WO2013163779A1

WO2013163779A1 - Multi-input flyback photovoltaic grid-connected inverter

Info

Publication number: WO2013163779A1
Application number: PCT/CN2012/000594
Authority: WO
Inventors: 高峰
Original assignee: 上海康威特吉能源技术有限公司
Priority date: 2012-05-02
Filing date: 2012-05-02
Publication date: 2013-11-07

Abstract

A multi-input flyback photovoltaic grid-connected inverter comprising multiple flyback circuits, multiple photovoltaic components, a clamped capacitor (C_p), an output filter circuit, an inverter circuit, and a power grid. Each flyback circuit comprises a positive input end, a negative input end, a clamp end, a positive output end, and a negative output end. The positive and negative input ends of each flyback circuit respectively are connected to the positive and negative output ends of the photovoltaic components. The clamp ends of all of the flyback circuits are connected to one end of the clamp capacitor (C_p). The output ends of all of the flyback circuits are parallel-connected and are connected to the output filter circuit. The photovoltaic grid-connected inverter is capable of connecting simultaneously to the multiple photovoltaic components, where tracking of the maximum power of all of the photovoltaic components is implemented via one inverter, and where all of the flyback circuits share the clamp capacitor, the output filter circuit, and the inverter circuit, and is provided with the advantages of reduced costs, great efficiency in power generation, and reduced grid-connected current harmonics.

Description

Multi-input flyback photovoltaic grid-connected inverter

The invention belongs to the technical field of power electronic converters, and particularly relates to the technical field of power converters in the field of new energy power generation technologies, and particularly relates to a multi-input flyback photovoltaic grid-connected inverter. Background technique

The development and utilization of solar energy has become an important measure to solve the problem of living production energy and improving environmental pollution, and it can achieve huge economic and social benefits.

Solar photovoltaic grid-connected power generation is the most important method for solar power generation applications. Solar photovoltaic grid-connected power generation applications have the advantages of low cost and maintenance-free. According to statistics, more than 90% of photovoltaic power generation equipment installation capacity in the world is grid-connected.

The solar photovoltaic grid-connected power generation system can be classified into a centralized type, a string type, a multi-string type, and an AC module type according to the connection manner of the solar module and the grid-connected inverter. The AC module integrates a grid-connected inverter with maximum power tracking (MPPT) for each PV module, ensuring that each PV module operates at its maximum power point, the system resists local shadowing and minimal electrical It has strong parameter matching ability, easy to expand, support plug and play and hot swap. The system is easy to repair and maintain, so it has become a hot spot of attention and research.

The flyback converter has gained more attention in the field of grid-connected inverters of AC modules due to its simple circuit structure, simple control, high reliability, low cost, suitable for medium and small power, such as Chinese patent CN1929276A. "Exercise design of the current-source flyback inverter for decentralized grid-connected photovoltaic systems" [IEEE Transactions on Energy Conversion, vol. 23, no.l, 2008] A flyback photovoltaic grid-connected inverter is also proposed.

Due to the low power of a single PV module (generally less than 300W), the power level of the traditional AC modular PV grid-connected inverter is correspondingly lower, but the corresponding control circuit of the PV grid-connected inverter needs to complete the MPPT control of the PV module at the same time. , grid-connected current control and various detection, protection and other functions, the cost of this part of the circuit does not decrease with the reduction of the power level of the grid-connected inverter, resulting in the unit power generation of the AC modular photovoltaic grid-connected inverter The power cost is significantly higher than the cost of grid-connected inverters in traditional centralized, string and multi-string grid-connected power generation systems, so to a large extent It limits the promotion and application of AC modular photovoltaic grid-connected power generation system; on the other hand, low-power photovoltaic grid-connected inverter also brings low energy conversion efficiency and large grid-connected current harmonics of grid-connected inverters. .

