Converter transient voltage active support method based on protection demand

Abstract

The invention discloses a converter transient voltage active support method based on a protection demand, and belongs to the technical field of power electronics, and the method comprises the steps: obtaining an instantaneous electric stress parameter of a converter, and obtaining a real-time thermal stress state in combination with a thermal response relation of a power semiconductor device; fusing the electric stress parameter and the thermal stress state, and combining the characteristic data of the safe working area to generate a dynamic safe working boundary; meanwhile, transient information of the power grid is detected, and an ideal transient supporting instruction is generated according to the supporting guide rule; and according to the boundary, constraining and reconstructing the instruction, and generating an adaptive transient support instruction by intelligently adjusting the amplitude or change rate of the instruction. According to the method, the electric thermal stress state of the power semiconductor device is sensed in real time to dynamically generate the safe working boundary, intelligent constraint and reconstruction are carried out on the ideal supporting instruction following the power grid guide rule according to the boundary, and the operation safety and reliability of equipment can be ensured while the transient supporting capacity of the converter can be exerted to the maximum extent.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method for actively supporting transient voltage of converters based on protection requirements. Background Technology

[0002] Converters, as key power electronic devices, play a vital role in modern power systems and are widely used in areas such as new energy grid integration, flexible DC transmission, and power quality management. Their core function is to convert and control electrical energy. With the increasing penetration of power electronic equipment in the power grid, converters are required not only to perform basic power transmission tasks but also to proactively provide transient voltage support during grid faults or disturbances, thereby enhancing the stability and resilience of the power grid.

[0003] In existing technologies, to ensure the safe operation of converters during transient processes, a protection strategy based on fixed thresholds is typically employed. The control system presets one or more static current limits, which are usually determined based on the rated parameters of the power semiconductor devices under the worst-case operating conditions, with a significant margin. When a grid transient event triggers a support demand, if the support current command calculated by the controller exceeds this preset limit, the protection logic will immediately activate. This typically involves forcibly clamping the current command to the limit, or, in more severe cases, directly blocking the converter's pulse output, disconnecting it from the grid.

[0004] Existing technical solutions have significant technical flaws. First, the fixed protection threshold set based on worst-case conditions is too conservative, resulting in a serious waste of the converter's actual carrying capacity under most non-extreme conditions, thus greatly reducing its transient support capability. Second, this protection strategy lacks awareness of the actual operating state of power semiconductor devices, failing to distinguish between short-term, tolerable current pulses and continuous overcurrents that could cause thermal damage, leading to a rather crude protection action. Simple current clamping methods may result in unsatisfactory support effects, while direct grid disconnection would exacerbate power imbalances in the grid, contradicting the original intention of providing transient support. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides an active transient voltage support method for converters based on protection requirements. This method employs real-time sensing of the electrothermal stress state of power semiconductor devices to dynamically generate a safe operating boundary. Based on this boundary, it intelligently constrains and reconstructs ideal support commands that comply with power grid guidelines. This approach can maximize the transient support capability of the converter while ensuring the operational safety and reliability of the equipment itself.

[0006] The above objectives can be achieved through the following approach: A method for proactive transient voltage support of converters based on protection requirements includes: acquiring instantaneous electrical stress parameters of the converter and combining them with the thermal response relationship of power semiconductor devices to obtain the real-time thermal stress state; fusing the instantaneous electrical stress parameters and the real-time thermal stress state, and combining the safe operating area characteristic data of the power semiconductor devices, to dynamically calculate and adaptively generate a dynamic safe operating boundary; acquiring grid transient information, identifying transient events by detecting grid voltage or current anomalies, and generating ideal transient support commands based on grid support guidelines; constraining and reconstructing the ideal transient support commands based on the dynamic safe operating boundary; if the ideal transient support commands exceed the boundary, intelligently adjusting their amplitude or rate of change based on margin to generate adaptive transient support commands that balance operational safety and improve power quality.

[0007] Optionally, obtaining the real-time thermal stress state includes: real-time monitoring of the instantaneous current flowing through the power semiconductor device and the DC-side voltage of the converter to obtain instantaneous electrical stress parameters; based on the instantaneous electrical stress parameters and combined with the thermal response relationship of the power semiconductor device, calculating the real-time junction temperature and its corresponding thermal stress quantification index to obtain the real-time thermal stress state.

[0008] Optionally, calculating the real-time junction temperature and its corresponding thermal stress quantification index includes: obtaining thermal characteristic data of power semiconductor devices under different operating conditions through offline experiments or simulations; fitting and calibrating the thermal response relationship structural parameters based on the thermal characteristic data; and performing discrete recursive calculations based on the thermal response relationship structural parameters to obtain the real-time junction temperature and thermal stress quantification index.

[0009] Optionally, dynamically calculating and adaptively generating the dynamic safe operating boundary includes: extracting the DC-side voltage from the real-time junction temperature and instantaneous electrical stress parameters in the real-time thermal stress state to generate combined state parameters; using the safe operating area characteristic data corresponding to the power semiconductor device and combining it with the combined state parameters to calculate the maximum permissible pulse current and the maximum permissible continuous current in the next control cycle; and combining the maximum permissible pulse current and the maximum permissible continuous current to dynamically calculate and adaptively generate the dynamic safe operating boundary.

