CN115663876B - Main loop parameter design method and system for hybrid cascade extra-high voltage direct current system - Google Patents

Abstract

The present invention relates to the field of direct current transmission, and provides a method and system for designing the main circuit parameters of a hybrid cascaded UHV DC system, including: determining the operation mode of the hybrid cascaded UHV DC system; determining the basic control mode of VSC and LCC at the receiving end, The voltage distribution mode between VSC and LCC and the current distribution mode between each VSC, construct the steady-state mathematical model of the hybrid cascaded system under the obtained constraint equation; calculate the DC voltage variation range of the VSC port under each operation mode, and design each Modulation ratio range in the operating mode; based on the constraints of the PQ operating range of the VSC, solve the PQ operating range of the VSC and determine the gear range; determine the maximum operating power of the hybrid cascaded UHVDC system in this operating mode; based on the system The maximum operating power and VSC reactive power are used to solve the steady-state mathematical model of the hybrid cascaded system to obtain the steady-state operating parameters of the system.

Description

Design method and system for main circuit parameters of hybrid cascaded UHVDC system

technical field

The invention relates to a method and system for designing parameters of a main circuit of a hybrid cascaded UHV direct current system, and relates to the field of direct current transmission.

Background technique

In order to realize long-distance large-capacity power transmission and multi-point power supply, and solve the problem of lower short-circuit ratio of multiple infeeds at the receiving end, hybrid cascaded UHVDC transmission technology can be used, that is, conventional DC converters and multiple flexible DC converters The technical solution of cascading connection, which combines the advantages of conventional DC and flexible DC, can effectively improve the stability of the AC power grid at the receiving end, has high reliability, flexible operation mode, and has broad application prospects. key technologies.

The purpose of the parameter design of the main circuit of the hybrid cascaded UHV DC system is to determine the key parameters of the DC main equipment, and to clarify the steady-state operating parameters of the DC system under various operating conditions. Transient steady-state performance of the system.

The prior art has not involved how to design the main circuit parameters of the hybrid cascade UHVDC transmission, complete the selection of the main equipment parameters of the hybrid cascade system, and obtain the steady-state operating characteristics.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a method, system, equipment and medium for designing the main circuit parameters of the hybrid cascaded UHV DC system capable of determining the parameters of the main DC equipment and the steady-state operating parameters.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

In the first aspect, the method for designing the main circuit parameters of the hybrid cascaded UHV DC system provided by the present invention includes:

Determine the operation mode of the hybrid cascaded UHVDC system;

Determine the basic control mode of VSC and LCC at the receiving end, the voltage distribution mode of VSC and LCC, and the current distribution mode between VSCs, and build a steady-state mathematical model of the hybrid cascaded system under the obtained constraint equations;

Calculate the DC voltage variation range of the VSC port under each operation mode, and design the modulation ratio range under each operation mode;

Based on the constraints of the PQ operating range of the VSC, the PQ operating range of the VSC is solved, and the gear range that needs to be configured for the soft direct commutation rheology is determined;

Determine the maximum operating power of the hybrid cascaded UHVDC system under this operating mode;

Based on the maximum operating power of the system and VSC reactive power, the steady-state mathematical model of the hybrid cascaded system is solved to obtain the steady-state operating parameters of the system.

Further, the voltage distribution method of VSC and LCC includes:

VSC and LCC are distributed according to equal DC voltage, and the corresponding constraint equation is U _dcvsc = U _dclcc , U _dcvsc and U _dclcc are the port DC voltages of VSC and LCC respectively;

The VSC does not consider the fluctuation of the DC voltage, and the line voltage drop is all borne by the LCC. The corresponding constraint equation is U _dcvsc = U _setvsc , where U _dcvsc is the DC voltage of the VSC port, and U _setvsc is the set value.

Further, the current distribution method among the VSCs includes:

The VSCs are distributed according to the method of equal current, then the constraint equation is: I _vsc1 = I _vsc2 =... I _vscn = I _dc / n , I _vsc1 , ... I _vscn are the 1st to nth VSCs respectively DC current, I _dc is the total current flowing into the VSC valve group;

The operating power is independently specified between each VSC, and the constraint equation is: I _vsc1 = P _vsc1 / U _setvsc , I _vsc2 = P _vsc2 / U _setvsc , _... I _vscn = I _dc - I _vsc1 - I _vsc2... I _vsc(n-1) , P _vsc1 and P _vsc2 are the active powers of VSC1 and VSC2.

Further, the method for determining the modulation ratio range in each operation mode includes:

According to the principle of maximum line resistance, calculate the flexible minimum port voltage U _dcinit in this operating mode;

Traverse the working conditions that require VSC power transfer under various faults, calculate the port voltage after VSC power transfer under each working condition, and determine the minimum port voltage U _dcfinal under each working condition;

Determine the maximum modulation ratio M _absmax that ensures that the VSC output voltage is not modulated, and calculate the maximum modulation ratio M _max in each operating mode, M _max = U _dcfinal × M _absmax / U _dcinit ;

Design the minimum modulation ratio M _min according to the number of levels that can meet the harmonic requirements of the system.

