Photovoltaic energy storage inverter and inversion system

Abstract

Disclosed in the present disclosure are a photovoltaic energy storage inverter and an inversion system. The photovoltaic energy storage inverter comprises a Boost circuit and a photovoltaic interface connected to the Boost circuit, the photovoltaic interface being configured to be connected to an external photovoltaic module. The inverter further comprises a high-voltage direct-current busbar; a low-voltage direct-current busbar, wherein the photovoltaic interface is connected to the low-voltage direct-current busbar by means of the Boost circuit; and a double-active-bridge converter, with one end connected to the low-voltage direct-current busbar, and the other end connected to the high-voltage direct-current busbar, the high-voltage direct-current busbar converting a direct current into an alternating current by means of a DC / AC circuit to be outputted to a power grid or a load. An energy storage interface of the inverter is coupled to the low-voltage direct-current busbar, and the energy storage interface is configured to be connected to a battery assembly. The photovoltaic energy storage inverter of the present disclosure saves device cost, and also greatly improves the safety of a photovoltaic module side and a battery assembly side.

Description

Photovoltaic energy storage inverter and inverter system Technical Field

[0001] The present disclosure belongs to the field of photovoltaic inverters, and particularly relates to a photovoltaic energy storage inverter and an inverter system. Background Art

[0002] Currently, most photovoltaic storage inverter systems adopt a DC energy storage and AC output architecture. DC energy storage is divided into low-voltage energy storage and high-voltage energy storage according to the voltage of the battery components.

[0003] As shown in Figure 1, high-voltage energy storage typically uses a non-isolated solution. That is, the battery assembly BAT is connected to the high-voltage DC bus BUS through a DC / DC circuit (BUCK / BOOST bidirectional step-up and step-down circuit). The high-voltage DC bus BUS is then converted into alternating current (AC) through a DC / AC circuit and output to the grid or load. Since this is a non-isolated solution, the circuit requires insulation testing and leakage current testing.

[0004] As shown in Figure 2, low-voltage energy storage battery modules typically employ isolation solutions. Common isolation schemes include DAB and LLC resonant circuits. Regardless of whether DAB or LLC isolation is used, the battery module (BAT) typically passes through an isolation conversion circuit to a high-voltage DC bus (BUS). The high-voltage DC bus (BUS) is then converted to AC through a DC / AC circuit and output to the grid or load. In this low-voltage energy storage battery module solution, the PV input remains high voltage and is not isolated. This means that insulation testing is still required on the PV side, and leakage current testing is required on the grid side, increasing device costs. Summary of the Invention

[0005] In order to solve the above technical problems, the present disclosure provides an improved photovoltaic energy storage inverter and inverter system, which saves device costs.

[0006] To achieve the above objectives, the present disclosure adopts the following technical solutions:

[0007] A photovoltaic energy storage inverter includes a boost circuit, a photovoltaic interface for connecting to an external photovoltaic module, an energy storage interface for connecting to a battery module, an inverter circuit, and an AC output interface for connecting to a power grid or a load. The photovoltaic energy storage inverter also includes:

[0008] A low-voltage DC bus, wherein the photovoltaic interface is connected to the low-voltage DC bus via the Boost circuit, and the energy storage interface of the inverter is connected to the low-voltage DC bus;

[0009] a high-voltage DC bus, the high-voltage DC bus being connected to the AC output interface via the inverter circuit;

[0010] A dual active bridge converter has a low voltage side and a high voltage side, wherein the low voltage side is connected to the low voltage DC bus, and the high voltage side is connected to the high voltage DC bus.

[0011] Preferably, the battery assembly has a charging state. In the charging state, the photovoltaic assembly is connected to the battery assembly through the Boost circuit and the low-voltage DC bus.

[0012] Preferably, the dual-active bridge converter includes a DC / AC converter located on the low-voltage side, an AC / DC converter located on the high-voltage side, and a transformer located between the DC / AC converter and the AC / DC converter, the DC / AC converter is connected to the low-voltage DC bus, and the AC / DC converter is connected to the high-voltage DC bus.