Therefore, the development and research of low-cost, high-efficiency, high-reliability, high-quality AC modular PV grid-connected inverters has become an urgent need. Summary of the invention

The present invention is directed to the deficiencies of the prior art, and provides a multi-input flyback photovoltaic grid-connected inverter having low cost, high efficiency, and small grid current harmonics.

In order to achieve the above object, the present invention adopts the following technical solutions:

A multi-input flyback photovoltaic grid-connected inverter, the multi-input flyback photovoltaic grid-connected inverter comprises a plurality of photovoltaic modules, a plurality of flyback circuits, a clamp capacitor (ς.), an output filter circuit And an inverter circuit and a power grid; the number of the photovoltaic modules corresponds to the number of the flyback circuits;

The flyback circuit includes a positive input terminal, a negative input terminal, a clamp terminal terminal, a positive output terminal and a negative output terminal, and the positive and negative input terminals of each of the flyback circuits are respectively connected to the positive and negative output terminals of a photovoltaic module. Connected, and the negative input terminals of the plurality of flyback circuits are connected to each other and simultaneously connected to the negative polarity end of the clamp capacitor (c _p ), and the clamp ends of the plurality of flyback circuits are connected to each other and simultaneously connected to the clamp a positive terminal of the bit capacitance (c _p ); the output ends of the plurality of flyback circuits are connected in parallel, that is, the positive outputs of the plurality of flyback circuits are connected to each other, and the negative outputs are connected to each other; The positive output terminal and the negative output terminal connected in parallel with the output terminal of the excitation circuit are respectively connected to the output filter circuit, and the output filter circuit is connected to the inverter circuit, and the inverter circuit is connected to the power grid.

In a preferred embodiment of the present invention, the flyback circuit includes an input filter capacitor (c^), a transformer (73⁄4, a main switch (&), a clamp switch, and a diode ^3⁄4).

Wherein: the transformer comprises a primary winding (N and a secondary winding (N _sA ), and the positive terminal of the input filter capacitor (c, „ _fc ) is respectively connected to the positive input terminal of the flyback circuit and the transformer (73⁄4 primary winding (N The same name end, the transformer (r non-identical end of the primary winding is connected to the drain of the main switch (&) and the source of the auxiliary switch, the drain of the auxiliary bypass and the clamp end of the flyback circuit) (^) connected, the source of the main switch (&) is connected to the negative terminal of the input filter capacitor and the negative input of the flyback circuit respectively. The anode of the diode is connected to the non-identical end of the secondary winding of the transformer, and the cathode of the diode is The flyback circuit is connected at the positive output (o), and the transformer (73⁄4 secondary side) The winding (the same name of N is connected to the negative output of the flyback circuit (^-).

Further, the number of the photovoltaic modules and the number of the flyback circuits are greater than or equal to two. Further, the output filter circuit is composed of an output filter capacitor (C.) and an output filter inductor. The inverter circuit is composed of first, second, third, and fourth inverter switches ₂ and S _G2 .

< _{3⁄4 4} ) constitutes;

One end of the output filter capacitor (C.) is simultaneously connected to a positive output terminal of one end of the output filter inductor (.) and the output terminal of the plurality of flyback circuits, and the other end of the output filter capacitor ( ) is simultaneously source connected to the negative output terminal of the plurality of the flyback circuit in parallel with the output terminal, a second inverter switch ₍₂₎ source and a fourth switching transistor inverter 0¾ ₄₎ pole; the output filter inductor ( The other end of the ::) is connected to the drain of the first inverter switch (<S _C1 ) and the drain of the third inverter switch ( ₃ ), respectively, and the sources of the first inverter switch CS _C1 ) a second inverter connected to the other end of the tube ₂ switch) and the drain of the grid) is, 0¾ ₃₎ the source of the third switch transistor inverters are connected to the fourth inverter pole switch 0¾ ₄₎ and a drain grid One end.

