further comprises: when the real-time junction temperature is low, relaxing the current limit defined by the dynamic safety working boundary to obtain a dynamic safety working boundary with improved transient support capability; and when the real-time junction temperature rises, smoothing and tightening the current limit defined by the dynamic safety working boundary to generate a dynamic safety working boundary that guarantees operation safety.

[0012] Optionally, generating the ideal transient support instruction comprises: performing abnormal detection on the grid voltage or current to identify the type, amplitude and duration of the transient event; and generating the ideal transient support instruction according to the response requirements for the transient event in the grid support guide.

[0013] Optionally, the response requirement for transient events in the grid support guideline comprises: constructing a correspondence relationship set of transient event types and ideal support strategies according to the power response, current response or voltage response requirements specified in the grid support guideline; retrieving a matched ideal support strategy from the correspondence relationship set according to the identified transient event type, amplitude and duration; calculating and outputting an instantaneous support current or voltage instruction capable of meeting the grid support guideline requirement according to the matched ideal support strategy, and generating an ideal transient support instruction.

[0014] Optionally, the constraining and reconstructing of the ideal transient support instruction according to the dynamic security operating boundary comprises: comparing the ideal transient support instruction with the current limit range defined by the dynamic security operating boundary to obtain a judgment result of whether the boundary is exceeded; if the judgment result of whether the boundary is exceeded is not exceeded, taking the ideal transient support instruction as the adaptive transient support instruction; if the judgment result of whether the boundary is exceeded is exceeded, obtaining an instruction exceeding margin according to the difference between the ideal transient support instruction and the dynamic security operating boundary, and actively adjusting the amplitude or change rate of the ideal transient support instruction based on the instruction exceeding margin to generate the adaptive transient support instruction.

[0015] Optionally, the actively adjusting of the amplitude or change rate of the ideal transient support instruction comprises: when it is judged that the ideal transient support instruction exceeds the dynamic security operating boundary, preferentially adjusting the change rate of the ideal transient support instruction to generate an intermediate support instruction with limited waveform slope; if the peak value of the intermediate support instruction is still outside the dynamic security operating boundary, further reducing the amplitude of the intermediate support instruction to obtain the adaptive transient support instruction.

[0016] Based on the same inventive concept, the application also provides a converter transient voltage active support system based on protection requirements, which comprises: a thermal stress real-time monitoring module for obtaining instantaneous electric stress parameters of the converter, and combining the thermal response relationship of the power semiconductor device to obtain the real-time thermal stress state of the power semiconductor device inside the converter; a dynamic security boundary generation module for fusing the instantaneous electric stress parameters and the real-time thermal stress state, and combining the safety operating zone characteristic data of the power semiconductor device to dynamically calculate and adaptively generate a dynamic security operating boundary; a transient instruction decision module for obtaining grid transient information, identifying transient events by detecting voltage or current abnormalities of the grid, and generating an ideal transient support instruction according to the grid support guideline; and an adaptive instruction reconstruction module for constraining and reconstructing the ideal transient support instruction according to the dynamic security operating boundary, intelligently adjusting the amplitude or change rate of the ideal transient support instruction based on a margin if the ideal transient support instruction exceeds the boundary, and generating an adaptive transient support instruction that takes into account the operation safety and improves the power quality.

[0017] Compared with the prior art, the application has the following advantages:

[0018] The application dynamically evaluates the real-time state of the power semiconductor device inside the converter, and adaptively adjusts the transient support strategy in combination with the power grid support demand, thereby improving the transient stability of the power grid while ensuring the safe operation of the converter itself. Compared with the traditional method of using a fixed protection threshold, the application can dynamically adjust the safety boundary according to the real-time thermal margin of the device, allowing the converter to output a larger transient current to provide stronger power grid support when the device is in a low-temperature or light-load state, thereby fully exploiting the potential of the device.

[0019] The application proposes a layered instruction reconstruction mechanism that, when the ideal support instruction exceeds the safety boundary, adjusts the change rate of the instruction first instead of directly reducing its amplitude. This smooth processing method effectively reduces the dynamic stress on the power semiconductor device caused by current impact, thereby improving the stability and reliability of the device operation. Only when the change rate adjustment still cannot meet the safety constraint, the amplitude is limited, thereby achieving more precise and friendly protection of the device.

[0020] The application realizes accurate estimation of the internal key parameters of the power semiconductor device, i.e., the real-time junction temperature, by constructing a high-precision device thermal model and performing online recursive calculation, which is equivalent to providing the converter with an invisible internal state "sensor". This accurate perception based on the real physical state provides a reliable basis for the generation and adaptive control of the dynamic safety boundary, thereby fundamentally improving the scientificity and effectiveness of the protection strategy.

[0021] The control strategy of the application always takes the power grid support guideline as the benchmark to ensure the compliance and effectiveness of its active support behavior. By intelligently integrating the external power grid demand with the internal safety constraint, the method ensures that the converter will not endanger its own safety due to blind response while fulfilling its power grid support obligations, thereby achieving an optimal dynamic balance between effective support for the power grid and protection of the device itself.

