MMC power module with bridge arm reactance and simulation construction method thereof

Abstract

The invention relates to the technical field of electrical equipment, in particular to an MMC power module with a bridge arm reactor and a simulation construction method thereof.The MMC power module comprises a first switch unit, a second switch unit, a module capacitor, a module reactor, a first connecting end and a second connecting end, and the first switch unit is connected with the second switch unit; the first connecting end is arranged between the first switch unit and the second switch unit, one end of the module capacitor is connected with the first switch unit, the other end of the module capacitor is connected with the second switch unit, one end of the module reactor is connected with the module capacitor and the second switch unit, and the other end of the module reactor is connected with the second connecting end; according to the MMC power module, the module reactance is additionally arranged at the second connecting end, when an offshore converter station is constructed, a plurality of MMC power modules are connected in series into a bridge arm circuit, namely, the distributed bridge arm reactor design is adopted, the bridge arm reactance is dispersed into the sub-modules of the corresponding bridge arm circuit, and the overall construction size and difficulty of the offshore converter station can be reduced.

Description

Technical Field

[0001] The present application relates to the technical field of electrical equipment, and in particular to an MMC power module with bridge arm reactance and a simulation construction method thereof. Background Art

[0002] The offshore converter station includes multiple bridge arm circuits and multiple bridge arm reactors. Each bridge arm circuit is composed of several sub-modules connected in series and with the same structure. The upper and lower bridge arm circuits constitute a phase unit. A bridge arm circuit is connected in series with a bridge arm reactor and then connected in series with a voltage source converter. The bridge arm reactor is mainly used to suppress the double frequency circulating current of the bridge arm. The sub-module in the bridge arm circuit can be an MMC power module (Modular Multilevel Converter, MMC for short). In the offshore converter station scheme, a centralized bridge arm reactor design scheme is mostly adopted, that is, multiple bridge arm reactors are usually concentrated in a separate room, and the electrical lines are dispersedly connected to other modules (such as MMC power modules and other modules) after passing through the room. The layout of the room needs to meet the anti-magnetic range and increase the DC wall bushing for connecting with upstream and downstream power equipment, etc. This leads to the continuous increase in the construction volume and difficulty of the offshore converter station with the continuous increase in transmission capacity and transmission distance. Summary of the invention

[0003] Based on the above technical problems, the present application provides an MMC power module with bridge arm reactance and a simulation construction method thereof, which increases the bridge arm reactance design, which is conducive to dispersing the bridge arm reactance to each sub-module of the corresponding bridge arm when building an offshore converter station, thereby reducing the construction volume and difficulty of the offshore converter station.

[0004] In a first aspect, the present application provides an MMC power module with a bridge arm reactance, comprising a first switch unit, a second switch unit, a module capacitor, a module reactance, a first connection end and a second connection end, the first switch unit and the second switch unit are connected, the first connection end is arranged between the first switch unit and the second switch unit, one end of the module capacitor is connected to the first switch unit, and the other end of the module capacitor is connected to the second switch unit, one end of the module reactance is connected to the module capacitor and the second switch unit, and the other end of the module reactance is connected to the second connection end.

[0005] Preferably, the first switch unit includes a first insulated gate bipolar transistor and a first diode, the emitter of the first insulated gate bipolar transistor and the anode of the first diode are connected to the first connection end, and the collector of the first insulated gate bipolar transistor and the cathode of the first diode are connected to the module capacitor.

[0006] Preferably, the second switch unit includes a second insulated gate bipolar transistor and a second diode, the emitter of the second insulated gate bipolar transistor and the anode of the second diode are connected to the module reactance, and the collector of the second insulated gate bipolar transistor and the cathode of the second diode are connected to the first connection terminal.

[0007] In a second aspect, the present application also provides a simulation construction method for an MMC power module with a bridge arm reactance, wherein the MMC power module with a bridge arm reactance includes a first switch unit, a second switch unit, a module capacitor, a module reactance, a first connection end and a second connection end, the first switch unit and the second switch unit are connected, the first connection end is arranged between the first switch unit and the second switch unit, one end of the module capacitor is connected to the first switch unit, the other end of the module capacitor is connected to the second switch unit, one end of the module reactance is connected to the module capacitor and the second switch unit, and the other end of the module reactance is connected to the second connection end; the simulation construction method for the MMC power module with a bridge arm reactance includes the following steps:

[0008] The dynamic components in the MMC power module with bridge arm reactance are equivalent by Dommel algorithm, and the passive equivalent circuit of the MMC power module with bridge arm reactance is obtained;

[0009] Based on the passive equivalent circuit, the bridge arm circuit containing the MMC power module with bridge arm reactance is subjected to the Thevenin equivalent circuit, and the bridge arm Thevenin equivalent circuit is obtained.

