Photovoltaic off-grid and grid-connected energy storage inverter

Abstract

The invention discloses a photovoltaic off-grid and grid-connected energy storage inverter, and belongs to the field of power electronic equipment, the photovoltaic off-grid and grid-connected energy storage inverter comprises a foldable photovoltaic assembly, the foldable photovoltaic assembly comprises a plurality of foldable photovoltaic panels, an air cylinder driving assembly, a moving plate and a supporting block, the output end of the air cylinder driving assembly is connected with the moving plate, the moving plate is hinged to the movable ends of the photovoltaic panels, and the supporting block is connected with the air cylinder driving assembly. The supporting blocks are arranged at folding nodes of the photovoltaic panel and are used for positioning and supporting the unfolded photovoltaic panel; the modularized inversion unit comprises at least two inversion power modules which are arranged in parallel, a module current sharing control unit, a direct current bus conditioning unit and a fault diagnosis sub-module; by means of modular combination and N + 1 redundancy design of the inverter power modules, power supply requirements of different scenes such as small families and small and medium-sized commercial buildings can be met, meanwhile, through a linkage mechanism of fault diagnosis and redundancy compensation, machine halt caused by faults of the inverter modules is avoided, and continuity and stability of system operation are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic devices, and particularly relates to a photovoltaic off-grid and grid-connected energy storage inverter. BACKGROUND

[0002] In the development process of the photovoltaic off-grid and grid-connected energy storage inverter, the existing products gradually expose many technical shortcomings to be solved in actual application, which become the key factors restricting the promotion and performance of the photovoltaic energy storage system, and are embodied in the following aspects.

[0003] There is a risk of power interruption in off-grid and grid-connected switching The off-grid and grid-connected switching circuit of the existing inverter mostly adopts a single-stage switching structure and a simple filtering method, the switching control strategy lacks precise use of the zero-crossing point of the grid voltage, and the switching response time usually exceeds 50 milliseconds, which is extremely easy to cause load power interruption in the case of grid abnormality (such as power failure and voltage drop). For precision equipment, medical instruments and other loads with high requirements for power continuity, it is impossible to meet their stable power demand.

[0004] The photovoltaic utilization efficiency and battery management level are limited The conventional MPPT (maximum power point tracking) algorithm mostly adopts a single perturbation and observation method or conductance increment method, which is difficult to quickly and accurately track the maximum power point of the photovoltaic module in complex light environments such as weak light and cloud cover, resulting in low photovoltaic power generation efficiency. Meanwhile, the battery management system is mostly designed for a single battery type, lacks the adaptation ability to multiple batteries such as lithium batteries and lead-acid batteries, and has insufficient SOC (battery remaining capacity) prediction accuracy, which is easy to cause the battery cycle life to be shortened due to unreasonable charging and discharging strategies.

[0005] The inductive load adaptation ability is weak The conventional inverter lacks the simulation capability of the grid characteristics, and the inertia and damping characteristics of the output power are insufficient. In the face of large current impact when the inductive load such as an air conditioner or a water pump is started, problems such as voltage drop and frequency deviation are easy to occur, and even the starting of the inductive load cannot be completed, which limits the application range of the inverter in household life, small-scale industrial and commercial production and other scenes.

[0006] The reliability and redundancy protection of the inverter unit are insufficient The inverter unit of part of the inverters adopts an integrated design without a redundancy backup mechanism. Once the inverter module fails, the whole machine will stop working, and the power supply stability is difficult to guarantee. Moreover, the module current sharing control precision is low, and when multiple modules are connected in parallel, the current distribution is easy to be uneven, which not only affects the inverter efficiency, but also accelerates the aging and damage of the power devices.

[0007] In summary, the defects of the existing photovoltaic off-grid and grid-connected energy storage inverter in portability, switching performance, energy utilization efficiency, load adaptability and reliability, etc. urgently need to develop a new type of inverter with integrated innovative design to break through the technical bottleneck and improve the comprehensive performance of the photovoltaic energy storage system. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a photovoltaic off-grid and grid-connected energy storage inverter, which solves the problems raised in the background art.