[0022] Other features and advantages of the application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the application. The objects and other advantages of the application will be realized and attained by the structure particularly pointed out in the description and claims, and the organization of the application. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0024] Figure 1 is a flowchart of a converter transient voltage active support method based on protection requirements according to an embodiment of the present application.

[0025] Figure 2 is a dynamic safety operating boundary characteristic diagram according to an embodiment of the present application.

[0026] Figure 3 is a corresponding distribution rule of maximum allowable continuous current according to an embodiment of the present application.

[0027] Figure 4 is a self-adaptive transient support instruction reconstruction timing diagram according to an embodiment of the present application.

[0028] Figure 5 is a structural diagram of a converter transient voltage active support system based on protection requirements according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0030] With reference to Figure 1 An embodiment of the present application proposes a converter transient voltage active support method based on protection requirements. The method dynamically generates a safety operating boundary by sensing an electro-thermal stress state of a power semiconductor device in real time, and intelligently constrains and reconstructs ideal support instructions in accordance with grid guidelines, so as to maximize the transient support capability of the converter while ensuring the operation safety and reliability of the device itself.

[0031] The method according to the embodiment specifically includes:

[0032] Obtain a transient electric stress parameter of the converter, and obtain a real-time thermal stress state in combination with a thermal response relationship of the power semiconductor device;

[0033] Fuse the transient electric stress parameter and the real-time thermal stress state, and dynamically calculate and self-adaptively generate a dynamic safety operating boundary in combination with safety operating zone characteristic data of the power semiconductor device;

[0034] Obtain grid transient information, identify a transient event by detecting voltage or current abnormalities of the grid, and generate ideal transient support instructions in accordance with grid support guidelines;

[0035] The ideal transient support command is constrained and reconstructed based on the dynamic safety working boundary. If the ideal transient support command exceeds the boundary, its amplitude or rate of change is intelligently adjusted based on the margin to generate an adaptive transient support command that takes into account both operational safety and power quality.

[0036] First, by real-time monitoring of electrical stress parameters and combining them with the device's thermal response model, precise online sensing of the internal thermal stress state of the power semiconductor device is achieved. Then, this real-time internal state sensing is integrated with the device's inherent safe operating area data to dynamically generate an operational safety boundary that adapts to changing operating conditions. Simultaneously, the method independently monitors the grid status and generates an ideal support command representing optimal grid benefits based on established grid support guidelines. Finally, this ideal command is examined and reconstructed under the constraints of the dynamic safety boundary. By intelligently adjusting the amplitude or rate of change of the command, external demands and internal capabilities are matched in real time, ultimately outputting an actual execution command that effectively supports the grid while ensuring its own absolute safety. This method significantly improves the overall performance of the converter during grid transient events, achieving the dual goals of transient support capability and equipment operational safety. It transforms the converter from a passive command-executing device into a system capable of sensing its own state and making intelligent decisions, enabling refined management and utilization of equipment potential.

[0037] The real-time thermal stress state is obtained including:

[0038] Real-time monitoring of the instantaneous current flowing through the power semiconductor device and the DC-side voltage of the converter yields instantaneous electrical stress parameters;

[0039] Based on instantaneous electrical stress parameters and combined with the thermal response relationship of power semiconductor devices, the real-time junction temperature and its corresponding thermal stress quantification index are calculated to obtain the real-time thermal stress state.

[0040] First, by using high-precision current and voltage sensors configured in the main circuit of the converter, the instantaneous current i flowing through the power semiconductor device is measured. dev With the DC side voltage V of the converter dc Real-time monitoring and data acquisition are performed, and these two parameters together constitute the instantaneous electrical stress parameters for evaluating the operating pressure of the device. Subsequently, based on the acquired instantaneous electrical stress parameters, the instantaneous total loss P of the power semiconductor device is calculated. loss The total loss mainly includes conduction loss and switching loss, which can be determined by the characteristic curves provided in the device datasheet or through an offline calibrated loss model, based on the instantaneous current i. dev and DC side voltage V dcThe real-time value is calculated. Then, the real-time junction temperature of the power semiconductor device is estimated in real time by combining the pre-established thermal response relationship and the real-time calculated instantaneous total loss. Finally, the calculated real-time junction temperature and the derived indicators such as the junction temperature change rate are selectively combined to form a thermal stress quantitative index, so as to comprehensively represent the real-time thermal stress state of the power semiconductor device. The method not only provides key and real-time state input for subsequent generation of a dynamic safety operating boundary, ensures strict compliance with the thermal limit of the device in the transient support process, but also enables the converter to fully exert its transient support potential according to the actual thermal margin on the premise of ensuring safety, so as to improve the transient stability of the power grid while ensuring the operation safety and long-term reliability of the equipment itself.

[0041] The real-time junction temperature and the corresponding thermal stress quantitative index include:

[0042] The thermal characteristic data of the power semiconductor device under different working conditions is obtained through offline experiments or simulation;

[0043] Based on the thermal characteristic data, the thermal response relationship structure parameters are fitted and calibrated;

[0044] The real-time junction temperature and the thermal stress quantitative index are obtained by discrete recursive calculation based on the thermal response relationship structure parameters.