[0010] Optionally, the method further includes: when the real-time junction temperature is low, relaxing the current limit defined by the dynamic safe operating boundary to obtain a dynamic safe operating boundary that enhances transient support capability; when the real-time junction temperature rises, smoothly tightening the current limit defined by the dynamic safe operating boundary to generate a dynamic safe operating boundary that ensures operational safety.

[0011] Optionally, generating ideal transient support instructions includes: detecting anomalies in grid voltage or current, identifying the type, magnitude, and duration of transient events, and generating ideal transient support instructions based on the response requirements for transient events in the grid support guidelines.

[0012] Optionally, the response requirements for transient events in the power grid support guidelines include: constructing a set of correspondences between transient event types and ideal support strategies based on the power response, current response, or voltage response requirements specified in the power grid support guidelines; retrieving a matching ideal support strategy from the set of correspondences based on the identified transient event type, amplitude, and duration; and calculating and outputting an instantaneous support current or voltage command that meets the requirements of the power grid support guidelines based on the matching ideal support strategy, thereby generating an ideal transient support command.

[0013] Optionally, constraining and reconstructing the ideal transient support command based on the dynamic safety operating boundary includes: comparing the ideal transient support command with the current limit range defined by the dynamic safety operating boundary to obtain a judgment result of exceeding the boundary; if the judgment result of exceeding the boundary is not exceeded, the ideal transient support command is used as an adaptive transient support command; if the judgment result of exceeding the boundary is exceeded, the command exceedance margin is obtained based on 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 exceedance margin to generate an adaptive transient support command.

[0014] Optionally, actively adjusting the amplitude or rate of change of the ideal transient support command includes: when it is determined that the ideal transient support command exceeds the dynamic safety working boundary, prioritizing the adjustment of the rate of change of the ideal transient support command to generate an intermediate support command with a limited waveform slope; if the peak value of the intermediate support command is still outside the dynamic safety working boundary, further reducing the amplitude of the intermediate support command to obtain an adaptive transient support command.

[0015] Based on the same inventive concept, this invention also provides an active transient voltage support system for converters based on protection requirements. The system includes: a real-time thermal stress monitoring module, used to acquire the instantaneous electrical stress parameters of the converter and, combined with the thermal response relationship of the power semiconductor devices, obtain the real-time thermal stress state of the power semiconductor devices inside the converter; a dynamic safety boundary generation module, used to fuse the instantaneous electrical stress parameters and the real-time thermal stress state, and, combined with the safe operating area characteristic data of the power semiconductor devices, dynamically calculate and adaptively generate a dynamic safe operating boundary; a transient command decision module, used to acquire grid transient information, identify transient events by detecting grid voltage or current anomalies, and generate ideal transient support commands according to grid support guidelines; and an adaptive command reconstruction module, used to constrain and reconstruct the ideal transient support commands based on the dynamic safe operating boundary. If the ideal transient support commands exceed the boundary, the amplitude or rate of change is intelligently adjusted based on the margin to generate adaptive transient support commands that balance operational safety and improve power quality.

[0016] Compared with the prior art, the present invention has the following advantages: This invention dynamically assesses the real-time status of the power semiconductor devices inside the converter and adaptively adjusts the transient support strategy based on grid support requirements. This improves grid transient stability while ensuring the converter's own operational safety. Compared to traditional methods using fixed protection thresholds, this invention dynamically adjusts the safety boundary based on the device's real-time thermal margin. When devices are at low temperatures or under light loads, it allows the converter to output larger transient currents to provide stronger grid support, fully utilizing the device's potential.

[0017] This invention proposes a hierarchical instruction reconfiguration mechanism that prioritizes adjusting the rate of change of instructions rather than directly reducing their amplitude when the ideal support instruction exceeds the safety boundary. This smoothing approach effectively reduces the dynamic stress caused by current surges to power semiconductor devices, improving the stability and reliability of equipment operation. Only when the safety constraints cannot be met after adjusting the rate of change is the amplitude limited, achieving more refined and user-friendly protection for the equipment.

[0018] This invention achieves accurate estimation of key internal parameters of power semiconductor devices, namely real-time junction temperature, by constructing a high-precision device thermal model and performing online recursive calculations. This is equivalent to equipping the converter with an invisible internal state "sensor." This precise perception based on real physical states provides a reliable basis for the subsequent generation of dynamic safety boundaries and adaptive control, fundamentally improving the scientific nature and effectiveness of protection strategies.

[0019] The control strategy of this invention is always based on the grid support guidelines to ensure the compliance and effectiveness of its proactive support behavior. By intelligently integrating external grid demand with internal safety constraints, this method ensures that the converter will not endanger its own safety due to blind response while fulfilling its grid support obligations, thus achieving an optimal dynamic balance between effective grid support and equipment self-protection.

[0020] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1This is a flowchart illustrating an active support method for transient voltage of a converter based on protection requirements, according to an embodiment of the present invention.

