Single-phase inverter based on primary energy conversion and modulation strategy thereof

Abstract

The invention provides a single-phase inverter based on primary energy conversion and a modulation strategy thereof, and relates to the technical field of inverters. The single-phase inverter reuses the inductor and the filter capacitor in the Buck mode and the Boost mode, so that the proposed circuit topology only needs a single inductor and a single filter capacitor element, and compared with a traditional circuit with a two-stage structure, the number of the inductors and the number of the filter capacitors are reduced, and the power density is improved. Meanwhile, based on first-stage energy conversion, only a first-stage switching tube works at high frequency to perform energy conversion, and the efficiency is improved. The invention provides a dual-carrier modulation strategy with different amplitudes for the proposed primary energy conversion single-phase inverter topology. And smooth switching of the converter between the Buck mode and the Boost mode can be realized. And the frequencies of the two carriers can be adjusted, so that the Buck mode and the Boost mode of the converter have the same or different switching frequencies.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a single-phase inverter based on primary energy conversion and a modulation strategy thereof. Background Art

[0002] In fields such as photovoltaic power generation, fuel cells and energy storage, the DC voltage on the input side fluctuates with changes in light intensity, battery charging and discharging, etc., so single-phase inverters are required to have the ability to operate over a wide input voltage range.

[0003] Taking photovoltaic power generation as an example, when the weather or light intensity changes at different times of the day or in different seasons of the year, the output DC voltage of the photovoltaic panel will drop below the minimum inverter voltage, requiring the single-phase photovoltaic inverter to have a boost capability. The existing practice generally adopts a two-stage structure with a front-stage DC boost chopper circuit and a rear-stage single-phase full-bridge inverter circuit. However, the energy of this two-stage single-phase photovoltaic inverter needs to be processed in two stages, and the energy conversion of the front and rear stages requires inductors and filter capacitors, resulting in a low power density of the inverter. Summary of the invention

[0004] 1. Technical issues to be resolved In view of the deficiencies of the prior art, the present invention provides a single-phase inverter based on primary energy conversion and a modulation strategy thereof, which solves the technical problem of low power density of the existing single-phase photovoltaic inverter.

[0005] (II) Technical solution To achieve the above objectives, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a single-phase inverter based on primary energy conversion, comprising a first switch tube, a second switch tube, an inductor, a single-phase full-bridge inverter circuit, a seventh switch tube, an eighth switch tube and a filter capacitor; The first end of the first switch tube is connected to the positive electrode of the DC input power supply, and the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the inductor; the second input end of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; The first end of the second switch tube is connected to the common end of the first switch tube and the inductor, and the second end of the second switch tube is connected to the common end of the DC input power supply and the single-phase full-bridge inverter circuit; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; The switching between the Buck mode and the Boost mode is achieved by controlling the on or off of the four bridge arms, the first switch tube, the second switch tube, the seventh switch tube and the eighth switch tube in the single-phase full-bridge inverter circuit.

[0006] Preferably, each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

[0007] In a second aspect, the present invention provides a modulation strategy for a single-phase inverter based on primary energy conversion, which is used to control the single-phase inverter based on primary energy conversion as described in the first aspect above. Through the modulation wave signal and the lower carrier signal u c1 , upper carrier signal u c2 By comparison, control signals of four bridge arms, a first switch tube, a second switch tube, a seventh switch tube and an eighth switch tube in a single-phase full-bridge inverter circuit are obtained; Among them, the modulated wave signal u m =| U omax *sin( ωt )| / U in ,in, U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the lower carrier signal u c1 The amplitude is set to n , upper carrier signal u c2 The amplitude is n ×( U omax / U in ),in, n >0, lower layer carrier signal u c1 , upper carrier signal u c2 The triangle wave, where the lower carrier signal u c1 The trough is 0, and the upper carrier signal u c2 The trough is n ; when u m ≥ u c1When , the first switch tube is turned on and the second switch tube is turned off; when u m < u c1 When , the second switch tube is turned on and the first switch tube is turned off; When the output voltage is in a positive half cycle, the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in a negative half cycle, the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in a negative half cycle, or when the output voltage is in a negative half cycle, the bridge arm between the second input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is positive half cycle, the bridge arm between the second input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, or when the output voltage is in the negative half cycle, the seventh switch tube is turned on, otherwise the seventh switch tube is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, or the output voltage is in the positive half cycle, the eighth switch tube is turned on, otherwise the eighth switch tube is turned off; By reducing the upper carrier signal u c2 frequency to reduce the switching frequency of the single-phase inverter in the Boost mode; by increasing the lower carrier signal u c1 frequency to increase the switching frequency of the single-phase inverter in Buck mode.

[0008] In a third aspect, the present invention provides a single-phase inverter based on primary energy conversion, characterized in that it includes a first switch tube, a second switch tube, a first inductor, a second inductor, a single-phase full-bridge inverter circuit, a seventh switch tube, an eighth switch tube, a ninth switch tube and a filter capacitor; Wherein, the first end of the first switch tube is connected to the positive electrode of the DC input power supply, and the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the first inductor; the second end of the ninth switch tube is connected to the negative electrode of the DC input power supply, and the first end of the ninth switch tube is connected to the second input end of the single-phase full-bridge inverter circuit via the second inductor; The first end of the second switch tube is connected to the common end of the first switch tube and the first inductor, and the second end of the second switch tube is connected to the common end of the ninth switch tube and the second inductor; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; By controlling the on or off of four bridge arms, the first switch tube, the second switch tube, the seventh switch tube, the eighth switch tube and the ninth switch tube in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is achieved.