[0013] More preferably, the voltage converted from the input voltage of the photovoltaic module by the Boost circuit is no higher than 60V.

[0014] Preferably, an EMI filter circuit is provided between the photovoltaic assembly and the Boost circuit.

[0015] Preferably, an EMI filter circuit is provided between the inverter circuit and the AC output interface.

[0016] Preferably, the number of the photovoltaic interfaces is one or more, and the number of the Boost circuits is less than or equal to the number of the photovoltaic interfaces.

[0017] Preferably, an input end of one of the Boost circuits is connected to at least one group of the photovoltaic interfaces.

[0018] Preferably, the photovoltaic energy storage inverter includes a controller, and the controller is electrically connected to the switch control terminal of the Boost circuit.

[0019] Preferably, the controller is electrically connected to the low-voltage side and the high-voltage side of the dual-active bridge converter.

[0020] The present disclosure also adopts the following technical solutions:

[0021] An inverter system includes the above-mentioned photovoltaic energy storage inverter, a battery assembly, and a photovoltaic assembly, wherein the photovoltaic interface of the photovoltaic energy storage inverter is connected to the photovoltaic assembly, the energy storage interface of the photovoltaic energy storage inverter is connected to the battery assembly, and the AC output interface of the photovoltaic energy storage inverter is connected to the power grid or the load.

[0022] The present disclosure adopts the above solution, which has the following advantages over the prior art:

[0023] In the photovoltaic energy storage inverter disclosed herein, the photovoltaic modules and battery modules are located on the low-voltage DC bus side, and the power grid or load is located on the high-voltage DC bus side. A dual-active bridge converter is provided between the low-voltage DC bus and the high-voltage DC bus for electrical isolation. No insulation testing is required for the photovoltaic modules, and no leakage current testing is required at the power grid. This saves device costs and greatly improves the safety of the photovoltaic modules and battery modules. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present disclosure, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] FIG1 is a schematic structural diagram of a photovoltaic energy storage inverter for high-voltage energy storage in the prior art;

[0026] FIG2 is a schematic structural diagram of a photovoltaic energy storage inverter for low-voltage energy storage in the prior art;

[0027] FIG3 is a schematic diagram of a photovoltaic energy storage inverter according to an embodiment of the present disclosure;

[0028] FIG4 is another schematic diagram of a photovoltaic energy storage inverter according to an embodiment of the present disclosure.

[0029] in,

[0030] 1. Low-voltage side unit bridge; 2. High-voltage side unit bridge; 3. Low-voltage DC bus; 4. High-voltage DC bus; 5. Transformer; 6. Photovoltaic interface; 7. Energy storage interface; 8. AC output interface. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present disclosure are described in detail below with reference to the accompanying drawings to make the advantages and features of the present disclosure more easily understood by those skilled in the art. It should be noted that the descriptions of these embodiments are intended to facilitate understanding of the present disclosure and do not constitute a limitation of the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below may be combined with each other as long as they do not conflict with each other.

[0032] In photovoltaic power generation systems, a common combination of photovoltaics and energy storage is used. When photovoltaic power generation exceeds load demand, the excess energy is stored by an energy storage device. When photovoltaic power generation falls short of load demand, the stored energy is released by the energy storage device to supplement load power. This embodiment provides an inverter system comprising a photovoltaic energy storage inverter, a photovoltaic module (PV), and a battery module (BAT). When photovoltaic power generation exceeds load demand, the excess energy is stored by the battery module (BAT). When photovoltaic power generation falls short of load demand, the stored energy is released by the battery module (BAT) to supplement load power. The photovoltaic energy storage inverter of this embodiment is described in detail below.

