Bidirectional multi-mode hybrid multilevel inverter circuit and battery energy storage system

Abstract

The invention discloses a bidirectional multi-mode hybrid multilevel inverter circuit and a battery energy storage system, the inverter circuit comprises a controller, a power frequency commutation and filter circuit, a controller and a plurality of batteries and power units which are correspondingly and electrically connected, the batteries and the power units are divided into two groups, the output of each group of power units is cascaded to form a unipolar multi-level step wave bus; the power frequency commutation and filter circuit comprises a power frequency commutation circuit and a filter circuit, the power frequency commutation circuit is composed of a full-bridge topology, and the filter circuit is composed of an AC filter inductor and an AC filter capacitor; the controller samples an AC side signal, controls the logic sequence of each power unit and a switching tube of the power frequency commutation circuit, and controls the active equalization of the battery and the bidirectional electric energy conversion of the energy storage system. Conversion efficiency can be improved, switch power consumption and size can be reduced, and global power supply and consumption requirements can be met.

Description

Technical Field

[0001] The present invention relates to the field of new energy power electronics technology, and particularly to a bidirectional multi-mode hybrid multi-level inverter circuit and a battery energy storage system. Background Art

[0002] Most countries in the world use single-phase and three-phase power systems. However, in the power supply systems of North America and some other countries, dual-phase (L1-L2), i.e., single-phase power systems, single-phase (L1-N and / or L2-N), or parallel dual-phase (L1 / L2-N) power supply modes are used. In order to adapt to the global market, new energy battery energy storage systems need to flexibly switch between these power supply modes and be able to achieve bidirectional power conversion.

[0003] Bidirectional multi-mode inverter circuits usually use symmetric double half-bridge circuits, such as Figure 1 shown. This circuit includes two DC filter capacitors Cd1, Cd2, four power switching transistors Q1~Q4 and their body diodes, AC filter inductors L1, L2, and AC filter capacitors Cf1, Cf2. The power conversion from DC to AC is called inverter discharge (DC / AC), and the power conversion from AC to DC is called rectifier charge (AC / DC). In the inverter discharge mode: in the dual-phase power supply mode, i.e., the single-phase power system, Cd1, Cd2 and Cf1, Cf2 are connected in series for filtering, Q1~Q4 form a traditional bidirectional full-bridge circuit, L1, L2 are connected in series for filtering, and electrical energy is provided to the series-connected AC power supplies Va, Vc. At the same time, the load RL1 and RL2 are connected in series to obtain electrical energy from the two live wires without passing through the N wire. In the single-phase power supply mode, Cd1, Q1, Q2, L1, Cf1 form the first bidirectional half-bridge circuit, and Cd2, Q3, Q4, L2, Cf2 form the second bidirectional half-bridge circuit, thus forming a bidirectional multi-mode inverter circuit. The two circuits respectively provide electrical energy to Va, RL1 and Vc, RL2 through the N wire.

[0004] The parallel dual-phase power supply mode is similar to the single-phase mode and still shares the N wire. The only difference is that the two live wires are directly connected in parallel. Therefore, the amplitudes, frequencies, and phases of the two sets of single-phase AC voltages must be exactly the same. Conversely, the rectifier charge mode is similar and will not be elaborated here. The traditional bidirectional inverter circuit can achieve bidirectional power conversion and has the main advantages of simple circuit structure and mature modulation method.

[0005] The traditional bidirectional multi-mode inverter circuit has simple control. However, whether in the dual-phase or single-phase mode, bipolar high-frequency sine wave pulse width modulation (SPWM) must be adopted. All four power switching tubes operate in the high-frequency switching state, resulting in relatively large switching power consumption. In particular, the reverse recovery power consumption of their body diodes is relatively large, leading to a low conversion efficiency. Moreover, the output voltage in different modes is only two-level, and its output filter inductor is relatively large, making it difficult to further improve the conversion efficiency. The bidirectional multi-level multi-mode technology has become one of the research hotspots in new energy power electronics, aiming to reduce the switching power consumption, achieve a smaller volume, and enable flexible switching between the inverter and rectifier operating modes and various power supply modes.

[0006] In the existing battery energy storage system, the boost ratio between the battery voltage and the DC bus voltage is relatively large. Moreover, the subsequent traditional inverter circuit operates in the high-frequency switching state and its output voltage is two-level. The main disadvantages are the relatively low conversion efficiency of the two-stage conversion, a relatively large volume of the inverter, and a relatively high system cost. Summary of the Invention

[0007] The technical problem to be solved by the embodiments of the present invention is to provide a bidirectional multi-mode hybrid multi-level inverter circuit and a battery energy storage system to improve the conversion efficiency, reduce the switching power consumption and volume.

[0008] To solve the above technical problem, the embodiments of the present invention propose a bidirectional multi-mode hybrid multi-level inverter circuit, including a controller, a power frequency commutation and filtering circuit, a controller, and a number of batteries and power units that are correspondingly electrically connected. The batteries and power units are divided into 2 groups, and the output stages of each group of power units are cascaded to form a unipolar multi-level stepped wave bus; the power frequency commutation and filtering circuit includes a power frequency commutation circuit and a filtering circuit. The power frequency commutation circuit is composed of a full-bridge topology, and the filtering circuit is composed of an AC filtering inductor and an AC filtering capacitor; the controller samples the AC side signal, controls the logical order of each power unit and the switching tubes of the power frequency commutation circuit, and controls the active equalization of the batteries and the bidirectional power conversion of the energy storage system.

[0009] Correspondingly, the embodiments of the present invention also provide a battery energy storage system, including the above-mentioned bidirectional multi-mode hybrid multi-level inverter circuit.

[0010] The beneficial effects of the present invention are as follows: (1) There is no direct series or parallel connection between the batteries of the present invention, and there is no cask effect of the traditional energy storage solution. Each battery of the present invention is independently managed and controlled. On the one hand, it prolongs the battery discharge time, shortens the battery charging time, and speeds up the battery charging speed; on the other hand, the battery thermal management is easier, preventing battery thermal runaway in advance and eliminating the safety risk of battery fire and combustion.