[0010] Using simulation software and bridge arm equivalent circuit, an equivalent circuit simulation model of the MMC power module with bridge arm reactance is established;

[0011] Perform simulation calculation and analysis on the equivalent circuit simulation model.

[0012] Specifically, the first switch unit includes a first insulated gate bipolar transistor and a first diode, the emitter of the first insulated gate bipolar transistor and the anode of the first diode are connected to the first connection end, the collector of the first insulated gate bipolar transistor and the cathode of the first diode are connected to the module capacitor; and the second switch unit includes a second insulated gate bipolar transistor and a second diode, the emitter of the second insulated gate bipolar transistor and the anode of the second diode are connected to the module reactance, the collector of the second insulated gate bipolar transistor and the cathode of the second diode are connected to the first connection end;

[0013] The method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain the passive equivalent circuit of the MMC power module with bridge arm reactance comprises the following steps:

[0014] Based on the component characteristics of the module capacitor, the capacitor voltage function formula u in the MMC power module with bridge arm reactance is obtained c (t);

[0015] Based on the trapezoidal integration method, the capacitance voltage function formula u c (t) is expanded to obtain the additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs ;

[0016] Among them, the capacitor voltage function formula is:

[0017]

[0018] Additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs for:

[0019]

[0020] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u c (t) is the capacitor voltage at the current moment, u c (t-Δt) is the capacitor voltage at the previous moment, C0 is the module capacitance value, i c (τ) Capacitor current.

[0021] Specifically, the method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain the passive equivalent circuit of the MMC power module with bridge arm reactance also includes the following steps:

[0022] Based on the component characteristics of the module inductor, the inductor current function formula u in the MMC power module with bridge arm reactance is obtained L (t);

[0023] Based on the trapezoidal integration method, the inductor current function formula u L (t) is expanded to obtain the additional inductor voltage source function formula U Ls And the inductor time-step resistance function formula R Ls ;

[0024] Among them, the inductor current function formula u L (t) is:

[0025]

[0026] Additional inductance voltage source function formula U Ls And the inductor time-step resistance function formula R Ls for:

[0027]

[0028] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u L (t) is the inductor voltage at the current moment, u L (t-Δt) is the inductor voltage at the previous moment, L1 is the module inductance value, i L (τ) Inductor current.

[0029] Specifically, the method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain the passive equivalent circuit of the MMC power module with bridge arm reactance also includes the following steps:

[0030] The first insulated gate bipolar transistor, the first diode, the second insulated gate bipolar transistor, and the second diode are respectively equivalent to variable binary resistors.

[0031] Specifically, the passive equivalent circuit is based on which the Thevenin equivalent of the bridge arm circuit of the MMC power module with the bridge arm reactance is performed to obtain the Thevenin equivalent circuit of the bridge arm, and the steps include:

[0032] Make a single bridge arm Thevenin equivalent circuit for the passive equivalent circuit;

[0033] The N MMC power modules with bridge arm reactances are simulated to be connected in series end to end in a bridge arm circuit to obtain the overall bridge arm Thevenin equivalent circuit of the bridge arm circuit; N is a positive integer.

[0034] Specifically, the Thevenin equivalent power supply U in the Thevenin equivalent circuit of a single bridge arm is SMeq And the equivalent resistance R SMeq The expression is:

[0035]

[0036] In the formula, R T1 is the equivalent resistance of the first switch unit, R T2 is the equivalent resistance of the second switch unit, R C is the module capacitor equivalent resistance, R L is the module inductor equivalent resistance, U Cs is the additional capacitor voltage source, U Ls is the additional inductor voltage source.

[0037] Specifically, the total resistance of the bridge arm in the overall bridge arm Thevenin equivalent circuit is R eq And the sum of the bridge arm voltage source U eq The expression is:

[0038]

[0039] Where N is the total number of MMC power modules connected in series in the bridge arm circuit. is the equivalent voltage of the i-th MMC power module of the bridge arm circuit, is the equivalent resistance of the i-th MMC power module in the bridge arm circuit.