[0033] 3 and 4 , the photovoltaic energy storage inverter of this embodiment includes a boost circuit, a photovoltaic interface 6, an energy storage interface 7, a DC / AC inverter circuit, an AC output interface 8 for connecting to a grid or load, a low-voltage DC bus 3, a high-voltage DC bus 4, a dual-active bridge converter (DAB), and a controller. The output voltage of the boost circuit is consistent with the voltage of the battery assembly (BAT). The photovoltaic interface 6 is used to connect to an external photovoltaic assembly (PV), the energy storage interface 7 is used to connect to the battery assembly (BAT), and the AC output interface 8 is used to connect to the grid (GRID) or load (LOAD).

[0034] Furthermore, the photovoltaic module PV is connected to the low-voltage DC bus 3 through the Boost circuit, and the energy storage interface 7 of the photovoltaic energy storage inverter is connected to the low-voltage DC bus 3; the high-voltage DC bus 4 is connected to the AC output interface 8 through the inverter circuit DC / AC; the dual-active bridge converter DAB has a low-voltage side and a high-voltage side, the low-voltage side is connected to the low-voltage DC bus 3, and the high-voltage side 8 is connected to the high-voltage DC bus 4. Specifically, as shown in Figure 4, the dual-active bridge converter DAB includes a low-voltage side unit bridge 1 and a high-voltage side unit bridge 2, the low-voltage side unit bridge 1 is connected to the low-voltage DC bus 3, and the high-voltage side unit bridge 2 is connected to the high-voltage DC bus 4.

[0035] Furthermore, the dual active bridge converter DAB includes a DC / AC converter located on the low-voltage side, an AC / DC converter located on the high-voltage side, and a transformer 5 located between the DC / AC converter and the AC / DC converter, wherein the transformer 5 is used for electrical isolation and energy transmission, the DC / AC converter is connected to the low-voltage DC bus 3, and the AC / DC converter is connected to the high-voltage DC bus 4.

[0036] The battery assembly BAT has a charging state. In the charging state, the photovoltaic assembly PV is connected to the battery assembly BAT through the Boost circuit and the low-voltage DC bus 3. Compared with the photovoltaic energy storage inverter shown in Figures 1 and 2, the charging efficiency is higher. Specifically, when the inverter shown in Figure 1 charges the battery assembly BAT, the photovoltaic assembly PV needs to be charged by the DC / DC circuit after passing through the Boost circuit and the bus BUS; when the inverter shown in Figure 2 charges the battery assembly BAT, the photovoltaic assembly PV needs to be charged by the dual-active bridge converter DAB after passing through the Boost circuit and the bus BUS. The dual-active bridge converter DAB or the DC / DC circuit will cause certain losses, and the charging efficiency is low.

[0037] The input voltage of the photovoltaic module PV of this embodiment is no more than 60V after being converted by the Boost circuit. The voltage of the low-voltage DC bus 3 is 40-60V and can be touched by human hands, which has high safety and good insulation performance.

[0038] The controller of this embodiment is electrically connected to the switch control terminal of the Boost circuit, and is also electrically connected to the low-voltage side and the high-voltage side of the dual-active bridge converter DAB. Specifically, the controller is a DSP controller.

[0039] An EMI filter circuit is provided between the photovoltaic module (PV) and the boost circuit, and between the inverter circuit (DC / AC) and the AC output interface 8. This EMI filter circuit is used to suppress electromagnetic interference, particularly in the circuits. Furthermore, there are one or more photovoltaic interfaces 6, and the number of boost circuits is less than or equal to the number of photovoltaic interfaces 6. The input of a boost circuit is connected to at least one set of photovoltaic interfaces 6.

