Three-channel staggered flyback parallel submodule conversion circuit, modeling method thereof and energy storage converter

Abstract

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

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and in particular relates to a three-channel interleaved flyback parallel submodule conversion circuit and a modeling method thereof, and an energy storage converter. Background Art

[0002] The typical MMC topology has three phases, each phase has two upper and lower bridge arms, each of which has N (N≥1) submodules (SM) in series and is used to control power and energy conversion. Compared with conventional topological structures, the unique submodule structure of MMC enables it to withstand higher voltage levels and respond faster, so it has broad development prospects. With the rapid development of the new energy field in recent years, MMC has also received great attention in the field of energy storage, that is, improvements are made in the submodule structure of MMC to improve the energy conversion efficiency of energy storage. The present invention also focuses on the description of this module. The existing MMC-BESS energy storage unit is connected to the submodule in parallel in three ways: replacement parallel, direct parallel, and direct DC / DC parallel. The replacement parallel method is that the energy storage battery unit directly replaces the submodule capacitor, and its control strategy is relatively simple. The secondary low-frequency oscillation current in the single system will relatively affect the service life of the battery, so it is necessary to consider the problem of eliminating the double frequency harmonics, resulting in the energy conversion efficiency of this method is not high. Direct parallel means connecting the battery energy storage unit in parallel after the MMC submodule infrastructure. Although this structure improves the energy conversion efficiency, it also leads to certain restrictions on the capacity selection of the energy storage system. The final direct DC / DC parallel connection, as the name implies, is to connect the energy storage unit to the sub-module through the DC / DC conversion module. This access method can achieve decoupling between the battery and the sub-module capacitor, while reducing the battery's DC filtering requirements. The added boost conversion link also improves the flexibility of the energy storage battery unit and even the entire system, and increases the service life of the system. At the same time, the added transformer link can greatly improve the reliability of the sub-module in the MMC-BESS system.

[0003] However, most of the existing MMC submodule structures are half-bridge type, and the control structure is relatively simple, which is its advantage. At the same time, with the continuous development and construction of new power systems, the control requirements for power electronic devices are also increasing. When faced with converter operation failures that cause uneven voltage distribution among submodules, the half-bridge structure is difficult to solve this problem. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a three-channel interleaved flyback parallel sub-module conversion circuit and its modeling method, and an energy storage inverter to achieve isolation of the battery and load DC bus ports, reduce input and output current ripple, effectively improve the voltage conversion ratio, and simultaneously achieve power distribution and stable voltage control.

[0005] Technical solution: The three-channel interleaved flyback parallel submodule conversion circuit of the present invention is used to isolate the battery energy storage side and the load DC bus side, 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, the other end of the first inductor L1 is connected to one end of the first switch tube 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 tube S7, one end of the fifth switch tube S5, and one end of the second switch tube S2, and the other end of the third inductor L3 is connected to one end of the 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 to one end of the primary coil N1 of the isolation transformer N, the other end of the fifth switch tube 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;

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

[0008] The two ends of the secondary coil N2 in the isolation transformer N are connected in parallel to the output side capacitor C d , at one end of the secondary coil N2 and the output side capacitor C d A fourth switch tube S4 is connected in series therebetween.

[0009] Furthermore, the output side capacitor C d Both ends are connected to the DC bus side of the load.

[0010] Based on the same inventive concept, a modeling method of a three-channel interleaved flyback parallel submodule conversion circuit of the present invention is applied to the above three-channel interleaved flyback parallel submodule conversion circuit, and the modeling method includes:

[0011] The first switch tube S1, the second switch tube S2 and the seventh switch tube S7 are turned on, and the other switch tubes are in the off state. 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 the first inductor L1, the second inductor L2 and the third inductor L3 increases continuously to store energy for them; at this time, a state equation model when the circuit is stable is established:

[0012]

[0013] Further, after obtaining the state equation model when the circuit is stable, the seventh switch tube S7 is turned off, the sixth switch tube S6 and the fifth switch tube S5 are turned on, and the remaining switch tubes are still in the off state. B Continue to charge the first inductor L1, and then establish B With the real-time state equation model in the L1 loop:

[0014]

[0015] Battery U B While continuing to charge the first inductor L1, the third inductor L3 charges the second parasitic capacitor C2. At this time, the voltage across the second parasitic capacitor C2 increases, and the voltage between the two ends of U B , real-time state equation model in L3 and C2 loops:

[0016]

[0017] The second inductor L2 charges the first parasitic capacitor C1 and the second parasitic capacitor C2, and the U B , L2, C1 and C2 loops in real-time state equation model:

[0018]

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

[0020]

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

[0022] Furthermore, the upper bridge arm also includes an upper bridge arm resistor and an upper bridge arm inductor connected in series to the output ends of the N submodules, and the negative terminal of the upper bridge arm is connected to one end of the upper bridge arm resistor.

