CLCC auxiliary branch capacity design and parameter optimization method taking power grid application demand as target

Abstract

The invention discloses a CLCC auxiliary branch capacity design and parameter optimization method taking a power grid application demand as a target, and the method comprises the steps: firstly building a capacity matching model of a main branch and an auxiliary branch based on the operation characteristics of a DC power transmission system, and reducing the overall loss of a converter valve through optimizing the switching time of the main branch and the auxiliary branch of the converter valve, and the reliability of the commutation process is improved. And then, introducing a loss calculation and economy evaluation model, carrying out quantitative analysis on the overall benefit of the CLCC, and carrying out system verification in combination with electromagnetic simulation to ensure that the optimized converter valve can effectively prevent commutation failures under various fault conditions. According to the invention, by analyzing different functions of the main branch and the auxiliary branch and the influence of the main branch and the auxiliary branch on the commutation process, an optimal design scheme based on system demand guidance is provided, so that the economical efficiency and engineering applicability of the CLCC converter valve are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct current (HVDC) transmission, and in particular to a method for capacity design and parameter optimization of CLCC auxiliary branches targeted at grid application requirements. The method aims to improve the adaptability of CLCC converter valves in multi-infeed DC transmission systems, optimize the configuration of their main and auxiliary branch capacities, and reduce the risk of commutation failure, thereby enhancing the safety and stability of the DC transmission system. Background Art

[0002] With the development of the global energy internet and the large-scale access to clean energy, the advantages of high-voltage direct current (HVDC) technology for long-distance, high-capacity power transmission are becoming increasingly prominent. However, traditional thyristor-commutated converters (LCC-HVDC) are highly dependent on the AC system to provide commutation voltage during operation. When the AC system fails, the converter may be unable to complete commutation, resulting in commutation failure and affecting the stable operation of the system.

[0003] In recent years, controlled-commutation converter (CLCC) technology has been proposed. Building on the LCC converter, this technology introduces an auxiliary branch, leveraging the active shutdown capability of insulated-gate bipolar transistors (IGBTs) for commutation control, thereby reducing the risk of commutation failure. However, existing CLCC design methods lack systematic research on optimizing the capacity of the main and auxiliary branches. Current engineering designs generally allocate capacity based on rated current capability, failing to fully consider factors such as grid operation requirements, commutation characteristics, and converter valve loss optimization.

[0004] Therefore, the present invention proposes a CLCC auxiliary branch capacity design and parameter optimization method targeting grid application requirements, aiming to optimize the capacity configuration of main and auxiliary branches, reduce commutation losses, and improve the economy of converter valves in combination with grid operation requirements. Summary of the Invention

[0005] The purpose of the present invention is to address the shortcomings of existing CLCC converter valve capacity design methods and propose a main and auxiliary branch capacity optimization method based on grid application requirements. By calculating key indicators such as the arc extinction angle and short-circuit ratio on the inverter side, the capacity matching of the main and auxiliary branches is optimized, and a CLCC loss calculation and economic analysis model is established to improve the reliability and engineering adaptability of the converter valve.

[0006] The purpose of the present invention is achieved through the following technical solutions: A method for designing the capacity and optimizing the parameters of a CLCC auxiliary branch circuit based on grid application requirements is provided, the method comprising the following steps: S1: Establish a capacity matching model for the main and auxiliary branches and calculate the basic parameters of the main and auxiliary branches; S2: Optimizing the switching time between the primary and auxiliary branches based on the basic parameters; S3: Based on the basic parameters, a loss model of the controllable phase-commutation valve is established to optimize the conduction time of the main and auxiliary branches; S4: Based on the loss model, an economic evaluation model for the controllable phase-changing valve is established to evaluate the economic efficiency of the optimized solution, and the feasibility of the optimization strategy is verified through simulation.

[0007] Preferably, the basic parameters include: the number of series connections, parallel configuration and current carrying capacity of thyristors and insulated gate bipolar transistors.

[0008] Preferably, the number of main branch thyristors connected in series is N Th Calculated by the following formula:

[0009] Among them, U AM is the maximum operating voltage of the converter valve bridge arm; K CU is the overvoltage impact coefficient; K b is the grid voltage rise coefficient; K AU is the voltage design margin; K U is the pressure equalization coefficient; U RM is the rated repetitive peak voltage of the thyristor.

