WO2013004110A1

WO2013004110A1 - Solar photovoltaic grid-connected interleaved parallel flyback inverter

Info

Publication number: WO2013004110A1
Application number: PCT/CN2012/075866
Authority: WO
Inventors: 罗宇浩; 高明智
Original assignee: 浙江昱能光伏科技集成有限公司
Priority date: 2011-07-05
Filing date: 2012-05-22
Publication date: 2013-01-10
Also published as: CN102231609A

Abstract

Provided is a solar photovoltaic grid-connected interleaved parallel flyback inverter, comprising an interleaved parallel flyback circuit; a DC detection module; an AC detection module; a reference current acquisition module for obtaining the reference current at each time point; a quasi-resonance control circuit for sampling the drain source voltage of a switching tube and comparing whether the drain source voltage equals to a quasi-resonance threshold value; a primary-side current sampling module; and a driving circuit for generating a driving signal. The driving circuit comprises: a comparator for comparing whether the primary-side current equals to the reference current; and a trigger for driving the switching tube to switch off when the primary-side current equals to the reference current, and driving the switching tube to switch on when the drain source voltage equals to the quasi-resonance threshold value. Also provided is another solar photovoltaic grid-connected interleaved parallel flyback inverter. The present invention uses the reference current to control the inverter to convert energy, improves the calculation method of the reference current in a two-stage circuit topology, and ensures that the grid-connected current has a sinusoidal waveform with the same frequency and phase as an electric grid, thus reducing the THD of the grid-connected current and improving the quality of output electric power.

Description

Solar photovoltaic grid-connected staggered parallel flyback inverter

The invention relates to the technical field of solar photovoltaic grid-connected inverters. In particular, the invention relates to a solar photovoltaic grid-connected staggered parallel flyback inverter. Background technique

The output current of the grid-tied inverter is usually mismatched with the sine wave shape of the grid current. The total Harmonic Distortion (THD) is usually used to define the size of the mismatch. Total Harmonic Distortion THD is defined as the square root of the ratio of the total rms value of the output harmonics to the rms value of the fundamental power input to the cosine signal of a single frequency. In order to ensure the stability of the grid and the efficient entry of the inverter into the grid, THD is usually required to be less than 5%.

In the prior art, the control of the flyback inverter generally adopts a reference current mode, and the peak envelope of the primary current is used as the reference current I. When the flyback inverter circuit is used, when the flyback operation is in the Bomidary Conducting Mode (BCM), since the flyback operating frequency is not fixed, the peak envelope of the primary current (ie, I _ref ) and the original The effective value of the side current is nonlinear, and thus the effective value of the push-out and output current is nonlinear.

FIG. 1 is a schematic diagram of a simple circuit of a solar photovoltaic grid-connected staggered flyback inverter in the prior art. The solar photovoltaic grid-connected staggered flyback inverter 100 is connected to the solar panel 101 on the left side and the grid 102 on the right side, respectively. The flyback inverter portion 100 is composed of a decoupling capacitor Cin, an interleaved parallel flyback circuit 103, and a power frequency grid-connected inverter circuit 104. The interleaved parallel flyback circuit 103 has two identical flyback circuits connected in parallel, each of which is mainly composed of primary side switching tubes S _M1 and S _M1 , transformers T1 and T2 , and flyback diodes D 1 and D2 . The output of the flyback current is determined by the control of the switching tubes S _AC1 ~ S _AC4 . As shown, the interleaved parallel flyback circuit 103 includes a switching transistor S _M1 /S _M2 , a transformer T1/T2 and a flyback diode D l/D2. The power frequency grid-connected inverter includes a full bridge and filter circuits L _f , C _f composed of four switch tubes S _AC1 ~ S _AC4 .

In order to ensure that the output current is a sinusoidal waveform with the same frequency as the grid voltage, it is necessary to have 1 to 2 points: (1) accurately model the function of the effective value of the output current;

(2) Design an effective hardware control circuit to implement the control method. Summary of the invention

The technical problem to be solved by the present invention is to provide a solar photovoltaic grid-connected staggered parallel flyback inverter, and improve the calculation method of the reference current to ensure that the grid-connected current is a sinusoidal waveform with the same frequency as the grid voltage, thereby greatly reducing and The total harmonic distortion of the grid current improves the quality of the output power.

