Hybrid multilevel battery energy storage system for three-port converter

Abstract

The application discloses a hybrid multi-level battery energy storage system of a three-port converter, which comprises a direct-current port, an alternating-current port, a battery port, a choke inductor, a power frequency module, a filter module, a controller and a plurality of switch modules; the switch modules are divided into two groups, the two groups of switch modules and the plurality of switch modules in each group are connected in cascade and connected to the direct-current port correspondingly; the choke inductor is arranged between the two groups of switch modules and connected to the filter module correspondingly; the power frequency module is connected to the direct-current port and the filter module; the power frequency module comprises a commutation circuit formed by two power switch tubes; the controller is electrically connected to the power frequency module and each switch module. When the direct-current port of new energy such as photovoltaic and wind power is accessed, the hybrid energy storage system does not need to additionally increase a new energy DC / AC circuit, thereby reducing the volume of the energy storage device and reducing the cost of the hybrid energy storage system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy power electronics, and particularly relates to a hybrid multi-level battery energy storage system of a three-port converter. BACKGROUND

[0002] In order to improve the output power and capacity of the battery energy storage system, the battery cells are connected in series and parallel to increase the voltage and current to form a battery pack, the battery packs are also connected in series and parallel to increase the voltage and current to form a battery cluster, and finally a plurality of parallel battery clusters form a battery pack. The traditional battery energy storage system mainly consists of a bidirectional DC / AC (direct current-alternating current conversion) circuit, a bidirectional DC / DC (direct current-direct current conversion) circuit and a battery pack. The battery pack is connected to the bidirectional DC / AC circuit through the bidirectional DC / DC circuit. In this system architecture, the battery packs are directly connected in series, and the battery clusters are directly connected in parallel, but there are inevitable differences in energy and internal resistance between the battery packs / battery clusters, and there are also differences in capacity between the battery packs / battery clusters. After the battery energy storage system runs for a long time, these differences will be more obvious and form a barrel effect, thus reducing the effective use of the battery capacity and shortening the service life of the battery.

[0003] In order to improve the barrel effect, expand the effective capacity of the battery and prolong the service life of the battery, the bidirectional DC / DC circuit in the traditional battery energy storage system can be subdivided from a centralized structure into a plurality of decentralized circuits, that is, each battery pack is connected in parallel with a bidirectional DC / DC conversion circuit and then connected in parallel to a DC bus, which is called a parallel optimizer, thereby forming a battery energy storage system containing a parallel optimizer. This system architecture can realize the mixed use of new and old battery packs and can eliminate circulating current power consumption. However, the bidirectional DC / DC conversion circuit must be matched with the battery pack power, and the voltage between the battery voltage and the DC bus voltage must be boosted, so the rated output power is large, and the main disadvantages are low conversion efficiency, high system cost, and complex output parallel current control mode. In addition, if the number of battery cells connected in series and parallel inside the battery pack is too large, the barrel effect will also be inevitable.

[0004] In order to improve the above problems, in recent years, the industry has proposed a hybrid multi-level battery charging and discharging system, which uses modular multi-level technology for battery energy storage charging and discharging, and replaces the intermediate capacitor with a plurality of energy storage batteries, such as Figure 1The main advantages are that bidirectional rectification charging or inverter discharging of the battery can be realized, and battery management functions are provided to balance the battery SOC / SOH and voltage, expand the effective capacity of the battery and prolong the service life of the battery; the rated voltage of the power switch tube in the switch module is low, the multi-level ladder wave bus voltage can reduce the filter inductance in the high-frequency filter circuit, and there is no high-frequency switching loss in the power frequency commutation circuit, thereby improving the conversion efficiency; and the switch module can use multiple types of batteries or mix different types of batteries.

[0005] The hybrid multi-level battery charging and discharging system is limited to a two-port architecture, that is, only includes multiple battery ports and an alternating current port, and the disadvantage is that there is no direct current port, so that only an alternating current coupled energy storage system can be formed. If a new energy direct current port such as photovoltaic and wind power is accessed, an additional new energy power conversion circuit must be added, thereby increasing the volume of the energy storage device and increasing the cost of the hybrid energy storage system. SUMMARY

[0006] The technical problem to be solved by the embodiments of the present application is to provide a hybrid multi-level battery energy storage system of a three-port converter to reduce the cost of the hybrid energy storage system.

[0007] In order to solve the above technical problems, the embodiments of the present application provide a hybrid multi-level battery energy storage system of a three-port converter, which comprises a direct current port for externally connecting a direct current input, an alternating current port for externally connecting an alternating current power supply and / or a load, and a plurality of battery ports, further comprises a choke inductor, a power frequency module, a filter module, a controller, and a plurality of switch modules respectively connected one by one with the battery ports; the switch modules are divided into two groups, the two groups of switch modules and the plurality of switch modules in each group form a cascade connection, and are connected to the direct current port; the choke inductor is arranged between the two groups of switch modules and is connected to the filter module; the power frequency module is connected to the direct current port and the filter module; the power frequency module comprises a commutation circuit composed of two power switch tubes; the controller is electrically connected to the power frequency module and each switch module, samples the direct current port signal, the alternating current port signal and the parameters of each battery port, and controls the battery active balancing and rectification charging or inverter discharging according to the sampling results, and adjusts the power factor.