[0009] Preferably, each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

[0010] In a fourth aspect, the present invention provides a modulation strategy for a single-phase inverter based on primary energy conversion, characterized in that it is used to control the single-phase inverter based on primary energy conversion as described in the third aspect above, Through the modulation wave signal and the lower carrier signal u c1 , upper carrier signal u c2 By comparison, control signals of four bridge arms, a first switch tube, a second switch tube, a seventh switch tube and an eighth switch tube in a single-phase full-bridge inverter circuit are obtained; Among them, the modulation wave signal u m =| U omax *sin( ωt )| / U in ,in, U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the lower carrier signal u c1 The amplitude is set to n , upper carrier signal u c2The amplitude is n ×( U omax / U in ),in, n >0, lower layer carrier signal u c1 , upper carrier signal u c2 The triangle wave, where the lower carrier signal u c1 The trough is 0, and the upper carrier signal u c2 The trough is n ; when u m ≥ u c1 When , the first switch tube and the ninth switch tube are turned on, and the second switch tube is turned off; when u m < u c1 When , the second switch tube is turned on, and the first switch tube and the ninth switch tube are turned off; When the output voltage is in a positive half cycle, the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in a negative half cycle, the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in a negative half cycle, or when the output voltage is in a negative half cycle, the bridge arm between the second input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is positive half cycle, the bridge arm between the second input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, or when the output voltage is in the negative half cycle, the seventh switch tube is turned on, otherwise the seventh switch tube is turned off; When the output voltage is in the negative half cycle and um < u c2 When the output voltage is in the positive half cycle, or the output voltage is in the positive half cycle, the eighth switch tube is turned on, otherwise the eighth switch tube is turned off; By reducing the upper carrier signal u c2 frequency to reduce the switching frequency of the single-phase inverter in the Boost mode; by increasing the lower carrier signal u c1 frequency to increase the switching frequency of the single-phase inverter in Buck mode.

[0011] In a fifth aspect, the present invention provides a single-phase inverter based on primary energy conversion, comprising a first switching tube, a first switch, a second switch, an inductor, a single-phase full-bridge inverter circuit, a seventh switching tube, an eighth switching tube and a filter capacitor; Wherein, the first end of the first switch tube is connected to the positive electrode of the DC input power supply, the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the inductor, and the second input end of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; The first output end of the single-phase full-bridge inverter circuit is connected to the common end of the first switch tube and the inductor via the second switch, and the second output end of the single-phase full-bridge inverter circuit is connected to the common end of the first switch tube and the inductor via the first switch; The switching between Buck mode and Boost mode is achieved by controlling the on or off of four bridge arms, the first switch tube, the seventh switch tube, the eighth switch tube, the first switch and the second switch in the single-phase full-bridge inverter circuit; wherein the first switch and the second switch are respectively unidirectionally conducted from the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit to the common end of the first switch tube and the inductor.

[0012] Preferably, the first switch and the second switch use two switch tubes, and the two switch tubes are controlled to be turned on when the current direction is from the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit to the common end of the first switch tube and the inductor, and disconnected otherwise.

[0013] Preferably, the first switch adopts a first diode and the second switch adopts a second diode; wherein the anode of the first diode is connected to the second output end of the single-phase full-bridge inverter circuit, and the cathode is connected to the common end of the first switch tube and the inductor; the anode of the second diode is connected to the first output end of the single-phase full-bridge inverter circuit, and the cathode is connected to the common end of the first switch tube and the inductor.

