High-Efficiency Non-Isolated Split-Phase Inverter and Its Control Method

Abstract

The present invention provides a high-efficiency non-isolated split-phase inverter and a control method thereof. The inverter includes: a voltage divider unit; a first inverter bridge arm and a second inverter bridge arm, for inverting the DC power output by the DC bus power supply into AC power to obtain an AC signal; a filter unit, one end of which is connected to the midpoint of the first inverter bridge arm and the other end of which is connected to the midpoint of the second inverter bridge arm, for filtering the AC signal to obtain a target AC signal; a first freewheeling bridge arm and a second freewheeling bridge arm, one end of the first freewheeling bridge arm being connected to the voltage divider unit and the other end being connected to the midpoint of the first inverter bridge arm, and one end of the second freewheeling bridge arm being connected to the voltage divider unit and the other end being connected to the midpoint of the second inverter bridge arm, for freewheeling the target AC signal; and a mode switching unit for switching the high-efficiency non-isolated split-phase inverter between a grid-connected operating mode and an off-grid operating mode. Thus, the efficiency, cost, and functionality of the inverter can be balanced.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a high-efficiency non-isolated split-phase inverter and a control method for the high-efficiency non-isolated split-phase inverter. Background Art

[0002] Among small and medium-power non-isolated grid-connected inverters, three-level topologies dominate the market due to their high efficiency and low common-mode voltage. Among them, T-type three-level topologies and Heric topologies are the mainstream.

[0003] In related technologies, when using the Heric topology for off-grid operation, an industrial frequency autotransformer is required. This transformer is large in size and heavy, and the overall cost of the system is very high. The T-type three-level topology has low conversion efficiency and places great demands on heat dissipation capabilities. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-efficiency non-isolated split-phase inverter. A mode switching unit is added to the T-type three-level topology structure to switch the working mode of the high-efficiency non-isolated split-phase inverter, thereby improving the conversion efficiency of the high-efficiency non-isolated split-phase inverter when working in grid-connected mode and reducing heat generation. When off-grid split-phase output is required, there is no need to add an additional power frequency autotransformer, thus taking into account efficiency, cost and function.

[0005] The technical solution adopted in the present invention is as follows:

[0006] A high-efficiency non-isolated split-phase inverter comprises: a voltage divider unit, wherein the voltage divider module is connected to a DC bus power supply; a first inverter bridge arm and a second inverter bridge arm, wherein one end of the first inverter bridge arm is connected to one end of the DC bus power supply, and the other end of the first inverter bridge arm is connected to the other end of the DC bus power supply, and one end of the second inverter bridge arm is connected to one end of the DC bus power supply, and the other end of the second inverter bridge arm is connected to the other end of the DC bus power supply, wherein the first inverter bridge arm and the second inverter bridge arm are used to invert the DC power output by the DC bus power supply into AC power to obtain an AC power signal; a filter unit, wherein one end of the filter unit is connected to the midpoint of the first inverter bridge arm, and the other end of the filter unit is connected to the midpoint of the second inverter bridge arm, and the filter The unit is used to filter the AC power signal to obtain a target AC power signal; a first freewheeling bridge arm and a second freewheeling bridge arm, one end of the first freewheeling bridge arm is connected to the voltage divider unit, the other end of the first freewheeling bridge arm is connected to the midpoint of the first inverter bridge arm, one end of the second freewheeling bridge arm is connected to the voltage divider unit, the other end of the second freewheeling bridge arm is connected to the midpoint of the second inverter bridge arm, the first freewheeling bridge arm and the second freewheeling bridge arm are used to freewheel the target AC power signal; a mode switching unit, one end of the mode switching unit is connected to the midpoint of the first freewheeling bridge arm, the other end of the mode switching unit is connected to the midpoint of the second freewheeling bridge arm, the mode switching unit is used to switch the high-efficiency non-isolated split-phase inverter between a grid-connected working mode and an off-grid working mode.

[0007] The voltage divider module includes a first voltage divider capacitor and a second voltage divider capacitor, wherein one end of the first voltage divider capacitor is connected to one end of the DC bus power supply, the other end of the first voltage divider capacitor is connected to one end of the second voltage divider capacitor, and the other end of the second voltage divider capacitor is connected to the other end of the DC bus power supply.