The invention formed according to the above scheme has the following advantages -

(1) The multi-input flyback photovoltaic grid-connected inverter provided by the invention can be connected to a plurality of photovoltaic modules simultaneously through a photovoltaic grid-connected inverter, and realize maximum power tracking of each photovoltaic component respectively. Maximizing the efficiency of power generation of photovoltaic modules;

(2) In the multi-input flyback photovoltaic grid-connected inverter of the present invention, a plurality of flyback circuits share an output filter circuit, a clamp capacitor, an inverter circuit, and a control circuit, which can greatly reduce system cost and reduce unit power generation. Power generation cost;

(3) The multi-input flyback photovoltaic grid-connected inverter according to the present invention can greatly reduce grid-connected current harmonics and improve grid-connected current waveform quality;

(4) The multi-input flyback photovoltaic grid-connected inverter provided by the invention supports hot plugging of photovoltaic modules and flexible system expansion. DRAWINGS

The invention is further described below in conjunction with the drawings and specific embodiments.

1 is a schematic diagram of a multi-input flyback photovoltaic grid-connected inverter of the present invention;

2 is a schematic diagram of a flyback circuit in a multi-input flyback photovoltaic grid-connected inverter according to the present invention; FIG. 3 is a schematic diagram of a multi-input flyback photovoltaic grid-connected inverter according to the present invention, including two flybacks Schematic diagram of a multi-input flyback photovoltaic grid-connected inverter of a circuit;

4 is an embodiment of a multi-input flyback photovoltaic grid-connected inverter of the present invention: a working waveform diagram of a multi-input flyback photovoltaic grid-connected inverter including two flyback circuits;

Figure 5 is an embodiment of the multi-input flyback photovoltaic grid-connected inverter of the present invention - an equivalent schematic diagram of a multi-input flyback photovoltaic grid-connected inverter including two flyback circuits when the 2# photovoltaic module is cut .

The symbols in the figure indicate: ~ clamp capacitance; C. An output filter capacitor; An output filter inductor; S _GI , S _G1 , S _G2 , < S _G4 — first, second, third, fourth inverter switch; wcr—grid; in2+, i”k+, z′«N+ respectively 1# flyback circuit, 2# flyback circuit, Λ# flyback circuit, positive input terminal of N# flyback circuit; z'«l -, i"2-, inks inJV- respectively 1# flyback circuit, 2# flyback circuit, flyback circuit, negative input terminal of flyback circuit; cl-, c2- ck -, c N- are 1# flyback circuit, 2# flyback circuit, Λ# flyback circuit, N # clampback terminal of the flyback circuit; ol+, o 2+, o k+, o N+ are the positive output terminals of the ## flyback circuit, the 2# flyback circuit, the A# flyback circuit, and the flyback circuit, respectively; ol-, o l-, o k-, O N- are the negative output terminals of the 1# flyback circuit, 2# flyback circuit, flyback circuit, and flyback circuit respectively; C _in , C, and 1# flyback circuits respectively , 2# flyback circuit, input filter capacitor of flyback circuit; S, , &, & respectively are 1# flyback circuit, 2# flyback circuit, main switch of flyback circuit; “3⁄4, S _c2 , & ₄ is the auxiliary drive of 1# flyback circuit, 2# flyback circuit and flyback circuit respectively. Closed; Τ, Γ ₂ , Γ _变压器 are 1# flyback circuit, 2# flyback circuit, flyback circuit transformer; N _p \, N _pl , N are 1# flyback circuit, 2# reverse Excitation circuit, excitation circuit transformer primary winding; N _s \, N _s2 , N^ are 1# flyback circuit, 2# flyback circuit, flyback circuit transformer secondary winding; A, D ₂ , A are 1 respectively #反激电路, 2# flyback circuit, diode of flyback circuit; u _GS , , _C52 are the drive signals of &, &respectively; u _Gsm , u _GSG2 ,

Drive signals of 5^, ₂ , S _m , ₄ respectively; diodes

Di, /3⁄4 current; is the current of the filter inductor ^. detailed description

In order to make the technical means, the authoring features, the achievement of the object and the effect of the present invention easy to understand, the present invention will be further described below in conjunction with the specific drawings.

