Photovoltaic energy storage main inverter circuit
By optimizing the design of silicon carbide switching transistors and filter inductors, the loss and reliability problems of the traditional H6 main inverter circuit in high-voltage and high-frequency applications are solved, realizing efficient integration of photovoltaic energy storage systems and low-cost inverter circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHANGHAI FENGDIE ENERGY TECH CO LTD
- Filing Date
- 2025-06-10
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional H6 main inverter circuits suffer from increased losses during high-voltage, high-frequency applications in medium-sized and larger photovoltaic energy storage systems, decreased reliability due to the inability of freewheeling diodes to adapt to high switching frequencies, and increased size and cost of passive filter components.
By adopting a topology of silicon carbide switching transistors and AC-side filter inductors, and optimizing the switching transistor configuration and inductor design, a photovoltaic energy storage main inverter circuit with low leakage current and high efficiency is achieved. The common-mode voltage remains constant, the inductance of the filter inductor decreases with the increase of the operating frequency, and the core size and wire length are reduced.
It significantly reduces the size and material cost of the filter inductor core, improves integration and conversion efficiency, enhances electromagnetic compatibility performance, and maintains low leakage current and high power quality.
Smart Images
Figure CN224385376U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of power electronic power converters, specifically to a photovoltaic energy storage main inverter circuit. Background Technology
[0002] With the rapid development of new energy technologies, photovoltaic energy storage systems have attracted widespread attention due to their ability to effectively improve the utilization rate of new energy sources, enhance grid stability, and realize user-side energy management. As the core power conversion unit in a photovoltaic energy storage system, the main inverter circuit not only undertakes the task of efficiently converting DC power into AC power, but also needs to realize bidirectional energy flow control of the energy storage unit, which has a decisive impact on the overall system performance, operating efficiency, and safety.
[0003] In recent years, photovoltaic systems have evolved from micro-inverters to single-phase small-to-medium power inverters, giving rise to various new main inverter circuit structures. The expansion and evolution of main inverter circuits aim to improve system energy efficiency, reduce costs, and enhance system stability and reliability. Non-isolated main inverter circuits, due to their compact structure, high efficiency, and low cost, have been widely used in residential photovoltaic-storage systems and distributed photovoltaic systems. However, due to the lack of transformer isolation, common-mode leakage current has become a key factor affecting the system's electromagnetic compatibility and safety. This current not only exacerbates EMI interference but may also cause AC filter saturation, leading to filter failure and device damage, and in severe cases, even triggering system protective shutdown.
[0004] Against this technological backdrop, various photovoltaic energy storage main inverter circuits have emerged, such as the H6 structure. This structure optimizes the configuration of switching devices to achieve both low leakage current and high efficiency. Traditional H6 main inverter circuits use Si MOSFETs as bridge arms and utilize fast recovery diodes for freewheeling, aiming to improve cost-effectiveness. However, medium-sized and larger photovoltaic energy storage systems require high-voltage, high-frequency inverter circuits. Increasing the operating frequency of traditional H6 topology inverter circuits increases the losses of Si MOSFETs, and the freewheeling diodes may not be able to adapt to the high switching frequency, potentially leading to inverter failure and decreased circuit reliability. Simply increasing the operating voltage of the inverter circuit increases the size and cost of passive filtering components. Utility Model Content
[0005] The purpose of this invention is to provide a photovoltaic energy storage main inverter circuit to address the aforementioned shortcomings in the technology.
[0006] To achieve the above objectives, this utility model provides the following technical solution: a photovoltaic energy storage main inverter circuit, including a DC bus capacitor, eight silicon carbide switching transistors, and two AC side filter inductors;
[0007] When the photovoltaic energy storage main inverter circuit is working, the DC bus capacitor, photovoltaic cells, and energy storage battery pack are connected in parallel. The DC bus capacitor is composed of multiple parallel electrolytic capacitors.
[0008] Preferably, the eight silicon carbide switching transistors are labeled S1-S8 respectively;
[0009] The drains of S1 and S3 are connected in parallel to the positive terminal of the energy storage battery;
[0010] The drain of S5 is connected to the source of S1 and the drain of S7, respectively.
[0011] The drain of S6 is connected to the source of S3 and the drain of S8, respectively.