[0010] Preferably, the number N of auxiliary branch insulated gate bipolar transistors connected in series is IGBT Calculated by the following formula:

[0011] Among them, U submodule The voltage of each submodule; V device It is the rated voltage of a single insulated gate bipolar transistor device.

[0012] Preferably, the optimization of the main-auxiliary branch switching time adopts an adjustment method based on the commutation dynamic process, specifically including: Set the turn-off time t of the main branch IGBT off and the conduction time t of the auxiliary branch IGBT on , adjust the current transfer time in the commutation stage to ensure that the main branch thyristor can quickly restore its blocking capacity after commutation.

[0013] Preferably, the loss model of the controllable phase-changing valve in S3 includes: The conduction loss P of the insulated gate bipolar transistor cond The calculation formula is as follows:

[0014] Where V CEis the saturation voltage of the insulated gate bipolar transistor, I C is the collector current of the insulated gate bipolar transistor, R CE is the on-state resistance of the insulated gate bipolar transistor.

[0015] Preferably, the loss mathematical model of the controllable phase-changing valve in S3 further includes: Thyristor conduction loss P Tcond The calculation formula is as follows:

[0016] Where V T is the on-state voltage of the thyristor, I TAV is the average value of the thyristor current, I TRMS is the effective value of the thyristor current, r T is the on-state slope resistance of the thyristor.

[0017] Preferably, the economic evaluation model of the controllable phase-changing valve in S4 includes: Calculate the total loss cost C of the controllable phase-changing valve loss :

[0018] Among them, C elec The unit electricity cost.

[0019] Preferably, the economic evaluation model of the controllable phase-changing valve in S4 further includes: Calculate the maintenance cost C of the controllable phase-changing valve maint And optimize to minimize the total cost C total :

[0020] Preferably, verifying the feasibility of the optimization solution through simulation specifically includes: Establish an electromagnetic transient simulation model of a controllable phase-commutation valve in PSCAD / EMTDC software; Simulate commutation failures under different fault conditions and verify the improvement effect of the optimized design on commutation stability.

[0021] The main innovations of the present invention include: (1) A CLCC capacity configuration and parameter optimization method based on grid demand is proposed, which can accurately match the main and auxiliary branch ratios of the CLCC. Specifically, based on the operating characteristics of the DC transmission system, the present invention establishes a capacity matching model for the main and auxiliary branches, which includes calculating key indicators such as commutation voltage, short-circuit ratio, and system commutation margin to determine the optimal number and configuration of main branch thyristors and auxiliary branch IGBTs. The commutation voltage includes the inverter side AC bus voltage, the DC side voltage, and the maximum operating voltage of the converter valve bridge arm (U AM ) and other key electrical parameters, whose values ​​directly affect the stability of the commutation process. The system commutation margin is determined by the voltage design margin factor (K AU ) to ensure the converter valve's safety margin under abnormal grid conditions. By analyzing the CLCC converter valve's performance under different operating conditions, the proportional relationship between the main branch and the auxiliary branch is precisely determined, ensuring their coordinated operation and reducing the risk of commutation failure.

[0022] (2) The dynamic control strategy of the commutation process is optimized, improving the controllability of the commutation process. Specifically, the present invention optimizes the switching time between the main and auxiliary branches, especially adjusting the reverse recovery time of the main branch thyristor and the on / off timing of the auxiliary branch IGBT to reduce the overall loss of the commutation valve and improve the stability of the commutation process. The present invention also introduces an adjustment method based on the dynamic commutation process. By finely regulating the current transfer time during the commutation phase, the controllability of the commutation process is enhanced, thereby improving the reliability of the entire system.

[0023] (3) This paper provides an analytical basis for the economic efficiency of CLCC converter valves and offers technical support for engineering applications. Specifically, this paper constructs a detailed converter valve loss calculation model, taking into account factors such as IGBT switching losses and thyristor conduction losses, and conducts a comprehensive economic evaluation based on equipment costs, power losses, and maintenance costs. Furthermore, this paper quantifies the overall benefits of CLCC converter valves through scientific methods and simulates and verifies the optimization scheme to ensure that it is not only technically feasible but also economically advantageous. Furthermore, this paper proposes an optimization strategy for minimizing total costs, providing solid technical support for engineering applications.

