CN105138799A

CN105138799A - Method for designing parameter of direct current reactor suitable for modular multi-level converter

Info

Publication number: CN105138799A
Application number: CN201510600686.2A
Authority: CN
Inventors: 孙树敏; 颜世昭; 行登江; 王昭鑫; 辛征; 石鑫; 李笋; 赵鹏; 李广磊; 张用; 程艳; 吴金龙
Original assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd; Xian XJ Power Electronics Technology Co Ltd
Current assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd; Xian XJ Power Electronics Technology Co Ltd
Priority date: 2015-09-18
Filing date: 2015-09-18
Publication date: 2015-12-09
Anticipated expiration: 2035-09-18
Also published as: CN105138799B

Abstract

The invention discloses a DC reactor parameter design method suitable for a modularized multilevel converter, comprising: determining the maximum instantaneous current value I _lim allowed by the bridge arm according to the converter valve parameters; calculating the occurrence of a DC pole line short circuit fault , the maximum value of the bridge arm current I _fault before the system is blocked; compare the maximum instantaneous current value I _lim of the bridge arm with the maximum value of the bridge arm current I _fault before the system is blocked, and calculate the lower limit value L of the DC reactor inductance _lim , and as the final design value of the inductance of the DC reactor. Beneficial effects of the invention: the inductance value of the DC reactor is designed according to the limit value condition of the maximum fault current that the bridge arm can withstand, and at the same time, the influence of AC feed-in and capacitor discharge on the fault current is considered, the calculation method is simple, and the calculation result is more accurate.

Description

Design Method of DC Reactor Parameters for Modular Multilevel Converter

技术领域technical field

本发明涉及电力系统柔性输配电技术领域，具体涉及一种适用于模块化多电平换流器的直流电抗器参数设计方法。The invention relates to the technical field of flexible power transmission and distribution of power systems, in particular to a parameter design method of a DC reactor suitable for a modular multilevel converter.

背景技术Background technique

随着全控型电力电子器件的发展和电力电子技术在电力系统中的应用，基于模块化多电平换流器的柔性直流输电技术日益受到重视。直流电抗器是模块化多电平换流站系统中的重要设备之一，其参数直接影响系统的故障电流抑制能力。直流电抗器参数的设计主要考虑两个方面的因素：With the development of fully-controlled power electronic devices and the application of power electronics technology in power systems, flexible DC transmission technology based on modular multilevel converters has attracted increasing attention. DC reactor is one of the important equipment in the modular multilevel converter station system, and its parameters directly affect the fault current suppression ability of the system. The design of DC reactor parameters mainly considers two factors:

一是桥臂子模块对故障电流终值的承受能力限制。最严酷的工况是系统发生直流双极短路故障，此时桥臂电流急速上升，考虑直流极线短路故障时，如果系统闭锁之前桥臂故障电流未达到子模块能够承受的电流终值，则不需要直流电抗器来限制故障电流上升速率；如果系统闭锁之前桥臂故障电流已经达到子模块能够承受的电流终值，此时需要设计直流电抗器来抑制故障电流上升率，以保障系统的安全。One is the limit of the bridge arm sub-module's ability to withstand the final value of the fault current. The most severe working condition is that the DC bipolar short-circuit fault occurs in the system. At this time, the current of the bridge arm rises rapidly. When considering the short-circuit fault of the DC pole line, if the fault current of the bridge arm does not reach the final current value that the sub-module can withstand before the system is locked, then There is no need for a DC reactor to limit the rising rate of the fault current; if the fault current of the bridge arm has reached the final current value that the sub-module can withstand before the system is locked, a DC reactor needs to be designed to suppress the rising rate of the fault current to ensure the safety of the system .