Further, solve the PQ operating interval of VSC, including:

a. Determine the limiting conditions of the PQ operating range of the VSC, including the DC voltage range of the VSC port, the modulation ratio range, the AC voltage range, the bridge arm current limit, and the transformer capacity limit;

b. Based on the constraint conditions, solve the PQ operation interval, and the PQ operation interval takes the intersection of different DC voltage and AC voltage combinations;

c. Determine whether the power range satisfies the system’s setting requirements for power exchange. If so, determine the PQ operation range and VCS gear position. If not, go to d;

d. If the output reactive power is insufficient or the bridge arm current causes power limitation, then increase the negative gear configuration; if the absorbed reactive power is insufficient, increase the positive gear configuration and go to step b.

Furthermore, the PQ operating interval is designed according to the union of the PQ operating intervals under all gears. When a single gear cannot meet the system requirements, gradually increase the configuration range of the gear to increase the PQ operating interval until the gear configuration meets In this operation mode, the system needs VSC exchange capacity, or until the exchange power between VSC and system can no longer be increased by increasing the gear position, the PQ operation range in this operation mode is obtained, and the combination of the gear positions obtained in each operation mode The set is the gear designed for VSC.

Further, the method for increasing the configuration range of gears includes: when the limitation of the bridge arm current causes the absorption or emission of active power or reactive power to be insufficient, increasing the negative gear configuration, when the limitation of the modulation ratio causes the absorption of reactive power to be insufficient , increase the positive gear configuration; when the modulation ratio limitation results in insufficient reactive power, increase the negative gear configuration.

In the second aspect, the present invention provides a hybrid cascaded UHV DC system main circuit parameter design system, including:

an operation mode determination unit configured to determine the operation mode of the hybrid cascaded UHVDC system;

The model construction unit is configured to determine the basic control mode of the VSC and LCC at the receiving end, the voltage distribution mode of the VSC and LCC, and the current distribution mode between each VSC, and construct the steady-state mathematics of the hybrid cascaded system under the set constraint equations Model;

The parameter determination unit is configured to calculate the variation range of the VSC port DC voltage in each operation mode, and design the modulation ratio range in each operation mode; based on the constraint conditions of the PQ operation interval of the VSC, solve the PQ operation interval of the VSC, and determine the flexible The gear range that needs to be configured for the direct-conversion rheology; determine the maximum operating power of the hybrid cascaded UHV DC system under this operating mode;

The model calculation unit is configured to solve the steady-state mathematical model of the hybrid cascaded system based on the system operating power and the VSC reactive power, and obtain the steady-state operating parameters of the system.

In a third aspect, the present invention provides an electronic device, including computer program instructions, wherein, when the program instructions are executed by a processor, they are used to implement the method for designing the main circuit parameters of the hybrid cascaded UHV DC system.

In a fourth aspect, the present invention provides a computer-readable storage medium, where computer program instructions are stored on the computer-readable storage medium, wherein the program instructions are used to implement the hybrid cascading when executed by a processor Design method of main circuit parameters of UHV DC system.

The present invention has the following characteristics due to the adoption of the above technical scheme:

1. The present invention solves the steady-state mathematical model of the hybrid cascade system within the determined system operating power and VSC reactive power by constructing the steady-state mathematical model of the hybrid cascade system, and obtains the steady-state operating parameters of the system. Therefore , the main circuit design scheme proposed by the present invention can ensure that the system still has full power operation capability after the exit of a single flexible DC converter, thereby reducing the forced capacity unavailability rate of the hybrid cascaded system from 0.5% of conventional DC to 0.375%, Effectively improve the reliability of the system.

2. For the first time, the present invention proposes a differential design method for modulation ratios in different operating modes, which effectively solves the problem of limited power transfer in hybrid cascaded systems due to insufficient VSC step-down operating capability.

To sum up, the present invention proposes the design scheme of the main circuit of the hybrid cascaded DC system for the first time, which fills the gap in the prior art, and can be widely applied to the parameters of the main circuit of the hybrid cascaded UHV DC system.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention. Throughout the drawings, the same reference numerals are used to refer to the same parts. In the attached picture:

Fig. 1 is an overall flowchart of parameter design of a hybrid cascaded UHV DC main circuit according to an embodiment of the present invention.

Fig. 2 is a flow chart of designing a modulation ratio range of a hybrid cascaded UHVDC VSC according to an embodiment of the present invention.

Fig. 3 is a flow chart of the hybrid cascaded UHVDC VSC operating range and gear design according to the embodiment of the present invention.

Fig. 4 is a topological structure diagram of a hybrid cascaded UHV DC system according to an embodiment of the present invention.

FIG. 5 is a structural diagram of an electronic device according to an embodiment of the present invention.

Detailed ways

It should be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may also be meant to include the plural forms unless the context clearly dictates otherwise. The terms "comprising", "comprising", "containing" and "having" are inclusive and thus indicate the presence of stated features, steps, operations, elements and/or parts but do not exclude the presence or addition of one or Various other features, steps, operations, elements, components, and/or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless an order of performance is specifically indicated. It should also be understood that additional or alternative steps may be used.