[0008] The present application has the following advantages:

[0009] (1) The batteries in the present application are not directly connected in series or parallel, and there is no traditional barrel effect. Each battery is independently managed and controlled, which on the one hand prolongs the battery discharge time, shortens the battery charging time and speeds up the battery charging speed, and on the other hand makes the battery thermal management easier, prevents battery thermal runaway in advance, and eliminates the risk of battery fire and combustion safety.

[0010] (2) The battery and its management and active balancing are deeply fused with the switching module, the hierarchical round-robin carrier superimposed modulation and its improved mode are adopted, and the battery and its switching module can be switched to a bypass state, thereby increasing the redundancy of the battery operation and improving the reliability of the energy storage system.

[0011] (3) The application can use various types of batteries, such as lithium batteries, sodium batteries or solid-state batteries, or mixed use of different types of batteries or mixed use of new and old batteries of the same type, and is suitable for battery pack level, cell level and battery cluster level battery management, realizes active balancing of battery SOC / SOH, expands the effective capacity of the battery and prolongs the service life of the battery.

[0012] (4) The application realizes bidirectional power conversion between the battery and the alternating current power supply or the power grid: rectification charging or inversion discharging, without the need for another charger or inverter. The direct current port is convenient for accessing photovoltaic and wind power and other types of new energy, and the battery port and the alternating current port can supplement power from the direct current port.

[0013] (5) The power factor of the application can be adjusted, and can be operated in active power and reactive power mode to meet the diversity requirements of power load and power grid scheduling.

[0014] (6) The bipolar multi-level ladder wave of the application has an output equivalent frequency number times the switching frequency, improves the conversion efficiency, reduces the output harmonics and electromagnetic interference, reduces the AC filter inductance and the size of the energy storage device, and reduces the system cost.

[0015] (7) The power switch tube inside the switching module of the application is of low voltage grade, and there is no high-frequency switching loss in the power frequency commutation and filter circuit, thereby further improving the conversion efficiency, reducing the size of the device, and reducing the system cost.

[0016] (8) The control method simplifies the controller design, easily expands new control strategies, and facilitates the expansion of the capacity of the energy storage system. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a structure diagram of the existing hybrid multi-level battery charging and discharging system.

[0018] Figure 2 is a structure diagram of the hybrid multi-level battery energy storage system of the three-port converter of the embodiment of the application.

[0019] Figure 3 is a main waveform diagram of the embodiment of the application.

[0020] Figure 4 is a flowchart of output control of the embodiment of the application.

[0021] Figure 5 is a flowchart of battery active balancing control of the embodiment of the application.

[0022] Figure 6 is a circuit diagram of Boost and half-bridge cascade circuit of the embodiment 1 of the present application.

[0023] Figure 7 is a circuit diagram of negative end inductance mode Boost circuit in DC unit of the embodiment 2 of the present application.

[0024] Figure 8 is a circuit diagram of Buck circuit in DC unit of the embodiment 3 of the present application, wherein (a) is positive end inductance mode and (b) is negative end inductance mode.

[0025] Figure 9 is a four-tube boost-buck circuit in DC unit of the embodiment 4 of the present application, wherein (a) is positive end inductance mode and (b) is negative end inductance mode.

[0026] Figure 10 is an isolation type topology diagram in DC unit of the embodiment 5 of the present application, wherein (a) is full-bridge LLC resonant circuit, (b) is half-bridge LLC resonant circuit and (c) is flyback circuit.

[0027] Figure 11 is a multi-winding mode isolation type topology diagram in DC unit of the embodiment 6 of the present application.

[0028] Figure 12 is a circuit diagram of half-bridge negative end cascade circuit in switching unit of the embodiment 7 of the present application.

[0029] Figure 13 is a circuit diagram of full-bridge cascade circuit in switching unit of the embodiment 8 of the present application.

[0030] Figure 14 is a circuit diagram of two-phase interleaved parallel mode in switching unit of the embodiment of the present application, wherein (a) is half-bridge cascade circuit and (b) is full-bridge cascade circuit. DETAILED DESCRIPTION

[0031] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict, and the present application will be further explained in detail in combination with the drawings and specific embodiments.

[0032] In the embodiments of the present application, if there is a directional indication (such as up, down, left, right, front, back, etc.), it is only used to explain the relative position relationship, movement condition, etc. between components in a certain specific posture (as shown in the drawings), if the specific posture changes, the directional indication will also change accordingly.

[0033] In addition, in the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implying the number of the indicated technical features. Therefore, the features defined as "first" and "second" can be explicitly or implicitly included at least one of the features.

[0034] The present application can be widely applied to various bidirectional or unidirectional charging or inverter circuits, such as lithium batteries, sodium batteries and solid-state batteries, new energy wind power and photovoltaic power generation and energy storage systems, battery formation and grading system equipment, battery charging and discharging systems in electric tools and engineering machinery, electric vehicles and off-road vehicle motor controllers.

[0035] Please refer to Figure 2 The hybrid multi-level battery energy storage system of the three-port converter of the embodiment of the present application includes a direct current port, an alternating current port, a power frequency module, a filter module, a controller and a plurality of battery ports, and can realize bidirectional rectification charging or inverter discharging of the battery and direct current access of new energy. Among them, the direct current port is connected with one or more photovoltaic or / and wind power and other new energy direct current inputs, and the alternating current port is connected with an alternating current power supply or a power grid or / and an output load. The direct current port is connected with a filter capacitor Cubs.