[0009] Technical solution: To solve the above technical problems, according to one aspect of the present application, more specifically, a photovoltaic off-grid and grid-connected energy storage inverter, comprising a foldable photovoltaic assembly, a modular inverter unit, an off-grid and grid-connected switching circuit module, an energy management module, and a load adaptation module, specifically as follows:

[0010] The foldable photovoltaic assembly comprises a plurality of foldable photovoltaic panels, a pneumatic cylinder driving assembly, a moving plate, and a support block, the pneumatic cylinder driving assembly is connected with two moving plates, the moving plate is rotationally connected with the photovoltaic panel, and the support block is arranged at the folding node of the photovoltaic panel for positioning and supporting after the photovoltaic panel is unfolded;

[0011] The modular inverter unit comprises at least two parallelly arranged inverter power modules, a module current sharing control unit, a DC bus conditioning unit, and a fault diagnosis sub-module; each inverter power module adopts a full-bridge inverter topology structure, which is composed of an IGBT power switch tube, a high-frequency transformer, and an output filter inductor; the input end of the inverter power module is connected with the DC output end of the foldable photovoltaic assembly and the energy storage battery; the output end is connected to the off-grid and grid-connected switching circuit module after being aggregated by the module current sharing control unit; the DC bus conditioning unit is connected in series between the input end of the inverter power module and the DC bus, and is used for stabilizing the bus voltage; the fault diagnosis sub-module collects the current, temperature, and voltage signals of each inverter power module in real time, and when a module fault is detected, the fault module is cut off and the power redundancy compensation of the remaining modules is triggered;

[0012] The off-grid and grid-connected switching circuit module comprises a multi-stage controllable switching circuit (K1-K6), a double-capacitor filter structure (C1, C2), and a switching control unit, the multi-stage controllable switching circuit is connected with the grid end, the inverter unit output end, and the load end respectively, the double-capacitor filter structure is connected in series between the switching circuit and the load end, the switching control unit pre-stores the time sequence control strategy of zero-crossing closing, and is used for driving the controllable switching circuit to complete mode switching when the grid is abnormal;

[0013] The energy management module comprises a multi-stage MPPT control unit and an intelligent battery management sub-module, the multi-stage MPPT control unit is used for collecting the output voltage and current signals of the photovoltaic assembly and executing a multi-stage MPPT algorithm, the intelligent battery management sub-module comprises a battery type identification unit, an SOC prediction unit, and a charge and discharge control unit, and is suitable for various battery types such as lithium batteries and lead-acid batteries;

[0014] The load adaptation module is equipped with a virtual synchronous generator control unit, which is used for simulating the voltage, frequency, and impedance characteristics of the grid and outputting power signals suitable for inductive load start.

[0015] Further, the inverter power module of the modular inverter unit adopts N+1 redundancy design, N is the number of working modules, and the value is 2-6, and 1 is a standby module; the module current sharing control unit adopts an active current sharing method, the output voltage amplitude and phase of each inverter power module are adjusted, so that the output current deviation of each module is controlled within 5%; the DC bus conditioning unit includes a DC-DC boost circuit and a bus capacitor group, the boost ratio of the DC-DC boost circuit can be adjusted within 1.2-3 times, and the wide voltage output range of the photovoltaic module and the energy storage battery is adapted.

[0016] Further, the fault diagnosis sub-module of the modular inverter unit has a built-in fault classification algorithm, which can identify four types of faults: overcurrent, overtemperature, open circuit and short circuit; when a fault is detected, the fault diagnosis sub-module sends a shutoff signal to the bypass switch of the fault module within 10 milliseconds, and sends a power compensation instruction to the energy management module, which adjusts the output power of the photovoltaic module and the battery, and cooperates with the redundant module to realize seamless power replacement.

[0017] Further, in the multi-stage controllable switching circuit, K1 and K2 are grid-side main switches, K3 and K4 are off-grid side main switches, and K5 and K6 are auxiliary switching switches; the switching control unit has a power grid state detection subunit for real-time acquisition of voltage, frequency and phase signals of the power grid; when the detection of the power grid signal exceeds the preset threshold, the time sequence control strategy is triggered.