[0024] This method can significantly reduce the risk of commutation failure in a high-voltage direct current transmission system and improve the stability and security of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of a parameter matching method for CLCC in one embodiment of the present invention; Figure 2 FIG1 is a structural diagram of an inverter-side system in one embodiment of the present invention; Figure 3FIG1 is a diagram showing the working principle of a CLCC converter valve in one embodiment of the present invention; Figure 4 FIG. 1 is a diagram showing the internal topological structure of a CLCC valve in one embodiment of the present invention; Figure 5 CLCC valve device loss distribution diagram in one embodiment of the present invention; Figure 6 This is a complete inverter circuit structure in a single valve in one embodiment of the present invention; Figure 7 A flowchart of parameter value optimization in one embodiment of the present invention; Figure 8 A parameter determination flow chart in one embodiment of the present invention; Figure 9 is a CLCC simulation model of PSCAD in one embodiment of the present invention; Figure 10 This is waveform data obtained after simulation in one embodiment of the present invention, and the data is the power emitted by each bridge arm in the main and auxiliary bridge arm branches. DETAILED DESCRIPTION

[0026] The following will refer to the attached Figures 1 to 10 Specific embodiments of the present invention will now be described in detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention may be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to facilitate a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0027] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the present invention shall be as defined in the attached claims.

[0028] To facilitate understanding of the embodiments of the present invention, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0029] The present invention provides a CLCC auxiliary branch capacity design and parameter optimization method based on the grid application requirements. Figure 1As shown, the method includes: Step 1: Establish a capacity matching model for the main and auxiliary branches. By analyzing the current distribution characteristics during the commutation process, reasonably determine the number of series / parallel connections of thyristors in the main branch and insulated gate bipolar transistors (IGBTs) in the auxiliary branch to achieve optimal capacity matching. Step 2: Optimize the commutation timing of the main and auxiliary branches, adjust the reverse recovery time of the main branch thyristor, and the on / off timing of the auxiliary branch IGBT to reduce the loss of the commutation valve and improve the controllability of the commutation process; Step 3: Construct a converter valve loss calculation and economic analysis model. Based on IGBT switching losses, thyristor conduction losses, on-state voltage, and energy loss during commutation, a complete converter valve loss calculation method is established to optimize its operating costs. Step 4: Verify the effectiveness of the optimization scheme through PSCAD / EMTDC simulation.

[0030] In one embodiment, the present invention provides a method for designing the capacity and optimizing the parameters of a CLCC auxiliary branch circuit based on grid application requirements, comprising: The system is modeled using PSCAD / EMTDC electromagnetic transient simulation software. The complete inverter circuit structure in a single valve is as follows: Figure 6 As shown in the figure, the converter valve is composed of six bridge arms, and the internal topology of each bridge arm is as follows: Figure 4 As shown in Figure 2. The inverter side system structure is as follows: Figure 2 When the CLCC valve is operating normally, the valve external triggering sequence is compatible with the grid commutation converter (LCC), and the main branch can start commutation at 120° natural commutation phase; after the commutation process is started, the main branch current is lower than the preset current threshold I v After that, the main branch is closed, the IGBT and thyristor of the auxiliary branch are turned on, and the load current is transferred to the auxiliary branch; after the natural commutation process is completed, the auxiliary branch current will drop to zero, and the auxiliary branch IGBT should be turned off. The commutation arm bears the forward voltage. The working principle is as follows Figure 3 shown.

[0031] Calculate the capacity that the receiving end should provide based on the sending end's needs and configure it appropriately: 1) Consider inverter efficiency System efficiency ( ): Includes inverter efficiency and transmission efficiency.

[0032] Inverters lose energy when converting DC to AC, and their efficiency is typically between 90% and 96%. Therefore, the capacity of the receiving inverter should be greater than the required capacity at the sending end divided by the inverter efficiency.

[0033] 2) Consider the transmission requirements of the sending end Required capacity at the sending end ( ):Determine the active power and reactive power requirements required at the sending end based on engineering practice requirements. 3) Consider transmission losses Transmission loss ( ):According to the transmission distance I, line impedance R, etc., estimate the power loss during the transmission process:

[0034] To ensure the inverter can still operate normally under extreme conditions, a safety factor Ks is required, generally set at 1.2-1.5. That is, the receiving-end inverter capacity = (sending-end required capacity ÷ inverter efficiency) × safety factor.