[0040] The beneficial effects of this application are as follows:

[0041] On the first aspect, the MMC power module with bridge arm reactor provided by the present application adds a module reactor at the second connection end, that is, the reactor is connected at the outlet to suppress the double frequency circulating current of the bridge arm. When an AC fault or a DC fault occurs inside, it can also suppress the fault current flowing through the bridge arm; multiple MMC power modules with bridge arm reactors are connected in series in a bridge arm circuit, that is, a distributed bridge arm reactor design is adopted. In this way, the overall solution of the offshore converter station can cancel the original centralized bridge arm reactor, and there is no need to specially design a room for laying out the bridge arm reactor, and the equipment configuration connected to the upstream and downstream power equipment is reduced. In other words, the present application will carry out a modular design of the bridge arm reactor. When the offshore converter station is constructed, the bridge arm reactor is dispersed in the sub-modules of the corresponding bridge arm. It is only necessary to connect the MMC power module with the bridge arm reactor to the corresponding bridge arm circuit, thereby reducing the construction volume and difficulty of the offshore converter station.

[0042] On the second aspect, the simulation construction method of the MMC power module with bridge arm reactance provided in the present application solves the problems of large computational workload and long simulation time when simulating a detailed MMC power module model with bridge arm reactance due to the increase in the number of dynamic components in the offshore converter station, thereby realizing efficient and fast simulation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A circuit schematic diagram of an MMC power module according to an embodiment of the present application;

[0044] Figure 2 A schematic diagram of a circuit principle of an application scenario of an MMC power module according to an embodiment of the present application;

[0045] Figure 3 A flowchart of the steps of the simulation construction method of the MMC power module of the embodiment of the present application;

[0046] Figure 4 This is a schematic diagram of an equivalent circuit of an MMC power module according to an embodiment of the present application;

[0047] Figure 5 A schematic diagram of an equivalent circuit principle of an application scenario of an MMC power module according to an embodiment of the present application;

[0048] Figure 6This is a schematic diagram of the circuit principle of an existing offshore converter station;

[0049] Figure 7 This is a schematic diagram of the steady-state simulation results of the existing offshore converter station solution;

[0050] Figure 8 A schematic diagram of steady-state simulation results of an offshore converter station solution according to an embodiment of the present application;

[0051] Fig. 9 This is a schematic diagram of transient simulation results of the existing offshore converter station solution;

[0052] Fig.10 Schematic diagram of transient simulation results of the offshore converter station solution according to an embodiment of the present application. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0054] In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. For ease of description, the concepts of "first", "second", etc. mentioned in this application are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units. The modifications of "one" and "multiple" mentioned in this application are illustrative and non-restrictive, and those skilled in the art should understand that unless otherwise clearly stated in the context, it should be understood as "one or more".

[0055] refer to Figure 1 , the embodiment of the present application provides an MMC power module with a bridge arm reactance, including a first switch unit, a second switch unit, a module capacitor C0, a module reactance L1, a first connection terminal A and a second connection terminal B, a first insulated gate bipolar transistor T1 and a first diode D1 are combined into a first switch unit, a second insulated gate bipolar transistor T2 and a second diode D2 are combined into a second switch unit, the first switch unit and the second switch unit are connected, the first connection terminal A is arranged between the first switch unit and the second switch unit, one end of the module capacitor C0 is connected to the first switch unit, the other end of the module capacitor C0 is connected to the second switch unit, one end of the module reactance L1 is connected to the module capacitor C0 and the second switch unit, and the other end of the module reactance L1 is connected to the second connection terminal B. Reference Figure 2In an application scenario of the MMC power module with bridge arm reactance, a bridge arm circuit includes multiple MMC power modules, represented by PM1, PM2...PMN. The MMC power modules PM1, PM2,..., PMN are connected end to end in series to form the bridge arm circuit. The upper and lower bridge arm circuits constitute a phase unit. Each MMC power module includes the above-mentioned first switch unit, the second switch unit, the module capacitor C0, the module reactance L1, the first connection terminal A, the second connection terminal B and other dynamic components, and the structure of each MMC power module is the same.