[0008] The first inverter bridge arm includes a first switching tube and a second switching tube, one end of the first switching tube is connected to one end of the DC bus power supply, the other end of the first switching tube is connected to one end of the second switching tube, and the other end of the second switching tube is connected to the other end of the DC bus power supply; the second inverter bridge arm includes a third switching tube and a fourth switching tube, one end of the third switching tube is connected to one end of the DC bus power supply, the other end of the third switching tube is connected to one end of the fourth switching tube, and the other end of the fourth switching tube is connected to the other end of the DC bus power supply.

[0009] The filtering unit includes: a first filter inductor, one end of which is connected to the other end of the first switching tube; a first filter capacitor, one end of which is connected to the other end of the first filter inductor, and the other end of the first filter capacitor is connected to the other end of the first voltage divider capacitor; a second filter capacitor, one end of which is connected to the other end of the first filter capacitor; and a second filter inductor, one end of which is connected to the other end of the second filter capacitor, and the other end of the second filter inductor is connected to the other end of the third switching tube.

[0010] The first freewheeling bridge arm includes a fifth switching tube and a sixth switching tube, one end of the fifth switching tube is connected to the other end of the first voltage-dividing capacitor, the other end of the fifth switching tube is connected to one end of the sixth switching tube, and the other end of the sixth switching tube is connected to the other end of the first switching tube; the second freewheeling bridge arm includes a seventh switching tube and an eighth switching tube, one end of the seventh switching tube is connected to the other end of the first voltage-dividing capacitor, the other end of the seventh switching tube is connected to one end of the eighth switching tube, and the other end of the eighth switching tube is connected to the other end of the third switching tube.

[0011] The mode switching unit includes a relay, one end of the relay is connected to the other end of the fifth switch tube, and the other end of the relay is connected to the other end of the seventh switch tube.

[0012] A control method for a high-efficiency non-isolated split-phase inverter comprises the following steps: obtaining a control instruction and identifying the control instruction; if the control instruction is identified as an instruction for controlling the high-efficiency non-isolated split-phase inverter to operate in a grid-connected mode, controlling the relay to close, wherein, when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle modulation mode, the first switch tube, the fourth switch tube, and the sixth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube, the seventh switch tube, and the eighth switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle freewheeling mode, the sixth switch tube and the eighth switch tube are controlled to be turned off. The eighth switch tube is turned on, and the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switch tube, the third switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube and the seventh switch tube are controlled to be turned on. The second switch tube, the third switch tube and the fourth switch tube are turned off; if the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in an off-grid working mode, the relay is controlled to be turned off, wherein, when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle modulation mode, the first switch tube, the fourth switch tube, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on. When the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switch tube, the third switch tube, the fifth switch tube, and the eighth switch tube are controlled to be turned on, and the first switch tube, the fourth switch tube, the sixth switch tube, and the seventh switch tube are controlled to be turned on; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube, and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube are controlled to be turned off.

[0013] Beneficial effects of the present invention:

[0014] The present invention adds a mode switching unit on the basis of the T-type three-level topology structure to switch the operating mode of the high-efficiency non-isolated split-phase inverter, thereby improving the conversion efficiency of the high-efficiency non-isolated split-phase inverter when working on the grid and reducing heat. In addition, when off-grid split-phase output is required, there is no need to add an additional power frequency autotransformer, thus taking into account efficiency, cost and function. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention;

[0016] Figure 2a This is a schematic diagram of a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention in a positive half-cycle modulation mode when connected to the grid;

[0017] Figure 2b Schematic diagram of a high-efficiency non-isolated split-phase inverter in a positive half-cycle freewheeling mode when connected to the grid according to an embodiment of the present invention;

[0018] Figure 2c This is a schematic diagram of a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention in a negative half-cycle modulation mode when connected to the grid;

[0019] Figure 2d Schematic diagram of a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention in a freewheeling mode in a negative half cycle when connected to the grid;

[0020] Figure 3a This is a schematic diagram of a high-efficiency non-isolated split-phase inverter according to another embodiment of the present invention in a freewheeling mode in a positive half-cycle when connected to the grid;

[0021] Figure 3b Schematic diagram of a high-efficiency non-isolated split-phase inverter according to another embodiment of the present invention in a negative half-cycle freewheeling mode when connected to the grid;