[0011] (2) The present invention deeply integrates the battery, its management, active balancing, and power electronics technology. By adopting hierarchical cyclic carrier stacking modulation and its improved methods, the battery and power unit can be switched to the bypass state, thereby increasing the operating redundancy of the battery and further improving the reliability of the energy storage system.

[0012] (3) The present invention can use various types of batteries, such as lithium batteries, sodium batteries, or solid-state batteries, or a mixture of different types of batteries or a mixture of new and old batteries of the same type. It is applicable to battery management at the battery pack level, cell level, and battery cluster level, realizing active balancing of battery SoC / SoH, expanding the effective capacity of the battery, and extending the service life of the battery.

[0013] (4) The present invention operates in a two-wire (i.e., single-phase) power system, single-wire, single-wire series, and two-wire parallel power supply modes, and can flexibly switch between these power supply modes to meet the global power supply and consumption requirements.

[0014] (5) The present invention enables bidirectional power conversion between the battery and the AC power supply or the power grid: rectifying for charging or inverting for discharging, without the need for an additional charger or inverter.

[0015] (6) The power factor of the present invention is adjustable, and it can operate in active power and reactive power modes to meet the diverse requirements of electrical loads and power grid dispatching; (7) The bus voltage of the present invention is a single-polarity multi-level stepped wave, and its output equivalent frequency is several times that of the switching frequency, improving the conversion efficiency, reducing the output harmonics and electromagnetic interference, reducing the AC filter inductance and the volume of the energy storage device, and lowering the system cost.

[0016] (8) The internal power switching tubes of the power unit of the present invention are of a low voltage level. When in the two-wire power supply mode, only one internal power switching tube of the power unit operates in high-frequency switching simultaneously. When in the single-wire or two-wire parallel power supply mode, only two internal power switching tubes of the power unit operate in high-frequency switching simultaneously, and there is no high-frequency switching loss in the power frequency commutation and filtering circuit, thereby further improving the conversion efficiency.

[0017] (9) The control method of the present invention simplifies the controller design, is easy to expand new control strategies, and is convenient for expanding the capacity of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a traditional bidirectional inverter circuit diagram.

[0019] Figure 2 is a schematic structural diagram of the bidirectional multi-mode hybrid multi-level inverter circuit of an embodiment of the present invention.

[0020] Figure 3 is the output control flowchart of an embodiment of the present invention.

[0021] Figure 4 It is the flowchart of the battery active balancing control in the embodiment of the present invention.

[0022] Figure 5 It is the circuit diagram of the bidirectional multi-mode hybrid multi-level inverter circuit in the embodiment of the present invention.

[0023] Figure 6 In it, (a) is the main working waveform diagram in the dual hot wire power supply mode (i.e., single-phase power system Vac) in the embodiment of the present invention, and (b) is the main working waveform diagram in the single hot wire or dual hot wire parallel power supply modes Va and Vc in the embodiment of the present invention.

[0024] Figure 7 It is the circuit diagram of the DC boost and half-bridge cascade in Embodiment 1 of the present invention.

[0025] Figure 8 It is the circuit diagram of the negative terminal inductor DC boost and half-bridge cascade in Embodiment 2 of the present invention.

[0026] Figure 9 It is the circuit diagram of the four-switch DC buck-boost and half-bridge cascade in Embodiment 3 of the present invention.

[0027] Figure 10 It is the circuit diagram of the negative terminal inductor four-switch DC buck-boost and half-bridge cascade in Embodiment 4 of the present invention.

[0028] Figure 11 It is the circuit diagram of the DC resonant buck-boost and half-bridge cascade in Embodiment 5 of the present invention.

[0029] Figure 12 In it, (a) is the circuit diagram when a protection switch is provided inside the positive terminal of the battery in Embodiment 6 of the present invention, (b) is the circuit diagram when a protection switch is provided outside the positive terminal of the battery in Embodiment 6 of the present invention, (c) is the circuit diagram when a protection switch is provided inside the negative terminal of the battery in Embodiment 6 of the present invention, and (d) is the circuit diagram when a protection switch is provided outside the negative terminal of the battery in Embodiment 6 of the present invention.

[0030] Figure 13 In it, (a) is the circuit diagram when a protection switch is provided inside the positive terminal of the battery in Embodiment 7 of the present invention, (b) is the circuit diagram when a protection switch is provided outside the positive terminal of the battery in Embodiment 7 of the present invention, (c) is the circuit diagram when a protection switch is provided inside the negative terminal of the battery in Embodiment 7 of the present invention, and (d) is the circuit diagram when a protection switch is provided outside the negative terminal of the battery in Embodiment 7 of the present invention.

[0031] Figure 14 It is the circuit diagram of the battery boost and positive terminal half-bridge cascade in Embodiment 8 of the present invention.

[0032] Figure 15 It is another form of the circuit diagram of the bidirectional multi-mode hybrid multi-level inverter in Embodiment 9 of the present invention. Detailed implementation manners

[0033] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0034] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back...), they are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0035] In addition, in the present invention, the descriptions such as "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature.

[0036] Please refer to Figures 2 to 5 , the bidirectional multi-mode hybrid multi-level inverter circuit in the embodiments of the present invention includes a controller, a power frequency commutation and filtering circuit, a controller, and several batteries and power units that are correspondingly electrically connected. The circuit connection relationship is preferably: battery ↔ power unit ↔ filtering circuit ↔ power frequency commutation circuit (Sync & Gate Drive) ↔ power grid (L1 / L2 / L3 / N).

[0037] The battery energy storage system in the embodiments of the present invention includes a bidirectional multi-mode hybrid multi-level inverter circuit. The present invention can be widely applied to various bidirectional or unidirectional charging or inverter circuits, such as new energy wind power and photovoltaic power generation and energy storage systems such as lithium batteries, sodium batteries, and solid-state batteries, battery formation and grading system equipment, as well as battery charge and discharge systems in power tools and construction machinery, motor controllers of electric vehicles and non-road vehicles, etc.

