Single-stage isolation inverter circuit and control method thereof

Abstract

The invention discloses a single-stage isolation inverter circuit and a control method thereof, and belongs to the technical field of new energy. The low-voltage inversion module is used for performing inversion processing on the photovoltaic module to obtain low-voltage alternating current; the transformer is provided with a resonant cavity on the secondary side and is used for converting the low-voltage alternating current into high-voltage alternating current; the rectification module is used for converting the high-voltage alternating current into direct current; the high-voltage filtering module is used for filtering the direct current; the midpoint of a bridge arm of the rectifier module and the midpoint of a capacitor bridge arm in the high-voltage filter module are respectively connected with two output ends of the resonant cavity; the high-voltage inversion module is used for converting the direct-current filtering electricity into high-voltage alternating-current electricity; a bridge arm midpoint of the high-voltage inversion module is connected with a power grid; and the alternating current filtering module is connected with the midpoint of the bridge arm of the rectifying module and is used for filtering the high-voltage alternating current and injecting the filtered current into a power grid. Through the circuit, the complexity of controlling the single-stage isolation inverter circuit can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and particularly relates to a single-stage isolated inverter circuit and a control method thereof. Background Art

[0002] A micro-inverter is a component-level power electronic device in a photovoltaic power generation system, which can achieve ( , maximum power point tracking), and convert the direct current generated by the photovoltaic module into alternating current and incorporate it into the power grid. Please refer to Figure 1 , Figure 1 which is the main power topology diagram of a micro-inverter in the prior art. Among them, a micro-inverter usually adopts a single-stage isolated inverter circuit with a flyback converter cascaded with a power frequency inverter as the main power topology. As Figure 1 shown, after the energy of the photovoltaic module passes through a current source type flyback converter composed of a switching tube , an isolation transformer T, and a rectifier diode D, it becomes a steamed bun wave current, and then a power frequency inverter circuit composed of a switching tube inverts the steamed bun wave current into alternating current and injects it into the power grid.

[0003] Limited by the operating characteristics of the flyback converter, the overall efficiency of a micro-inverter adopting this circuit topology is relatively low. Moreover, the current of the flyback converter cannot be reversed. Therefore, when this circuit operates at a non-unit power factor, current clipping will occur, which will further lead to poor reactive power compensation ability of the micro-inverter. Please refer to Figure 2 , Figure 2 which is Figure 1 a schematic diagram of the circuit shown when current clipping occurs during operation.

[0004] Currently, a series resonance structure is usually added to the primary or secondary side of the transformer, and a matrix converter in the form of a half-bridge or full-bridge is adopted on the rectifier side of the transformer to perform reactive power compensation on the single-stage isolated inverter circuit shown in Figure 1 . Please refer to Figures 3 to 5 , Figure 3 which is the topology diagram of a resonant isolated inverter circuit in the prior art, Figure 4 which is the structure diagram of another resonant isolated inverter circuit in the prior art, Figure 5 which is the structure diagram of yet another resonant isolated inverter circuit in the prior art. However, Figures 3 to 5 the resonant isolated inverter circuits described above all use different forms of matrix converters to achieve AC output, and under these circuit architectures, it is necessary to perform AC-to-AC power conversion on the current output by the photovoltaic module, which will lead to a relatively high control complexity of the single-stage isolated inverter circuit. Currently, there is no relatively effective solution to this technical problem. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a single-stage isolated inverter circuit and its control method to solve the technical problem of high complexity in controlling the single-stage isolated inverter circuit in the prior art. The specific solutions are as follows:

[0006] To solve the above technical problems, the present invention provides a single-stage isolated inverter circuit, including:

[0007] A photovoltaic module;

[0008] A low-voltage inverter module for inverting the output voltage of the photovoltaic module to obtain low-voltage alternating current;

[0009] A transformer with a resonant cavity on the secondary side for voltage transformation of the low-voltage alternating current to obtain high-voltage alternating current;

[0010] A rectification module for rectifying and transforming the high-voltage alternating current to obtain direct current;

[0011] A high-voltage filtering module for filtering the direct current to obtain filtered direct current; the midpoint of the bridge arm of the rectification module and the midpoint of the capacitor bridge arm of the high-voltage filtering module are respectively connected to the two output ends of the resonant cavity;

[0012] A high-voltage inverter module for inverting the filtered direct current to obtain high-voltage alternating current; the midpoint of the bridge arm of the high-voltage inverter module is connected to the power grid;

[0013] An AC filtering module connected to the midpoint of the bridge arm of the rectification module for filtering the high-voltage alternating current to obtain filtered AC and injecting the filtered AC into the power grid.

[0014] Preferably, when there is only one photovoltaic component in the photovoltaic module, the photovoltaic module includes: the photovoltaic component and a first capacitor; wherein, both ends of the first capacitor are respectively connected to both ends of the photovoltaic component.

[0015] Preferably, when there are photovoltaic components in the photovoltaic module, ; the photovoltaic module includes: a second capacitor and component sub-modules connected in parallel to the second capacitor, and each component sub-module includes: the photovoltaic component, a third capacitor connected in parallel to the photovoltaic component, and a transformation module for voltage transformation of the output voltage of the photovoltaic component.

[0016] Preferably, the low-voltage inverter module includes: a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube;

[0017] Wherein, the first end of the first switching tube is respectively connected to the first output end of the photovoltaic module and the first end of the third switching tube. The second end of the first switching tube is respectively connected to the first end of the second switching tube and the first end of the primary winding of the transformer. The second end of the second switching tube is respectively connected to the second end of the photovoltaic module and the second end of the fourth switching tube. The first end of the fourth switching tube is respectively connected to the second end of the third switching tube and the second end of the primary winding of the transformer.

[0018] Preferably, the rectification module includes: a fifth switching tube and a sixth switching tube;

[0019] Wherein, the second end of the fifth switching tube is respectively connected to the first end of the sixth switching tube and the resonant inductor in the resonant cavity;

[0020] Correspondingly, the connection point of the fifth switching tube and the sixth switching tube is the midpoint of the bridge arm of the rectification module. The first end of the fifth switching tube is connected to the AC filtering module, and the second end of the sixth switching tube is connected to the high-voltage filtering module.