[0056] The MMC power module with bridge arm inductance is connected to the bridge arm circuit through the first connection end and the second connection end. The first switch unit and the second switch unit are used to control the MMC power module with bridge arm inductance to be in a locked or non-locked state in the bridge arm circuit. The module capacitor C0 cooperates with the first switch unit and the second switch unit to realize charging and discharging, so as to cope with equipment failure and realize stable operation. The MMC power module with bridge arm inductance adds a module inductance L1 at the second connection end B, that is, the inductance is connected at the outlet to suppress the double frequency circulating current of the bridge arm. When an AC fault or a DC fault occurs inside, it can also suppress Fault current flowing through the bridge arm; multiple MMC power modules with bridge arm reactors are connected in series in a bridge arm circuit, that is, a distributed bridge arm reactor design is adopted. In this way, the overall solution of the offshore converter station can cancel the original centralized bridge arm reactor, and there is no need to specially design a room for laying out the bridge arm reactor, and also reduce the equipment configuration connected to the upstream and downstream power equipment, etc. That is, this application will carry out a modular design of the bridge arm reactor. When the offshore converter station is constructed, the bridge arm reactor will be dispersed in the sub-modules of the corresponding bridge arm. It is only necessary to connect the MMC power module with the bridge arm reactor to the corresponding bridge arm circuit, thereby reducing the construction volume and difficulty of the offshore converter station.

[0057] like Figure 1 As shown, in the MMC power module of the embodiment of the present application, the emitter of the first insulated gate bipolar transistor T1 and the anode D1 of the first diode are connected to the first connection terminal A, and the collector of the first insulated gate bipolar transistor T1 and the cathode of the first diode D1 are connected to the module capacitor. Similarly, the emitter of the second insulated gate bipolar transistor T2 and the anode of the second diode D2 are connected to the module reactance L1, and the collector of the second insulated gate bipolar transistor T2 and the cathode of the second diode D2 are connected to the first connection terminal A; the first insulated gate bipolar transistor T1 and the first diode D1 are reversely connected in parallel to form the first switch unit, and the second insulated gate bipolar transistor T2 and the second diode D2 are reversely connected in parallel to form the second switch unit, and the second switch unit cooperates with the first switch unit and the module capacitor C0 to realize the locking or non-locking state of the corresponding bridge arm circuit.

[0058] Due to the increase in the number of dynamic components in offshore converter stations, the use of detailed MMC power module model simulation with bridge arm reactance has problems such as large computational workload and long simulation time. Therefore, an equivalent simulation method for MMC power module with bridge arm reactance is proposed to achieve efficient and fast simulation of the system.

[0059] Combination Figure 1 and Figure 2 The MMC power module with bridge arm reactance includes a first switch unit, a second switch unit, a module capacitor C0, a module reactance L1, a first connection terminal A and a second connection terminal B, a first insulated gate bipolar transistor T1 and a first diode D1 are combined into a first switch unit, a second insulated gate bipolar transistor T2 and a second diode D2 are combined into a second switch unit, the first switch unit and the second switch unit are connected, the first connection terminal A is arranged between the first switch unit and the second switch unit, one end of the module capacitor C0 is connected to the first switch unit, the other end of the module capacitor C0 is connected to the second switch unit, one end of the module reactance L1 is connected to the module capacitor C0 and the second switch unit, and the other end of the module reactance L1 is connected to the second connection terminal B. Reference Figure 3 The embodiment of the present application also provides a simulation construction method of an MMC power module with a bridge arm reactance. The simulation construction method of an MMC power module with a bridge arm reactance includes the following steps: Steps S100 to S400.

[0060] First, in step S100, the dynamic elements in the MMC power module with bridge arm reactance are equivalently processed using the Dommel algorithm to obtain a passive equivalent circuit of the MMC power module with bridge arm reactance.

[0061] Combination Figure 1 The first switch unit includes a first insulated gate bipolar transistor and a first diode, the emitter of the first insulated gate bipolar transistor T1 and the anode D1 of the first diode are connected to the first connection terminal A, and the collector of the first insulated gate bipolar transistor T1 and the cathode of the first diode D1 are connected to the module capacitor; and the second switch unit includes a second insulated gate bipolar transistor and a second diode, the emitter of the second insulated gate bipolar transistor T2 and the anode of the second diode D2 are connected to the module reactor L1, and the collector of the second insulated gate bipolar transistor T2 and the cathode of the second diode D2 are connected to the first connection terminal A.

[0062] Step S100 includes the following steps S110 to S150:

[0063] Step S110, based on the component characteristics of the module capacitor, obtain the capacitor voltage function formula u in the MMC power module with bridge arm reactance c (t).

[0064] The capacitor voltage function formula is:

[0065]

[0066] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u c (t) is the capacitor voltage at the current moment, u c (t-Δt) is the capacitor voltage at the last moment, C0 is the module capacitance value, i c (τ) Capacitor current.

[0067] Step S120, based on the trapezoidal integration method, the capacitance voltage function formula u c (t) is expanded to obtain the additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs .

[0068] Combined with the capacitance voltage function formula u c (t), expanded by the trapezoidal integration method:

[0069]

[0070] The capacitor voltage observation at the previous moment is used as the additional capacitor voltage source U Cs , and define the capacitor time step resistor R Cs , then we get the additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs for:

[0071]

[0072] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u c (t) is the capacitor voltage at the current moment, u c (t-Δt) is the capacitor voltage at the last moment, C0 is the module capacitance value, i c (τ) Capacitor current.

[0073] Similarly, the additional inductor voltage source function formula U Ls And the inductor time-step resistance function formula R Ls , such as steps S130 to S140.

[0074] Step S130, based on the component characteristics of the module inductance, obtain the inductor current function formula u in the MMC power module with bridge arm reactance L (t).

[0075] Among them, the inductor current function formula u L (t) is:

[0076]

[0077] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u L (t) is the inductor voltage at the current moment, u L (t-Δt) is the inductor voltage at the previous moment, L1 is the module inductance value, i L (τ) Inductor current.

[0078] It should be noted that Figure 2 It can be seen that no matter whether the submodule in the bridge arm circuit is turned on or not, the submodule inductance is in the turned-on state, and in the same bridge arm circuit, each submodule inductance is in series state. Therefore, the sum of all distributed reactance values ​​in a bridge arm circuit can be made equal to the centralized bridge arm reactance value under the same voltage level and capacity.

[0079]

[0080] In the formula, L1 is the inductance value distributed in the bridge arm submodule (MMC power module), and L0 is the inductance value of the corresponding traditional centralized bridge arm reactor with the same capacity. From this, the parameter design of the bridge arm reactor of the MMC power module can be obtained.

[0081] Next, in step S140, based on the trapezoidal integration method, the inductor current function formula u L (t) is expanded to obtain the additional inductor voltage source function formula U Ls And the inductor time-step resistance function formula R Ls .

[0082] Combined with step S130, according to the inductor current function formula u L (t), and the additional inductor voltage source function formula U is obtained Ls And the inductor time-step resistance function formula R Ls for:

[0083]

[0084] In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u L (t) is the inductor voltage at the current moment, u L (t-Δt) is the inductor voltage at the previous moment, L1 is the module inductance value, i L (τ) Inductor current.

[0085] In step S150 , the first insulated gate bipolar transistor T1 , the first diode D1 , the second insulated gate bipolar transistor T2 , and the second diode D2 are respectively equivalent to variable binary resistors.

[0086] It should be noted that, combined with Figure 1 and Figure 4 , the IGBT transistors T1, T2 and diodes D1, D2 are equivalent to variable two-state resistors, that is, when they are turned on, R on =0.01Ω, when off, R off =5MΩ, and finally the passive equivalent circuit of the MMC power module is as follows Figure 4 shown.

[0087] Secondly, in step S200, based on the passive equivalent circuit, the bridge arm circuit including the MMC power module with the bridge arm reactance is subjected to the Thevenin equivalent to obtain the bridge arm Thevenin equivalent circuit. Specifically, step 200 includes the following steps S210 to S220.

[0088] Step S210, making a single bridge arm Thevenin equivalent circuit for the passive equivalent circuit.

[0089] like Figure 4 As shown, in step S100, the passive equivalent circuit of the MMC power module is obtained, R T1 is the equivalent resistance of the first switch unit, R T2 is the equivalent resistance of the second switch unit, U SMeq and R SMeq They are the Thevenin equivalent power supply and equivalent resistance of the MMC power module respectively. Figure 4 The application scenario of including an MMC power module for each bridge arm circuit is obtained, thereby obtaining the Thevenin equivalent power supply U in the Thevenin equivalent circuit of a single bridge arm SMeq And the equivalent resistance R SMeq The expression is:

[0090]

[0091] In the formula, R T1 is the equivalent resistance of the first switch unit, R T2 is the equivalent resistance of the second switch unit, R C is the module capacitor equivalent resistance, R L is the module inductor equivalent resistance, U Cs is the additional capacitor voltage source, U Ls is the additional inductor voltage source.

[0092] Step S220, simulating N MMC power modules with bridge arm reactances connected end to end in series in a bridge arm circuit to obtain an overall bridge arm Thevenin equivalent circuit of the bridge arm circuit; N is a positive integer.

