A method for optimizing loss of CLCC main and auxiliary branches and commutation transient characteristics

Abstract

The application relates to a CLCC main and auxiliary branch loss and commutation transient characteristic cooperative optimization method, which comprises the following steps: firstly, a time-varying transient loss model of the main and auxiliary branches is established based on commutation transient characteristics, and the multi-dimensional loss distribution of a device is quantified in real time; secondly, a safety operation boundary is defined by multi-dimensional indexes such as commutation voltage time integral and current transfer rate, and a multi-dimensional safety constraint system of the commutation transient trajectory is constructed; subsequently, a double-layer cooperative optimization solving model is built, and the optimal control parameters and the number of device series are iteratively solved by an adaptive particle swarm algorithm; on this basis, the IGBT switching time sequence and the current distribution proportion are dynamically fine-tuned by using a closed-loop feedback control, and an adaptive switching control strategy is executed. Finally, through electromagnetic transient simulation verification and feedback correction, the adaptive cooperative optimization of loss optimization and transient safety is realized. The application can effectively inhibit commutation failure, reduce system loss and improve operation reliability.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission technology, and in particular to a method for synergistic optimization of losses and commutation transient characteristics of CLCC main and auxiliary branches. Background Technology

[0002] In recent years, ultra-high voltage direct current (UHVDC) transmission projects have formed a hybrid AC / DC power grid characterized by long distances, large capacity, multiple infeeds, and strong interconnection. Controllable commutator converters (CLCCs), as a new generation of inverter-side converter technology, adopt a hybrid topology of thyristor main branch + IGBT auxiliary branch. This effectively combines the advantages of traditional grid commutator converters (LCCs)—high current carrying capacity, low steady-state loss, and economical cost—with the characteristics of voltage source converters (VSCs)—autonomous turn-off, active commutation voltage construction, and rapid disturbance suppression. It can suppress commutation failure caused by AC voltage drops on the inverter side from a mechanistic perspective, significantly improving the operational safety margin of the receiving-end power grid.

[0003] In steady-state operation, the CLCC's main branch thyristors carry the full rated current, while the auxiliary branch remains blocked to reduce losses. During commutation transients or AC faults, the auxiliary branch IGBTs quickly engage, actively transferring the commutation current and forcing the thyristors to recover their blocking capability early, thus completing reliable commutation. Because the main and auxiliary branches differ significantly in current carrying capacity, switching frequency, voltage stress, dynamic response, and junction temperature characteristics, their loss distribution is strongly coupled with the commutation transient process: the commutation current transfer rate, IGBT switching timing, and voltage settling rate directly determine the device losses, while the loss distribution affects junction temperature, device lifespan, and system operating efficiency.

[0004] Current CLCC converter valve design and control methods have significant limitations: loss calculations often rely on simple superposition of steady-state rated parameters, failing to consider transient additional losses caused by current redistribution, voltage surges, and junction temperature fluctuations during commutation; commutation transient control focuses solely on suppressing commutation failures, neglecting loss costs and lifetime degradation; the switching sequence of main and auxiliary branches is fixed and cannot be adaptively adjusted according to grid conditions; and a unified collaborative optimization framework for loss, transient, lifetime, and economy has not yet been established, making it difficult to achieve global optimization of safety and efficiency.

[0005] Patent CN120728693B discloses a method for designing and optimizing the capacity and parameters of CLCC auxiliary branches based on the needs of power grid applications. First, based on the operating characteristics of DC transmission systems, a capacity matching model for the main and auxiliary branches is established. Then, by optimizing the switching time of the main and auxiliary branches of the converter valve, the overall loss of the converter valve is reduced, improving the reliability of the commutation process. Subsequently, a loss calculation and economic evaluation model is introduced to quantitatively analyze the overall benefits of CLCC, and system verification is performed using electromagnetic simulation to ensure that the optimized converter valve can effectively prevent commutation failure under various fault conditions. However, this method only calculates steady-state and maintenance losses based on fixed rated parameters, and the commutation control lacks adaptive adjustment capabilities for multi-dimensional safety boundaries. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for adaptively optimizing the losses and commutation transient characteristics of CLCC main and auxiliary branches by constructing a transient loss mathematical model and a multi-dimensional safety constraint system for two-level iterative solution, and combining real-time closed-loop feedback control and simulation verification correction.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for synergistic optimization of losses and commutation transient characteristics in CLCC main and auxiliary branches includes the following steps: Based on the characteristics of current transfer, voltage change and junction temperature dynamic change during commutation, time-varying transient loss models of the thyristor main branch and IGBT auxiliary branch are established respectively to quantify the conduction loss, dynamic switching loss and transient additional loss of each device in real time during the entire commutation process. The commutation safety operation boundary is defined with commutation voltage time integral, current transfer rate, real-time commutation margin, transient voltage overshoot and device junction temperature as the core, and a multi-dimensional safety constraint system for commutation transient trajectory is established. A two-layer collaborative optimization solution model is constructed. The time-varying transient loss model is used as the loss calculation basis for the objective function of minimizing the total cost of the entire life cycle in the upper layer optimization. The multi-dimensional safety constraint system of the commutation transient trajectory is used as the hard constraint boundary in the lower layer optimization. The optimal switching timing, optimal current distribution coefficient, and optimal number of devices connected in series that satisfy the hard constraint boundary are solved iteratively by the adaptive particle swarm algorithm. Using the optimal switching timing and optimal current distribution coefficient as the control benchmark, and combining the real-time collected AC bus voltage, DC current, device junction temperature and commutation margin, an adaptive main and auxiliary branch switching control strategy is executed. Closed-loop feedback control is used to dynamically adjust the IGBT turn-on delay, turn-off delay and main and auxiliary branch current distribution ratio. A CLCC model incorporating loss calculation, junction temperature simulation, and commutation trajectory monitoring is built in electromagnetic transient simulation software. The optimal number of connected devices, dynamically adjusted IGBT turn-on delay, turn-off delay, and main / auxiliary branch current distribution ratio are input into the CLCC model for multi-condition electromagnetic transient simulation verification. The actual loss data and actual transient trajectory data obtained from the simulation verification are fed back to the two-layer collaborative optimization solution model for sensitivity verification. Based on this, the optimal switching timing and current distribution coefficients are corrected until the simulation verification results simultaneously satisfy the goal of minimizing the total cost over the entire life cycle and the multi-dimensional safety constraint system of the commutation transient trajectory, thereby achieving the collaborative optimization of the CLCC main / auxiliary branch losses and commutation transient characteristics.

