Isolated split-phase inverter circuit and control method thereof

Abstract

The invention discloses an isolation type split-phase inverter circuit and a control method thereof. The isolation type split-phase inverter circuit comprises an isolation DC / DC module circuit and a power frequency rectification module circuit. The isolation DC / DC module circuit comprises an input-side full bridge, a three-end transformer and two output-side circuits, an input-side winding of the three-end transformer is connected with a midpoint of a bridge arm of the input-side full bridge, and the input-side full bridge is connected with a filter capacitor C1 in parallel; two output side windings of the three-end transformer are respectively connected with corresponding output circuits through a resonance network circuit, the two output circuits are connected to a power frequency rectification module circuit through filter capacitors C4 and C5, and the negative electrode of the first output circuit and the positive electrode of the second output circuit are connected to form an interface N; the power frequency rectification module circuit comprises a rectification full-bridge circuit, and an interface L1 and an interface L2 are obtained after rectification. Through cooperative control of direct transmission of integrated topology and voltage signals, a complex parameter matching algorithm is not needed, breakthrough in structure simplification, energy conversion efficiency, control convenience, cost control and safety is achieved, and the method is suitable for various power conversion scenes.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic grid-connected inverter technology, and particularly relates to an isolated split-phase inverter circuit and its control method. Background Technology

[0002] With the rapid development of new energy technologies, photovoltaic systems, as a clean and sustainable form of energy utilization, are increasingly widely used in residential and commercial sectors. Among them, off-grid or hybrid photovoltaic systems often require inverters to achieve energy conversion, that is, to convert the low-voltage DC power output from solar panels or energy storage batteries into high-voltage AC power that meets the needs of electrical equipment.

[0003] In North America (such as the United States), the power system uses a special voltage standard, requiring two-phase voltages of 120V and 240V to meet the power needs of devices with different power ratings. Therefore, split-phase inverters have become key equipment in photovoltaic systems in this region. In practical applications, to ensure power safety and stable equipment operation, electrical isolation is usually required between the DC side (such as energy storage batteries and photovoltaic modules) and the AC side (such as the power grid and loads). Therefore, isolated split-phase inverters have become an important choice for energy storage and photovoltaic applications. They use isolation components such as transformers to cut off the direct electrical connection between the DC and AC sides, effectively avoiding the risks to equipment and personnel caused by faults such as leakage and surges, while also reducing common-mode interference and improving the reliability of system operation.

[0004] However, existing isolated split-phase inverters still have many shortcomings in energy storage applications, mainly in the following aspects: Traditional isolated split-phase inverters often employ multi-stage power conversion schemes, typically requiring multiple series stages such as a boost converter circuit, an isolated DC / DC converter circuit, and a power frequency inverter circuit to achieve the conversion from low-voltage DC to split-phase AC. Each stage requires a large number of power switches, inductors, capacitors, and other components, resulting in a large overall circuit size, low integration, and an increased probability of failure due to the increased number of components. Summary of the Invention

[0005] To address the technical deficiencies of existing isolated phase-splitting inverters, this application proposes an isolated phase-splitting inverter circuit. Through optimized circuit topology and integrated design, the control core of this circuit focuses on the dual-loop control of the isolated DC / DC module and the timing control of the power frequency rectifier module. The two achieve coordination through direct transmission of voltage signals, eliminating the need for complex multi-stage parameter matching algorithms. This effectively solves the core defects of existing isolated phase-splitting inverters and achieves breakthroughs in structure, efficiency, control, cost, and safety.

[0006] Specifically, the isolated split-phase inverter circuit of the present invention includes an isolated DC / DC module circuit and a power frequency rectifier module circuit; The isolated DC / DC module circuit includes an input-side full bridge, a three-terminal transformer, and two output-side circuits. The input winding of the three-terminal transformer is connected to the midpoint of the bridge arm of the input full bridge. The input-side full bridge is connected in parallel with the filter capacitor C1; The first output winding of the three-terminal transformer is connected to the first output circuit through a first resonant network circuit; the first output circuit is connected to the power frequency rectifier module circuit through a filter capacitor C4. The first output winding of the three-terminal transformer is connected to the second output circuit through the second resonant network circuit; the second output circuit is connected to the power frequency rectifier module circuit through the filter capacitor C5. The negative terminal of the first output circuit is connected to the positive terminal of the second output circuit as interface N; The power frequency rectifier module circuit includes a full-bridge rectifier circuit, which rectifies and isolates the voltage of the DC / DC module circuit to obtain interfaces L1 and L2.