[0022] Figure 4a Schematic diagram of a high-efficiency non-isolated split-phase inverter in a positive half-cycle modulation mode when operating off-grid according to an embodiment of the present invention;

[0023] Figure 4b Schematic diagram of a high-efficiency non-isolated split-phase inverter in a positive half-cycle freewheeling mode when operating off-grid according to an embodiment of the present invention;

[0024] Figure 4c Schematic diagram of a high-efficiency non-isolated split-phase inverter in a negative half-cycle modulation mode when operating off-grid according to an embodiment of the present invention;

[0025] Figure 4dSchematic diagram of a high-efficiency non-isolated split-phase inverter in a negative half-cycle freewheeling mode when operating off-grid according to an embodiment of the present invention;

[0026] Figure 5 Flowchart of a control method for a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Figure 1 4 is a schematic structural diagram of a high-efficiency non-isolated split-phase inverter according to an embodiment of the present invention.

[0029] like Figure 1 As shown, the high-efficiency non-isolated split-phase inverter of an embodiment of the present invention may include: a voltage divider unit 100, a first inverter bridge arm 200, a second inverter bridge arm 300, a filter unit 400, a first freewheeling bridge arm 500 and a second freewheeling bridge arm 600 and a mode switching unit 700.

[0030] Among them, the voltage divider module 100 is connected to the DC bus power supply; one end of the first inverter bridge arm 200 is connected to one end of the DC bus power supply, the other end of the first inverter bridge arm 200 is connected to the other end of the DC bus power supply, one end of the second inverter bridge arm 300 is connected to one end of the DC bus power supply, and the other end of the second inverter bridge arm 300 is connected to the other end of the DC bus power supply, wherein the first inverter bridge arm 200 and the second inverter bridge arm 300 are used to invert the DC power output by the DC bus power supply into AC power to obtain an AC signal; one end of the filter unit 400 is connected to the midpoint of the first inverter bridge arm 200, and the other end of the filter unit 400 is connected to the midpoint of the second inverter bridge arm 300, and the filter unit 400 is used to invert the AC signal Filtering is performed to obtain the target AC power signal; one end of the first freewheeling bridge arm 500 is connected to the voltage divider unit, the other end of the first freewheeling bridge arm 500 is connected to the midpoint of the first inverter bridge arm 200, one end of the second freewheeling bridge arm 600 is connected to the voltage divider unit, the other end of the second freewheeling bridge arm 600 is connected to the midpoint of the second inverter bridge arm 300, the first freewheeling bridge arm 500 and the second freewheeling bridge arm 600 are used to freewheel the target AC power signal; one end of the mode switching unit 700 is connected to the midpoint of the first freewheeling bridge arm 500, the other end of the mode switching unit 700 is connected to the midpoint of the second freewheeling bridge arm 500, the mode switching unit 700 is used to switch the high-efficiency non-isolated split-phase inverter between the grid-connected working mode and the off-grid working mode.

[0031] According to one embodiment of the present invention, Figure 1 As shown, the voltage divider module 100 includes a first voltage divider capacitor C1 and a second voltage divider capacitor C2, wherein one end of the first voltage divider capacitor C1 is connected to one end of the DC bus power supply, the other end of the first voltage divider capacitor C1 is connected to one end of the second voltage divider capacitor C2, and the other end of the second voltage divider capacitor C2 is connected to the other end of the DC bus power supply.

[0032] According to one embodiment of the present invention, Figure 1 As shown, the first inverter bridge arm 200 includes a first switching tube Q1 and a second switching tube Q2, where one end of the first switching tube Q1 is connected to one end of the DC bus power supply, the other end of the first switching tube Q1 is connected to one end of the second switching tube Q2, and the other end of the second switching tube Q2 is connected to the other end of the DC bus power supply; the second inverter bridge arm 300 includes a third switching tube Q3 and a fourth switching tube Q4, where one end of the third switching tube Q3 is connected to one end of the DC bus power supply, the other end of the third switching tube Q3 is connected to one end of the fourth switching tube Q4, and the other end of the fourth switching tube Q4 is connected to the other end of the DC bus power supply.