[0008] Furthermore, the expression for the time-varying transient loss model of the thyristor main branch is as follows: Among them, V T0 This refers to the thyristor threshold voltage, measured in volts; i Th (t) represents the real-time transient current of the thyristor, in amperes; r T (T j ΔP represents the junction temperature-dependent dynamic on-state resistance of the thyristor, in ohms; Th (t) represents the transient additional loss during commutation, in watts.

[0009] Furthermore, the expression for the thyristor junction temperature-dependent dynamic on-state resistance is as follows: in, The on-state resistance at room temperature; It is the temperature coefficient of resistance; For real-time junction temperature; This is the reference junction temperature.

[0010] Furthermore, the expression for the commutation transient additional loss is: Where, k γ γ(t) is the loss coefficient due to commutation margin variation; γ(t) is the real-time commutation margin angle, i Th (t) represents the real-time transient current of the thyristor.

[0011] Furthermore, the expression for the time-varying transient loss model of the IGBT auxiliary branch is as follows: Among them, V CE (T j ) represents the junction temperature-dependent saturation voltage drop of the IGBT, in volts; i IGBT (t) represents the real-time current of the IGBT, in amperes; rCE (T j ΔP represents the junction temperature-dependent on-state resistance of the IGBT, in ohms; SW (t) represents the dynamic switching loss.

[0012] Furthermore, the closed-loop feedback control logic for executing the adaptive main / auxiliary branch switching control strategy is divided into three layers, specifically including: Operating condition perception layer: Real-time acquisition and calculation of key state variables of the system, including AC voltage, DC current, thyristor junction temperature, IGBT junction temperature, commutation voltage time integral, and turn-off angle. Deviation Calculation Layer: The key state quantities are compared with the set target reference values ​​to calculate the corresponding device junction temperature deviation, commutation voltage integral margin deviation, and DC output current deviation. Correction Decision Layer: Perform dynamic correction based on the deviation amount. When the device junction temperature deviation is greater than zero, increase the proportion of auxiliary branch current. When the commutation voltage integral margin deviation is greater than zero, adjust the switching time to improve the commutation safety margin. Dynamically fine-tune the IGBT turn-on delay and turn-off delay based on the deviation amount, and adaptively adjust the main and auxiliary branch current distribution ratio by changing the current transfer time.

[0013] Furthermore, when solving for the optimal number of devices connected in series, the total number N of devices required in series for the thyristor main branch is... Th The optimization formula is: Among them, U AM K represents the maximum operating peak voltage of the converter valve bridge arm. CU K is the overvoltage impulse coefficient. b K is the voltage rise factor of the power grid; T K is the junction temperature derating factor for thyristors; U U is the series equalization voltage coefficient; RM This is the rated repetitive peak voltage of a single thyristor.

[0014] Furthermore, when solving for the optimal number of devices in series, the total number N of devices N required for the IGBT auxiliary branch is... IGBT The optimization formula is: Where, N IGBT U represents the total number of series-connected devices required for the IGBT auxiliary branch; sub The rated operating voltage for the converter valve submodule; K re K is the system redundancy coefficient. temp V is the temperature redundancy factor for the IGBT; IGBT This refers to the rated blocking voltage of a single IGBT.

[0015] Furthermore, in the aforementioned two-layer collaborative optimization solution model, the objective function for minimizing the total lifecycle cost of the upper-layer optimization is expressed as: Among them, C loss For loss cost; C life Cost of lifespan depletion; C maint To cover maintenance costs.

[0016] Furthermore, the multi-dimensional safety constraint system for commutation transient trajectory is fed back to the upper-level adaptive particle swarm algorithm through a penalty function mechanism. The actual values ​​of commutation margin, turn-off angle, current change rate, overvoltage peak value and device junction temperature are calculated and compared with the safety threshold. A multi-constraint weighted penalty term is constructed and superimposed on the upper-level fitness function to update the particle position and velocity, guiding the population to converge toward the safe and feasible region.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improve the accuracy of loss calculation and device junction temperature assessment: By establishing a time-varying transient loss mathematical model for the thyristor main branch and IGBT auxiliary branch, the real-time quantification of the dynamic loss distribution of each device during the entire commutation process is realized.