[0023] Furthermore, 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 terminal of the lower bridge arm is connected to one end of the lower bridge arm resistor.

[0024] Furthermore, the output voltage of the isolated modular multi-level energy storage converter is controlled by controlling the number of sub-modules put into operation.

[0025] Furthermore, the plurality of submodules work together to control the bidirectional flow of energy, thereby realizing the transformation from direct current to alternating current, from alternating current to direct current, and from low voltage to high voltage, and from high voltage to low voltage.

[0026] Beneficial effect: Compared with the prior art, the present invention adopts an innovative three-channel interleaved flyback parallel sub-module conversion circuit, which solves the problem of input and output ripples and ultimately achieves an effective improvement in the voltage conversion ratio.

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

[0028] The three-channel interleaved flyback parallel submodule conversion circuit of the present invention can simultaneously realize power distribution and stable voltage control, which can not only avoid the relatively low reliability problem in traditional submodules, but also improve the energy utilization rate of submodules in MMC compared with traditional boost conversion links.

[0029] The transmission efficiency and reliability of the sub-modules in the system are improved by controlling the opening and closing of the switch tubes in the three-channel interleaved flyback parallel sub-module conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A topological diagram of a three-channel interleaved flyback parallel sub-module conversion circuit disclosed in an embodiment of the present invention;

[0031] Figure 2 A topological diagram of an energy storage converter disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods and the accompanying drawings of the specification.

[0033] In view of the problems of poor isolation faced by sub-modules of a half-bridge structure, the present invention designs a novel three-channel interleaved flyback parallel sub-module conversion circuit, and proposes an MMC-BESS energy storage converter with high isolation based on the three-channel interleaved flyback parallel sub-module conversion circuit. The output voltage is controlled by controlling the mode switching of the switch tube, and the reliability of the use of the MMC is greatly improved.

[0034] Example 1

[0035] like Figure 1 As shown, a three-channel interleaved flyback parallel submodule conversion circuit of the present invention can isolate the battery energy storage side and the load DC bus side, including a first inductor L1, a second inductor L2, a third inductor L3, a battery U B , Battery side capacitor C B , output side capacitor C d , the first parasitic capacitor C1, the second parasitic capacitor C2, the first switch tube S1, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7, and the isolation transformer N. The specific connection method 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 tube 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 tube S7, one end of the fifth switch tube S5, and one end of the second switch tube S2, and the other end of the third inductor L3 is connected to one end of the sixth switch tube S6 and the other end of the seventh switch tube S7. One end of the sixth switch tube S6 is connected to one end of the primary coil N1 of the isolation transformer N, the other end of the fifth switch tube 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. A battery U is connected between one end of the first inductor L1 and the other end of the first switch tube S1. B , battery U B The two ends are connected in parallel with the battery side capacitor C B The other end of the first switch tube S1 is connected to the other end of the second switch tube S2 and then connected to the other end of the primary coil N1 of the isolation transformer N through the third switch tube S3. The two ends of the secondary coil N2 in the isolation transformer N are connected in parallel to the output side capacitor C d , at one end of the secondary coil N2 and the output side capacitor C d The fourth switch tube S4 is connected in series between the output side capacitor C d Both ends are connected to the DC bus side of the load.

[0036] From the overall working status analysis, the converter is in the application process, U B The bridge arm is the battery terminal, and the load is the DC bus terminal. In the blocking mode, regardless of the direction of the current, there is always a capacitor in the bridge arm, so it can play the role of clearing the fault current.