[0033] According to one embodiment of the present invention, Figure 1 As shown, the filtering unit 400 includes: a first filter inductor L1, one end of the first filter inductor L1 is connected to the other end of the first switch tube Q1; a first filter capacitor C3, one end of the first filter capacitor C3 is connected to the other end of the first filter inductor L1, and the other end of the first filter capacitor C3 is connected to the other end of the first voltage-dividing capacitor C1; a second filter capacitor C4, one end of the second filter capacitor C4 is connected to the other end of the first filter capacitor C3; a second filter inductor L2, one end of the second filter inductor L2 is connected to the other end of the second filter capacitor C4, and the other end of the second filter inductor L2 is connected to the other end of the third switch tube Q3.

[0034] According to one embodiment of the present invention, Figure 1 As shown, the first freewheeling bridge arm 500 includes a fifth switch tube Q5 and a sixth switch tube Q6, one end of the fifth switch tube Q5 is connected to the other end of the first voltage-dividing capacitor C1, the other end of the fifth switch tube Q5 is connected to one end of the sixth switch tube Q6, and the other end of the sixth switch tube Q6 is connected to the other end of the first switch tube Q1; the second freewheeling bridge arm 600 includes a seventh switch tube Q7 and an eighth switch tube Q8, one end of the seventh switch tube Q7 is connected to the other end of the first voltage-dividing capacitor C1, the other end of the seventh switch tube Q7 is connected to one end of the eighth switch tube Q8, and the other end of the eighth switch tube Q8 is connected to the other end of the third switch tube Q3.

[0035] According to one embodiment of the present invention, Figure 1As shown, the mode switching unit 700 includes a relay K1, one end of the relay K1 is connected to the other end of the fifth switch tube Q5, and the other end of the relay K1 is connected to the other end of the seventh switch tube Q7. Among them, the other end of the fifth switch tube Q5 can serve as the midpoint of the first freewheeling bridge arm 500, and the other end of the seventh switch tube Q7 can serve as the midpoint of the second freewheeling bridge arm 600. In other words, one end of the relay K1 is connected to the midpoint of the first freewheeling bridge arm 500, and the other end of the relay K1 is connected to the midpoint of the second freewheeling bridge arm 600.

[0036] Specifically, based on the high-efficiency non-isolated split-phase inverter of the above embodiment, by adding a mode switching unit 700 composed of a relay K1 to the structure of the T-type three-level topology, switching the conduction state of relay K1, and adjusting the corresponding control strategy, the high-efficiency non-isolated split-phase inverter operates in a Heric structure when connected to the grid, achieving high conversion efficiency and low heat generation. When off-grid split-phase output is required, the high-efficiency non-isolated split-phase inverter operates in a T-type three-level topology mode, eliminating the need for an additional power-frequency autotransformer, and achieving a balance between efficiency, cost, and functionality.

[0037] The following describes in detail how to switch the operating mode of a high-efficiency non-isolated split-phase inverter with reference to specific embodiments.

[0038] Specifically, when connected to the grid, relay K1 is closed. At this time, the high-efficiency non-isolated split-phase inverter has four working modes, namely positive half-cycle modulation mode, positive half-cycle freewheeling mode, negative half-cycle modulation mode and negative half-cycle freewheeling mode. Ignoring the dead time, the control modes of each component in the high-efficiency non-isolated split-phase inverter are as follows: Figures 2a-2d shown.

[0039] like Figure 2a As shown, the first switch tube Q1, the fourth switch tube Q4 and the sixth switch tube Q6 are controlled to be turned on, and the second switch tube Q2, the third switch tube Q3, the fifth switch tube Q5, the seventh switch tube Q7 and the eighth switch tube Q8 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle modulation mode; Figure 2b As shown, the sixth switch tube Q6 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the second switch tube Q2, the third switch tube Q3, the fourth switch tube Q4, the fifth switch tube Q5 and the seventh switch tube Q7 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle freewheeling mode; Figure 2c As shown, the second switch tube Q2, the third switch tube Q3 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the fourth switch tube Q4, the fifth switch tube Q5, the sixth switch tube Q6 and the seventh switch tube Q7 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode; Figure 2dAs shown, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode.

[0040] It should be noted that when working in grid-connected mode, another modulation method can also be used to clamp the common-mode voltage to the bus midpoint during the inductor current freewheeling phase, thereby reducing common-mode voltage noise and optimizing EMC performance.