In order to solve the problem that the conventional AC modular photovoltaic grid-connected inverter has high power generation cost per unit, the technical solution of the present invention is to integrate a plurality of flyback photovoltaic grid-connected inverters, so that their power circuit parts are structurally connected to each other. Sharing, thereby reducing the cost of the power circuit, while integrating The latter circuit can share a set of control circuits, thereby greatly reducing the cost of the entire system.

In order to improve the grid-connected current quality, by interleaving multiple flyback circuits, the current harmonics of each flyback circuit cancel each other, thereby greatly improving the quality of the entire system output current waveform in order to improve the overall photovoltaic grid-connected inverter. Conversion efficiency, the flyback circuit uses an active clamp flyback circuit, and each flyback circuit shares a clamp circuit. Combined with the corresponding control scheme, the soft switch of the main switch tube in the flyback circuit can be realized, thereby effectively improving the entire photovoltaic system. The conversion efficiency of the network inverter.

Based on the above principle, the multi-input flyback photovoltaic grid-connected inverter provided by the present invention includes two or more photovoltaic modules, N flyback circuits, clamp capacitors (C _p ), and output filtering as shown in FIG. 1 . The circuit, the inverter circuit and the power grid, wherein the output filter circuit is composed of an output filter capacitor (C:.) and an output filter inductor ( ), and the inverter circuit is composed of the first, second, third, and fourth inverter switches (S _G i, S (n, S _G3 , constitute.

The flyback circuit of the present invention comprises a positive input terminal, a negative input terminal, a clamp terminal, a positive output terminal and a negative output terminal, wherein the positive and negative input terminals of each flyback circuit are respectively positive with a photovoltaic component. The negative output is connected.

The negative inputs of all N flyback circuits are connected to each other and to the negative terminal of the clamp capacitor (C _p ) at the same time; the clamp terminals of all N flyback circuits are connected to each other and connected to the clamp at the same time. The positive terminal of the capacitor (c _p ), that is, all N flyback circuits share the clamp capacitance (c _p ).

The outputs of all w flyback circuits are connected in parallel, that is, the positive outputs of all w flyback circuits are connected to each other and to the output filter capacitor (one end of 0 and one end of the output filter inductor (£.); The negative outputs of the w flyback circuits are connected to each other and connected to the other end of the output filter capacitor (c:.), the source of the second inverter switch cs _C2 ), and the fourth inverter switch cs _C4. The source of ).

The other ends of the output filter inductors ( ) are respectively connected to the drains of the first inverter switch tube and the drain of the third inverter switch tube 03⁄4 ₃ ), and the sources of the first inverter switch tube os _cl ) are respectively connected to the first The drain of the inverter switch 03⁄4 ₂ ) and the end of the grid ( _c ), the source of the third inverter switch (& ₃ ) is connected to the drain and the grid of the fourth inverter switch 03 ₄ , respectively The other end.

The N flyback circuits in the present invention have exactly the same circuit structure, and any of them k flyback circuits are used to illustrate the circuit structure. The schematic diagram of the circuit is shown in Figure 2. Any kth flyback circuit includes input filter capacitors (C, „, transformer ( ), main switch (&), pliers. Bit switch tube 03⁄4 and diode 3⁄4).

Wherein: the transformer (7) comprises a primary winding (N) and a secondary winding (Λ), and the positive terminal of the input filter capacitor is respectively connected to the positive input terminal of the flyback circuit and the transformer (the same name end of the primary winding of the 7) (7 The non-identical ends of the primary windings are respectively connected to the drain of the main switch (&) and the source of the auxiliary switch, and the drain of the auxiliary switch is connected to the clamp terminal (^) of the flyback circuit, the main switch The source of the transistor 03⁄4) is respectively connected to the negative terminal of the input filter capacitor (C^) and the negative input terminal of the flyback circuit, and the anode of the diode is connected to the non-identical end of the secondary winding of the transformer (7;), and the cathode of the diode The positive output terminal of the flyback circuit is connected, and the secondary winding of the transformer (the same name end of N is connected to the negative output terminal (^-) of the flyback circuit.

