DC power stabilizing device of MMC bridge arm cascade dual-port switching type energy storage module

Abstract

The invention relates to the technical field of flexible direct-current power transmission, and discloses a direct-current power stabilizing device of an MMC bridge arm cascade dual-port switching type energy storage module. Two ends of an upper bridge arm and a lower bridge arm of the MMC are respectively connected with a dual-port switching type energy storage module in series, and the MMC is connected with a positive electrode and a negative electrode of a direct current bus through the dual-port switching type energy storage modules. The dual-port switching type energy storage module comprises a bipolar DC / DC converter, the bipolar DC / DC converter is provided with two output ports, the voltage polarity (positive voltage or negative voltage) of the output ports can be switched according to the surplus or vacancy condition of the direct current side power, rapid charging and discharging control of the energy storage module is achieved, and therefore the direct current side power fluctuation is effectively stabilized, and the stability of the voltages at the two ends of the MMC is maintained. According to the invention, the stability is improved and the power is stabilized while the work of the MMC is not influenced, and the switching loss and the cost are effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible direct current transmission, in particular to a direct current power stabilizing device of an MMC bridge arm cascaded dual-port switching type energy storage module. BACKGROUND

[0002] Voltage Source Converter based High Voltage Direct Current Transmission (VSC-HVDC) can realize independent and bidirectional flexible regulation of active power and reactive power, and is regarded as an ideal technical solution for large-scale renewable energy grid connection. Modular Multilevel Converter (MMC) has been widely used due to its low output voltage harmonic content, low switching frequency and high modularization. However, the inherent intermittency and randomness of new energy lead to unstable output power, which brings great challenges to the stable operation of the power grid, and the introduction of energy storage can effectively solve the above problems.

[0003] In the flexible direct current transmission scenario, embedding the energy storage module into the converter bridge arm or sub-module can reduce additional equipment, reduce installation and maintenance costs, and realize flexible multi-port energy flow, effectively improving the peak clipping and valley filling capacity of the system. The MMC with traditional centralized energy storage structure has the problem of poor flexibility in capacity selection, and the MMC with distributed energy storage structure has the problems of scattered use of energy storage units and inconvenience in assembly and maintenance. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a direct current power stabilizing device of an MMC bridge arm cascaded dual-port switching type energy storage module, which can realize stability improvement and power stabilization under the premise of effectively reducing switching loss and cost, and obtain a grid connection effect not inferior to that of the traditional energy storage structure MMC. The technical scheme is as follows:

[0005] The direct current power stabilizing device of the MMC bridge arm cascaded dual-port switching type energy storage module comprises three-phase units, each phase unit contains two upper and lower bridge arms, each bridge arm comprises a bridge arm reactor , and N cascaded ordinary half-bridge sub-modules SM connected in series with the bridge arm reactor , each bridge arm is completely symmetrical and connected to the positive and negative poles of the DC bus through the dual-port switching type energy storage module at both ends of the upper and lower bridge arms

[0006] The double-port switching energy storage module includes a bipolar DC / DC converter, a battery and two switching tubes S3 and S4; the switching tubes S3 and S4 are connected in series, and the common end of the two switching tubes is used as an input end V+ of the double-port switching energy storage module; the emitter of the switching tube S4 is used as an output end V- and a port 2 of the double-port switching energy storage module; the collector of the switching tube S3 is used as a port 1 of the double-port switching energy storage module; the input end V+ and the output end V- are connected to a DC bus side and a DC side of the MMC respectively;

[0007] The bipolar DC / DC converter has two output ports for being connected with the port 1 and the port 2, and is used for switching the voltage polarity of the output port according to the surplus or deficiency of the DC side power, so as to realize the fast charging and discharging control of the double-port switching energy storage module, thereby suppressing the DC side power fluctuation.

[0008] Further, the common half-bridge sub-module SM includes a capacitor C and two switching tubes S1 and S2; the switching tubes S1 and S2 are connected in series, and then are connected in parallel with the capacitor C; the common end of the switching tubes S1 and S2 is used as a connection port a of the common half-bridge sub-module SM, and the common end of the capacitor C and the switching tube S2 is used as a connection port b of the common half-bridge sub-module SM. The common half-bridge sub-modules SM are cascaded through the port a and the port b.

[0009] Further, the bipolar DC / DC converter includes an inductor L1, an inductor L2, an inductor L3, a switching tube S5 and a switching tube S6 connected in anti-parallel, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a diode D, an output resistor R1 and an output resistor R2.