[0041] Specifically, when the high-efficiency non-isolated split-phase inverter is connected to the grid, when the grid is in the positive half-frequency cycle, the high-efficiency non-isolated split-phase inverter can be connected to the grid according to the Figure 2a The modulation method shown is used. At this time, the fifth switch tube Q5 and the seventh switch tube Q7 are in the off state, and the inverter common mode voltage is half of the bus input voltage. When the first switch tube Q1 and the fourth switch tube Q4 are turned off, the first filter inductor L1 and the second filter inductor L2 are freewheeling through the sixth switch tube Q6 and the eighth switch tube Q8. At this time, according to Figure 3a As shown, the seventh switch tube Q7 can be controlled to be turned on, so that the common terminal of the sixth switch tube Q6 and the eighth switch tube Q8 is forcibly clamped to the bus midpoint through the channel and body diode of the seventh switch tube Q7 and the body diode of the fifth switch tube Q5. At this time, the common-mode voltage of the high-efficiency non-isolated split-phase inverter is still half of the bus voltage (assuming that the two half-bus voltages are balanced).

[0042] When the grid is in the negative half-frequency cycle, the high-efficiency non-isolated split-phase inverter can be used according to Figure 2c The modulation method shown is used. At this time, the fifth switch tube Q5 and the seventh switch tube Q7 are in the off state, and the inverter common mode voltage is half of the bus input voltage. When the second switch tube Q2 and the third switch tube Q3 are turned off, the first filter inductor L1 and the second filter inductor L2 are freewheeling through the sixth switch tube Q6 and the eighth switch tube Q8. At this time, according to Figure 3b As shown, the fifth switch tube Q5 can be controlled to be turned on, so that the common end point of the sixth switch tube Q6 and the eighth switch tube Q8 can be forcibly clamped to the bus midpoint through the channel and body diode of the fifth switch tube Q5 and the body diode of the seventh switch tube Q7. At this time, the common mode voltage of the high-efficiency non-isolated split-phase inverter is still half of the bus voltage (assuming that the two half-bus voltages are balanced). Since the output capacitance of the switch tube is small, it is easy to resonate with parasitic inductances such as PCB traces, resulting in large oscillations of the common mode voltage in the traditional Heric topology during the inductor current freewheeling stage. Therefore, the method of forcibly clamping to the bus midpoint during the freewheeling stage proposed in the embodiment of the present invention can effectively absorb part of the oscillation energy, reduce the amplitude of the oscillation, reduce the noise source of EMC, and improve EMC performance.

[0043] Furthermore, when working off-grid, relay K1 is disconnected. At this time, the high-efficiency non-isolated split-phase inverter has a total of four working modes, namely positive half-cycle modulation mode, positive half-cycle freewheeling mode, negative half-cycle modulation mode and negative half-cycle freewheeling mode. Ignoring the dead time, the control methods of each component in the high-efficiency non-isolated split-phase inverter are as follows: Figures 4a-4d shown.

[0044] Specifically, if Figure 4a As shown, the first switch tube Q1, the fourth switch tube Q4, the sixth switch tube Q6 and the eighth switch tube Q8 can be controlled to be turned on, and the second switch tube Q2, the third switch tube Q3, the fifth switch tube Q5 and the seventh switch tube Q7 can be controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle modulation mode; Figure 4b As shown, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle freewheeling mode; Figure 4c As shown, the second switch tube Q2, the third switch tube Q3, the fifth switch tube Q5 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the fourth switch tube Q4, the sixth switch tube Q6 and the seventh switch tube Q7 are controlled to be turned on, so that the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode; Figure 4d As shown, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are controlled to be turned on, and the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 are controlled to be turned off, so that the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode.

[0045] Therefore, a mode switching unit is added on the basis of the T-type three-level topology structure to switch the working mode of the high-efficiency non-isolated split-phase inverter, thereby improving the conversion efficiency of the high-efficiency non-isolated split-phase inverter when working on the grid and reducing heat. In addition, when off-grid split-phase output is required, there is no need to add an additional power frequency autotransformer, thus taking into account efficiency, cost and function.

[0046] It is understandable that due to the long-term operation of relay K1, it may become sticky or unable to close. If the relay K1 is damaged and power conversion is still carried out, it will cause damage to the switching tube. Therefore, it is necessary to perform a self-test of relay K1 before starting the machine.