To solve the above technical problem, the present invention provides a solar photovoltaic grid-connected staggered parallel flyback inverter, including:

An interleaved parallel flyback circuit comprising a primary winding and a secondary winding, the primary winding being connected to a solar panel, the secondary winding being connected to the grid for paralleling the DC generated by the solar panel After the flyback, the output is connected to the grid;

a DC detection module is connected to the solar panel for detecting a DC signal generated by the DC panel; and an AC detection module is connected to the secondary winding of the interleaved flyback circuit for detecting an AC signal connected to the grid ;

a reference current obtaining module is respectively connected to the DC detecting module and the AC detecting module, and configured to acquire a reference current at each time point according to the DC signal and the AC signal;

a quasi-resonant control circuit is connected to the switching tube of the primary winding of the interleaved parallel flyback circuit for sampling a drain-source voltage of the switching transistor, and comparing whether the drain-source voltage is equal to a quasi-resonant threshold;

a primary current sampling module, connected to the primary winding, for sampling the current of the primary winding; a driving circuit for generating an opening or closing driving signal to the switching transistor of the primary winding; The driving circuit includes:

a comparator, respectively connected to the reference current acquisition module and the primary current sampling module, for comparing whether the primary current is equal to the reference current;

a flip-flop, respectively connected to the comparator, the quasi-resonant control circuit and the switching tube of the primary winding, for driving the switch when the primary current increases to be equal to the reference current Turning off, and when the drain-source voltage of the switch tube drops to be equal to the quasi-resonance threshold, the switch tube is driven to turn on.

Optionally, the reference current is:

Where is the reference current at each time point, i _c is the DC input voltage, which is the value of the AC output voltage, 1 _A is the value of the AC output current, and ω is the phase of the AC output voltage, which is the primary winding The inductance value, ₂ is the inductance value of the secondary winding, and t is the time in one cycle.

Optionally, when the drain-source voltage of the switch tube is higher than the quasi-resonance threshold, the quasi-resonance control circuit outputs 0; when the drain-source voltage of the switch tube falls to be equal to the quasi-resonance threshold The quasi-resonance control circuit outputs 1 .

Optionally, the driving circuit further includes:

Diodes are respectively connected to the flip-flops and the switching tubes of the primary windings for ensuring that the driving signals are in a forward flow direction.

The invention also provides a solar photovoltaic grid-connected staggered parallel flyback inverter, comprising:

An interleaved parallel flyback circuit comprising a plurality of primary windings and a secondary winding, wherein the primary winding is connected to a solar panel, and one of the secondary windings is connected to a power grid, and the interleaved parallel flyback circuit is used And parallelizing the direct current generated by the solar panel to be connected to the grid;

a DC detection module, connected to the solar panel, for detecting a DC signal generated by the DC panel; and an AC detection module connected to a secondary winding connected to the grid in the interleaved flyback circuit, Detecting the AC signal of the grid connection;

a quasi-resonant control circuit connected to another secondary winding of the interleaved flyback circuit for sampling a voltage generated by a current of the secondary winding, and comparing whether a sampling voltage of the secondary current is equal to a command;

a flip-flop, respectively connected to the comparator, the quasi-resonant control circuit and the switching tube of the primary winding, for driving the switch when the primary current increases to be equal to the reference current Turning off, and when the sampling voltage of the secondary current drops to be equal to zero, the switching transistor is driven to be turned on.

Optionally, the reference current acquisition module acquires the reference current according to the following formula: Where is the reference current at each time point, i _c is the DC input voltage, which is the value of the AC output voltage, 1 _A is the value of the AC output current, and ω is the phase of the AC output voltage, which is the inductance value of the primary winding ₂ is the inductance value of the secondary winding, and t is the time in one cycle.

Optionally, the quasi-resonant control circuit is a voltage comparator.

Optionally, when the sampling voltage of the secondary current drops to equal to 0, the quasi-resonant control circuit outputs 0; otherwise, the quasi-resonant control circuit outputs 1 .

Optionally, the driving circuit further includes:

Compared with the prior art, the present invention has the following advantages:

The invention uses the reference current control flyback inverter for energy conversion, and ensures the calculation method of the reference current and the hardware control circuit in the two-stage topology of the interleaved parallel flyback circuit and the power frequency grid-connected inverter circuit. The grid-connected current is a sinusoidal waveform with the same frequency as the grid voltage, which greatly reduces the total harmonic distortion of the grid-connected current and improves the output power quality. DRAWINGS

The above and other features, properties and advantages of the present invention will become more apparent from the following description in conjunction with the appended claims

1 is a schematic diagram of a simple circuit of a solar photovoltaic grid-connected staggered flyback inverter in the prior art;