[0035]

[0036] Among them, S r is the receiving-end inverter capacity, K s is the safety factor.

[0037] 4) Consider the power factor of the sending end load Sending end load power factor ( ): Determines the power factor requirement at the sending end, which affects the inverter's reactive power supply capability.

[0038] In practical applications, the load's power factor affects the calculation of the inverter's output power. The power factor is the cosine of the phase difference between the load current and voltage, indicating the load's efficiency in utilizing the current. If the required power and power factor at the sending end are known, the power required by the receiving inverter can be more accurately calculated using the following formula:

[0039] 5) The active power P that the receiving inverter should output r

[0040] 6) Receiving-end inverter capacity design The capacity of the receiving inverter depends not only on the active power but also on the reactive power requirement. The capacity (apparent power) of the receiving inverter can be determined by the following formula:

[0041] The reactive power Q r , should be calculated based on the power factor of the sending end load:

[0042] Capacity S when inverters are connected in parallel 总 :

[0043] 7) Consider some extra margin In actual design, the system operation margin and spare capacity must be considered, including the following two aspects: Overload capacity: A margin of 1.1 times or more is usually considered when designing an inverter.

[0044] Fault and dynamic response: In power systems, load fluctuations may cause changes in instantaneous power demand, and the inverter capacity should be able to cope with these dynamic changes.

[0045] Calculation formula for the inverter side arc extinction angle γ:

[0046] Where, k is the transformer ratio on the inverter side; I d is the DC current; X r is the equivalent commutation reactance on the inverter side; U L is the AC bus line voltage on the inverter side (effective value); β is the Echizen trigger angle.

[0047] For example, suppose the transformer ratio k in a system is 1.0, I d =5000A,X r =0.1Ω,U L =565.7KV, β=20°. Then:

[0048] Compare the arc extinction angle γ on the inverter side with the safety threshold: if γ ≥ the safety threshold, reduce the auxiliary branch redundancy; if γ < the safety threshold, increase the number of GBTs or the conduction time, such as Figure 7 shown.

[0049] Calculation method of short circuit ratio SCR:

[0050] Where S AC is the short-circuit capacity of the converter station AC system (MVA); P DC is the rated DC transmission power of the converter station (MW); For example: Assume that S in a system AC =9000MVA, P DC =3000MW. Then, SCR = 3.0. A larger SCR indicates a stronger system AC support capability and a lower likelihood of commutation failure.

[0051] Main and auxiliary branch capacity configuration: By calculating the power capacity of the inverter-side converter valve at the receiving end, the number of components connected in series in the main and auxiliary branches of the converter valve can be obtained. Based on the number of components, a more reasonable calculation of the switching time of the main and auxiliary branches can be made, and the optimal auxiliary branch conduction time that can prevent system commutation failure under different demand conditions can be calculated.

[0052] Here is an example: Assume that there is a project parameter as follows:

[0053] Calculation of receiving-end inverter capacity:

[0054] Configuration of the number of components of the main and auxiliary branches: The number of thyristors in the main branch is:

[0055] Right now

[0056] Parameter description: KCU=1.5 is the overvoltage impact coefficient; Kb=1.1 is the grid voltage rise coefficient; KAU=1.2 is the voltage design margin; KU=0.85 is the voltage equalization coefficient.

[0057] The number of auxiliary branch IGBTs is as follows: Figure 4 ): Submodule voltage Usubmodule=2 kV Redundancy coefficient Kredundancy = 1.4 (due to SCR = 2.1 being weak)

[0058] Design adjustment: Considering the dynamic voltage impact, two IGBTs in series / sub-modules were finally used (1) The basic timing is set as follows:

[0059] (2) Dynamic adjustment strategy (based on γ and SCR) like Figure 8 As shown, if γ<8°, increase t on to 85μs, otherwise maintain t on =70μs. If SCR<2.5, increase K redundancy To 1.5. If SCR ≥ 2.5, then K redundancy The CLCC converter valve consists of multiple submodules, such as Figure 2 As shown, each submodule generally includes a main branch and an auxiliary branch, and each submodule includes one or more IGBTs and diodes. The power capacity of each submodule can be calculated using the following formula:

[0060] in:

[0061] P submodule is the power capacity of each submodule; V submodule is the voltage of each submodule; I submodule The current of each submodule, P r It is the active power that the receiving inverter should output.