[0040] The photovoltaic energy storage inverter of this embodiment uses the low-voltage battery assembly BAT as the system's low-voltage DC bus 3. The photovoltaic assembly PV, after being boosted by a boost circuit, is directly fed into the low-voltage DC bus 3. The low-voltage DC bus 3 is then converted to a high-voltage DC bus 4 via a dual-active bridge converter (DAB). The high-voltage DC bus 4 is then connected to an AC output interface 8 via an inverter circuit (DC / AC). The AC output interface 8 is then connected to the grid (GRID) or a load (LOAD). This photovoltaic energy storage inverter isolates the photovoltaic assembly PV and the battery assembly BAT from the system's high-voltage side, significantly improving the safety of both the photovoltaic assembly PV and the battery assembly BAT. Furthermore, because the battery assembly BAT directly serves as the low-voltage bus, the photovoltaic assembly PV only needs to pass through a single-stage boost circuit to charge the battery assembly BAT, improving the charging efficiency from the photovoltaic assembly PV to the battery assembly BAT. Furthermore, because the PV modules are isolated from the AC power supply, the entire circuit does not require insulation testing or leakage current detection. The DC / AC inverter circuit can also use a common-mode topology, which is relatively low-cost. Furthermore, because it is an isolated topology, the grid-connected relay can be implemented using a single-stage relay. However, the inverters shown in Figures 1 and 2 require insulation testing on the PV side and leakage current detection on the grid side, as the PV module input is not isolated. Furthermore, a DC / AC topology with low common-mode current is used, requiring a two-stage grid-connected relay, resulting in relatively high costs.

[0041] The working principle of the photovoltaic energy storage inverter in this embodiment is as follows:

[0042] After the inputs of multiple photovoltaic modules PV are merged, they pass through the EMI filter circuit and the Boost circuit and are then aggregated to the low-voltage DC bus 3. The battery module BAT is directly connected to the low-voltage DC bus 3. The system adjusts the duty cycle of the Boost circuit on the photovoltaic module PV side according to the battery module BAT voltage, so that its output voltage is consistent with the battery module BAT voltage. When the battery module BAT or photovoltaic module PV transmits energy to the grid side, the drive signal sent by the DSP controller controls the phase shift angle of the unit bridges on both sides of the dual active bridge converter DAB, so that the low-voltage side unit bridge 1 leads the high-voltage side unit bridge 2. Power flows from the low-voltage DC bus 3 to the high-voltage DC bus 4. The high-voltage DC bus 4 then outputs industrial frequency AC power to the grid GRID or supplies power to the load LOAD through the DC / AC inverter circuit. When the grid GRID needs to charge the battery assembly BAT, the grid GRID voltage is rectified to the high-voltage DC bus 4 through the DC / AC inverter circuit. The DSP controller controls the phase shift angle of the unit bridges on both sides of the dual-active bridge converter DAB, making the high-voltage side unit bridge 4 lead the low-voltage side unit bridge 3. Power flows from the high-voltage DC bus 4 to the low-voltage DC bus 3, realizing the grid GRID charging function for the battery assembly BAT.

[0043] The photovoltaic energy storage inverter of this embodiment has at least the following advantages:

[0044] (1) The dual active bridge converter DAB is used to electrically isolate the PV side of the photovoltaic module and the grid GRID. The battery module BAT and the photovoltaic module PV are located on the low-voltage DC bus 3 side. The photovoltaic module PV does not need to be tested for insulation, and the grid GRID output side does not need to be tested for leakage current, which greatly saves device costs.

[0045] (2) The battery module BAT is directly connected to the low-voltage DC bus 3. The photovoltaic module PV is boosted by the BOOST circuit and then aggregated to the low-voltage DC bus 3. This allows the photovoltaic module PV to charge the battery module BAT through only one level of the Boost circuit, thereby improving the efficiency of charging the battery module BAT from the photovoltaic module PV.

[0046] (3) Since the low-voltage side and high-voltage side of the dual-active bridge converter DAB circuit are isolated by a transformer, the PV side of the photovoltaic module and the BAT side of the battery module are isolated from the high-voltage side of the system, which improves the safety of the PV side of the photovoltaic module and the BAT side of the battery module. At the same time, the insulation level of the PV side of the photovoltaic module and the BAT side of the battery module is reduced, thereby reducing the difficulty of PCB LAYOUT.