[0036] The switch module includes a switch unit, that is, a half-bridge composed of two power switch tubes or a full-bridge cascade circuit composed of four power switch tubes. Optionally, the switch module includes a direct current unit, which includes a DC / DC circuit using a non-isolated or isolated topology, including but not limited to Buck, Boost, Buck-Boost, Cuk, SEPIC, ZETA and other non-isolated topologies, and half-bridge, full-bridge, push-pull, flyback, forward, forward-reverse and other isolated topologies, or combined with LLC, LCC, LCLC, CLCL, basic series-parallel and other resonance technologies. The power frequency module includes a commutation circuit composed of two power switch tubes.

[0037] The controller can be a single controller, including sampling, conditioning and feedback circuits, switch tube driving circuits and the like. It can also be a master controller and a slave controller, and wired or wireless communication is used between the master and slave controllers. The controller can be built using discrete electronic components, or can be designed and used with special integrated circuits, such as analog control chips, single-chip microcomputers (MCU) programmed through software, digital signal processors (DSP) or programmable logic devices (FPGA / CPLD) and the like. Both discrete device and integrated device can be used, and they can be integrated into the controller to form a large-scale hybrid integrated circuit. This high-integration controller design can further reduce the size of the energy storage device.

[0038] The main controller samples the direct current port and alternating current port signals, controls the commutation circuit switch tubes in each switch module and the power frequency module, controls the battery active balancing and rectification charging or inversion discharging, and adjusts the power factor, while realizing external communication; the slave controller samples the electrical parameters of each battery port, calculates the SOC and SOH, reports the battery parameters to the main controller, accepts and executes the instructions of the main controller, and controls the operation of each switch tube in the corresponding switch unit. In specific implementation, the slave controller can be placed inside the corresponding switch module.

[0039] The switch modules are divided into two groups, each containing n switch modules, i.e., the switch modules are divided into upper group switch modules 1-n and lower group switch modules 1-n, and the two groups of switch modules and the multiple switch modules in each group form a cascade, and choke inductors L1 and L2 are arranged between the two groups of switch modules and correspondingly connected to the direct current port and the power frequency module.

[0040] The positive and negative poles of each battery port are respectively connected to the first port and the second port of the corresponding switch module. The first port of the upper group switch module n is connected to the ninth port of the power frequency module and the direct current bus capacitor Cbus and the positive pole of the direct current port, and the third port of the lower group switch module 1 is connected to the tenth port of the power frequency module and Cbus and the negative pole of the direct current port. The third port of the upper group switch module 1 and the first port of the lower group switch module n are connected to the fifth port of the filter module through the choke inductors, which is the midpoint of the switch module, and the sixth port of the power frequency module is connected to the sixth port of the filter module. The choke inductors L1 and L2 prevent the direct current port from being directly connected to the battery, avoiding safety problems, and reduce the impact current transmitted from the direct current port to the battery. Optionally, the filter module does not use the alternating current filter inductor, and the filter function is realized by the choke inductor.

[0041] Optionally, the choke inductors are removed. The third port of the upper group switch module n is connected to the first port of the upper group switch module n-1, the third port of the upper group switch module n-1 is connected to the first port of the upper group switch module n-2, and so on. The third port of the upper group switch module 1 is connected to the first port of the lower group switch module n. Then, the third port of the lower group switch module n is connected to the first port of the lower group switch module n-1. In this way, the third port of the lower group switch module 2 is connected to the first port of the lower group switch module 1. The sixth port and the seventh port of the filter module are connected to the alternating current port, i.e., the alternating current power supply or the power grid or / and the output load, and the voltage difference between them is the alternating current power supply AC. The controller is connected to the fourth port of each switch module and the power frequency module.

[0042] The direct current input side of the filter module is connected between the power frequency module and the two groups of battery ports. The filter module includes an alternating current filter inductor and an alternating current filter capacitor, thereby forming a symmetrical LC filter.

[0043] The DC / DC circuit in the direct current unit adopts high-frequency PWM modulation, each battery and its switching unit is sorted according to the SOC power sorting algorithm, the cascaded circuit in the switching unit adopts hierarchical carrier superimposed modulation or its improved type, and the commutation circuit in the power frequency module adopts power frequency modulation.

[0044] The instruction and data issued by the main controller are received and executed by the slave controller, and the switching module output is cascaded to form a power frequency positive and negative half cycle symmetrical bipolar multi-level ladder wave between the fifth port and the tenth port of the filter module, and the number of bipolar multi-level ladder wave levels is (2n+1). When the direct current port accesses photovoltaic or / and wind power and other types of new energy, the battery provides power to the output port through the high-frequency operation of the switching module on one hand, and charges the battery and provides power to the output port on the other hand, and the new energy direct current port is equivalent to supplementing the power of the battery. When the alternating current port is a power frequency sine wave positive half cycle voltage, the lower group of switching modules 1~n and the power frequency module realize multi-level ladder wave, and the number of levels is (n+1); when the alternating current port is a power frequency sine wave negative half cycle voltage, the lower group of switching modules 1~n and the power frequency module realize multi-level ladder wave, and the number of levels is also (n+1). Each slave controller also receives and executes the instruction and data issued by the main controller, and then charges the respective battery in a constant current or constant voltage mode through the cascaded switching module. When inverting discharging or rectifying charging, the switching module, the internal direct current unit and the switching unit, and the power frequency module and the filter module are all bidirectional conversion circuits.