[0018] Further, the time sequence control strategy is as follows: after the grid abnormal signal is triggered, the switching control unit first opens K1 and K2, and then closes K3 and K4 when the grid voltage zero-crossing point is reached, and at the same time, the charging and discharging state of the double-capacitor filter structure is adjusted through K5 and K6, completing the switching from grid-connected to off-grid, and the response time of the whole switching process is not more than 20 milliseconds.

[0019] Further, the multi-stage MPPT algorithm includes two stages of global MPPT search and local MPPT tracking, the global MPPT search stage adopts a particle swarm optimization algorithm to scan the power output curve of the photovoltaic module to determine the approximate interval of the maximum power point; the local MPPT tracking stage adopts a perturbation and observation method to accurately track the maximum power point.

[0020] Further, the SOC prediction unit adopts Kalman filtering algorithm combined with the voltage, current and temperature parameters of the battery to establish an SOC prediction model, and the charge and discharge control unit dynamically adjusts the charge and discharge current and cutoff voltage according to the SOC prediction result and the battery type.

[0021] Further, the virtual synchronous generator control unit comprises an inertia simulation subunit and a damping simulation subunit, the inertia simulation subunit is used for simulating the rotational inertia characteristic of the synchronous generator, and the damping simulation subunit is used for compensating frequency deviation caused by load fluctuation, so that the overload capacity of the inverter reaches 120%-150% of the rated power.

[0022] The photovoltaic off-grid energy storage inverter has the following advantages:

[0023] (1) The modular combination and N+1 redundancy design of the inverter power module are used to realize flexible configuration of the 10kW-30kW inverter power of the whole machine, so that the power supply demand of different scenes such as small families and small and medium-sized commercial buildings can be met, and through the linkage mechanism of fault diagnosis and redundancy compensation, the machine shutdown caused by inverter module failure is avoided, and the continuity and stability of system operation are ensured.

[0024] (2) Through the multi-stage controllable switch of the grid-connected and off-grid switching circuit module and the zero-crossing switching strategy, combined with the rapid fault processing capability of the modular inverter unit, the grid-connected and off-grid switching response time of the present application is controlled within 20 milliseconds, and the response rhythm of fault processing and power compensation matches the switching time sequence, which eliminates the risk of load power interruption from the aspects of switching process and fault emergency, meets the strict requirements of precision equipment, medical instruments and other equipment on power continuity, and the cooperation of the double-capacitor filter structure and the DC bus conditioning unit effectively filters voltage harmonics and stabilizes the bus voltage, ensuring the stability of power supply quality.

[0025] (3) The multi-stage MPPT algorithm and the intelligent battery management sub-module of the present application form a cooperation to accurately track the maximum power point of photovoltaic under complex light environment, improve the photovoltaic power generation efficiency, realize the adaptation and accurate SOC prediction of lithium battery, lead-acid battery and other batteries, and prolong the battery cycle life through dynamic regulation and control of charging and discharging; the power output capability of the virtual synchronous generator control unit of the load adaptation module and the modular inverter unit is combined, so that the inverter has an overload capacity of 120%-150% of the rated power, can simulate the inertia and damping characteristics of the power grid, and ensures the stable start and operation of inductive loads such as air conditioners and water pumps, breaks through the application scene limitation of traditional inverters, and realizes the double improvement of energy utilization efficiency and load adaptation capability. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described in detail below in combination with the drawings and specific implementation methods.

[0027] Figure 1 The figure is a schematic diagram of the framework of the present application.

[0028] Figure 2 The figure is a structural schematic diagram of the foldable photovoltaic assembly in the present application.

[0029] In the figure: 1, foldable photovoltaic assembly; 11, photovoltaic panel; 12, cylinder driving assembly; 13, moving plate; 14, supporting block; 2, modular inverter unit; 3, on-off grid switching circuit module; 4, energy management module; 5, load adaptation module. DETAILED DESCRIPTION

[0030] Hereinafter, the present application will be described in detail with reference to the accompanying drawings and embodiments. 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.