[0007] Preferably, the input-side full bridge includes MOSFETs Q2 and Q3 connected in series with the input-side windings; The resonant network circuit adopts a symmetrical topology structure, which is composed of three inductor elements and three capacitor elements. The three inductor elements are connected in a delta configuration to form a closed inductor branch, and the three capacitor elements are also connected in a delta configuration to form a closed capacitor branch. The inductor branch and the capacitor branch are coupled to each other through preset nodes to form a resonant network with four-port transmission characteristics. The first output circuit includes a first high-voltage side full-bridge circuit, which is composed of MOSFETs Q5, Q6, Q7, and Q8. The second output circuit includes a second high-voltage side full-bridge circuit, which is composed of MOSFETs Q9, Q10, Q11, and Q12.

[0008] Preferably, one end of the first output winding is connected to the midpoint of the bridge arm of the first high-voltage side full-bridge circuit through the first resonant network circuit, and the other end is connected to the resonant inductor L6 through the first resonant network circuit; the first high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C2.

[0009] Preferably, one end of the second output winding is connected to the midpoint of the bridge arm of the second high-voltage side full-bridge circuit through the second resonant network circuit, and the other end is connected to the resonant inductor L5 through the second resonant network circuit; the second high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C3.

[0010] Preferably, the power frequency rectifier module circuit includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series, and the midpoint of the bridge arm is connected to the interface L1; The third switch S3 and the fourth switch S4 are connected in series, and the midpoint of the bridge arm is connected to the interface L2.

[0011] Based on the same inventive concept, this application also proposes a control method for an isolated split-phase inverter circuit, comprising: The input DC voltage is inverted into a high-frequency square wave voltage by alternating conduction of the full bridge on the input side, and the energy is coupled to the first output winding and the second output winding through the input winding of the three-terminal transformer. The first output-side winding and the second output-side winding respectively transmit energy to the first high-voltage-side full bridge and the second high-voltage-side full bridge through the first resonant network circuit and the second resonant network circuit. The first high-voltage side full bridge and the second high-voltage side full bridge are voltage rectified and isolated by the power frequency rectifier module circuit and output by interface L1 and interface L2.

[0012] Preferably, voltage rectification and isolation are performed through a power frequency rectifier module circuit, and the output is provided through interfaces L1 and L2, specifically including: When the first switch S1 and the fourth switch S4 are turned on, the positive voltage of the first output circuit is output through interface L1, and the negative voltage of the second output circuit is output through interface L2, forming a half-cycle in which interface L1 is positive to interface N and interface L2 is negative to interface N. When the second switch S2 and the third switch S3 are turned on, the voltage direction is reversed, forming a half-cycle where interface L1 is negative to interface N and interface L2 is positive to interface N. Among them, a split-phase AC voltage with a phase difference of 180° is formed between interface L1 and interface L2, and interface N is the neutral line.

[0013] Furthermore, by detecting the output voltage VO1 of the first output circuit and comparing it with the given signal, an error signal is generated, which is then adjusted by a PI or PID controller to set the given value of the inner loop of the output current. Furthermore, the current of resonant inductor L5 or resonant inductor L6 is detected and compared with the given current output by the outer voltage loop. The phase shift angle of the full bridge on the input side is adjusted by a PI / PID controller to suppress current ripple and load disturbance.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This application integrates a three-terminal transformer and dual-output circuits into a compact power transmission unit, forming an input-side full-bridge, a three-terminal transformer, and two output-side circuits. The input winding of the three-terminal transformer is directly connected to the midpoint of the input-side full-bridge arm, and the two output windings correspond to the first and second output circuits, respectively. The two output circuits are cleverly interconnected through interface N, which significantly reduces the number of discrete components and external connection lines, reduces the impact of parasitic line parameters on system performance, simplifies the circuit layout, and improves the overall mechanical stability and electromagnetic interference resistance.