[0012] The drain of S2 is connected to the source of S5 and the source of S8, respectively.
[0013] The drain of S4 is connected to the source of S6 and the source of S7, respectively.
[0014] The source of S2 and the source of S4 are connected in parallel to the negative terminal of the energy storage battery.
[0015] Eight silicon carbide switching transistors are mounted on the same heat sink and electrically isolated by ceramic insulating sheets.
[0016] Preferably, the two AC-side filter inductors include two inductors, L1 and L2;
[0017] One end of inductor L1 is connected to the drain of S2, and the other end of inductor L1 is connected to one end of a single-phase power grid.
[0018] One end of inductor L2 is connected to the drain of S4, and the other end of inductor L2 is connected to the other end of a single-phase power grid.
[0019] Preferably, in inverter mode:
[0020] During the positive half-cycle of the power grid: S5 is continuously on, and S1 and S4 are simultaneously on, forming the current path: Energy storage battery V+ → S1 → S5 → L1 → Power grid → L2 → S4 → Energy storage battery V-; During the freewheeling phase: S1 and S4 are off, and S7 is on, forming the freewheeling path: L1 → S5 → S7 → L2; During the negative half-cycle of the power grid: S6 is continuously on, and S2 and S3 are simultaneously on, forming the current path: Energy storage battery V+ → S3 → S6 → L2 → Power grid → L1 → S2 → Energy storage battery V-; During the freewheeling phase: S2 and S3 are off, and S5 and S6 remain on to achieve freewheeling.
[0021] Preferably, the silicon carbide switching transistor operates at a working voltage below 1200V and a working frequency of 10KHz-50Hz.
[0022] Preferably, as the operating frequency increases, the inductance of the AC-side filter inductor is reduced accordingly according to the following formula:
[0023] ;
[0024] Where L is the required inductance, f is the switching frequency of the main inverter circuit, and ∆Iout is the maximum ripple current in inverter or rectification mode; to determine a core size large enough to accommodate the required energy storage, the following formula is used to allocate the core size:
[0025] ;
[0026] Where E is the energy that the filter inductor needs to store, L is the filter inductance, and I is the maximum current. Select the appropriate core size using inductor design tools, and then obtain the required number of turns of the filter inductor using the following formula:
[0027] ;
[0028] Where N represents the number of turns of the filter inductor wire, and A is the inductance factor of the magnetic core.
[0029] Preferably, the topology remains unchanged when the photovoltaic and energy storage battery power is insufficient.
[0030] Preferably, the system common-mode voltage remains a constant value of Vdc / 2 in all operating modes.
[0031] The technical effects and advantages provided by this utility model in the above technical solution are as follows:
[0032] In this invention, the increased operating frequency of the filter inductor significantly reduces the required inductance, thereby significantly reducing the size of the filter inductor core and the total wire length. This further improves the integration of the photovoltaic energy storage main inverter circuit and reduces the weight and cost of the filter material. Attached Figure Description
[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this utility model. For those skilled in the art, other drawings can be obtained based on these drawings.
[0034] Figure 1 This is a structural diagram of the inverter circuit of this utility model;
[0035] Figures 2a-2f This is a schematic diagram of the inverter's working mode according to this utility model;
[0036] Figure 3This is a comparison diagram of the dimensions of the AC filter inductor in Embodiment 1 of this utility model;
[0037] Figure 4 This is a statistical graph of inverter efficiency in Embodiment 1 of this utility model;
[0038] Figure 5 This is a statistical chart of rectification efficiency in Embodiment 1 of this utility model. Detailed Implementation
[0039] To enable those skilled in the art to better understand the technical solution of this utility model, the present utility model will be further described in detail below with reference to the accompanying drawings.
[0040] This utility model provides, for example Figures 1-5 The photovoltaic energy storage main inverter circuit shown includes a DC bus capacitor, eight silicon carbide switching transistors, and two AC side filter inductors.
[0041] When the photovoltaic energy storage main inverter circuit is working, the DC bus capacitor, photovoltaic cells, and energy storage battery pack are connected in parallel. The DC bus capacitor is composed of multiple parallel electrolytic capacitors.