[0047] Specifically, first, the voltage between the other end of relay K1 and the busbar negative (reference ground of the control system) can be detected. At this time, the voltage should be equal to the busbar midpoint voltage. Secondly, the relay K1 is attracted, and after a delay is made to ensure that the relay K1 is fully actuated, the first switch Q1 is turned on for a short time (for example, 1ms). At the same time, the voltage between the other end of relay K1 and the busbar negative (reference ground of the control system) is detected again. If the voltage is still equal to the busbar midpoint voltage, it means that the relay K1 has failed and cannot be attracted. If the voltage is approximately equal to the busbar voltage, it means that the relay K1 can be attracted normally and the first switch Q1 is turned off. Then, the drive of relay K1 is disconnected, and a delay is made to wait for the inductor current to drop to 0. The first switch Q1 is turned on again for a short time (for example, 1ms). At the same time, the voltage between the other end of relay K1 and the busbar negative (reference ground of the control system) is detected again. If the voltage is equal to the busbar midpoint voltage, it means that the relay K1 is working abnormally and a adhesion fault has occurred. If the voltage is equal to the busbar voltage, it means that the relay K1 is working abnormally and a adhesion fault has occurred.

[0048] In addition to performing self-test on the relay K1 in the above manner, self-test can also be completed by detecting the voltage between one end of the relay K1 and the bus negative (reference ground of the control system) in cooperation with the third switch tube Q3.

[0049] In summary, according to the high-efficiency non-isolated split-phase inverter of the embodiment of the present invention, the voltage divider module is connected to the DC bus power supply, one end of the first inverter bridge arm is connected to one end of the DC bus power supply, the other end of the first inverter bridge arm is connected to the other end of the DC bus power supply, one end of the second inverter bridge arm is connected to one end of the DC bus power supply, and the other end of the second inverter bridge arm is connected to the other end of the DC bus power supply, wherein the first inverter bridge arm and the second inverter bridge arm are used to invert the DC power output by the DC bus power supply into AC power to obtain an AC signal, and one end of the filter unit is connected to the midpoint of the first inverter bridge arm. The first freewheeling bridge arm is connected to the first inverter bridge arm, the other end of the filtering unit is connected to the midpoint of the second inverter bridge arm, the filtering unit is used to filter the AC signal to obtain the target AC signal, one end of the first freewheeling bridge arm is connected to the voltage divider unit, the other end of the first freewheeling bridge arm is connected to the midpoint of the first inverter bridge arm, one end of the second freewheeling bridge arm is connected to the voltage divider unit, the other end of the second freewheeling bridge arm is connected to the midpoint of the second inverter bridge arm, the first freewheeling bridge arm and the second freewheeling bridge arm are used to freewheel the target AC signal, and the mode switching unit is used to switch the high-efficiency non-isolated split-phase inverter between the grid-connected working mode and the off-grid working mode. Therefore, a mode switching unit is added on the basis of the T-type three-level topology structure to switch the working mode of the high-efficiency non-isolated split-phase inverter, improve the conversion efficiency of the high-efficiency non-isolated split-phase inverter when working on the grid, reduce heat generation, and when off-grid split-phase output is required, there is no need to add an additional power frequency autotransformer, taking into account efficiency, cost and function.

[0050] Based on the high-efficiency non-isolated split-phase inverter of the above embodiment, the present invention further proposes a control method for the high-efficiency non-isolated split-phase inverter.

[0051] like Figure 5 As shown, the control method of the high-efficiency non-isolated split-phase inverter according to the embodiment of the present invention may include the following steps:

[0052] S1, obtain control instructions and identify the control instructions.

[0053] S2, if the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in the grid-connected working mode, the control relay is closed. Among them, when the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle modulation mode, the first switch tube, the fourth switch tube and the sixth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle freewheeling mode, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switch tube, the third switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube and the eighth switch tube are controlled to be turned off. When the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are controlled to be turned off.

[0054] S3: If the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in an off-grid operation mode, the control relay is turned off. Among them, when the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle modulation mode, the first switch tube, the fourth switch tube, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the positive half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switch tube, the third switch tube, the fifth switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the fourth switch tube, the sixth switch tube and the seventh switch tube are controlled to be turned on; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are controlled to be turned off.

[0055] It should be noted that the control method of the high-efficiency non-isolated split-phase inverter according to the embodiment of the present invention can refer to the above-mentioned embodiment of the high-efficiency non-isolated split-phase inverter, which will not be described in detail here.