2 is a schematic diagram showing waveforms of a primary current, a secondary current, and a primary side switching tube control signal of a solar photovoltaic grid-connected parallel-connected flyback inverter according to an embodiment of the present invention;

3 is a simplified schematic diagram of a solar photovoltaic grid-connected staggered flyback inverter according to an embodiment of the present invention;

4 is a simplified schematic diagram of a solar photovoltaic grid-connected staggered flyback inverter according to another embodiment of the present invention. detailed description

The present invention will be further described below in conjunction with the specific embodiments and the accompanying drawings, which are set forth in the following description. In order to fully understand the present invention, the present invention is obviously capable of being implemented in various other ways than those described herein, and those skilled in the art can make similar promotion according to actual application without departing from the connotation of the present invention. The scope of the present invention should not be limited by the contents of the specific embodiments.

2 is a schematic diagram showing waveforms of a primary current, a secondary current, and a primary side switching tube control signal of a solar photovoltaic grid-connected parallel-connected flyback inverter according to an embodiment of the present invention. When the switch is turned on, the primary current increases linearly from zero. When the primary current value reaches the reference current value, the primary switch is closed, the primary current drops to zero, and the secondary current gradually decreases linearly. When it reaches zero, the primary switch is turned on. During the same power frequency cycle, the flyback operating frequency is different due to the difference in input power. Since the flyback operating frequency is not fixed, the peak envelope of the primary current (ie, I _ref , is nonlinear with the effective value of the primary current. Thus, the effective values of the reference current and the output current / are nonlinear. .

In order to guarantee the output current /. For the sinusoidal waveform with the same frequency as the grid voltage, it needs ^1 to two points: (1) Design an effective hardware control circuit to realize the control method; (2) Accurately build the functional relationship between the reference current and the effective value of the output current. mold.

The solar photovoltaic grid-connected staggered flyback inverter of the present invention, in particular, the control circuit of the solar-powered photovoltaic grid-connected parallel-connected flyback inverter will be described in detail below with reference to the accompanying drawings. First embodiment

3 is a simplified schematic diagram of a solar photovoltaic grid-connected staggered flyback inverter according to an embodiment of the present invention. As shown, the solar photovoltaic grid-connected staggered flyback inverter 300 can include: an interleaved parallel flyback circuit 301, a DC detection module 302, an AC detection module 303, a reference current acquisition module 304, a quasi-resonance control circuit 305, The primary current sampling module 306 and the driving circuit 307, wherein the driving circuit 307 may further include: a comparator 308 and a trigger 309.

In this embodiment, the interleaved parallel flyback circuit 301 may include a primary winding 301 1 and a secondary winding 3012. The primary winding 301 1 is connected to a solar panel (not shown, only represented by a DC source DC). The side winding 3012 is connected to the grid 31 1 for parallel excitation of the DC power generated by the solar panel and then connected to the grid; the DC detection module 302 can be connected to the solar panel for detecting the DC signal generated by the DC panel; The detecting module 303 can be connected to the secondary winding 3012 of the interleaved flyback circuit 301 for detecting the connected alternating current signal; the reference current obtaining module 304 can be respectively connected to the direct current detecting module 302 and the alternating current detecting module 303. Obtaining time points according to DC signals and AC signals The reference current; the quasi-resonant control circuit 305 can be connected to the switching transistor S _M of the primary winding 301 1 of the interleaved flyback circuit 301 for sampling the drain-source voltage of the switching transistor S _M and comparing whether the drain-source voltage is equal to a quasi-resonance threshold, when the drain-source voltage of the switch S _M is higher than the quasi-resonance threshold, the output of the quasi-resonant control circuit 305 is 0; when the drain-source voltage of the switch S _M falls to be equal to the quasi-resonant threshold, the quasi-resonant control circuit 305 output is 1; the primary current sampling module 306 can be winding and is connected to the primary 3011, 3011 for the current sample of the primary winding; and a driving circuit 307 for the original winding 3011 generates switch S _M Drive signal that is turned on or off.

In addition, the comparator 308 in the driving circuit 307 can be respectively connected to the reference current obtaining module 304 and the primary current sampling module 306 for comparing whether the primary current is equal to the reference current; and the flip-flop 309 can be respectively connected to the comparator 308, when the quasi-resonant control circuit 305 and a primary winding switch S _M 301 1 is connected, for, when the primary current equal to the reference current is increased, the driving switch S _M is off, and when the drain-source voltage of the switch S _M When falling to the quasi-resonance threshold, the drive switch S _{M is} turned on.