[0031] In order to make the technical scheme of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Reference Figure 1 A photovoltaic on-off grid energy storage inverter, comprising a foldable photovoltaic assembly 1, a modular inverter unit 2, an on-off grid switching circuit module 3, an energy management module 4, and a load adaptation module 5.

[0033] The foldable photovoltaic assembly 1 comprises a plurality of foldable photovoltaic panels 11, a cylinder driving assembly 12, a moving plate 13, and a supporting block 14. The output end of the cylinder driving assembly 12 is connected with the moving plate 13, the moving plate 13 is hinged with the movable end of the photovoltaic panel 11, and the supporting block 14 is arranged at the folding node of the photovoltaic panel 11. The cylinder driving assembly 12 can drive the moving plate 13 to move linearly, thereby driving the photovoltaic panel 11 to unfold or be stored, and the supporting block 14 supports the photovoltaic panel 11 after it is unfolded, thereby ensuring the stability of the photovoltaic panel 11. This structure greatly reduces the overall volume of the system and improves the portability of the equipment, which is suitable for mobile scenarios such as outdoor camping and temporary power supply.

[0034] The inverter power module is the core execution component of the modular inverter unit 2, adopts a full-bridge inverter topology, the switching frequency of the IGBT power switch tube is set to 10kHz-20kHz, the transformation ratio of the high-frequency transformer is 1:12, the direct current (24V / 48V / 96V) output by the photovoltaic assembly and the battery is inverted into high-frequency alternating voltage, and then the sine wave alternating current is obtained after the harmonic is filtered out by the output filter inductor. The input ends of the inverter power modules are connected in parallel to the DC bus, and the output ends form a unified AC output end after being collected by the module current sharing control unit, and are connected to the on-off grid switching circuit module 3.

[0035] And off-grid switching circuit module 3 by multi-stage controllable switch circuit (K1-K6), double capacitor filter structure (C1, C2) and switching control unit is composed of. Multi-stage controllable switch circuit is connected with grid terminal, inverter unit output terminal and load terminal respectively, double capacitor filter structure is connected in series between switch circuit and load terminal, for filtering voltage harmonic in switching process, ensure the quality of power supply. The switching control unit is built-in grid state detection subunit, can real-time acquisition voltage, frequency and phase signal of grid, when detecting grid abnormality (such as power failure, voltage drop, frequency deviation), trigger pre-stored zero-closing timing control strategy, complete grid-connected to off-grid switching within 20 milliseconds, avoid load power interruption.

[0036] Energy management module 4 contains multi-stage MPPT control unit and intelligent battery management sub-module. Multi-stage MPPT control unit acquires output voltage and current signal of photovoltaic module, through the combination of global MPPT search and local MPPT tracking, multi-stage MPPT algorithm can still accurately track the maximum power point in weak light environment such as rainy days, improve photovoltaic power generation efficiency. Intelligent battery management sub-module includes battery type identification unit, SOC prediction unit and charge-discharge control unit, which can automatically identify various battery types such as lithium battery and lead-acid battery, and establish SOC prediction model through Kalman filtering algorithm combined with voltage, current and temperature parameters of battery, dynamically optimize charge-discharge strategy according to SOC prediction result, prolong the cycle life of battery.

[0037] Load adaptation module 5 carries virtual synchronous generator control unit, which includes inertia simulation subunit and damping simulation subunit, which can simulate the voltage, frequency and impedance characteristics of synchronous generator, so that the inverter has inertia and damping characteristics similar to the grid. At the same time, the overload capacity of inverter can reach 120%-150% of rated power, which can guarantee the stable start and operation of inductive loads such as air conditioners and water pumps.