[0015] Furthermore, this application directly transmits the stable voltage output from the isolated DC / DC module to the power frequency rectifier module via filter capacitors C4 and C5. The full-bridge rectifier circuit rectifies this voltage according to a preset timing sequence, quickly outputting the required interface L1 and L2 voltages. This control logic not only simplifies the design complexity of the control system and shortens the debugging cycle, but also reduces the computing power requirements of the control chip, reduces algorithm development and maintenance costs, and improves the dynamic response speed of the system, ensuring stable output even under load fluctuations and other operating conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an isolated split-phase inverter circuit in this embodiment. Detailed Implementation

[0017] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0018] Specifically, such as Figure 1 As shown, the isolated split-phase inverter circuit of the present invention includes an isolated DC / DC module circuit and a power frequency rectifier module circuit; The isolated DC / DC module circuit includes an input-side full bridge, a three-terminal transformer, and two output-side circuits. The input winding of the three-terminal transformer is connected to the midpoint of the bridge arm of the input full bridge. The input-side full bridge is connected in parallel with the filter capacitor C1; The first output winding of the three-terminal transformer is connected to the first output circuit through a first resonant network circuit; the first output circuit is connected to the power frequency rectifier module circuit through a filter capacitor C4. The first output winding of the three-terminal transformer is connected to the second output circuit through the second resonant network circuit; the second output circuit is connected to the power frequency rectifier module circuit through the filter capacitor C5. The negative terminal of the first output circuit is connected to the positive terminal of the second output circuit as interface N; The power frequency rectifier module circuit includes a full-bridge rectifier circuit, which rectifies and isolates the voltage of the DC / DC module circuit to obtain interfaces L1 and L2.

[0019] In this application, both the input-side and output-side full-bridge circuits utilize MOSFETs. MOSFETs offer advantages such as high switching speed and low conduction loss, effectively reducing switching and conduction losses compared to traditional circuits using IGBTs or other switching devices. Simultaneously, the specialized winding design of the three-terminal transformer enables efficient energy transfer between the input and dual outputs, minimizing core and winding losses. Furthermore, the optimized configuration of filter capacitors C1, C4, and C5 further reduces voltage ripple, ensuring minimal energy loss during power transmission.

[0020] In this application, the three-terminal transformer achieves effective electrical isolation between the input side and the dual output side, with an isolation voltage level of over 2kV. Meanwhile, all MOSFETs in the full-bridge circuit are equipped with overcurrent and overvoltage protection mechanisms. When the circuit experiences overload, short circuit, or abnormal voltage, the control module can quickly cut off the drive signal of the corresponding MOSFET to achieve fault protection.

[0021] Preferably, the input-side full bridge includes MOSFETs Q2 and Q3 connected in series with the input-side windings; The resonant network circuit of this invention adopts a symmetrical topology, consisting of three inductors and three capacitors. The three inductors are connected in a delta configuration to form a closed inductive branch, and the three capacitors are also connected in a delta configuration to form a closed capacitive branch. These inductor and capacitor branches are coupled together through preset nodes, forming a resonant network with four-port transmission characteristics. This structure, through its symmetrical double-triangular topology design, effectively optimizes impedance matching between ports, reduces insertion loss and reflection interference during signal transmission, and, relying on the synergistic resonance effect of inductors and capacitors, enables signal gating and filtering within a specific frequency range. It is suitable for high-frequency communication, power electronics, and other technical fields with high requirements for transmission stability and frequency selectivity.

[0022] The first output circuit includes a first high-voltage side full-bridge circuit, which is composed of MOSFETs Q5, Q6, Q7, and Q8; wherein MOSFETs Q5 and Q6 are connected in series, MOSFETs Q7 and Q8 are connected in series, and MOSFETs Q5 and Q6 are connected in parallel with MOSFETs Q7 and Q8.