二是直流电抗器与桥臂电抗器的优化配置。直流电抗器越大，系统时间常数越大，暂态响应时间越长，同时增加了建造成本，因此，在满足桥臂电抗器的设计条件以及对故障电流的限值条件的情况下，应尽可能的降低直流电抗器的电感值。The second is the optimal configuration of DC reactor and bridge arm reactor. The larger the DC reactor, the larger the system time constant, the longer the transient response time, and increase the construction cost. Therefore, in the case of meeting the design conditions of the bridge arm reactor and the limit conditions for the fault current, it should be Possibly reduce the inductance value of the DC reactor.

现有技术中通过故障电流上升率抑制条件、直流动态响应速度条件确定直流电抗器电感取值的上下限值，但该方法忽略了交流馈入故障点对故障电流的影响，计算结果存在较大误差。In the prior art, the upper and lower limits of the inductance of the DC reactor are determined by the fault current rise rate suppression condition and the DC dynamic response speed condition, but this method ignores the influence of the AC feed-in fault point on the fault current, and the calculation results have large differences. error.

发明内容Contents of the invention

本发明的目的就是解决上述问题，提供了一种适用于模块化多电平换流器的直流电抗器参数设计方法，该方法通过桥臂所能承受的最大故障电流限值条件来设计直流电抗器的参数，同时考虑了交流馈入、电容放电对故障电流的影响，并最终计算得到了直流电抗器值。The purpose of the present invention is to solve the above problems and provide a DC reactor parameter design method suitable for modular multilevel converters. The method designs the DC reactor through the limit condition of the maximum fault current that the bridge arm can bear The parameters of the reactor are considered, and the influence of AC feed and capacitor discharge on the fault current is considered, and the value of the DC reactor is finally calculated.

为实现上述目的，本发明采用下述技术方案，包括：To achieve the above object, the present invention adopts the following technical solutions, including:

一种适用于模块化多电平换流器的直流电抗器参数设计方法，包括：A DC reactor parameter design method suitable for modular multilevel converters, including:

(1)根据换流阀参数确定桥臂允许的最大瞬时电流值I_lim；(1) Determine the maximum instantaneous current value I _lim allowed by the bridge arm according to the parameters of the converter valve;

(2)计算发生直流极线短路故障时，换流站闭锁前的桥臂电流最大值I_fault；(2) Calculate the maximum bridge arm current I _fault before the converter station is blocked when the DC pole line short-circuit fault occurs;

(3)将桥臂允许的最大瞬时电流值I_lim和系统闭锁前的桥臂电流最大值I_fault进行比较，如果I_lim>I_fault，则不设置直流电抗器；如果I_lim<I_fault，则计算直流电抗器电感的下限值L_lim，并作为直流电抗器电感的最终设计值。(3) Compare the maximum instantaneous current value I _lim allowed by the bridge arm with the maximum value I _fault of the bridge arm current before the system is locked. If I _lim >I _fault , no DC reactor is installed; if I _lim <I _fault , Then calculate the lower limit value L _lim of the inductance of the DC reactor, and use it as the final design value of the inductance of the DC reactor.

所述步骤(1)中桥臂允许的最大瞬时电流值I_lim根据换流阀中各元器件的电流限制参数来设定。The maximum instantaneous current value I _lim allowed by the bridge arm in the step (1) is set according to the current limit parameters of the components in the converter valve.

所述步骤(2)中，系统闭锁前桥臂电流最大值I_fault的计算方法为：In the described step (2), the calculation method of the system locking front bridge arm current maximum value I _fault is:

发生直流极线短路故障后，桥臂故障电流由两部分组成：一部分为子模块电容放电电流，一部分为交流系统馈入产生的电流；After the DC pole line short-circuit fault occurs, the fault current of the bridge arm is composed of two parts: one part is the sub-module capacitor discharge current, and the other part is the current generated by the AC system feed-in;

直流极线短路故障时支路等效电感L_eq等于桥臂电抗器电感值L_arm；Branch equivalent inductance L _eq is equal to the inductance value L _arm of the bridge arm reactor when the DC pole line is short-circuited;

分别计算子模块电容放电电流上升率和交流系统馈入产生的电流上升率，根据上述电流上升率与桥臂过流保护时间整定值T_pro，得到系统闭锁前桥臂电流最大值I_fault。Calculate the rising rate of the sub-module capacitor discharge current and the current rising rate generated by the AC system feed-in respectively. According to the above-mentioned current rising rate and the setting value T _pro of the bridge arm overcurrent protection time, the maximum value of the bridge arm current I _fault before the system is blocked is obtained.