[0056] According to the control method of the high-efficiency non-isolated split-phase inverter of the embodiment of the present invention, a control instruction is obtained and identified, and when the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in a grid-connected working mode, the relay is controlled to close, wherein, when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle modulation mode, the first switch tube, the fourth switch tube and the sixth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle freewheeling mode , control the sixth switch tube and the eighth switch tube to be turned on, and control the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube and the seventh switch tube to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, control the second switch tube, the third switch tube and the eighth switch tube to be turned on, and control the first switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube and the seventh switch tube to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, control the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube to be turned on, and control the first switch tube , the second switch tube, the third switch tube and the fourth switch tube are turned off, and when the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to work in the off-grid working mode, the relay is controlled to be turned off, wherein, when the high-efficiency non-isolated split-phase inverter works in the positive half-cycle modulation mode, the first switch tube, the fourth switch tube, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter works in the positive half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on. The eighth switch is turned on and controls the first, second, third, and fourth switches to be turned off. When the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second, third, fifth, and eighth switches are controlled to be turned on, and the first, fourth, sixth, and seventh switches are controlled to be turned on. When the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth, sixth, seventh, and eighth switches are controlled to be turned on, and the first, second, third, and fourth switches are controlled to be turned off. Thus, a mode switching unit is added to the T-type three-level topology structure to switch the operating mode of the high-efficiency non-isolated split-phase inverter, thereby improving the conversion efficiency of the high-efficiency non-isolated split-phase inverter when it is connected to the grid and reducing heat generation. Furthermore, when off-grid split-phase output is required, there is no need to add an additional power frequency autotransformer, thus achieving a balance between efficiency, cost, and functionality.

[0057] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. "Multiple" means two or more, unless otherwise specifically defined.

[0058] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0059] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0060] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0061] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0062] Those skilled in the art will understand that all or part of the steps in the method of the above embodiment can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiment.

[0063] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing module, or each unit may exist physically separately, or two or more units may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or in the form of software functional modules. If the integrated modules are implemented in the form of software functional modules and sold or used as independent products, they may also be stored in a computer-readable storage medium.

[0064] The storage medium mentioned above may be a read-only memory, a magnetic disk, or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limiting the present invention. Persons skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A high-efficiency non-isolated split-phase inverter, characterized in that: include: A voltage dividing unit, wherein the voltage dividing unit is connected to a DC bus power supply; a first inverter bridge arm and a second inverter bridge arm, wherein one end of the first inverter bridge arm is connected to one end of the DC bus power supply, the other end of the first inverter bridge arm is connected to the other end of the DC bus power supply, one end of the second inverter bridge arm is connected to one end of the DC bus power supply, and the other end of the second inverter bridge arm is connected to the other end of the DC bus power supply, wherein the first inverter bridge arm and the second inverter bridge arm are used to invert the DC power output by the DC bus power supply into AC power to obtain an AC power signal; a filter unit, one end of the filter unit being connected to the midpoint of the first inverter bridge arm, and the other end of the filter unit being connected to the midpoint of the second inverter bridge arm, the filter unit being configured to filter the AC power signal to obtain a target AC power signal; a first freewheeling bridge arm and a second freewheeling bridge arm, wherein one end of the first freewheeling bridge arm is connected to the midpoint of the voltage dividing unit, the other end of the first freewheeling bridge arm is connected to the midpoint of the first inverter bridge arm, one end of the second freewheeling bridge arm is connected to the midpoint of the voltage dividing unit, the other end of the second freewheeling bridge arm is connected to the midpoint of the second inverter bridge arm, and the first freewheeling bridge arm and the second freewheeling bridge arm are used to freewheel the target AC power signal; A mode switching unit, one end of the mode switching unit is connected to the midpoint of the first freewheeling bridge arm, and the other end of the mode switching unit is connected to the midpoint of the second freewheeling bridge arm, and the mode switching unit is used to switch the high-efficiency non-isolated split-phase inverter between a grid-connected operating mode and an off-grid operating mode.