[0023] The second output circuit includes a second high-voltage side full-bridge circuit, which is composed of MOSFETs Q9, Q10, Q11, and Q12. MOSFETs Q9 and Q10 are connected in series, MOSFETs Q11 and Q12 are connected in series, and MOSFETs Q9 and Q10 are connected in parallel with MOSFETs Q11 and Q12.

[0024] Preferably, one end of the first output winding is connected to the midpoint of the bridge arm of the first high-voltage side full-bridge circuit through the first resonant network circuit, and the other end is connected to the resonant inductor L6 through the first resonant network circuit; the first high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C2.

[0025] Preferably, one end of the second output winding is connected to the midpoint of the bridge arm of the second high-voltage side full-bridge circuit through the second resonant network circuit, and the other end is connected to the resonant inductor L5 through the second resonant network circuit; the second high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C3.

[0026] It should be noted that in this embodiment, resonant inductors L5 and L6 can effectively suppress current spikes in the circuit and reduce stress on switching devices. Filter capacitors C2 and C3 further filter out high-frequency ripple on the output side, forming a multi-stage filtering system with the front-end filter capacitors C1, C4, and C5, which significantly improves the stability of the output voltage.

[0027] Preferably, the power frequency rectifier module circuit includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series, and the midpoint of the bridge arm is connected to the interface L1; The third switch S3 and the fourth switch S4 are connected in series, and the midpoint of the bridge arm is connected to the interface L2.

[0028] Example 2: This application also proposes a control method for an isolated split-phase inverter circuit, including: The input DC voltage is inverted into a high-frequency square wave voltage by alternating conduction of the full-bridge circuit on the input side. This voltage is then coupled to the first and second output windings via the input windings of the three-terminal transformer. In other words, the input DC voltage is inverted into a high-frequency square wave voltage by alternating conduction of MOSFETs Q1, Q2, Q3, and Q4 on the input full-bridge circuit. The control module outputs a drive signal to alternately conduct the two bridge arms of MOSFETs Q1 and Q4, and MOSFETs Q2 and Q3, with the conduction frequency set to 20kHz-50kHz, thus generating a high-frequency square wave voltage that is applied to the input windings of the three-terminal transformer.

[0029] The first output-side winding and the second output-side winding respectively transmit energy to the first high-voltage-side full bridge and the second high-voltage-side full bridge through the first resonant network circuit and the second resonant network circuit. The first high-voltage side full bridge and the second high-voltage side full bridge are voltage rectified and isolated by the power frequency rectifier module circuit and output by interface L1 and interface L2.

[0030] Preferably, voltage rectification and isolation are performed through a power frequency rectifier module circuit, and the output is provided through interfaces L1 and L2, specifically including: When the first switch S1 and the fourth switch S4 are turned on, the positive voltage of the first output circuit is output through interface L1, and the negative voltage of the second output circuit is output through interface L2, forming a half-cycle in which interface L1 is positive to interface N and interface L2 is negative to interface N. When the second switch S2 and the third switch S3 are turned on, the voltage direction is reversed, forming a half-cycle where interface L1 is negative to interface N and interface L2 is positive to interface N. Among them, a split-phase AC voltage with a phase difference of 180° is formed between interface L1 and interface L2, and interface N is the neutral line.

[0031] Furthermore, by detecting the output voltage VO1 of the first output circuit and comparing it with the given signal, an error signal is generated, which is then adjusted by a PI or PID controller to set the given value of the inner loop of the output current. Furthermore, the current in resonant inductor L5 or L6 is detected and compared with the given current output from the outer voltage loop. The phase shift angle of the full-bridge input is adjusted by a PI / PID controller to suppress current ripple and load disturbances. The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. An isolated split-phase inverter circuit, characterized in that, This includes isolated DC / DC module circuits and power frequency rectifier module circuits; The isolated DC / DC module circuit includes an input-side full bridge, a three-terminal transformer, and two output-side circuits. The input winding of the three-terminal transformer is connected to the midpoint of the bridge arm of the input full bridge. The input-side full bridge is connected in parallel with the filter capacitor C1; The first output winding of the three-terminal transformer is connected to the first output circuit through a first resonant network circuit; the first output circuit is connected to the power frequency rectifier module circuit through a filter capacitor C4. The first output winding of the three-terminal transformer is connected to the second output circuit through the second resonant network circuit; the second output circuit is connected to the power frequency rectifier module circuit through the filter capacitor C5. The negative terminal of the first output circuit is connected to the positive terminal of the second output circuit as interface N; The power frequency rectifier module circuit includes a full-bridge rectifier circuit, which rectifies and isolates the voltage of the DC / DC module circuit to obtain interfaces L1 and L2.