所述子模块电容放电电流上升率的确定方法为：The method for determining the rate of rise of the submodule capacitor discharge current is:

${k k}_{c c} = = {U u}_{d d c c} * * \sqrt{\frac{{C C}_{s the s m m}}{N N * * {L L}_{e e q q}}} * * \frac{44}{{T T}_{c c}} = = \frac{{U u}_{d d c c}}{π π * * {L L}_{e e q q}};;$

其中，L_eq为回路等效电感；R_eq为回路等效电阻；C_sm为子模块电容；N为桥臂子模块数；T_c为电容放电周期；U_dc为直流母线电压。Among them, L _eq is the equivalent inductance of the loop; R _eq is the equivalent resistance of the loop; C _sm is the capacitance of the sub-module; N is the number of sub-modules of the bridge arm; T _c is the capacitor discharge cycle; U _dc is the DC bus voltage.

所述交流系统馈入产生的电流上升率的确定方法为：The method for determining the rate of rise of the current generated by the feed-in of the AC system is:

${k k}_{g g} = = \frac{{U u}_{s the s}}{{L L}_{e e q q} + + 22 {L L}_{σ σ}};;$

其中，U_s为换流阀侧交流相电压峰值；L_σ为变压器短路阻抗。Among them, U _s is the peak value of the AC phase voltage on the side of the converter valve; L _σ is the short-circuit impedance of the transformer.

系统闭锁前桥臂电流最大值I_fault具体为：The maximum value I _fault of the front bridge arm current before the system is blocked is specifically:

${I I}_{f f a a u u l l t t} = = {I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{((22 {L L}_{σ σ} + + {L L}_{a a r r m m}))} + + \frac{{U u}_{d d c c}}{{πL πL}_{a a r r m m}}]] \cdot \cdot {T T}_{p p r r o o};;$

其中，I_pro为桥臂过流保护整定值；U_s为换流阀侧交流相电压峰值；U_dc为直流母线电压；L_arm为桥臂电抗器电感值；L_σ为变压器短路阻抗值；T_pro为桥臂过流保护时间整定值。Among them, I _pro is the setting value of the bridge arm overcurrent protection; U _s is the peak value of the AC phase voltage on the side of the converter valve; U _dc is the DC bus voltage; L _arm is the inductance value of the bridge arm reactor; L _σ is the short-circuit impedance value of the transformer; T _pro is the setting value of the bridge arm over-current protection time.

所述步骤(3)中计算直流电抗器电感的下限值L_lim的方法具体为：The method for calculating the lower limit value L _lim of the DC reactor inductance in the step (3) is specifically:

${I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{((22 {L L}_{σ σ} + + {L L}_{a a r r m m} + + {L L}_{lim lim}))} + + \frac{{U u}_{d d c c}}{π π (({L L}_{a a r r m m} + + {L L}_{lim lim}))}]] \cdot \cdot {T T}_{p p r r o o} = = {I I}_{lim lim};;$

其中，I_pro为桥臂过流保护整定值，U_s为换流阀侧交流相电压峰值；U_dc为直流母线电压；L_arm为桥臂电抗器电感值；L_σ为变压器短路阻抗；T_pro为桥臂过流保护时间整定值。Among them, I _pro is the setting value of the bridge arm overcurrent protection, U _s is the peak value of the AC phase voltage on the side of the converter valve; U _dc is the DC bus voltage; L _arm is the inductance value of the bridge arm reactor; L _σ is the short-circuit impedance of the transformer; T _pro is the setting value of the bridge arm overcurrent protection time.