[0023] Figure 2 This is a dynamic safety working boundary characteristic diagram of an embodiment of the present invention.

[0024] Figure 3 This is the corresponding distribution law of the maximum permissible continuous current in the embodiments of the present invention.

[0025] Figure 4 This is a timing diagram of adaptive transient support instruction reconstruction according to an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the structure of an active support system for transient voltage of a converter based on protection requirements, according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Reference Figure 1 One embodiment of the present invention proposes an active support method for transient voltage of converters based on protection requirements. It adopts real-time sensing of the electrothermal stress state of power semiconductor devices to dynamically generate a safe operating boundary, and intelligently constrains and reconstructs the ideal support command that follows the grid guidelines based on the boundary. This method can maximize the transient support capability of the converter while ensuring the operational safety and reliability of the equipment itself.

[0029] The method in this embodiment specifically includes: The instantaneous electrical stress parameters of the converter are obtained, and the real-time thermal stress state is obtained by combining the thermal response relationship of power semiconductor devices. By integrating instantaneous electrical stress parameters and real-time thermal stress state, and combining the safe operating area characteristic data of power semiconductor devices, dynamic safe operating boundaries are dynamically calculated and adaptively generated. Acquire power grid transient information, identify transient events by detecting abnormal power grid voltage or current, and generate ideal transient support instructions based on power grid support guidelines; 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.

[0030] 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.

[0031] The real-time thermal stress state is obtained including: 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; 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.

[0032] 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 values ​​are calculated. Then, combined with the pre-established thermal response relationship of power semiconductor devices and the instantaneous total loss calculated in real time, the junction temperature of the device is estimated in real time. Finally, the calculated real-time junction temperature is selectively combined with derived indicators such as the junction temperature change rate to form a thermal stress quantification index, thereby comprehensively characterizing the real-time thermal stress state of the power semiconductor device. This method not only provides key, real-time state input for the subsequent generation of dynamic safe operating boundaries, ensuring strict adherence to the thermal limits of the device during transient support, but also enables the converter to fully utilize its transient support potential based on the actual thermal margin while ensuring safety. This improves the transient stability of the power grid while ensuring the operational safety and long-term reliability of the equipment itself.

[0033] The calculation of real-time junction temperature and its corresponding thermal stress quantification index includes: Offline experiments or simulations are used to obtain thermal characteristic data of power semiconductor devices under different operating conditions. Based on thermal property data, the structural parameters of the thermal response relationship are obtained by fitting and calibrating. Discrete recursive calculations were performed based on the thermal response relationship structural parameters to obtain real-time junction temperature and thermal stress quantitative indicators.

[0034] To calculate the real-time junction temperature and its corresponding thermal stress quantification, an accurate device thermal model must first be established through offline work. This stage involves offline experiments on a dedicated power cycling test platform or refined electrothermal coupling simulations using finite element analysis software, with the aim of obtaining thermal characteristic data for the target power semiconductor device. Specifically, a known step power loss is applied to the device, and its junction temperature response curve over time is accurately measured or simulated. This curve represents the device's transient thermal impedance curve, constituting the core thermal characteristic data. Next, based on this acquired transient thermal impedance curve, model fitting is performed, and the structural parameters of the thermal response relationship are calibrated. An equivalent thermal network model, such as a Foster network or Cauer network, is typically used to mathematically describe the dynamic heat transfer process from the junction to the case. Mathematically, this thermal response relationship is expressed as the sum of multiple exponential terms. Numerical optimization algorithms, such as nonlinear least squares, are used to fit the experimentally or simulated transient thermal impedance curve to the mathematical expression of the equivalent thermal network model, thereby identifying various thermal resistances and capacities in the model. These identified thermal resistances R... th,i and heat capacity C th,i The combination of these parameters constitutes the thermal response structure parameters. Finally, during online operation of the converter, based on the thermal response structure parameters obtained in the previous step, the continuous-time thermal model is discretized and converted into a discrete recursive calculation suitable for execution in a digital controller. For example, for an nth-order Foster network model, the discrete recursive calculation of its junction temperature can be expressed as:

[0035] Where Δt is the calculation period of the control system; P loss [k-1] is the instantaneous total power semiconductor device loss calculated in the previous cycle; R th,i With τ i These are the thermal resistance and thermal time constant of the i-th order equivalent heat network, respectively; these are all structural parameters of the calibrated thermal response relationship; ΔT i [k] represents the temperature rise of the i-th order thermal network in the current period k; T c [k] is the device casing or heatsink temperature measured in real time by a sensor. By iteratively performing this recursive calculation in each control cycle, the real-time junction temperature T, which changes dynamically over time, can be obtained. j [k]. The real-time junction temperature T j [k], as the most important quantitative indicator characterizing the internal thermal stress level of a device, is a core element constituting a comprehensive thermal stress state characterization. This method constructs a high-precision "virtual junction temperature sensor," overcoming the difficulties of physical sensors being unable to directly measure junction temperature, high cost, and low reliability.

