A photovoltaic power conversion system for photovoltaic solar panels

Abstract

This utility model discloses a photovoltaic power conversion system for a photovoltaic solar panel, including a photovoltaic input terminal, a DC support unit, a switching inverter unit, an AC filter unit, and an AC output terminal. The switching inverter unit includes a first switching inverter unit and a second switching inverter unit. The positive terminal PV+ and the negative terminal PV- of the photovoltaic input terminal are connected to the DC support unit. A transformer T1 is provided between the photovoltaic input terminal and the DC support unit. A transformer T2 is provided between the first switching inverter unit and the second switching inverter unit. The first switching inverter unit includes MOSFETs S1, S2, S3, and S4. The second switching inverter unit includes MOSFETs S5, S6, S7, and S8. The source of MOSFET S1 is connected to the drain of MOSFET S2, and the connection point is defined as the midpoint A of the bridge arm. The source of MOSFET S3 is connected to the drain of MOSFET S4, and the connection point is defined as the midpoint B of the bridge arm.

Description

Technical Field

[0001] This utility model relates to the field of photovoltaic power generation, and in particular to a photovoltaic power conversion system for photovoltaic solar panels. Background Technology

[0002] Existing bidirectional inverters typically employ a multi-stage power conversion architecture (such as first boosting the voltage through a DC-DC converter and then converting it through a DC-AC inverter) when converting low-voltage DC power provided by batteries, photovoltaic solar panels, etc., to AC power for grid connection.

[0003] This multi-level conversion has significant drawbacks: First, each stage of conversion generates switching losses and conduction losses, resulting in low overall energy conversion efficiency of the system. Secondly, the multi-stage structure requires more power switching components, magnetic components, and especially large-capacity DC bus capacitors, which increases the complexity, cost, and size of the system. Furthermore, traditional architectures exhibit poor adaptability and energy efficiency when the input voltage fluctuates significantly (such as when photovoltaic panels change with sunlight), and they also struggle to efficiently balance voltage boosting and bucking functions.

[0004] Therefore, there is an urgent need for a bidirectional inverter solution that is simpler in structure, more efficient, lower in cost, and can adapt to a wide range of input voltages. Utility Model Content

[0005] The main purpose of this invention is to propose a photovoltaic power conversion system for photovoltaic solar panels, which is a buck-boost bidirectional inverter with a compact structure, high conversion efficiency, low cost, and the ability to achieve single-stage bidirectional power flow under a wide range of voltage input.

[0006] To achieve the above objectives, this utility model proposes a photovoltaic power conversion system for photovoltaic solar panels, including a photovoltaic input terminal, a DC support unit, a switching inverter unit, an AC filter unit, and an AC output terminal; The switching inverter unit includes a first switching inverter unit and a second switching inverter unit; The positive electrode PV+ and the negative electrode PV- of the photovoltaic input terminal are connected to the DC support unit; A transformer T1 is provided between the photovoltaic input terminal and the DC support unit; A transformer T2 is provided between the first switching inverter unit and the second switching inverter unit; The first switching inverter unit includes MOSFET S1, MOSFET S2, MOSFET S3, and MOSFET S4; The second switching inverter unit includes MOSFETs S5, S6, S7, and S8; The source of the MOS transistor S1 is connected to the drain of the MOS transistor S2, and the connection point is defined as the midpoint A of the bridge arm. The source of the MOS transistor S3 is connected to the drain of the MOS transistor S4, and the connection point is defined as the midpoint B of the bridge arm. The drains of MOS transistors S1 and S3 are connected to the positive bus of the DC support unit. The sources of the MOS transistors S2 and S4 are connected to the negative bus of the DC support unit. The drain of the MOS transistor S5 is connected to the midpoint A of the bridge arm, and its source is connected to the drain of the MOS transistor S6; the source of the MOS transistor S6 is connected to the negative bus of the DC support unit. The drain of the MOS transistor S7 is connected to the positive bus of the DC support unit, and its source is connected to the drain of the MOS transistor S8. The source of the MOS transistor S8 is connected to the midpoint B of the bridge arm; The AC filter unit includes inductor L1 and inductor L2; one end of inductor L1 is connected between the source of MOSFET S5 and the drain of MOSFET S6, and one end of inductor L2 is connected between the source of MOSFET S7 and the drain of MOSFET S8; the other ends of inductor L1 and inductor L2 together constitute one end of the AC output terminal. The other end of the AC output terminal is connected to a common reference point between inductors L1 and L2, or grounded through a capacitor network.