直流电抗器电感取值的下限值L_lim具体为：The lower limit value L _lim of the inductance value of the DC reactor is specifically:

L_lim＝max(L_dc1,L_dc2)；L _lim = max(L _dc1 ,L _dc2 );

其中， $\{\begin{matrix} L_{d c 1} = \frac{- b + \sqrt{b^{2} - 4 a c}}{2 a} \\ L_{d c 2} = \frac{- b - \sqrt{b^{2} - 4 a c}}{2 a} \\ a = π \cdot \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \\ b = 2 π (L_{σ} + L_{a r m}) \cdot \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} - U_{d c} - {πU}_{s} \\ c = (2 L_{σ} + L_{a r m}) \cdot (π \cdot \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \cdot L_{a r m} - U_{d c}) - π \cdot U_{s} \cdot L_{a r m} \end{matrix}$ in, $\{\begin{matrix} L_{d c 1} = \frac{- b + \sqrt{b^{2} - 4 a c}}{2 a} \\ L_{d c 2} = \frac{- b - \sqrt{b^{2} - 4 a c}}{2 a} \\ a = π &Center Dot; \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \\ b = 2 π (L_{σ} + L_{a r m}) &Center Dot; \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} - u_{d c} - {π U}_{the s} \\ c = (2 L_{σ} + L_{a r m}) \cdot (π &Center Dot; \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \cdot L_{a r m} - u_{d c}) - π &Center Dot; u_{the s} &Center Dot; L_{a r m} \end{matrix}$

L_arm为桥臂电抗器值；L_σ为变压器短路阻抗，I_pro为桥臂过流保护整定值，I_fault为系统闭锁前桥臂电流最大值，U_s为换流阀侧交流相电压峰值；U_dc为直流母线电压，T_pro为桥臂过流保护时间整定值。L _arm is the bridge arm reactor value; L _σ is the short-circuit impedance of the transformer, I _pro is the setting value of the bridge arm overcurrent protection, I _fault is the maximum value of the bridge arm current before the system is blocked, and U _s is the peak value of the AC phase voltage at the converter valve side ; U _dc is the DC bus voltage, T _pro is the setting value of the bridge arm over-current protection time.

本发明有益效果：Beneficial effects of the present invention:

本发明直流电抗器参数设计方法通过桥臂所能承受的最大故障电流限值条件来设计直流电抗器电感值，考虑了交流馈入、电容放电对故障电流的影响，计算方法简单，同时计算结果表达式中不含电容参数，消除了电容参数误差对直流电抗器参数计算的影响，结果更加准确。The DC reactor parameter design method of the present invention designs the inductance value of the DC reactor through the limit condition of the maximum fault current that the bridge arm can bear, and considers the influence of AC feed-in and capacitor discharge on the fault current, the calculation method is simple, and the calculation results are simultaneously The expression does not contain capacitance parameters, which eliminates the influence of capacitance parameter errors on the calculation of DC reactor parameters, and the results are more accurate.

附图说明Description of drawings

图1是本发明提供的直流电抗器参数设计过程流程图；Fig. 1 is a flow chart of the DC reactor parameter design process provided by the present invention;

图2是本发明提供的电容放电等效回路；Fig. 2 is the capacitive discharge equivalent circuit that the present invention provides;

图3是本发明提供的交流馈入故障电流等效回路。Fig. 3 is the equivalent circuit of AC feed-in fault current provided by the present invention.

具体实施方式Detailed ways

下面结合附图与实施例对本发明做进一步说明：Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

本发明所述直流电抗器设计方法设计流程框图如图1所示。The flow chart of the DC reactor design method of the present invention is shown in FIG. 1 .