For the convenience of description, spatial relative terms may be used herein to describe the relationship of one element or feature as shown in the figures with respect to another element or feature, such as "inner", "outer", "inner". ", "Outside", "Below", "Above", etc. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

The main circuit parameter design method of hybrid cascaded UHV DC is quite different from the conventional DC and flexible DC projects in the past, and its operating capacity is limited by the number of conventional DC converter valves, flexible DC converter valves, flexible DC Various factors, such as fault ride-through capability, need to integrate the transient steady-state operation characteristics of the system to obtain the system operation capability under hundreds of modes considering different numbers of flexible and direct operations. In addition, the flexible DC presents a large-scale fluctuation of DC voltage of 0.7~1pu for the first time, and the design of its power operation range needs to focus on the factors of large-scale fluctuations of DC voltage, and it is difficult to realize the adaptation of a single active power-reactive power circle diagram (PQ circle diagram). Various modes of operation. At the same time, the configuration of the voltage regulating switch of the flexible DC is also the focus of the parameter design of the main circuit, which needs to be designed in conjunction with the modulation ratio to ensure the operation ability under the large-scale fluctuation of the DC voltage.

Based on the above design ideas, the design method for the main circuit parameters of the hybrid cascaded UHV DC system proposed in this embodiment includes: determining the operation mode of the hybrid cascaded UHV DC system; determining the basic control mode of the VSC and LCC at the receiving end, VSC and The LCC voltage distribution method and the current distribution method between each VSC, construct the steady-state mathematical model of the hybrid cascade system under the obtained constraint equation; calculate the DC voltage variation range of the VSC port under each operation mode, and design each operation mode Lower the modulation ratio range; based on the constraints of the PQ operating range of the VSC, solve the PQ operating range of the VSC, and determine the range of gears that need to be configured for the flexible DC converter; determine the maximum Operating power: within the determined system operating power and VSC reactive power, solve the steady-state mathematical model of the hybrid cascade system to obtain the steady-state operating parameters of the system.

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided for more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

As shown in Figure 1, the method for designing the main circuit parameters of the hybrid cascaded UHV DC system provided in this embodiment includes:

S1. Determine the operation mode of the hybrid cascaded UHV DC system according to the system requirements and the topology characteristics of the hybrid cascaded UHV DC system.

In this embodiment, the operation mode of hybrid cascaded UHV DC is classified. Firstly, according to the classification method of conventional UHV DC operation mode, bipolar/unipolar ground/unipolar metal, double valve group/single valve group and The combination of valve groups, among them, there are 45 types of VSC (voltage source converter) valve groups according to the integrated consideration method, further considering the number of VSC operating with different positive and negative poles and the operating VSC valves, it can be combined to determine the operation of each sub-category Included below are the modes of operation.

Furthermore, since VSC and LCC (Line Commutated Converter) reverse the power flow, the voltage cannot be reversed and the current cannot be reversed respectively. Therefore, the topology characteristics of the hybrid cascade determines that the hybrid cascade UHV DC does not consider power feedback. Configure the power mutual aid mode between multiple VSCs according to system requirements, that is, some VSCs run in the rectification state, and some VSCs run in the inverter state. Step-down operation is realized by switching to half-pressure operation, avoiding double-valve group step-down operation through constant straight and soft straight asymmetric step-down. On the one hand, the configuration and action frequency of the tap changer are reduced, and the frequent action of the tap changer is greatly reduced. On the one hand, it avoids the severe limitation of the power transfer belt caused by the withdrawal of the LCC during the asymmetric step-down.

S2. According to the topology structure of the hybrid cascade, determine the basic control mode of the VSC and LCC at the receiving end, the voltage distribution mode of the VSC and LCC, and the current distribution mode between each VSC, and list the constraint equations to build a stable hybrid cascade system. state mathematical model.

In this embodiment, the voltage distribution methods of VSC and LCC include two types:

The first way: VSC and LCC are distributed according to equal DC voltage, then the corresponding constraint equation is U _dcvsc = U _dclcc , U _dcvsc and U _dclcc are the port DC voltages of VSC and LCC respectively;

The second method: VSC does not consider the fluctuation of the DC voltage, and all the line voltage drops are borne by the LCC. The corresponding constraint equation is U _dcvsc = U _setvsc , U _dcvsc is the DC voltage of the VSC port, and U _setvsc is the set value.

Among them, in the first method, the port voltage of the VSC fluctuates greatly, and the VSC needs to be configured with more gears. In the second method, the port voltage fluctuation of the LCC is twice the original, and the LCC gear configuration is large, and the voltage drop of the unipolar metal return is large. When the gear is adjusted to the limit, the cut-off angle needs to be increased. The reactive power of the converter valve increases, and because the LCC and VSC voltages operate asymmetrically, if the LCC fails and exits, the voltage difference between the sending and receiving terminals will be huge, and the power transfer capability will be severely limited. According to the principle of being friendly to the system, when the VSC gear configuration is not limited, the first method is adopted.

In this embodiment, the current distribution methods among the VSCs include two types:

The first method is: all VSCs are distributed according to equal current, then the constraint equation is: I _vsc1 = I _vsc2 =... I _vscn = I _dc / n , I _vsc1 , ... I _vscn are respectively The direct current of 1 to n VSCs, I _dc is the total current flowing into the VSC valve group;

The second method: independently specify the operating power between each VSC, then the constraint equation is: I _vsc1 = P _vsc1 / U _setvsc , I _vsc2 = P _vsc2 / U _setvsc , _... I _vscn = I _dc - I _vsc1 - I _vsc2... I _vsc(n-1) , P _vsc1 and P _vsc2 are the active powers of VSC1 and VSC2.