[0018] 2. To achieve synergistic constraints between loss optimization and transient control: By constructing a two-layer synergistic optimization solution model with upper-level economy and lower-level transient safety and using an adaptive particle swarm optimization algorithm for iterative solution, a balance between system operation safety, device lifetime and full life cycle economy is achieved.

[0019] 3. Reduced losses and transient safety hazards under different load and fault scenarios: By designing an adaptive main and auxiliary branch switching control strategy and using closed-loop feedback control to dynamically adjust the switching timing and current distribution ratio, the main and auxiliary branch switching strategy is adaptively adjusted according to the real-time operating conditions of the system.

[0020] 4. It avoids the problem of limited space for loss optimization caused by an overly conservative single safety criterion: By constructing a transient trajectory safety constraint system that includes multi-dimensional indicators such as commutation voltage time integral and current transfer rate, it achieves precise constraints on the safe operation boundary of commutation.

[0021] 5. Ensuring the practicality of optimized parameters under various typical operating conditions of the power system: By performing multi-condition simulation verification in electromagnetic transient simulation software and feeding the data back to the two-layer model for sensitivity verification and iterative correction, the coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics was achieved. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a block diagram of the inverter-side system structure; Figure 3 This is a diagram of the internal structure of a CLCC converter valve. Figure 4 Comparison chart before and after CLCC loss optimization; Figure 5 This is a transient constraint diagram for CLCC commutation. Figure 6 Comparison of waveforms optimized for CLCC. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] Example 1 This embodiment provides a method for the coordinated optimization of losses and commutation transient characteristics in CLCC main and auxiliary branches, such as... Figure 1 As shown, it includes the following steps: Step 1: A model of the UHVDC transmission system, including the CLCC converter valve, is built using PSCAD / EMTDC electromagnetic transient simulation software. The overall system structure is as follows: Figure 2 As shown, the inverter side adopts a multi-pulsating converter valve group topology composed of multiple CLCC converter valve modules connected in series and parallel. The DC side is equipped with a smoothing reactor and a bipolar DC line, while the AC side is connected to a converter transformer, an AC filter, and the receiving-end AC system group. The overall topology of the inverter-side CLCC converter valve is as follows: Figure 3 As shown, a three-phase bridge six-pulse topology is adopted. Each bridge arm of its valve group adopts a hybrid topology, including a thyristor main branch (including a series-connected anti-parallel thyristor diode assembly and an RC snubber circuit) and an IGBT auxiliary branch connected in parallel (including a fully controlled IGBT device, a fast diode, and a snubber circuit). The main and auxiliary branches together constitute a controllable commutation valve arm unit with autonomous turn-off and dynamic current transfer capabilities.

[0025] Step 2: Initialize system operating parameters and device basic parameters 1) Determine the rated operating parameters of the DC system, including rated DC voltage, rated DC current, and maximum operating voltage U of the converter valve bridge arm. AM The rated voltage of the AC system, commutation reactance, and system short-circuit ratio are used to determine the voltage and current stress boundaries of the devices.

[0026] 2) Determine the parameters of the thyristor and IGBT devices, including the thyristor threshold voltage V. T0 Room temperature on-state resistance r T0 Temperature coefficient of resistance αT Rated repetitive peak voltage U RM IGBT saturation voltage drop V CE On-state resistance R CE Rated blocking voltage V IGBT Energy parameters such as power on / off.

[0027] 3) Determine safety constraints and economic parameters, including the minimum safety commutation margin γ. min Minimum integral value S of commutation voltage min Maximum permissible transient overvoltage multiple, highest junction temperature T of the device jmax Unit electricity price, component cost, maintenance factor, etc.

[0028] Step 3: Calculation of the number of main and auxiliary branch devices connected in series and parameter configuration The number of thyristors connected in series in the main branch is determined by the maximum operating voltage of the bridge arm, the overvoltage coefficient, the voltage rise coefficient, the junction temperature derating coefficient, the voltage equalization coefficient, and the rated voltage of the devices. The calculation formula is as follows: In the formula: U AM K represents the maximum operating peak voltage of the converter valve bridge arm. CU K represents the overvoltage impulse coefficient, with a value ranging from 1.3 to 1.6. b K is the grid voltage rise factor, with a value ranging from 1.05 to 1.1. T K represents the junction temperature derating factor for the thyristor, with a value ranging from 0.85 to 0.95. U U is the series voltage equalization coefficient, with a value ranging from 0.8 to 0.9. RM Let N be the rated repetitive peak voltage of the thyristor. Substituting the above parameters into the formula, we calculate the theoretical number of thyristors in series. Rounding up and adding engineering redundancy, we obtain the final number of thyristors in series, N. Th .

[0029] Substituting the above parameters into the formula, the theoretical number of thyristors connected in series is calculated. Rounding up and adding engineering redundancy, the final number of thyristors connected in series, N, is obtained. Th .

[0030] The number of IGBTs connected in series in the auxiliary branch is determined by the submodule voltage, redundancy factor, temperature redundancy factor, and rated voltage of a single IGBT. The calculation formula is as follows: In the formula: U sub The rated voltage of the converter valve submodule; K re K represents the system redundancy factor, with a value ranging from 1.1 to 1.3. temp V represents the IGBT temperature redundancy factor, with a value ranging from 0.9 to 0.95. IGBTThe rated blocking voltage of a single IGBT. Substitute the parameters into the formula, calculate, and round up to determine the number of IGBTs N connected in series. IGBT .

