Single-phase Inverter Based on First-Order Energy Conversion and Its Modulation Strategy

Abstract

The present invention provides a single-phase inverter based on one-stage energy conversion and a modulation strategy thereof, and relates to the technical field of inverters. The single-phase inverter of the present invention reuses inductors and filter capacitors in Buck mode and Boost mode, so the proposed circuit topology only requires a single inductor and filter capacitor component, 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, based on the one-stage energy conversion, the present invention only has one-stage switching tube working at a high frequency to perform energy conversion, thereby improving efficiency. The present invention proposes a dual-carrier modulation strategy with different amplitudes for the proposed one-stage energy conversion single-phase inverter topology. Smooth switching of the converter between Buck mode and Boost mode can be achieved. The frequencies of the two carriers can be adjusted so that the Buck mode and 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 particularly relates to a single-phase inverter based on first-stage energy conversion and its modulation strategy. Background Art

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

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

[0004] (1) Technical Problems to be Solved

[0005] Aiming at the deficiencies of the prior art, the present invention provides a single-phase inverter based on first-stage energy conversion and its modulation strategy, solving the technical problem of the low power density of the existing single-phase photovoltaic inverter.

[0006] (2) Technical Solutions

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0008] In a first aspect, the present invention provides a single-phase inverter based on first-stage energy conversion, including a first switching tube, a second switching tube, an inductor, a single-phase full-bridge inverter circuit, a seventh switching tube, an eighth switching tube, and a filter capacitor;

[0009] Wherein, the first end of the first switching tube is connected to the positive pole of the DC input power supply, and the second end of the first switching 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 pole of the DC input power supply;

[0010] The first end of the second switching tube is connected to the common end of the first switching tube and the inductor, and the second end of the second switching tube is connected to the common end of the DC input power supply and the single-phase full-bridge inverter circuit;

[0011] 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 switching 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 switching tube;

[0012] Both ends of the filtering capacitor are respectively connected to the first output terminal and the second output terminal of the single-phase inverter;

[0013] By controlling the conduction or disconnection 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, the switching between the Buck mode and the Boost mode is realized.

[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] In a second aspect, the present invention provides a modulation strategy for a single-phase inverter based on first-level energy conversion, which is used to control the single-phase inverter based on first-level energy conversion as described in the first aspect above.

[0016] By comparing the modulation wave signal and the lower carrier signal u c1 and the upper carrier signal u c2 the control signals 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 are obtained;

[0017] Among them, the modulation wave signal u m =| U omax *sin( ωt )| / U in , where U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the amplitude of the lower carrier signal u c1 is set to n , the amplitude of the upper carrier signal u c2 is n ×( U omax / U in ), where n >0, the lower carrier signal u c1 and the upper carrier signal u c2 are both triangular waves, where the trough of the lower carrier signal u c1 is 0, and the upper carrier signal uc2 The trough of n ;

[0018] When u m ≥ u c1 the first switching tube conducts and the second switching tube disconnects;

[0019] When u m < u c1 the second switching tube conducts and the first switching tube disconnects;

[0020] When the output voltage is in the positive half - cycle, the arm between the first input terminal and the first output terminal of the single - phase full - bridge inverter circuit conducts, and the arm between the first input terminal and the second output terminal of the single - phase full - bridge inverter circuit disconnects;

[0021] When the output voltage is in the negative half - cycle, the arm between the first input terminal and the second output terminal of the single - phase full - bridge inverter circuit conducts, and the arm between the first input terminal and the first output terminal of the single - phase full - bridge inverter circuit disconnects;

[0022] When the output voltage is in the positive half - cycle and u m ≥ u c2 or when the output voltage is in the negative half - cycle, the arm between the second input terminal and the first output terminal of the single - phase full - bridge inverter circuit conducts, otherwise the arm disconnects;

[0023] When the output voltage is in the negative half - cycle and u m < u c2 or when the output voltage is in the positive half - cycle, the arm between the second input terminal and the second output terminal of the single - phase full - bridge inverter circuit conducts, otherwise the arm disconnects;

[0024] When the output voltage is in the positive half - cycle and u m < u c2 or when the output voltage is in the negative half - cycle, the seventh switching tube conducts, otherwise the seventh switching tube turns off;

[0025] When the output voltage is in the negative half - cycle and u m < u c2 or when the output voltage is in the positive half - cycle, the eighth switching tube conducts, otherwise the eighth switching tube turns off;

[0026] By reducing the upper - layer carrier signal u c2The frequency is used to reduce the switching frequency of the single-phase inverter in Boost mode; by increasing the frequency of the lower carrier signal u c1 The frequency is used to increase the switching frequency of the single-phase inverter in Buck mode.