S3. According to the maximum line resistance, maximum operating current, minimum line resistance, and minimum operating current, the DC voltage variation range of the VSC port is solved in each operating mode, and the VSC voltage drop requirements for various transfer power requirements are calculated in each operating mode. And design the modulation ratio range under each operation mode.

In this embodiment, the variation range of the DC voltage at the port of the VSC in each operating mode is calculated to be [ U _dcmin , U _dcmax ].

In this embodiment, as shown in Figure 2, the method for determining the modulation ratio range under each operating mode is:

According to the principle of maximum line resistance, calculate the flexible minimum port voltage U _dcinit in this operating mode;

Traverse the working conditions that require VSC power transfer under various faults, calculate the port voltage after VSC power transfer under each working condition, and determine the minimum port voltage U _dcfinal under each working condition;

Determine the maximum modulation ratio M _absmax that ensures that the VSC output voltage is not modulated, and calculate the maximum modulation ratio M _max in each operating mode, M _max = U _dcfinal × M _absmax / U _dcinit , where U _dcfinal is the maximum voltage drop caused by the transfer power The post-fault DC voltage under the working condition, U _dcinit is the pre-fault DC voltage under the working condition where the transfer power causes the largest voltage drop, and M _absmax is the maximum modulation ratio to ensure that the flexible DC output voltage is not modulated. If the third harmonic Injection, generally between 1.05 and 1.15.

Design the minimum modulation ratio M _min according to the number of levels that can meet the harmonic requirements of the system, generally 0.7~0.85.

Furthermore, different modulation ratio ranges can be designed for each operation mode. In order to simplify the control and protection strategy, the 45 operation modes can be further divided into 2~3 categories according to the modulation ratio range required for power transfer. The intersection of the modulation ratio ranges of all operating modes satisfying the power transfer band requirement determines a unified modulation ratio range.

S4. Based on the determined port DC voltage and DC current of LCC and VSC, according to the selection method of the main equipment parameters of LCC and VSC, independently calculate the equipment parameters such as rated voltage, rated capacity and short-circuit impedance of the converter transformer of LCC and VSC respectively.

S5. Based on the constraints of the PQ operating interval of the VSC, solve the PQ operating interval of the VSC, and determine the range of gears that need to be configured for the soft direct commutation rheology;

In this embodiment, as shown in Figure 3, the PQ operating interval of the VSC is solved, including:

S51. Determine the constraints of the PQ operating range of the VSC, including constraints such as the VSC port DC voltage variation range, modulation ratio range, AC voltage variation range, bridge arm current limitation, and transformer capacity limitation;

S52. Solve the PQ operation interval based on the constraint conditions, and the PQ operation interval takes the intersection of different DC voltage and AC voltage combinations;

S53. Determine whether the power range meets the system's setting requirements for power exchange, if yes, determine the PQ operation range and the VCS gear, if no, then enter S54;

S54. If the reactive power generated is insufficient or the bridge arm current causes power limitation, increase the negative gear configuration; if the absorbed reactive power is insufficient, increase the positive gear configuration, and enter step S52.

Furthermore, the PQ operating interval is designed according to the union of the PQ operating intervals under all gears. When a single gear cannot meet the system requirements, the configuration range of the gear is gradually increased to increase the PQ operating interval. Until the gear configuration meets the requirements of the system for VSC switching capacity in this operating mode, or the switching power between the VSC and the system can no longer be increased by increasing the gear, the PQ operating range in this operating mode can be obtained, and obtained in each operating mode The union of the gears is the gear designed by VSC.

Furthermore, different PQ operation intervals can be designed for each operation mode. In order to simplify the control and protection strategy, the 45 operation modes can be further divided into 2~3 categories, and each category provides a unified PQ that satisfies all the operation modes in the category. Operation interval, each unified PQ operation interval is the intersection of PQ operation intervals of all operation modes of this type.

Further, the method of increasing the configuration range of gears is: when the limit of the bridge arm current causes insufficient active power or reactive power to be absorbed or emitted, increase the negative gear configuration; when the limitation of the modulation ratio results in insufficient absorbed reactive power, Add a positive gear configuration; when the modulation ratio limitation results in insufficient reactive power, add a negative gear configuration.

S6. Determine the maximum operating power P _vscmax1 corresponding to the VSC according to the PQ operating interval, and calculate the maximum operating power of the rectification side corresponding to the maximum operating power, that is, the maximum operating power P _max1 of the system, and calculate according to the minimum line resistance.

S7. Based on the PSCAD/EMTDC software, establish the electromagnetic transient simulation model of the hybrid cascaded system. The maximum operating power of the system that meets the requirements of AC fault ride-through in each operating mode is simulated and scanned to be P _max2 . When calculating, the system power is first set to Rated value, simulation calculation of the overvoltage of the converter valve and the energy of the controllable self-restoring energy dissipation device when the AC system fails, if the limit is not exceeded, the maximum power P _max2 is the rated power of the system, otherwise, P _max2 is gradually reduced until it can Until the overpressure of the converter valve and the energy requirements of the energy dissipation device are met.