[0045] The DC / DC circuit in the direct current unit and the half-bridge or full-bridge cascaded circuit in the switching unit, and the commutation circuit in the power frequency module, can use interleaving or cascading technology, various multi-level circuits, or three-phase alternating current circuits, so as to achieve higher power levels or higher voltage levels.

[0046] The DC / DC circuit and the half-bridge or full-bridge cascaded circuit in the switching module 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 use different working modes such as current continuous conduction mode (CCM), current discontinuous mode (DCM), or current critical conduction mode (CRM) etc.

[0047] The power switching tube in the switching module uses fully controlled devices such as MOSFET, IGBT, etc., and can use third-generation wide-bandgap power devices such as SiC, GaN MOSFET, etc., and can also use a mixture of these fully controlled power switching tubes. The power switching tube in the power frequency module can use fully controlled devices, and can also use semi-controlled devices such as SCR, TRIAC, etc., and can also use a mixture of fully controlled and semi-controlled devices.

[0048] Inversion discharge: receive and execute the instructions and data from the controller, control the switch module output cascade, form the power frequency positive and negative half cycle symmetrical bipolar multi-level ladder wave between the filter module 5th and 6th ports, the bipolar multi-level ladder wave level number is (2n+1). After filtering, the output sine wave voltage is formed between the 7th and 8th ports, which is provided to the load or into the AC power grid. When the DC port accesses photovoltaic and wind power and other types of new energy, the battery provides power to the output port through the high-frequency operation of the switch module; on the other hand, the DC port charges the battery, and also provides power to the output port. The new energy DC port is equivalent to supplementing the battery with power. When the battery port and the DC port provide power to the AC port at the same time, the energy management software in the controller needs to allocate the discharge energy of each other. The main waveform is shown in Figure 3 The lower group of switch modules 1-n and the power frequency module realize multi-level ladder wave and output sine wave power frequency positive half cycle voltage, and the upper group of switch modules 1-n and the power frequency module realize multi-level ladder wave and output sine wave power frequency negative half cycle voltage. The main controller samples the DC port and AC port signals, controls the logical ordering of the switch unit in each switch module and the switch tube in the power frequency module, and simultaneously realizes external communication; the slave controller samples the electrical parameters of each battery port, detects voltage, current, power and temperature, calculates the state of charge (SOC) and the state of health (SOH), which is equivalent to completing the battery management function, and reports the battery parameters such as SOC / SOH to the main controller, accepts and executes its instructions, such as switch unit logical ordering arrangement, battery quantity information, and controls the operation of each switch tube in the switch module.

[0049] Rectification charging: the input and output of the switch module are interchanged, i.e. the input is the 1st and 3rd ports, and the output is the 1st and 2nd ports. The AC power grid provides a sine wave voltage AC through the filter module, enters the power frequency module 6th and 8th ports, and after high-frequency filtering, forms a bipolar multi-level ladder wave at the 5th and 6th ports, with a level number of (2n+1). Then it enters the power frequency module 6th port and the switch module midpoint, respectively. When the DC port accesses photovoltaic and wind power and other types of new energy, the DC port and the AC port charge the battery at the same time, and the new energy DC port can supplement the battery with power. When the AC port and the DC port provide power to the battery port at the same time, the energy management software in the controller needs to allocate the charging energy of each other. Each slave controller also receives and executes the instructions and data from the main controller, and then controls the constant current or constant voltage charging of each battery through the cascade switch module.

[0050] When the AC port is the positive half cycle voltage of the power frequency sine wave, the lower group of switch modules 1-n and the power frequency module realize multi-level ladder wave, and the number of levels is (n+1); when the AC port is the negative half cycle voltage of the power frequency sine wave, the lower group of switch modules 1-n and the power frequency module realize multi-level ladder wave, and the number of levels is also (n+1). The power frequency module works in a low frequency mode, so its switching loss is low. When the inverter discharges or the rectifier charges, the switch module, the internal DC unit and the switch unit, and the power frequency module and the filter module are all bidirectional conversion circuits. By sampling the AC and DC voltage and current signals, the main controller identifies the input and output power flow direction, determines and controls the power switch tube according to the actual operating conditions, and stabilizes the output voltage or current through real-time feedback of the working state in a closed loop to realize adaptive control in the inverter discharge or rectifier charging mode, and realize bidirectional power conversion of the energy storage system. The controller can flexibly change the phase of the AC voltage and the AC current respectively, realize adjustable power factor, can work in active power and reactive power mode, and meet the diversity requirements of power load and power grid scheduling.

[0051] The main controller issues instructions to the slave controller according to the SOC / SOH information of each battery, and controls the logical order of the switch units in the corresponding switch module. When the inverter discharges or the rectifier charges, the controller uses a software algorithm to real-time switch the SOC highest / lowest battery and its upper and lower switch modules to the bottom layer of the multi-level ladder wave, i.e. the upper and lower switch modules 1, for power frequency square wave modulation (NLM); and switch the SOC lowest / highest battery and its upper and lower switch modules to the top layer of the multi-level ladder wave, i.e. the upper and lower switch modules n, for high-frequency sine wave pulse width modulation (SPWM). Other batteries and their switch modules are arranged in order according to their respective SOC values, and also work in NLM. For a power frequency sine wave cycle, the bottom layer of the multi-level ladder wave means that the corresponding battery has more charging and discharging energy, and the top layer means that the corresponding battery has less charging and discharging energy, so that the high-energy battery has more discharging energy and less charging energy, and the low-energy battery has less discharging energy and more charging energy. According to the real-time SOC energy of each battery, the dynamic sorting from the bottom layer to the top layer is realized, and the dynamic battery management and active balancing are deeply combined. In addition, this control method for realizing dynamic sorting of switch modules is called hierarchical round-robin carrier superimposed modulation. The output voltage control method is as shown in Figure 4 The output control steps are as follows:

[0052] The voltage and current values of each battery or AC power supply are dynamically obtained.