[0021] Preferably, the high-voltage filtering module includes: a fourth capacitor and a fifth capacitor;

[0022] Wherein, the first end of the fourth capacitor is connected to the first end of the fifth switching tube. The second end of the fourth capacitor is respectively connected to the resonant capacitor in the resonant cavity and the first end of the fifth capacitor. The second end of the fifth capacitor is connected to the second end of the sixth switching tube;

[0023] Correspondingly, the connection point of the fourth capacitor and the fifth capacitor is the midpoint of the capacitor bridge arm in the high-voltage filtering module.

[0024] Preferably, the high-voltage inversion module includes: a seventh switching tube and an eighth switching tube;

[0025] Wherein, the first end of the seventh switching tube is connected to the first end of the fifth switching tube. The second end of the seventh switching tube is respectively connected to the first end of the eighth switching tube and the neutral line of the power grid. The second end of the eighth switching tube is connected to the second end of the fifth capacitor.

[0026] To solve the above technical problems, the present invention also provides a control method for a single-stage isolated inverter circuit, which is applied to the single-stage isolated inverter circuit disclosed above, and includes:

[0027] Determine the primary and secondary side voltages of the transformer within one switching period according to the working characteristics of the single-stage isolated inverter circuit;

[0028] Determine the time-domain equations of the single-stage isolated inverter circuit in different operating modes to obtain a time-domain equation set;

[0029] According to the primary and secondary side voltages, the time-domain equation set, and the conduction conditions of each switching tube in the single-stage isolated inverter circuit, determine the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal to control the single-stage isolated inverter circuit.

[0030] Preferably, the primary and secondary side voltages include: the primary side voltage and the secondary side voltage;

[0031] Among them, the expression of the primary side voltage is:

[0032] ;

[0033] The expression of the secondary side voltage is:

[0034] ;

[0035] In the formula, is the primary side voltage, is the output voltage of a photovoltaic module in the photovoltaic module, is the negative value of the output voltage of a photovoltaic module in the photovoltaic module, is time, is the duty cycle of each switching tube in the low-voltage inverter module, is the switching period, is the secondary side voltage, is the voltage at the midpoint of the capacitor bridge arm in the high-voltage filter module, is the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal, is the switching angular frequency.

[0036] Preferably, the step of determining the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal according to the primary and secondary side voltages, the time-domain equation set, and the conduction conditions of each switching tube in the single-stage isolated inverter circuit to control the single-stage isolated inverter circuit includes: According to the primary side voltage, the secondary side voltage, and the time-domain equation set, determine the effective value of the current in the resonant cavity;

[0037] Based on the conduction conditions of each switching tube in the single-stage isolated inverter circuit,

[0038] ​The conduction condition is used to determine the phase shift angle of the high-voltage side drive signal of the transformer relative to the low-voltage side drive signal with the minimum effective value of the current in the resonant cavity as the boundary condition, so as to control the single-stage isolated inverter circuit.

[0039] Beneficial effects: In the single-stage isolated inverter circuit provided by the present invention, first, the low-voltage inverter module is used to invert the output voltage of the photovoltaic module to obtain low-voltage alternating current; second, the transformer with a resonant cavity on the secondary side is used to transform the low-voltage alternating current output by the low-voltage inverter module to obtain high-voltage alternating current; then, the rectification module is used to rectify and transform the high-voltage alternating current output by the transformer to obtain direct current; after that, the high-voltage filter module is used to filter the direct current output by the rectification module to obtain filtered direct current, and the high-voltage inverter module is used to invert the filtered direct current to obtain high-voltage alternating current; finally, the AC filter module is used to filter the high-voltage alternating current output by the high-voltage inverter module to obtain filtered AC, and the obtained filtered AC is injected into the power grid.

[0040] Compared with the prior art, the single-stage isolated inverter circuit provided by the present invention avoids direct AC-AC conversion of high-frequency resonant current, reducing the control complexity of the entire system; at the same time, the high-voltage filter module can reduce the high-frequency harmonics contained in the injected grid current, further reducing the requirements for the AC filter, which is beneficial to reducing the volume and cost of the AC filter. Finally, the control method of the single-stage isolated inverter circuit provided by the present invention does not require dynamic adjustment of the switching frequency, reducing the difficulty of implementing the solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0042] Figure 1 It is the main power topology diagram of a micro-inverter in the prior art;

[0043] Figure 2 is Figure 1 the schematic diagram when the current clipping phenomenon occurs during the operation of the circuit shown;

[0044] Figure 3 It is the topology diagram of a resonant isolated inverter circuit in the prior art;

[0045] Figure 4 It is the structural diagram of another resonant isolated inverter circuit in the prior art;

[0046] Figure 5 It is a structural diagram of another resonant isolation inverter circuit in the prior art;

[0047] Figure 6 It is a schematic diagram of a single-stage isolation inverter circuit provided by an embodiment of the present invention;

[0048] Figure 7 It is a structural diagram of a single-stage isolation inverter circuit provided by an embodiment of the present invention;

[0049] Figure 8 It is a flowchart of a control method for a single-stage isolation circuit provided by an embodiment of the present invention;

[0050] Figure 9 It is Figure 7 the modulation timing diagram of the single-stage isolation inverter circuit shown;

[0051] Figure 10 It is Figure 7 the schematic diagram of the single-stage isolation inverter circuit shown in the first working mode;

[0052] Figure 11 It is Figure 7 the schematic diagram of the single-stage isolation inverter circuit shown in the second working mode;

[0053] Figure 12 It is Figure 7 the schematic diagram of the single-stage isolation inverter circuit shown in the third working mode;

[0054] Figure 13 It is a structural diagram of another single-stage isolation inverter circuit provided by an embodiment of the present invention. Detailed implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] Please refer to Figure 6 , Figure 6 which is a schematic diagram of a single-stage isolation inverter circuit provided by an embodiment of the present invention. The single-stage isolation inverter circuit includes:

[0057] Photovoltaic module 11;

[0058] A low-voltage inverter module 12, configured to invert the output voltage of the photovoltaic module 11 to obtain low-voltage alternating current;

[0059] A transformer 13 with a resonant cavity is provided on the secondary side for voltage conversion of low-voltage alternating current to obtain high-voltage alternating current;

[0060] A rectification module 14 for rectifying and converting the high-voltage alternating current to obtain direct current;

[0061] A high-voltage filtering module 15 for filtering the direct current to obtain filtered direct current; the midpoints of the bridge arms of the rectification module 14 and the midpoints of the capacitor bridge arms in the high-voltage filtering module 15 are respectively connected to the two output terminals of the resonant cavity;

[0062] A high-voltage inversion module 16 for inverting the filtered direct current to obtain high-voltage alternating current; the midpoint of the bridge arm of the high-voltage inversion module 16 is connected to the power grid;

[0063] An AC filtering module 17 is connected to the midpoint of the bridge arm of the rectification module 14 for filtering the high-voltage alternating current to obtain filtered AC current and injecting the filtered AC current into the power grid.

[0064] In this embodiment, a single-stage isolated inverter circuit is provided, and using this circuit can significantly reduce the complexity in controlling the single-stage isolated inverter circuit. In the single-stage isolated inverter circuit, a photovoltaic module 11, a low-voltage inversion module 12, a transformer 13, a rectification module 14, a high-voltage filtering module 15, a high-voltage inversion module 16, and an AC filtering module 17 are provided.

[0065] When the single-stage isolated inverter circuit is in operation, the low-voltage inversion module 12 first performs inversion processing on the output voltage of the photovoltaic module 11 to obtain low-voltage alternating current; secondly, the transformer 13 with a resonant cavity on the secondary side performs voltage conversion on the low-voltage alternating current output by the low-voltage inversion module 12 to obtain high-voltage alternating current; then, the rectification module 14 performs rectification conversion on the high-voltage alternating current output by the transformer 13 to obtain direct current; afterwards, the high-voltage filtering module 15 filters the direct current output by the rectification module 14 to obtain filtered direct current, and further, the high-voltage inversion module 16 inverts the filtered direct current output by the high-voltage filtering module 15 to obtain high-voltage alternating current; finally, the AC filtering module 17 filters the high-voltage alternating current output by the high-voltage inversion module 16 to obtain filtered AC current and injects the obtained filtered AC current into the power grid.

[0066] In this embodiment, the resonant cavity connected to the secondary side of the transformer 13 is used to enable the switching tubes in each functional module to achieve ( , zero-voltage switching) function to reduce switching losses and thus improve the working efficiency of the single-stage isolated inverter circuit.

[0067] Specifically, in this embodiment, the low-voltage inverter module 12, the transformer 13, the rectifier module 14, the high-voltage filter module 15, the high-voltage inverter module 16, and the AC filter module 17 can be set to any circuit structure capable of realizing their corresponding functions. Moreover, in practical applications, the AC filter module 17 can be set as a low-pass filter, where the low-pass filter can be either a single inductor or ( , an inductor-capacitor-inductor filter) circuit, or a low-pass filter in other structural forms.

[0068] It should be noted that, in this embodiment, two output terminals are led out from the resonant cavity on the secondary side of the transformer 13. One output terminal is connected to the midpoint of the bridge arm of the rectifier module 14, and the other output terminal is connected to the midpoint of the capacitor bridge arm in the high-voltage filter module 15. Moreover, the midpoint of the bridge arm of the high-voltage inverter module 16 is connected to the power grid, which is the main improvement compared with the existing single-stage isolated inverter circuit. Through this setting structure, the voltage output by the transformer 13 can be first converted from AC to DC, and then from DC to AC. Compared with the existing single-stage isolated inverter circuit that directly performs AC-to-AC power conversion on the voltage output by the photovoltaic module, using this setting structure is equivalent to performing decoupling control on the single-stage isolated inverter circuit, thereby greatly reducing the complexity of controlling the single-stage isolated inverter circuit.

[0069] Compared with the prior art, the single-stage isolated inverter circuit provided in this embodiment avoids directly performing AC-AC conversion on the high-frequency resonant current, reducing the control complexity of the entire system; at the same time, the high-voltage filter module can reduce the high-frequency harmonics contained in the grid-injected current, further reducing the requirements for the AC filter, which is beneficial to reducing the volume and cost of the AC filter.

[0070] Based on the above embodiment, this embodiment further illustrates and optimizes the technical solution. Please refer to Figure 7 , Figure 7 which is a structural diagram of a single-stage isolated inverter circuit provided by an embodiment of the present invention. As a preferred implementation manner, when there is only one photovoltaic component in the photovoltaic module 11 , the photovoltaic component module 11 includes: a photovoltaic component and a first capacitor ; wherein, both ends of the first capacitor are respectively connected to both ends of the photovoltaic component .

[0071] In order to enable those skilled in the art to more clearly understand the implementation principle of the present invention, in this embodiment, a simplest application scenario of the photovoltaic module 11 is first introduced. That is, only one photovoltaic component is provided in the photovoltaic module 11 ( ).

[0072] When only one photovoltaic component is provided in the photovoltaic module 11 , after the photovoltaic component converts solar energy into electric energy, it is stored through the first capacitor . When the first capacitor stores the electric energy converted by the photovoltaic component , the subsequent low-voltage inverter module 12 can invert the voltage output by the photovoltaic component and continue to execute the subsequent process.

[0073] Please continue to refer to Figure 7 , as a preferred implementation manner, the low-voltage inverter module 12 includes: a first switching tube , a second switching tube , a third switching tube and a fourth switching tube ;

[0074] Among them, the first end of the first switching tube is respectively connected to the first output end of the photovoltaic module 11 and the first end of the third switching tube , the second end of the first switching tube is respectively connected to the first end of the second switching tube and the first end of the primary winding of the transformer T, the second end of the second switching tube is respectively connected to the second end of the photovoltaic module 11 and the second end of the fourth switching tube , and the first end of the fourth switching tube is respectively connected to the second end of the third switching tube and the second end of the primary winding of the transformer T.