[0014] Preferably, each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

[0015] (III) Beneficial effects The present invention provides a single-phase inverter based on primary energy conversion and its modulation strategy. Compared with the prior art, it has the following beneficial effects: The single-phase inverter of the present invention reuses the inductor and the filter capacitor in the Buck mode and the Boost mode, so the proposed circuit topology only needs a single inductor and filter capacitor element, which reduces the number of inductors and filter capacitors compared to the traditional two-stage structure circuit, and improves the power density. At the same time, the present invention is based on the one-stage energy conversion, and only one-stage switch tube works at high frequency to perform energy conversion, thereby improving efficiency. At the same time, the present invention proposes a dual-carrier modulation strategy with different amplitudes for the proposed one-stage energy conversion single-phase inverter topology, which can reduce the switching frequency of the Boost mode by reducing the frequency of the upper carrier; increase the switching frequency of the Buck mode by increasing the frequency of the lower carrier, and in the Boost mode, the high-frequency switch tube of the positive and negative half cycles switches between the two bridge arms, so that the circuit loss distribution is more uniform, the inverter working life is extended, and the stability of the inverter is improved. Reducing the switching frequency of the Boost mode and increasing the switching frequency of the Buck mode also makes the inductor ripple pressure smaller, which is conducive to a more reasonable design of the inductor parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a structural schematic diagram of an existing single-phase photovoltaic inverter; Figure 2 The circuit diagram of the existing single-phase photovoltaic inverter is as follows; Figure 3 This is a structural diagram of a single-phase inverter based on primary energy conversion in Example 1; Figure 4 for Figure 3 The specific circuit diagram of the architecture diagram shown; Figure 5 for Figure 4 The schematic diagram of the working mode 1 of the single-phase inverter based on the primary energy conversion is shown; Figure 6 for Figure 4 The schematic diagram of the working mode 2 of the single-phase inverter based on the primary energy conversion is shown; Figure 7 for Figure 4 The schematic diagram of the working mode 3 of the single-phase inverter based on the primary energy conversion is shown; Figure 8 for Figure 4 The schematic diagram of the working mode 4 of the single-phase inverter based on the primary energy conversion is shown; Fig. 9 for Figure 4 The schematic diagram of the working mode 5 of the single-phase inverter based on the primary energy conversion is shown; Fig.10 for Figure 4 The schematic diagram of the working mode 6 of the single-phase inverter based on the primary energy conversion is shown; Fig.11 This is a structural diagram of a single-phase inverter based on primary energy conversion in Example 2; Fig.12 for Fig.11 The specific circuit diagram of the architecture diagram shown; Fig.13 The modulation waveform, carrier waveform and Q 1- Q Schematic diagram of driving pulse width signal of 8; Fig.14 for Figure 4 The instantaneous voltage on the output side of the circuit diagram shown is u o , the instantaneous current is i o , then the schematic diagram of the instantaneous output power processed by the inverter in Buck mode and Boost mode; Fig.15 This is a structural diagram of a single-phase inverter based on primary energy conversion in Example 4; Fig.16 for Fig.15 The first specific circuit diagram of the architecture diagram shown; Fig.17 for Fig.15 The second specific circuit diagram of the shown architecture diagram. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0019] It should be noted that, for the convenience of description, the switch IGBT is used to represent the controllable (on and off) switch tube in the embodiment of the present invention, but the switch tube in the present invention is not limited to IGBT. Take IGBT as an example for explanation. The first end of the IGBT refers to the collector, the second end is the emitter, and the control end refers to the gate. A driving control signal is applied to the control end of each switch tube in the embodiment of the present invention. For the sake of brevity, it will not be repeated later. The power switch tube in the embodiment of the present invention can also be implemented by other controllable switch tube devices other than IGBT, such as MOSFET. At the same time, in order to ensure the normal operation of each switch device in the embodiment of the present invention, a freewheeling diode needs to be connected in parallel to each switch device. The parallel connection direction of the freewheeling diode is related to the type of the switch device. The technician can set it according to the type of the switch device, which is not limited here. If not specified, the switch device defaults to including a freewheeling diode, which will be pointed out in this embodiment in special cases.

[0020] The embodiment of the present application solves the technical problem of low power density of existing single-phase photovoltaic inverters by providing a single-phase inverter based on primary energy conversion and its modulation strategy, and realizes DC / AC conversion and voltage reduction or voltage increase through primary energy conversion. The single-phase inverter with primary energy conversion only needs one inductor and filter capacitor, which reduces the number of inductors and filter capacitors, thereby reducing the volume and weight of the inverter and improving the power density.

[0021] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows: The structure of the existing single-phase photovoltaic inverter is as follows: Figure 1 As shown, the input voltage is U in Boost to a fixed value U bus , U bus The voltage must be higher than the minimum inverter voltage, and the subsequent single-phase multi-level inverter is responsible for completing the voltage inversion output. For example, a common circuit such as Figure 2As shown. The circuit uses a Boost circuit in the front stage and a single-phase full-bridge inverter in the back stage to output a sinusoidal AC voltage. The energy needs to be processed in two stages, and the front and back stages work at high frequencies at the same time, which reduces the efficiency. At the same time, the energy conversion of the front and back stages requires inductors and filter capacitors, and the bus filter capacitor needs to use a large electrolytic filter capacitor to complete the energy decoupling of the front and back stages, which reduces the power density of the inverter. In addition, when using a structure such as Figure 1 When using a single-phase photovoltaic inverter as shown, if the subsequent single-phase inverter does not use a topology that specifically suppresses leakage current, such as H5, H6, and Heric, there will be leakage current problems, such as Figure 2 When the H4 full bridge is used, the single-phase photovoltaic inverter has leakage current.

[0022] In order to solve the above problems, the embodiment of the present invention proposes a single-phase inverter based on one-stage energy conversion and its modulation strategy. The single-phase inverter is based on one-stage energy conversion. According to the instantaneous value of the input DC voltage being higher or lower than the instantaneous value of the output AC voltage, the inverter working mode is divided into Buck mode and Boost mode. In each mode, only one stage works at high frequency for energy conversion, which reduces the number of high-frequency switches and improves efficiency. At the same time, inductors and filter capacitors are reused in Buck mode and Boost mode, so the proposed circuit topology only requires a single inductor and filter capacitor element, which reduces the number of inductors and filter capacitors compared to the traditional two-stage structure circuit, and improves power density. In addition, a dual-carrier modulation method with different carrier amplitudes and frequencies is proposed for the proposed topology, which can reduce the switching frequency of the Boost mode by reducing the frequency of the upper carrier; increase the switching frequency of the Buck mode by increasing the frequency of the lower carrier, and in the Boost mode, the high-frequency switch tubes of the positive and negative half cycles are switched between the two bridge arms, so that the circuit loss distribution is more uniform, the working life of the inverter is extended, and the stability of the inverter is improved. Reducing the switching frequency in Boost mode and increasing the switching frequency in Buck mode also reduces the inductor ripple pressure, which is conducive to more reasonable inductor parameter design.