[0053] The obtained current actual output value is compared with the target value.

[0054] According to the comparison result, the adjustment instructions of the duty cycle and the working or not of the switch module are dynamically determined.

[0055] The switch module executes the instruction to dynamically control the energy storage / discharge time of the AC filter inductor, so that the current actual output value approximates to the target value.

[0056] The battery active balancing control method comprises the following steps of Figure 5 As shown in the figure, the battery active balancing control steps are as follows:

[0057] The SOC / SOH voltage, current and temperature values of each battery are dynamically acquired.

[0058] The current battery capacity of all the batteries is acquired and sorted according to the actual value.

[0059] It is judged whether the SOC / SOH capacity of the battery is the highest, if yes, the switch module corresponding to the battery is placed at the bottom layer of the ladder wave during inverter discharging, and the switch module corresponding to the battery is placed at the top layer of the ladder wave during rectifier charging.

[0060] If not, it is judged whether the SOC / SOH capacity of the battery is the lowest, if yes, the switch module corresponding to the battery is placed at the top layer of the ladder wave during inverter discharging, and the switch module corresponding to the battery is placed at the bottom layer of the ladder wave during rectifier charging.

[0061] If not, according to the order of the actual capacity value of the battery, the switch module corresponding to the high-capacity battery is placed at the low layer of the ladder wave during inverter discharging, and the switch module corresponding to the low-capacity battery is placed at the high layer of the ladder wave, the switch module corresponding to the high-capacity battery is placed at the high layer of the ladder wave during rectifier charging, and the switch module corresponding to the low-capacity battery is placed at the low layer of the ladder wave.

[0062] The control mode of the battery can simplify the design of the controller, easily expand new control strategies, and facilitate the expansion of the capacity of the energy storage system.

[0063] When the battery power difference is large, it is equivalent to different types of batteries or mixed use of new and old batteries of the same type. With this control method, multiple types of batteries can be used, and different types of batteries can be mixed or new and old batteries of the same type can be mixed. Each switch module is independently controlled by the controller, and the batteries do not need to be directly connected in series or parallel, and there is no traditional barrel effect. Each battery is independently managed and controlled, which on the one hand 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, which can prevent battery thermal runaway in advance and eliminate the risk of battery fire and combustion safety. Optionally, the hierarchical round-robin carrier superposition modulation method is further improved, and the SOC of the lowest battery and its switch module can be switched to a bypass state under normal operating conditions without affecting the normal operation of the inverter discharge or rectifier charging. That is, the corresponding upper or lower tube in the half-bridge or full-bridge cascade circuit that needs to be bypassed is continuously turned on. In this way, the battery and its switch module that fails in advance or fails can be cut out online, thereby increasing the redundancy of the battery operation and improving the reliability of the energy storage system.

[0064] Optionally, the number of the upper and lower groups of batteries and their switch modules can be different, which does not affect the normal operation of the circuit, but the peak values of the multi-level ladder wave positive and negative voltages need to be kept consistent. In addition, the switch module can be applicable to the battery pack level, the battery cell level, and the battery cluster level. Optionally, the filter module only includes a single alternating current filter inductor. Optionally, the filter module includes a multi-stage filter network composed of multiple alternating current filter inductors and multiple alternating current filter capacitors. Optionally, the filter module only includes an alternating current filter capacitor.

[0065] It should be noted that the battery port and the alternating current port are bidirectional power conversion, and the direct current port to the battery port or the alternating current port is unidirectional or bidirectional power conversion. In the inverter discharge or rectifier charging mode, multiple switch modules output cascade to form a bipolar multi-level ladder wave, and the alternating current filter inductor has a small voltage change rate (dv / dt), so the alternating current filter inductor has a small inductance in the filter circuit. The switch module output voltage and current and power are small, which can reduce the rated voltage level of the internal power switch tube. At the same time, only one top switch module works at high frequency SPWM at any time, and the other switch modules and the power frequency module work at power frequency NLM, thereby greatly reducing power consumption and improving conversion efficiency. In addition, there is no high-frequency switching loss in the commutation circuit in the power frequency module and the filter circuit in the filter module. The output equivalent frequency of the multi-port converter is several times the switching frequency, thereby improving the conversion efficiency, reducing the output harmonic and electromagnetic interference, reducing the size of the energy storage device, and reducing the system cost. The proposed technical solution is mainly aimed at the energy storage system, and the direct current side of the switch module uses the battery. Optionally, the direct current side uses a direct current power supply, thereby further expanding the application range of the multi-port converter.