[0036] Dynamically calculating and adaptively generating dynamic safety working boundaries includes: Extract the DC-side voltage from the real-time junction temperature and instantaneous electrical stress parameters in the real-time thermal stress state to generate combined state parameters; By utilizing the safe operating area characteristic data corresponding to power semiconductor devices and combining them with combined state parameters, the maximum permissible pulse current and the maximum permissible continuous current in the next control cycle are calculated. The maximum permissible pulse current and the maximum permissible continuous current are combined to dynamically calculate and adaptively generate dynamic safe operating boundaries.

[0037] First, the real-time junction temperature T of the core is extracted from the real-time thermal stress state. j And extract the DC side voltage V from the instantaneous electrical stress parameters. dc These two parameters together constitute the combined state parameters characterizing the current operating state of a power semiconductor device, where the real-time junction temperature T... j This reflects the internal thermal margin of the device, while the DC side voltage V dcThis 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.

[0038] The method also includes: When the real-time junction temperature is low, the current limit defined by the dynamic safe operating boundary is relaxed to obtain a dynamic safe operating boundary that improves transient support capability. When the real-time junction temperature rises, the current limit defined by the dynamic safety operating boundary is smoothly tightened to generate a dynamic safety operating boundary that ensures safe operation.

[0039] The core of this adjustment mechanism lies in establishing a negative correlation function between the current limit and the real-time junction temperature to dynamically balance transient support capability and operational safety. When the converter is operating under light load, in low ambient temperature, or in the early stages of a transient event, the real-time junction temperature T obtained through the real-time monitoring module... j It will be at a relatively low level. At this point, the power semiconductor device is close to its maximum allowable junction temperature T. j，max A significant thermal margin exists. The control algorithm utilizes this thermal margin to relax the dynamic safety operating boundaries. Specifically, in calculating the maximum permissible pulse current... and maximum allowable continuous current In this case, a gain function or lookup table positively correlated with the thermal margin is used. For example, a function of the following form can be used to correct the reference current limit to obtain a relaxed current limit:

[0040] in, This is the adjusted current limit. It is a baseline limit based on a reference temperature, while f(T) j,max -T j ) is a variable with heat margin (T) j,max -T j The function increases monotonically. This generates a dynamic safe operating boundary with a higher current upper limit, allowing the converter to legally output larger transient currents when the grid requires strong support, thus achieving a dynamic safe operating boundary that enhances transient support capabilities. Conversely, when the converter undergoes prolonged heavy-load operation, or when the junction temperature continues to rise due to large output current during transient support, the real-time junction temperature T... j As the device approaches its safety threshold, the thermal margin decreases accordingly. To prevent damage from overheating, the control algorithm smoothly tightens the current limit defined by the dynamic safe operating boundary. This tightening process is also achieved through the aforementioned functional relationship, but at this time, due to T... j As the temperature rises, the heat margin decreases, and the output value of function f also decreases, thus affecting the calculated value. The corresponding reduction is achieved. To ensure control stability, this tightening process is smooth and continuous, avoiding abrupt changes in the current limit. In this way, the range of the dynamic safe operating boundary is actively narrowed, creating stronger constraints on the ideal transient support command, prioritizing the protection of power semiconductor devices from exceeding their thermal limits, and generating a dynamic safe operating boundary that ensures safe operation. This adaptive mechanism enables in-depth exploration and refined utilization of the potential of power semiconductor devices, significantly enhancing the converter's support capability and flexibility in responding to grid transient events without sacrificing long-term system reliability.

[0041] The instructions for generating ideal transient support include: Detect anomalies in grid voltage or current, and identify the type, magnitude, and duration of transient events; Based on the response requirements for transient events in the power grid support guidelines, generate ideal transient support instructions.

[0042] The first step is the detection and identification of transient events. High-speed sampling and data processing units configured at the converter grid connection point continuously monitor the waveforms of grid voltage or current. When the monitored instantaneous voltage or current value, or its calculated characteristic quantity, such as the effective voltage value or frequency, deviates from the normal operating range and exceeds a certain threshold, anomaly detection is triggered. Once an anomaly is detected, the transient event is immediately characterized and identified to determine its key parameters, including the type of transient event (e.g., voltage dip, voltage swell, or frequency disturbance); the amplitude of the transient event (e.g., the depth of the voltage dip); and the duration of the transient event, recorded by a timer from the start of the event. The second step is the generation of specific support instructions based on grid support guidelines. These guidelines, issued by grid operators, stipulate the support obligations that grid-connected equipment must fulfill when grid disturbances occur, such as low-voltage ride-through (LVRT) or high-voltage ride-through (HVRT) requirements. This method first digitizes and logically organizes these guidelines to form a pre-built rule base. Once a transient event is identified, a corresponding response strategy is matched against the rule base based on its type, amplitude, and duration, thereby calculating and generating an ideal transient support command. This method provides a clear and explicit control objective for subsequent control processes, making the converter's transient support behavior purposeful and compliant. It transforms complex power grid regulations into specific, executable electrical commands, serving as a crucial foundation for the decision-making level in the entire active support method.