[0038] Multiple batteries and their power units can be divided into two groups. The first group of batteries and their power units are A1~An, and the second group is B1~Bn, where n is the number of batteries or power units inside each group of batteries. The power unit includes a half-bridge cascaded circuit. All batteries are connected to the corresponding power units. The AC side includes electrical loads RLa and RLc, as well as AC power sources Va and Vc and AC. The power frequency commutation and filtering circuit consists of a full-bridge topology with four switching tubes for power frequency modulation, and an AC filter inductor and an AC filter capacitor.

[0039] Each battery anode and cathode are respectively connected to the corresponding ports ① and ② of the power unit. The port ④ of the first group of bottom power units A1 is connected to the port ⑩ of the industrial frequency commutation and filtering circuit, that is, the negative pole of the unipolar multi-level stepped wave bus. Its port ③ is connected to the port ④ of another power unit A2 in the adjacent upper layer. Its port ③ is then connected to the port ④ of another power unit in the adjacent upper layer, and so on. After cascading multiple power units, the port ③ of the top power unit An is connected to the midpoint port ⑧ of the industrial frequency commutation and filtering circuit, that is, the midpoint of the unipolar multi-level stepped wave bus. The port ④ of the second group of bottom power units B1 is also connected to the midpoint port ⑧ of the industrial frequency commutation and filtering circuit. Its port ③ is connected to the port ④ of another power unit B2 in the adjacent upper layer. Its port ③ is then connected to the port ④ of another power unit in the adjacent upper layer, and so on. After cascading multiple power units, the port ③ of the top power unit Bn is connected to the port ⑨ of the industrial frequency commutation and filtering circuit, that is, the positive pole of the unipolar multi-level stepped wave bus. The controller is connected to the port ⑤ of the power unit and the port ⑪ of the industrial frequency commutation and filtering circuit. The port ⑧ of the industrial frequency commutation and filtering circuit is connected to the neutral line N, the port ⑦ is connected to the first live wire L1, and the port ⑥ is connected to the second live wire L2. The voltage difference between L1 and N is the AC power supply Va, the voltage difference between N and L2 is the AC power supply Vc, and the series equivalent of Va and Vc is the AC power supply AC.

[0040] The controller can be a single controller, including a sampling, conditioning and feedback circuit, and a switching tube drive circuit, etc. Optionally, it is divided into a master controller and a slave controller, and there is a wired or wireless communication between the master and slave controllers. The master controller samples the AC side signals, controls the logical order of each power unit and the switching tubes of the industrial frequency commutation circuit, and at the same time realizes external communication; the slave controller detects battery-side electrical parameters such as voltage, current, power and temperature, calculates the state of charge / health (SOC / SOH), that is, it is equivalent to completing the battery management function, reports its respective battery parameters such as SOC / SOH to the master controller, and receives and executes the instructions and data issued by the master controller, such as rectification charging / inverter discharging and battery active equalization control, the logical order arrangement of the power unit, the stepped wave output voltage and the battery quantity information, etc., and controls the operation of each switching tube inside the power unit. Optionally, the slave controller is placed inside the corresponding power unit. It works in a dual live wire, that is, a single-phase electrical system, a single live wire, a single live wire series, and a dual live wire parallel power supply mode, and can flexibly switch between these power supply modes.

[0041] Bidirectional DC-AC circuit (DC / AC), which can flexibly operate in off-grid inverter discharge, grid-connected inverter discharge, and rectifier charging modes according to actual application requirements. The power flow path from the battery to the AC power supply (inverter discharge) is as follows: In the double hot wire or single hot wire series power supply mode, that is, when the grid voltage or AC output of the single-phase power system is 220V / 230V / 240V, all batteries and power units A1~An and B1~Bn form the same inverter circuit, forming a single-polarity multi-level stepped wave bus between the 9th and 10th ports of the power frequency commutation and filtering circuit, and forming a power frequency cycle positive and negative symmetric stepped wave between the midpoints of the two bridge arms of its full-bridge topology. After filtering through the AC inductor and AC capacitor, an AC sine wave voltage is generated to supply power to the series-connected AC power supplies Va, Vc, that is, Vac or the grid. At the same time, the load RLa and RLc are connected in series to obtain power from the two hot wires L1 and L2 without passing through the N wire. Therefore, the double hot wire power supply mode is essentially a single-phase power system. In the single hot wire power supply mode, when the grid voltage or AC output is 100V / 110V / 120V, the first group of batteries and the first group of power units A1~An form the first inverter circuit; the second group of batteries and the second group of power units B1~Bn form the second inverter circuit. The two respectively form two single-polarity multi-level stepped wave buses between the 9th and 8th ports, and the 8th and 10th ports of the power frequency commutation and filtering circuit. Similarly, two power frequency cycle positive and negative symmetric stepped waves are formed between the midpoints of the two bridge arms of their full-bridge topology. After filtering through the AC inductor and AC capacitor respectively, two AC sine wave voltages are generated, and then supply power to Va, RLa, and Vc, RLc or the grid respectively from the two hot wires L1 and L2 through the N wire. In the single hot wire power supply mode, the two AC output powers can be different, so it can adapt to different types of electrical loads.

