A three-way staggered flyback parallel submodule conversion circuit and a modeling method thereof and an energy storage converter

Abstract

The application discloses a three-path interleaved flyback parallel sub-module conversion circuit, a modeling method thereof and an energy storage converter. The three-path interleaved flyback parallel sub-module conversion circuit can realize isolation of a storage battery and a load DC bus port, reduces input and output current ripples, and effectively improves a voltage conversion ratio. The effectiveness of the circuit is verified through modeling.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power electronics, and particularly relates to a three-path interleaved flyback parallel sub-module conversion circuit and a modeling method and energy storage converter thereof. BACKGROUND

[0002] A typical MMC topology structure has three phases, and each phase has upper and lower bridge arms, each of which is in series with N (N>1) sub-modules (SM) and is used for controlling power and energy conversion. Compared with conventional topological structures, the sub-module structure of MMC can withstand higher voltage levels and has faster response speed, so it has broad development prospects. With the rapid development of the new energy field in recent years, MMC has also attracted great attention in the energy storage field, that is, the sub-module structure of MMC is improved to improve the energy conversion efficiency of energy storage. The present application also focuses on this module. The existing MMC-BESS energy storage unit parallel connection sub-module method is mainly divided into three types: replacement parallel, direct parallel and direct DC / DC parallel. The replacement parallel method directly replaces the sub-module capacitor with the energy storage battery unit, and its control strategy is relatively simple. The secondary low-frequency oscillation current in the single system will affect the service life of the battery, so the problem of eliminating the double-frequency harmonic needs to be considered, which results in low energy conversion efficiency. Direct parallel is to connect the battery energy storage unit in parallel to the MMC sub-module structure. Although this structure improves the energy conversion efficiency, it also limits the capacity selection of the energy storage system. The last direct DC / DC parallel, as the name implies, is to connect the energy storage unit through a DC / DC conversion module to the sub-module. This connection method can decouple the battery and the sub-module capacitor, reduce the DC filtering demand of the battery, and improve the use flexibility of the energy storage battery unit and the entire system, prolong the service life of the system, and the added transformer link can greatly improve the reliability of the sub-module in the MMC-BESS system.

[0003] However, the existing MMC sub-module structure is mostly half-bridge type, and the relatively simple control structure is its advantage. At the same time, with the continuous development and construction of new power systems, the control requirements of power electronic devices are also increasing. When facing the problem of uneven voltage distribution of each sub-module caused by converter operation failure, the half-bridge structure is difficult to solve this problem. SUMMARY

[0004] The purpose of the present application is to provide a three-path interleaved flyback parallel sub-module conversion circuit and a modeling method and energy storage converter thereof, which can realize the isolation of the battery and the load DC bus port, reduce the input and output current ripple, effectively improve the voltage conversion ratio, and realize the control of power distribution and stable voltage.

[0005] Technical solution: The three-way staggered flyback parallel submodule conversion circuit of the application is used for isolating the battery energy storage side and the load DC bus side, and comprises a first inductor L1, a second inductor L2 and a third inductor L3; one end of the first inductor L1, one end of the second inductor L2 and one end of the third inductor L3 are connected, the other end of the first inductor L1 is connected with one end of a first switch tube S1 and one end of a first parasitic capacitor C1, the other end of the second inductor L2 is connected with one end of a seventh switch tube S7, one end of a fifth switch tube S5 and one end of a second switch tube S2, and the other end of the third inductor L3 is connected with one end of a sixth switch tube S6 and the other end of the seventh switch tube S7;

[0006] One end of the sixth switch tube S6 is connected with one end of a primary coil N1 of an isolation transformer N, the other end of the fifth switch tube S5 is connected with one end of the primary coil N1 of the isolation transformer N through a second parasitic capacitor C2, and the other end of the first parasitic capacitor C1 is connected with one end of the primary coil N1 of the isolation transformer N;

[0007] One end of the first inductor L1 and the other end of the first switch tube S1 are connected with a battery U B , and the battery U B is connected with a battery side capacitor C B in parallel across two ends, and the other end of the first switch tube S1 and the other end of the second switch tube S2 are connected and then connected to the other end of the primary coil N1 of the isolation transformer N through a third switch tube S3;

[0008] The isolation transformer N comprises a secondary coil N2, and output side capacitors C d are connected in parallel across two ends of the secondary coil N2, and a fourth switch tube S4 is connected in series between one end of the secondary coil N2 and the output side capacitor C d .

[0009] Further, the output side capacitor C d is connected with a load DC bus side across two ends.