[0007] The advantages of this application are: 1. The first switching inverter unit constitutes the core part of the full-bridge inverter topology. Through the orderly switching of S1-S4, it converts the stable DC power from the DC support unit into square wave AC power, providing the basic waveform for subsequent fine inversion. The other function of the bridge arm midpoint, namely the connection point of S1 and S2 (bridge arm midpoint A) and the connection point of S3 and S4 (bridge arm midpoint B), serves as the connection interface with the second inverter unit, realizing the power coordination of the two inverter units.

[0008] The second switching inverter unit mainly functions as a step-up / step-down converter and waveform optimization unit. In conjunction with the first inverter unit, it achieves wide-range voltage step-up / step-down regulation through the complementary switching of S5-S8 (without the need for an additional DC-DC converter), while refining the square wave waveform to approximate a sine wave.

[0009] Additionally, it also serves as a current path control mechanism, that is, by controlling the on / off state of S5 (connecting the midpoint of the bridge arm A) and S8 (connecting the midpoint of the bridge arm B), the direction of power transmission is adjusted to achieve bidirectional power flow (photovoltaic grid-connected power generation or grid reverse power supply energy storage). 2. By using a single-stage topology of "dual inverter unit + transformer coupling", the conversion from "low-voltage DC to high-voltage AC" is directly completed, reducing intermediate conversion steps; 3. Through the voltage adaptation function of T1 and T2 transformers, and the coordinated adjustment of dual inverter units, it can be compatible with a wide range of input voltages (such as 20V-100V). Regardless of whether the input voltage is higher or lower than the output AC voltage, it can efficiently complete the power conversion. 4. Electrical isolation design (T1 and T2 transformers) reduces the risk of fault propagation and improves the overall reliability of the system. Attached Figure Description

[0010] Figure 1 This is the circuit diagram for this application. Detailed Implementation

[0011] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0012] It should be noted that if any directional indication (such as up, down, left, right, front, back, top, bottom, inside, outside, vertical, horizontal, longitudinal, counterclockwise, clockwise, circumferential, radial, axial, etc.) is involved in the embodiments of this utility model, the directional indication is only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0013] Furthermore, if the embodiments of this utility model involve descriptions such as "" or "", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "" or "" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0014] like Figure 1 As shown, a photovoltaic power conversion system for photovoltaic solar panels includes a photovoltaic input terminal, a DC support unit, a switching inverter unit, an AC filter unit, and an AC output terminal. The switching inverter unit includes a first switching inverter unit and a second switching inverter unit; The positive electrode PV+ and the negative electrode PV- of the photovoltaic input terminal are connected to the DC support unit; A transformer T1 is provided between the photovoltaic input terminal and the DC support unit; A transformer T2 is provided between the first switching inverter unit and the second switching inverter unit; The first switching inverter unit includes MOSFET S1, MOSFET S2, MOSFET S3, and MOSFET S4; The second switching inverter unit includes MOSFETs S5, S6, S7, and S8; The first switching inverter unit constitutes the core of the full-bridge inverter topology. Through the orderly switching of S1-S4, it converts the stable DC power from the DC support unit into square wave AC power, providing the basic waveform for subsequent fine inversion. The other function of the bridge arm midpoint, namely the connection point between S1 and S2 (bridge arm midpoint A) and the connection point between S3 and S4 (bridge arm midpoint B), serves as the connection interface with the second inverter unit, realizing power coordination between the two inverter units.

[0015] The second switching inverter unit mainly functions as a step-up / step-down converter and waveform optimization unit. In conjunction with the first inverter unit, it achieves wide-range voltage step-up / step-down regulation through the complementary switching of S5-S8 (without the need for an additional DC-DC converter), while refining the square wave waveform to approximate a sine wave.