[0042] When the grid voltage or AC output of the dual live-wire parallel power supply mode is 100V / 110V / 120V, similar to the single live-wire power supply mode, two inverter circuits are still formed. The difference is only that the two live wires L1 and L2 are directly paralleled, and the switching modes of the full-bridge topology switch tubes in the industrial-frequency commutation and filtering circuit are appropriately adjusted: the two upper tubes are turned on and off simultaneously, and the two lower tubes are turned on and off simultaneously. The amplitudes, frequencies, and phases of the two AC voltages Va and Vc are exactly the same, so they can work in parallel. Conversely, the power flow path from the AC power supply to the battery (rectification and charging) is as follows: the input and output ends of the industrial-frequency commutation and filtering circuit are interchanged, that is, the input ends are the ⑥th and ⑦th ports respectively, the output ends are the ⑨th and ⑩th ports respectively, the ⑧th port is the N wire, and the input and output ends of the power unit also need to be interchanged, that is, the input positive and negative poles are the ③rd and ④th ports respectively, and the output positive and negative poles are the ①st and ②nd ports respectively. The sinusoidal voltage provided by the AC power supply is filtered by the AC inductor and AC capacitor in the industrial-frequency commutation and filtering circuit and then enters the full-bridge topology for industrial-frequency rectification. The full-bridge topology can also work in the synchronous rectification mode, that is, the switch tubes work at industrial frequency to replace the conduction of their body diodes to reduce the power loss of the full-bridge topology. The cascaded power units at the input form a single-polarity multi-level stepped-wave bus to charge each battery in a constant current or constant voltage manner. Its working principle is similar to the inverter discharge mode and will not be elaborated here. It should be noted that the power unit and the industrial-frequency commutation and filtering circuit are both bidirectional conversion circuits under these modes.

[0043] The main controller issues commands to the slave controllers according to the SOC / SOH information of each battery to control the corresponding power unit logic sequence. During inverter discharge / rectification charging, the controller switches the battery with the highest / lowest SOC and its corresponding power unit to the bottom layer of the single-polarity multi-level stepped-wave bus for low-frequency square wave modulation (NLM), and switches the battery with the lowest SOC and its corresponding power unit to the top layer for high-frequency sine wave pulse width modulation (SPWM). During inverter discharge or rectification charging, this hybrid modulation method of high-frequency SPWM and low-frequency NLM is called carrier stacking modulation, which is mainly used for multi-level conversion switch modulation and is further combined with battery management and active balancing to deeply integrate the battery and its management and active balancing with power electronics technology, thus forming a hierarchical cyclic carrier stacking modulation. The control method flow chart is as Figure 3 、 4 shown.

[0044] For a power frequency sine wave cycle, the bottom layer of the unipolar multi-level stepped wave bus means more charge and discharge energy, and the top layer means less charge and discharge energy. Other batteries and their power units are arranged in sequence according to the SOC level rule, so that the high-SOC batteries have more discharge energy and less charge energy, while the low-SOC batteries have less discharge energy and more charge energy, thus realizing the functions of battery management and active SOC / SOH balancing. By adopting this control method, the battery energy storage system can use various types of batteries, including mixed use of different types of batteries or mixed use of new and old batteries of the same type. In the dual-firewire power supply mode, only one top-layer power unit's high-frequency SPWM switch works, and one bottom-layer power unit's low-frequency NLM switch works, while the switches of other power units work between SPWM and NLM; in the single-firewire or dual-firewire parallel power supply mode, only two top-layer power unit's high-frequency SPWM switches work respectively, and two bottom-layer low-frequency NLM switches work respectively, and the switches of other power units work between SPWM and NLM, and the full-bridge topology in the power frequency commutation circuit also works as a power frequency switch. Each power unit is independently controlled by its respective slave controller. There is no need for direct series or parallel connection between batteries, and there is no barrel effect in the traditional scheme. Each battery in the energy storage system is independently managed and controlled. On the one hand, it prolongs the battery discharge time, shortens the battery charging time, and speeds up the battery charging speed; on the other hand, battery thermal management is easier, preventing battery thermal runaway in advance and eliminating the safety risk of battery fire and combustion. Optionally, the hierarchical cyclic carrier stacking modulation method can be further improved. When the normal operation is not affected during inverter discharge or rectifier charging, the battery with the lowest SOC and its power unit can be switched to the bypass state, that is, the main switch in the half-bridge cascade circuit to be bypassed is continuously turned on. In this way, the batteries and their power units that have failed in advance or have faults can be cut out online, thereby increasing the redundancy of battery operation and further improving the reliability of the energy storage system.

[0045] In the dual live-wire power supply mode, i.e., in a single-phase power system, two groups of monomers and their power units work together as a whole. The number of levels of the unipolar multi-level stepped wave bus is (2n + 1), and the equivalent number of levels of the positive and negative symmetric stepped wave or sine wave output in the power frequency period is (4n + 1). In the single live-wire or dual live-wire parallel power supply mode, two groups of monomers and their power units work independently. The number of levels of the two unipolar multi-level stepped wave buses is both (n + 1), and the equivalent number of levels of the positive and negative symmetric stepped wave or sine wave output in the two power frequency periods is both (2n + 1). It should be noted that when in the single live-wire series power supply mode and changing the multi-level modulation method, the number of levels is not the same as that in the dual live-wire power supply mode, i.e., the single-phase power system. The number of levels of the unipolar multi-level stepped wave bus formed by superimposing two voltages is (n + 1), and the equivalent number of levels of the positive and negative symmetric stepped wave or sine wave output in the power frequency period is (2n + 1). Optionally, the number of batteries or power units inside the two groups of monomers or their respective power modules can be different, which does not affect the normal operation of the circuit. In addition, the power unit can be applied to the battery pack level, the cell level, or the battery cluster level. Optionally, in the dual live-wire power supply mode, i.e., in a single-phase power system, one of the two AC filter inductors in the power frequency commutation and filter circuit can also be removed, and a single AC filter inductor does not affect the normal operation of the circuit. Optionally, the AC filter inductor and the AC filter capacitor in the filter circuit can also be located between the unipolar multi-level stepped wave bus and the full-bridge topology. By sampling the AC and DC side voltage and current signals, the controller identifies the input and output power flow directions, determines and controls the operation of the power switch tubes according to the actual operating conditions, and stabilizes the output voltage or current by real-time feedback of the working state in a closed loop, adaptively controlling to operate in the inverter discharge or rectifier charge mode to achieve bidirectional power conversion of the energy storage system. The controller can flexibly change the phases of the AC voltage and the AC current respectively, achieve adjustable power factor, and can operate in the active power and reactive power modes to meet the diverse requirements of the electrical load and the power grid dispatching. The control method simplifies the controller design, is easy to expand new control strategies, and is convenient for the energy storage system to increase its capacity.