[0031] The initial setting of the main and auxiliary branch current distribution coefficients is based on commutation safety as a constraint and minimizing equivalent losses as an objective, to determine the optimal current distribution coefficient k. opt The formula is: st Where, k opt The optimal current distribution coefficient between the main and auxiliary branches characterizes the proportional relationship between the current carried by the main and auxiliary branches during steady-state and transient processes; P eq The equivalent loss of the CLCC converter valve throughout its entire life cycle; S γ S represents the commutation voltage-time integral value, a quantitative indicator of the voltage support capability during the commutation process; min为 The minimum voltage integration threshold for reliable commutation; below this value, safe commutation cannot be completed; γ(t) is the real-time commutation margin angle, which changes dynamically with the system operating conditions; γ min The minimum safe commutation margin angle is the lower limit threshold to ensure that commutation failure does not occur.

[0032] Step 4: Calculation of transient coupling loss of CLCC main and auxiliary branches First, based on the AC side current of the converter valve i ac (t) Combining the topological Kirchhoff's current law, it satisfies i Th (t)+ i IGBT (t)=i ac (t) Secondly, during the individual algorithm evaluation phase, the current optimization variables (main and auxiliary branch capacity, commutation control timing, etc.) are substituted into the CLCC electromagnetic transient simulation model to extract the branch current waveforms at each moment during the commutation process; or an analytical model of current distribution is established based on the commutation transient process, and the current is obtained by mapping the optimization variables. i Th (t) and i IGBT (t) The time series data provides input for subsequent calculations of transient losses and junction temperatures.

[0033] 1) The formula for calculating the time-varying transient loss of the thyristor main branch is: Among them, V T0 This refers to the thyristor threshold voltage, measured in volts; i Th(t) represents the real-time transient current of the thyristor, in amperes; r T (T j ΔP represents the junction temperature-dependent dynamic on-state resistance of the thyristor, in ohms; Th (t) represents the transient additional loss during commutation, in watts.

[0034] The formula for calculating the junction temperature-dependent dynamic on-state resistance is: in, The on-state resistance at room temperature; It is the temperature coefficient of resistance; For real-time junction temperature; This is the reference junction temperature.

[0035] The formula for calculating the time-varying transient loss of the IGBT auxiliary branch is: Among them, V CE (T j ) represents the junction temperature-dependent saturation voltage drop of the IGBT, in volts; i IGBT (t) represents the real-time current of the IGBT, in amperes; r CE (T j ΔP represents the junction temperature-dependent on-state resistance of the IGBT, in ohms; SW (t) represents the dynamic switching loss.

[0036] The formula for calculating dynamic switching losses is: Among them, E on (t) represents the IGBT turn-on energy; E off (t) represents the IGBT turn-off energy; T comm The commutation period is measured in seconds.

[0037] Turning energy on and off: Among them, t on1为 The moment when the starting current reaches 10% of the rated value; t on9 The end time when the turn-on current reaches 90% of the rated value; v ce (t) represents the instantaneous collector-emitter voltage of the IGBT; i c (t) represents the instantaneous collector current of the IGBT; t off9 The starting moment when the turn-off current drops to 90% of its rated value; t off1 The point at which the turn-off current drops to 10% of its rated value; v ce (t), i c(t) represents the instantaneous collector-emitter voltage and instantaneous collector current of the IGBT during the turn-off process, respectively.

[0038] The formula for calculating the equivalent loss over the entire lifecycle is: Among them, P IGBT (t) represents the time-varying transient loss of the IGBT auxiliary branch, P Th (t) represents the time-varying transient loss of the thyristor main branch, T cycle This is the complete working cycle of the power frequency.

[0039] Specific loss optimizations for example Figure 4 As shown. Figure 4 It includes a comparison chart of total loss under different operating conditions, a time-domain waveform of loss during commutation process, a pie chart of loss distribution before and after optimization, a curve showing the influence of current distribution coefficient on loss, and a curve showing junction temperature-loss coupling characteristics. The comparison of total losses under different operating conditions shows that, compared with the original method, the optimized method of this invention reduces losses by 5.6% under rated steady-state conditions, reduces total losses from 1850kW to 1620kW (a reduction of 12.4%) when the AC voltage drops to 0.7 pu, reduces losses by 16.7% under continuous commutation conditions, and reduces losses from 1650kW to 1430kW (a reduction of 13.7%) under alternating light and heavy load conditions. As can be seen from the time-domain waveform of the commutation process, within the commutation interval of 20ms to 35ms, the optimized instantaneous loss peak waveform is significantly smoothed out, and its transient loss peak value is reduced by 21.7%. The comparison of loss distribution shows that the equivalent total loss over the entire cycle decreased from 1550kW before optimization to 1400kW after optimization (an overall reduction of 9.7%), and the switching loss of the IGBT auxiliary branch was reduced by 25% after optimization. The auxiliary branch current distribution coefficient k opt The impact curve on total loss shows that there exists an optimal value point within the 30% to 45% co-optimization range that brings the total loss to a stable trough, i.e., the optimal current distribution coefficient k. opt =38%; As can be seen from the junction temperature-loss coupling characteristic curve, when the system moves from the rated operating range below 85°C to the high-temperature operating range above 85°C due to operating condition fluctuations, the optimized loss growth slope slows down significantly, achieving the technical effect of reducing losses by 18% in the high-temperature range.