[0038] Further, the modular inverter unit 2 supports flexible configuration of power level, and the rated power of a single inverter power module is 5kW. By increasing or decreasing the number of inverter power modules, the inverter power of the whole machine can be covered from 10kW to 30kW:

[0039] When 2 inverter power modules are configured, the inverter power of the whole machine is 10kW, which is suitable for small family photovoltaic system;

[0040] When 6 inverter power modules are configured, the inverter power of the whole machine is 30kW, which can meet the photovoltaic power supply demand of small and medium-sized commercial buildings. At the same time, N+1 redundancy design ensures that when any working module fails, the standby module will immediately put into operation, and the inverter power of the whole machine will only decrease by the rated power of a single module, avoiding power interruption.

[0041] Further, the module current sharing control unit: using active current sharing method, real-time acquisition of each inverter power module output current signal, if a module output current exceeds the average current of 5%, by adjusting the module IGBT drive pulse width, change its output voltage amplitude and phase, so that the module current re-balance, ensure the output stability of inverter unit;

[0042] The DC bus conditioning unit: DC-DC boost circuit using Boost topology, can be photovoltaic components in the weak light environment output low voltage (such as 18V) to the DC bus rated voltage (400V), bus capacitor group by a plurality of electrolytic capacitor in series, the capacity of 2000 μF, used to absorb the bus voltage ripple, the bus voltage fluctuation rate control within ±2%;

[0043] Fault diagnosis sub-module: through the current sensor, temperature sensor and voltage sensor acquisition of each inverter power module operating parameters, after fault classification algorithm to identify fault type, if the overcurrent, over-temperature fault, first trigger the module soft off protection; if the open circuit, short circuit fault, then directly cut off the bypass switch of the fault module, and start the redundant module. The fault handling response time is not more than 20 milliseconds, matching the response time of grid-connected and off-grid switching, to ensure the continuity of power supply.

[0044] Further, in the multi-stage controllable switch circuit, K1, K2 are grid-connected side main switch, K3, K4 are off-grid side main switch, K5, K6 are auxiliary switching switch. When the grid is abnormal, the switching control unit first opens K1, K2, cutting off the grid connection, and closes K3, K4 when the grid voltage is zero, connecting the inverter unit and the load. At the same time, through K5, K6, adjust the charge and discharge state of the double capacitor filter structure, to ensure the smooth transition of voltage in the switching process.

[0045] Further, the global MPPT search stage of multi-stage MPPT algorithm uses particle swarm optimization algorithm to scan the power output curve of photovoltaic module, quickly determines the approximate interval of the maximum power point; the local MPPT tracking stage uses perturbation and observation method to accurately track the maximum power point, taking into account the search speed and tracking accuracy.

[0046] Further, the inertia simulation subunit of the virtual synchronous generator control unit simulates the rotational inertia characteristics of the synchronous generator, and suppresses the frequency fluctuation caused by load mutation; the damping simulation subunit compensates the frequency deviation caused by load fluctuation, further improving the stability of power supply.

[0047] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A photovoltaic grid-connected and off-grid energy storage inverter, comprising a foldable photovoltaic module (1), a modular inverter unit (2), a grid-connected and off-grid switching circuit module (3), an energy management module (4), and a load adaptation module (5), characterized in that: The foldable photovoltaic module (1) includes several foldable photovoltaic panels (11), a cylinder drive assembly (12), a moving plate (13), and a support block (14). The cylinder drive assembly (12) is connected to two moving plates (13), and the moving plates (13) are rotatably connected to the photovoltaic panels (11). The support block (14) is set at the folding node of the photovoltaic panel (11) and is used for positioning support after the photovoltaic panel (11) is unfolded. The modular inverter unit (2) includes at least two inverter power modules connected in parallel, a module current sharing control unit, a DC bus conditioning unit, and a fault diagnosis submodule. Each inverter power module adopts a full-bridge inverter topology and consists of IGBT power switching transistors, a high-frequency transformer, and an output filter inductor. The input terminal of the inverter power module is connected to the DC output terminal of the foldable photovoltaic module (1) and the energy storage battery. The output terminal is connected to the off-grid switching circuit module (3) after being aggregated by the module current sharing control unit. The DC bus conditioning unit is connected in series between the input terminal of the inverter power module and the DC bus to stabilize the bus voltage. The fault diagnosis submodule collects the current, temperature, and voltage signals of each inverter power module in real time. When a module fault is detected, the faulty module is disconnected and the power redundancy compensation of the remaining modules is triggered. The grid-connected / off-grid switching circuit module (3) includes a multi-level controllable switching circuit (K1-K6), a dual-capacitor filter structure (C1, C2), and a switching control unit. The multi-level controllable switching circuit is connected to the grid end, the inverter unit output end, and the load end, respectively. The dual-capacitor filter structure is connected in series between the switching circuit and the load end. The switching control unit pre-stores a timing control strategy for closing at the zero-crossing point, which is used to drive the controllable switching circuit to complete the mode switching when the grid is abnormal. The energy management module (4) includes a multi-level MPPT control unit and an intelligent battery management sub-module. The multi-level MPPT control unit is used to collect the output voltage and current signals of the photovoltaic module and execute the multi-level MPPT algorithm. The intelligent battery management sub-module includes a battery type identification unit, a SOC prediction unit and a charge and discharge control unit, which are compatible with various battery types such as lithium battery and lead-acid battery. The load adaptation module (5) is equipped with a virtual synchronous generator control unit, which is used to simulate the voltage, frequency and impedance characteristics of the power grid and output power signals to adapt to the start-up of inductive loads.

2. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: The inverter power module of the modular inverter unit (2) adopts an N+1 redundancy design, where N is the number of working modules, ranging from 2 to 6, and 1 is a spare module; the module current sharing control unit adopts an active current sharing method, which adjusts the output voltage amplitude and phase of each inverter power module to control the output current deviation of each module within 5%; the DC bus conditioning unit includes a DC-DC boost circuit and a bus capacitor bank, and the boost ratio of the DC-DC boost circuit can be adjusted within the range of 1.2-3 times to adapt to the wide voltage output range of photovoltaic modules and energy storage batteries.

3. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: The fault diagnosis submodule of the modular inverter unit (2) has a built-in fault classification algorithm that can identify four types of faults: overcurrent, overtemperature, open circuit, and short circuit. When a fault is detected, the fault diagnosis submodule sends a cut-off signal to the bypass switch of the fault module within 10 milliseconds and sends a power compensation command to the energy management module (4). The energy management module (4) adjusts the output power of the photovoltaic module and the battery, and works with the redundant module to achieve seamless power replacement.

4. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: In the multi-level controllable switching circuit, K1 and K2 are the grid-connected main switches, K3 and K4 are the off-grid main switches, and K5 and K6 are auxiliary switching switches. The switching control unit has a built-in grid status detection subunit, which is used to collect the voltage, frequency and phase signals of the grid in real time. When the grid signal is detected to exceed the preset threshold, the timing control strategy is triggered.

5. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 4, characterized in that: The timing control strategy is as follows: after the grid abnormality signal is triggered, the switching control unit first disconnects K1 and K2, and then closes K3 and K4 when the grid voltage crosses zero. At the same time, the charging and discharging state of the dual capacitor filter structure is adjusted through K5 and K6 to complete the switching from grid connection to off-grid.

6. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: The multi-level MPPT algorithm includes two stages: global MPPT search and local MPPT tracking. In the global MPPT search stage, the particle swarm optimization algorithm is used to scan the power output curve of the photovoltaic module to determine the approximate range of the maximum power point. In the local MPPT tracking stage, the perturbation observation method is used to accurately track the maximum power point.

7. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: The SOC prediction unit uses a Kalman filter algorithm combined with the battery's voltage, current, and temperature parameters to establish an SOC prediction model. The charge and discharge control unit dynamically adjusts the charge and discharge current and cutoff voltage based on the SOC prediction results and the battery type.

8. A photovoltaic grid-connected / off-grid energy storage inverter according to claim 1, characterized in that: The virtual synchronous generator control unit includes an inertia simulation subunit and a damping simulation subunit. The inertia simulation subunit is used to simulate the rotational inertia characteristics of the synchronous generator, and the damping simulation subunit is used to compensate for frequency deviations caused by load fluctuations.

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