[0062] Each submodule typically consists of a main branch and an auxiliary branch. The number of components connected in series in the main branch and the auxiliary branch can be calculated using the following formula:

[0063] N devices is the number of components connected in series in each submodule; V device is the rated voltage of each component.

[0064] Considering some economic factors, the main branch IGBT in the CLCC converter valve generally uses 1~2 to take on the role of shutting off the bridge arm, so the present invention mainly needs to consider the capacity and number of thyristors. Th The calculation method is:

[0065] K CU U is the overvoltage impact coefficient, ranging from 1.3 to 1.6, depending on the completeness of the overvoltage protection measures in the equipment. AM It is the working peak voltage of the arm, which refers to the forward peak voltage U ATM Or the reverse peak voltage U ARM , take the larger of the two when calculating. K b K is the grid voltage rise coefficient, generally ranging from 1.05 to 1.1, and can be higher in special cases. AU It is the voltage design margin, which is generally 1 to 2, depending on the reliability of the device and the reliability requirements of the equipment. U It is the pressure equalization coefficient, which is usually between 0.8 and 0.9. RM is the rated repetitive peak voltage of the series connected devices.

[0066] Optimize the switching time of the main and auxiliary branches: set the main IGBT turn-off time t through the gate drive circuit off (controls the shutdown command timing) and the auxiliary IGBT on-time t on(Controls the timing of the on-command), adjusts the current transfer time to near the main IGBT's fall time, and adds dead time. This ensures smooth current transfer and sufficient carrier clearance time for the main IGBT in the zero-current state, allowing it to quickly restore its blocking capability after commutation.

[0067] Specifically, such as Figure 3 As shown, when the current flows normally, the main branch IGBT is turned on and the auxiliary branch IGBT is turned off, so that the current flows normally through the main branch thyristor and the main branch IGBT; When natural commutation is required, the main branch IGBT is controlled to be turned off, and the auxiliary branch IGBT is controlled to be turned on, so that the current is transferred from the main branch to the auxiliary branch, and the auxiliary branch thyristor and auxiliary branch IGBT continue to carry the current; During the freewheeling process of the auxiliary branch, the current state is monitored. When it is detected that the current drops to 0, the auxiliary branch IGBT is controlled to be turned off to complete the natural commutation process.

[0068] This method achieves smooth current transfer during the commutation process, ensuring the stability and reliability of the system.

[0069] Loss analysis of controllable phase-changing valve: Most of the losses that need to be calculated in the CLCC converter valve are borne by its main components. The specific losses are as follows: Figure 5 As shown in Figure 2, the CLCC converter valve loss includes: IGBT loss, thyristor loss and other losses (negligible).

[0070] Among them, IGBT losses include: Static loss: includes conduction loss and cutoff loss (negligible). Conduction loss refers to the power loss generated when the IGBT is in the on state.

[0071] Switching loss: includes necessary switching loss and additional switching loss. Necessary switching loss is the unavoidable loss during the normal switching process of the IGBT; additional switching loss is the additional loss caused by additional factors (the additional switching loss value is too small to be ignored).

[0072] Thyristor losses include: Static loss: includes conduction loss and cutoff loss (negligible). Similar to IGBT, conduction loss refers to the power loss of the thyristor when it is in the on state.

[0073] Switching loss: includes necessary switching loss and additional switching loss. Necessary switching loss is the inevitable loss of thyristor during normal switching process; additional switching loss is the additional loss caused by additional factors (the additional switching loss value is too small to be ignored). Among them, the on-state loss of IGBT is and the conduction loss P of the thyristorTcond The calculation is as follows:

[0074] Among them I C is the IGBT collector current, R CE is the on-state resistance between the collector and emitter, V CE is the saturation voltage of the IGBT; I TAV is the average value of the thyristor current, I TRMS is the effective value of the thyristor current, V T is the average on-state voltage of the thyristor, r T is the on-state slope resistance of the thyristor.