[0093] It should be noted that each bridge arm circuit is composed of multiple MMC power modules connected in series end to end, so combined with the Thevenin equivalent power supply U in the above-mentioned single bridge arm Thevenin equivalent circuit SMeqAnd the equivalent resistance R SMeq , calculate the overall bridge arm Thevenin equivalent circuit of the bridge arm circuit, the total resistance of the bridge arm in the overall bridge arm Thevenin equivalent circuit R eq And the sum of the bridge arm voltage source U eq The expression is:

[0094]

[0095] Where N is the total number of MMC power modules connected in series in the bridge arm circuit. is the equivalent voltage of the i-th MMC power module of the bridge arm circuit, is the equivalent resistance of the i-th MMC power module in the bridge arm circuit.

[0096] Next, in step S300, using simulation software and a bridge arm equivalent circuit, an equivalent circuit simulation model of the MMC power module with a bridge arm reactance is established.

[0097] It should be noted that the bridge arm equivalent circuit may include the Thevenin equivalent power supply U in the Thevenin equivalent circuit of a single bridge arm. SMeq And the equivalent resistance R SMeq The total resistance R of the bridge arm in the Thevenin equivalent circuit of the whole bridge arm eq And the sum of the bridge arm voltage source U eq The expression of and other parameters are used to solve the equivalent circuit model of the MMC power module with bridge arm reactance in the simulation with the help of EMTDC software.

[0098] Finally, in step S400, simulation calculation and analysis are performed on the equivalent circuit simulation model.

[0099] In the above simulation, the equivalent circuit model of the MMC power module with bridge arm reactance is solved by using EMTDC software, and then the bridge arm current, an external electrical quantity of the bridge arm circuit, is obtained, and then the capacitance and inductance state quantities at the current moment are derived using the bridge arm current as an excitation source, thereby realizing the rapid solution of the MMC power module model with bridge arm reactance. It should be noted that this step can use conventional simulation software and simulation tools, which will not be repeated here.

[0100] In order to verify the feasibility of the offshore converter station solution containing the MMC power module with bridge arm reactor of the embodiment of the present application, the offshore converter station solution containing the traditional centralized bridge arm reactor (reference Figure 6 ) and offshore converter station solution containing the MMC power module with bridge arm reactor (reference Figure 2 ) is simulated and compared with the system steady-state characteristics and transient characteristics.

[0101] Based on PSCAD / EMTDC software simulation, a 1000MW offshore wind power double-end flexible DC transmission system is established. The rectifier-side converter adopts island control, the inverter-side converter adopts constant DC voltage and constant reactive power control, and the receiving-end power grid adopts voltage source equivalent. The remaining parameters are shown in Table 1. It should be noted that the bridge arm reactance value of the offshore converter station solution containing the traditional centralized bridge arm reactor is 0.1. The offshore converter station solution containing the MMC power module with bridge arm reactor cancels the original centralized bridge arm reactor and disperses the upper and lower bridge arm reactance of the original converter to the N submodules of the corresponding bridge arm. Figure 1 It can be seen that no matter whether the submodule (that is, the MMC power module) in the bridge arm circuit is turned on or not, the submodule inductance is in the turned-on state, and in the same bridge arm circuit, each submodule inductance is in a series state. Therefore, the sum of all distributed reactance values ​​in a bridge arm circuit can be made equal to the centralized bridge arm reactance value under the same voltage level and capacity, that is, the parameter value of the reactance value of the MMC power module in the embodiment of the present application can be set to L0 is the inductance value of the traditional centralized bridge arm reactor corresponding to the same capacity, that is, the bridge arm reactance value / H in the following table, and N is the number of half-bridge submodules, that is, the number of MMC power modules on one bridge arm. The other component parameter settings of the submodules in the existing offshore converter station solution and the offshore converter station solution of the embodiment of the present application are consistent.

[0102] Table 1 System parameters

[0103]

[0104] (1) Comparative analysis of steady-state characteristics simulation

[0105] The control sequence is that the wind turbine starts at 0.5s and the wind farm transmits power stably at 1s. The AC bus voltage on the grid side of the offshore converter, the AC current at the converter station outlet, the DC voltage, the DC current, the active power and the reactive power generated by the wind farm corresponding to the two schemes are as follows: Figure 7 and Figure 8 As shown. Figure 7 and Figure 8 It can be seen that by adopting the offshore converter station solution containing the MMC power module with bridge arm reactance, a 1GW wind farm can stably transmit power, thereby verifying the feasibility of the offshore converter station solution containing the MMC power module with bridge arm reactance to achieve stable transmission.