[0010] Based on the same inventive concept, the modeling method of the three-way staggered flyback parallel submodule conversion circuit of the application comprises:

[0011] The first switch tube S1, the second switch tube S2 and the seventh switch tube S7 are turned on, and the remaining switch tubes are in an off state, at this time, the battery U B is charged to the first inductor L1, the second inductor L2 and the third inductor L3, and the current flowing through the first inductor L1, the second inductor L2 and the third inductor L3 continuously increases to store energy; at this time, a state equation model of the circuit in a stable state is established:

[0012]

[0013] Further, after obtaining the state equation model of the circuit in the stable state, the seventh switch S7 is turned off, the sixth switch S6 and the fifth switch S5 are turned on, and the remaining switches are still in the off state. The battery U B The first inductor L1 continues to be charged, and at this time, the voltage established across U B The real-time state equation model in the L1 loop is:

[0014]

[0015] The battery U B The third inductor L3 charges the second parasitic capacitor C2 while the first inductor L1 continues to be charged, and at this time, the voltage established across U B The real-time state equation model in the L3 and C2 loop is:

[0016]

[0017] The second inductor L2 charges the first parasitic capacitor C1 and the second parasitic capacitor C2, and at this time, the voltage established across U B The real-time state equation model in the L2, C1 and C2 loop is:

[0018]

[0019] Further, after obtaining the model of the second inductor L2 charging the first parasitic capacitor C1 and the second parasitic capacitor C2, the first switch S1 and the sixth switch S6 are turned off, the second switch S2, the seventh switch S7, the third switch S3 and the fifth switch S5 are turned on, and the remaining switches are in the off state. At this time, the battery continues to charge the third inductor L3, and the voltage established across U B The real-time state equation model in the L3 loop is:

[0020]

[0021] Based on the same inventive concept, an energy storage converter of the present application comprises three phase units with the same structure, each phase unit comprising an upper bridge arm and a lower bridge arm with the same structure; the upper bridge arm comprises N sub-modules connected in series, and the sub-modules adopt the three-path interleaved flyback parallel sub-module conversion circuit described above.

[0022] Further, the upper bridge arm further comprises an upper bridge arm resistor and an upper bridge arm inductor connected in series at the output end of the N sub-modules, and the negative electrode of the upper bridge arm is connected to one end of the upper bridge arm resistor.

[0023] Further, the lower bridge arm comprises a lower bridge arm inductor, a lower bridge arm resistor and N sub-modules connected in series, and the positive electrode of the lower bridge arm is connected to one end of the lower bridge arm resistor. Further, the lower bridge arm comprises a lower bridge arm inductor, a lower bridge arm resistor and N sub-modules connected in series, and the positive electrode of the lower bridge arm is connected to one end of the lower bridge arm resistor.

[0024] Further, the output voltage of the isolated modular multilevel energy storage converter is controlled by controlling the number of sub-modules.

[0025] Further, the plurality of sub-modules work cooperatively to control the bidirectional flow of energy, realize the conversion from DC to AC, from AC to DC, and from low voltage to high voltage, from high voltage to low voltage.

[0026] Advantages: Compared with the prior art, the application adopts an innovative three-path interleaved flyback parallel sub-module conversion circuit, solves the input and output ripple problems, and finally realizes effective improvement of the voltage conversion ratio

[0027] The three-path interleaved flyback parallel sub-module conversion circuit of the application realizes the isolation of the battery and the load DC bus port, reduces the input and output current ripple, and effectively improves the voltage conversion ratio; compared with the traditional boost converter single inductor structure, the overall fluctuation of the circuit structure is reduced, and the fluctuation frequency is increased, which is more conducive to filtering.

[0028] The three-path interleaved flyback parallel sub-module conversion circuit of the application can simultaneously realize power distribution and stable voltage control, not only can avoid the problem of relatively low reliability in traditional sub-modules, but also can improve the energy utilization rate of the sub-modules in the MMC compared with the traditional boost conversion link.

[0029] The transmission efficiency and reliability of the sub-modules in the system are improved by controlling the turn-on and turn-off of the switching tubes in the three-path interleaved flyback parallel sub-module conversion circuit. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A topology diagram of the three-path interleaved flyback parallel sub-module conversion circuit disclosed in the embodiment of the application is disclosed.

[0031] Figure 2 A topology diagram of the energy storage converter disclosed in the embodiment of the application is disclosed. DETAILED DESCRIPTION

[0032] The technical solutions of the application will be described in detail below in combination with specific embodiments and the drawings of the specification.