[0075] The switching loss of IGBT is divided into necessary switching loss and additional switching loss. SW-T The calculation method is:

[0076] f SW is the switching frequency of the IGBT, E on is the turn-on loss, E off is the turn-off loss.

[0077] The turn-on loss E on Refers to the energy loss generated when IGBT changes from cut-off state to on-state, turn-on loss E on It can be calculated by the following formula:

[0078] where t on(10%) and t on(90%) The time required for the IGBT collector current to rise to 10% and 90% of its normal value. CE (t) is the saturation voltage of the IGBT, I C (t) is the collector current.

[0079] Similarly, the turn-off loss E off The calculation is as follows:

[0080] where t off (10%) and t off (90%) is the time required for the IGBT collector current to drop to 10% and 90% of its normal value. CE (t) is the voltage between the collector and emitter, I C (t) is the collector current.

[0081] Necessary switching losses of thyristors Mainly caused by the opening loss (P TT ) and turn-off loss (P RQ ) consists of two parts, and its calculation formula is:

[0082] Among them, P TT and P RQ The calculation method is:

[0083]

[0084] Where T is the modulation period, P TT t in on (10%) and t on (90%) is the time it takes for the thyristor current to rise to 10% and 90% of its normal value, t off (10%) and t off (90%) is the time it takes for the thyristor current to drop to 10% and 90% of its normal value, V T is the average on-state voltage of the thyristor, I T is the current flowing through the thyristor in the on-time interval. The economic evaluation model of the controllable phase-commutated valve includes: Calculate the total loss cost C of the controllable phase-changing valve loss :

[0085] Among them, C elec The unit electricity cost.

[0086] Calculate the maintenance cost C of the controllable phase-changing valve maint And optimize to minimize the total cost C total :

[0087] In another embodiment, the calculation process is as follows:

[0088] The total loss cost is:

[0089]

[0090] Maintenance costs ,in : Equipment cost (thyristor unit price is 100,000 yuan / piece, IGBT unit price is 150,000 yuan / piece); Km: Maintenance rate (4%).

[0091] The final optimization effect of the case is:

[0092] In another embodiment, it is assumed that the design requirements of a CLCC converter valve are as follows: the maximum operating voltage of the converter valve bridge arm U AM =800kV; overvoltage impulse coefficient K CU =1.5; grid voltage rise coefficient K b =1.1; voltage design margin K AU =1.2; pressure equalization coefficient K U =0.85; thyristor rated repetitive peak voltage U RM =8.5kV; submodule voltage U submodule =2kV; single IGBT rated voltage V device =3.3kV.

[0093] According to the number of main branch thyristors in series N Th formula:

[0094]

[0095] Substituting the parameters, we get:

[0096] According to the number of auxiliary branch IGBTs in series formula:

[0097]

[0098] Assume that the redundancy coefficient K redundancy =1.2 Substituting the parameters, we can get: After determining the number of thyristors and IGBTs in series, the parallel configuration is mainly to meet the current carrying capacity requirements. This means that if a single path cannot withstand the required current, it is necessary to add parallel paths to share the current load. Specifically:

[0099] The number of thyristors connected in parallel can be selected appropriately based on the required current capacity and the rated current of a single thyristor. If a single thyristor cannot carry the expected current, multiple thyristors need to be connected in parallel to increase the total current capacity.

[0100] Similarly, the IGBT can decide whether to connect more IGBTs in parallel to enhance the current carrying capacity based on actual needs.

[0101] Results correction: After rounding up and adding redundancy, the final number of thyristors in series in the main branch is determined to be 242. This is rounded up to 1 IGBT, but considering dynamic voltage fluctuations, 2 IGBTs are finally used in series.

[0102] Assume that under certain working conditions: IGBT saturation voltage V CE =2.1 V; collector current I C =1500 A; on-state resistance R CE =0.001 Ω. According to the conduction loss P of IGBT cond formula:

[0103] Substitute the parameters and calculate:

[0104] PSCAD model parameter setting: Build CLCC converter valve model, such as Figure 9 As shown in the figure, 242 thyristors are set in the main branch and 2 IGBTs are set in the auxiliary branch. The AC bus voltage is simulated to drop to 0.7pu and last for 100ms.