首先要根据换流阀参数得到桥臂允许的最大瞬时电流值I_lim。在换流阀的设计过程中，需要对主回路器件进行选型，桥臂允许流过的最大瞬时电流值受开关器件、电容等元件的限值，通过查阅相关元件的数据手册或者咨询厂家即可得到桥臂允许流过的最大瞬时电流值I_lim。Firstly, the maximum instantaneous current value I _lim allowed by the bridge arm must be obtained according to the parameters of the converter valve. In the design process of the converter valve, it is necessary to select the main circuit components. The maximum instantaneous current value allowed to flow through the bridge arm is limited by the switching devices, capacitors and other components. By consulting the data sheets of relevant components or consulting the manufacturer The maximum instantaneous current value I _lim allowed to flow through the bridge arm can be obtained.

其次是计算发生直流极线短路故障时，系统闭锁前的桥臂电流最大值I_fault。The second is to calculate the maximum value I _fault of the bridge arm current before the system is locked when a DC pole line short circuit fault occurs.

由于加入直流电抗器之后会造成系统暂态调节时间变长，且增加换流站的建造成本，因此需要对加入直流电抗器的必要性进行验证。本发明选择直流极线短路故障时，系统闭锁前的桥臂最大电流值I_fault与I_lim相比较，来确定是否需要设计直流电抗器。Since adding a DC reactor will result in longer system transient adjustment time and increase the construction cost of the converter station, it is necessary to verify the necessity of adding a DC reactor. In the present invention, when the short-circuit fault of the DC pole line is selected, the maximum current value I _fault of the bridge arm before the system is locked is compared with I _lim to determine whether a DC reactor needs to be designed.

发生直流极线短路故障后，桥臂故障电流由两部分组成，一部分为子模块电容放电电流，一部分为交流系统馈入产生的电流。短时间内可以认为二者为线性变化，则其变化率可以计算为：After the DC pole line short-circuit fault occurs, the fault current of the bridge arm is composed of two parts, one part is the sub-module capacitor discharge current, and the other part is the current generated by the AC system feed-in. In a short period of time, the two can be considered as linear changes, and the rate of change can be calculated as:

①子模块电容放电电流变化率计算。① Calculation of the rate of change of the sub-module capacitor discharge current.

子模块放电回路等效电路如图2所示。其中L_eq为回路等效电感，R_eq为回路等效电阻，C_sm为子模块电容，N为桥臂子模块数。The equivalent circuit of the sub-module discharge circuit is shown in Figure 2. Among them, L _eq is the loop equivalent inductance, R _eq is the loop equivalent resistance, C _sm is the sub-module capacitance, and N is the number of bridge arm sub-modules.

其中R_eq相对较小，可以忽略不计，因此电容放电周期可以计算为：where R _eq is relatively small and can be ignored, so the capacitor discharge cycle can be calculated as:

${T T}_{c c} = = 22 π π \sqrt{\frac{22 \cdot &Center Dot; {C C}_{s the s m m} \cdot \cdot 22 \cdot &Center Dot; {L L}_{e e q q}}{N N}} - - - - - - ((33))$

则子模块放电电流上升率可以计算为：Then the sub-module discharge current rising rate can be calculated as:

${k k}_{c c} = = {U u}_{d d c c} * * \sqrt{\frac{{C C}_{s the s m m}}{N N * * {L L}_{e e q q}}} * * \frac{44}{{T T}_{c c}} = = \frac{{U u}_{d d c c}}{π π * * {L L}_{e e q q}} - - - - - - ((44))$

②交流馈入电流上升率计算。② Calculation of the rate of rise of the AC feed current.

交流馈入电流等效回路如图3所示。其中R_eq、R_stray为回路等效电阻，L_σ为变压器短路阻抗，u_s为电网相电压，L_eq为支路等效电感。The equivalent circuit of AC feeding current is shown in Fig.3. Among them, R _eq and R _stray are the equivalent resistance of the loop, L _σ is the short-circuit impedance of the transformer, u _s is the phase voltage of the grid, and L _eq is the equivalent inductance of the branch.