[0027] In a third aspect, the present invention provides a single-phase inverter based on a first-level energy conversion, characterized by comprising a first switching tube, a second switching tube, a first inductor, a second inductor, a single-phase full-bridge inverter circuit, a seventh switching tube, an eighth switching tube, a ninth switching tube, and a filter capacitor;

[0028] Wherein, the first end of the first switching tube is connected to the positive pole of the DC input power supply, and the second end of the first switching 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 switching tube is connected to the negative pole of the DC input power supply, and the first end of the ninth switching tube is connected to the second input end of the single-phase full-bridge inverter circuit via the second inductor;

[0029] The first end of the second switching tube is connected to the common end of the first switching tube and the first inductor, and the second end of the second switching tube is connected to the common end of the ninth switching tube and the second inductor;

[0030] 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 switching 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 switching tube;

[0031] Both ends of the filter capacitor are respectively connected to the first output end and the second output end of the single-phase inverter;

[0032] By controlling the conduction or disconnection of the four arms, the first switching tube, the second switching tube, the seventh switching tube, the eighth switching tube, and the ninth switching tube in the single-phase full-bridge inverter circuit, the switching between Buck mode and Boost mode is realized.

[0033] Preferably, each arm of the single-phase full-bridge inverter circuit includes a switching tube, and the conduction or disconnection of the arm is controlled by the conduction or disconnection of the switching tube.

[0034] In a fourth aspect, the present invention provides a modulation strategy for a single-phase inverter based on a first-level energy conversion, characterized by being used to control the single-phase inverter based on a first-level energy conversion as described in the third aspect above,

[0035] By comparing a modulation wave signal and a lower carrier signal u c1 and an upper carrier signal u c2 control signals for the four arms, the first switching tube, the second switching tube, the seventh switching tube, and the eighth switching tube in the single-phase full-bridge inverter circuit are obtained;

[0036] Among them, the modulation wave signal u m =| U omax *sin( ωt )| / U in , where U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, and the amplitude of the lower carrier signal u c1 is set to n , and the amplitude of the upper carrier signal u c2 is n × ( U omax / U in ), where n > 0, the lower carrier signal u c1 , the upper carrier signal u c2 are both triangular waves. Among them, the trough of the lower carrier signal u c1 is 0, and the trough of the upper carrier signal u c2 is n ;

[0037] When u m ≥ u c1 , the first switch tube and the ninth switch tube are turned on, and the second switch tube is turned off;

[0038] When u m < u c1 , the second switch tube is turned on, and the first switch tube and the ninth switch tube are turned off;

[0039] When the output voltage is in the 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;

[0040] When the output voltage is in the 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;

[0041] When the output voltage is in the positive half cycle andu m ≥ u c2 When it is, or during the negative half - cycle of the output voltage, the arm between the second input terminal and the first output terminal of the single - phase full - bridge inverter circuit conducts, otherwise the arm is disconnected;

[0042] When the output voltage is in the negative half - cycle and u m < u c2 When it is, or during the positive half - cycle of the output voltage, the arm between the second input terminal and the second output terminal of the single - phase full - bridge inverter circuit conducts, otherwise the arm is disconnected;

[0043] When the output voltage is in the positive half - cycle and u m < u c2 When it is, or during the negative half - cycle of the output voltage, the seventh switching tube conducts, otherwise the seventh switching tube is turned off;

[0044] When the output voltage is in the negative half - cycle and u m < u c2 When it is, or during the positive half - cycle of the output voltage, the eighth switching tube conducts, otherwise the eighth switching tube is turned off;

[0045] By reducing the frequency of the upper - layer carrier signal u c2 to reduce the switching frequency of the single - phase inverter in the Boost mode; by increasing the frequency of the lower - layer carrier signal u c1 to increase the switching frequency of the single - phase inverter in the Buck mode.

[0046] In a fifth aspect, the present invention provides a single - phase inverter based on a first - stage energy conversion, including 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;

[0047] Wherein, the first end of the first switching tube is connected to the positive pole of the DC input power supply, the second end of the first switching tube is connected to the first input terminal of the single - phase full - bridge inverter circuit via an inductor, and the second input terminal of the single - phase full - bridge inverter circuit is connected to the negative pole of the DC input power supply;

[0048] The first output terminal of the single - phase full - bridge inverter circuit is connected to the first output terminal of the single - phase inverter via the seventh switching tube, and the second output terminal of the single - phase full - bridge inverter circuit is connected to the second output terminal of the single - phase inverter via the eighth switching tube;

[0049] Both ends of the filter capacitor are respectively connected to the first output terminal and the second output terminal of the single - phase inverter;

[0050] The first output terminal of the single-phase full-bridge inverter circuit is connected to the common terminal of the first switching tube and the inductor via the second switch, and the second output terminal of the single-phase full-bridge inverter circuit is connected to the common terminal of the first switching tube and the inductor via the first switch;

[0051] By controlling the conduction or disconnection of the four arms, the first switching tube, the seventh switching tube, the eighth switching tube, the first switch and the second switch in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is realized; wherein, the first switch and the second switch are respectively conductively connected from the second output terminal of the single-phase full-bridge inverter circuit and the first output terminal of the single-phase full-bridge inverter circuit to the common terminal of the first switching tube and the inductor unidirectionally.