[0042] Furthermore, the eight silicon carbide switching transistors are respectively labeled S1-S8;
[0043] The drains of S1 and S3 are connected in parallel to the positive terminal of the energy storage battery;
[0044] The drain of S5 is connected to the source of S1 and the drain of S7, respectively.
[0045] The drain of S6 is connected to the source of S3 and the drain of S8, respectively.
[0046] The drain of S2 is connected to the source of S5 and the source of S8, respectively.
[0047] The drain of S4 is connected to the source of S6 and the source of S7, respectively.
[0048] The source of S2 and the source of S4 are connected in parallel to the negative terminal of the energy storage battery.
[0049] Eight silicon carbide switching transistors are mounted on the same heat sink and electrically isolated by ceramic insulating sheets.
[0050] Furthermore, the two AC-side filter inductors include two inductors, L1 and L2;
[0051] One end of inductor L1 is connected to the drain of S2, and the other end of inductor L1 is connected to one end of a single-phase power grid.
[0052] One end of inductor L2 is connected to the drain of S4, and the other end of inductor L2 is connected to the other end of a single-phase power grid.
[0053] Furthermore, when the photovoltaic energy storage battery has sufficient energy or the photovoltaic battery is directly connected, this photovoltaic energy storage main inverter circuit inverts the DC power into AC power and feeds it into the AC power grid, experiencing the following four operating modes in each grid cycle:
[0054] During the positive half-cycle of the power grid, such as Figure 2a As shown,
[0055] 1. During the positive half-cycle of the power grid, the drive signal keeps the gate of S5 continuously conducting, simultaneously driving S1 and S4 to conduct synchronously, such as... Figure 2a As shown, the current path is: energy storage battery V+ → S1 → S5 → L1 → grid → L2 → S4 → energy storage battery V-. During this time, the inductor current in L1 and L2 increases, and the common-mode output voltage is Vdc / 2. During the grid's positive half-cycle freewheeling phase, as shown... Figure 2b As shown, the drive signal turns off S1 and S4, and simultaneously turns on S7, achieving complementary commutation with S1 and S4. At this time, the current path of L1 and L2 is L1→S5→S7→L2. The voltage of inductor L1 decreases and the voltage of L2 increases until the two voltages are equal. The common-mode voltage is Vdc / 2, realizing energy freewheeling. During this stage, active power is provided to the grid.
[0056] II. Negative power region during the positive half-cycle of the power grid, as follows Figure 2c As shown, the gate drive turns on the switching transistors S2, S3 and S6. During this stage, the inverter output voltage is negative and the current is still positive. The inductor currents of L1 and L2 freewheel through the body diodes of S2, S6 and S3, and decrease rapidly under the action of reverse voltage. The common mode voltage is Vdc / 2, which provides reactive power to the grid.
[0057] III. During the negative half-week of the power grid, if Figure 2d As shown, the gate drive keeps switch S6 continuously on, simultaneously driving S2 and S3 to conduct synchronously. The current path is: energy storage battery V+ → S3 → S6 → L2 → grid → L1 → S2 → energy storage battery V-. The inductor current increases in reverse, and the differential mode voltage is -Vdc. During the negative half-cycle freewheeling phase, as shown... Figure 2e As shown, when S2 and S3 are turned off, the inductor current freewheels through S5 and S6, the voltage of inductor L1 rises, and the voltage of L2 falls until they are equal. The common-mode voltage is Vdc / 2, maintaining the energy freewheeling process and providing active power to the grid.
[0058] IV. Negative power regions during the negative half-cycle of the power grid, such as Figure 2f As shown, the gate drive turns on the switches S1 and S4, and the inductor current is freewheeled by the body diodes of S1, S4 and S6. Then, it decreases rapidly under reverse voltage, and the common-mode voltage Vdc / 2 provides reactive power to the grid.
[0059] Furthermore, the silicon carbide switching transistor operates at a working voltage below 1200V and a working frequency of 10KHz-50Hz. The high DC working voltage will reduce line losses in the photovoltaic energy storage system, allowing the use of smaller bus capacitors and reducing the hardware cost and size of the bus capacitors.