2. The high-efficiency non-isolated split-phase inverter according to claim 1, characterized in that: The voltage dividing unit includes a first voltage dividing capacitor and a second voltage dividing capacitor, wherein one end of the first voltage dividing capacitor is connected to one end of the DC bus power supply, the other end of the first voltage dividing capacitor is connected to one end of the second voltage dividing capacitor, and the other end of the second voltage dividing capacitor is connected to the other end of the DC bus power supply.

3. The high-efficiency non-isolated split-phase inverter according to claim 2, characterized in that: The first inverter bridge arm includes a first switching tube and a second switching tube, one end of the first switching tube is connected to one end of the DC bus power supply, the other end of the first switching tube is connected to one end of the second switching tube, and the other end of the second switching tube is connected to the other end of the DC bus power supply; The second inverter bridge arm includes a third switching tube and a fourth switching tube, one end of the third switching tube is connected to one end of the DC bus power supply, the other end of the third switching tube is connected to one end of the fourth switching tube, and the other end of the fourth switching tube is connected to the other end of the DC bus power supply.

4. The high-efficiency non-isolated split-phase inverter according to claim 3, characterized in that: The filtering unit comprises: a first filter inductor, one end of the first filter inductor being connected to the other end of the first switching tube; a first filter capacitor, wherein one end of the first filter capacitor is connected to the other end of the first filter inductor, and the other end of the first filter capacitor is connected to the other end of the first voltage-dividing capacitor; a second filter capacitor, one end of the second filter capacitor being connected to the other end of the first filter capacitor; A second filter inductor, one end of the second filter inductor is connected to the other end of the second filter capacitor, and the other end of the second filter inductor is connected to the other end of the third switch tube.

5. The high-efficiency non-isolated split-phase inverter according to claim 4, characterized in that: The first freewheeling bridge arm includes a fifth switching tube and a sixth switching tube, one end of the fifth switching tube is connected to the other end of the first voltage-dividing capacitor, the other end of the fifth switching tube is connected to one end of the sixth switching tube, and the other end of the sixth switching tube is connected to the other end of the first switching tube; The second freewheeling bridge arm includes a seventh switching tube and an eighth switching tube, one end of the seventh switching tube is connected to the other end of the first voltage-dividing capacitor, the other end of the seventh switching tube is connected to one end of the eighth switching tube, and the other end of the eighth switching tube is connected to the other end of the third switching tube.

6. The high-efficiency non-isolated split-phase inverter according to claim 5, characterized in that: The mode switching unit includes a relay, one end of the relay is connected to the other end of the fifth switch tube, and the other end of the relay is connected to the other end of the seventh switch tube.

7. A control method for a high-efficiency non-isolated split-phase inverter according to claim 6, characterized in that: The following steps are involved: Obtaining a control instruction and identifying the control instruction; If the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in a grid-connected working mode, the relay is controlled to be closed, wherein, when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle modulation mode, the first switch tube, the fourth switch tube and the sixth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle freewheeling mode, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube, the second switch tube, the third switch tube the first switching tube, the second switching tube, the third switching tube, and the eighth switching tube are turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switching tube, the third switching tube, and the eighth switching tube are controlled to be turned on, and the first switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, and the seventh switching tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switching tube, the sixth switching tube, the seventh switching tube, and the eighth switching tube are controlled to be turned on, and the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube are controlled to be turned off; If the control instruction is identified as an instruction to control the high-efficiency non-isolated split-phase inverter to operate in an off-grid operating mode, the relay is controlled to be turned off, wherein, when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle modulation mode, the first switch tube, the fourth switch tube, the sixth switch tube and the eighth switch tube are controlled to be turned on, and the second switch tube, the third switch tube, the fifth switch tube and the seventh switch tube are controlled to be turned off; when the high-efficiency non-isolated split-phase inverter operates in a positive half-cycle freewheeling mode, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are controlled to be turned on, and the first switch tube is controlled to be turned off. The first switching tube, the second switching tube, the third switching tube and the fourth switching tube are turned off; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle modulation mode, the second switching tube, the third switching tube, the fifth switching tube and the eighth switching tube are controlled to be turned on, and the first switching tube, the fourth switching tube, the sixth switching tube and the seventh switching tube are controlled to be turned on; when the high-efficiency non-isolated split-phase inverter operates in the negative half-cycle freewheeling mode, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are controlled to be turned on, and the first switching tube, the second switching tube, the third switching tube and the fourth switching tube are controlled to be turned off.

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