[0052] Preferably, the first switch and the second switch are two switching tubes, and the two switching tubes are controlled to conduct when the current direction is from the second output terminal of the single-phase full-bridge inverter circuit and the first output terminal of the single-phase full-bridge inverter circuit to the common terminal of the first switching tube and the inductor, and to disconnect otherwise.

[0053] Preferably, the first switch is a first diode and the second switch is a second diode; wherein, the anode of the first diode is connected to the second output terminal of the single-phase full-bridge inverter circuit, and the cathode is connected to the common terminal of the first switching tube and the inductor; the anode of the second diode is connected to the first output terminal of the single-phase full-bridge inverter circuit, and the cathode is connected to the common terminal of the first switching tube and the inductor.

[0054] Preferably, each arm of the single-phase full-bridge inverter circuit includes a switching tube, and the conduction or disconnection of the arm is controlled by the conduction or disconnection of the switching tube.

[0055] (III) Beneficial effects

[0056] 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:

[0057] 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

[0058] 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.

[0059] Figure 1 It is a structural schematic diagram of an existing single-phase photovoltaic inverter;

[0060] Figure 2 The circuit diagram of the existing single-phase photovoltaic inverter is as follows;

[0061] Figure 3 This is a structural diagram of a single-phase inverter based on primary energy conversion in Example 1;

[0062] Figure 4 for Figure 3 The specific circuit diagram of the architecture diagram shown;

[0063] 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;

[0064] 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;

[0065] Figure 7 for Figure 4Schematic diagram of operating mode 3 of a single-phase inverter based on first-order energy conversion as shown;

[0066] Figure 8 For Figure 4 Schematic diagram of operating mode 4 of a single-phase inverter based on first-order energy conversion as shown;

[0067] Figure 9 For Figure 4 Schematic diagram of operating mode 5 of a single-phase inverter based on first-order energy conversion as shown;

[0068] Figure 10 For Figure 4 Schematic diagram of operating mode 6 of a single-phase inverter based on first-order energy conversion as shown;

[0069] Figure 11 Frame diagram of a single-phase inverter based on first-order energy conversion in Embodiment 2;

[0070] Figure 12 For Figure 11 Specific circuit diagram of the frame diagram as shown;

[0071] Figure 13 For the modulation wave form, carrier wave form and Q 1 - Q Drive pulse width signal schematic diagrams of 8 in Embodiment 3;

[0072] Figure 14 For Figure 4 The instantaneous voltage at the output side of the circuit diagram as shown is u o , and the instantaneous current is i o , then schematic diagrams of the instantaneous output power processed in the Buck mode and Boost mode of the inverter;

[0073] Figure 15 Frame diagram of a single-phase inverter based on first-order energy conversion in Embodiment 4;

[0074] Figure 16 For Figure 15 The first specific circuit diagram of the frame diagram as shown;

[0075] Figure 17 For Figure 15 The second specific circuit diagram of the frame diagram as shown. Specific implementation manners

[0076] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0077] It should be noted that for the convenience of description, the switching IGBT is used as a representative of the controllable (turn-on and turn-off) switching tube in the embodiments of the present invention. However, the switching tube in the present invention is not limited to the IGBT. Taking the IGBT as an example for illustration. The first end of the IGBT refers to the collector, the second end refers to the emitter, and the control end refers to the gate. A drive control signal is applied to the control end of each switching tube in the embodiments of the present invention. For the sake of simplicity, it will not be elaborated hereinafter. The power switching tube in the embodiments of the present invention can also be implemented by other controllable switching tube devices other than the IGBT, such as MOSFET. At the same time, in the embodiments of the present invention, to ensure the normal operation of each switching device, a freewheeling diode needs to be connected in parallel to each switching device. The parallel connection direction of the freewheeling diode is related to the type of the switching device, and those skilled in the art can set it according to the type of the switching device, which is not limited herein. If not specified, the switching device is default to include a freewheeling diode, and it will be pointed out in this embodiment in special cases.

[0078] The embodiments of the present application provide a single-phase inverter based on a first-stage energy conversion and its modulation strategy, which solves the technical problem of the low power density of the existing single-phase photovoltaic inverter, and realizes the DC / AC conversion and buck or boost through the first-stage energy conversion. The single-phase inverter based on the first-stage energy conversion only requires an inductor and a filter capacitor, reduces the number of the inductor and the filter capacitor, and thus reduces the volume and weight of the inverter and improves the power density.