[0045] To calculate the real-time junction temperature and the corresponding thermal stress quantitative index, an accurate device thermal model needs to be established through offline work first. In this stage, a special power cycle test platform is built for offline experiments, or a finite element analysis software is used for fine electric-thermal coupling simulation, aiming to obtain the thermal characteristic data of the target power semiconductor device. The specific operation is to apply a known step power loss to the device, and accurately measure or simulate the response curve of the junction temperature over time, which is the transient thermal impedance curve of the device and constitutes the core thermal characteristic data. Then, based on the obtained transient thermal impedance curve as the thermal characteristic data, the model fitting and calibration of the thermal response relationship structure parameters are performed. Usually, an equivalent thermal network model such as Foster network or Cauer network is used to mathematically describe the dynamic heat transfer process from the junction to the shell of the device. The thermal response relationship is mathematically expressed as the sum of multiple exponential terms. By using a numerical optimization algorithm such as nonlinear least squares method, the transient thermal impedance curve obtained by experiment or simulation is fitted with the mathematical expression of the equivalent thermal network model, so as to identify the thermal resistance R th,i and the thermal capacity C th,iThe combination of the two is the thermal response relationship structure parameter. Finally, when the converter is running online, the thermal model in continuous time domain is discretized according to the thermal response relationship structure parameter obtained in the previous step, and is converted into a discrete recursive calculation suitable for execution in a digital controller. For example, for an n-order Foster network model, the discrete recursive calculation of the junction temperature can be expressed as:

[0046]

[0047] Where Δt is the calculation period of the control system; P loss [k-1] is the instantaneous total loss of the power semiconductor device calculated in the previous period; R th,i And τ i are the thermal resistance and thermal time constant of the i-th equivalent thermal network, which belong to the calibrated thermal response relationship structure parameters; ΔT i [k] represents the temperature rise of the i-th thermal network in the current period k; T c [k] is the device shell or heat sink temperature measured in real time by the sensor. By iteratively performing this recursive operation at each control period, the real-time junction temperature T j [k] that changes dynamically over time can be obtained. The real-time junction temperature T j [k] is the most important quantitative indicator of the internal thermal stress level of the device, and is the core element of the comprehensive thermal stress state representation. This method constructs a high-precision "virtual junction temperature sensor", overcoming the problems of physical sensors that cannot directly measure the junction temperature, high cost and low reliability.

[0048] Dynamic calculation and adaptive generation of dynamic safety operating boundary include:

[0049] Extracting the real-time junction temperature in the real-time thermal stress state and the DC side voltage in the instantaneous electrical stress parameter to generate a combined state parameter;

[0050] Using the safety operating area characteristic data corresponding to the power semiconductor device and combining the combined state parameter to calculate the maximum allowed pulse current and the maximum allowed continuous current in the next control period;

[0051] Combining the maximum allowed pulse current and the maximum allowed continuous current to dynamically calculate and adaptively generate the dynamic safety operating boundary.

[0052] First, the core real-time junction temperature T j is extracted from the real-time thermal stress state, and the DC side voltage V dc is extracted from the instantaneous electrical stress parameter. These two parameters together constitute the combined state parameter representing the current operating state of the power semiconductor device, in which the real-time junction temperature T j reflects the internal thermal margin of the device, and the DC side voltage Vdc This determines the voltage stress the device must withstand during switching. The next step is to utilize the safe operating area (SOA) characteristic data that perfectly corresponds to this power semiconductor device. The safe operating area, or SOA, is key data provided by the device manufacturer that defines the voltage and current range within which the device can safely operate under different operating conditions. It is usually given in the form of graphs or datasheets, and this data is often based on a specific reference junction temperature or case temperature. The core of this method is that instead of directly using the static SOA data, it combines it with real-time updated combined state parameters for dynamic calculation. Specifically, based on the current DC-side voltage V... dc and real-time junction temperature T j This involves online dynamic interpretation and correction of SOA data. For example, by consulting or interpolating the SOA curve after temperature derating correction, the system can determine the appropriate SOA level at the current V... dc and T j Under the given conditions, the maximum permissible pulse current that the device can withstand in the next control cycle. and maximum allowable continuous current The maximum permissible pulse current typically corresponds to short-time overload capability, and its value is highly dependent on the permissible pulse width and the current junction temperature; the maximum permissible continuous current corresponds to the limiting current-carrying capacity under steady-state thermal equilibrium, and its calculation must ensure that the steady-state losses generated at this current will not cause the junction temperature to exceed the device's maximum permissible junction temperature. For example... Figure 2 , 3 As shown, the characteristic distribution of the dynamic safe operating boundary of power semiconductor devices is illustrated. Figure 2 This displays the characteristics of the maximum permissible pulse current as a function of real-time junction temperature and DC-side voltage. Figure 3 The distribution pattern of the maximum permissible continuous current is shown. Finally, the calculated maximum permissible pulse current is... With maximum allowable continuous current These two factors, when combined, define the safe upper limit of the converter output current in the next control cycle. This boundary, consisting of the pulse limit and the duration limit, is not a fixed value, but rather varies with the real-time junction temperature T. j and DC side voltage V dc The system adapts to changes in transient conditions, thus constituting a dynamic safety operating boundary. This boundary provides real-time, accurate, and dynamic constraints for subsequent transient support command reconfiguration. This method maximizes the transient support capability of the converter while ensuring that power semiconductor devices always operate within their physical limits, significantly improving the system's safety, reliability, and grid support performance.