由于R_eq、R_stray相对较小，可以忽略不计，则桥臂电流可以计算为：Since _Req and R _stray are relatively small and can be ignored, the arm current can be calculated as:

$\{\begin{matrix} {i i}_{u u} = = \frac{{U u}_{s the s}}{{ω ω}_{s the s} (({L L}_{e e q q} + + 22 {L L}_{σ σ}))} [[11 - - cos cos (({ω ω}_{s the s} t t))]] \\ {i i}_{d d} = = \frac{{U u}_{s the s}}{{ω ω}_{s the s} (({L L}_{e e q q} + + 22 {L L}_{σ σ}))} [[11 + + cos cos (({ω ω}_{s the s} t t))]] \end{matrix} - - - - - - ((55))$

考虑最严重的工况，则桥臂电流上升率最大值可以计算为：Considering the most serious working condition, the maximum value of the bridge arm current rise rate can be calculated as:

${k k}_{g g} = = \frac{{U u}_{s the s}}{{L L}_{e e q q} + + 22 {L L}_{σ σ}} - - - - - - ((66))$

系统保护动作前的桥臂最大电流可以计算为(直流极线短路故障时L_eq等于L_arm)：The maximum current of the bridge arm before the system protection action can be calculated as (L _eq is equal to L _arm when the DC pole line is short-circuited):

${I I}_{f f a a u u l l t t} = = {I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{{L L}_{a a r r m m} + + 22 {L L}_{σ σ}} + + \frac{{U u}_{d d c c}}{π π \cdot \cdot {L L}_{a a r r m m}}]] \cdot \cdot {T T}_{p p r r o o} - - - - - - ((77))$

式中，I_pro为桥臂过流保护电流整定值；T_pro为桥臂过流保护时间整定值，U_dc为直流母线电压。In the formula, I _pro is the setting value of the bridge arm over-current protection current; T _pro is the setting value of the bridge arm over-current protection time, and U _dc is the DC bus voltage.

最后比较I_lim和I_fault的大小关系，并确定直流电抗器的最终设计值。Finally, compare the size relationship between I _lim and I _fault , and determine the final design value of the DC reactor.

直流电抗器最终设计值的确定方法为：The method for determining the final design value of the DC reactor is:

当I_lim大于I_fault时，理论上可以不设置直流电抗器。When I _lim is greater than I _fault , theoretically, no DC reactor can be set.

当I_lim小于I_fault时，需要设置直流电抗器来抑制故障电流，此时需要通过解方程来计算直流电抗器下限值L_lim，方程如下(接入直流电抗器后的直流双极短路故障回路等效电感L_eq为L_arm与直流电抗器的和)：When I _lim is less than I _fault , a DC reactor needs to be installed to suppress the fault current. At this time, the lower limit value L _lim of the DC reactor needs to be calculated by solving the equation. The equation is as follows (DC bipolar short-circuit fault after connecting the DC reactor The loop equivalent inductance L _eq is the sum of L _arm and DC reactor):

${I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{{L L}_{a a r r m m} + + 22 {L L}_{σ σ} + + {L L}_{lim lim}} + + \frac{{U u}_{d d c c}}{π π \cdot &Center Dot; (({L L}_{a a r r m m} + + {L L}_{l l i i m m}))}]] \cdot &Center Dot; {T T}_{p p r r o o} = = {I I}_{f f a a u u l l t t} - - - - - - ((88))$

解方程(8)，可以得到直流电抗器取值的下限值：Solving equation (8), the lower limit of the value of the DC reactor can be obtained:

L_lim＝max(L_dc1,L_dc2)(9)L _lim = max(L _dc1 ,L _dc2 )(9)

式中：In the formula:

$\{\begin{matrix} {L L}_{d d c c 11} = = \frac{- - b b + + \sqrt{{b b}^{22} - - 44 a a c c}}{22 a a} \\ {L L}_{d d c c 22} = = \frac{- - b b - - \sqrt{{b b}^{22} - - 44 a a c c}}{22 a a} \\ a a = = π π \cdot &Center Dot; \frac{{I I}_{f f a a u u l l t t} - - {I I}_{p p r r o o}}{{T T}_{s the s}} \\ b b = = 22 π π (({L L}_{σ σ} + + {L L}_{a a r r m m})) \cdot \cdot \frac{{I I}_{f f a a u u l l t t} - - {I I}_{p p r r o o}}{{T T}_{s the s}} - - {U u}_{d d c c} - - {πU πU}_{s the s} \\ c c = = ((22 {L L}_{σ σ} + + {L L}_{a a r r m m})) \cdot &Center Dot; ((π π \cdot \cdot \frac{{I I}_{f f a a u u l l t t} - - {I I}_{p p r r o o}}{{T T}_{s the s}} \cdot \cdot {L L}_{a a r r m m} - - {U u}_{d d c c})) - - π π \cdot &Center Dot; {U u}_{s the s} \cdot &Center Dot; {L L}_{a a r r m m} \end{matrix} - - - - - - ((1010))$

考虑直流电抗器的优化配置，则选择计算得到的直流电抗器下限值L_lim作为直流电抗器的最终设计值，即L_dc＝L_lim。Considering the optimal configuration of the DC reactor, the calculated lower limit value L _lim of the DC reactor is selected as the final design value of the DC reactor, that is, L _dc =L _lim .

上述虽然结合附图对本发明的具体实施方式进行了描述，但并非对本发明保护范围的限制，所属领域技术人员应该明白，在本发明的技术方案的基础上，本领域技术人员不需要付出创造性劳动即可做出的各种修改或变形仍在本发明的保护范围以内。Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims

1. A DC reactor parameter design method suitable for modular multilevel converters, characterized in that it comprises:

(1) Determine the maximum instantaneous current value I _lim allowed by the bridge arm according to the parameters of the converter valve;

(2) Calculate the maximum bridge arm current I _fault before the converter station is blocked when the DC pole line short-circuit fault occurs;

(3) Compare the maximum instantaneous current value I _lim allowed by the bridge arm with the maximum value I _fault of the bridge arm current before the system is locked. If I _lim >I _fault , no DC reactor is installed; if I _lim <I _fault , Then calculate the lower limit value L _lim of the inductance of the DC reactor, and use it as the final design value of the inductance of the DC reactor.

2. a kind of DC reactor parameter design method that is applicable to modular multilevel converter as claimed in claim 1, is characterized in that, the maximum instantaneous current value I _lim that bridge arm allows in described step (1) Set according to the current limit parameters of each component in the converter valve.

3. a kind of DC reactor parameter design method that is applicable to modularized multilevel converter as claimed in claim 1, is characterized in that, in described step (2), system locks front bridge arm current maximum value I The calculation method of _fault is:

After the DC pole line short-circuit fault occurs, the fault current of the bridge arm is composed of two parts: one part is the sub-module capacitor discharge current, and the other part is the current generated by the AC system feed-in;

Branch equivalent inductance L _eq is equal to the inductance value L _arm of the bridge arm reactor when the DC pole line is short-circuited;

Calculate the rising rate of the sub-module capacitor discharge current and the current rising rate generated by the AC system feed-in respectively. According to the above-mentioned current rising rate and the setting value T _pro of the bridge arm overcurrent protection time, the maximum value of the bridge arm current I _fault before the system is blocked is obtained.

4. A method for designing DC reactor parameters suitable for modular multilevel converters as claimed in claim 3, wherein the method for determining the rising rate of the submodule capacitor discharge current is:

{k k}_{c c} = = {U u}_{d d c c} * * \sqrt{\frac{{C C}_{s the s m m}}{N N * * {L L}_{e e q q}}} * * \frac{44}{{T T}_{c c}} = = \frac{{U u}_{d d c c}}{π π * * {L L}_{e e q q}};;

Among them, L _eq is the equivalent inductance of the loop; R _eq is the equivalent resistance of the loop; C _sm is the capacitance of the sub-module; N is the number of sub-modules of the bridge arm; T _c is the capacitor discharge cycle; U _dc is the DC bus voltage.