[0079] The technical solutions in the embodiments of the present application for solving the above technical problems are generally as follows:

[0080] The structure of the existing single-phase photovoltaic inverter is as Figure 1 shown. The input voltage U in is boosted to a fixed value U bus , U bus which needs to be higher than the minimum inversion voltage, and the subsequent single-phase multilevel inverter is responsible for completing the voltage inversion output. For example, a common circuit is as Figure 2As shown. The front stage of this circuit uses a Boost circuit, and the rear stage uses a single-phase full-bridge inverter to output sinusoidal AC voltage. The energy needs to be processed in two stages. The front and rear stages work at high frequency simultaneously, reducing the efficiency. At the same time, inductors and filter capacitor components are required for the energy conversion of both the front and rear stages, and a large electrolytic filter capacitor is needed for the bus filter capacitor to complete the energy decoupling of the front and rear stages, reducing the power density of the inverter. And when using a single-phase photovoltaic inverter with a structure as Figure 1 shown, if the rear-stage single-phase inverter does not use topologies such as H5, H6, and Heric that specifically suppress leakage current, there will be a problem of leakage current. For example Figure 2 when using the H4 full bridge in

[0081] To solve the above problems, the embodiments of the present invention propose a single-phase inverter based on one-stage energy conversion and its modulation strategy. This single-phase inverter is based on one-stage energy conversion. According to whether the instantaneous value of the input DC voltage is higher or lower than the instantaneous value of the output AC voltage, the working mode of the inverter is divided into Buck mode and Boost mode. In each mode, only one stage works at high frequency for energy conversion, reducing the number of high-frequency switches and improving the efficiency. At the same time, the inductor and filter capacitor are reused in the Buck mode and Boost mode. Therefore, the proposed circuit topology only requires a single inductor and filter capacitor component, reducing the number of inductors and filter capacitors compared with the traditional two-stage structure circuit, and improving the power density. In addition, a dual-carrier modulation method with different carrier amplitudes and frequencies is proposed for the proposed topology. The switching frequency of the Boost mode can be reduced by lowering the frequency of the upper carrier; the switching frequency of the Buck mode can be increased by increasing the frequency of the lower carrier. And in the Boost mode, the high-frequency switching tubes in the positive and negative half-cycles switch between the two bridge arms, making the circuit loss distribution more uniform, extending the working life of the inverter, and improving the stability of the inverter. Reducing the switching frequency of the Boost mode and increasing the switching frequency of the Buck mode also make the inductor ripple pressure smaller, which is beneficial to the more reasonable design of the inductor parameters.

[0082] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0083] Embodiment 1:

[0084] This embodiment provides a single-phase inverter based on one-stage energy conversion, as Figure 3 shown, including the first switching tube Q 1, the second switching tube Q 2, inductor L, single-phase full-bridge inverter circuit, the seventh switching tube Q 7, the eighth switching tube Q 8 and filter capacitor C. Among them, the first switching tubeQ The first end of 1 is connected to the positive pole of the DC input power supply, and the first switching tube Q The second end of 1 is connected to the first input terminal I1 of the single-phase full-bridge inverter circuit via the inductor L; the second input terminal I2 of the single-phase full-bridge inverter circuit is connected to the negative pole of the DC input power supply; the second switching tube Q The first end of 2 is connected to the common terminal of the first switching tube Q 1 and the inductor L, and the second end of the second switching tube Q 2 is connected to the common terminal of the DC input power supply and the single-phase full-bridge inverter circuit; the first output terminal O1 of the single-phase full-bridge inverter circuit is connected to the first output terminal of the single-phase inverter via the seventh switching tube Q 7, and the second output terminal O2 of the single-phase full-bridge inverter circuit is connected to the second output terminal of the single-phase inverter via the eighth switching tube Q 8; both ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter;

[0085] By controlling the conduction or disconnection of the four bridge arms, the first switching tube Q 1, the second switching tube Q 2, the seventh switching tube Q 7 and the eighth switching tube Q 8 in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is realized.

[0086] As Figure 4 shown, in the specific implementation process, the single-phase full-bridge inverter circuit includes four switching tubes Q 3~ Q 6 (it should be noted that in the specific implementation process, the single-phase full-bridge inverter circuit is also composed of other devices, such as four simple switches, diode-clamped type, flying capacitor type and other multi-level single-phase full-bridge inverters).

[0087] As Figure 4 shown, the single-phase inverter based on the first-level energy conversion includes 6 operating modes.

[0088] Three operating modes for the positive half-cycle of the output sinusoidal voltage:

[0089] Mode 1: As Figure 5 shown, the first switching tube Q 1, the third switching tube Q 3, the fourth switching tube Q 4, the sixth switching tube Q 6 and the eighth switching tube Q 8 are conducting, and other switching tubes are off. The current starts from the positive pole of the power supply U in and successively passes through the switching tubes Q 1, the inductor L, the switching tube Q 3,Q The current flows to the power supply U in at the negative electrode, outputting the Boost mode in the positive half-cycle of the sinusoidal voltage.