[0053] The method also includes:

[0054] When the real-time junction temperature is low, the current limit defined by the dynamic safety operating boundary is relaxed to obtain a dynamic safety operating boundary with enhanced transient support capability;

[0055] When the real-time junction temperature is high, the current limit defined by the dynamic safety operating boundary is smoothly tightened to obtain a dynamic safety operating boundary that guarantees operation safety.

[0056] The core of the adjustment mechanism is to establish a negative correlation function relationship between the current limit and the real-time junction temperature, so as to dynamically balance the transient support capability and the operation safety. When the converter is in a state of light load operation, low ambient temperature, or early stage of transient event, the real-time junction temperature T j obtained by the real-time monitoring module will be at a low level. At this time, the power semiconductor device has a large thermal margin from its maximum allowable junction temperature T j，max The control algorithm utilizes this thermal margin to perform the operation of relaxing the dynamic safety operating boundary. Specifically, when calculating the maximum allowable pulse current I and the maximum allowable continuous current I , a gain function or lookup table that is positively correlated with the thermal margin will be used. For example, the following function can be used to modify the reference current limit to obtain the relaxed current limit:

[0057]

[0058] wherein I is the adjusted current limit, I is the reference limit based on the reference temperature, and f(T j,max -T j ) is a monotonically increasing function that increases with the thermal margin (T j,max -T j ). The dynamic safety operating boundary generated in this way has a higher current upper limit, so that the converter can legally output a larger transient current when the power grid needs strong support, thereby obtaining a dynamic safety operating boundary with enhanced transient support capability. Conversely, when the converter experiences long-time heavy load operation, or the junction temperature continuously rises due to output of large current during transient support, the real-time junction temperature T j will approach its safety threshold, and the thermal margin will decrease accordingly. To prevent the device from being damaged due to overheating, the control algorithm will smoothly tighten the current limit defined by the dynamic safety operating boundary. This tightening process is also achieved through the above function relationship, but at this time, since T j is high and the thermal margin is small, the output value of the function f will also decrease, thereby resulting in a smaller I The tightening process is smooth and continuous to ensure the stability of the control, avoiding sudden changes in the current limit. In this way, the range of the dynamic safety operating boundary is actively shrunk, forming a stronger constraint on the ideal transient support instruction, prioritizing the protection of power semiconductor devices from exceeding their thermal limits, and generating a dynamic safety operating boundary that ensures safe operation. This adaptive mechanism achieves deep excavation and fine utilization of the potential of power semiconductor devices, significantly enhancing the support capacity and flexibility of the converter in response to grid transient events without sacrificing long-term reliability.

[0059] Generating the ideal transient support instruction includes:

[0060] Abnormal detection of grid voltage or current to identify the type, amplitude, and duration of the transient event;

[0061] Generating the ideal transient support instruction according to the response requirements of the grid support guidelines for transient events.

[0062] First, the detection and identification of transient events. Through the high-speed sampling and data processing unit configured at the grid-connected point of the converter, the waveform of the grid voltage or current is continuously monitored. When the instantaneous value of the monitored voltage or current or the calculated characteristic quantity, such as the voltage effective value or frequency, deviates from the normal operating range and exceeds a certain threshold, abnormal detection is triggered. Once an abnormality is detected, the key parameters of the transient event are determined, including the type of the transient event, such as voltage sag, voltage surge, or frequency disturbance; the amplitude of the transient event, such as the depth of voltage sag; and the duration of the transient event, recorded by a timer from the start time of the event. Second, generating specific support instructions based on grid support guidelines. The grid support guidelines are issued by the grid operator and specify the support obligations that grid-connected devices must fulfill when the grid is disturbed, such as low voltage ride through (LVRT) or high voltage ride through (HVRT) requirements. This method first digitizes and logicizes these guidelines to form a pre-set rule base. When the transient event is identified, the corresponding response strategy is matched in the rule base according to the type, amplitude, and duration of the event, and the ideal transient support instruction is calculated and generated. This method provides a clear and explicit control target for the subsequent control link, making the transient support behavior of the converter purposeful and compliant. It converts complex grid regulations into a specific and executable electrical instruction, which is the key foundation of the decision-making level in the entire active support method.

[0063] Generating the ideal transient support instruction according to the response requirements of the grid support guidelines for transient events includes:

[0064] According to the power response, current response, or voltage response requirements specified in the grid support guidelines, a corresponding relationship set between the type of transient event and the ideal support strategy is constructed;

[0065] According to the identified transient event type, amplitude and duration, the corresponding ideal support strategy is retrieved from the correspondence set;

[0066] According to the matched ideal support strategy, the instantaneous support current or voltage instruction that meets the requirements of the grid support guideline is calculated and output, and the ideal transient support instruction is generated.