[0023] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] Embodiment 1: This embodiment provides a single-phase inverter based on primary energy conversion, such as Figure 3 As shown, the first switch tube Q 1. Second switch tube Q 2. Inductor L, single-phase full-bridge inverter circuit, seventh switch tube Q 7. The eighth switch tube Q 8 and filter capacitor C, wherein the first switch tube QThe first end of 1 is connected to the positive electrode of the DC input power supply, and the first switch tube Q The second end of the inductor 1 is connected to the first input end I1 of the single-phase full-bridge inverter circuit via the inductor L; the second input end I2 of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; the second switch tube Q The first end of 2 is connected to the first switch tube Q 1 and the common end of the inductor L, the second switch tube Q The second end of 2 is connected to the common end of the DC input power supply and the single-phase full-bridge inverter circuit; the first output end O1 of the single-phase full-bridge inverter circuit is connected to the common end of the single-phase full-bridge inverter circuit via the seventh switch tube Q 7 is connected to the first output terminal of the single-phase inverter, and the second output terminal O2 of the single-phase full-bridge inverter circuit is connected to the first output terminal of the single-phase inverter circuit through the eighth switch tube Q 8 is connected to the second output terminal of the single-phase inverter; the two ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter; By controlling the four bridge arms and the first switch tube in the single-phase full-bridge inverter circuit Q 1. Second switch tube Q 2. Seventh switch tube Q 7 and the eighth switch tube Q 8 is turned on or off to realize the switching between Buck mode and Boost mode.

[0025] like Figure 4 As shown, in the specific implementation process, the single-phase full-bridge inverter circuit includes four switch tubes Q 3~ Q 6 (It should be noted that, in the specific implementation process, other devices are also used to form a single-phase full-bridge inverter circuit, such as four simple switches, a diode clamp type, a floating filter capacitor type, and other multi-level structured single-phase full-bridge inverters).

[0026] like Figure 4 The single-phase inverter based on one-stage energy conversion shown includes 6 operating modes.

[0027] Three operating modes of the positive half cycle of the output sinusoidal voltage: Mode 1: If Figure 5 As shown, the first switch tube Q 1. The third switch tube Q 3. The fourth switch tube Q 4. The sixth switch tube Q 6 and the eighth switch tube Q 8 is turned on, the other switches are turned off, and the current flows from the power supply U in Starting from the positive electrode, it passes through the switch tube in turn Q 1. Inductor L, switch tube Q 3. Q 4 Flow to power supply U inNegative pole, Boost mode that outputs the positive half cycle of the sinusoidal voltage.

[0028] Mode 2: If Figure 6 As shown, the first switch tube Q 1. The third switch tube Q 3. The sixth switch tube Q 6. Seventh switch tube Q 7 and the eighth switch tube Q 8 is turned on, the other switches are turned off, and the current flows from the power supply U in Starting from the positive electrode, it passes through the switch tube in turn. Q 1. Inductor L, switch tube Q 3. Q 7. Load R L , switch tube Q 8. Q 6 Flow to power supply U in Negative pole, outputs Boost or Buck mode freewheeling in the positive half cycle of the sinusoidal voltage.

[0029] Mode 3: If Figure 7 As shown, the second switch tube Q 2. The third switch tube Q 3. The sixth switch tube Q 6. Seventh switch tube Q 7 and the eighth switch tube Q 8 is turned on, the other switches are turned off, and the current flows through the inductor L and the switch tube Q 3. Q 7. Load R L , switch tube Q 8. Q 6. Q 2. Buck mode that outputs the positive half cycle of sinusoidal voltage.

[0030] Three operating modes of the negative half cycle of the output sinusoidal voltage: Mode 4: If Figure 8 As shown, the first switch tube Q 1. The fourth switch tube Q 4. The fifth switch tube Q 5. The sixth switch tube Q 6 and 7th switch tube Q 7 is turned on, the other switches are turned off, and the current flows from the power supply U in Starting from the positive electrode, the current flows through the switch tube Q1, the inductor L, the switch tubes Q5 and Q6 to the power supply U in Negative pole, Boost mode that outputs the negative half cycle of the sinusoidal voltage.

[0031] Mode 5: If Fig. 9 As shown, the first switch tube Q1. The fourth switch tube Q 4. The fifth switch tube Q 5. Seventh switch tube Q 7 and the eighth switch tube Q 8 is turned on, the other switches are turned off, and the current flows from the power supply U in Starting from the positive electrode, it passes through the switch tube in turn Q 1. Inductor L, switch tube Q 5. Q 8. Load R L , switch tube Q 7. Q 4 Flow to power supply U in Negative pole, outputs Boost or Buck mode freewheeling in the negative half cycle of the sinusoidal voltage.

[0032] Mode 6: If Fig.10 As shown, the second switch tube Q 2. The fourth switch tube Q 4. The fifth switch tube Q 5. Seventh switch tube Q 7 and the eighth switch tube Q 8 is turned on, the other switches are turned off, and the current flows through the inductor L and the switch tube Q 5. Q 8. Load R L ,switch Q 7. Q 4. Q 2. Buck mode that outputs the negative half cycle of sinusoidal voltage.

[0033] Through the above modal analysis, it can be seen that in the positive half cycle of the output sinusoidal voltage, when the input DC voltage is lower than the output sinusoidal voltage, the switch tube Q 4 and Q The driving signal of 7 is a complementary PWM wave, which works at a high frequency. Q 1. Q 3. Q 6 and Q 8 is always on, switch Q 2. Q 5 is turned off, and the circuit works in Boost mode, corresponding to Mode 1 and Mode 2. When the input DC voltage is higher than the output sinusoidal voltage, the switch tube Q 1 and Q The driving signal of 2 is a complementary PWM wave, which works at a high frequency. Q 3. Q 6. Q 7 and Q 8 is always on, switch Q 4. Q5 is turned off. At this time, the circuit works in Buck mode, corresponding to mode 2 and mode 3.