[0033] The application designs a new three-path interleaved flyback parallel sub-module conversion circuit for the problems of poor isolation and the like faced by the sub-modules of the half-bridge structure, and proposes a MMC-BESS energy storage converter with high isolation based on the three-path interleaved flyback parallel sub-module conversion circuit, controls the output voltage by controlling the mode switching of the switching tubes, and greatly improves the use reliability of the MMC.

[0034] Embodiment 1

[0035] As Figure 1 shown, a three-way staggered flyback parallel submodule conversion circuit of the application can isolate the battery energy storage side and the load DC bus side, and comprises a first inductor L1, a second inductor L2, a third inductor L3, a battery U B , a battery side capacitor C B , an output side capacitor C d , a first parasitic capacitor C1, a second parasitic capacitor C2, a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, a sixth switch S6, a seventh switch S7, and an isolation transformer N. The specific connection mode is as follows: one end of the first inductor L1, one end of the second inductor L2 and one end of the third inductor L3 are connected, the other end of the first inductor L1 is connected to one end of the first switch S1 and one end of the first parasitic capacitor C1, the other end of the second inductor L2 is connected to one end of the seventh switch S7, one end of the fifth switch S5 and one end of the second switch S2, the other end of the third inductor L3 is connected to one end of the sixth switch S6 and the other end of the seventh switch S7. One end of the sixth switch S6 is connected to one end of the primary coil N1 of the isolation transformer N, the other end of the fifth switch S5 is connected to one end of the primary coil N1 of the isolation transformer N through the second parasitic capacitor C2, and the other end of the first parasitic capacitor C1 is connected to one end of the primary coil N1 of the isolation transformer N. The battery U B is connected between one end of the first inductor L1 and the other end of the first switch S1, and the battery side capacitor C B is connected in parallel across the two ends of the battery U B , and the other end of the first switch S1 and the other end of the second switch S2 are connected to the other end of the primary coil N1 of the isolation transformer N through the third switch S3. The output side capacitor C d is connected in parallel across the two ends of the secondary coil N2 of the isolation transformer N, and the fourth switch S4 is connected in series between one end of the secondary coil N2 and the output side capacitor C d . The two ends of the output side capacitor C d are connected to the load DC bus side.

[0036] From the overall working state analysis, in the application process of the converter, U B is the battery end, and the load is the DC bus end. In the blocking mode, no matter the direction of the current, there is always a capacitor in the bridge arm, so it can play the function of clearing the fault current.

[0037] Embodiment 2

[0038] The modeling method of the three-way staggered flyback parallel submodule conversion circuit of the application is applied to the three-way staggered flyback parallel submodule conversion circuit in embodiment 1, and the effectiveness of the topology in embodiment 1 is verified through modeling simulation. The modeling method comprises the following steps:

[0039] When the MMC-BESS sub-module works in the Boost mode, assuming that the energy storage converter works in the continuous conduction mode, first, turn on the first switch S1, the second switch S2 and the seventh switch S7, and the remaining switches are in the off state, at this time, the battery U B Charge the first inductor L1, the second inductor L2 and the third inductor L3, the current flowing through the first inductor L1, the second inductor L2 and the third inductor L3 increases, storing energy for them; At this time, the state equation model of the stable circuit can be established:

[0040]

[0041] On this basis, turn off the seventh switch S7, turn on the sixth switch S6 and the fifth switch S5, and the remaining switches are still in the off state, the battery U B Continue to charge the first inductor L1, at this time, the real-time state equation model in the U B and L1 circuit can be established:

[0042]

[0043] The battery U B Continue to charge the first inductor L1, at the same time, the third inductor L3 charges the second parasitic capacitor C2, at this time, the voltage across the second parasitic capacitor C2 rises, and the real-time state equation model in the U B , L3 and C2 circuit can be established:

[0044]

[0045] The second inductor L2 charges the first parasitic capacitor C1 and the second parasitic capacitor C2, and the real-time state equation model in the U B , L2, C1 and C2 circuit can be established:

[0046]

[0047] Subsequently, turn off the first switch S1 and the sixth switch S6, turn on the second switch S2, the seventh switch S7, the third switch S3 and the fifth switch S5, and the remaining switches are in the off state; The real-time state equation model in the U B and L3 circuit can be established:

[0048]