[0075] In this embodiment, the low-voltage inverter module 12 is specifically described. Among them, both ends of the first capacitor are respectively the first output end and the second output end of the photovoltaic module 11. The low-voltage inverter module 12 is composed of a first switching tube , a second switching tube , a third switching tube and a fourth switching tube , and is actually a full-bridge circuit.

[0076] Since the full-bridge circuit can achieve the soft-switching function compared with other types of low-voltage inverter modules, and make the voltage and current changes in the subsequent circuit relatively gentle, which helps to reduce the switching loss and improve the reliability of the circuit during operation. Therefore, in this embodiment, the first switch tube , the second switch tube , the third switch tube and the fourth switch tube are used to build the low-voltage inverter module 12.

[0077] Please continue to refer to Figure 7 . As a preferred embodiment, the rectification module 14 includes: a fifth switch tube and a sixth switch tube ;

[0078] Among them, the second end of the fifth switch tube is respectively connected to the first end of the sixth switch tube and the resonant inductor in the resonant cavity;

[0079] Correspondingly, the connection point of the fifth switch tube and the sixth switch tube is the midpoint of the bridge arm of the rectification module . The first end of the fifth switch tube is connected to the AC filtering module 17, and the second end of the sixth switch tube is connected to the high-voltage filtering module 15.

[0080] In this embodiment, the rectification module 14 is specifically described. Among them, the rectification module 14 is built by the fifth switch tube and the sixth switch tube . The rectification module 14 is essentially a half-bridge circuit. Since this type of rectification module has the advantages of simple structure, flexible control, low design cost, etc., when using the fifth switch tube and the sixth switch tube to build the rectification module 14, it can not only reduce the difficulty of building a single-stage isolated inverter circuit, but also reduce the control difficulty and the required cost investment of the single-stage isolated circuit.

[0081] As a preferred embodiment, the high-voltage filtering module 15 includes: a fourth capacitor and a fifth capacitor ;

[0082] Among them, the first end of the fourth capacitor is connected to the first end of the fifth switch tube . The second end of the fourth capacitor is respectively connected to the resonant capacitor in the resonant cavity is connected to the first terminal of the fifth capacitor , and the second terminal of the fifth capacitor is connected to the second terminal of the sixth switching transistor ;

[0083] Correspondingly, the connection point of the fourth capacitor and the fifth capacitor is the midpoint of the capacitor bridge arm in the high-voltage filtering module 15.

[0084] In this embodiment, the high-voltage filtering module 15 is specifically described. Through the high-voltage filtering module 15, the direct current output by the rectifying module 14 can be filtered to obtain a filtered direct current. It should be noted that in this embodiment, only one implementation manner with the simplest structure of the high-voltage filtering module 15 is listed. In actual applications, more capacitors can also be provided in the high-voltage filtering module 15 to filter the direct current output by the rectifying module 14 to obtain a filtered direct current, and only the midpoint of the capacitor bridge arm in the high-voltage filtering module 15 needs to be connected to the output end of the resonant cavity.

[0085] Obviously, through the technical solution provided by this embodiment, the structural complexity of the high-voltage filtering module can be relatively reduced.

[0086] Please continue to refer to Figure 7 , as a preferred embodiment, the high-voltage inverter module 16 includes: a seventh switching transistor and an eighth switching transistor ;

[0087] Among them, the first terminal of the seventh switching transistor is connected to the first terminal of the fifth switching transistor , the second terminal of the seventh switching transistor is respectively connected to the first terminal of the eighth switching transistor and the neutral line of the power grid, and the second terminal of the eighth switching transistor is connected to the second terminal of the fifth capacitor .

[0088] In this embodiment, the high-voltage inverter module 16 is specifically described. Among them, the high-voltage inverter module 16 is composed of the seventh switching transistor and the eighth switching transistor . The high-voltage inverter module 16 is essentially a half-bridge circuit. Since the structure of the half-bridge circuit is simple and the setting cost is low, when using the seventh switching transistor and the eighth switching transistor to build the high-voltage inverter module 16, not only can the structural complexity of the single-stage isolated inverter circuit be reduced, but also the design cost of the single-stage isolated inverter circuit can be reduced.

[0089] In addition, Figure 7 In the single-stage isolated inverter circuit shown in FIG. 1 , the AC filter module 17 is set to be an AC filter inductor. That is, it uses AC filter inductance The high voltage AC power outputted by the high voltage inverter module 16 is filtered, and the filtered high voltage AC power is injected into the power grid. Obviously, the structural complexity of the single-stage isolation inverter circuit can be further reduced through such a configuration structure.

[0090] See also Figure 8 , Figure 8 A flow chart of a control method for a single-stage isolation circuit provided in an embodiment of the present invention is applied to a single-stage isolation inverter circuit disclosed above. The method includes:

[0091] Step S11: determining the primary and secondary voltages of the transformer in one switching cycle according to the working characteristics of the single-stage isolated inverter circuit;

[0092] Step S12: Determine the single-stage isolated inverter circuit in different working modes Time domain equations, and obtain the time domain equations;

[0093] Step S13: According to the original secondary voltage, the time domain equations and the switching tubes in the single-stage isolation inverter circuit The conduction condition determines the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal, so as to control the single-stage isolated inverter circuit.

[0094] In the above-mentioned single-stage isolated inverter circuit, the switch tubes connected to the two bridge arms in the low-voltage inverter module on the primary side of the transformer will be turned on and off alternately and complementary, and the driving signal of the switch tube on the latter bridge arm in the low-voltage inverter module will lag behind the driving signal of the switch tube at the corresponding position on the former bridge arm. In this case, it can be assumed that the duty cycle of each switch tube in the low-voltage inverter module is The switch tubes in the secondary rectifier module of the transformer will be turned on and off alternately and complementary, and the duty cycle is , and the high-voltage side drive signal of the transformer will lag behind the low-voltage side drive signal by an angle When the grid voltage is in the positive half cycle and the negative half cycle, the on and off states of the switch tube in the high-voltage inverter module are also known.