In the multi-input flyback photovoltaic grid-connected inverter provided by the invention, the main switch tube and the auxiliary switch tube in the flyback circuit are both high-frequency switching, and the inverter switch tube in the inverter circuit operates at a low frequency, The operating frequency is equal to the frequency of the grid voltage.

In a specific embodiment of the invention, the multi-input flyback photovoltaic grid-connected inverter uses two flyback circuits respectively connected to two photovoltaic modules, the schematic diagram of which is shown in FIG. 3:

All of the switching transistors use metal oxide semiconductor field effect transistors (MOSFETs), in which the switching frequency of the switching transistors in the flyback circuit varies from 80 kHz to 400 kHz, and the grid voltage frequency is 50 Hz, which is connected to each flyback circuit. The maximum output power of the PV module is 300W, and the system power rating of the multi-input flyback PV grid-connected inverter is 600W. The grid-connected inverter implements all control functions through a digital processor (DSP).

The specific working principle of this embodiment will be described below with reference to Figs. 3 to 5.

The multi-input flyback photovoltaic grid-connected inverter including two flyback circuits shown in FIG. 3 is respectively connected to the 1# photovoltaic component and the 2# photovoltaic component, and simultaneously realizes the MPPT of the output power of the two photovoltaic components, the system MPPT Control, phase-locked loop control, grid-connected current waveform control, islanding detection and protection control are all implemented by DSP. The output of the MPPT controller provides the grid-connected power corresponding to the grid-connected power reference value of the PV module. The output provides the electrical angle of the grid-connected current and the grid voltage amplitude. The DSP adjusts the duty cycle of the main switch tube (&, &) of the flyback circuit in real time according to the grid-connected power and the grid voltage (^) electrical angle. The envelope of the flyback circuit output current (^, i _D2 ) is a half-wave sinusoid, and the main switch tubes of the two flyback circuits (&, the drive signals are interlaced with each other, The output current of the two flyback circuits ( _D1 , high frequency superposition, the envelope is still half-wave sinusoidal, and the smoothed half-wave sinusoidal inductor current is obtained by the output filter circuit.

After the full-bridge inverter circuit is constructed, a sinusoidal grid-connected current whose phase is consistent with the grid voltage is obtained. In the inverter circuit, four inverter switching tubes ^^guang^^) work complementarily at the grid voltage frequency. When the grid voltage (^:) is positive, the second and third inverter switches 03⁄4 ₂ , > _{3⁄4 3} ) Conduction, when the grid voltage is negative, the first and fourth inverter switching tubes "S _C4 " are turned on.

The principle operational waveform of the multi-input flyback photovoltaic grid-connected inverter shown in Figure 3 is shown in Figure 4.

In a multi-input flyback photovoltaic grid-connected inverter, each flyback circuit works independently of each other but works in the same principle. All flyback circuits operate in a current interrupt mode, that is, a flyback circuit output current in each switching cycle. It can be naturally reduced to zero; after each main switching tube is turned off, the auxiliary switching tube is turned on, and the auxiliary switching tube is turned off before the output current of the flyback circuit is reduced to zero. The effect is as follows: The clamp of the main off-tube shutdown voltage is realized, and the leakage energy of the transformer is recovered.

The multi-input flyback photovoltaic grid-connected inverter provided by the invention is connected to a plurality of photovoltaic components at the same time, but the working states of each photovoltaic component are independent of each other, and work on other photovoltaic components when a photovoltaic component is blocked from output power is reduced. The state will not have any effect. In particular, when a PV module is cut off due to failure or other reasons, it will not affect the working state of other PV modules. The multi-input flyback photovoltaic grid-connected inverter of the flyback circuit is taken as an example. When the 2# photovoltaic module is cut off, the equivalent circuit of the photovoltaic grid-connected inverter is as shown in FIG. 5.