[0010] The positive electrode of the battery is connected with one end of the inductor L1, and the negative electrode of the battery is connected with the emitter of the switching tube S5, the negative electrode of the diode D, one end of the capacitor C2, one end of the output resistor R1, one end of the inductor L3, one end of the capacitor C4 and one end of the output resistor R2; one end of the output resistor R1, that is, one end of the output resistor R2, is used as a port B for being connected with the port 2 when the output port is switched;

[0011] The collector of the switching tube S5 is connected with the other end of the inductor L1, one end of the capacitor C1 and one end of the capacitor C3; the other end of the capacitor C1 is connected with the positive electrode of the diode D and one end of the inductor L2; the other end of the inductor L2 is connected with the other end of the capacitor C2 and the other end of the output resistor R1; the other end of the output resistor R1 is used as a port A for being connected with the port 1 when the output port is switched;

[0012] The other end of the capacitor C3 is connected with the other end of the inductor L3 and the emitter of the switch tube S6; the collector of the switch tube S6 is connected with the other end of the capacitor C4 and the other end of the output resistor R2; the other end of the output resistor R2 is used as a port C, which is connected with the port 1 when the output port is switched;

[0013] When the system power is surplus, the drive signal of the switch tube S5 and the drive signal of the switch tube S6 are complementary in the case of ignoring the dead zone.

[0014] Further, the working process comprises:

[0015] The input and cut-off state of the dual-port switching type energy storage module is controlled through the switch tubes S3 and S4;

[0016] When the system is normally operated, the switch tube S4 is turned on;

[0017] After a fault occurs, the voltage across the MMC is detected to determine whether it exceeds the set allowable fluctuation deviation range, if yes, the dual-port switching type energy storage module is input, the switch tube S3 is turned on, and then the specific situation of the current fault is determined;

[0018] When the DC side power is deficient and the voltage drops, the port 1 and the port 2 of the dual-port switching type energy storage module are connected with the port A and the port B of the bipolar DC / DC converter respectively, and negative voltage is output; the switch tube S5 is controlled to make the converter in Cuk mode, and the battery is discharged to supplement the deficient power;

[0019] When the DC side power is surplus and the voltage rises, the port 1 and the port 2 of the dual-port switching type energy storage module are connected with the port C and the port B of the bipolar DC / DC converter respectively, and positive voltage is output; the switch tubes S5 and S6 are controlled to make the converter in Zeta mode, and the battery is charged to absorb the surplus power.

[0020] The present application has the following advantages:

[0021] The present application has the following advantages: BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1It is a schematic diagram of the topological structure of the DC power smoothing device of the MMC bridge arm cascade dual-port switching type energy storage module of the present invention.

[0023] Figure 2 It is a structural diagram of the MMC ordinary half-bridge submodule SM.

[0024] Figure 3 It is a structural diagram of a dual-port switching energy storage module in which a battery is connected to two anti-parallel switching tubes through a bipolar DC / DC converter.

[0025] Figure 4 It is a flow chart of a control method for a DC power smoothing device of an MMC bridge arm cascade dual-port switching energy storage module.

[0026] Figure 5 This is the voltage diagram across the MMC when the system power is insufficient in the verification experiment.

[0027] Figure 6 It is the voltage diagram across the MMC when the system power is surplus in the verification experiment. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 The topology of the DC power smoothing device of the MMC bridge arm cascade dual-port switching energy storage module shown in the figure includes three phases ABC. Each phase unit contains two upper and lower bridge arms, and each bridge arm contains one bridge arm reactor. and N identical ordinary half-bridge submodules SM, and each bridge arm is completely symmetrical and connected to the AC grid through the bridge arm reactor; the upper and lower bridge arms of the MMC are respectively connected to the positive and negative poles of the DC bus; two dual-port switching energy storage modules are respectively connected in series at the upper and lower bridge arms of the MMC. dc is the DC side voltage.

[0030] like Figure 2 As shown in the figure, the MMC standard half-bridge submodule SM consists of two anti-parallel switches S1 and S2 (composed of IGBTs and diodes connected in anti-parallel) and a capacitor C. Switches S1 and S2 are connected in series, and capacitor C is connected in parallel. The common end of S1 and S2 serves as the connection port a of the half-bridge submodule, and the common end of capacitor C and S2 serves as the connection port b of the half-bridge submodule.

[0031] like Figure 3As shown, the double-port switching energy storage module is composed of two anti-parallel switch tubes S3, S4 (composed of IGBT and diode in anti-parallel), a bipolar DC / DC converter and a battery. The switch tubes S3 and S4 are connected in series, the common terminal of S3 and S4 is the input terminal V+ of the double-port switching energy storage module, the emitter of S4 is the output terminal V- and port 2 of the double-port switching energy storage module, and the collector of S3 is port 1 of the double-port switching energy storage module.

[0032] The bipolar DC / DC converter includes inductor L1, inductor L2, inductor L3, anti-parallel switch tubes S5 and S6, capacitor C1, capacitor C2, capacitor C3, capacitor C4, diode D, output resistor R1 and output resistor R2.