2. The isolated split-phase inverter circuit according to claim 1, characterized in that, The input-side full bridge includes MOSFETs Q2 and Q3 connected in series with the input-side windings; Both the first and second resonant network circuits adopt a symmetrical topology and are composed of three inductor elements and three capacitor elements. The three inductor elements form a closed inductor branch in a delta connection manner, and the three capacitor elements also form a closed capacitor branch in a delta connection manner. The inductor branch and the capacitor branch are coupled to each other through a preset node to form a resonant network with four-port transmission characteristics. The first output circuit includes a first high-voltage side full-bridge circuit, which is composed of MOSFETs Q5, Q6, Q7, and Q8. The second output circuit includes a second high-voltage side full-bridge circuit, which is composed of MOSFETs Q9, Q10, Q11, and Q12.

3. The isolated split-phase inverter circuit according to claim 2, characterized in that, One end of the first output winding is connected to the midpoint of the bridge arm of the first high-voltage side full-bridge circuit through the first resonant network circuit, and the other end is connected to the resonant inductor L6 through the first resonant network circuit; the first high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C2.

4. The isolated split-phase inverter circuit according to claim 3, characterized in that, One end of the second output winding is connected to the midpoint of the bridge arm of the second high-voltage side full-bridge circuit through the second resonant network circuit, and the other end is connected to the resonant inductor L5 through the second resonant network circuit; the second high-voltage side full-bridge circuit is also connected in parallel with a filter capacitor C3.

5. The isolated split-phase inverter circuit according to claim 4, characterized in that, The power frequency rectifier module circuit includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series, and the midpoint of the bridge arm is connected to the interface L1; The third switch S3 and the fourth switch S4 are connected in series, and the midpoint of the bridge arm is connected to the interface L2.

6. A control method for an isolated split-phase inverter circuit according to any one of claims 1-5, characterized in that, include: The input DC voltage is inverted into a high-frequency square wave voltage by alternating conduction of the full bridge on the input side, and the energy is coupled to the first output winding and the second output winding through the input winding of the three-terminal transformer. The first output-side winding and the second output-side winding respectively transmit energy to the first high-voltage-side full bridge and the second high-voltage-side full bridge through the first resonant network circuit and the second resonant network circuit. The first high-voltage side full bridge and the second high-voltage side full bridge are voltage rectified and isolated by the power frequency rectifier module circuit and output by interface L1 and interface L2.

7. The control method according to claim 6, characterized in that, include: Voltage rectification and isolation are performed through a power frequency rectifier module circuit, and the output is provided through interfaces L1 and L2. Specifically, this includes: When the first switch S1 and the fourth switch S4 are turned on, the positive voltage of the first output circuit is output through interface L1, and the negative voltage of the second output circuit is output through interface L2, forming a half-cycle in which interface L1 is positive to interface N and interface L2 is negative to interface N. When the second switch S2 and the third switch S3 are turned on, the voltage direction is reversed, forming a half-cycle where interface L1 is negative to interface N and interface L2 is positive to interface N. Among them, a split-phase AC voltage with a phase difference of 180° is formed between interface L1 and interface L2, and interface N is the neutral line.

8. The control method according to claim 7, characterized in that, Also includes: The output voltage VO1 of the first output circuit is detected and compared with the given signal to generate an error signal. This error signal is then adjusted by a PI or PID controller to determine the given value of the inner loop of the output current.

9. The control method according to claim 8, characterized in that, Also includes: The current of resonant inductor L5 or L6 is detected and compared with the given current output by the outer voltage loop. The phase shift angle of the full bridge on the input side is adjusted by the PI / PID controller to suppress current ripple and load disturbance.

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