[0090] Mode 2: As Figure 6 shown, the first switching tube Q 1, the third switching tube Q 3, the sixth switching tube Q 6, the seventh switching tube Q 7 and the eighth switching tube Q 8 are conducting, and the other switching tubes are off. The current starts from the positive electrode of the power supply U in and successively passes through the switching tubes Q 1, the inductor L, the switching tube Q 3, Q 7, the load R L , the switching tube Q 8, Q 6 and flows to the negative electrode of the power supply U in to output the freewheeling of the Boost or Buck mode in the positive half-cycle of the sinusoidal voltage.

[0091] Mode 3: As Figure 7 shown, the second switching tube Q 2, the third switching tube Q 3, the sixth switching tube Q 6, the seventh switching tube Q 7 and the eighth switching tube Q 8 are conducting, and the other switching tubes are off. The current flows through the inductor L, the switching tube Q 3, Q 7, the load R L , the switching tube Q 8, Q 6, Q 2 to output the Buck mode in the positive half-cycle of the sinusoidal voltage.

[0092] Three operating modes for outputting the negative half-cycle of the sinusoidal voltage:

[0093] Mode 4: As Figure 8 shown, the first switching tube Q 1, the fourth switching tube Q 4, the fifth switching tube Q 5, the sixth switching tube Q 6 and the seventh switching tube Q 7 are conducting, and the other switching tubes are off. The current starts from the positive electrode of the power supply U in and successively passes through the switching tube Q1, the inductor L, the switching tubes Q5, Q6 and flows to the negative electrode of the power supply U in to output the Boost mode in the negative half-cycle of the sinusoidal voltage.

[0094] Mode 5: As shown in Figure 9 Figure, the first switching transistor Q 1, the fourth switching transistor Q 4, the fifth switching transistor Q 5, the seventh switching transistor Q 7 and the eighth switching transistor Q 8 are turned on, and the other switching transistors are turned off. The current starts from the positive pole of the power supply U in and passes through the switching transistors Q 1, the inductor L, the switching transistors Q 5, Q 8, the load R L , the switching transistors Q 7, Q 4 and flows to the negative pole of the power supply U in , and the Boost or Buck mode freewheeling of the negative half cycle of the output sine voltage is output.

[0095] Mode 6: As shown in Figure 10 Figure, the second switching transistor Q 2, the fourth switching transistor Q 4, the fifth switching transistor Q 5, the seventh switching transistor Q 7 and the eighth switching transistor Q 8 are turned on, and the other switching transistors are turned off. The current flows through the inductor L, the switching transistors Q 5, Q 8, the load R L , the switch Q 7, Q 4, Q 2, and the Buck mode of the negative half cycle of the output sine voltage is output.

[0096] It can be seen from the above mode analysis that in the positive half cycle of the output sine voltage, when the input DC voltage is lower than the output sine voltage, the drive signals of the switching transistors Q 4 and Q 7 are complementary PWM waves and work at high frequency. The switches Q 1, Q 3, Q 6 and Q 8 are always turned on, and the switches Q 2, Q 5 are turned off. At this time, the circuit works in the Boost mode, corresponding to Mode 1 and Mode 2. When the input DC voltage is higher than the output sine voltage, the drive signals of the switching transistors Q 1 and Q 2 are complementary PWM waves and work at high frequency. The switches Q 3, Q 6, Q 7 and Q8 conducts continuously, and the switch Q 4. Q 5 turns off. At this time, the circuit operates in the Buck mode, corresponding to Mode 2 and Mode 3.

[0097] In the negative half - cycle of the output sinusoidal voltage, when the input DC voltage is lower than the output sinusoidal voltage, the switching transistors Q 6 and Q 8 have complementary PWM waves as drive signals and operate at high frequency. The switches Q 1,[[]] Q 4,[[]] Q 5 and Q 7 conduct continuously, and the switches Q 2 and Q 3 turn off. At this time, the circuit operates in the Boost mode, corresponding to Mode 4 and Mode 5. When the input DC voltage is higher than the output sinusoidal voltage, the switching transistors Q 1 and Q 2 have complementary PWM waves as drive signals and operate at high frequency. The switches Q 4,[[]] Q 5,[[]] Q 7 and Q 8 conduct continuously, and the switches Q 3,[[]] Q 6 turn off. At this time, the circuit operates in the Buck mode, corresponding to Mode 5 and Mode 6.