[0095] Under this modulation mode, the primary and secondary voltages of the transformer in one switching cycle can be determined according to the working characteristics of the single-stage isolated inverter circuit. The primary and secondary voltages of the transformer in one switching cycle refer to the voltage on the primary node of the transformer and the voltage on the secondary node of the transformer.

[0096] When the switching tubes in each functional module of the single-stage isolated inverter circuit conduct and turn off in different time periods, the single-stage isolated inverter circuit will operate in different working modes. At this time, according to ( , Kirchhoff's voltage law), the time-domain equations of the single-stage inverter in different working modes can be determined, thus obtaining a system of time-domain equations.

[0097] Since the conducting conditions of the switching tubes in each of the single-stage isolated inverter circuit are also determined and known. In this case, based on the primary and secondary side voltages, the system of time-domain equations, and the conducting conditions of the switching tubes in each of the single-stage isolated inverter circuit, the phase shift angle of the drive signal on the high-voltage side of the transformer compared to the drive signal on the low-voltage side can be determined . And the duty cycles of the switching tubes in the low-voltage inverter module will be regulated according to the grid current. Therefore, through the above method, the conducting and turning-off states corresponding to each switching tube in the single-stage isolated inverter circuit at different moments can be determined, and thus the purpose of controlling the single-stage isolated inverter circuit can be achieved.

[0098] In the single-stage isolated inverter circuit provided in this embodiment, the structure of the high-voltage side of the transformer is set in the form of rectification plus inversion. In this way, it is equivalent to converting the high-frequency alternating current transmitted by the resonant cavity into a DC mode, and then converting it from the DC mode into a power-frequency alternating current. Compared with the single-stage isolated inverter circuit described in the prior art, which directly converts the high-frequency alternating current transmitted by the resonant cavity into a power-frequency alternating current, using the circuit structure and control method described in this embodiment is equivalent to performing decoupling control on the single-stage isolated inverter circuit. In this case, it is not necessary to adjust the frequencies of the switching tubes in the rectification module, and there is no need to dynamically adjust the switching frequency, which reduces the difficulty of implementing the solution. It is only necessary to pay attention to whether the voltages on the primary and secondary sides of the transformer match and whether the current waveform injected into the grid is sinusoidal. Thus, the complexity of controlling the single-stage isolated inverter circuit can be significantly reduced.

[0099] Here, take the Figure 7 single-stage isolated inverter circuit shown as an example for specific illustration. In the Figure 7 single-stage isolated inverter circuit shown, within one switching period , in the full-bridge circuit on the low-voltage side of the transformer T, the first switching tube and the second switching tube perform high-frequency complementary actions, and the third switching tube and the fourth switching tube perform high-frequency complementary actions. The first switching tube and the third switching transistor both have a duty cycle of , and the driving signal of the third switching transistor lags behind that of the first switching transistor . The fifth switching transistor on the high-voltage side of the transformer T and the sixth switching transistor are high-frequency complementary. The duty cycles of these two switching transistors are both , and moreover, the driving signal of the fifth switching transistor lags behind that of the first switching transistor . To complete the grid connection operation of the photovoltaic module , when the grid voltage is in the positive half-cycle, the eighth switching transistor conducts while the seventh switching transistor turns off; when the grid voltage is in the negative half-cycle, the seventh switching transistor conducts while the eighth switching transistor turns off. Please refer to

[0100] , Figure 9 , Figure 9 which is Figure 7 the modulation timing diagram of the single-stage isolated inverter circuit shown. In Figure 9 , , , , , and respectively represent the conduction times corresponding to the first switching transistor , the second switching transistor , the third switching transistor , the fourth switching transistor , the fifth switching transistor and the sixth switching transistor . In the coordinate system involving , , , , and , the horizontal axis represents time , and the vertical axis represents the high and low levels 0 and 1. The green line represents the primary voltage of the transformer T, the blue line represents the voltage of the resonant cavity connected to the secondary side of the transformer T, and the orange line represents the resonant current in the resonant cavity. In the coordinate system where , and are located, the horizontal axis represents time The vertical axis represents voltage .

[0101] Under the above modulation method, according to the working characteristics of the single-stage isolated inverter circuit, the primary and secondary side voltages of the transformer within one switching period can be deduced. Specifically, the primary and secondary side voltages of the transformer include: the primary side voltage and the secondary side voltage;

[0102] Among them, the expression of the primary side voltage is:

[0103] Formula 1: ;

[0104] The expression of the secondary side voltage is:

[0105] Formula 2: ;

[0106] In the formula, is the primary side voltage, is the secondary side voltage, is the output voltage of a photovoltaic module in the photovoltaic module assembly, is time, is the duty cycle of the first switch and the third switch. Then, the duty cycles of the second switch and the fourth switch are , is the switching period, is the voltage of the secondary side bridge arm, is the voltage on the capacitor in the high-voltage filtering module, is the phase shift angle of the high-voltage side driving signal of the transformer compared to the low-voltage side driving signal, is the switching angular frequency.

[0107] As a preferred implementation method, the above steps: determining the time-domain equations of the single-stage isolated inverter circuit in different working modes to obtain a time-domain equation set, including:

[0108] When the first switch tube, the fourth switch tube, the sixth switch tube, and the eighth switch tube are all in the on state, and the second switch tube, the third switch tube, the fifth switch tube, and the seventh switch tube are all in the off state, it is determined that the single-stage isolated inverter circuit is in the first working mode, and the time-domain equation of the single-stage isolated inverter circuit in the first working mode is determined to obtain the first time-domain equation;

[0109] When the first switch tube, the fourth switch tube, the fifth switch tube, and the eighth switch tube are all in the on state, and the second switch tube, the third switch tube, the sixth switch tube, and the seventh switch tube are all in the off state, it is determined that the single-stage isolated inverter circuit is in the second working mode, and the The time-domain equation is obtained to get the second time-domain equation;

[0110] When the second switch tube, the fourth switch tube, the fifth switch tube, and the eighth switch tube are all in the conducting state, and the first switch tube, the third switch tube, the sixth switch tube, and the seventh switch tube are all in the off state, it is determined that the single-stage isolated inverter circuit is in the third operating mode, and the time-domain equation of the single-stage isolated inverter circuit in the third operating mode is obtained to get the third time-domain equation.