[0016] Additionally, it also serves as a current path control mechanism, that is, by controlling the on / off state of S5 (connecting the midpoint of the bridge arm A) and S8 (connecting the midpoint of the bridge arm B), the direction of power transmission is adjusted to achieve bidirectional power flow (photovoltaic grid-connected power generation or grid reverse power supply energy storage).

[0017] The source of the MOS transistor S1 is connected to the drain of the MOS transistor S2, and the connection point is defined as the midpoint A of the bridge arm. The source of the MOS transistor S3 is connected to the drain of the MOS transistor S4, and the connection point is defined as the midpoint B of the bridge arm. The drains of MOS transistors S1 and S3 are connected to the positive bus of the DC support unit. The sources of the MOS transistors S2 and S4 are connected to the negative bus of the DC support unit. The drain of the MOS transistor S5 is connected to the midpoint A of the bridge arm, and its source is connected to the drain of the MOS transistor S6; the source of the MOS transistor S6 is connected to the negative bus of the DC support unit. The drain of the MOS transistor S7 is connected to the positive bus of the DC support unit, and its source is connected to the drain of the MOS transistor S8. The source of the MOS transistor S8 is connected to the midpoint B of the bridge arm; The AC filter unit includes inductor L1 and inductor L2; one end of inductor L1 is connected between the source of MOSFET S5 and the drain of MOSFET S6, and one end of inductor L2 is connected between the source of MOSFET S7 and the drain of MOSFET S8; the other ends of inductor L1 and inductor L2 together constitute one end of the AC output terminal. The other end of the AC output terminal is connected to a common reference point between inductors L1 and L2, or grounded through a capacitor network.

[0018] The MOS transistor used here is a MOSFET, but IGBTs or thyristors can also be used.

[0019] Transformer T1 and transformer T2 are among them; Transformer T1 mainly serves the function of voltage adaptation (i.e., detecting the voltage at the input terminal): it achieves the matching of the low-voltage DC input from the photovoltaic system with the bus voltage of the DC support unit, and can perform preliminary voltage boosting or bucking as needed, reducing the voltage conversion pressure of the subsequent inverter unit; In addition, it also serves as an electrical isolation mechanism, isolating the photovoltaic panel from the internal circuitry of the system, reducing the impact of a fault on one side on the other, and improving the electrical safety of the system.

[0020] Transformer T2 mainly serves as a power coupler and voltage regulator (primarily on the AC side), coupling the power transmission of the two inverter units and assisting in the step-up and step-down functions, enabling the system to efficiently complete power conversion when the input voltage is higher or lower than the output AC voltage. Furthermore, it can suppress harmonics (i.e., avoid the occurrence of peaks or troughs that cause abnormal AC power), and filter out some harmonics generated by switching operations through magnetic coupling characteristics, thereby improving the power quality of the inverter output.

[0021] Specifically, the DC support unit includes an input capacitor C1 and an input capacitor C2; The input capacitors C1 and C2 are connected in series and then in parallel at the photovoltaic input terminal, and their common connection point forms the midpoint of the DC bus.

[0022] The input capacitors C1 and C2 of the DC support unit mainly serve to divide the voltage and stabilize the bus. After being connected in series, they are connected in parallel at the photovoltaic input terminal. They not only divide the input DC voltage into positive and negative bus voltages, but their common connection point, which forms the "DC bus midpoint", also provides a symmetrical voltage reference for the subsequent inverter unit, ensuring the balance of the operating voltage of the switching transistors.

[0023] It also serves as a filter and energy storage, absorbing the ripple of the photovoltaic input voltage, stabilizing the DC bus voltage, and preventing voltage fluctuations from impacting the inverter unit; at the same time, it stores short-term electrical energy, providing an energy buffer for power conversion and improving the system's operational stability.

[0024] Specifically, the AC filtering unit further includes filter capacitor C3 and filter capacitor C4; One end of the filter capacitor C3 is connected to the connection point between the inductor L1 and the AC output terminal, and the other end is connected to the midpoint of the DC bus or the common reference point of the AC output terminal. One end of the filter capacitor C4 is connected to the connection point between the inductor L2 and the AC output terminal, and the other end is connected to the midpoint of the DC bus or the common reference point of the AC output terminal.