[0098] Embodiment 2:

[0099] This embodiment takes into account the possible influence of leakage current and makes adjustments to the single - phase inverter in Embodiment 1. As Figure 11 shown, a ninth switching transistor Q 9 and a second inductor L L2 are added. Other components are the same as those in Embodiment 1, including the first switching transistor Q 1, the second switching transistor Q 2, the first inductor L L1, the single - phase full - bridge inverter circuit, the seventh switching transistor Q 7, the eighth switching transistor Q 8 and the filter capacitor C. Among them, the second terminal of the first switching transistor Q 1 is connected to the first input terminal I1 of the single - phase full - bridge inverter circuit via the first inductor L1; the second terminal of the ninth switching transistor Q 9 is connected to the negative pole of the DC input power supply, and the first terminal of the ninth switching transistor Q 9 is connected to the second input terminal I2 of the single - phase full - bridge inverter circuit via the second inductor L2; the first terminal of the second switching transistor Q 2 is connected to the common terminal of the first switching transistor Q 1 and the first inductor L1, and the first terminal of the second switching transistor QThe second terminal of 2 is connected to the ninth switching transistor Q at the common terminal of 9 and the second inductor L2; the first output terminal O1 of the single-phase full-bridge inverter circuit is connected to the first output terminal of the single-phase inverter via the seventh switching transistor Q 7; the second output terminal O2 of the single-phase full-bridge inverter circuit is connected to the second output terminal of the single-phase inverter via the eighth switching transistor Q 8; both ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter;

[0100] By controlling the conduction or disconnection of the four arms, the first switching transistor Q 1, the second switching transistor Q 2, the seventh switching transistor Q 7, the eighth switching transistor Q 8 and the ninth switching transistor Q 9 in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is realized.

[0101] It should be noted that in the specific implementation process, the first inductor L1 and the second inductor L2 are two inductors with the same characteristic parameters. In the whole circuit, if the parameters of other components are the same as those in Embodiment 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 Embodiment 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 Embodiment 1. Such a setting makes the circuit parameter distribution uniform and maximally reduces the influence on the leakage current.

[0102] In addition, the input side of the single-phase inverter in this embodiment is clamped by the input voltage in the Boost mode, while in the Buck mode, the freewheeling mode switches Q 1 and Q 9 are disconnected, so it has the ability to suppress leakage current.

[0103] As Figure 12 shown, in the specific implementation process, the single-phase full-bridge inverter circuit includes four switching transistors Q 3~ Q 6.

[0104] In this embodiment, the working mode of the single-phase inverter is the same as that of the single-phase inverter in Embodiment 1, and the control signal for the conduction or disconnection of the ninth switching transistor Q 9 is kept the same as that of the first switching transistor Q 1.

[0105] Embodiment 3:

[0106] This embodiment provides a modulation strategy for a single-phase inverter based on one-stage energy conversion, which is used to control the single-phase inverter based on one-stage energy conversion in Embodiment 1 and Embodiment 2. Through the modulation wave signal and the lower carrier signalu c1 and the upper carrier signal u c2 are compared to obtain the control signals of the four bridge arms, the first switch Q 1, the second switch Q 2, the seventh switch Q 7 and the eighth switch Q 8 in the single-phase full-bridge inverter circuit. 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, by comparing the modulation wave signal u m and the lower carrier signal u c1 and the upper carrier signal u c2 to obtain the drive signals of the switches Q 1- Q 8.

[0107] Among them, the modulation wave signal u m = | U omax * sin( ωt )| / U in , where U omax* sin( ωt ) is the output sinusoidal voltage of the single-phase inverter, U in is the input voltage, the amplitude of the lower carrier signal u c1 is set to n , the amplitude of the upper carrier signal u c2 is n × ( U omax / U in ), both the lower carrier signal u c1 and the upper carrier signal u c2 are triangular waves. Among them, the trough of the lower carrier signal u c1 is 0, and the trough of the upper carrier signal u c2 is n (in this embodiment, n = 1);

[0108] When u m ≥u c1 When, switch Q 1 is turned on, otherwise Q 1 is turned off. When u m < u c1 When, switch Q 2 is turned on, otherwise Q 2 is turned off;

[0109] When the output voltage is in the positive half - cycle, switch Q 3 is turned on, switch Q 5 is turned off;

[0110] When the output voltage is in the negative half - cycle, switch Q 5 is turned on, switch Q 3 is turned off;

[0111] When the output voltage is in the positive half - cycle and u m ≥ u c2 When, or when the output voltage is in the negative half - cycle, switch Q 4 is turned on, otherwise Q 4 is turned off;

[0112] When the output voltage is in the negative half - cycle and u m < u c2 When, or when the output voltage is in the positive half - cycle, switch Q 6 is turned on, otherwise Q 6 is turned off;

[0113] When the output voltage is in the positive half - cycle and u m < u c2 When, or when the output voltage is in the negative half - cycle, switch Q 7 is turned on, otherwise switch Q 7 is turned off;

[0114] When the output voltage is in the negative half - cycle and u m < u c2 When, or when the output voltage is in the positive half - cycle, switch Q 8 is turned on, otherwise switch Q 8 is turned off.

[0115] The following is a detailed description of this modulation strategy:

[0116] Its modulation wave waveform, carrier waveform, and Q 1 - Q The drive pulse width signals of 8 (Q The driving pulse width signal of 9 and Q 1 is kept consistent) as Figure 13 shown.