[0049] In addition, the energy stored in the first parasitic capacitor C1 and the second parasitic capacitor C2 is released and flows into the primary coil N1 of the isolation transformer N. At this time, since the fourth switch S4 on the right side of the isolation transformer N is in an off state, no energy flows through the circuit on the right side of the isolation transformer N. At this time, the primary coil N1 can be equivalent to an inductor, which induces a positive voltage on the top and a negative voltage on the bottom. Then, the third switch S3 is turned off. At this time, the inductor prevents the current from changing abruptly, and induces a negative voltage on the top and a positive voltage on the bottom. At the same time, the secondary coil N2 on the right side induces a positive voltage on the top and a negative voltage on the bottom. Then, the fourth switch S4 is turned on. At this time, a current flows through the right side, part of which charges the output capacitor C d Charges, maintains the stability of the output voltage, and the remaining part supplies power to the load side of the negative electrode. This process can completely release the energy stored in the primary coil N1 to power the load side. The above process is the Boost mode operation principle of the three-path interleaved flyback parallel sub-module conversion circuit. This design can effectively isolate the battery energy storage side and the load DC bus side, so that they are controlled separately, greatly increasing the use reliability and flexibility of the MMC-BESS sub-module. At the same time, the first inductor L1, the second inductor L2, and the third inductor L3 added to the circuit can effectively reduce the overall fluctuation of the circuit, increase the fluctuation frequency, and be more conducive to filtering.

[0050] Embodiment 3

[0051] As shown in Figure 2 The energy storage converter of the present application is a modular multilevel energy storage converter (MMC-BESS) with high isolation, which includes three phase units with the same structure, each phase unit including an upper bridge arm and a lower bridge arm with the same structure, a total of six bridge arms. The upper bridge arm includes N sub-modules (SM) connected in series, where N≥1, and the sub-modules adopt the three-path interleaved flyback parallel sub-module conversion circuit in Embodiment 1. The output voltage of the isolation type modular multilevel energy storage converter is controlled by controlling the number of sub-modules. Each sub-module works cooperatively to control the bidirectional flow of energy, realizing the conversion from DC to AC, from AC to DC, and from low voltage to high voltage, and from high voltage to low voltage.

[0052] The upper bridge arm further includes an upper bridge arm resistor and an upper bridge arm inductor connected in series at the output end of the N sub-modules, and the negative electrode end of the upper bridge arm is connected to one end of the upper bridge arm resistor. The lower bridge arm includes a lower bridge arm inductor, a lower bridge arm resistor, and N sub-modules connected in series, and the positive electrode end of the lower bridge arm is connected to one end of the lower bridge arm resistor.

[0053] As shown in Figure 1 and Figure 2As shown, taking a sub-module in the main topology as an example, the leftmost side of the sub-module is a battery end, which provides charging and discharging and power conversion effect for the converter through the battery, and a new type of DC / DC converter device is connected after the battery, a transformer is connected after the new type of boost converter to form a small flyback power supply, and the load port after the port is the output side of the DC bus. The energy storage converter mainly consists of three DC / DC converters in parallel, which is equivalent to the battery delivering energy to the load DC bus side.

[0054] Compared with the conventional converter topology, the sub-module structure of MMC-BESS can withstand higher voltage level and has faster response speed, and has broad development prospect. The present application mainly designs the power conversion link in the sub-module of MMC-BESS, i.e. the DC / DC module of embodiment 1; and models and simulates its effectiveness, i.e. the technical scheme of embodiment 2. The present application realizes the isolation of the battery and the load DC bus port by improving the DC / DC link, reduces the input and output current ripple, effectively improves the voltage conversion ratio, and finally improves the reliability of MMC-BESS by adding the transformer link.

[0055] Since the MMC energy storage converter belongs to modular design and has no difference among three phases, a certain phase and a single module are taken as specific examples for illustrating the working principle.

[0056] The energy storage converter involved in the present application belongs to a non-energy consumption type circuit, i.e. using a capacitor as a representative energy storage element to transfer energy between sub-modules. For the traditional Boost circuit, its voltage gain is determined by the following formula:

[0057]

[0058] Where D is the duty cycle of the switch tube, and the voltage gain is directly related to the duty cycle. For the traditional Boost circuit modeling, there is still the problem of high output EMI and small voltage gain. The three-channel interleaved flyback type parallel sub-module conversion circuit described in embodiment 1 is adopted to solve the problem.