[0046] During the inverter discharge or rectifier charging mode, the bus voltage is a single-polarity multi-level stepped wave, and the rate of change of voltage (dv / dt) across the AC filter inductor is small. Therefore, the inductance of the AC filter inductor in the filter circuit is small. The output voltage, current, and power of the power unit are small, which can reduce the rated voltage level of the internal power switch tubes. In the dual-line power supply mode, only the internal power switch tubes of one power unit operate with high-frequency switching simultaneously; in the single-line or dual-line parallel power supply mode, only the internal power switch tubes of two power units operate with high-frequency switching simultaneously, and there is no high-frequency switching loss in the power frequency phase conversion and filter circuit. Its output equivalent frequency is several times the switching frequency, thereby improving the conversion efficiency, reducing the output harmonics and electromagnetic interference, reducing the volume of the energy storage device, and lowering the system cost. The proposed technical solution is mainly aimed at the energy storage system, and batteries are used on both the DC sides of the bidirectional circuit. Optionally, a DC power supply is used on the DC side, thereby further expanding the application scope of the bidirectional DC / AC.

[0047] Optionally, to adapt to different power levels and battery capacities, the power unit internally includes a high-frequency pulse width modulation (PWM) DC-DC circuit (DC / DC). The input end of the DC / DC is connected to the battery, and its output end passes through a half-bridge cascaded circuit and then is connected to the power frequency phase conversion and filter circuit. The DC / DC circuit uses non-isolated or isolated topologies, including but not limited to non-isolated topologies such as Buck, Boost, Buck-Boost, Cuk, SEPIC, ZETA, etc., and isolated topologies such as half-bridge, full-bridge, push-pull, flyback, forward, forward-flyback, etc., or combines resonant circuits such as LLC, LCC, LCLC, CLCL, basic series-parallel, etc. The DC / DC circuit adopts high-frequency PWM modulation. Each battery and its switching unit are sorted according to the SOC level algorithm. The half-bridge or full-bridge cascaded circuit adopts hierarchical cyclic carrier stacking modulation or its improved type, and the power frequency phase conversion circuit adopts power frequency modulation. The batteries and the output stages of the power units are cascaded to form a single-polarity multi-level stepped wave bus.

[0048] In the power unit, the DC / DC circuit, the half-bridge cascaded circuit, and the power frequency phase conversion circuit can use interleaved parallel or series technologies, and can also use various multi-level circuits to achieve higher power levels or higher voltage levels. It should be noted that the DC / DC circuit and the half-bridge cascaded circuit adopt voltage mode control, and can also adopt average current mode, peak current mode control, quasi-resonant control, single-cycle control, etc., and can also adopt different working modes, such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), or critical conduction mode (CRM), etc.

[0049] Full-controlled devices are used for the power switching transistors in the power unit, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), etc. Third-generation wide-bandgap (WBG) power devices can also be used, such as silicon carbide (SiC), gallium nitride (GaN) MOSFETs, etc. These full-controlled power switching transistors can also be used in combination. For the power switching transistors in the power-frequency commutation circuit, either full-controlled devices or semi-controlled devices can be used, such as silicon-controlled rectifiers (SCRs), triacs (TRIACs), etc., or full-controlled and semi-controlled devices can be used in combination.

[0050] The controller can be built using discrete electronic components or designed and used with application-specific integrated circuits, such as analog control chips, microcontrollers (MCUs) programmed by software, digital signal processors (DSPs), or programmable logic devices (FPGAs / CPLDs), etc. It can be in the form of discrete devices or integrated form, or integrated into the controller to form a large-scale hybrid integrated circuit. This highly integrated controller design can further reduce the volume of the energy storage device.

[0051] The embodiments of the present invention, for example Figure 5As shown, four batteries and their power units are used. They can be divided into two groups, namely two groups of batteries and their power units. The power unit includes a half-bridge cascaded circuit. The first group of batteries includes batteries A1 and A2, and the second group of batteries includes batteries B1 and B2. The first power unit A1 of the first group of power units includes a DC filter capacitor C11 and MOSFET switches Q11 and Q12, and the second power unit A2 includes a DC filter capacitor C12 and MOSFET switches Q13 and Q14. The first power unit B1 of the second group of power units includes a DC filter capacitor C21 and MOSFET switches Q21 and Q22, and the second power unit B2 includes a DC filter capacitor C22 and MOSFET switches Q23 and Q24. All batteries are connected to the corresponding power units. The AC side includes electrical loads RLa and RLc, as well as AC power supplies Va and Vc. The industrial frequency commutation and filtering circuit internally includes four IGBT switches Q5 to Q8 to form a full-bridge topology, AC filter inductors Lf1 and Lf2, and AC filter capacitors Cf1 and Cf2. Two series power switches form an arm, such as Q11 and Q12, Q5 and Q6, etc., each forming an arm. For the convenience of explaining the basic principle, the internal or external diodes of the power switches are not drawn in the figure, but it does not affect their actual functions and performances. The DC sides of power units A1 to B2 are connected to their respective batteries A1 to B2. The midpoint of the half-bridge cascaded circuit arm inside each power unit is connected to the negative pole of the half-bridge cascaded circuit of another adjacent power unit. After forming the output cascade, a single-polarity multi-level stepped wave bus is formed between the midpoints of the Q23 and Q24 arms and the midpoints of the Q11 and Q12 arms. The midpoint of the Q7 and Q8 arms is connected to one end of Lf1, and the midpoint of the Q5 and Q6 arms is connected to one end of Lf2. The other ends of Lf1 and Lf2 are respectively connected to one end of Cf1, Cf2, RLa, RLc, and two live wires L1 and L2 of the AC voltage Vac. The other ends of Cf1, Cf2, RLa, and RLc are connected to the connection point of the two-module cascade, that is, the connection point of Q13 and Q22 and the neutral line N. In addition, a positive and negative symmetric stepped wave of the industrial frequency period is formed between the midpoints of the Q5 and Q6 arms and the midpoints of the Q7 and Q8 arms.