In this embodiment, the reference current I _{ref is taken.}

^ is the reference current at each time point, is the DC input voltage, _ρ is the value of the AC output voltage, ^ is the value of the AC output current, ω is the phase of the AC output voltage, is the inductance value of the primary winding 301 1 , ₂ is The inductance value of the secondary winding 3012, t is the time in one cycle.

Among the above various parameters, the following signals are obtained by the DC detection module 302: The DC input voltage V _dc supplied from the input voltage detection circuit. The following signals are obtained by the AC detection module 303: the value of the AC output voltage supplied by the output voltage detection circuit _Vp , the phase ω of the AC output voltage supplied from the output voltage detection circuit, and the value of the AC output current supplied by the output current detection circuit. According to the above formula, the reference current value I _ref at each time point can be conveniently calculated.

Further, the drive circuit 307 of this embodiment may further include a diode 310 which are connected to the flip-flop 309 and the primary winding switch S _M 301 1 for ensuring the flow of the forward drive signal is to avoid reverse flow of the signal Possible damage to the drive circuit 307. Second embodiment

4 is a simplified schematic diagram of a solar photovoltaic grid-connected staggered flyback inverter according to another embodiment of the present invention. As shown, the solar photovoltaic grid-connected staggered flyback inverter 400 can include: interleaved parallel The flyback circuit 401, the DC detection module 402, the AC detection module 403, the reference current acquisition module 404, the quasi-resonance control circuit 405, the primary current sampling module 406, and the driving circuit 407, wherein the driving circuit 407 may further include: a comparator 408, Trigger 409.

In this embodiment, the interleaved parallel flyback circuit 401 may include a plurality of primary windings 401 1 and secondary windings 4012, Ls2, primary windings 401 1 and solar panels (not shown, only represented by DC source DC) Connected, one of the secondary windings 4012 is connected to the grid 41 1 , and the staggered parallel flyback circuit 401 is used for parallel excitation of the DC power generated by the solar panel and then connected to the grid; the DC detection module 402 can be combined with the solar panel Connected to detect the DC signal generated by the AC detection module 403, which can be connected to the secondary winding 4012 connected to the grid 411 in the interleaved flyback circuit 401 for detecting the AC signal of the grid connection; The obtaining module 404 can be respectively connected to the DC detecting module 402 and the AC detecting module 403 for acquiring the reference current at each time point according to the DC signal and the AC signal; the quasi-resonant control circuit 405 can be coupled with the interleaved flyback circuit 401 A secondary winding Ls2 is connected, which may be a voltage comparator, and the input positive terminal is the sampling voltage of the secondary current, and the input is negative. 0, used to sample the voltage generated by the current of the secondary windings 4012, Ls2, and compare whether the sampling voltage of the secondary current is equal to zero; when the sampling voltage of the secondary current drops to equal 0, the output of the quasi-resonant control circuit 405 is 0. Otherwise, the output of the quasi-resonant control circuit 405 is 1; the primary current sampling module 406 can be connected to the primary winding 4012 for sampling the current of the primary winding 4012; and the driving circuit 407 can be used for the switching transistor of the primary winding 4012. The S _M generates a drive signal that is turned on or off.

The comparator 408 in the driving circuit 407 can be respectively connected to the reference current obtaining module 404 and the primary current sampling module 406 for comparing whether the primary current is equal to the reference current, when the primary current is 'J, and the reference current is The output of the comparator 408 is 0. When the primary current reaches the reference current, the output of the comparator 408 is 1; and the flip-flop 409 can be respectively connected to the comparator 408, the quasi-resonant control circuit 405, and the switch of the primary winding 401 1 . S _M is connected to the tube, for, when the primary current equal to the reference current is increased, the driving switch S _M is turned off, and when the secondary current sampling voltage drops to zero, the driving switch S _M is turned on.

In this embodiment, the reference current I _{ref is taken.}

Where is the reference current at each time point, i _c is the DC input voltage, which is the peak value of the AC output voltage, ^ is the peak value of the AC output current, ω is the phase of the AC output voltage, and is the inductance value of the primary winding, ₂ is The inductance of the secondary winding, t is the time in one cycle. Among the above various parameters, the following signals are obtained by the DC detection module 402: The DC input voltage V _dc provided by the input voltage detection circuit. The following is obtained by the AC signal detection module 403: phase ω of the AC output voltage of the AC output voltage detection circuit provides an output voltage value V _p, the output voltage detection circuit is provided, the output current value of the alternating output current detection circuit provided ^. According to the above formula, the reference current value at each time point can be conveniently calculatedΙ

Further, the driving circuit 407 of this embodiment may further include a diode 410 which are connected to the flip-flop 409 and the primary winding switch S _M 401 1 for ensuring the flow of the forward drive signal is to avoid reverse flow of the signal Possible damage to the drive circuit 407. The invention uses the reference current control flyback inverter for energy conversion, and ensures the calculation method of the reference current and the hardware control circuit in the two-stage topology of the interleaved parallel flyback circuit and the power frequency grid-connected inverter circuit. The grid-connected current is a sinusoidal waveform with the same frequency as the grid voltage, which greatly reduces the total harmonic distortion of the grid-connected current and improves the output power quality.