[0037] Example 2

[0038] A modeling method of a three-channel interleaved flyback parallel submodule conversion circuit of the present invention is applied to the three-channel interleaved flyback parallel submodule conversion circuit in Example 1, and the effectiveness of the topology in Example 1 is verified by modeling simulation. It includes:

[0039] When the MMC-BESS submodule works in Boost mode, assuming that the energy storage converter works in continuous conduction mode, the first switch tube S1, the second switch tube S2 and the seventh switch tube S7 are turned on first, and the remaining switch tubes are in the off state. 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 the first inductor L1, the second inductor L2 and the third inductor L3 increases continuously to store energy for them; at this time, a state equation model when the circuit is stable can be established:

[0040]

[0041] On this basis, the seventh switch tube S7 is turned off, the sixth switch tube S6 and the fifth switch tube S5 are turned on, and the remaining switch tubes are still in the off state. B Continue to charge the first inductor L1, and then establish B With the real-time state equation model in the L1 loop:

[0042]

[0043] Battery U B While continuing to charge the first inductor L1, the third inductor L3 charges the second parasitic capacitor C2. At this time, the voltage across the second parasitic capacitor C2 increases, and the voltage between the two ends of U B , real-time state equation model in L3 and C2 loops:

[0044]

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

[0046]

[0047] Then, the first switch tube S1 and the sixth switch tube S6 are turned off, and the second switch tube S2, the seventh switch tube S7, the third switch tube S3 and the fifth switch tube S5 are turned on, and the remaining switch tubes are in the off state; B The real-time state equation model in the L3 loop:

[0048]

[0049] The energy stored in the first parasitic capacitor C1 and the second parasitic capacitor C2 is released and converges into the primary coil N1 in the isolation transformer N. At this time, since the fourth switch tube S4 on the right side of the isolation transformer N is in the off state, there is no energy flow in the circuit on the right side of the isolation transformer N. At this time, the primary coil N1 can be equivalent to an inductor, inducing a positive voltage at the top and a negative voltage at the bottom; then the third switch tube S3 is turned off. At this time, the inductor induces a reverse voltage of negative at the top and positive at the bottom to prevent the sudden change of the current. At the same time, the secondary coil N2 on the right side induces a positive voltage at the top and a negative voltage at the bottom. On this basis, the fourth switch tube S4 is turned on. At this time, current appears in the right path, and part of the current is the output side capacitor C d Charging maintains the stability of the output voltage, and the rest is used to power the load side of the rear pole. This process can completely release the energy stored in the primary coil N1 to power the rear load side. The above process is the Boost mode operation principle of the three-channel 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 can be controlled separately in pairs, which greatly increases the 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 are more conducive to filtering.

[0050] Example 3

[0051] like Figure 2 As shown, the energy storage converter of the present invention is a modular multi-level energy storage converter (MMC-BESS) with high isolation, including three phase units with the same structure, each phase unit includes 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, wherein N≥1, and the sub-module adopts the three-channel staggered flyback parallel sub-module conversion circuit in Example 1. The output voltage of the isolated modular multi-level energy storage converter is controlled by controlling the number of sub-modules put into operation. The sub-modules work together to control the bidirectional flow of energy, and realize the transformation 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 also includes an upper bridge arm resistor and an upper bridge arm inductor connected in series to the output ends of the N submodules, and the negative terminal 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 submodules connected in series, and the positive terminal of the lower bridge arm is connected to one end of the lower bridge arm resistor.

[0053] like Figure 1 and Figure 2As shown, taking a submodule in the main topology as an example, the leftmost side of the submodule is the battery end, which provides charging, discharging and power conversion effects for the converter through the battery. A new DC / DC converter device is connected after the battery, and a transformer is connected after the new boost converter to form a small flyback power supply, which is then connected to the load port, i.e. the DC bus output port. This energy storage converter is mainly composed 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 submodule structure of MMC-BESS enables it to withstand higher voltage levels and has a faster response speed, and has broad development prospects. This solution mainly designs the power conversion link in the submodule of MMC-BESS, namely the DC / DC module, which is the technical solution of Example 1; and models and simulates its effectiveness, which is the technical solution of Example 2. The present invention improves the DC / DC link to achieve isolation between the battery and the load DC bus port, reduces the input and output current ripple, and effectively improves the voltage conversion ratio. By adding a transformer link, the reliability of MMC-BESS can be ultimately improved.