[0052] When the double hot wire or single hot wire series power supply mode, that is, the single-phase power system, all batteries A1~B2 and their power units A1~B2, industrial frequency commutation switch tubes Q5~Q8, two series filter inductors Lf1, Lf2, two series filter capacitors Cf1, Cf2 form the same inverter circuit, a unipolar multi-level stepped wave bus, and a positive and negative symmetric stepped wave in one industrial frequency cycle, to provide or obtain electrical energy from the series AC power supplies Va, Vc, that is, Vac or the power grid. At the same time, the loads RLa and RLc are connected in series to obtain electrical energy from the two hot wires L1 and L2 without passing through the N wire. In the single hot wire power supply mode, all batteries A1~B2 and their power units A1~B2, industrial frequency commutation switch tubes Q7, Q8, filter inductor Lf1, and filter capacitor Cf1 form the first inverter circuit, the first unipolar multi-level stepped wave bus, and the first positive and negative symmetric stepped wave in one industrial frequency cycle; all batteries A1~B2 and their power units A1~B2, industrial frequency commutation switch tubes Q5, Q6, filter inductor Lf2, and filter capacitor Cf2 form the second inverter circuit, the second unipolar multi-level stepped wave bus, and the second positive and negative symmetric stepped wave in one industrial frequency cycle, thus forming a multi-mode circuit, and then respectively providing or obtaining electrical energy from the two hot wires L1 and L2 through the N wire to Va, RLa and Vc, RLc or the power grid. The double hot wire parallel power supply mode is similar to the single hot wire power supply mode, still forming a multi-mode circuit. The difference is only that the two hot wires L1 and L2 are directly connected in parallel, and the full-bridge topology switch tubes in the industrial frequency commutation and filter circuits appropriately adjust the switching mode: Q5 and Q7 are turned on and off simultaneously, Q6 and Q8 are turned on and off simultaneously, and the amplitudes, frequencies and phases of the two AC voltages Va and Vc are exactly the same, so they can work in parallel.

[0053] During the inverting discharge, the energy is provided by batteries A1 to B2. The bidirectional half-bridge cascaded circuit operates in the DC buck mode. At this time, the MOSFET switches Q11, Q13, Q21, and Q23 are the main switches, and the MOSFET switches Q12, Q14, Q22, and Q24 are the synchronous rectifier diodes. In each high-frequency switching cycle, the synchronous rectifier diodes turn on slightly later after the internal or externally added diodes are turned on, so that zero-voltage switching (ZVS) can be achieved. According to different power supply modes and the active equalization requirements of SoC / SoH, the main controller generates a logical sequence configuration, and the slave controller selects single or double switches to work in the high-frequency SPWM switching state simultaneously, and the others work in the low-frequency NLM switching state. The power-frequency commutation and the filter inductors Lf1 and Lf2 in the filter circuit can be used as energy storage inductors. When the main switches of the half-bridge cascaded circuit are turned on, Lf1 and Lf2 store energy and provide energy to the unipolar multi-level stepped wave bus at the same time. When they are turned off, the energy stored in the inductors discharges through the synchronous rectifier diodes to the unipolar multi-level stepped wave bus for freewheeling. The unipolar multi-level stepped wave bus then undergoes power-frequency commutation through the IGBT switches Q5 to Q8 in the full-bridge topology of the power-frequency commutation and filter circuit to form a positive and negative symmetric stepped wave in the power-frequency cycle and output a sine wave voltage to provide energy to the single-phase AC power Vac or Va, Vc. The main working waveforms are as shown in Figure 6 Figure. Among them, (a) shows the double-hot-wire power supply mode, that is, in the single-phase power system Vac, from top to bottom are the unipolar stepped wave bus voltage, the positive and negative symmetric stepped wave in the power-frequency cycle, and the output sine wave voltage; (b) shows the single-hot-wire or double-hot-wire parallel power supply modes Va, Vc, from top to bottom are the unipolar stepped wave bus voltage, the positive and negative symmetric stepped wave in the power-frequency cycle, and the output sine wave voltage.

[0054] During rectifier charging, energy is provided by the single-phase power Vac or Va, Vc of the AC power supply or the power grid. After passing through the filter capacitors Cf1 and Cf2, Vac or Va, Vc enters the full-bridge topology composed of IGBT switching tubes Q5~Q8 in the full-bridge topology of the industrial-frequency commutation and filtering circuit for industrial-frequency rectification, forming a positive-negative symmetric stepped wave of the industrial-frequency period. Then, it passes through the cascaded power units A1~B2 to form a unipolar multi-level stepped-wave bus. Q5~Q8 can also operate in the synchronous rectification mode, that is, the switching tubes operate at industrial frequency instead of their body diodes conducting, so as to reduce the power loss of the full-bridge topology. The bidirectional half-bridge cascaded circuit operates in the DC boost (Boost) mode. At this time, the MOSFET switching tubes Q12, Q14, Q22, Q24 are the main tubes, and the MOSFET switching tubes Q11, Q13, Q21, Q23 are the synchronous rectifier tubes. In each high-frequency switching cycle, the synchronous rectifier tube turns on slightly later after the internal or externally added diode conducts, so that ZVS can be achieved. According to different power supply modes and the active balancing requirements of SoC / SoH, the main controller generates a logical sequence configuration, and the slave controller selects single tubes or double tubes to work in the high-frequency SPWM switching state at the same time, and the others work in the low-frequency NLM switching state: the filter inductors Lf1 and Lf2 in the industrial-frequency commutation and filtering circuit can be used as energy storage inductors. When the main tubes of the half-bridge cascaded circuit are conducting, Lf1 and Lf2 store energy. When they are turned off, the energy stored in the inductor discharges to the batteries A1~B2 through the synchronous rectifier tubes, so that each battery can be charged separately. Rectifier charging can adopt the constant current or constant voltage method, which are traditional control measures and will not be elaborated here.