The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing embodiments and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

Rights request

A multi-input flyback photovoltaic grid-connected inverter, wherein the multi-input flyback photovoltaic grid-connected inverter comprises a plurality of photovoltaic modules, a plurality of flyback circuits, and a clamp capacitor (c _p ), an output filter circuit, an inverter circuit, and a power grid; the number of the photovoltaic modules corresponds to the number of the flyback circuits;

The flyback circuit includes a positive input terminal, a negative input terminal, a clamp terminal terminal, a positive output terminal and a negative output terminal, and the positive and negative input terminals of each of the flyback circuits are respectively connected to the positive and negative output terminals of a photovoltaic module. Connected, and the negative input terminals of the plurality of flyback circuits are connected to each other and simultaneously connected to the negative polarity end of the clamp capacitor, and the clamp ends of the plurality of flyback circuits are connected to each other and simultaneously connected to the clamp capacitor (Cp a positive polarity end; the output ends of the plurality of flyback circuits are connected in parallel, that is, the positive output ends of the plurality of flyback circuits are connected to each other, and the negative output ends are connected to each other; the output terminals of the plurality of flyback circuits are connected in parallel The latter positive output terminal and the negative output terminal are respectively connected to the output filter circuit, and the output filter circuit is connected to the inverter circuit, and the inverter circuit is connected to the power grid.

2 . The multi-input flyback photovoltaic grid-connected inverter according to claim 1 , wherein the flyback circuit comprises an input filter capacitor (C ), a transformer (Γ _Α ), and a main switch tube ( &), clamp switch tube 03⁄4) and diode

Wherein: the transformer (Γ _Α ) includes the primary side winding and the secondary winding input filter capacitor (c^), the positive terminal is connected to the positive input end of the flyback circuit and the same name end of the transformer primary winding (N), the transformer original The non-identical ends of the side windings (Λ) are respectively connected to the drains of the main shunt tubes 03⁄4) and the sources of the auxiliary shunt tubes, and the drains of the auxiliary shunt tubes are connected to the clamp terminals ( ) of the flyback circuit, the main The source of the switch (&) is connected to the negative terminal of the input filter capacitor (c, „ _A ) and the negative input of the flyback circuit, respectively. The anode of the diode (A) and the non-identical end of the secondary winding of the transformer (7) Connected, the cathode of the diode is connected to the positive output terminal of the flyback circuit, and the same name end of the secondary winding of the transformer (7;) is connected to the negative output terminal (^-) of the flyback circuit.

3. A multi-input flyback photovoltaic grid-connected inverter according to claim 1, wherein the number of the photovoltaic modules and the number of the flyback circuits is greater than or equal to two.

4. A multi-input flyback photovoltaic grid-connected inverter according to claim 1, wherein said output filter circuit is composed of an output filter capacitor (<^.) and an output filter inductor (£.). The inverter circuit is composed of first, second, third, and fourth inverter switching tubes S _G2 , S _G3 < _{3⁄4 4} ) to make;

One end of the output filter capacitor ( ) is simultaneously connected to one end of the output filter inductor ( . . ) and the positive output end of the plurality of flyback circuit outputs, and the other end of the output filter capacitor ( ) is simultaneously connected a negative output terminal and a second inverter switch tube connected in parallel with the output ends of the plurality of flyback circuits

a source of (s _C2 ) and a source of the fourth inverter switch c _C4 ); the other end of the output filter inductor ( . . ) is respectively connected to the drain of the first inverter switch and the third inverter The drain of the switch transistor 03⁄4 ₃ ), the source of the first inverter switch tube is respectively connected to the drain of the second inverter switch tube and one end of the power grid, and the sources of the third inverter switch tube 03⁄4 ₃ ) are respectively connected to The drain of the fourth inverter switch ₄ ) and the other end of the grid ( ).