[0034] In the negative half cycle of the output sinusoidal voltage, when the input DC voltage is lower than the output sinusoidal voltage, the switch tube Q 6 and Q The driving signal of 8 is a complementary PWM wave, which works at a high frequency. Q 1. Q 4. Q 5 and Q 7 is always on, switch Q 2 and Q 3 is turned off, and the circuit works in Boost mode, corresponding to Mode 4 and Mode 5. When the input DC voltage is higher than the output sinusoidal voltage, the switch tube Q 1 and Q The driving signal of 2 is a complementary PWM wave, which works at a high frequency. Q 4. Q 5. Q 7 and Q 8 is always on, switch Q 3. Q 6 is turned off, and the circuit works in Buck mode, corresponding to mode 5 and mode 6.

[0035] Embodiment 2: This embodiment takes into account the possible influence of leakage current and makes adjustments to the single-phase inverter in Embodiment 1, such as Fig.11 As shown, a ninth switch is added Q 9 and a second inductor L 2. Other components are the same as those in Example 1, including the first switch tube Q 1. Second switch tube Q 2. First Inductor L 1. Single-phase full-bridge inverter circuit, seventh switch tube Q 7. The eighth switch tube Q 8 and filter capacitor C, wherein the first switch tube Q The second end of the ninth switch tube is connected to the first input end I1 of the single-phase full-bridge inverter circuit via the first inductor L1; Q The second end of 9 is connected to the negative pole of the DC input power supply, and the ninth switch tube Q The first end of the second inductor L2 is connected to the second input end I2 of the single-phase full-bridge inverter circuit; the second switch tube Q The first end of 2 is connected to the first switch tube Q 1 and the common end of the first inductor L1, the second switch tube Q The second end of 2 is connected to the ninth switch tube Q9 and the common end of the second inductor L2; the first output end O1 of the single-phase full-bridge inverter circuit is connected to the common end of the second inductor L2 via the seventh switch tube Q 7 is connected to the first output terminal of the single-phase inverter, and the second output terminal O2 of the single-phase full-bridge inverter circuit is connected to the first output terminal of the single-phase inverter circuit through the eighth switch tube Q 8 is connected to the second output terminal of the single-phase inverter; the two ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter; By controlling the four bridge arms and the first switch tube in the single-phase full-bridge inverter circuit Q 1. Second switch tube Q 2. Seventh switch tube Q 7. The eighth switch tube Q 8 and 9 switch tubes Q The conduction or disconnection of 9 realizes the switching between Buck mode and Boost mode.

[0036] It should be noted that, in the specific implementation process, the first inductor L1 and the second inductor L2 are two inductors with consistent characteristic parameters. In the entire circuit, if the parameters of other components are consistent with those in Example 1, the inductance values ​​of the first inductor L1 and the second inductor L2 are half of the inductance value of the inductor L in Example 1, that is, the sum of the inductance values ​​of the first inductor L1 and the second inductor L2 is equal to the inductance value of the inductor L in Example 1. This setting makes the circuit parameters evenly distributed and minimizes the impact on the leakage current.

[0037] In addition, the input side of the single-phase inverter of this embodiment is clamped by the input voltage in the Boost mode, while in the Buck mode, the freewheeling mode switch Q 1 and Q 9 is disconnected, so it has the ability of leakage current suppression.

[0038] like Fig.12 As shown, in the specific implementation process, the single-phase full-bridge inverter circuit includes four switch tubes Q 3~ Q 6.

[0039] In this embodiment, the working mode of the single-phase inverter is consistent with the working mode of the single-phase inverter in Embodiment 1. Q 9 is turned on or off by a control signal and the first switch tube Q 1Save consistent.

[0040] Embodiment 3: This embodiment provides a modulation strategy for a single-phase inverter based on primary energy conversion, which is used to control the single-phase inverter based on primary energy conversion in Embodiment 1 and Implementation 2, by modulating the wave signal and the lower carrier signal. u c1 , upper carrier signal uc2 By comparison, the four bridge arms and the first switch tube in the single-phase full-bridge inverter circuit are obtained. Q 1. Second switch tube Q 2. Seventh switch tube Q 7 and the eighth switch tube Q 8 control signal, it should be noted that, in the embodiment of the invention, the four bridge arms in the single-phase full-bridge inverter circuit are Q 3- Q 6, that is, through the modulation wave signal u m and the lower carrier signal u c1 , upper carrier signal u c2 By comparison, the switch tube Q 1- Q 8 driving signal.

[0041] Among them, the modulated wave signal u m =| U omax *sin( ωt )| / U in ,in U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the lower carrier signal u c1 The amplitude is set to n , upper carrier signal u c2 The amplitude is n ×( U omax / U in ), the lower carrier signal u c1 , upper carrier signal u c2 The triangle wave, where the lower carrier signal u c1 The trough is 0, and the upper carrier signal u c2 The trough is n (In this embodiment, n =1); when u m ≥ u c1 When the switch Q 1 is on, otherwise Q1 is off. u m < u c1 When the switch Q 2 conduction, otherwise Q 2Shut down; When the output voltage is in the positive half cycle, the switch Q 3 conduction, switch Q 5 disconnect; When the output voltage is in the negative half cycle, the switch Q 5 conduction, switch Q 3 disconnect; When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in the negative half cycle, the switch Q 4 conduction, otherwise Q 4. Shut down; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, the switch Q 6 conduction, otherwise Q 6. Shut down; When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, the switch Q 7 is on, otherwise the switch Q 7 Shutdown; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, the switch Q 8 is on, otherwise the switch Q 8 Shut down.