In this embodiment, a detailed controllable self-restoring energy dissipation device model is established in PSCAD/EMTDC software, and the principle to meet the fault ride-through requirements of the AC system is: the voltage of the module does not exceed the overvoltage protection setting value for the unlocking operation of the converter valve, and the bridge arm If the current does not reach the protection setting value, the energy of the energy dissipation device is within its maximum design energy. Among them, the surge arrester of the energy dissipation device needs to be simulated separately when it has a large characteristic and a small characteristic.

S8. Determine the maximum operating power P _max =max( P _max1 , P _max2 ) of the system in this operating mode. If the maximum operating power is less than the rated operating power of the system, power limit processing is required, or methods such as using IGBT devices with greater current capacity, increasing the number of modules, and increasing the module capacitance to further increase P _max1 and P _max2 until the system power requirements are met .

S9. Within the final determined system operating power and VSC reactive power, solve the constructed steady-state mathematical model of the hybrid cascaded system, and calculate the operating characteristics of the operating power from 0.1pu to 1pu in each operating mode to form a stable system. State running parameters.

In this embodiment, under each operating mode, the Newton-Raphson method is used to solve the steady-state mathematical model.

The application of the method for designing the parameters of the main circuit of the hybrid cascaded UHV DC system provided by the present invention will be described in detail below through specific embodiments.

As shown in Figure 4, the sending end of the hybrid cascaded UHVDC transmission system adopts a conventional UHV DC topology, and each pole is composed of two twelve-pulse conventional DC converters cascaded; the receiving end adopts a hybrid cascaded UHVDC topology. Topology, each pole consists of a high-voltage side (ie 800kV~400kV) twelve-pulse conventional DC converter and a low-voltage side (400kV~neutral line) multiple (3 shown in the figure) parallel-connected flexible DC converters It is formed by cascading, and the flexible DC converter adopts a half-bridge modular multilevel converter, and the conventional DC converter at the receiving end and each flexible DC converter are fed into different AC buses.

In the following, the present invention will be further described in detail by taking the design of the main circuit parameters of the ±800kV/8000MW UHVDC power transmission system mixed cascaded with a single LCC and 3 VSCs at the receiving end as a specific example.

1. First, determine the operation mode of the hybrid cascaded UHVDC system according to the system requirements and the topology characteristics of the hybrid cascaded UHVDC system.

Specifically, the operation mode of the hybrid cascaded UHVDC is divided into 7 categories and 45 subcategories according to the conventional UHVDC. Considering that the number of VSCs with different positive and negative poles is 1, 2 or 3, the combination is determined. There are a total of 621 operation modes included in each sub-category of operation.

2. According to the topology structure of the hybrid cascade, determine the basic control mode, voltage distribution mode and current distribution mode of the VSC and LCC at the receiving end, and build a steady-state mathematical model of the hybrid cascade system.

Specifically, the LCC at the sending end adopts constant DC current control, and the LCC at the receiving end adopts constant DC voltage control. Among the three VSCs at the receiving end, one is controlled by constant DC voltage, and the other two are controlled by constant active power.

Determine the voltage distribution method of VSC and LCC, for example, adopt the method of balancing high and low voltage voltages.

Determine the current distribution mode among the VSCs, for example, divide the currents equally among the three VSCs.

Then the constraint equations are: I _dc = I _set , U _dcvsc = U _dclcc = U _set , I _vsc1 = I _vsc2 = I _vsc3 , and finally build a steady-state mathematical model of the hybrid cascaded system:

In the formula, UdR and UdI are the terminal voltage of a single LCC converter at the sending end and the receiving end, R _eq is _the equivalent resistance of the DC circuit, U _di0R and U _di0I are the rectification side and the inverter side each ₆ The ideal no-load DC voltage of the pulse converter, U _di0NR and U _di0NI are the ideal no-load DC voltage ratings of each 6-pulse converter on the rectification side and the inverter side, respectively, α is the firing angle of the rectification side, and γ is the inverse The turn-off angle of the variable side, d _xR and d _xI are the nominal value of the inductance voltage drop on the rectifier side and the inverter side respectively, d _rR and d _rI are the standard value of the resistance voltage drop on the rectifier side and the inverter side respectively, I _dN is the DC current rating, U _T is the inherent voltage drop of a 6-pulse converter, P _vscn and Q _vscn are the active power and reactive power of the nth VSC, M _n is the modulation ratio of the nth VSC, U _sn and U _cn are the AC bus voltage of the nth VSC and the output voltage of the converter, X is the equivalent reactance between the AC bus of the VSC and the converter, δ n is the AC bus voltage and the converter output voltage of the nth VSC The phase angle difference of the converter output voltage.

3. According to the maximum line resistance, maximum operating current, minimum line resistance, and minimum operating current, solve the DC voltage variation range of the VSC port in each operating mode, and design the maximum modulation ratio M _max and the minimum modulation ratio M in each operating mode _min .