[0067] First, in the design and configuration phase, the support guideline of the target grid needs to be comprehensively analyzed and structured to build a correspondence set of transient event types and ideal support strategies. This set is a pre-established rule base or multi-dimensional lookup table stored in the controller memory. Its construction process includes one-to-one mapping of various transient events specified in the guideline, such as voltage sag or transient rise of different depths and durations, and the corresponding response requirements, such as specific strategies for power response, current response or voltage response. For example, a mapping entry can be defined as "when the voltage drops to 50% to 90% of the rated value, dynamic reactive current support needs to be performed, and the support current amplitude is proportional to the voltage drop depth". Secondly, during the real-time operation of the converter, once the type, amplitude and duration of the transient event are identified, these parameters are immediately used as indexes for fast retrieval in the constructed correspondence set. Through this retrieval operation, the ideal support strategy corresponding to the current transient event can be accurately matched. This strategy not only indicates the type of response to be taken, such as injecting reactive current, but also includes the specific parameters and calculation methods required to implement the strategy. Finally, according to the matched ideal support strategy retrieved, specific calculations are performed to generate the ideal transient support instruction. For example, if the matched strategy is "linearly inject reactive current according to the voltage drop depth", the pre-set calculation formula will be called and the real-time monitored grid parameters will be substituted into the formula to calculate the instruction value. A typical reactive current support instruction calculation formula is shown below:

[0068]

[0069] wherein, is the ideal transient support instruction calculated, specifically the reference value of instantaneous reactive current; K is the reactive support gain coefficient, whose value is directly specified by the retrieved ideal support strategy and comes from the grid support guideline; I N is the rated current of the converter, which is a device inherent parameter; V th is the voltage threshold for starting reactive support, also defined by the guideline; V gis the real-time detected grid voltage amplitude. The instantaneous support current or voltage command output by this calculation is the ideal transient support command that fully complies with grid regulation requirements and aims to maximize grid benefits. This method establishes a clear, quantified and regulation-based initial target for the transient response of the converter, thereby avoiding the blindness and randomness of the response and providing a precise and ideal input benchmark for the subsequent reconstruction of the command considering the safety constraints of the device.

[0070] The constraint and reconstruction of the ideal transient support command according to the dynamic safety operating boundary include:

[0071] The ideal transient support command is compared with the current limit range defined by the dynamic safety operating boundary to obtain a judgment result of exceeding the boundary;

[0072] If the judgment result of exceeding the boundary is not exceeded, the ideal transient support command is taken as the adaptive transient support command;

[0073] If the judgment result of exceeding the boundary is exceeded, the command exceeding margin is obtained according to the difference between the ideal transient support command and the dynamic safety operating boundary, and the amplitude or rate of change of the ideal transient support command is actively adjusted based on the command exceeding margin to generate the adaptive transient support command.

[0074] First, the ideal transient support command is compared with the current limit range defined by the dynamic safety operating boundary in terms of its amplitude For example, the current limit range defined by the dynamic safety operating boundary is usually jointly defined by the maximum allowed pulse current and the maximum allowed continuous current , which is represented by a comprehensive boundary value here. The comparison process obtains a clear judgment result of exceeding the boundary. If the judgment result of exceeding the boundary is not exceeded, i.e. the amplitude of is within the range defined by , it indicates that the converter is fully capable of executing the ideal command without endangering its own safety. In this case, no modification is made, and the ideal transient support command is directly output as the adaptive transient support command to the inner loop controller of the converter for execution. If the judgment result of exceeding the boundary is exceeded, it indicates that executing the ideal transient support command will cause the electrical stress or thermal stress of the power semiconductor device to exceed its safety limit. At this time, the active adjustment mechanism is started. First, the difference between the ideal transient support command and the dynamic safety operating boundary is calculated to obtain a quantitative command exceeding margin ΔI, which is calculated as follows:

[0075]

[0076] where ΔI is the command exceeding margin, which quantifies the degree of intrusion of the ideal command into the safety boundary. is the amplitude of the ideal transient support instruction generated according to the grid support guideline; is the current maximum allowable current limit calculated by the dynamic security operating boundary module in real time. Then, the amplitude or the rate of change of the ideal transient support instruction is actively adjusted based on the instruction exceeding the margin ΔI. For example, the most direct amplitude adjustment method is to clamp the instruction amplitude at the boundary value, i.e. the adjusted instruction amplitude is equal to . Alternatively, the rate of change of the instruction can also be adjusted, i.e. the rising speed of the instruction is slowed down, so that the instruction waveform becomes flat to avoid generating excessive impact in a short time. The new instruction generated after such intelligent adjustment, i.e. the adaptive transient support instruction, takes into account both the operation safety and the power quality improvement. This method does not simply cut off the support, but through fine adjustment of the instruction, it approaches the ideal support target as much as possible under the premise of ensuring safety, achieving the optimal dynamic balance between operation safety and grid support benefit.

[0077] The active adjustment of the amplitude or the rate of change of the ideal transient support instruction includes:

[0078] When it is judged that the ideal transient support instruction exceeds the dynamic security operating boundary, the rate of change of the ideal transient support instruction is adjusted first to generate an intermediate support instruction with a limited waveform slope;

[0079] If the peak value of the intermediate support instruction is still outside the dynamic security operating boundary, the amplitude of the intermediate support instruction is further reduced to obtain the adaptive transient support instruction.