[0043] The response requirements for transient events in the power grid support guidelines include: Based on the power response, current response, or voltage response requirements specified in the power grid support guidelines, construct a set of correspondences between transient event types and ideal support strategies; Based on the identified transient event types, amplitudes, and durations, a matching ideal support strategy is retrieved from the corresponding relationship set; Based on the matching ideal support strategy, calculate and output the instantaneous support current or voltage command that meets the requirements of the power grid support guidelines, and generate the ideal transient support command.

[0044] First, during the design and configuration phase, the support guidelines for the target power grid need to be comprehensively analyzed and structured to construct a set of correspondences between transient event types and ideal support strategies. This set is a pre-built rule base or multidimensional lookup table stored in the controller's memory. Its construction process involves mapping various transient events specified in the guidelines, such as voltage dips or swells of different depths and durations, to corresponding response requirements, such as specific strategies for power response, current response, or voltage response. For example, a mapping entry might be defined as "When the voltage dips to 50% to 90% of the rated value, dynamic reactive current support must be implemented, and the support current amplitude is proportional to the voltage dip depth." Second, during the real-time operation of the converter, once the type, amplitude, and duration of a transient event are identified, these parameters are immediately used as indexes for rapid retrieval within the constructed set of correspondences. This retrieval operation accurately matches the ideal support strategy corresponding to the current transient event. This strategy not only specifies the response type to be taken, such as injecting reactive current, but also includes the specific parameters and calculation methods required to implement the strategy. Finally, based on the retrieved ideal support strategy, specific calculations are performed to generate the ideal transient support command. For example, if the matched strategy is "linearly inject reactive current based on voltage dip depth," a preset calculation formula will be invoked, and real-time monitored grid parameters will be substituted to calculate the command value. A typical reactive current support command calculation formula is shown below:

[0045] in, It is the calculated ideal transient support command, specifically the reference value of instantaneous reactive current; K is the reactive power support gain coefficient, whose value is directly specified by the retrieved ideal support strategy and derived from the power grid support guidelines; I N This is the rated current of the converter, an inherent parameter of the equipment; V th It is the voltage threshold for starting reactive power support, also defined by the guidelines; V gThis refers to the real-time detected grid voltage amplitude. The instantaneous support current or voltage command calculated from this is the ideal transient support command that fully complies with grid regulations and aims to maximize grid benefits. This method establishes a clear, quantifiable, and regulatory-based initial target for the converter's transient response, thereby avoiding blind and arbitrary responses and providing a precise and idealized input benchmark for the subsequent command reconfiguration stage that considers equipment safety constraints.

[0046] Constraining and reconstructing the ideal transient support command based on the dynamic safety working boundary includes: The ideal transient support command is compared with the current limit range defined by the dynamic safe operating boundary to obtain the judgment result of exceeding the boundary; If the result of the boundary judgment is that it has not exceeded the boundary, the ideal transient support instruction will be used as the adaptive transient support instruction. If the boundary is exceeded, the instruction exceedance margin is obtained based on the difference between the ideal transient support instruction and the dynamic safety working boundary. Based on the instruction exceedance margin, the amplitude or rate of change of the ideal transient support instruction is actively adjusted to generate an adaptive transient support instruction.

[0047] First, the ideal transient support command is set with its amplitude. For example, a real-time comparison is performed with the current limit range defined by the dynamic safety operating boundary. This current limit range is typically defined by the maximum permissible pulse current. and maximum allowable continuous current Commonly defined, here using a comprehensive boundary value. This comparison process yields a clear result indicating whether the boundary has been exceeded. If the result indicates that the boundary has not been exceeded, then... The amplitude is Within the defined range, this indicates that the converter is fully capable of executing the ideal command in its current state without jeopardizing its own safety. In this case, without any modification, the ideal transient support command is directly output as the adaptive transient support command to the converter's inner loop controller for execution. If the boundary exceedance judgment result is "exceeding," it indicates that executing the ideal transient support command will cause the electrical or thermal stress of the power semiconductor devices to exceed their safety limits. At this time, the active adjustment mechanism is activated. First, the difference between the ideal transient support command and the dynamic safe operating boundary is calculated to obtain a quantified command exceedance margin ΔI, which is calculated as follows:

[0048] Where ΔI is the instruction overrun margin, which quantifies the degree to which an ideal instruction intrudes into the safety boundary; It is the amplitude of the ideal transient support command generated according to the power grid support guidelines; This is the current maximum permissible current limit calculated in real time by the dynamic safety operating boundary module. Then, based on this instruction exceedance margin ΔI, the amplitude or rate of change of the ideal transient support instruction is actively adjusted. For example, the most direct amplitude adjustment method is to clamp the instruction amplitude at the boundary value, that is, the adjusted instruction amplitude equals... Alternatively, the rate of change of the command can be adjusted, i.e., the rise speed of the command can be slowed down to make the command waveform smoother, thus avoiding excessive shocks in a short period of time. The new command generated after this intelligent adjustment is an adaptive transient support command that takes into account both operational safety and power quality improvement. This method does not simply and crudely cut off the support, but rather, through fine-tuning the command, it approaches the ideal support target as closely as possible while ensuring safety, achieving the optimal dynamic balance between operational safety and grid support benefits.