[0066] In the power unit of this invention, fully controllable devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs) are used as power switches. Third-generation wide-bandgap (WBG) power devices such as silicon carbide (SiC) and gallium nitride (GaN) MOSFETs can also be used, or a combination of these fully controllable power switches can be employed. In the commutation circuit of the power frequency module, fully controllable or semi-controllable devices such as silicon controlled rectifiers (SCRs) and thyristors (TRIACs) can be used as power switches, or a mixture of fully controllable and semi-controllable devices can be used.

[0067] This invention controls the switching module to work in coordination with the power frequency module and the filtering module. To adapt to different power levels and battery capacities, the switching module optionally includes a DC unit, namely a high-frequency pulse width modulation (PWM) DC-DC circuit. The DC / DC input is connected to the battery, and its output is connected to the input of the switching unit. The commutation circuit in the power frequency module and the inductor-capacitor filter circuit in the filtering module are relatively fixed, mainly because the switching module has a switching unit and / or a DC unit, and its internal half-bridge or full-bridge cascaded circuit and DC / DC circuit have various types. It should also be noted that the DC / DC circuit and the half-bridge or full-bridge cascaded circuit can be controlled in voltage mode, or in average current mode, peak current mode, quasi-resonant control, single-cycle control, etc., and can also use different operating modes, such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), or critical conduction mode (CRM).

[0068] Example 1, as Figure 6 As shown, the DC unit in the switching module is composed of a bidirectional Boost circuit, and the switching unit is composed of a cascaded half-bridge circuit. Figure 2 Correspondingly, the positive terminal of the battery is connected to port ①, and the negative terminal is connected to port c. Ports ③ and ② are the positive and negative terminals of the output voltage, respectively. Power switches Q1 and Q2, along with their body diodes D1 and D2, the energy storage inductor Lb, the input filter capacitor Ci, and the DC bus capacitor Cb constitute a bidirectional boost circuit. Q3 and Q4, along with their body diodes D3 and D4, constitute a bidirectional half-bridge cascade circuit, achieving both high and low output voltage levels. Port ① is connected to the positive terminal of Ci and one end of Lb. Port ② is connected to the source (S) of Q2 and Q4 and the negative terminals of Ci and Cb. Port ③ is connected to the source (S) of Q3 and the drain (D) of Q4. The drain (D) of Q1 is connected to the drain (D) of Q3 and the positive terminal of Cb. The source (S) of Q1 is connected to the drain (D) of Q2 and the other end of Lb.

[0069] During rectification and charging, power is transferred from the AC port and the DC port to the battery port. The bidirectional Boost circuit operates in Buck mode, in which power switch Q1 is the main switch and power switch Q2 is the synchronous rectifier. During each switching cycle, Q2 is turned on after its body diode D2 is turned on, so that Q2 can achieve zero-voltage switching (ZVS). Meanwhile, the bidirectional half-bridge cascade circuit operates in Boost mode, in which power switch Q4 is the main switch and power switch Q3 is the synchronous rectifier. During each switching cycle, Q3 is turned on after its body diode D3 is turned on, so that Q3 can also achieve ZVS. Q1 and Q4 are controlled by the controller to operate in high-frequency PWM switching state: when Q1 is turned on, Cb provides energy to the battery and Lb stores energy; when Q1 is turned off, the stored energy in Lb is discharged to the battery through the synchronous rectifier Q2; the half-bridge cascade circuit uses the filter inductor in the high-frequency filter circuit as an energy storage inductor, and when Q4 is turned on, the filter inductor stores energy and Cb is discharged to the Boost circuit; when Q4 is turned off, the stored energy in the filter inductor is discharged to Cb and the Boost circuit through the synchronous rectifier Q3. Therefore, part of the energy of Cb comes from the half-bridge cascade circuit and the other part comes from the external DC port. Rectification and charging can be in constant current or constant voltage mode, which are traditional control measures and will not be described here. During inversion and discharging, power is transferred from the battery port and the DC port to the AC port. The bidirectional Boost circuit operates in Boost mode, in which power switch Q2 is the main switch and power switch Q1 is the synchronous rectifier. During each switching cycle, Q1 is turned on after its body diode D1 is turned on, so that Q1 can achieve ZVS. Meanwhile, the bidirectional half-bridge cascade circuit operates in Buck mode, in which power switch Q3 is the main switch and power switch Q4 is the synchronous rectifier. During each switching cycle, Q4 is turned on after its body diode D4 is turned on, so that Q4 can also achieve ZVS. Q2 and Q3 are controlled by the controller to operate in high-frequency PWM switching state: when Q2 is turned on, the battery stores energy in Lb and Cb is discharged to the cascade circuit; when Q2 is turned off, the stored energy in Lb is discharged to Cb and the cascade circuit through the synchronous rectifier Q1; the half-bridge cascade circuit uses the filter inductor in the high-frequency filter circuit as an energy storage inductor, and when Q3 is turned on, Cb provides energy to the output and the filter inductor stores energy; when Q3 is turned off, the stored energy in the filter inductor is discharged to the output through the synchronous rectifier Q4. Therefore, part of the energy of Cb comes from the Boost circuit and the other part comes from the external DC port. It should be noted that the battery boost and the half-bridge cascade circuit use voltage mode control, but they can also use average current mode, peak current mode control, quasi-resonant control, single-cycle control, etc. Different operating modes can also be used, such as current continuous conduction mode (CCM), current discontinuous mode (DCM), or current critical conduction mode (CRM), etc.