[0033] The positive terminal of the battery is connected to one end of the inductor L1, and the negative terminal of the battery is connected to the emitter of the switch tube S5, the negative terminal of the diode D, one end of the capacitor C2, one end of the output resistor R1, one end of the inductor L3, one end of the capacitor C4 and one end of the output resistor R2. The one end of the output resistor R1, i.e. the one end of the output resistor R2 (the negative terminal of the battery), is port B, which is used to connect with port 2 when switching the output port.

[0034] The collector of the switch tube S5 is connected to the other end of the inductor L1, one end of the capacitor C1 and one end of the capacitor C3, the other end of the capacitor C1 is connected to the positive terminal of the diode D and one end of the inductor L2, the other end of the inductor L2 is connected to the other end of the capacitor C2 and the other end of the output resistor R1. The other end of the output resistor R1 is port A, which is used to connect with port 1 when switching the output port.

[0035] The other end of the capacitor C3 is connected to the other end of the inductor L3 and the emitter of the switch tube S6, and the collector of the switch tube S6 is connected to the other end of the capacitor C4 and the other end of the output resistor R2. The other end of the output resistor R2 is port C, which is used to connect with port 1 when switching the output port.

[0036] When the system power is surplus, the drive signal of the switch tube S5 and the drive signal of the switch tube S6 are complementary in the case of ignoring the dead zone.

[0037] As shown in FIG. 2, the double-port switching energy storage module is connected to the input terminal V+ of the double-port switching energy storage module through the input terminal V+ of the double-port switching energy storage module, and the output terminal V- of the double-port switching energy storage module is connected to the output terminal V- of the double-port switching energy storage module. Figure 4As shown, the switch tubes S3 and S4 are used to control the input and cut-off state of the dual-port switching energy storage module. In normal operation, the switch tube S4 is turned on. After a fault occurs, the voltage across the MMC is detected to determine whether it exceeds the set allowable fluctuation deviation range, that is, whether the absolute value of the voltage change across the MMC exceeds the threshold ΔU. If it exceeds, the dual-port switching energy storage module is put into operation, the switch tube S3 is turned on, and then the specific situation of the current fault is determined. When the DC side power deficiency voltage drops, the port 1 and the port 2 of the dual-port switching energy storage module are connected to the port A and the port B of the bipolar DC / DC converter respectively, and a negative voltage is output. The switch tube S5 is controlled to make the converter in Cuk mode, and the battery is discharged to supplement the power deficiency; when the DC side power surplus voltage rises, the port 1 and the port 2 of the dual-port switching energy storage module are connected to the port C and the port B of the bipolar DC / DC converter respectively, and a positive voltage is output. The switch tubes S5 and S6 are controlled to make the converter in Zeta mode, and the battery is charged to absorb the excess power.

[0038] The specific steps are as follows:

[0039] Step 1: A three-phase 23-level MMC system is built in the Matlab / Simulink environment. In order to verify the principle and speed up the simulation, a DC voltage source is used instead of the DC bus voltage of the MMC, and the DC voltage of the system is selected as 11 kV, and the grid AC voltage is selected as 6.6 kV.

[0040] Step 2: The dual-port switching energy storage module is built. According to the established power system, the selection of the battery is determined. The selected lithium battery has a rated voltage of 400 V and a rated capacity of 1000 Ah.

[0041] Verification experiment:

[0042] The voltage amplitude of the DC voltage source is changed to simulate the fluctuation of the DC bus voltage. At 0.5 s, a fault is simulated. First, the amplitude of the DC voltage source is reduced from 11 kV to 10.5 kV, which is equivalent to a power deficiency of the system. At 0.8 s, the dual-port switching energy storage module is put into operation, and the voltage across the MMC is as shown in Figure 5 At this time, the port 1 and the port 2 of the dual-port switching energy storage module are connected to the port A and the port B of the bipolar DC / DC converter respectively, a negative voltage is output, and the dual-port switching energy storage module is in Cuk discharge mode, the battery is discharged to supplement the power deficiency, and the voltage across the MMC is restored within about 0.1 s after the dual-port switching energy storage module is put into operation.

[0043] The amplitude of the DC voltage source is increased from 11 kV to 11.5 kV, which is equivalent to a surplus power of the system. At 0.8 s, the dual-port switching energy storage module is put into operation, and the voltage across the MMC is as shown in Figure 6The port 1 and the port 2 of the dual-port switching energy storage module are connected with the port C and the port B of the bipolar DC / DC converter respectively, and a positive pressure is output, so that the dual-port switching energy storage module is in a Zeta charging mode, the battery is controlled to charge and absorb excess power, and the voltage between the two MMCs is restored in about 0.1s after the dual-port switching energy storage module is put into operation.