[0040] Step 5: Commutation Transient Trajectory Constraint Calculation and Verification. A multi-dimensional safety constraint system for the commutation transient trajectory is established and calculated and verified. In this embodiment, the commutation safety operation boundary is defined using commutation voltage time integral, current transfer rate, real-time commutation margin, transient voltage overshoot, and device junction temperature as the core, thus establishing a multi-dimensional safety constraint system for the commutation transient trajectory.

[0041] Specifically, the calculation formulas for each core boundary index in the multidimensional safety constraint system for commutation transient trajectories are as follows: Commutation voltage time integral constraint Among them, S γ Δt represents the integral of the AC side voltage over time during the commutation process; t0 is the commutation start time; Δt comm Commutation duration; u ac (t) represents the instantaneous AC voltage during commutation; S min The minimum voltage integral required to ensure reliable commutation.

[0042] Current transfer rate constraint Among them, i trans (t) represents the instantaneous transfer current of the branch during the commutation process; K di The allowable rate of change of current constraint coefficient; I rated This is the rated operating current of the converter valve branch.

[0043] Real-time commutation margin constraints Where γ(t) is the real-time commutation margin angle of the system; γ0 is the reference no-load commutation margin angle; Δ γ(t) represents the commutation margin attenuation caused by operating condition disturbances; γ min The minimum commutation margin angle limit for safe system operation.

[0044] Transient overvoltage constraint Among them, U peak (t) represents the instantaneous peak overvoltage that the device withstands; K ov U is the overvoltage margin factor for the bridge arm; arm The rated pressure of the single bridge arm of the converter valve.

[0045] Device junction temperature constraint Among them, T j (t) represents the real-time junction temperature of the power device; T jmax为 The maximum allowable junction temperature of the device.

[0046] The formula for calculating the real-time junction temperature of power devices is: Among them, T j0 Rth is the reference junction temperature / initial junction temperature (unit: °C); Rth is the total thermal resistance of the device (unit: °C / W); P TH (t) represents the transient loss of the thyristor (W); P IGBT (t) represents the transient loss of the thyristor (W); C th R is the device's heat capacity (J / °C); th The thermal resistance of the device is given in °C / W. Each of the above constraints is calculated in real time to determine whether the safety boundary requirements are met.

[0047] In traditional or unoptimized control scenarios where loss optimization and commutation transient control are mismatched, the specific transient constraint curves are as follows: Figure 5 As shown, the quantitative analysis includes the following constraint trajectories and the synthesis plane: 1) As can be seen from the commutation voltage time integral constraint curve, in the early stage of commutation with a time of 0.2 to 0.35, the voltage time integral curve falls into the red unsafe area below, indicating that the system has failed to actively build up sufficient commutation voltage at this time, and the commutation safety margin is extremely low.

[0048] 2) As can be seen from the current transfer rate constraint curve, at the fault instant with a time interval of 0.2, the current transfer rate is... A drastic change occurred, and its peak value far exceeded the set upper limit of 3.5 pu, directly plunging into the red over-limit danger zone above, showing a huge transient current stress impact.

[0049] 3) As can be seen from the real-time commutation margin constraint curve, the system sacrifices commutation margin in the pursuit of reducing losses. As a result, the green solid line drops significantly below the safety control lower limit of 10° after the time reaches 0.5. Moreover, due to the lack of a multi-dimensional coordinated adjustment mechanism, it cannot recover after falling below the limit. As a result, it remains in the lower pink commutation failure risk zone for a long time in the middle and late stages of commutation, which poses a major technical risk of causing continuous commutation failure.

[0050] 4) As can be seen from the transient overvoltage constraint curve, during the turn-off transient period around time 0.75, the voltage amplitude generates a severe transient overshoot, and its voltage multiple peak directly breaks through the 1.4pu withstand voltage red line boundary, cutting into the red overvoltage danger zone above, which can easily lead to insulation breakdown and damage of the power devices inside the converter valve.

[0051] 5) As can be seen from the junction temperature constraint curve of the device, the junction temperature of the thyristor and the junction temperature of the IGBT both show a continuous dynamic upward trend within the commutation interval. The junction temperature of the thyristor approaches the limit threshold of 125℃ (black dashed line) at the moment when the commutation ends at 0.8℃, which is on the critical edge of overheating and thermal breakdown.

[0052] 6) As can be seen from the comprehensive safety trajectory diagram, due to the above-mentioned mismatch defects such as the inability to recover the margin and the voltage stress exceeding the limit, most of the operating points of the commutation transient trajectory curve fall within the red unsafe area, making it impossible to achieve a balance between loss, lifespan and safety using existing strategies.

[0053] Step 6: Solving the two-layer collaborative optimization problem A two-layer collaborative optimization solution model is constructed and iteratively solved. In this embodiment, a two-layer collaborative optimization solution model is constructed, with an upper-layer economic model and a lower-layer transient safety model. The time-varying transient loss model described in step 4 is used as the loss calculation basis for the objective function of minimizing the total cost of the entire life cycle in the upper-layer optimization. The multi-dimensional safety constraint system of the commutation transient trajectory described in step 5 is used as the hard constraint boundary in the lower-layer optimization. The optimal switching timing, optimal current distribution coefficient, and optimal number of devices connected in series that satisfy the hard constraint boundary are solved iteratively using an adaptive particle swarm optimization algorithm.