[0111] Within one switching period, Figure 7 the single-stage isolated inverter circuit shown has a total of 6 operating modes. Due to the good symmetry of the full-bridge circuit on the low-voltage side of the transformer, Figure 7 the single-stage isolated inverter circuit shown can be represented by Figures 10 to 12 the circuit shown.

[0112] Please refer to Figure 10 , Figure 10 which is Figure 7 a schematic diagram of the single-stage isolated inverter circuit shown in the first operating mode. When the first switch tube , the fourth switch tube , the sixth switch tube , and the eighth switch tube are all in the conducting state, and the second switch tube , the third switch tube , the fifth switch tube , and the seventh switch tube are all in the off state, it indicates that Figure 7 the single-stage isolated inverter circuit shown is in the first operating mode.

[0113] When Figure 7 the single-stage isolated inverter circuit shown is in the first operating mode , before the first switch tube conducts, the resonant cavity current connected to the secondary side of the transformer T reverses, and the current of the low-voltage side transformer T flows through the body diode of the first switch tube . Therefore, the first switch tube is conducting. At this time, since the fourth switch tube remains in the on state, the bridge arm voltage on the low-voltage side is clamped to the input voltage of the photovoltaic module . At this time, the current on the resonant inductor increases linearly, and the resonant current flows through the AC filter inductor , the power grid, the eighth switch tube , and the fifth capacitor , where the AC filter inductor and the fifth capacitor form the low-pass filter module can filter out the high-frequency components in the resonant current, so that the current injected into the power grid only contains fundamental components. Since the sixth switch is in the on state, therefore, the voltage between the high-voltage side bridge arms is equal to 0. At this time, based on the time-domain equation of the single-stage isolated inverter circuit in the first operating mode can be determined, and the first time-domain equation is obtained.

[0114] Among them, the expression of the first time-domain equation is:

[0115] Formula 3: ;

[0116] Please refer to Figure 11 , Figure 11 is Figure 7 the schematic diagram of the single-stage isolated inverter circuit in the second operating mode as shown. When Figure 7 the single-stage isolated inverter circuit shown is in the second operating mode , the sixth switch turns off and the fifth switch turns on. Before the fifth switch turns on, the resonant current in the resonant cavity flows forward through the body diode of the fifth switch , so the fifth switch is also on. When the fifth switch turns on, the resonant inductor in the resonant cavity and the resonant capacitor resonate together, the exciting current in the transformer T increases linearly, and the resonant current in the resonant cavity will show a non-linear state. A part of the resonant current in the resonant cavity will flow through the AC filter inductor , the power grid, the eighth switch and the fifth capacitor , and another part of the resonant current will flow back to the resonant cavity through the fourth capacitor . At this time, since the sixth switch is in the off state, therefore, the voltage between the high-voltage side bridge arms is equal to . In this case, based on the time-domain equation of the single-stage isolated inverter circuit in the second operating mode can be determined, and the second time-domain equation is obtained.

[0117] Among them, the expression of the second time-domain equation is:

[0118] ​​Formula 4: ;

[0119] Please refer to Figure 12 , Figure 12 which is Figure 7 a schematic diagram of the single-stage isolated inverter circuit in the third operating mode as shown. When Figure 7 the single-stage isolated inverter circuit shown is in the third operating mode , the first switching tube turns off while the second switching tube turns on. Before the second switching tube turns on, the resonant current in the resonant cavity flows forward through its body diode. Therefore, the second switching tube also turns on. At this time, since the fourth switching tube remains on, the voltage between the low-voltage side bridge arms is equal to 0. And the circuit state on the high-voltage side remains the same as when the single-stage isolated inverter circuit is in the second operating mode. A part of the resonant current in the resonant cavity flows through the AC filter inductor , the power grid, the eighth switching tube and the fifth capacitor , and another part of the resonant current returns to the resonant cavity after flowing through the fourth capacitor . And the voltage between the high-voltage side bridge arms remains equal to because the sixth switching tube is off. In this case, based on the time-domain equation of the single-stage isolated inverter circuit in the third operating mode can be determined, and the third time-domain equation is obtained.

[0120] Among them, the expression of the third time-domain equation is:

[0121] Formula 5: ;

[0122] In the above first time-domain equation, second time-domain equation and third time-domain equation, represents the primary current of the transformer T, represents time, represents the voltage between nodes a and b, represents the equivalent inductance of the transformer T on the low-voltage side, represents the turns ratio of the transformer T, represents the resonant inductor 's inductance value, represents the voltage across the resonant capacitor , represents the voltage between nodes c and d, represents the resonant capacitor​ The capacitance value, represents the current amplitude of the power grid, Indicates AC filter inductance The inductance value, represents the voltage between nodes c and e, Indicates the voltage amplitude of the power grid, Indicates the voltage value at the midpoint of the high-voltage side bridge arm, Represents the fourth capacitor or the fifth capacitor Capacitance value.

[0123] Obviously, through the technical solution provided in this embodiment, the corresponding single-stage isolation inverter circuit in different working modes can be accurately characterized. Time domain equations.

[0124] As a preferred implementation, the above steps: according to the primary and secondary voltages, the time domain equations and the switching tubes in the single-stage isolated inverter circuit The conduction condition determines the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal to control the single-stage isolated inverter circuit, including:

[0125] Determine the effective value of the current of the resonant cavity according to the primary voltage, the secondary voltage, the first time domain equation, the second time domain equation and the third time domain equation;

[0126] Based on the switching tubes in the single-stage isolated inverter circuit The conduction condition is determined, and the phase shift angle of the high-voltage side drive signal of the transformer compared with the low-voltage side drive signal is determined with the minimum effective value of the current in the resonant cavity as the boundary condition, so as to control the single-stage isolated inverter circuit.