[0106] (2) Comparative analysis of transient characteristics simulation

[0107] At t = 2s, the system has reached a steady state. At t = 3.0s, a DC bipolar short circuit fault occurs at the outlet of the smoothing reactor, and the fault resistance is 0.01Ω. 5ms after the fault occurs, the MMC power module is locked. The instantaneous maximum voltage of the bridge arm, the instantaneous current of the bridge arm, the AC current, and the average value of the submodule capacitor voltage in the two schemes are as follows: Fig. 9 and Fig.10 As shown. Fig. 9 and Fig.10 It can be seen that the maximum valve-side voltage of the offshore converter station solution containing the MMC power module with bridge arm reactor is 347kV after the fault, and the voltage is about 80kV when locked. However, the maximum three-phase voltage of the offshore converter station solution containing the traditional centralized bridge arm reactor is about 300kV when locked.

[0108] The submodule capacitor voltages of the existing solution and the solution of the embodiment of the present application are approximately 70.7% and 70.9% of the rated value respectively when locked. It can be seen that the capacitor of the solution of the embodiment of the present application will not consume most of the energy after a failure, nor will it prolong the time it takes for the system to enter a stable state after restarting.

[0109] After a DC bipolar fault occurs, when the MMC power module is locked, that is, at t = 3.005s, the maximum bridge arm current of the solution of the embodiment of the present application is about 12.53kA, and the maximum AC current is 13.39kA, which is about 1.1pu during normal operation. It can be seen that the offshore converter station solution containing the MMC power module with bridge arm reactance can limit the fault current. This verifies the feasibility of the offshore converter station solution containing the MMC power module with bridge arm reactance to achieve stable transmission.

[0110] The offshore converter station solution containing the MMC power module with bridge arm reactance cancels the original centralized bridge arm reactor, that is, cancels the special bridge arm reactor and the corresponding room, and disperses the upper and lower bridge arm reactances in the N sub-modules of the corresponding bridge arm. Since the sub-module reactance value is very small, the increased volume of the MMC power module with bridge arm reactance is also small. Therefore, after integrated processing, the offshore converter station solution containing the MMC power module with bridge arm reactance can operate stably, and compared with the existing offshore converter station solution, the offshore converter station solution described in the embodiment of the present application has a smaller construction volume.

[0111] It should be noted that the difference between steady-state characteristics and transient characteristics is that steady-state is normal operation, and transient is a fault process. In short, the simulation analysis results of the above steady-state characteristics and transient characteristics show that the waveforms of the scheme of the embodiment of the present application and the existing scheme are basically the same, and the parameters are within the limit, that is, the embodiment of the present application is also stable transmission.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An MMC power module with bridge arm reactance, characterized in that: It includes a first switch unit, a second switch unit, a module capacitor, a module reactance, a first connection end and a second connection end. The first switch unit and the second switch unit are connected, the first connection end is arranged between the first switch unit and the second switch unit, one end of the module capacitor is connected to the first switch unit, the other end of the module capacitor is connected to the second switch unit, one end of the module reactance is connected to the module capacitor and the second switch unit, and the other end of the module reactance is connected to the second connection end.

2. The MMC power module with bridge arm reactance according to claim 1, characterized in that: The first switch unit includes a first insulated gate bipolar transistor and a first diode, the emitter of the first insulated gate bipolar transistor and the anode of the first diode are connected to the first connection end, and the collector of the first insulated gate bipolar transistor and the cathode of the first diode are connected to the module capacitor.

3. The MMC power module with bridge arm reactance according to claim 1, characterized in that: The second switch unit includes a second insulated gate bipolar transistor and a second diode, the emitter of the second insulated gate bipolar transistor and the anode of the second diode are connected to the module reactance, and the collector of the second insulated gate bipolar transistor and the cathode of the second diode are connected to the first connection end.

4. A simulation construction method of an MMC power module with bridge arm reactance, characterized in that: The MMC power module with bridge arm reactance includes a first switch unit, a second switch unit, a module capacitor, a module reactance, a first connection end and a second connection end, the first switch unit and the second switch unit are connected, the first connection end is arranged between the first switch unit and the second switch unit, one end of the module capacitor is connected to the first switch unit, the other end of the module capacitor is connected to the second switch unit, one end of the module reactance is connected to the module capacitor and the second switch unit, and the other end of the module reactance is connected to the second connection end; the simulation construction method of the MMC power module with bridge arm reactance includes the following steps: The dynamic components in the MMC power module with bridge arm reactance are equivalent by Dommel algorithm, and the passive equivalent circuit of the MMC power module with bridge arm reactance is obtained; Based on the passive equivalent circuit, the bridge arm circuit containing the MMC power module with bridge arm reactance is subjected to the Thevenin equivalent circuit, and the bridge arm Thevenin equivalent circuit is obtained. Using simulation software and bridge arm equivalent circuit, an equivalent circuit simulation model of the MMC power module with bridge arm reactance is established; Perform simulation calculation and analysis on the equivalent circuit simulation model.