5. A method for designing parameters of a DC reactor suitable for a modular multilevel converter as claimed in claim 3, wherein the method for determining the rate of rise of the current generated by the feed-in of the AC system is:

{k k}_{g g} = = \frac{{U u}_{s the s}}{{L L}_{e e q q} + + 22 {L L}_{σ σ}};;

Among them, U _s is the peak value of the AC phase voltage on the side of the converter valve; L _σ is the short-circuit impedance of the transformer.

6. A method for designing DC reactor parameters suitable for modular multilevel converters as claimed in claim 3, wherein the maximum value I _fault of the bridge arm current before the system is locked is specifically:

{I I}_{f f a a u u l l t t} = = {I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{((22 {L L}_{σ σ} + + {L L}_{a a r r m m}))} + + \frac{{U u}_{d d c c}}{{πL πL}_{a a r r m m}}]] \cdot &Center Dot; {T T}_{p p r r o o};;

Among them, I _pro is the setting value of the bridge arm overcurrent protection; U _s is the peak value of the AC phase voltage on the side of the converter valve; U _dc is the DC bus voltage; L _arm is the inductance value of the bridge arm reactor; L _σ is the short-circuit impedance value of the transformer; T _pro is the setting value of the bridge arm over-current protection time.

7. a kind of DC reactor parameter design method suitable for modular multilevel converter as claimed in claim 1, is characterized in that, in the described step (3), calculate the lower limit value L of DC reactor inductance The specific method of _lim is:

{I I}_{p p r r o o} + + [[\frac{{U u}_{s the s}}{((22 {L L}_{σ σ} + + {L L}_{a a r r m m} + + {L L}_{lim lim}))} + + \frac{{U u}_{d d c c}}{π π (({L L}_{a a r r m m} + + {L L}_{lim lim}))}]] \cdot &Center Dot; {T T}_{p p r r o o} = = {I I}_{lim lim};;

Among them, I _pro is the setting value of the bridge arm overcurrent protection, U _s is the peak value of the AC phase voltage on the side of the converter valve; U _dc is the DC bus voltage; L _arm is the inductance value of the bridge arm reactor; L _σ is the short-circuit impedance of the transformer; T _pro is the setting value of the bridge arm overcurrent protection time.

8. A method for designing DC reactor parameters suitable for modular multilevel converters as claimed in claim 4, wherein the lower limit value L _lim of the DC reactor inductance value is specifically:

L _lim = max(L _dc1 ,L _dc2 );

in,

\{\begin{matrix} L_{d c 1} = \frac{- b + \sqrt{b^{2} - 4 a c}}{2 a} \\ L_{d c 2} = \frac{- b - \sqrt{b^{2} - 4 a c}}{2 a} \\ a = π &Center Dot; \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \\ b = 2 π (L_{σ} + L_{a r m}) \cdot \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} - u_{d c} - {π U}_{the s} \\ c = (2 L_{σ} + L_{a r m}) &Center Dot; (π &Center Dot; \frac{I_{f a u l t} - I_{p r o}}{T_{p r o}} \cdot L_{a r m} - u_{d c}) - π &Center Dot; u_{the s} &Center Dot; L_{a r m} \end{matrix}

L _arm is the bridge arm reactor value; L _σ is the short-circuit impedance of the transformer, I _pro is the setting value of the bridge arm overcurrent protection, I _fault is the maximum value of the bridge arm current before the system is blocked, and U _s is the peak value of the AC phase voltage at the converter valve side ; U _dc is the DC bus voltage, T _pro is the setting value of the bridge arm over-current protection time.