[0054] 1) Upper-level optimization: The objective function for optimal economic performance throughout the entire life cycle: Among them, C loss For the cost of loss, C life For the cost of lifespan depletion, C maint To maintain costs; Loss cost: Among them, T life Design the full life cycle duration for converter valve equipment; P eq (t) represents the real-time equivalent power loss of the converter valve; c clcc This refers to the industrial electricity price, which is the unit price for purchasing active electrical energy.

[0055] Lifetime cost: Among them, C device The cost of purchasing a single set of power devices; L loss This represents the lifespan loss coefficient corresponding to the accelerated aging of the device due to wear and tear.

[0056] Maintenance costs: Where, k m The unit failure maintenance rate corresponding to overstress conditions; U over I represents the instantaneous overvoltage amplitude of the device. over The instantaneous overcurrent amplitude of the device; the integral term is the cumulative overvoltage and overcurrent over the entire cycle.

[0057] Lower-level optimization: Commutation transient safety constraints In the two-layer optimization framework of this invention, the lower-layer commutation transient safety constraints are fed back to the upper-layer adaptive particle swarm optimization algorithm through a penalty function mechanism: First, the optimization variables corresponding to each particle are passed to the lower-layer commutation transient model to calculate the actual values ​​of commutation margin, turn-off angle, current change rate, overvoltage peak value, and device junction temperature, and compare them with the safety threshold to quantify the degree of violation of each constraint; Second, a multi-constraint weighted penalty term is constructed and superimposed on the fitness function of the upper-layer particles to form a constrained comprehensive fitness; Finally, the upper-layer particle swarm optimization algorithm performs iterative updates of particle position and velocity based on this fitness value, prioritizing the selection of particles that satisfy all safety constraints as the global optimal solution, guiding the population to converge toward the safe feasible region, and achieving synergy between loss optimization and transient safety. The lower-layer commutation transient safety constraint set is as follows: in, S γ S is the integral of the AC side voltage over time during the commutation process. min To ensure reliable commutation, the minimum voltage integral required is given by γ(t), which represents the system's real-time commutation margin angle. min U is the minimum commutation margin angle limit for safe system operation. peak (t) represents the instantaneous peak overvoltage that the device withstands. The instantaneous rate of change of commutation current; T is the maximum allowable rate of change of current for the device. j (t) represents the real-time junction temperature of the power device; T jmax为 The maximum allowable junction temperature of the device.

[0058] An adaptive particle swarm optimization algorithm is used to iteratively solve the problem and obtain the optimal current distribution coefficient kopt and IGBT turn-on delay t. on Shutdown delay t off Commutation trigger lead angle β.

[0059] The adaptive particle swarm optimization algorithm used in this invention has the following adaptive characteristics: First, the core parameters of the algorithm are dynamically adjusted with each iteration stage, taking into account both global exploration and local convergence performance; second, the penalty intensity for commutation transient safety constraints is adaptively adjusted, relaxing the constraints in the early stage to expand the solution space exploration, and tightening the constraints in the later stage to ensure the safety of the solution; third, the loss optimization objective and safety constraints are adaptively balanced to guide the population to converge toward the optimal solution that takes into account both economy and safety.

[0060] Step 7: Adaptive main and auxiliary branch switching control realizes the dynamic correction of IGBT turn-on and turn-off times based on real-time collected AC voltage, DC current, device junction temperature, and commutation margin, and adjusts the current distribution ratio of the main and auxiliary branches to achieve adaptive collaborative optimization operation under all operating conditions.

[0061] The adaptive main and auxiliary branch switching control dynamically corrects the IGBT turn-on / turn-off timing by taking real-time collected AC voltage, DC current, device junction temperature, and commutation margin as inputs, and then adjusts the current distribution ratio through closed-loop feedback control to achieve full-condition collaborative optimization.

[0062] The control logic is divided into 3 layers: 1) Operating Condition Sensing Layer: Collects and calculates key system state variables: AC voltage u ac (t), DC current i dc (t); Thyristor junction temperature T j,Th (t), IGBT junction temperature T j,IGBT (t); Commutation margin S γ (t), shut-off angle γ(t); Deviation Calculation Layer: Compares real-time state variables with the target / safety threshold to calculate the deviation. In the formula, the ref subscript represents the target / reference value of the parameter. This refers to the real-time junction temperature deviation of the device. This refers to the current real-time junction temperature of the power device. This is the target reference value for the device junction temperature; Commutation voltage integral margin deviation; This represents the real-time voltage integral value during the commutation process. Ensure reliable commutation by maintaining the rated reference value of the voltage integral; DC output current deviation; The converter valve outputs real-time DC current; The system operates with a DC current reference value.