[0049] Active adjustment of the amplitude or rate of change of the ideal transient support command includes: When it is determined that the ideal transient support command exceeds the dynamic safety working boundary, the rate of change of the ideal transient support command is adjusted first to generate an intermediate support command with a limited waveform slope. If the peak value of the intermediate support command is still outside the dynamic safety working boundary, the amplitude of the intermediate support command is further reduced to obtain the adaptive transient support command.

[0050] This method further refines the proactive adjustment strategy when the ideal transient support command exceeds the dynamic safe operating boundary, employing a layered, gradual adjustment logic. When it is determined that the ideal transient support command exceeds the dynamic safe operating boundary, its amplitude is not immediately reduced; instead, the rate of change of the ideal transient support command is adjusted first. This operation is implemented through a rate limiter. This limiter sets a maximum permissible rate of change of current, dV / dt, related to the device's tolerance capability. max Ideal transient support instructions After input to the slope limiter, the output intermediate support command is... The following rules will be followed:

[0051] Here, and These are the intermediate support instructions for the current and previous control cycles, respectively. It is the ideal transient support instruction for the current cycle; dV / dt maxΔt is the set maximum allowable rate of change; Δt is the control period. Through this operation, even if the ideal command is a step change, the waveform of the actually generated intermediate support command will rise smoothly with a controlled slope, generating an intermediate support command with a slope-limited waveform. This step aims to mitigate rapid current surges, as some failure modes of power semiconductor devices are highly sensitive to the rate of current change. Subsequently, the peak value of this slope-limited intermediate support command is re-verified. The intermediate support command... peak Current limits defined by the dynamic safety operating boundary A comparison is made. If the peak value of the intermediate support command is still outside the dynamic safety operating boundary, that is... If this happens, a second-level adjustment is initiated, further reducing the amplitude of the intermediate support command. The most direct method is to hard-clamp the amplitude of the command, ensuring its maximum value does not exceed [a certain value]. The formula is as follows:

[0052] in, This results in the final generated adaptive transient support command. Through this two-step strategy of first adjusting the rate of change and then adjusting the amplitude, a safe-to-execute adaptive transient support command that satisfies both the rate of change and amplitude constraints is ultimately obtained. For example... Figure 4 As shown, the adaptive transient support command is obtained by adjusting the amplitude of the ideal command, ensuring that the dynamic safety working boundary constraints are met throughout the entire time domain, reflecting the command reconfiguration concept based on real-time thermal stress constraints. This hierarchical and progressive adjustment method, compared with a single amplitude current limiting, can retain the effective components of the ideal support command to a greater extent, achieving better utilization of transient support capabilities while ensuring absolute safety, making the entire support process smoother, more stable, and more efficient.

[0053] Based on the same inventive concept, such as Figure 5 As shown, the present invention also provides an active support system for transient voltage of a converter based on protection requirements, the system comprising: The real-time thermal stress monitoring module is used to acquire the instantaneous electrical stress parameters of the converter and, in combination with the thermal response relationship of the power semiconductor devices, obtain the real-time thermal stress state of the power semiconductor devices inside the converter. The dynamic safety boundary generation module is used to fuse instantaneous electrical stress parameters with real-time thermal stress state, and combine them with the safe operating area characteristic data of power semiconductor devices to dynamically calculate and adaptively generate dynamic safety operating boundaries. The transient command decision module is used to acquire power grid transient information, identify transient events by detecting abnormal power grid voltage or current, and generate ideal transient support commands based on power grid support guidelines. The adaptive instruction reconfiguration module is used to constrain and reconfigure the ideal transient support instruction based on the dynamic safety operating boundary. If the ideal transient support instruction exceeds the boundary, its amplitude or rate of change is intelligently adjusted based on the margin to generate an adaptive transient support instruction that takes into account both operational safety and power quality.

[0054] To verify the feasibility of this invention in practice, it was applied to the grid-connected converter system of a large photovoltaic power plant. To meet the transient voltage support requirements of the power grid, the grid-connected converter of this photovoltaic power plant must respond quickly and inject reactive current to support the grid voltage when transient events such as voltage dips occur. Traditional methods use a fixed overcurrent protection threshold, which is usually conservatively set to cope with the worst operating conditions. This results in the transient support capability of the converter being limited in most cases, preventing it from being fully utilized. This invention aims to solve this problem by dynamically adjusting the safety boundary to achieve the optimal balance between transient support capability and equipment operational safety.

[0055] In this embodiment, the 1MW grid-connected converter of the photovoltaic power station integrates the transient voltage active support system of this invention. The system's real-time thermal stress monitoring module monitors the instantaneous current and DC-side voltage of the power semiconductor device (IGBT) in real time using high-precision sensors, and obtains the real-time junction temperature T of the IGBT through discrete recursive calculation based on the offline-calibrated Foster thermal network model parameters. j The dynamic safety boundary generation module integrates real-time junction temperature T. j With DC side voltage V dc Furthermore, by combining the secure working area (SOA) characteristic data of the IGBT, a dynamic secure working boundary is generated in real time.