[0055] Since this MMC energy storage converter is modular in design and has no difference in three phases, a certain phase and a single module are used as specific examples when analyzing the working principle.

[0056] The energy storage converter involved in the present invention belongs to a non-energy consumption type circuit, that is, energy storage elements represented by capacitors are used to transfer energy between submodules. For a traditional Boost circuit, its voltage gain is given by the following formula:

[0057]

[0058] Wherein, D is the duty cycle of the switch tube, and the value of its voltage gain is directly related to the duty cycle. For the traditional Boost circuit modeling, it still has the problem of high output EMI and small voltage gain. This scheme adopts the three-channel interleaved flyback parallel submodule conversion circuit described in Example 1 to solve this problem.

Claims

1. A three-channel interleaved flyback parallel submodule conversion circuit, characterized in that: Used to isolate the battery energy storage side and the load DC bus side, 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, the other end of the first inductor L1 is connected to one end of the first switch tube 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 tube S7, one end of the fifth switch tube S5, and one end of the second switch tube S2, and the other end of the third inductor L3 is connected to one end of the sixth switch tube S6 and the other end of the seventh switch tube S7; One end of the sixth switch tube S6 is connected to one end of the primary coil N1 of the isolation transformer N, the other end of the fifth switch tube 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; A battery U is connected between one end of the first inductor L1 and the other end of the first switch tube S1. B , battery U B The two ends are connected in parallel with the battery side capacitor C B , the other end of the first switch tube S1 is connected to the other end of the second switch tube S2 and then connected to the other end of the primary coil N1 of the isolation transformer N through the third switch tube S3; The two ends of the secondary coil N2 in the isolation transformer N are connected in parallel to the output side capacitor C d , at one end of the secondary coil N2 and the output side capacitor C d A fourth switch tube S4 is connected in series therebetween.

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

3. A modeling method for a three-channel interleaved flyback parallel submodule conversion circuit, characterized in that: Applied to the three-channel interleaved flyback parallel submodule conversion circuit of claim 1, the modeling method comprises: The first switch tube S1, the second switch tube S2 and the seventh switch tube S7 are turned on, and the other switch tubes are in the off state. 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 the first inductor L1, the second inductor L2 and the third inductor L3 increases continuously to store energy for them; at this time, a state equation model when the circuit is stable is established:

4. The modeling method of the three-channel interleaved flyback parallel submodule conversion circuit according to claim 3 is characterized in that: After obtaining the state equation model when the circuit is stable, the seventh switch tube S7 is turned off, the sixth switch tube S6 and the fifth switch tube S5 are turned on, and the remaining switch tubes are still in the off state. B Continue to charge the first inductor L1, and then establish B With the real-time state equation model in the L1 loop: Battery U B While continuing to charge the first inductor L1, the third inductor L3 charges the second parasitic capacitor C2. At this time, the voltage across the second parasitic capacitor C2 increases, and the voltage between the two ends of U B , real-time state equation model in L3 and C2 loops: The second inductor L2 charges the first parasitic capacitor C1 and the second parasitic capacitor C2, and the U B , L2, C1 and C2 loops in real-time state equation model:

5. The modeling method of the three-channel interleaved flyback parallel submodule conversion circuit according to claim 3 is characterized in that: After obtaining the model of the second inductor L2 as the first parasitic capacitor C1 and the second parasitic capacitor C2 in the charging state, the first switch tube S1 and the sixth switch tube S6 are turned off, the second switch tube S2, the seventh switch tube S7, the third switch tube S3 and the fifth switch tube S5 are turned on, and the remaining switch tubes are in the disconnected state; at this time, the battery continues to charge the third inductor L3, and the U B The real-time state equation model in the L3 loop:

6. An energy storage converter, characterized in that: It comprises three phase units with the same structure, each of which comprises 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-channel 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 to the output ends of the N submodules, and the negative terminal of the upper bridge arm is 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 comprises a lower bridge arm inductor, a lower bridge arm resistor and N sub-modules connected in series, and 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 multi-level energy storage converter is controlled by controlling the number of sub-modules put into operation.

10. The energy storage converter according to claim 6, characterized in that: The plurality of submodules work together to control the bidirectional flow of energy, and realize the transformation from direct current to alternating current, from alternating current to direct current, and from low voltage to high voltage, and from high voltage to low voltage.

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