In this embodiment, the rated resistance is 10Ω, the maximum resistance is 12Ω, the minimum line resistance is 8Ω, the maximum operating current is 5kA, and the minimum short-circuit current is 0.5kA. Taking the unipolar metal return operation as an example, the port voltage range of the VSC in this mode is [340, 396]kV. In this mode, under various rotating conditions, the working condition with the largest possible pressure drop is the single valve When the group exits, the VSC voltage needs to be reduced from 340kV to 280kV. Considering that the maximum modulation ratio that cannot be guaranteed to be modulated is 1.05, the maximum modulation ratio in this mode is further determined to be 0.86.

4. Based on the determined port DC voltage and DC current of LCC and VSC, according to the selection method of main equipment parameters of LCC and VSC, independently calculate the equipment parameters such as rated voltage, rated capacity and short-circuit impedance of LCC and VSC respectively.

In this embodiment, under rated working conditions, the port DC voltage of the sending end LCC is 400kV, and the DC current is 5kA; the port DC voltage of the receiving end LCC is 375kV, and the DC current is 5kA; the port DC voltage of the receiving end VSC is 375kV, The DC current is 5kA, and the basic equipment parameters of LCC and VSC are calculated according to the traditional method.

5. Based on the constraints of VSC port DC voltage variation range, modulation ratio range, AC voltage variation range, bridge arm current limit, transformer capacity limit, etc., and solve the PQ operating range of VSC.

The PQ operating interval is designed according to the union of the PQ operating intervals under all gears. When a single gear cannot meet the system requirements, gradually increase the configuration range of the gear to increase the PQ operating interval. Until the gear configuration meets the requirements of the system for VSC switching capacity in this operating mode, or the switching power between the VSC and the system can no longer be increased by increasing the gear, the PQ operating range in this operating mode can be obtained, and obtained in each operating mode The union of the gears is the gear designed by VSC.

The maximum operating power of the VSC is determined as follows: when the VSC valve group operates at full pressure and the current is symmetrical to the current of the other pole, the maximum operating power of a single VSC (unipolar) is 1000MW; the VSC valve group operates at extremely full pressure and is connected to another pole. When the current in one pole is asymmetrical or the VSC valve group operates at half pressure and is symmetrical with the current of the other pole, the maximum operating power of a single VSC (unipolar) is 960MW; When symmetrical, the maximum operating power of a single VSC (unipolar) is 800MW. The gears that VSC should design are +24, -6 gears.

6. Then, according to the maximum operating power P _vscmax1 corresponding to the VSC determined in the PQ operating interval, calculate the maximum operating power of the rectification side corresponding to the maximum operating power, that is, the maximum operating power P _max1 of the system, and calculate according to the minimum line resistance.

In this embodiment, when the number of VSCs is 3, the maximum operating power of the system is the same as that of conventional DC; when the number of VSCs is 2, the maximum operating power of the system in most modes is the same as that of conventional DC, and only one The situation is limited, that is, unipolar half-voltage operation with VSC, and the maximum operating power of the system is 1730MW at this time.

7. Establish the PSCAD simulation model _of the hybrid cascaded system, and simulate and scan _the maximum operating power of the system that meets the AC fault ride-through requirements under each operating mode to be Pmax2 . In this embodiment, by optimizing the parameters of the energy dissipation device, Pmax2 and Regular DC works the same.

8. Determine the maximum operating power P _max =max( P _max1 , P _max2 ) of the system in this operating mode. For the limited unipolar half-voltage operation and the number of VSCs is 2, the maximum operating power is limited.

9. Within the final determined system operating power and VSC reactive power, solve the constructed steady-state mathematical model of the hybrid cascaded system, and calculate the operating characteristics of the operating power from 0.1pu to 1pu in each operating mode to form a stable system. State running parameters. Among them, Table 1 and Table 2 show the steady-state operation parameter table under the bipolar full-pressure 1+3 operation mode in this embodiment.

Table 1 Normal straight part

Table 2 Soft straight part

Embodiment 2: The first embodiment above provides a method for designing the parameters of the main circuit of the hybrid cascaded UHV DC system. Correspondingly, this embodiment provides a system for designing the parameters of the main circuit of the hybrid cascaded UHV DC system. The system provided in this embodiment can implement the method for designing the parameters of the main circuit of the hybrid cascaded UHV DC system in Embodiment 1, and the system can be realized by software, hardware, or a combination of software and hardware. For the convenience of description, when describing this embodiment, functions are divided into various units and described separately. Of course, the functions of each unit can be realized in one or more pieces of software and/or hardware during implementation. For example, the system may include integrated or separate functional modules or functional units to execute corresponding steps in the methods of the first embodiment. Since the system of this embodiment is basically similar to the method embodiment, the description process of this embodiment is relatively simple. For relevant points, please refer to the part of the description of Embodiment 1. The parameters of the main circuit of the hybrid cascaded UHV DC system provided by the present invention The embodiments of the design system are illustrative only.