[0063] This set of deviations is the core input for subsequent dynamic correction of IGBT switching timing and adjustment of the main and auxiliary branch current distribution ratio: when ΔT j(t) A value >0 indicates that the junction temperature is too high, requiring an increase in the proportion of auxiliary branch current and a reduction in the main branch loss. when ΔS γ (t) A value >0 indicates insufficient commutation margin, requiring adjustment of switching timing to increase commutation safety margin; when Δi dc (t) A value greater than 0 indicates that the load current is too high, and the current distribution needs to be optimized to reduce overall losses and thermal stress. 3) Correction decision layer: Dynamically adjust the IGBT turn-on delay t based on the deviation.on Shutdown delay t off The current distribution coefficient k(t) of the main and auxiliary branches can be adjusted by changing the current transfer time.

[0064] Step 8: Multi-condition simulation verification and result analysis First, a CLCC model including loss calculation, junction temperature simulation, and commutation trajectory monitoring is built in electromagnetic transient simulation software. Then, the optimal number of devices connected in series, obtained in step 3, and the IGBT turn-on delay, turn-off delay, and main / auxiliary branch current distribution ratio dynamically adjusted by closed-loop feedback control in step 7 are input into the CLCC model for the following multi-condition electromagnetic transient simulation verification: 1) Rated steady-state operating conditions: Verify total loss, device junction temperature, and operating efficiency before and after optimization.

[0065] 2) AC voltage drops to 0.7 pu: Verify the ability to suppress commutation failure, transient overvoltage, and current surge.

[0066] 3) Continuous commutation condition: Verify the stability of the commutation trajectory, device stress and life loss.

[0067] 4) Light / heavy load alternating conditions: Verify the response speed and robustness of the adaptive strategy.

[0068] During the simulation, the actual loss data and actual transient trajectory data obtained from the simulation verification are fed back in real time or in batches to the two-layer collaborative optimization solution model described in step 6 for sensitivity verification. Based on this, the optimal switching timing and current distribution coefficients are corrected until the simulation verification results simultaneously satisfy the goal of minimizing the total cost over the entire lifecycle and the multi-dimensional safety constraint system for commutation transient trajectories, thus achieving collaborative optimization of the CLCC main and auxiliary branch losses and commutation transient characteristics. A specific comparison of CLCC parameters before and after optimization is provided. Figure 6 As shown. Figure 6 The diagram shows a comparison of voltage, current, and margin waveforms during the commutation process before and after CLCC optimization. The sub-diagrams within the diagram correspond to the verification results for the aforementioned operating conditions: Figure 6 Figures ①, ②, ⑤, and ⑥ respectively illustrate the transient voltage and commutation margin waveforms: By comparing the waveforms before and after optimization (red and green curves), it is intuitively shown that under AC voltage drop conditions, this invention reduces the voltage drop depth by 42% and shortens the recovery time by 33%; at the same time, it increases the grid integral safety margin by 30%, the minimum commutation margin by 130%, and smooths out 35% of the transient overvoltage peak, effectively verifying the commutation failure suppression capability and transient overvoltage.

[0069] Figure 6Figures ③ and ④ show the waveforms of the current transfer characteristics of the main and auxiliary branches: the green waveform shows that the current transfer rate of the thyristor main branch is significantly improved by 50%, the current is transferred to the IGBT auxiliary branch quickly and safely, and the transfer rate is limited to within the safety threshold, which effectively verifies the current impact and device stress during commutation.

[0070] Step 9: Parameter Correction and Engineering Output. Perform statistical analysis on the simulation results, correct key parameters such as the number of devices connected in series, switching timing, and control coefficients, and output a report on the CLCC main and auxiliary branch capacity configuration, control parameters, and optimization effect that can be used in engineering.

[0071] The following key parameters are corrected item by item based on the aforementioned multidimensional safety constraint simulation statistical results: Number of devices connected in series: Statistically analyze overvoltage and junction temperature data. If the transient overvoltage breakdown threshold / junction temperature exceeds the limit, increase the number of thyristors and IGBTs connected in series; if there is sufficient margin redundancy, reduce the number of devices connected in series to control costs.

[0072] Switching timing: Based on the commutation margin and the current change rate exceeding the limit waveform, the switching trigger time of the auxiliary branch IGBT is adaptively fine-tuned. In fault conditions, the auxiliary branch is switched on in advance, the commutation voltage is compensated, and the commutation margin is increased.

[0073] Control coefficient: Based on the capacity optimization algorithm, the current distribution coefficient of the main and auxiliary branches is corrected to balance the losses and transient safety under all operating conditions, so that the voltage integral and commutation margin fall within the safety boundary throughout the entire process.

[0074] After the parameters are corrected and solidified, the final output is a capacity configuration and control document that can be implemented in engineering.