5. The simulation construction method according to claim 4, characterized in that: The first switch unit includes a first insulated gate bipolar transistor and a first diode, the emitter of the first insulated gate bipolar transistor and the anode of the first diode are connected to the first connection terminal, the collector of the first insulated gate bipolar transistor and the cathode of the first diode are connected to the module capacitor; and the second switch unit includes a second insulated gate bipolar transistor and a second diode, the emitter of the second insulated gate bipolar transistor and the anode of the second diode are connected to the module reactance, the collector of the second insulated gate bipolar transistor and the cathode of the second diode are connected to the first connection terminal; The method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain the passive equivalent circuit of the MMC power module with bridge arm reactance comprises the following steps: Based on the component characteristics of the module capacitor, the capacitor voltage function formula u in the MMC power module with bridge arm reactance is obtained c (t); Based on the trapezoidal integration method, the capacitance voltage function formula u c (t) is expanded to obtain the additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs ; The capacitance-voltage function formula is: Additional capacitance voltage source function formula U Cs The capacitance-step resistance function formula R Cs for: In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u c (t) is the capacitor voltage at the current moment, u c (t-Δt) is the capacitor voltage at the previous moment, C0 is the module capacitance value, i c (τ) Capacitor current.

6. The simulation construction method according to claim 5, characterized in that: The method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain a passive equivalent circuit of the MMC power module with bridge arm reactance also includes the following steps: Based on the component characteristics of the module inductor, the inductor current function formula u in the MMC power module with bridge arm reactance is obtained L (t); Based on the trapezoidal integration method, the inductor current function formula u L (t) is expanded to obtain the additional inductor voltage source function formula U Ls And the inductor time-step resistance function formula R Ls ; Among them, the inductor current function formula u L (t) is: Additional inductance voltage source function formula U Ls And the inductor time-step resistance function formula R Ls for: In the formula, t is the current moment, Δt is the time increment between the current moment and the previous moment, t-Δt is the previous moment, and u L (t) is the inductor voltage at the current moment, u L (t-Δt) is the inductor voltage at the last moment, L1 is the module inductance value, i L (τ) Inductor current.

7. The simulation construction method according to claim 5, characterized in that: The method of performing Dommel algorithm equivalence on the dynamic elements in the MMC power module with bridge arm reactance to obtain a passive equivalent circuit of the MMC power module with bridge arm reactance also includes the following steps: The first insulated gate bipolar transistor, the first diode, the second insulated gate bipolar transistor, and the second diode are respectively equivalent to variable binary resistors.

8. The simulation construction method according to claim 5, characterized in that: The method of performing Thevenin equivalent on a bridge arm circuit of an MMC power module with a bridge arm reactance based on a passive equivalent circuit to obtain a bridge arm Thevenin equivalent circuit includes the following steps: Make a single bridge arm Thevenin equivalent circuit for the passive equivalent circuit; The N MMC power modules with bridge arm reactances are simulated to be connected in series end to end in a bridge arm circuit to obtain the overall bridge arm Thevenin equivalent circuit of the bridge arm circuit; N is a positive integer.

9. The simulation construction method according to claim 8, characterized in that: Thevenin equivalent power supply U in the Thevenin equivalent circuit of a single bridge arm SMeq And the equivalent resistance R SMeq The expression is: In the formula, R T1 is the equivalent resistance of the first switch unit, R T2 is the equivalent resistance of the second switch unit, R C is the module capacitor equivalent resistance, R L is the module inductor equivalent resistance, U Cs is the additional capacitor voltage source, U Ls is the additional inductor voltage source.

10. The simulation construction method according to claim 9, characterized in that: The total resistance of the bridge arm in the Thevenin equivalent circuit of the whole bridge arm is R eq And the sum of the bridge arm voltage source U eq The expression is: Where N is the total number of MMC power modules connected in series in the bridge arm circuit. is the equivalent voltage of the i-th MMC power module of the bridge arm circuit, is the equivalent resistance of the i-th MMC power module in the bridge arm circuit.

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