[0127] In this embodiment, by combining Formulas 1 to 5 and the volt-second balance characteristic of the single-stage isolated inverter circuit, the voltage gain characteristic of the single-stage isolated inverter circuit can be determined. The expression of the voltage gain characteristic of the single-stage isolated inverter circuit is:

[0128] Formula 6: ;

[0129] In the formula, Indicates the voltage amplitude of the power grid, Indicates the voltage of the photovoltaic module, Indicates the grid-side equivalent load, represents the number of turns of the transformer, represents the phase shift angle, represents the duty cycle, represents the resonant frequency of the resonant cavity, Represents the switching angular frequency.

[0130] From formula 6, we can know that when the phase shift angle and the switching angular frequency When taking a fixed value, you only need to adjust the duty cycle The output voltage or output current of the single-stage isolated inverter circuit can be controlled, which can significantly reduce the control complexity compared with the method of controlling the single-stage isolated inverter circuit in the prior art. It can be found that the positive and negative of the grid-connected current has nothing to do with the grid voltage. Therefore, the single-stage isolated inverter circuit described in this application can realize four-quadrant operation and achieve a power factor of Operation, with extremely strong reactive power compensation capability.

[0131] It can be seen from Formula 6 that for different grid-connected loads, the voltage gain of the single-stage isolated inverter circuit will change, which will cause unexpected voltages to be generated at both ends of the resonant cavity, thereby causing the current on the resonant cavity to deviate from the theoretical value.

[0132] If the current in the resonant cavity is too small, the switching tube may not be able to be switched. If the current in the resonant cavity is too large, it will cause additional circuit losses. In order to reduce the power loss of the entire single-stage isolated inverter circuit, it is necessary to adjust the phase shift angle at different power points. .

[0133] To determine the phase angle , we can first combine formula 1, formula 2, formula 3, formula 4 and formula 5 to solve the effective value of the current of the resonant cavity. Specifically, the expression of the effective value of the current of the resonant cavity is:

[0134] Formula 7: ;

[0135] In the formula, is the effective value of the current in the resonant cavity, Indicates the inductance value of the resonant inductor, represents the frequency of the switching angle, is the voltage amplitude of the power grid, is the inductance of the magnetizing inductor, is the voltage between node c and node d, is the duty cycle of the switch tube in the low-voltage side bridge arm, is the phase shift angle.

[0136] In order to reduce the power loss of the single-stage isolated inverter circuit, the power consumption of each switch tube in the single-stage isolated inverter circuit can be reduced. The conduction condition is set, and the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal is determined with the minimum effective value of the current in the resonant cavity as the boundary condition. 。

[0137] Since the conduction conditions of the first switching transistor and the fifth switching transistor of can be derived, the conduction conditions of all the switching transistors in the single-stage isolated inverter circuit can be obtained. Therefore, only the conduction conditions corresponding to the first switching transistor and the fifth switching transistor are listed here. Among them, the conduction conditions corresponding to the first switching transistor and the fifth switching transistor are as follows: and the fifth switching transistor are: Formula 8:

[0138] ; ;

[0139] Based on Formula 7 and Formula 8, the phase-shift angle can be solved. Among them, the expression of the phase-shift angle is:

[0140] Formula 9: ;

[0141] In the formula, is the phase-shift angle, represents the inductance value of the resonant inductor, represents the frequency of the switching angle, represents the grid-connected power, represents the inductance value of the exciting inductor, represents the voltage amplitude of the power grid.

[0142] After the phase-shift angle is determined, the single-stage isolated inverter circuit can be controlled. In practical applications, to reduce the control complexity of the single-stage isolated inverter circuit, the switching frequency of the switching transistor can be set to a fixed value, and the power hysteresis loop can be used to adjust the phase-shift angle . In addition, according to the grid-connected current, a proportional-resonant controller or a proportional-integral controller can be used to adjust the duty cycle , so as to achieve the efficient grid connection of the photovoltaic modules.

[0143] In summary, through the topology structure of the single-stage isolated inverter circuit described in this application, not only can the reactive power compensation ability of the single-stage isolated inverter circuit be improved and the circuit loss be reduced, but also the modulation method is simple and easy to implement.

[0144] Please refer to Figure 13 , Figure 13The structure diagram of another single-stage isolated inverter circuit provided by the embodiments of the present invention. As a preferred implementation, when there are photovoltaic modules in the component module, ; the component module includes: a second capacitor and parallel to the second capacitor component sub-modules, and the component sub-module includes: a photovoltaic module , a third capacitor parallel to the photovoltaic module and a conversion module for voltage conversion of the output voltage of the photovoltaic module .

[0145] In actual grid-connected applications, there are also cases of multiple inputs of photovoltaic modules. In this case, the topology structure as Figure 13 shown can be used. Each path of photovoltaic modules after passing through the conversion module is boosted to a certain range and then paralleled on the low-voltage DC bus , and then the output energy of each photovoltaic module is incorporated into the power grid through the aforementioned single-stage isolated inverter circuit.

[0146] It should be noted that in actual applications, in order to reduce the complexity of the circuit topology, the conversion module can be set as circuit. In the circuit diagram as Figure 13 shown, the inductor , the switching tube and form circuit.

[0147] In addition, in actual applications, the low-voltage DC bus will be adjusted in real time according to the grid-connected power. When the grid-connected power is small, the voltage on the low-voltage DC bus can be set to a lower voltage value to improve the conversion efficiency of the previous-stage circuit, and when the grid-connected power is large, the voltage on the low-voltage DC bus can be set to a higher voltage value to reduce the on-state loss of the low-voltage side of the subsequent-stage isolated inverter circuit.