Claims

1. A three-path interleaved flyback parallel sub-module conversion circuit, characterized in that: It is used to isolate the energy storage side of the battery and the DC bus side of the load, including a first inductor L1, a second inductor L2, and a third inductor L3; one end of the first inductor L1, one end of the second inductor L2, and one end of the third inductor L3 are connected together, the other end of the first inductor L1 is connected to one end of the first switch S1 and one end of the first parasitic capacitance C1, the other end of the second inductor L2 is connected to one end of the seventh switch S7, one end of the fifth switch S5, and one end of the second switch S2, and the other end of the third inductor L3 is connected to one end of the sixth switch S6 and the other end of the seventh switch S7; The other end of the sixth switch S6 is connected to one end of the primary coil N1 of the isolation transformer N, and the other end of the fifth switch S5 is connected to one end of the primary coil N1 of the isolation transformer N through the second parasitic capacitor C2. The other end of the first parasitic capacitor C1 is connected to one end of the primary coil N1 of the isolation transformer N. One end of the first inductor L1 is connected to the other end of the first switching transistor S1 via the battery U. B Storage battery U B The two ends are connected in parallel to the battery-side capacitor C. B The other end of the first switch S1 is connected to the other end of the second switch S2, and then connected to the other end of the primary coil N1 of the isolation transformer N through the third switch S3. The output capacitor C is connected in parallel across the two ends of the secondary coil N2 of the isolation transformer N. d One end of the secondary coil N2 is connected to the output capacitor C. d The fourth switch S4 is connected in series between them.

2. The three-path interleaved flyback parallel sub-module conversion circuit according to claim 1, characterized in that: Output side capacitor C d Both ends are connected to the DC bus side of the load.

3. A modeling method for a three-path interleaved flyback parallel sub-module conversion circuit, characterized in that, The modeling method applied to the three-path interleaved flyback parallel sub-module conversion circuit of claim 1 includes: The first switch S1, the second switch S2, and the seventh switch S7 are turned on, while the remaining switches are turned off. At this time, the battery U B The first inductor L1, the second inductor L2, and the third inductor L3 are charged, and the current flowing through them continuously increases, storing energy. At this point, a state equation model for a stable circuit is established: 。 4. The modeling method for the three-path interleaved flyback parallel submodule conversion circuit according to claim 3, characterized in that, After obtaining the state equation model of the circuit when it is stable, turn off the seventh switch S7, turn on the sixth switch S6 and the fifth switch S5, and keep the other switches off. The battery U... B Continue charging the first inductor L1; at this point, U can be established. B With the real-time state equation model in the L1 loop: ； Storage battery U B While the first inductor L1 continues to charge, the third inductor L3 charges the second parasitic capacitor C2. At this time, the voltage across the second parasitic capacitor C2 increases, establishing a U B Real-time state equation model in L3 and C2 loops: ； The second inductor L2 charges the first parasitic capacitance C1 and the second parasitic capacitance C2, based on U B Real-time state equation model in loops L2, C1, and C2: 。 5. The modeling method for the three-path interleaved flyback parallel submodule conversion circuit according to claim 3, characterized in that, After obtaining the model of the second inductor L2 under the charging state of the first parasitic capacitance C1 and the second parasitic capacitance C2, the first switch S1 and the sixth switch S6 are disconnected, and the second switch S2, the seventh switch S7, the third switch S3 and the fifth switch S5 are turned on, while the remaining switches are in the off state; at this time, the battery continues to charge the third inductor L3, based on U B Real-time state equation model in L3 loop: 。 6. An energy storage converter, characterized in that: It includes three phase units with identical structures, each phase unit including an upper bridge arm and a lower bridge arm with identical structures; the upper bridge arm includes N sub-modules connected in series, and the sub-modules adopt the three-path interleaved flyback parallel sub-module conversion circuit as described in claim 1.

7. The energy storage converter according to claim 6, characterized in that: The upper bridge arm also includes an upper bridge arm resistor and an upper bridge arm inductor connected in series at the output terminals of the N sub-modules, with the negative terminal of the upper bridge arm connected to one end of the upper bridge arm resistor.

8. The energy storage converter according to claim 6, characterized in that: The lower bridge arm includes a lower bridge arm inductor, a lower bridge arm resistor, and N sub-modules connected in series. The positive terminal of the lower bridge arm is connected to one end of the lower bridge arm resistor.

9. The energy storage converter according to claim 6, characterized in that: The output voltage of the isolated modular multilevel energy storage converter is controlled by controlling the number of sub-modules in operation.

10. The energy storage converter according to claim 6, characterized in that: Multiple sub-modules work together to control the bidirectional flow of energy, enabling the conversion from DC to AC, from AC to DC, and from low voltage to high voltage, and from high voltage to low voltage.

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