[0080] This method further refines the active adjustment strategy when the ideal transient support instruction exceeds the dynamic security operating boundary, and adopts a hierarchical and progressive adjustment logic. When it is judged that the ideal transient support instruction exceeds the dynamic security operating boundary, the amplitude of the ideal transient support instruction is not immediately reduced, but the rate of change of the ideal transient support instruction is adjusted first. This operation is realized through a slope limiter (Rate Limiter). The limiter sets a maximum allowable current rate of change dV / dt max related to the device tolerance capability. The ideal transient support instruction After input into the slope limiter, the output intermediate support instruction will follow the following rules:

[0081]

[0082] Here, and are the current and the previous control period intermediate support instructions, respectively; is the ideal transient support instruction of the current period; dV / dt maxis the set maximum allowable rate of change; Δt is the control period. By this operation, even if the ideal command is a step change, the waveform of the actual generated intermediate support command will be smoothly rising with a controlled slope, generating an intermediate support command with a limited waveform slope. This step aims to alleviate the rapid impact of current, because certain failure modes of power semiconductor devices are highly sensitive to the rate of current change. Subsequently, the peak of this slope-limited intermediate support command is re-checked. The peak of the intermediate support command is compared with the current limit defined by the dynamic safety operating boundary . If the peak of the intermediate support command is still outside the dynamic safety operating boundary, i.e. , a second level of adjustment is initiated, i.e. further reducing the amplitude of the intermediate support command. The most direct way is to hard clamp the amplitude of the command so that its maximum value does not exceed , as follows:

[0083]

[0084] wherein is the finally generated adaptive transient support command. Through this two-step strategy of adjusting the rate of change first and then adjusting the amplitude, the adaptive transient support command that meets both the rate constraint and the amplitude constraint and can be safely executed is finally obtained. As shown in Figure 4 , the adaptive transient support command is obtained by adjusting the amplitude of the ideal command, ensuring that the dynamic safety operating boundary constraint is met in the entire time domain, embodying the command reconstruction idea based on real-time thermal stress constraint. This hierarchical and progressive adjustment method can retain the effective components of the ideal support command to a greater extent compared to single amplitude limiting, achieving more optimal utilization of transient support capability under the premise of absolute safety, making the entire support process smoother, more stable and efficient.

[0085] Based on the same inventive concept, as shown in Figure 5 , the present application also provides a converter transient voltage active support system based on protection demand, the system comprising:

[0086] a thermal stress real-time monitoring module for obtaining the instantaneous electrical stress parameters of the converter, and combining the thermal response relationship of the power semiconductor device to obtain the real-time thermal stress state of the power semiconductor device inside the converter;

[0087] a dynamic safety boundary generation module for fusing the instantaneous electrical stress parameters and the real-time thermal stress state, and combining the safety operating zone characteristic data of the power semiconductor device to dynamically calculate and adaptively generate a dynamic safety operating boundary;

[0088] ​a transient instruction decision module, configured to acquire power grid transient information, identify a transient event by detecting abnormal power grid voltage or current, and generate ideal transient support instructions according to power grid support guidelines;

[0089] an adaptive instruction reconstruction module, configured to constrain and reconstruct the ideal transient support instructions according to a dynamic security operating boundary, intelligently adjust the amplitude or change rate of the ideal transient support instructions based on a margin if the ideal transient support instructions exceed the boundary, and generate adaptive transient support instructions that take into account both operating safety and improved power quality.

[0090] In order to verify the feasibility of the application in implementation, the application is applied to a grid-connected converter system of a certain large-scale photovoltaic power station. In order to meet the requirements of transient voltage support of the power grid, the grid-connected converter of the photovoltaic power station must quickly respond and inject reactive current to support the voltage of the power grid when the voltage sag and other transient events occur in the power grid. The traditional method uses a fixed overcurrent protection threshold, which is usually conservatively set to cope with the worst case, resulting in that the transient support capability of the converter is limited in most cases and cannot be fully utilized. The application aims to solve this problem by dynamically adjusting the safety boundary to achieve the best balance between transient support capability and device operating safety.

[0091] In this embodiment, a 1MW grid-connected converter of a photovoltaic power station integrates the transient voltage active support system of the application. The thermal stress real-time monitoring module in the system monitors the instantaneous current and DC side voltage of the power semiconductor device (IGBT) in real time through high-precision sensors, and calculates the real-time junction temperature T j of the IGBT through discrete recursion based on the offline calibrated Foster thermal network model parameters. The dynamic safety boundary generation module fuses the real-time junction temperature T j and the DC side voltage V dc , and combines the safety operating area (SOA) characteristic data of the IGBT to generate a dynamic safety operating boundary in real time.

[0092] In order to verify the beneficial effects of the application, two typical working condition scenarios are selected for testing: scenario one is in the morning of spring, the environmental temperature is low, and the converter is lightly loaded; scenario two is in the afternoon of summer, the environmental temperature is high, and the converter is close to full load operation. In both scenarios, a voltage sag event of 200ms duration and 50% depth occurs in the power grid. The power grid support guideline requires the converter to inject 1.2 times the rated current (1.2p.u.) of reactive current as ideal transient support instructions during this period.