[0047] As used in this specification and claims, the terms "comprises" and "include" merely indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list; a method or apparatus may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the associated listed items.

[0048] It should be noted that, unless otherwise specified, when a feature is referred to as being "fixed" or "connected" to another feature, it may be directly fixed or connected to the other feature or indirectly fixed or connected to the other feature. Furthermore, terms such as "upper," "lower," "left," and "right" used in this disclosure are intended solely to describe the relative positions of the components of this disclosure as shown in the accompanying drawings.

[0049] The above embodiment is intended only to illustrate the technical concepts and features of the present disclosure and is a preferred embodiment. Its purpose is to enable those familiar with the art to understand the contents of the present disclosure and implement them accordingly. It is not intended to limit the scope of protection of the present disclosure. Any equivalent transformations or modifications made based on the principles of the present disclosure are intended to be included in the scope of protection of the present disclosure.

Claims

1. A photovoltaic energy storage inverter, comprising a Boost circuit, a photovoltaic interface for connecting to an external photovoltaic module, an energy storage interface for connecting to a battery module, an inverter circuit, and an AC output interface for connecting to a power grid or a load, characterized in that: The photovoltaic energy storage inverter also includes: A low-voltage DC bus, wherein the photovoltaic interface is connected to the low-voltage DC bus through the Boost circuit, and the energy storage interface of the photovoltaic energy storage inverter is connected to the low-voltage DC bus; A high-voltage DC bus, the high-voltage DC bus being connected to the AC output interface via the inverter circuit; A dual active bridge converter comprises a low voltage side and a high voltage side, wherein the low voltage side is connected to the low voltage DC bus, and the high voltage side is connected to the high voltage DC bus.

2. The photovoltaic energy storage inverter according to claim 1, characterized in that: The battery assembly has a charging state. In the charging state, the photovoltaic assembly is connected to the battery assembly through the Boost circuit and the low-voltage DC bus.

3. The photovoltaic energy storage inverter according to claim 1, characterized in that: The dual-active bridge converter includes a DC / AC converter located on the low-voltage side, an AC / DC converter located on the high-voltage side, and a transformer located between the DC / AC converter and the AC / DC converter. The DC / AC converter is connected to the low-voltage DC bus, and the AC / DC converter is connected to the high-voltage DC bus.

4. The photovoltaic energy storage inverter according to claim 2, characterized in that: The voltage of the photovoltaic module converted by the Boost circuit is no higher than 60V.

5. The photovoltaic energy storage inverter according to claim 2, characterized in that: An EMI filter circuit is provided between the photovoltaic assembly and the Boost circuit.

6. The photovoltaic energy storage inverter according to claim 2, characterized in that: An EMI filter circuit is provided between the inverter circuit and the AC output interface.

7. The photovoltaic energy storage inverter according to claim 1, characterized in that: The number of the photovoltaic interfaces is one or more, and the number of the Boost circuits is less than or equal to the number of the photovoltaic interfaces; the input end of one Boost circuit is connected to at least one group of the photovoltaic interfaces.

8. The photovoltaic energy storage inverter according to claim 7, characterized in that: The photovoltaic energy storage inverter includes a controller, and the controller is electrically connected to a switch control terminal of the Boost circuit.

9. The photovoltaic energy storage inverter according to claim 8, characterized in that: The controller is electrically connected to the low voltage side and the high voltage side of the dual active bridge converter.

10. An inverter system, characterized in that: It comprises the photovoltaic energy storage inverter, battery assembly and photovoltaic assembly as described in any one of claims 1 to 9, the photovoltaic interface of the photovoltaic energy storage inverter is connected to the photovoltaic assembly, the energy storage interface of the photovoltaic energy storage inverter is connected to the battery assembly, and the AC output interface of the photovoltaic energy storage inverter is connected to the power grid or the load.

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