[0025] Specifically, each of the MOS transistors S1-S8 has a built-in or externally connected diode D in reverse parallel.

[0026] Specifically, a buffer capacitor is connected between the midpoint A of the bridge arm and the midpoint of the DC bus, and / or between the midpoint B of the bridge arm and the midpoint of the DC bus.

[0027] In the design and development of inverters, using MOSFETs (i.e., controlling the PWM band to achieve a predetermined band) to switch current / circuit is a relatively conventional design. However, how to combine them and achieve the desired control effect is the key point of the design.

[0028] The above description is only a preferred embodiment of the present utility model and does not limit the patent scope of the present utility model. All equivalent structural transformations made under the inventive concept of the present utility model using the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A photovoltaic power conversion system for photovoltaic solar panels, characterized in that, It includes a photovoltaic input terminal, a DC support unit, a switching inverter unit, an AC filter unit, and an AC output terminal; The switching inverter unit includes a first switching inverter unit and a second switching inverter unit; The positive electrode PV+ and the negative electrode PV- of the photovoltaic input terminal are connected to the DC support unit; A transformer T1 is provided between the photovoltaic input terminal and the DC support unit; A transformer T2 is provided between the first switching inverter unit and the second switching inverter unit; The first switching inverter unit includes MOSFET S1, MOSFET S2, MOSFET S3, and MOSFET S4; The second switching inverter unit includes MOSFETs S5, S6, S7, and S8; The source of the MOS transistor S1 is connected to the drain of the MOS transistor S2, and the connection point is defined as the midpoint A of the bridge arm. The source of the MOS transistor S3 is connected to the drain of the MOS transistor S4, and the connection point is defined as the midpoint B of the bridge arm. The drains of MOS transistors S1 and S3 are connected to the positive bus of the DC support unit. The sources of the MOS transistors S2 and S4 are connected to the negative bus of the DC support unit. The drain of the MOS transistor S5 is connected to the midpoint A of the bridge arm, and its source is connected to the drain of the MOS transistor S6; the source of the MOS transistor S6 is connected to the negative bus of the DC support unit. The drain of the MOS transistor S7 is connected to the positive bus of the DC support unit, and its source is connected to the drain of the MOS transistor S8. The source of the MOS transistor S8 is connected to the midpoint B of the bridge arm; The AC filter unit includes inductor L1 and inductor L2; one end of inductor L1 is connected between the source of MOSFET S5 and the drain of MOSFET S6, and one end of inductor L2 is connected between the source of MOSFET S7 and the drain of MOSFET S8; the other ends of inductor L1 and inductor L2 together constitute one end of the AC output terminal. The other end of the AC output terminal is connected to a common reference point between inductors L1 and L2, or grounded through a capacitor network.

2. The photovoltaic power conversion system of the photovoltaic solar panel as described in claim 1, characterized in that, The DC support unit includes an input capacitor C1 and an input capacitor C2; The input capacitors C1 and C2 are connected in series and then in parallel at the photovoltaic input terminal, and their common connection point forms the midpoint of the DC bus.

3. The photovoltaic power conversion system of the photovoltaic solar panel as described in claim 1, characterized in that, The AC filtering unit also includes filter capacitor C3 and filter capacitor C4; One end of the filter capacitor C3 is connected to the connection point between the inductor L1 and the AC output terminal, and the other end is connected to the midpoint of the DC bus or the common reference point of the AC output terminal. One end of the filter capacitor C4 is connected to the connection point between the inductor L2 and the AC output terminal, and the other end is connected to the midpoint of the DC bus or the common reference point of the AC output terminal.

4. The photovoltaic power conversion system of the photovoltaic solar panel as described in claim 1, characterized in that, Each of the MOS transistors S1-S8 has a built-in or externally connected reverse parallel diode D.

5. The photovoltaic power conversion system of the photovoltaic solar panel as described in claim 1, characterized in that, A buffer capacitor is connected between the midpoint A of the bridge arm and the midpoint of the DC bus, and / or between the midpoint B of the bridge arm and the midpoint of the DC bus.

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