[0042] The modulation strategy is described in detail below: Its modulation waveform, carrier waveform and Q 1- Q 8 driving pulse width signal ( Q 9 driving pulse width signal and Q 1Save consistent) such as Fig.13 shown.

[0043] Fig.13 The input voltage is assumed to be U in , the output sinusoidal voltage is Uomax* sin( ωt ), the lower carrier is u c1 , the upper carrier is u c2 The modulated wave in the figure is u m =| U omax *sin( ωt )| / U in , the amplitude of the lower carrier is set to 1, then the upper carrier amplitude of the inverter to correctly track the output sinusoidal voltage is U omax / U in . The modulated wave signal and the carrier signal u c1 And the carrier signal u c2 By comparison, we can get the switch tube Q 1- Q The driving signal of 8 is as follows Fig.13 shown.

[0044] set up Fig.13 The modulation wave is u m , then when u m ≥ u c1 When the switch Q 1 is on, otherwise Q 1 is off. u m < u c1 When the switch Q 2 conduction, otherwise Q 2 is turned off. When the output voltage is in the positive half cycle, the switch Q 3 conduction, otherwise Q 3. When the output voltage is in the negative half cycle, the switch Q 5 conduction, otherwise Q 5 shutdown. When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in the negative half cycle, the switch Q 4 conduction, otherwise Q 4. When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, the switch Q 6 conduction, otherwiseQ 6 shutdown. When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, the switch Q 7 is on, otherwise the switch Q 7. When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, the switch Q 8 is on, otherwise the switch Q 8 Shut down.

[0045] Set carrier u c1 The frequency is f c1 , carrier u c2 The frequency is f c2 , then we can know that the switching frequency of the inverter working in Buck mode is f c1 , the switching frequency working in Boost mode is f c2 By adjusting f c1 and f c2 The value of can be used to adjust the switching frequency of the inverter working in Buck mode and Boost mode respectively.

[0046] Assume the instantaneous voltage on the output side is u o , the instantaneous current is i o , then the instantaneous output power, i.e., energy, processed by the inverter in Buck mode and Boost mode is as follows: Fig.14 As shown: The instantaneous output voltage of the converter is u o , the instantaneous output current is i o And the instantaneous output power is p o ,Depend on Fig.14 It can be seen that the instantaneous output power p oFor power with double frequency fluctuation, the converter mainly processes most of the energy in Boost mode, while the energy processed in Buck mode is relatively small. Therefore, in Boost mode, the voltage and current stress of the switch tube during high-frequency switching is high, and the energy consumption of high-frequency energy conversion is large, while in Buck mode, the voltage and current stress of the switch tube during high-frequency switching is low, and the energy consumption of high-frequency energy switching is small. However, due to Q 1- Q The maximum voltage stress and maximum current stress of 8 are the same, so the same device is used. It can be seen that in Buck mode, the performance of the switch tube is redundant, which can increase the switching frequency of the high-frequency switch in Buck mode and appropriately reduce the switching frequency in Boost mode. f c1 > f c2 , thereby balancing the difference in loss distribution caused by high-frequency operation on each switch tube and improving the reliability of the converter. In addition, under the same current ripple conditions, the demand for inductance in Boost mode is smaller, and the demand for inductance in Buck mode is larger. f c1 > f c2 Making the Buck mode switching frequency higher than the Boost mode is beneficial to reducing the original inductance requirement in the Buck mode and balancing the parameter design of the converter. In addition, increasing the Buck mode switching frequency reduces the original inductance requirement in the Buck mode, which is also beneficial to the stable operation of the converter.

[0047] Embodiment 4: In this embodiment, in order to suppress leakage current and reduce the number of on-state switches, the on-state loss is reduced. This embodiment provides a single-phase inverter based on one-stage energy conversion, such as Fig.15 As shown, the first switch tube Q 1. First switch, second switch, inductor L, single-phase full-bridge inverter circuit, seventh switch tube Q 7. The eighth switch tube Q 8 and filter capacitor C, wherein the first switch tube Q The first end of 1 is connected to the positive electrode of the DC input power supply, and the first switch tube Q The second end of the inductor 1 is connected to the first input end I1 of the single-phase full-bridge inverter circuit via the inductor L; the second input end I2 of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; the first output end O1 of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply via the seventh switch tube Q 7 is connected to the first output terminal of the single-phase inverter, and the second output terminal O2 of the single-phase full-bridge inverter circuit is connected to the first output terminal of the single-phase inverter circuit through the eighth switch tube Q8 is connected to the second output terminal of the single-phase inverter; the two ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter; The first output terminal O1 of the single-phase full-bridge inverter circuit is connected to the first switch tube via the second switch. Q 1 and the common end of the inductor L, the second output end O2 of the single-phase full-bridge inverter circuit is connected to the first switch tube via the first switch. Q 1 and the common end of inductor L.

[0048] By controlling the four bridge arms and the first switch tube in the single-phase full-bridge inverter circuit Q 1. The seventh switch tube Q 7. The eighth switch tube Q 8. The first switch and the second switch are turned on or off to realize the switching between the Buck mode and the Boost mode; wherein the first switch and the second switch are respectively connected to the first switch tube by the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit in a unidirectional manner. Q 1 and the common end of inductor L are connected.

[0049] like Fig.16 As shown in FIG. 1 , in a specific implementation process, the single-phase full-bridge inverter circuit includes four switch tubes Q3 to Q6. At the same time, a filter capacitor C for filtering is connected between the first output terminal and the second output terminal. The first switch and the second switch can be selected from two switch tubes. Q 2 and Q 9 is responsible for controlling the current direction from the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit to the first switch tube Q 1 and the common end of inductor L are turned on, otherwise they are disconnected.