[0075] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for synergistic optimization of losses and commutation transient characteristics in CLCC main and auxiliary branches, characterized in that, Includes the following steps: Based on the characteristics of current transfer, voltage change and junction temperature dynamic change during commutation, time-varying transient loss models of the thyristor main branch and IGBT auxiliary branch are established respectively to quantify the conduction loss, dynamic switching loss and transient additional loss of each device in real time during the entire commutation process. The commutation safety operation boundary is defined with commutation voltage time integral, current transfer rate, real-time commutation margin, transient voltage overshoot and device junction temperature as the core, and a multi-dimensional safety constraint system for commutation transient trajectory is established. A two-layer collaborative optimization solution model is constructed. The time-varying transient loss model is used as the loss calculation basis for the objective function of minimizing the total cost of the entire life cycle in the upper layer optimization. The multi-dimensional safety constraint system of the commutation transient trajectory is used as the hard constraint boundary in the lower layer optimization. The optimal switching timing, optimal current distribution coefficient, and optimal number of devices connected in series that satisfy the hard constraint boundary are solved iteratively by the adaptive particle swarm algorithm. Using the optimal switching timing and optimal current distribution coefficient as the control benchmark, and combining the real-time collected AC bus voltage, DC current, device junction temperature and commutation margin, an adaptive main and auxiliary branch switching control strategy is executed. Closed-loop feedback control is used to dynamically adjust the IGBT turn-on delay, turn-off delay and main and auxiliary branch current distribution ratio. A CLCC model incorporating loss calculation, junction temperature simulation, and commutation trajectory monitoring is built in electromagnetic transient simulation software. The optimal number of connected devices, dynamically adjusted IGBT turn-on delay, turn-off delay, and main / auxiliary branch current distribution ratio are input into the CLCC model for multi-condition electromagnetic transient simulation verification. The actual loss data and actual transient trajectory data obtained from the simulation verification are fed back to the two-layer collaborative optimization solution model for sensitivity verification. Based on this, the optimal switching timing and current distribution coefficients are corrected until the simulation verification results simultaneously satisfy the goal of minimizing the total cost over the entire life cycle and the multi-dimensional safety constraint system of the commutation transient trajectory, thereby achieving the collaborative optimization of the CLCC main / auxiliary branch losses and commutation transient characteristics.

2. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, The expression for the time-varying transient loss model of the thyristor main branch is as follows: Among them, V T0 This refers to the thyristor threshold voltage, measured in volts; i Th (t) represents the real-time transient current of the thyristor, in amperes; r T (T j ΔP represents the junction temperature-dependent dynamic on-state resistance of the thyristor, in ohms; Th (t) represents the transient additional loss during commutation, in watts.

3. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 2, characterized in that, The expression for the thyristor junction temperature-dependent dynamic on-state resistance is: in, The on-state resistance at room temperature; It is the temperature coefficient of resistance; For real-time junction temperature; This is the reference junction temperature.

4. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 2, characterized in that, The expression for the commutation transient additional loss is: Where, k γ γ(t) is the loss coefficient due to commutation margin variation; γ(t) is the real-time commutation margin angle, i Th (t) represents the real-time transient current of the thyristor.

5. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, The expression for the time-varying transient loss model of the IGBT auxiliary branch is as follows: Among them, V CE (T j (i) represents the junction temperature-dependent IGBT saturation voltage drop, in volts; IGBT (t) represents the real-time current of the IGBT, in amperes; r CE (T j ΔP represents the junction temperature-dependent on-state resistance of the IGBT, in ohms; SW (t) represents the dynamic switching loss.

6. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, The closed-loop feedback control logic for implementing the adaptive main / auxiliary branch switching control strategy is divided into three layers, specifically including: Operating condition perception layer: Real-time acquisition and calculation of key state variables of the system, including AC voltage, DC current, thyristor junction temperature, IGBT junction temperature, commutation voltage time integral, and turn-off angle. Deviation Calculation Layer: The key state quantities are compared with the set target reference values ​​to calculate the corresponding device junction temperature deviation, commutation voltage integral margin deviation, and DC output current deviation. Correction Decision Layer: Perform dynamic correction based on the deviation amount. When the device junction temperature deviation is greater than zero, increase the proportion of auxiliary branch current. When the commutation voltage integral margin deviation is greater than zero, adjust the switching time to improve the commutation safety margin. Dynamically fine-tune the IGBT turn-on delay and turn-off delay based on the deviation amount, and adaptively adjust the main and auxiliary branch current distribution ratio by changing the current transfer time.

7. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, When determining the optimal number of devices connected in series, the total number N of devices required in series for the thyristor main branch is... Th The optimization formula is: Among them, U AM K represents the maximum operating peak voltage of the converter valve bridge arm. CU K is the overvoltage impulse coefficient. b K is the voltage rise factor of the power grid; T K is the junction temperature derating factor for thyristors; U U is the series equalization voltage coefficient; RM This is the rated repetitive peak voltage of a single thyristor.

8. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, When determining the optimal number of devices in series, the total number N of devices required in series for the IGBT auxiliary branch is... IGBT The optimization formula is: Where, N IGBT U represents the total number of series-connected devices required for the IGBT auxiliary branch. sub The rated operating voltage for the converter valve submodule; K re K is the system redundancy coefficient. temp V is the temperature redundancy factor for the IGBT; IGBT This is the rated blocking voltage for a single IGBT.

9. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, In the aforementioned two-layer collaborative optimization solution model, the objective function for minimizing the total cost throughout the entire lifecycle of the upper-layer optimization is expressed as follows: Among them, C loss For loss cost; C life Cost of lifespan depletion; C maint To cover maintenance costs.

10. The method for coordinated optimization of CLCC main and auxiliary branch losses and commutation transient characteristics according to claim 1, characterized in that, The multi-dimensional safety constraint system for commutation transient trajectory is fed back to the upper-level adaptive particle swarm algorithm through a penalty function mechanism. The actual values ​​of commutation margin, turn-off angle, current change rate, overvoltage peak value and device junction temperature are calculated and compared with the safety threshold. A multi-constraint weighted penalty term is constructed and superimposed on the upper-level fitness function to update the particle position and velocity, guiding the population to converge toward the safe and feasible region.

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