[0070] The DC / DC circuit in the DC unit can also use other non-isolated or isolated topologies, including but not limited to non-isolated topologies such as Buck, Boost, Buck-Boost, Cuk, SEPIC, and ZETA, as well as isolated topologies such as half-bridge, full-bridge, push-pull, flyback, forward, and forward-flyback, or combined with LLC, LCC, LCLC, CLCL, and basic series-parallel resonant circuits. Example 2, as... Figure 7 As shown, the DC / DC converter in the DC unit uses a negative-terminal inductor boost circuit. The power frequency module and filter module, along with the master-slave controller and its control method, employ... Figures 2-5 Similarly, the switching unit still adopts the following method: Figure 6 The half-bridge cascaded circuit shown is similar in principle to this one, so it will not be described in detail here.

[0071] Example 3, as Figure 8 As shown, the DC / DC converter in the DC unit uses a Buck step-down circuit, where (a) is the positive terminal inductor method and (b) is the negative terminal inductor method. The power frequency module and filter module, along with the master-slave controller and its control method, employ... Figures 2-5 Similarly, the switching unit still adopts the following method: Figure 6 The half-bridge cascaded circuit shown is similar in principle to this one, so it will not be described in detail here.

[0072] Example 4, as Figure 9 As shown, the DC / DC converter in the DC unit uses a four-transistor buck-boost circuit, where (a) is a positive-terminal inductor and (b) is a negative-terminal inductor. During inverter discharge and rectified charging, this circuit can achieve two unidirectional boost and buck conversions. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5 Similarly, the switching unit still adopts the following method: Figure 6 The half-bridge cascaded circuit shown is similar in principle to this one, so it will not be described in detail here.

[0073] Example 5, as Figure 10 As shown, the DC / DC converter in the DC unit adopts an isolated topology, where (a) is a full-bridge LLC resonant circuit, (b) is a half-bridge LLC resonant circuit, and (c) is a flyback circuit. All power switches in the LLC resonant circuit operate at ZVS, further improving the converter's conversion efficiency. Other circuit configurations can also be used for the isolated topology. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5 Similarly, the switching unit still adopts the following method: Figure 6 The half-bridge cascaded circuit shown is similar in principle to this one, so it will not be described in detail here.

[0074] Example 6, as Figure 11As shown, the DC / DC converter in the DC unit adopts an isolated topology with a multi-winding configuration, where the isolated topology is a full-bridge LLC resonant circuit. The multi-winding isolated topology reduces the number of batteries used in the energy storage system, potentially achieving the desired effect with only a single battery. Other circuit configurations can also be used in the multi-winding isolated topology, such as a half-bridge LLC resonant circuit or a flyback circuit. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5 Similarly, the switching unit still adopts the following method: Figure 6 The half-bridge cascaded circuit shown is similar in principle to this one, so it will not be described in detail here.

[0075] Example 7, as Figure 12 As shown, the half-bridge cascade circuit in the switching unit adopts a negative-terminal cascade method, that is, changing the positions of ports ② and ③. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5 Similar methods and basic operating principles are used, so they will not be elaborated here. Optionally, the DC / DC converter in the switching unit adopts... Figures 6-11 The circuit configuration and working principle are the same, so they will not be described in detail here.

[0076] Example 8, as Figure 13 As shown, the half-bridge cascade circuit in the switching unit is replaced with a full-bridge configuration. A single half-bridge cascade circuit can only generate two voltage levels, while a full-bridge cascade circuit can generate three voltage levels. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5 Similar methods and basic operating principles are used, so they will not be elaborated here. Optionally, the DC / DC converter in the switching unit adopts... Figures 6-11 The circuit configuration and working principle are the same, so they will not be described in detail here.

[0077] The DC / DC circuits in the DC unit of the switching module, the half-bridge or full-bridge cascaded circuits in the switching unit, and the commutation circuits in the power frequency module can use interleaved parallel or series techniques, as well as various multi-level circuits, to form a three-phase AC circuit, thereby achieving higher power or higher voltage levels. When forming a three-phase AC circuit, the power frequency bridge arm needs to be removed. Each of the three sets of upper and lower level switching modules has one output terminal, which constitutes a single-phase AC circuit. At the same time, the other ends of the three single-phase AC circuits are connected together to form a virtual neutral point, so that star and delta wave connections with or without neutral (N) can be formed respectively.

[0078] Example 9, as Figure 14 As shown, the cascaded circuit in the switching unit is replaced with a two-phase or multi-phase interleaved parallel connection. This interleaved parallel connection reduces current ripple, improves conversion efficiency, and reduces heat dissipation. The power frequency module and filter module, along with the master-slave controller and its control method, adopt... Figures 2-5In a similar way, the working principle is basically similar, and details are not repeated here. Optionally, the DC / DC in the switching unit adopts Figures 6-11 The circuit form, the working principle is the same, and details are not repeated here.

[0079] The specific experimental data and test results of the embodiment are shown in Table 1. The test conditions are as follows: 2 groups of batteries: 2 batteries in each group, a total of 4 48V lithium batteries, and the DC port voltage is 192V. Electronic component electrical parameters: MOSFET 1mΩ / 40V in the switching module, IGBT 50A / 650V in the power frequency module, filter inductance 20uH, SPWM switching frequency 20kHz, and power frequency AC frequency 50Hz. The 2 groups of 4 batteries only verify the basic principle. Since the total voltage of the batteries corresponding to the upper and lower switching modules is DC 96V, the AC voltage will be lower than that.