[0093] In scenario one (April 10, 2025, 10:00), the environmental temperature is 15℃, the converter load is light, and the real-time junction temperature T jis 65℃. At this time, the dynamic safety margin generation module calculates the maximum pulse current allowed by the dynamic safety operating margin according to sufficient thermal margin is 1.4 p.u.. The ideal transient support instruction generated by the transient instruction decision module is 1.2 p.u.. The adaptive instruction reconstruction module compares the two and determines that the ideal instruction does not exceed the safety margin (1.2 p.u. < 1.4 p.u.), so the ideal instruction is directly issued as the adaptive transient support instruction, and the converter successfully outputs 1.2 p.u. of reactive current, effectively supporting the grid voltage.

[0094] In scenario two (June 22, 2025, 14:30), the ambient temperature is 35℃, the light is strong, and the converter is running under heavy load for a long time. The measured real-time junction temperature T j has reached 115℃ (close to the maximum allowed junction temperature of 125℃). At this time, the dynamic safety margin generation module smoothly tightens the dynamic safety operating margin to When the grid voltage dip event occurs, the ideal transient support instruction is still 1.2 p.u.. The adaptive instruction reconstruction module determines that the ideal instruction exceeds the safety margin (1.2 p.u. > 1.05 p.u.). The system immediately starts the adjustment mechanism, which prioritizes limiting the rate of change of the instruction, generating a waveform-smooth intermediate support instruction. Then, the peak value of the intermediate instruction is still checked to exceed the safety margin of 1.05 p.u., so its amplitude is further clamped at 1.05 p.u.. Finally, the converter outputs an adaptive transient support instruction with an amplitude of 1.05 p.u.. Although this does not fully meet the ideal support requirement, it ensures that the junction temperature of the IGBT does not exceed the safety limit, avoiding thermal damage to the device.

[0095] The comparison data shows that, using the method of the present application, the converter can "use what it has" to provide strong transient support when the device is safe, and can "do what it can" to prioritize its own safety when the device is close to danger. This method significantly improves the operating flexibility and overall reliability of the converter under different operating conditions.

[0096] Table 1 Dynamic safety operating margin generation data table

[0097] Time Ambient Temperature (°C) Initial Junction Temperature Operating Load (%) Dynamic Safety Margin 2025-04-10 10:00 15 65 40 1.40 2025-04-10 14:30 22 85 80 1.25 2025-06-22 10:00 30 95 70 1.15 2025-06-22 14:30 35 115 95 1.05

[0098] Table 2 Transient event response and instruction reconstruction data table

[0099] Table 3 Comparison of transient support effects of different methods

[0100] From the data recorded in the above Tables 1 to 3, it can be seen that the application effect of the present application in the photovoltaic grid-connected converter is remarkable. Table 1 clearly shows how the dynamic safe operating boundary is self-adaptively adjusted according to the real-time junction temperature changes caused by the ambient temperature and the load. When the junction temperature is low (65℃), the safe boundary is relaxed to 1.40 p.u., while when the junction temperature is close to the limit (115℃), the boundary is actively tightened to 1.05 p.u., embodying the intelligent sensing capability of the system.

[0101] The data comparison of Tables 2 and 3 further proves the superiority of the present application. In scenario one, the present application can enable the converter to output a current of up to 1.20 p.u., fully meeting the ideal support demand of the power grid, while the traditional fixed protection method can only output 1.0 p.u., causing a waste of support capability. In scenario two, in the face of severe thermal stress state, the present application limits the output current to 1.05 p.u. through intelligent instruction reconstruction, so that the junction temperature peak value is accurately controlled within the safety limit of 125℃, successfully avoiding equipment damage. This ability to maximize support benefits under the premise of ensuring safety is unmatched by the traditional fixed protection strategy, fully proving the great application value of the present application in improving the performance and reliability of new energy grid-connected equipment.

[0102] It should be noted that the electrical connection between the above-mentioned units does not necessarily represent the direct connection of the line, and the indirect connection mode can also be applied to the embodiments of the present application as long as the purpose of the present application is achieved. The above is only an exemplary embodiment of the present application, and cannot limit the scope of the present application.

[0103] That is, any equivalent changes and modifications made according to the teachings of the present application are still within the scope of the present application. Other embodiments of the present application will be readily apparent to those skilled in the art upon considering the specification and practice of the true principles disclosed herein. The present application is intended to cover any variations, uses, or adaptive changes of the present application following the general principles of the present application and including common knowledge or conventional technical means in the art not disclosed by the present application.

Claims

1. A method of active support of transient voltages in a converter based on protection requirements, characterized in that the method The method comprises the following steps: Obtain the instantaneous electric stress parameter of the converter, and combine the thermal response relationship of the power semiconductor device to obtain the real-time thermal stress state; Fuse the instantaneous electric stress parameter and the real-time thermal stress state, and combine the safety working area characteristic data of the power semiconductor device to dynamically calculate and adaptively generate the dynamic safety working boundary; Obtain the power grid transient information, identify the transient event by detecting the abnormality of the power grid voltage or current, and generate the ideal transient support instruction according to the power grid support guide; According to the dynamic safety working boundary, the ideal transient support instruction is constrained and reconstructed, if the ideal transient support instruction exceeds the boundary, the amplitude or change rate thereof is intelligently adjusted based on the margin, and the adaptive transient support instruction which takes into account the operation safety and improves the power quality is generated.