[0148] Obviously, through the technical solution provided by this embodiment, the single-stage isolated inverter circuit provided by the present application can be applied to more application scenarios.

[0149] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0150] Finally, it should also 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, so 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 also includes 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 the said element.

[0151] The above has introduced in detail a single-stage isolated inverter circuit and its control method provided by the present invention. Specific examples are used in this document to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A single-stage isolated inverter circuit, characterized in that: include: Photovoltaic panel modules; A low voltage inverter module, used for inverting the output voltage of the photovoltaic module to obtain low voltage alternating current; A transformer with a resonant cavity on the secondary side is used to convert the low-voltage AC power into high-voltage AC power; A rectifier module, used to rectify and transform the high voltage alternating current to obtain direct current; A high-voltage filtering module is used to filter the DC power to obtain filtered DC power; the midpoint of the bridge arm of the rectifier module and the midpoint of the capacitor bridge arm in the high-voltage filtering module are respectively connected to the two output ends of the resonant cavity; A high-voltage inverter module is used to invert the DC filter power to obtain high-voltage AC power; the midpoint of the bridge arm of the high-voltage inverter module is connected to the power grid; The AC filtering module is connected to the midpoint of the bridge arm of the rectifier module and is used to filter the high-voltage AC power to obtain AC filtered power, and inject the AC filtered power into the power grid.

2. A single-stage isolated inverter circuit according to claim 1, characterized in that: When there is only one photovoltaic component in the photovoltaic component module, the photovoltaic component module includes: the photovoltaic component and a first capacitor; wherein two ends of the first capacitor are respectively connected to two ends of the photovoltaic component.

3. A single-stage isolated inverter circuit according to claim 1, characterized in that: When the photovoltaic module has When a photovoltaic module ; The photovoltaic assembly module includes: a second capacitor and a A component submodule, the component submodule includes: the photovoltaic component, a third capacitor connected in parallel with the photovoltaic component, and a capacitor for converting the output voltage of the photovoltaic component. Transformation module.

4. The single-stage isolated inverter circuit according to claim 1, characterized in that: The low voltage inverter module comprises: a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; Among them, the first end of the first switch tube is respectively connected to the first output end of the photovoltaic component module and the first end of the third switch tube, the second end of the first switch tube is respectively connected to the first end of the second switch tube and the first end of the primary winding of the transformer, the second end of the second switch tube is respectively connected to the second end of the photovoltaic component module and the second end of the fourth switch tube, and the first end of the fourth switch tube is respectively connected to the second end of the third switch tube and the second end of the primary winding of the transformer.

5. A single-stage isolated inverter circuit according to any one of claims 1 to 4, characterized in that: The rectifier module includes: a fifth switch tube and a sixth switch tube; Wherein, the second end of the fifth switch tube is respectively connected to the first end of the sixth switch tube and the resonant inductor in the resonant cavity; Correspondingly, the connection point between the fifth switch tube and the sixth switch tube is the midpoint of the bridge arm of the rectifier module, the first end of the fifth switch tube is connected to the AC filter module, and the second end of the sixth switch tube is connected to the high-voltage filter module.

6. The single-stage isolated inverter circuit according to claim 5, characterized in that: The high-voltage filter module includes: a fourth capacitor and a fifth capacitor; Wherein, the first end of the fourth capacitor is connected to the first end of the fifth switch tube, the second end of the fourth capacitor is respectively connected to the resonant capacitor in the resonant cavity and the first end of the fifth capacitor, and the second end of the fifth capacitor is connected to the second end of the sixth switch tube; Correspondingly, the connection point between the fourth capacitor and the fifth capacitor is the midpoint of the capacitor bridge arm in the high-voltage filtering module.

7. The single-stage isolated inverter circuit according to claim 6, characterized in that: The high-voltage inverter module includes: a seventh switch tube and an eighth switch tube; Among them, the first end of the seventh switch tube is connected to the first end of the fifth switch tube, the second end of the seventh switch tube is respectively connected to the first end of the eighth switch tube and the neutral line of the power grid, and the second end of the eighth switch tube is connected to the second end of the fifth capacitor.

8. A control method for a single-stage isolated inverter circuit, characterized in that: A single-stage isolated inverter circuit as claimed in any one of claims 1 to 7, comprising: Determining the primary and secondary voltages of the transformer in one switching cycle according to the operating characteristics of the single-stage isolated inverter circuit; Determine the single-stage isolated inverter circuit in different working modes Time domain equations, and obtain the time domain equations; According to the primary and secondary voltages, the time domain equations and the switching tubes in the single-stage isolation inverter circuit The conduction condition determines the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal, so as to control the single-stage isolated inverter circuit.

9. The control method of a single-stage isolated inverter circuit according to claim 8, characterized in that: The primary and secondary voltages include: a primary voltage and a secondary voltage; Wherein, the expression of the primary voltage is: ； The expression of the secondary voltage is: ； In the formula, is the primary voltage, is the output voltage of a photovoltaic module in the photovoltaic module module, is the negative value of the output voltage of a photovoltaic module in the photovoltaic module module, For time, is the duty cycle of each switch tube in the low voltage inverter module, is the switching period, is the secondary voltage, is the voltage at the midpoint of the capacitor bridge arm in the high-voltage filter module, is the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal, is the switching angular frequency.

10. The control method of a single-stage isolated inverter circuit according to claim 9, characterized in that: The method according to the primary-secondary voltage, the time domain equation group and each switch tube in the single-stage isolation inverter circuit The conduction condition determines the phase shift angle of the high-voltage side drive signal of the transformer compared to the low-voltage side drive signal to control the single-stage isolated inverter circuit, including: Determining an effective value of the current of the resonant cavity according to the primary voltage, the secondary voltage and the time domain equation group; Based on the switching tubes in the single-stage isolation inverter circuit The conduction condition is set, and the phase shift angle of the high-voltage side drive signal of the transformer compared with the low-voltage side drive signal is determined with the minimum effective value of the current in the resonant cavity as the boundary condition, so as to control the single-stage isolated inverter circuit.

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