[0050] like Fig.17 As shown, in order to Fig.16 Based on the circuit shown in the figure, the use of switching tubes is further reduced by replacing two switching tubes with two diodes. Q 2 and Q 9. To realize the unidirectional conversion of the second output end of the single-phase full-bridge inverter circuit to the first switch tube Q 1 and the common end of the inductor L are turned on, and the first output end of the single-phase full-bridge inverter circuit unidirectionally supplies power to the first switch tube Q 1 and the common end of inductor L are connected.

[0051] In summary, compared with the prior art, the present invention has the following beneficial effects: 1. The embodiment of the present invention is based on one-stage energy conversion, and proposes a new single-phase inverter topology with a wide input DC voltage range. According to whether the input voltage is higher or lower than the output voltage, the inverter operates in Buck mode or Boost mode at high frequency. Compared with the traditional two-stage conversion topology, only one switch tube of the circuit operates at high frequency for energy conversion, which improves efficiency. At the same time, compared with the traditional two-stage conversion topology, only one inductor and filter capacitor are needed, which reduces the number of inductors and filter capacitors, thereby reducing the volume and weight of the converter and improving the power density.

[0052] 2. The embodiment of the present invention proposes a dual-carrier modulation strategy with different amplitudes for the proposed primary energy conversion single-phase inverter topology. The converter can smoothly switch between the Buck mode and the Boost mode. The frequencies of the two carriers can be adjusted so that the Buck mode and the Boost mode of the converter have the same or different switching frequencies.

[0053] 3. The embodiment of the present invention reduces the switching frequency of the Boost mode by reducing the frequency of the upper carrier wave, and increases the switching frequency of the Buck mode by increasing the frequency of the lower carrier wave. At the same time, in the Boost mode, the high-frequency switch tubes of the positive and negative half cycles switch between the two bridge arms, thereby balancing the difference in loss distribution caused by the high-frequency operation of each switch tube and improving the reliability of the converter. In addition, under the same current ripple conditions, the demand for inductance in the Boost mode is smaller, and the demand for inductance in the Buck mode is larger. f c1 > f c2 Making the Buck mode switching frequency higher than the Boost mode is beneficial to reducing the original inductance requirement in the Buck mode and balancing the parameter design of the converter. In addition, increasing the Buck mode switching frequency reduces the original inductance requirement in the Buck mode, which is also beneficial to the stable operation of the converter.

[0054] 4. In the Boost mode, the input side of the single-phase inverter in Example 2 is clamped by the input voltage, and in the Buck mode, the freewheeling mode switches Q1 and Q9 are disconnected, so it has the ability to suppress leakage current. In the Buck mode, the freewheeling mode switches Q1, Q4 and Q6 of the single-phase inverter in Example 4 are disconnected, so it also has the ability to suppress leakage current.

[0055] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-phase inverter based on primary energy conversion, characterized in that: It includes a first switch tube, a second switch tube, an inductor, a single-phase full-bridge inverter circuit, a seventh switch tube, an eighth switch tube and a filter capacitor; The first end of the first switch tube is connected to the positive electrode of the DC input power supply, and the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the inductor; the second input end of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; The first end of the second switch tube is connected to the common end of the first switch tube and the inductor, and the second end of the second switch tube is connected to the common end of the DC input power supply and the single-phase full-bridge inverter circuit; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; The switching between the Buck mode and the Boost mode is achieved by controlling the on or off of the four bridge arms, the first switch tube, the second switch tube, the seventh switch tube and the eighth switch tube in the single-phase full-bridge inverter circuit.

2. The single-phase inverter based on primary energy conversion according to claim 1, characterized in that: Each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

3. A modulation strategy for a single-phase inverter based on primary energy conversion, characterized in that: Used to control the single-phase inverter based on primary energy conversion as described in any one of claims 1 to 2, Through the modulation wave signal and the lower carrier signal u c1 , upper carrier signal u c2 By comparison, control signals of four bridge arms, a first switch tube, a second switch tube, a seventh switch tube and an eighth switch tube in a single-phase full-bridge inverter circuit are obtained; Among them, the modulation wave signal u m =| U omax *sin( ωt )| / U in ,in, U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the lower carrier signal u c1 The amplitude is set to n , upper carrier signal u c2 The amplitude is n ×( U omax / U in ),in, n >0, lower layer carrier signal u c1 , upper carrier signal u c2 The triangle wave, where the lower carrier signal u c1 The trough is 0, and the upper carrier signal u c2 The trough is n ; when u m ≥ u c1 When , the first switch tube is turned on and the second switch tube is turned off; when u m < u c1 When , the second switch tube is turned on and the first switch tube is turned off; When the output voltage is in a positive half cycle, the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in a negative half cycle, the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in a negative half cycle, or when the output voltage is in a negative half cycle, the bridge arm between the second input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is positive half cycle, the bridge arm between the second input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, or when the output voltage is in the negative half cycle, the seventh switch tube is turned on, otherwise the seventh switch tube is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, or the output voltage is in the positive half cycle, the eighth switch tube is turned on, otherwise the eighth switch tube is turned off; By reducing the upper carrier signal u c2 frequency to reduce the switching frequency of the single-phase inverter in the Boost mode; by increasing the lower carrier signal u c1 frequency to increase the switching frequency of the single-phase inverter in Buck mode.