Specifically, the hybrid cascaded UHV DC system main circuit parameter design system provided in this embodiment includes:

an operation mode determination unit configured to determine the operation mode of the hybrid cascaded UHVDC system;

The model construction unit is configured to determine the basic control mode of the VSC and LCC at the receiving end, the voltage distribution mode of the VSC and LCC, and the current distribution mode between each VSC, and construct the steady-state mathematics of the hybrid cascaded system under the set constraint equations Model;

The parameter determination unit is configured to calculate the variation range of the VSC port DC voltage in each operation mode, and design the modulation ratio range in each operation mode; based on the constraint conditions of the PQ operation interval of the VSC, solve the PQ operation interval of the VSC, and determine the flexible The gear range that needs to be configured for the direct-conversion rheology; determine the maximum operating power of the hybrid cascaded UHV DC system under this operating mode;

The model calculation unit is configured to solve the steady-state mathematical model of the hybrid cascaded system based on the system operating power and the VSC reactive power, and obtain the steady-state operating parameters of the system.

Embodiment 3: This embodiment provides an electronic device corresponding to the method for designing the main circuit parameters of the hybrid cascaded UHV DC system provided in Embodiment 1. The electronic device can be an electronic device for the client, such as a mobile phone, a notebook Computers, tablet computers, desktop computers, etc., to execute the method of Embodiment 1.

As shown in FIG. 5 , the electronic device includes a processor, a memory, a communication interface and a bus, and the processor, the memory and the communication interface are connected through the bus to complete mutual communication. The bus can be an Industry Standard Architecture (ISA, Industry Standard Architecture) bus, a Peripheral Component Interconnect (PCI, Peripheral Component) bus, or an Extended Industry Standard Architecture (EISA, Extended Industry Standard Component) bus, etc. A computer program that can run on the processor is stored in the memory, and when the processor runs the computer program, the method for designing the parameters of the main circuit of the hybrid cascaded UHV DC system provided in Embodiment 1 is executed. Those skilled in the art can understand that the structure shown in FIG. 5 is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computing device to which the solution of the application is applied. The specific computing device can be More or fewer components than shown in the figures may be included, or some components may be combined, or have a different arrangement of components.

In some implementations, the above logic instructions in the memory may be implemented in the form of software functional units and may be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or the part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including Several instructions are used to make a computer device (which may be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage media include: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), CD-ROM and other media that can store program codes.

In other implementations, the processor may be various types of general-purpose processors such as a central processing unit (CPU) and a digital signal processor (DSP), which are not limited herein.

Embodiment 4: The method for designing the main circuit parameters of the hybrid cascaded UHV DC system in Embodiment 1 can be embodied as a computer program product, and the computer program product can include a computer-readable storage medium, which is loaded with a Computer-readable program instructions of the method for designing the parameters of the main circuit of the hybrid cascaded UHV DC system described in Example 1.

A computer readable storage medium may be a tangible device that holds and stores instructions for use by an instruction execution device. A computer readable storage medium may be, for example, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the above.

Each embodiment in this specification is described in a progressive manner, the same and similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for relevant parts, refer to part of the description of the method embodiment. In the description of this specification, descriptions with reference to the terms "one embodiment", "some implementations" and the like mean that specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one implementation of the embodiments of this specification. example or examples. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

The present application is described with reference to flowcharts and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each procedure and/or block in the flowchart and/or block diagram, and combinations of procedures and/or blocks in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions may be provided to a general purpose computer, special purpose computer, embedded processor, or processor of other programmable data processing equipment to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing equipment produce a Means for realizing the functions specified in one or more steps of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to operate in a specific manner, such that the instructions stored in the computer-readable memory produce an article of manufacture comprising instruction means, the instructions The device realizes the function specified in one or more procedures of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions can also be loaded onto a computer or other programmable data processing device, causing a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby The instructions provide steps for implementing the functions specified in the flow chart flow or flows and/or block diagram block or blocks.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (9)