[0055] In the dual live-wire power supply mode, that is, in the single-phase power system, two groups of batteries and their power units work together as a whole. The number of levels of the unipolar multi-level stepped-wave bus is (5), and the equivalent number of levels of the positive-negative symmetric stepped wave or sine wave output in the industrial-frequency period is (9); in the single live-wire or dual live-wire parallel power supply mode, two groups of monomers and their power units work independently. The number of levels of the two unipolar multi-level stepped-wave buses is both (3), and the equivalent number of levels of the two positive-negative symmetric stepped waves or sine wave outputs in the industrial-frequency period is both (5). It should be noted that in the single live-wire series power supply mode, the number of levels of the unipolar multi-level stepped-wave bus formed by superimposing two voltages is (3), and the equivalent number of levels of the positive-negative symmetric stepped wave or sine wave output in the industrial-frequency period is (5).

[0056] Optionally, in order to adapt to different power levels and battery capacities, the power unit includes a high-frequency pulse width modulation (PWM) DC-DC circuit (DC / DC) inside. The input end of the DC / DC is connected to the battery, and its output end passes through the half-bridge cascaded circuit and then is connected to the industrial-frequency commutation and filtering circuit. Optionally, the DC / DC circuit uses the DC boost topology (Boost). Example 1 is as Figure 7 shown, and the power unit is composed of a DC boost and a half-bridge cascaded circuit. The industrial-frequency commutation and filtering circuit and the controller adopt Figures 2 - 6In a similar manner, the working principle is basically the same and will not be elaborated here.

[0057] Optionally, the DC / DC circuit uses the Boost topology negative terminal inductor form. Example 2 is as Figure 8 shown. The power unit is composed of a negative terminal inductor DC boost and a half-bridge cascade circuit. The industrial frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar manner. The working principle is basically the same and will not be elaborated here.

[0058] Optionally, the DC / DC circuit uses a four-switch buck-boost topology. Example 3 is as Figure 9 shown. The power unit is composed of a four-switch DC buck-boost and a half-bridge cascade circuit. When performing bidirectional power conversion for inverter discharge and rectifier charging, two single-direction DC boosts and buckings can be achieved. The industrial frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar manner. The working principle is basically the same and will not be elaborated here.

[0059] Optionally, the DC / DC circuit uses a negative terminal inductor four-switch buck-boost topology. Example 4 is as Figure 10 shown. The power unit is composed of a negative terminal inductor four-switch DC buck-boost and a half-bridge cascade circuit. The industrial frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar manner. The working principle is basically the same and will not be elaborated here.

[0060] Optionally, the DC / DC circuit uses a bidirectional LLC resonant circuit. Example 5 is as Figure 11 shown. The power unit is composed of an LLC and a half-bridge cascade circuit. The LLC resonant circuit enables all power switch tubes to operate in ZVS mode, thereby further improving the conversion efficiency. Optionally, the LLC resonant circuit can use various types such as half-bridge, full-bridge, push-pull, etc. Optionally, combined with other LCC, LCLC, CLCL, basic series-parallel, etc. resonant technologies. The industrial frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar manner. The working principle is basically the same and will not be elaborated here.

[0061] Optionally, a battery bidirectional protection switch is used inside the power unit. Example 6 is as Figure 12 shown, that is, Figure 5A bidirectional protection switch is added. In the bidirectional protection switch, the power switch tubes are in a face-to-face series form, that is, the drains of the two MOSFETs in the protection switch are connected to each other. Among them, (a) the protection switch is located inside the positive terminal of the battery, (b) the protection switch is located outside the positive terminal of the battery, (c) the protection switch is located inside the negative terminal of the battery, and (c) the protection switch is located outside the negative terminal of the battery. After adding the battery protection switch, the battery connection can be disconnected in time when the battery or the system has an abnormality, thereby improving the system safety. Optionally, the power switch tubes in the bidirectional protection switch are in a back-to-back series form, that is, the sources of the two MOSFETs are connected to each other. Optionally, the bidirectional protection switch is composed of a full-bridge rectifier circuit and a power switch tube connected in series. Optionally, the power unit internally includes a DC / DC circuit and can adopt Figures 7 - 11 The circuit form, and its working principle is the same, so it will not be elaborated here. The power frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 A similar method, and its working principle is basically similar, so it will not be elaborated here.

[0062] Optionally, a battery bidirectional protection switch is used inside the power unit. Example 7 is as Figure 13 shown, that is, in Figure 12 one power switch tube in the bidirectional protection switch is removed, and a single power switch tube combined with a half-bridge cascade circuit can also achieve the purpose of battery bidirectional protection. Among them, (a) the protection switch is located inside the positive terminal of the battery, (b) the protection switch is located outside the positive terminal of the battery, (c) the protection switch is located inside the negative terminal of the battery, and (c) the protection switch is located outside the negative terminal of the battery. After adding the battery protection switch, the battery connection can be disconnected in time when the battery or the system has an abnormality, thereby improving the system safety. Taking Figure 13 (a) as an example to illustrate the basic working principle: during the inverter discharge, the internal or externally added diode of the battery protection MOSFET conducts, and this MOSFET can also work in the synchronous rectification mode, but uses the continuous turn-off of the upper tube on the bridge arm of the half-bridge inverter circuit to achieve battery protection; during the rectification charging, the battery protection MOSFET is continuously turned off, thereby achieving battery protection. Therefore, the single-tube structure in the protection switch can also achieve the purpose of battery bidirectional protection. Optionally, it is also possible not to add an external battery bidirectional protection switch, but to achieve the purpose of battery bidirectional protection by the upper and lower power switch tubes in the half-bridge cascade circuit. Optionally, the power unit internally includes a DC / DC circuit and can adopt Figures 7 - 11 The circuit form, and its working principle is the same, so it will not be elaborated here. The power frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 A similar method, and its working principle is basically similar, so it will not be elaborated here.