[0056] To verify the beneficial effects of this invention, two typical operating scenarios were selected for testing: Scenario 1 was a spring morning with low ambient temperature and the converter operating under light load; Scenario 2 was a summer afternoon with high ambient temperature and the converter operating near full load. In both scenarios, a voltage drop event lasting 200ms and with a depth of 50% was simulated in the power grid. The grid support guidelines require the converter to inject 1.2 times the rated current (1.2 pu) of reactive current during this period as an ideal transient support command.

[0057] In Scenario 1 (10:00 AM, April 10, 2025), the ambient temperature is 15℃, the converter load is light, and the real-time junction temperature T of the IGBT is measured. j The temperature is 65℃. At this temperature, the dynamic safety boundary generation module calculates the maximum allowable pulse current of the dynamic safety operating boundary based on sufficient thermal margin. The ideal transient support instruction generated by the transient instruction decision module is 1.4 PU. The ideal reactive current is 1.2 pu. The adaptive command reconfiguration module compares the two values ​​and determines that the ideal command does not exceed the safety boundary (1.2 pu < 1.4 pu). Therefore, it directly issues the ideal command as the adaptive transient support command, and the converter successfully outputs 1.2 pu of reactive current, effectively supporting the grid voltage.

[0058] In Scenario 2 (14:30 on June 22, 2025), the ambient temperature was 35℃, the sunlight was strong, and the converter was operating under heavy load for a long time. The real-time junction temperature T of the IGBT was measured. j The temperature has reached 115℃ (close to the maximum allowable junction temperature of 125℃). At this point, the dynamic safety boundary generation module smoothly tightens the dynamic safety operating boundary to a minimum based on a very small thermal margin. When a grid voltage dip occurs, the ideal transient support command... The amplitude remains at 1.2 pu. The adaptive instruction reconfiguration module determines that the ideal instruction exceeds the safety boundary (1.2 pu > 1.05 pu). The system then initiates an adjustment mechanism, prioritizing the limitation of the instruction's rate of change to generate a smooth intermediate support instruction. Subsequently, the peak value of this intermediate instruction is checked and found to still exceed the 1.05 pu safety boundary, so its amplitude is further clamped to 1.05 pu. Finally, the converter outputs an adaptive transient support instruction with an amplitude of 1.05 pu. Although this measure does not fully meet the ideal support requirements, it ensures that the IGBT junction temperature does not exceed the safety limit, preventing thermal damage to the equipment.

[0059] Comparative data shows that, using the method of this invention, the converter can "make the most of its capabilities" and provide strong transient support when the equipment is safe; while when the equipment is near danger, it can "act within its limits" and prioritize its own safety. This method significantly improves the converter's operational flexibility and overall reliability under different operating conditions.

[0060] Table 1. Data table for generating dynamic safety working boundaries time Ambient temperature (°C) Initial junction temperature Operating load (%) Dynamic security boundary 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 Table 2 Transient Event Response and Command Reconstruction Data Table Table 3 Comparison of Transient Support Effects of Different Methods As can be seen from the data recorded in Tables 1 to 3 above, the application effect of this invention in photovoltaic grid-connected converters is significant. Table 1 clearly shows how the dynamic safe operating boundary adaptively adjusts according to the real-time junction temperature changes caused by ambient temperature and load. When the junction temperature is low (65℃), the safe boundary is widened to 1.40 pu, while when the junction temperature is close to the limit (115℃), the boundary actively tightens to 1.05 pu, demonstrating the intelligent sensing capability of the system.

[0061] The data comparison in Tables 2 and 3 further demonstrates the superiority of this invention. In Scenario 1, this invention enables the converter to output a current as high as 1.20 pu, fully meeting the ideal support requirements of the power grid, while traditional fixed protection methods can only output 1.0 pu, resulting in a waste of support capacity. In Scenario 2, facing severe thermal stress, this invention, through intelligent command reconfiguration, limits the output current to 1.05 pu, precisely controlling the junction temperature peak within the safe limit of 125℃, successfully preventing equipment damage. This ability to maximize support benefits while ensuring safety is unparalleled by traditional fixed protection strategies, fully demonstrating the significant application value of this invention in improving the performance and reliability of new energy grid-connected equipment.

[0062] It should be noted that the electrical connections between the various units described above do not necessarily represent direct or indirect connections. Any indirect connection method can be applied to the embodiments of the present invention as long as it achieves the purpose of the present invention. The above are merely exemplary embodiments of the present invention and should not be construed as limiting the scope of the present invention.

[0063] All equivalent changes and modifications made in accordance with the teachings of this invention are still within the scope of this invention. Those skilled in the art will readily conceive of other embodiments of this invention upon considering the specification and the disclosure of practical truth. This application is intended to cover any variations, uses, or adaptations of this invention that follow the general principles of this invention and include common knowledge or conventional techniques in the art not described herein.

Claims

1. A method for actively supporting transient voltage in a converter based on protection requirements, characterized in that the method... include: The instantaneous electrical stress parameters of the converter are obtained, and the real-time thermal stress state is obtained by combining the thermal response relationship of power semiconductor devices. By integrating instantaneous electrical stress parameters and real-time thermal stress state, and combining the safe operating area characteristic data of power semiconductor devices, dynamic safe operating boundaries are dynamically calculated and adaptively generated. Acquire power grid transient information, identify transient events by detecting abnormal power grid voltage or current, and generate ideal transient support instructions based on power grid support guidelines; 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.