1. A method for designing the main circuit parameters of a hybrid cascaded UHV DC system, characterized in that it comprises: Determine the operation mode of the hybrid cascaded UHVDC system; Determine the basic control mode of VSC and LCC at the receiving end, the voltage distribution mode of VSC and LCC, and the current distribution mode between VSCs, and build a steady-state mathematical model of the hybrid cascaded system under the obtained constraint equations; Calculate the variation range of the VSC port DC voltage in each operating mode, and design the modulation ratio range in each operating mode, where the modulation ratio range in each operating mode is: Calculate the maximum modulation ratio M _max = U _dcfinal × M _absmax / U _dcinit in each operating mode, U _dcfinal is the post-fault DC voltage under the condition where the transfer power causes the largest voltage drop, and U _dcinit is the voltage drop caused by the transfer power The DC voltage before the fault under the maximum working condition, M _absmax is the maximum modulation ratio to ensure that the flexible DC output voltage is not modulated; the minimum modulation ratio M _min is designed according to the level number that can meet the harmonic requirements of the system; Based on the constraints of the PQ operating range of the VSC, the PQ operating range of the VSC is solved, and the gear range that needs to be configured for the soft direct commutation rheology is determined; Determine the maximum operating power of the hybrid cascaded UHVDC system under this operating mode; Based on the maximum operating power of the system and VSC reactive power, the steady-state mathematical model of the hybrid cascaded system is solved to obtain the steady-state operating parameters of the system. 2. The method for designing the main circuit parameters of the hybrid cascaded UHVDC system according to claim 1, wherein the voltage distribution method of VSC and LCC includes: VSC and LCC are distributed according to equal DC voltage, and the corresponding constraint equation is U _dcvsc = U _dclcc , U _dcvsc and U _dclcc are the port DC voltages of VSC and LCC respectively; The VSC does not consider the fluctuation of the DC voltage, and the line voltage drop is all borne by the LCC. The corresponding constraint equation is U _dcvsc = U _setvsc , where U _dcvsc is the DC voltage of the VSC port, and U _setvsc is the set value. 3. The method for designing the main circuit parameters of the hybrid cascaded UHVDC system according to claim 2, wherein the current distribution mode between each VSC includes: The VSCs are distributed according to the method of equal current, then the constraint equation is: I _vsc1 = I _vsc2 =... I _vscn = I _dc / n , I _vsc1 , ... I _vscn are the 1st to nth VSCs respectively DC current, I _dc is the total current flowing into the VSC valve group; The operating power is independently specified between each VSC, and the constraint equation is: I _vsc1 = P _vsc1 / U _setvsc , I _vsc2 = P _vsc2 / U _setvsc … I _vscn = P _vscn / U _setvsc and I _vscn = I _dc - I _vsc1 - I _vsc2 ... I _{vsc (n-1)} , P _vsc1 , P _vsc2 ... P _vscn are active powers of VSC1, VSC2 ... VSCn. 4. The method for designing the main circuit parameters of the hybrid cascaded UHV DC system according to claim 1, wherein solving the PQ operating interval of the VSC includes: a. Determine the limiting conditions of the PQ operating range of the VSC, including the DC voltage range of the VSC port, the modulation ratio range, the AC voltage range, the bridge arm current limit and the transformer capacity limit; b. Based on the constraint conditions, solve the PQ operation interval, and the PQ operation interval takes the intersection of different DC voltage and AC voltage combinations; c. Judging whether the power range meets the system’s setting requirements for power exchange, if yes, then determine the PQ operation range and VCS gear, if no, then enter d; d. If the output reactive power is insufficient or the bridge arm current causes power limitation, then increase the negative gear configuration; if the absorbed reactive power is insufficient, increase the positive gear configuration and go to step b. 5. The method for designing the main circuit parameters of the hybrid cascaded UHVDC system according to claim 1, wherein the PQ operating interval is designed according to the union of the PQ operating intervals under all gears, and when a single gear cannot meet the requirements of the system When required, gradually increase the configuration range of gears to increase the PQ operating range until the gear configuration meets the system's demand for VSC switching capacity in this operating mode, or until the switching power of the VSC and the system can no longer be increased by increasing the gear , that is, the PQ operating interval under this operating mode is obtained, and the union of the gears obtained under each operating mode is the gear designed by the VSC. 6. The method for designing the parameters of the main circuit of the hybrid cascaded UHVDC system according to claim 4 or 5, wherein the method for increasing the configuration range of gear positions includes: when the current limitation of the bridge arm causes the absorption or emission of active power When the power or reactive power is insufficient, increase the negative gear configuration; when the modulation ratio limit results in insufficient absorbed reactive power, increase the positive gear configuration; when the modulation ratio limit results in insufficient outgoing reactive power, increase the negative gear configuration. 7. A hybrid cascaded UHV DC system main circuit parameter design system, characterized in that it includes: an operation mode determination unit configured to determine the operation mode of the hybrid cascaded UHVDC system; The model construction unit is configured to determine the basic control mode of the VSC and LCC at the receiving end, the voltage distribution mode of the VSC and LCC, and the current distribution mode between each VSC, and construct the steady-state mathematics of the hybrid cascaded system under the set constraint equations Model; The parameter determination unit is configured to calculate the variation range of the VSC port DC voltage in each operation mode, and design the modulation ratio range in each operation mode; based on the constraint conditions of the PQ operation interval of the VSC, solve the PQ operation interval of the VSC, and determine the flexible The range of gears that need to be configured for direct-conversion rheology; determine the maximum operating power of the hybrid cascaded UHV DC system in this operating mode; among them, the design range of modulation ratios in each operating mode is: Calculate the maximum modulation ratio M in each operating mode _max = U _dcfinal × M _absmax / U _dcinit , U _dcfinal is the post-fault DC voltage under the condition of the largest voltage drop caused by the rotating power, U _dcinit is the pre-fault DC voltage under the operating condition of the largest voltage drop caused by the rotating power , M _absmax is the maximum modulation ratio to ensure that the flexible DC output voltage is not modulated; the minimum modulation ratio M _min is designed according to the number of levels that can meet the harmonic requirements of the system; The model calculation unit is configured to solve the steady-state mathematical model of the hybrid cascaded system based on the maximum operating power of the system and the VSC reactive power, and obtain the steady-state operating parameters of the system. 8. An electronic device, characterized in that it includes computer program instructions, wherein the program instructions are used to implement the main circuit of the hybrid cascaded UHV DC system according to any one of claims 1 to 6 when executed by a processor Parametric Design Method. 9. A computer-readable storage medium, wherein computer program instructions are stored on the computer-readable storage medium, wherein the program instructions are used to implement any one of claims 1-6 when executed by a processor. The design method of the main circuit parameters of the hybrid cascaded UHV DC system described in the item.

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