[0060] Furthermore, as the operating frequency increases, the inductance of the AC-side filter inductor is reduced accordingly according to the following formula:
[0061] ;
[0062] Where L is the required inductance, f is the switching frequency of the main inverter circuit, and ∆Iout is the maximum ripple current in inverter or rectification mode; to determine a core size large enough to accommodate the required energy storage, the following formula is used to allocate the core size:
[0063] ;
[0064] Where E is the energy that the filter inductor needs to store, L is the filter inductance, and I is the maximum current. Select the appropriate core size using inductor design tools, and then obtain the required number of turns of the filter inductor using the following formula:
[0065] ;
[0066] Where N represents the number of turns of the filter inductor wire, and A is the inductance factor of the magnetic core.
[0067] Furthermore, when the photovoltaic and energy storage batteries are low on power, the topology remains unchanged, allowing the AC power to be rectified into DC power to reverse charge the energy storage batteries.
[0068] Furthermore, the system common-mode voltage remains constant at Vdc / 2 in all operating modes, thereby improving the conversion efficiency of the main inverter circuit while achieving low leakage current and high power quality.
[0069] In this invention, the increased operating frequency of the filter inductor significantly reduces the required inductance, thereby significantly reducing the size of the filter inductor core and the total wire length. This further improves the integration of the photovoltaic energy storage main inverter circuit and reduces the weight and cost of the filter material.
[0070] When both the energy storage battery and the photovoltaic cell have low energy, this photovoltaic energy storage main inverter circuit, without changing the topology, provides a path to rectify and output the AC power from the single-phase grid to the energy storage battery to maintain the DC bus voltage. The working processes of its switching transistors S1-S8 and AC side filter inductors L1 and L2 are similar, but the current direction is opposite, and will not be described in detail.
[0071] Example 1
[0072] A photovoltaic energy storage inverter with a maximum rated power of 5KW was developed using the circuit structure of this utility model. It operates at a DC working voltage of 380Vdc, with two 500V withstand voltage and 2200uF DC bus filter capacitor banks connected in parallel on the DC side. The AC grid voltage and frequency are 220V and 50Hz, respectively. Eight silicon carbide switching transistors were selected. Figure 1 The circuit is connected as shown, allowing it to operate at a switching frequency of 20kHz. Taking advantage of the high energy conversion efficiency of its main inverter circuit, eight silicon carbide switching transistors are pressed onto the two sides of the same rectangular heat sink. S1-S8 are thermally coupled to the heat sink using ceramic plates and silicone.
[0073] The photovoltaic energy storage inverter using the main inverter circuit of this utility model maintains a stable common-mode voltage output of Vdc / 2190V during the grid cycle, with low leakage current and improved electromagnetic compatibility performance. The electromagnetic compatibility filter circuit after the main inverter circuit is simplified to a more cost-effective ordinary two-stage power filter.
[0074] The filter inductors on the grid side, calculated according to the formula described in this utility model and based on the operating frequency of 20kHz, use two 470uH cables, each connected to the source of the symmetrical silicon carbide switching transistor in the middle of the two inverter bridge arms. Compared to the 990uH filter inductor required in the traditional H6 inverter circuit operating at a switching frequency of 10kHz, this is significantly improved. Figure 3 As shown, its size and total wire length are significantly reduced, and the integration level of the inverter circuit board is further improved;
[0075] When the photovoltaic energy storage inverter developed using the main circuit of this utility model is working, the energy storage battery pack is connected in parallel to the DC bus filter capacitor. The series voltage of the battery pack is 380V. When the inverter is set to meet the inversion conditions, i.e., the battery pack exceeds 80% of its design capacity, or the photovoltaic power generation exceeds the set charging current of the energy storage battery, the inverter starts the inversion working mode. In the main inverter circuit, S1-S8 and L1, L2 cycle through four working modes according to different stages of the grid cycle. The conversion efficiency of the circuit varies according to the severity of the load. Figure 4 The highest efficiency obtained from the test occurred under 20% load conditions, i.e., at 1kW power, with a conversion efficiency as high as 98.2%. When the inverter is set to meet rectification conditions, i.e., the battery pack is below 10% of its design capacity, or the photovoltaic power generation is low and the battery pack is below 30% of its design capacity, the inverter enters charging mode. In rectification mode, the voltage and current waveforms of the S1-S8 silicon carbide switches in the main inverter circuit are similar to those in the inverter mode. Figure 5 It can be seen that its conversion efficiency is between 96.7% and 98%, and its peak also occurs at 20% load;
[0076] The photovoltaic energy storage inverter developed according to this utility model achieves the goal of reducing size and increasing integration within the design capacity, while maintaining low leakage current and high-quality grid-connected output, and further improving conversion efficiency.