2. The method of claim 1, wherein, Obtaining the real-time thermal stress state comprises: Real-time monitoring of the instantaneous current flowing through the power semiconductor device and the DC side voltage of the converter to obtain the instantaneous electric stress parameter; Based on the instantaneous electric stress parameter, the real-time junction temperature and the corresponding thermal stress quantitative index are calculated by combining the thermal response relationship of the power semiconductor device, and the real-time thermal stress state is obtained.

3. The method of claim 2, wherein, The calculation of the real-time junction temperature and the corresponding thermal stress quantitative index comprises: Obtain the thermal characteristic data of the power semiconductor device under different working conditions through offline experiment or simulation; Based on the thermal characteristic data, the thermal response relationship structure parameters are fitted and calibrated; According to the thermal response relationship structure parameters, the real-time junction temperature and the thermal stress quantitative index are obtained by discrete recursive calculation.

4. The method of claim 3, wherein, Dynamically calculating and adaptively generating the dynamic safety working boundary comprises: Extracting the real-time junction temperature in the real-time thermal stress state and the DC side voltage in the instantaneous electric stress parameter to generate a combined state parameter; Using the safety working area characteristic data corresponding to the power semiconductor device and combining the combined state parameter to calculate the maximum allowed pulse current and the maximum allowed continuous current in the next control period; Combining the maximum allowed pulse current and the maximum allowed continuous current, the dynamic safety working boundary is dynamically calculated and adaptively generated.

5. The method of claim 4, wherein, It also includes: When the real-time junction temperature is low, the current limit defined by the dynamic safety working boundary is relaxed to obtain the dynamic safety working boundary with improved transient support capability; When the real-time junction temperature rises, the current limit defined by the dynamic safety working boundary is smoothly tightened to generate a dynamic safety working boundary that guarantees the operation safety.

6. The method of claim 1, wherein, Generating the ideal transient support instruction comprises: Abnormal detection of the power grid voltage or current to identify the type, amplitude and duration of the transient event; According to the response requirements of the power grid support guide for transient events, the ideal transient support instruction is generated.

7. The method of claim 6, wherein, According to the response requirements of the power grid support guide for transient events comprises: According to the power response, current response or voltage response requirements specified in the power grid support guide, a corresponding relationship set of transient event type and ideal support strategy is constructed; According to the identified transient event type, amplitude and duration, the matching ideal support strategy is retrieved from the corresponding relationship set; According to the matching ideal support strategy, the instantaneous support current or voltage instruction that can meet the requirements of the power grid support guide is calculated and output, and the ideal transient support instruction is generated.

8. The method of claim 7, wherein, The method comprises the following steps: comparing the ideal transient support instruction with the current limit range defined by the dynamic safety working boundary to obtain a judgment result of whether the ideal transient support instruction exceeds the boundary; if the judgment result is that the ideal transient support instruction does not exceed the boundary, the ideal transient support instruction is taken as the adaptive transient support instruction; if the judgment result is that the ideal transient support instruction exceeds the boundary, an instruction excess margin is obtained according to the difference between the ideal transient support instruction and the dynamic safety working boundary, and the amplitude or the change rate of the ideal transient support instruction is actively adjusted based on the instruction excess margin to generate the adaptive transient support instruction.

9. The method of claim 8, wherein, The active adjustment of the amplitude or the change rate of the ideal transient support instruction comprises the following steps: when it is judged that the ideal transient support instruction exceeds the dynamic safety working boundary, the change rate of the ideal transient support instruction is preferentially adjusted to generate an intermediate support instruction with limited waveform slope; if the peak value of the intermediate support instruction is still outside the dynamic safety working boundary, the amplitude of the intermediate support instruction is further reduced to obtain the adaptive transient support instruction.

10. A protection demand based converter transient voltage active support system applied to a protection demand based converter transient voltage active support method according to any one of claims 1-9, characterized in that, The system comprises: a thermal stress real-time monitoring module for obtaining an instantaneous electric stress parameter of the converter and combining a thermal response relationship of the power semiconductor device to obtain a real-time thermal stress state of the power semiconductor device inside the converter; a dynamic safety boundary generation module for fusing the instantaneous electric stress parameter and the real-time thermal stress state and combining safety working zone characteristic data of the power semiconductor device to dynamically calculate and adaptively generate the dynamic safety working boundary; a transient instruction decision module for obtaining grid transient information, identifying a transient event by detecting abnormal grid voltage or current and generating an ideal transient support instruction according to a grid support guideline; an adaptive instruction reconstruction module for constraining and reconstructing the ideal transient support instruction according to the dynamic safety working boundary, intelligently adjusting the amplitude or the change rate of the ideal transient support instruction based on a margin if the ideal transient support instruction exceeds the boundary to generate an adaptive transient support instruction that takes both operation safety and power quality improvement into consideration.

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