[0044] In conclusion, the feasibility and effectiveness of the DC power smoothing device and the control method of the MMC bridge arm cascaded dual-port switching energy storage module are verified, the system power is effectively balanced, the stability of the voltage is improved, and the response speed is relatively fast.

Claims

1. A DC power smoothing device for an MMC bridge arm cascaded dual-port switching energy storage module, characterized in that: It includes three-phase units, each phase unit contains two upper and lower bridge arms, and each bridge arm includes a bridge arm reactor , and N cascaded ordinary half-bridge sub-modules SM connected in series, each bridge arm is completely symmetrical, and is connected through the bridge arm reactor Connect to the AC grid; the upper and lower bridge arms of the MMC are connected to the positive and negative poles of the DC bus through dual-port switching energy storage modules; The dual-port switching energy storage module includes a bipolar DC / DC converter, a battery, and two switching tubes S3 and S4; the switching tubes S3 and S4 are connected in series, and the common end of the two serves as the input end V+ of the dual-port switching energy storage module; the emitter of the switching tube S4 serves as the output end V- and port 2 of the dual-port switching energy storage module; the collector of the switching tube S3 serves as port 1 of the dual-port switching energy storage module; the input end V+ and the output end V- are connected to the DC bus side and the DC side of the MMC, respectively; The bipolar DC / DC converter has two output ports for connecting to port 1 and port 2. It is used to switch the voltage polarity of the output ports according to the surplus or shortage of DC side power, realize the rapid charge and discharge control of the dual-port switching energy storage module, and thus smooth the DC side power fluctuations.

2. The DC power smoothing device of the MMC bridge arm cascade dual-port switching type energy storage module according to claim 1, characterized in that: The common half-bridge sub-module SM includes a capacitor C and two switching tubes S1 and S2; the switching tubes S1 and S2 are connected in series and then in parallel with the capacitor C; the common end of the switching tubes S1 and S2 serves as the connection port a of the common half-bridge sub-module SM, and the common end of the capacitor C and the switching tube S2 serves as the connection port b of the common half-bridge sub-module SM; each common half-bridge sub-module SM is cascaded through port a and port b.

3. The DC power smoothing device of the MMC bridge arm cascade dual-port switching type energy storage module according to claim 1, characterized in that: The bipolar DC / DC converter includes an inductor L1, an inductor L2, an inductor L3, anti-parallel switching tubes S5 and S6, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a diode D, an output resistor R1 and an output resistor R2; The positive electrode of the battery is connected to one end of the inductor L1, and the negative electrode of the battery is connected to the emitter of the switch tube S5, the negative electrode of the diode D, one end of the capacitor C2, one end of the output resistor R1, one end of the inductor L3, one end of the capacitor C4, and one end of the output resistor R2; one end of the output resistor R1, that is, one end of the output resistor R2, serves as port B, which is connected to port 2 when switching the output port; The collector of the switch tube S5 is connected to the other end of the inductor L1, one end of the capacitor C1, and one end of the capacitor C3; the other end of the capacitor C1 is connected to the anode of the diode D and one end of the inductor L2; the other end of the inductor L2 is connected to the other end of the capacitor C2 and the other end of the output resistor R1; the other end of the output resistor R1 serves as port A, which is connected to port 1 when switching the output port; The other end of capacitor C3 is connected to the other end of inductor L3 and the emitter of switch S6; the collector of switch S6 is connected to the other end of capacitor C4 and the other end of output resistor R2; the other end of output resistor R2 serves as port C, which is connected to port 1 when switching the output port; When the system power is surplus, the driving signal of the switch S5 and the driving signal of the switch S6 complement each other while ignoring the dead zone.

4. The DC power smoothing device of the MMC bridge arm cascade dual-port switching type energy storage module according to claim 3, characterized in that: Its working process includes: The switching state of the dual-port switching energy storage module is controlled by the switch tubes S3 and S4; During normal operation, the switch tube S4 is turned on; After a fault occurs, the voltage across the MMC is detected to determine whether it exceeds the set allowable fluctuation deviation range. If it exceeds, the dual-port switching energy storage module is put into operation, the switch tube S3 is turned on, and then the specific situation of the current fault is determined; When the DC side power shortage voltage drops, ports 1 and 2 of the dual-port switching energy storage module are connected to ports A and B of the bipolar DC / DC converter, respectively, to output a negative voltage. Switch S5 is controlled to put the converter into Cuk mode, controlling the battery discharge to supplement the power shortage. When the DC side power surplus voltage rises, ports 1 and 2 of the dual-port switching energy storage module are connected to ports C and B of the bipolar DC / DC converter, respectively, to output a positive voltage. Switches S5 and S6 are controlled to put the converter in Zeta mode, controlling battery charging to absorb excess power.

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