4. A single-phase inverter based on primary energy conversion, characterized in that: It includes a first switch tube, a second switch tube, a first inductor, a second inductor, a single-phase full-bridge inverter circuit, a seventh switch tube, an eighth switch tube, a ninth switch tube and a filter capacitor; Wherein, the first end of the first switch tube is connected to the positive electrode of the DC input power supply, and the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the first inductor; the second end of the ninth switch tube is connected to the negative electrode of the DC input power supply, and the first end of the ninth switch tube is connected to the second input end of the single-phase full-bridge inverter circuit via the second inductor; The first end of the second switch tube is connected to the common end of the first switch tube and the first inductor, and the second end of the second switch tube is connected to the common end of the ninth switch tube and the second inductor; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; By controlling the on or off of four bridge arms, the first switch tube, the second switch tube, the seventh switch tube, the eighth switch tube and the ninth switch tube in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is achieved.

5. The single-phase inverter based on primary energy conversion according to claim 4, characterized in that: Each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

6. A modulation strategy for a single-phase inverter based on primary energy conversion, characterized in that: Used to control the single-phase inverter based on primary energy conversion as described in any one of claims 4 to 5, Through the modulation wave signal and the lower carrier signal u c1 , upper carrier signal u c2 By comparison, control signals of four bridge arms, a first switch tube, a second switch tube, a seventh switch tube and an eighth switch tube in a single-phase full-bridge inverter circuit are obtained; Among them, the modulation wave signal u m =| U omax *sin( ωt )| / U in ,in, U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the lower carrier signal u c1 The amplitude is set to n , upper carrier signal u c2 The amplitude is n ×( U omax / U in ),in, n >0, lower layer carrier signal u c1 , upper carrier signal u c2 The triangle wave, where the lower carrier signal u c1 The trough is 0, and the upper carrier signal u c2 The trough is n ; when u m ≥ u c1 When , the first switch tube and the ninth switch tube are turned on, and the second switch tube is turned off; when u m < u c1 When , the second switch tube is turned on, and the first switch tube and the ninth switch tube are turned off; When the output voltage is in a positive half cycle, the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in a negative half cycle, the bridge arm between the first input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, and the bridge arm between the first input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned off; When the output voltage is in the positive half cycle and u m ≥ u c2 When the output voltage is in a negative half cycle, or when the output voltage is in a negative half cycle, the bridge arm between the second input terminal and the first output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is positive half cycle, the bridge arm between the second input terminal and the second output terminal of the single-phase full-bridge inverter circuit is turned on, otherwise the bridge arm is turned off; When the output voltage is in the positive half cycle and u m < u c2 When the output voltage is in the negative half cycle, or when the output voltage is in the negative half cycle, the seventh switch tube is turned on, otherwise the seventh switch tube is turned off; When the output voltage is in the negative half cycle and u m < u c2 When the output voltage is in the positive half cycle, or the output voltage is in the positive half cycle, the eighth switch tube is turned on, otherwise the eighth switch tube is turned off; By reducing the upper carrier signal u c2 frequency to reduce the switching frequency of the single-phase inverter in the Boost mode; by increasing the lower carrier signal u c1 frequency to increase the switching frequency of the single-phase inverter in Buck mode.

7. A single-phase inverter based on primary energy conversion, characterized in that: It includes a first switching tube, a first switch, a second switch, an inductor, a single-phase full-bridge inverter circuit, a seventh switching tube, an eighth switching tube and a filter capacitor; Wherein, the first end of the first switch tube is connected to the positive electrode of the DC input power supply, the second end of the first switch tube is connected to the first input end of the single-phase full-bridge inverter circuit via the inductor, and the second input end of the single-phase full-bridge inverter circuit is connected to the negative electrode of the DC input power supply; The first output end of the single-phase full-bridge inverter circuit is connected to the first output end of the single-phase inverter via the seventh switch tube, and the second output end of the single-phase full-bridge inverter circuit is connected to the second output end of the single-phase inverter via the eighth switch tube; The two ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter; The first output end of the single-phase full-bridge inverter circuit is connected to the common end of the first switch tube and the inductor via the second switch, and the second output end of the single-phase full-bridge inverter circuit is connected to the common end of the first switch tube and the inductor via the first switch; The switching between Buck mode and Boost mode is achieved by controlling the on or off of four bridge arms, the first switch tube, the seventh switch tube, the eighth switch tube, the first switch and the second switch in the single-phase full-bridge inverter circuit; wherein the first switch and the second switch are respectively unidirectionally conducted from the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit to the common end of the first switch tube and the inductor.

8. The single-phase inverter based on primary energy conversion according to claim 7, characterized in that: The first switch and the second switch use two switch tubes, and the two switch tubes are controlled to be turned on when the current direction is from the second output end of the single-phase full-bridge inverter circuit and the first output end of the single-phase full-bridge inverter circuit to the common end of the first switch tube and the inductor, and otherwise turned off.

9. The single-phase inverter based on primary energy conversion according to claim 7, characterized in that: The first switch uses a first diode and the second switch uses a second diode; wherein the anode of the first diode is connected to the second output end of the single-phase full-bridge inverter circuit, and the cathode is connected to the common end of the first switch tube and the inductor; the anode of the second diode is connected to the first output end of the single-phase full-bridge inverter circuit, and the cathode is connected to the common end of the first switch tube and the inductor.

10. The single-phase inverter based on primary energy conversion according to any one of claims 7 to 9, characterized in that: Each bridge arm of the single-phase full-bridge inverter circuit includes a switch tube, and the conduction or disconnection of the bridge arm is controlled by the conduction or disconnection of the switch tube.

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