[0080]

[0081] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalent scope.

Claims

1. A hybrid multilevel battery energy storage system with a three-port converter, comprising a DC port for external DC input, an AC port for external AC power supply and / or load, and multiple battery ports, characterized in that, It also includes a choke inductor, a power frequency module, a filter module, a controller, and multiple switch modules connected one-to-one with the battery ports. The switch modules are divided into two groups, which are cascaded together with each other and with multiple switch modules within each group. The cascaded switch modules are connected to the DC ports. The choke inductor is located between the two groups of switch modules and is connected to the filter module. The power frequency module is connected to the DC ports and the filter module. The power frequency module includes a commutation circuit composed of two power switching transistors. The controller is electrically connected to the power frequency module and each switch module. The controller samples the DC port signal, the AC port signal, and the parameters of each battery port. Based on the sampling results, it controls the battery to actively balance and perform rectified charging or inverted discharging, and adjusts the power factor. The switching module includes a switching unit, which is a half-bridge cascaded circuit composed of two power switching transistors or a full-bridge cascaded circuit composed of four power switching transistors; the switching module also includes a DC unit, which contains a DC / DC circuit and uses a non-isolated or isolated topology. The controller includes a master controller and slave controllers, with the number of slave controllers being the same as the number of battery ports. Each slave controller is electrically connected to a switching module of a battery port. The master controller samples the DC and AC port signals, controls each switching module and the power frequency module, controls the battery's active balancing and rectified charging or inverter discharging, and achieves adjustable power factor. The slave controller samples the electrical parameters of each battery port, calculates SOC and SOH, reports the battery parameters to the master controller, receives and executes its instructions, and controls the operation of each switching transistor in the corresponding switching module. The switching module is divided into two groups, upper and lower, each containing n switching modules; the controller receives and executes the instructions and data issued by the main controller, and controls the cascaded output of the switching modules to form a symmetrical bipolar multilevel stepped wave with positive and negative half-cycles at the power frequency between the two ports of the filter module, and the number of levels of the bipolar multilevel stepped wave is (2n+1). When the AC port is at the positive half-cycle of a power frequency sine wave, the lower group of switching modules and power frequency modules implement a multi-level stepped wave with (n+1) levels; when the AC port is at the negative half-cycle of a power frequency sine wave, the upper group of switching modules and power frequency modules implement a multi-level stepped wave with (n+1) levels; each slave controller also receives and executes instructions and data issued by the master controller, and then controls its respective battery to charge in constant current or constant voltage mode through the corresponding switching module; when the inverter discharges or rectifies and charges, the switching module and its DC unit and switching unit, as well as the power frequency module and filter module, are all bidirectional conversion circuits; The controller performs active battery balancing control according to the following steps: Dynamically acquire the SOC / SOH, voltage, current, and temperature values ​​of each battery; Sort all current battery levels according to their actual values ​​from highest to lowest. Determine if the battery's SOC is at its maximum. If so, during inverter discharge, place the corresponding switch module at the bottom of the stepped wave, and during rectifier charging, place the corresponding switch module at the top of the stepped wave. If not, determine whether the SOC of the battery is at its lowest. If it is, place the corresponding switch module of the battery on the top layer of the stepped wave during inverter discharge and on the bottom layer of the stepped wave during rectifier charging. If it is not the lowest, then according to the order of the actual battery capacity, during inverter discharge, the switching module corresponding to the high-capacity battery is placed on the lower layer of the stepped wave, and the switching module corresponding to the low-capacity battery is placed on the upper layer of the stepped wave; during rectifier charging, the switching module corresponding to the high-capacity battery is placed on the upper layer of the stepped wave, and the switching module corresponding to the low-capacity battery is placed on the lower layer of the stepped wave.

2. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 1, characterized in that, The filtering module may include an AC filter inductor and an AC filter capacitor; or it may include only a single AC filter inductor.

3. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 1, characterized in that, The DC / DC circuit uses high-frequency PWM modulation, the commutation circuit uses power frequency modulation, and the controller sorts the battery ports according to the SOC power level.

4. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 1, characterized in that, DC / DC circuits, switching units, and commutation circuits use interleaved parallel connections, cascaded connections, or multi-level circuits.

5. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 1, characterized in that, The DC / DC circuits and half-bridge or full-bridge cascaded circuits in the switching module adopt voltage mode control, average current mode control, peak current mode control, quasi-resonant control or single-cycle control, or adopt one of the following operating modes: continuous current conduction mode, discontinuous current mode, or critical current conduction mode.

6. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 1, characterized in that, There are two choke inductors connected in series, and the filter module is connected between the two choke inductors.

7. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 2, characterized in that, When the filter module has an AC filter inductor, the AC filter inductor in the filter module is used as the choke inductor.

8. The hybrid multilevel battery energy storage system with a three-port converter as described in claim 2, characterized in that, The controller performs output control according to the following steps: Dynamically acquire the voltage and current values ​​of each battery or AC power source; Compare the current actual output value with the target value; Based on the comparison results, the duty cycle and operation / non-operation adjustment instructions of the switching module are dynamically determined; The switching module executes the instruction to dynamically control the energy storage / discharge time of the AC filter inductor, so that the current actual output value approaches the target value.

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