[0105] Figure 10 The waveform data is obtained after simulation of the CLCC model built using the PSCAD simulation software. This data is the power emitted by each bridge arm in the main and auxiliary bridge arm branches. Among them, P1_1 is the power waveform of the main branch in the CLCC, and P1_2 is the power waveform of the auxiliary branch in the CLCC.

[0106] The simulation results are compared as follows: Before optimization: 5 commutation failures / fault; total loss is 12.8MW.

[0107] After optimization: the number of commutation failures was reduced to 1 per fault; the total loss was 9.2MW.

[0108] Loss cost savings: (12.8-9.2)×0.1 yuan / kWh×8760 h=315,000 yuan / year.

[0109] The economic feasibility was verified based on the total losses before and after optimization. After the optimization using the present invention, the maintenance cost was reduced by 20%, verifying the economic feasibility of the optimization scheme.

[0110] The above general description of the invention and the description of its specific embodiments involved in this application should not be construed as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art may, without violating the constituent elements of the invention involved, add to, subtract from, or combine the disclosed technical features in the above general description and / or specific embodiments (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. A CLCC auxiliary branch capacity design and parameter optimization method targeting grid application requirements, characterized in that: The method comprises the following steps: S1: Establish a capacity matching model for the main and auxiliary branches and calculate the basic parameters of the main and auxiliary branches; S2: Optimizing the switching time between the primary and auxiliary branches based on the basic parameters; S3: Based on the basic parameters, a loss model of the controllable phase-commutation valve is established to optimize the conduction time of the main and auxiliary branches; S4: Based on the loss model, an economic evaluation model for the controllable phase-changing valve is established to evaluate the economic efficiency of the optimized solution, and the feasibility of the optimization strategy is verified through simulation.

2. The method according to claim 1, characterized in that The basic parameters include: the number of series connections, parallel configuration and current carrying capacity of thyristors and insulated gate bipolar transistors.

3. The method according to claim 2, characterized in that Number of main branch thyristors connected in series N Th Calculated by the following formula: ； Among them, U AM is the maximum operating voltage of the converter valve bridge arm; K CU is the overvoltage impact coefficient; K b is the grid voltage rise coefficient; K AU is the voltage design margin; K U is the pressure equalization coefficient; U RM is the rated repetitive peak voltage of the thyristor.

4. The method according to claim 2, characterized in that Number N of auxiliary branch insulated gate bipolar transistors connected in series IGBT Calculated by the following formula: ； Among them, U submodule The voltage of each submodule; V device It is the rated voltage of a single insulated gate bipolar transistor device.

5. The method according to claim 1, wherein The optimization of the main-auxiliary branch switching time adopts an adjustment method based on the commutation dynamic process, which specifically includes: Set the turn-off time t of the main branch IGBT off and the conduction time t of the auxiliary branch IGBT on , adjust the current transfer time in the commutation stage to ensure that the main branch thyristor can quickly restore its blocking capacity after commutation.

6. The method according to claim 1, characterized in that The loss model of the controllable commutation valve in S3 includes: The conduction loss P of the insulated gate bipolar transistor cond The calculation formula is as follows: ； Where V CE is the saturation voltage of the insulated gate bipolar transistor, I C is the collector current of the insulated gate bipolar transistor, R CE is the on-state resistance of the insulated gate bipolar transistor.

7. The method according to claim 1, characterized in that The loss mathematical model of the controllable commutation valve in S3 also includes: Thyristor conduction loss P Tcond The calculation formula is as follows: ； Where V T is the on-state voltage of the thyristor, I TAV is the average value of the thyristor current, I TRMS is the effective value of the thyristor current, r T is the on-state slope resistance of the thyristor.

8. The method according to claim 1, characterized in that The economic evaluation model of the controllable phase-changing valve in S4 includes: Calculate the total loss cost C of the controllable phase-changing valve loss : ； Among them, C elec The unit electricity cost.

9. The method according to claim 1, characterized in that The economic evaluation model of the controllable phase-changing valve in S4 also includes: Calculate the maintenance cost C of the controllable phase-changing valve maint And optimize to minimize the total cost C total : 。 10. The method according to claim 1, characterized in that The feasibility of the optimization scheme is verified by simulation, specifically including: Establish an electromagnetic transient simulation model of the controllable phase-changing valve in the software; Simulate commutation failures under different fault conditions and verify the improvement effect of the optimized design on commutation stability.

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