[0117] Figure 13 Set the input voltage as U in , and the output sinusoidal voltage as U omax* sin( ωt ). The lower carrier wave is u c1 , and the upper carrier wave is u c2 . Then the modulation wave in the figure is u m = | U omax * sin( ωt )| / U in . Set the amplitude of the lower carrier wave as 1, then to make the inverter correctly track the upper carrier wave amplitude of the output sinusoidal voltage is U omax / U in . Compare the modulation wave signal and the carrier wave signal u c1 and the carrier wave signal u c2 , and the drive signals of the switching tubes Q 1 - Q 8 can be obtained as Figure 13 shown.

[0118] Set Figure 13 the modulation wave in u m . Then when u m ≥ u c1 , switch Q 1 is turned on, otherwise Q 1 is turned off. When u m < u c1 , switch Q 2 is turned on, otherwise Q 2 is turned off. When the output voltage is in the positive half - cycle, switch Q 3 is turned on, otherwise Q 3 is turned off. When the output voltage is in the negative half - cycle, switch Q 5 is turned on, otherwise Q 5 is turned off. When the output voltage is in the positive half - cycle and u m ≥ u c2When, or during the negative half-cycle of the output voltage, switch Q 4 conducts; otherwise Q 4 turns off. When during the negative half-cycle of the output voltage and u m < u c2 When, or during the positive half-cycle of the output voltage, switch Q 6 conducts; otherwise Q 6 turns off. When during the positive half-cycle of the output voltage and u m < u c2 When, or during the negative half-cycle of the output voltage, switch Q 7 conducts; otherwise switch Q 7 turns off. When during the negative half-cycle of the output voltage and u m < u c2 When, or during the positive half-cycle of the output voltage, switch Q 8 conducts; otherwise switch Q 8 turns off.

[0119] Assume the frequency of the carrier u c1 is f c1 , and the frequency of the carrier u c2 is f c2 , then it can be known that the switching frequency of the inverter operating in the Buck mode is f c1 , and the switching frequency of the inverter operating in the Boost mode is f c2 . By adjusting the values of f c1 and f c2 , the switching frequencies of the inverter operating in the Buck mode and the Boost mode can be adjusted respectively.

[0120] Assume the instantaneous voltage on the output side is u o , and the instantaneous current is i o , then the instantaneous output power, i.e., energy, processed by the inverter in the Buck mode and the Boost mode is as shown in Figure 14 :

[0121] 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, from Figure 14 it can be seen that the instantaneous output power p o is the power with double - frequency fluctuation. The converter mainly processes most of the energy in the Boost mode, while the energy processed in the Buck mode is smaller. Therefore, in the Boost mode, when the switching tube performs high - frequency switching, the voltage and current stresses are relatively high, and the energy consumption for high - frequency energy conversion is large. While in the Buck mode, when the switching tube performs high - frequency switching, the voltage and current stresses are relatively low, and the energy consumption for high - frequency energy switching is small. However, since Q 1 - Q 8 has the same maximum voltage stress and maximum current stress, the same devices are used. It can be seen that in the Buck mode, there is redundancy in the performance of the switching tube. The switching frequency of the high - frequency switch in the Buck mode can be increased, and the switching frequency in the Boost mode can be appropriately reduced, so that f c1 > f c2 , thus balancing the difference in loss distribution caused by high - frequency operation on each switching tube and improving the reliability of the converter. In addition, under the condition of the same current ripple, the demand for inductance in the Boost mode is smaller, while the demand for inductance in the Buck mode is larger. By setting f c1 > f c2 to make the switching frequency of the Buck mode higher than that of the Boost mode, it is beneficial to reduce the original inductance demand in the Buck mode and balance the parameter design of the converter. In addition, increasing the switching frequency of the Buck mode reduces the original inductance demand in the Buck mode, which is also beneficial to the stable operation of the converter.

[0122] Embodiment 4:

[0123] In this embodiment, in order to suppress the leakage current and reduce the number of conducting switching tubes, thereby reducing the conduction loss. This embodiment provides a single - phase inverter based on first - stage energy conversion, as Figure 15 shown, including the first switching tube Q 1, the first switch, the second switch, the inductor L, the single - phase full - bridge inverter circuit, the seventh switching tube Q 7, the eighth switching tube Q 8 and the filter capacitor C. Among them, the first end of the first switching tube Q 1 is connected to the positive pole of the DC input power supply, and the second end of the first switching tube Q 1 is connected to the first input terminal I1 of the single - phase full - bridge inverter circuit via the inductor L; the second input terminal I2 of the single - phase full - bridge inverter circuit is connected to the negative pole of the DC input power supply; the first output terminal O1 of the single - phase full - bridge inverter circuit is connected via the seventh switching tube Q7 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 via the eighth switching tube Q 8 is connected to the second output terminal of the single-phase inverter; both ends of the filter capacitor C are respectively connected to the first output terminal and the second output terminal of the single-phase inverter;

[0124] The first output terminal O1 of the single-phase full-bridge inverter circuit is connected via the second switch to the common terminal of the first switching tube Q 1 and the inductor L, and the second output terminal O2 of the single-phase full-bridge inverter circuit is connected via the first switch to the common terminal of the first switching tube Q 1 and the inductor L.