The present invention has been disclosed in the above preferred embodiments, and is not intended to limit the scope of the invention, and may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes and modifications of the above-described embodiments in accordance with the technical scope of the present invention are intended to be within the scope of the invention as defined by the appended claims.

Claims

Rights request

1. A solar photovoltaic grid-connected staggered parallel flyback inverter, comprising:

a DC detection module, connected to the solar panel, for detecting a DC signal generated by the DC signal;

An AC detection module is connected to the secondary winding of the interleaved parallel flyback circuit for detecting an AC signal connected to the grid;

a reference current acquisition module, respectively connected to the DC detection module and the AC detection module, configured to acquire a reference current at each time point according to the DC signal and the AC signal; a quasi-resonance control circuit, a switching tube of the primary winding of the staggered parallel flyback circuit is connected, for sampling a drain-source voltage of the switching tube, and comparing whether the drain-source voltage is equal to a quasi-resonant threshold; a primary current sampling module, and the original The side windings are connected to each other, and the electric driving circuit for sampling the primary winding is used to generate an opening or closing driving signal to the switching tube of the primary winding; wherein the driving circuit comprises:

a comparator, respectively connected to the reference current acquisition module and the primary current sampling module, configured to compare whether the primary current is equal to the reference current;

2. The flyback inverter of claim 1, wherein the reference current acquisition module acquires the reference current according to the following formula:

I ■ I _A - sin(ot)

Wherein, the reference current for each time point is the DC input voltage, which is the AC output power. The peak value of the voltage is the peak value of the AC output current, ω is the phase of the AC output voltage, the inductance value of the primary winding, ₂ is the inductance value of the secondary winding, and t is the time in one cycle.

The flyback inverter according to claim 1 or 2, wherein when the drain-source voltage of the switch transistor is higher than the quasi-resonance threshold, the output of the quasi-resonant control circuit is 0; When the drain-source voltage of the switch tube falls to be equal to the quasi-resonance threshold, the quasi-resonance control circuit outputs 1 .

The flyback inverter according to claim 3, wherein the driving circuit further comprises: a diode respectively connected to the flip-flop and the switching tube of the primary winding, for ensuring The drive signal is in the forward direction.

5. A solar photovoltaic grid-connected staggered parallel flyback inverter, comprising:

An AC detection module is connected to the secondary winding connected to the power grid in the interleaved parallel flyback circuit for detecting an AC signal connected to the grid;

a reference current acquisition module, respectively connected to the DC detection module and the AC detection module, configured to acquire a reference current at each time point according to the DC signal and the AC signal; a quasi-resonance control circuit, The other secondary winding of the interleaved parallel flyback circuit is connected for sampling a voltage generated by the current of the secondary winding, and comparing whether the sampling voltage of the secondary current is equal to zero;

a primary current sampling module, connected to the primary winding, for sampling an electric drive circuit of the primary winding, for generating an open or closed driving signal to the switching transistor of the primary winding; The drive circuit includes:

a comparator connected to the reference current acquisition module and the primary current sampling module, respectively Used to compare whether the primary current is equal to the reference current;

6. The flyback inverter according to claim 5, wherein the reference current acquisition module is obtained according to the following formula

Where is the reference current at each time point, i _c is the DC input voltage, is the peak value of the AC output voltage, is the peak value of the AC output current, and ω is the phase of the AC output voltage, which is the inductance value of the primary winding, ₂ For the inductance value of the secondary winding, t is the time in one cycle.

The flyback inverter according to claim 5 or 6, wherein the quasi-resonant control circuit is a voltage comparator.

8. The flyback inverter according to claim 7, wherein the quasi-resonant control circuit outputs 0 when the sampling voltage of the secondary current drops to be equal to 0; otherwise the quasi-resonant control The circuit output is 1.

The flyback inverter of claim 7, wherein the driving circuit further comprises: a diode connected to the flip-flop and the switching tube of the primary winding, respectively, for ensuring The drive signal is in the forward direction.