2. The active support method for transient voltage of a converter based on protection requirements according to claim 1, characterized in that, The real-time thermal stress state is obtained including: 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; 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.

3. The active support method for transient voltage of a converter based on protection requirements according to claim 2, characterized in that, The calculation of real-time junction temperature and its corresponding thermal stress quantification index includes: Offline experiments or simulations are used to obtain thermal characteristic data of power semiconductor devices under different operating conditions. Based on thermal property data, the structural parameters of the thermal response relationship are obtained by fitting and calibrating. Discrete recursive calculations were performed based on the thermal response relationship structural parameters to obtain real-time junction temperature and thermal stress quantitative indicators.

4. The active support method for transient voltage of a converter based on protection requirements according to claim 3, characterized in that, Dynamically calculating and adaptively generating dynamic safety working boundaries includes: Extract the DC-side voltage from the real-time junction temperature and instantaneous electrical stress parameters in the real-time thermal stress state to generate combined state parameters; By utilizing the safe operating area characteristic data corresponding to power semiconductor devices and combining them with combined state parameters, the maximum permissible pulse current and the maximum permissible continuous current in the next control cycle are calculated. The maximum permissible pulse current and the maximum permissible continuous current are combined to dynamically calculate and adaptively generate dynamic safe operating boundaries.

5. The active support method for transient voltage of a converter based on protection requirements according to claim 4, characterized in that, Also includes: When the real-time junction temperature is low, the current limit defined by the dynamic safe operating boundary is relaxed to obtain a dynamic safe operating boundary that improves transient support capability. When the real-time junction temperature rises, the current limit defined by the dynamic safety operating boundary is smoothly tightened to generate a dynamic safety operating boundary that ensures safe operation.

6. The active support method for transient voltage of a converter based on protection requirements according to claim 1, characterized in that, The instructions for generating ideal transient support include: Detect anomalies in grid voltage or current, and identify the type, magnitude, and duration of transient events; Based on the response requirements for transient events in the power grid support guidelines, generate ideal transient support instructions.

7. A method for active support of transient voltage in a converter based on protection requirements, as described in claim 6, is characterized in that, The response requirements for transient events in the power grid support guidelines include: Based on the power response, current response, or voltage response requirements specified in the power grid support guidelines, construct a set of correspondences between transient event types and ideal support strategies; Based on the identified transient event types, amplitudes, and durations, a matching ideal support strategy is retrieved from the corresponding relationship set; Based on the matching ideal support strategy, calculate and output the instantaneous support current or voltage command that meets the requirements of the power grid support guidelines, and generate the ideal transient support command.

8. The active support method for transient voltage of a converter based on protection requirements according to claim 7, characterized in that, Constraining and reconstructing the ideal transient support command based on the dynamic safety working boundary includes: The ideal transient support command is compared with the current limit range defined by the dynamic safe operating boundary to obtain the judgment result of exceeding the boundary; If the result of the boundary judgment is that it has not exceeded the boundary, the ideal transient support instruction will be used as the adaptive transient support instruction. If the boundary is exceeded, the instruction exceedance margin is obtained based on the difference between the ideal transient support instruction and the dynamic safety working boundary. Based on the instruction exceedance margin, the amplitude or rate of change of the ideal transient support instruction is actively adjusted to generate an adaptive transient support instruction.

9. A method for actively supporting transient voltage of a converter based on protection requirements, as described in claim 8, is characterized in that, Active adjustment of the amplitude or rate of change of the ideal transient support command includes: When it is determined that the ideal transient support command exceeds the dynamic safety working boundary, the rate of change of the ideal transient support command is adjusted first to generate an intermediate support command with a limited waveform slope. If the peak value of the intermediate support command is still outside the dynamic safety working boundary, the amplitude of the intermediate support command is further reduced to obtain the adaptive transient support command.

10. A converter transient voltage active support system based on protection requirements, applied to the converter transient voltage active support method based on protection requirements as described in any one of claims 1-9, characterized in that, The system includes: The real-time thermal stress monitoring module is used to acquire the instantaneous electrical stress parameters of the converter and, in combination with the thermal response relationship of the power semiconductor devices, obtain the real-time thermal stress state of the power semiconductor devices inside the converter. The dynamic safety boundary generation module is used to fuse instantaneous electrical stress parameters with real-time thermal stress state, and combine them with the safe operating area characteristic data of power semiconductor devices to dynamically calculate and adaptively generate dynamic safety operating boundaries. The transient command decision module is used to acquire power grid transient information, identify transient events by detecting abnormal power grid voltage or current, and generate ideal transient support commands based on power grid support guidelines. The adaptive instruction reconfiguration module is used to constrain and reconfigure the ideal transient support instruction based on the dynamic safety operating boundary. If the ideal transient support instruction exceeds the boundary, its amplitude or rate of change is intelligently adjusted based on the margin to generate an adaptive transient support instruction that takes into account both operational safety and power quality.

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