[0125] By controlling the conduction or disconnection of the four bridge arms, the first switching tube Q 1, the seventh switching tube Q 7, the eighth switching tube Q 8, the first switch and the second switch in the single-phase full-bridge inverter circuit, the switching between the Buck mode and the Boost mode is realized; among them, the first switch and the second switch are respectively conductively connected from the second output terminal of the single-phase full-bridge inverter circuit and the first output terminal of the single-phase full-bridge inverter circuit unidirectionally to the common terminal of the first switching tube Q 1 and the inductor L.

[0126] As Figure 16 shown, in the specific implementation process, the single-phase full-bridge inverter circuit includes four switching tubes Q3~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 two switching tubes Q 2 and Q 9 responsible for controlling conduction when the current direction is from the second output terminal of the single-phase full-bridge inverter circuit, the first output terminal of the single-phase full-bridge inverter circuit to the common terminal of the first switching tube Q 1 and the inductor L, and vice versa for disconnection.

[0127] As Figure 17 shown, in order to further reduce the use of switching tubes on the basis of the circuit shown in Figure 16 shown, two diodes are used to replace the two switching tubes Q 2 and Q 9 to realize the unidirectional conduction of the second output terminal of the single-phase full-bridge inverter circuit to the common terminal of the first switching tube Q 1 and the inductor L, and the unidirectional conduction of the first output terminal of the single-phase full-bridge inverter circuit to the common terminal of the first switching tube Q 1 and the inductor L.

[0128] In summary, compared with the prior art, the following beneficial effects are achieved:

[0129] 1. Based on single-stage energy conversion, the embodiment of the present invention proposes a novel single-phase inverter topology with a wide input DC voltage range. It operates in Buck mode or Boost mode at high frequency according to whether the input voltage is higher or lower than the output voltage. Compared with the traditional two-stage conversion topology, only one stage of switching tubes operates at high frequency for energy conversion, improving the efficiency. At the same time, compared with the traditional two-stage conversion topology, only one inductor and one filter capacitor are required, reducing the number of inductors and filter capacitors, thereby reducing the volume and weight of the converter and increasing the power density.

[0130] 2. The embodiment of the present invention proposes a dual-carrier modulation strategy with different amplitudes for the proposed single-stage energy conversion single-phase inverter topology. It can achieve smooth switching between Buck mode and Boost mode of the converter. The frequencies of the two carriers can be adjusted so that the Buck mode and Boost mode of the converter have the same or different switching frequencies.

[0131] 3. The embodiment of the present invention reduces the frequency of the upper carrier to reduce the switching frequency of the Boost mode; increases the frequency of the lower carrier to increase the switching frequency of the Buck mode. At the same time, in the Boost mode, the high-frequency switching tubes in the positive and negative half-cycles switch between the two bridge arms, thereby balancing the difference in loss distribution caused by high-frequency operation on each switching tube and improving the reliability of the converter. In addition, under the condition of the same current ripple, the demand for inductance in the Boost mode is smaller, and the demand for inductance in the Buck mode is larger. By setting f c1 > f c2 the switching frequency of the Buck mode is higher than that of the Boost mode, which is beneficial to reducing the original inductance demand in the Buck mode and balancing the parameter design of the converter. In addition, increasing the switching frequency of the Buck mode reduces the original inductance demand in the Buck mode, which is also beneficial to the stable operation of the converter.

[0132] 4. In Embodiment 2, the input side of the single-phase inverter is clamped by the input voltage in the Boost mode, while in the Buck mode, the freewheeling mode switches Q1 and Q9 are turned off, so it has the ability to suppress leakage current. In Embodiment 4, in the Buck mode of the single-phase inverter, the freewheeling mode switches Q1, Q4, and Q6 are turned off, so it also has the ability to suppress leakage current.

[0133] It should be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0134] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate 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; Wherein, each switch device is connected in parallel with a freewheeling diode; 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 Buck mode and Boost mode is achieved by controlling the on or off of 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, and the single-phase inverter is a single-phase photovoltaic inverter.

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, each switch device is connected in parallel with a freewheeling diode; 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 conduction or disconnection of four bridge arms, a first switch tube, a second switch tube, a seventh switch tube, an eighth switch tube and a ninth switch tube in a single-phase full-bridge inverter circuit, switching between Buck mode and Boost mode is achieved, and the single-phase inverter is a single-phase photovoltaic inverter.

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, each switch device is connected in parallel with a freewheeling diode; 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, and the single-phase inverter is a single-phase photovoltaic inverter.

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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