[0077] The foregoing description only illustrates certain exemplary embodiments of the present invention. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.
Claims
1. A photovoltaic energy storage main inverter circuit, characterized in that: Includes DC bus capacitor, eight silicon carbide switching transistors, and two AC side filter inductors; When the photovoltaic energy storage main inverter circuit is working, the DC bus capacitor, photovoltaic cells, and energy storage battery pack are connected in parallel. The DC bus capacitor is composed of multiple parallel electrolytic capacitors.
2. The photovoltaic energy storage main inverter circuit according to claim 1, characterized in that: The eight silicon carbide switching transistors are labeled S1-S8 respectively; The drains of S1 and S3 are connected in parallel to the positive terminal of the energy storage battery; The drain of S5 is connected to the source of S1 and the drain of S7, respectively. The drain of S6 is connected to the source of S3 and the drain of S8, respectively. The drain of S2 is connected to the source of S5 and the source of S8, respectively. The drain of S4 is connected to the source of S6 and the source of S7, respectively. The source of S2 and the source of S4 are connected in parallel to the negative terminal of the energy storage battery. Eight silicon carbide switching transistors are mounted on the same heat sink and electrically isolated by ceramic insulating sheets.
3. The photovoltaic energy storage main inverter circuit according to claim 2, characterized in that: The two AC-side filter inductors include inductors L1 and L2; One end of inductor L1 is connected to the drain of S2, and the other end of inductor L1 is connected to one end of a single-phase power grid. One end of inductor L2 is connected to the drain of S4, and the other end of inductor L2 is connected to the other end of a single-phase power grid.
4. The photovoltaic energy storage main inverter circuit according to claim 3, characterized in that: In inverter mode: During the positive half-cycle of the power grid: S5 is continuously on, and S1 and S4 are simultaneously on, forming the current path: Energy storage battery V+ → S1 → S5 → L1 → Power grid → L2 → S4 → Energy storage battery V-, with a common-mode output voltage of Vdc / 2; During the freewheeling phase: S1 and S4 are off, and S7 is on, forming the freewheeling path: L1 → S5 → S7 → L2, with a common-mode output voltage of Vdc / 2; During the negative half-cycle of the power grid: S6 is continuously on, and S2 and S3 are simultaneously on, forming the current path: Energy storage battery V+ → S3 → S6 → L2 → Power grid → L1 → S2 → Energy storage battery V-, with a common-mode output voltage of Vdc / 2; During the freewheeling phase: S2 and S3 are off, and S5 and S6 remain on to achieve freewheeling, with a common-mode output voltage of Vdc / 2.
5. The photovoltaic energy storage main inverter circuit according to claim 2, characterized in that: The silicon carbide switching transistor operates at a working voltage below 1200V and a working frequency of 10KHz-50Hz.
6. The photovoltaic energy storage main inverter circuit according to claim 4, characterized in that: As the operating frequency increases, the inductance of the AC-side filter inductor is reduced accordingly according to the following formula: ； Where L is the required inductance, f is the switching frequency of the main inverter circuit, and ∆Iout is the maximum ripple current in inverter or rectification mode; to determine a core size large enough to accommodate the required energy storage, the following formula is used to allocate the core size: ； in E is the energy that the filter inductor needs to store, L is the filter inductance, and I is the maximum current. Select the appropriate core size using inductor design tools, and then obtain the required number of turns of the filter inductor using the following formula: ； Where N represents the number of turns of the filter inductor wire, and A is the inductance factor of the magnetic core.
7. A photovoltaic energy storage main inverter circuit according to claim 6, characterized in that: The topology remains unchanged when the photovoltaic and energy storage batteries are low on power.
8. The photovoltaic energy storage main inverter circuit according to claim 4, characterized in that: The common-mode output voltage remains constant at Vdc / 2 in all operating modes.