[0063] Optionally, the half-bridge cascade circuit in the power unit adopts a positive terminal cascade form. Example 8 is as Figure 14 shown, that is, the positions of output ports ③ and ④ are changed. Optionally, the DC / DC circuit adoptsFigures 7 - 11 Circuit form, the battery protection switch adopts Figure 12 , 13 Circuit form, whose working principle is the same, so it will not be elaborated here. The power frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar method, and its working principle is basically the same, so it will not be elaborated here.

[0064] Optionally, in Embodiment Figure 4 the power frequency commutation circuit can be removed, and the half-bridge in the power unit can be replaced with a full-bridge circuit, also known as an H-bridge. Embodiment 9 is as shown in Figure 15 shown. Optionally, the DC / DC circuit adopts Figures 7 - 11 Circuit form, the battery protection switch adopts Figure 12 , 13 Circuit form, the battery boost and positive terminal half-bridge cascade circuit adopts Figure 14 Circuit form, whose working principle is the same, so it will not be elaborated here. The power frequency commutation and filtering circuit and the controller adopt Figures 2 - 6 a similar method, and its working principle is basically the same, so it will not be elaborated here.

[0065] Specific experimental data and test results of each embodiment of the present invention are shown in Table 1 in detail. The test conditions are as follows: 2 groups of batteries, 2 batteries in each group, and a total of 4 48V lithium batteries are used. Electrical parameters of electronic components: MOSFET 1mΩ / 40V, IGBT 50A / 650V, filtering inductor 20uH, SPWM switching frequency 20kHz, power frequency alternating current frequency 50Hz. Only the basic principle is verified for 2 groups of 4 batteries. In fact, it can also be extended to multiple batteries. Since the total voltage of the batteries corresponding to the power unit is 192V DC, the AC voltage will be lower than it.

[0066] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalent scope.

Claims

1. A bidirectional multi-mode hybrid multi-level inverter circuit, comprising a controller, a power frequency commutation and filtering circuit, a controller, and a number of batteries and power units electrically connected correspondingly, characterized in that, The battery and the power unit are divided into two groups, and the output stages of the power units in each group are cascaded to form a unipolar multi-level stepped wave bus; the industrial frequency commutation and filtering circuit includes an industrial frequency commutation circuit and a filtering circuit. The industrial frequency commutation circuit is composed of a full-bridge topology, and the filtering circuit is composed of an AC filtering inductor and an AC filtering capacitor; the controller samples the AC side signals, controls the logical order of each power unit and the switching tubes of the industrial frequency commutation circuit, and controls the active balancing of the battery and the bidirectional power conversion of the energy storage system.

2. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 1, characterized in that, The power unit includes a half-bridge cascaded circuit composed of two power switching tubes or a full-bridge cascaded circuit composed of four power switching tubes.

3. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 2, characterized in that, The power unit further includes a PWM-modulated DC / DC circuit, and a non-isolated or isolated topology is used.

4. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 3, wherein The DC / DC circuit adopts high-frequency PWM modulation. The controller sorts each battery and its power unit according to the SOC level. When inverting and discharging / rectifying and charging, the controller switches the battery with the highest / lowest SOC and its corresponding power unit to the bottom layer of the unipolar multi-level stepped wave bus for low-frequency square wave modulation, and switches the battery with the lowest SOC and its corresponding power unit to the top layer for high-frequency sine wave pulse width modulation, forming a hierarchical cyclic carrier stacking modulation; the industrial frequency commutation circuit adopts industrial frequency modulation.

5. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 4, characterized in that, The controller dynamically obtains the voltage and current values of the battery or the AC power supply; then compares the obtained current actual output value with the target value; dynamically determines the duty cycle and whether the power unit switching tubes work according to the comparison result, adjusts the command according to the confirmation result; controls the power unit switching tubes to execute the command, and dynamically controls the energy storage / discharge time of the AC filtering inductor, so that the current actual output value approaches the target value.

6. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 4, wherein The controller dynamically obtains the SoC / SoH voltage, current, and temperature values of each battery, and sorts the currently obtained actual power values of all batteries according to the level. If the SoC / SoH of the battery is the highest, when inverting and discharging, the power unit corresponding to this battery is placed at the bottom layer of the stepped wave bus, and when rectifying and charging, the power unit corresponding to this battery is placed at the top layer of the stepped wave bus; If the SoC / SoH of the battery is the lowest, when inverting and discharging, the power unit corresponding to this battery is placed at the top layer of the stepped wave bus, and when rectifying and charging, the power unit corresponding to this battery is placed at the bottom layer of the stepped wave bus; According to the actual power values in sequence from high to low, when inverting and discharging, the power units corresponding to the batteries with high power are placed at the lower layer of the stepped wave bus, and the power units corresponding to the batteries with low power are placed at the higher layer of the stepped wave bus; when rectifying and charging, the power units corresponding to the batteries with high power are placed at the higher layer of the stepped wave bus, and the power units corresponding to the batteries with low power are placed at the lower layer of the stepped wave bus.

7. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 1, characterized in that The AC filtering inductor and the AC filtering capacitor are located between the industrial frequency commutation and filtering circuit and the AC power supply; or The AC filtering inductor and the AC filtering capacitor are located between the unipolar multi-level stepped wave bus and the industrial frequency commutation circuit.

8. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 2, characterized in that, The controller is a single controller, including a sampling, conditioning and feedback circuit and a switching tube driving circuit; or It includes a main controller and a slave controller, and wired and / or wireless communication is adopted between the main controller and the slave controller.

9. The bidirectional multi-mode hybrid multi-level inverter circuit according to claim 8, characterized in that, The main controller samples the AC-side signals, controls the logical sequence of each power unit and the switching tubes of the power-frequency commutation circuit, controls the active battery equalization and the bidirectional power conversion of the energy storage system, and simultaneously realizes external communication; the slave controller samples the battery-side electrical parameters, calculates the SOC and SOH, reports the battery parameters to the main controller, accepts and executes its instructions, and controls the operation of each switching tube.

10. A battery energy storage system, characterized in that, It includes the bidirectional multi-mode hybrid multi-level inverter circuit according to any one of claims 1-9.

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