CN101783611B - Split induction three-level photovoltaic grid-connected inverter and control method thereof - Google Patents

Abstract

The invention discloses a split induction three-level photovoltaic grid-connected inverter and a control method thereof and belongs to the technical field of a power electric transformer. The inverter comprises a power supply circuit (A), a first converting branch (B) and a second converting branch (C), wherein the power supply circuit (A) consists of a direct current power supply and two voltage-dividing capacitors; the first converting branch (B) and the second converting branch (C) respectively consist of a power diode, a split inductance and two power switching tubes. The inverter can be expanded into a three-phase circuit structure according to the capacitance requirement and has the same principle with the single-phase structure. The control method of the inverter comprises two parts which respectively are the hysteresis ring width frequency-fixing control of the inverter side inductance current and the early closing of the high-frequency switch driving signal. The invention does not generate high-frequency leakage current when working in the single-polar PWM modulation mode, and does not have the bridge arm direct-connection danger, and the voltage stress of the power switching tubes and the diode are respectively equal to or smaller than one half of the input voltage.

Description

Division induction three-level photovoltaic grid-connected inverter and control method thereof

Technical field

The present invention relates to a kind of inverter, relate in particular to a kind of division inductance and three levels non-isolated grid-connected inverter and control method thereof, belong to the converters technical field.

Background technology

Energy crisis and ecological deterioration make the countries in the world active development comprise regenerative resources such as photovoltaic, wind energy.Along with the universal utilization of photovoltaic generation, be applicable to that inverter topology and control method that solar array is parallelly connected with electrical network obtain extensive studies.Advantage such as the non-isolation type photovoltaic combining inverter has the efficient height, volume is little, in light weight and cost is low; But because the cell panel existence of parasitic capacitance over the ground; Time variant voltage acts on the parasitic capacitance when making the switch motion of combining inverter switching device to produce high frequency, and the leakage current that brings out thus possibly exceed allowed band.The generation of high-frequency leakage current can bring the increase of conduction and radiated interference, network access current harmonics and loss, even jeopardizes equipment and personal security.The another one key issue is exactly the reliability of inverter, and there is the danger of bridge arm direct pass in the conventional bridge structure, becomes the killer who reduces the photovoltaic parallel in system reliability.

The diode clamping tri-level converter topology is extensively approved in the non-isolation type photovoltaic combining inverter.This mainly is to remedy the leakage current that no isolating transformer brings and the structural advantage of network access DC component problem because the diode clamping tri-level inverter has.Yet, the same with other bridge-type inverter, the straight-through danger of the same existence of the brachium pontis of diode clamping tri-level inverter, its functional reliability still has to be hoisted.

Dual buck half bridge inverter has the structural advantage of anti-bridge arm direct pass, and its fly-wheel diode can be optimized and chooses, and can adopt the half period working method to reduce conduction loss, but it can only work in the bipolarity modulation system, and the voltage stress of device is big.To the shortcoming of dual buck half bridge inverter, the introducing multilevel converter can make it be operated in the unipolarity modulation system and reduce device voltage stress at double.Patent CN 100431255C substitutes the effective diode-clamped tri-level switch of the power switch in dual buck half bridge inverter unit; Obtained the main circuit topology of three-level dual-buck half-bridge inverter; Though this circuit topology has reduced the voltage stress of power switch pipe; But its brachium pontis fly-wheel diode still bears input voltage; Be not suitable for the application of high voltage input occasion,, can make circuit structure complicated more like this though can further substitute through introducing diode-clamped three level diodes.

Summary of the invention

The technical problem that the present invention will solve is: to the defective of combining inverter existence in the background technology, and propose division induction three-level photovoltaic grid-connected inverter and the control method thereof that a kind of circuit structure is simple, reliability is high.

Division induction three-level photovoltaic grid-connected inverter of the present invention; Comprise power circuit; This power circuit comprises DC power supply, the first dividing potential drop electric capacity and the second dividing potential drop electric capacity; The positive pole of DC power supply connects the anode of the first dividing potential drop electric capacity; The negative pole of DC power supply connects the negative terminal of the second dividing potential drop electric capacity, and the negative terminal of the first dividing potential drop electric capacity connects the anode and the ground connection of the second dividing potential drop electric capacity, and this inverter also comprises the first inversion branch road and the second inversion branch road; Wherein: the first inversion branch road comprises first power switch pipe, second power switch pipe, first power diode and first division inductance; The drain electrode of first power switch pipe connects the anode of the first dividing potential drop electric capacity, and the source electrode of first power switch pipe connects the drain electrode of second power switch pipe and the negative electrode of first power diode respectively, and the source electrode of second power switch pipe connects an end of first division inductance; The second inversion branch road comprises the 3rd power switch pipe, the 4th power switch pipe, second power diode and the second division inductance; The source electrode of the 4th power switch pipe connects the negative terminal of the second dividing potential drop electric capacity; The drain electrode of the 4th power switch pipe connects the source electrode of the 3rd power switch pipe and the anode of second power diode respectively; The drain electrode of the 3rd power switch pipe connects an end of the second division inductance; The negative electrode of second power diode connects the anode of first power diode, the negative terminal of the first dividing potential drop electric capacity and the anode and the ground connection of the second dividing potential drop electric capacity respectively, ground connection after the other end of the second division inductance and the other end of first division inductance connect and compose the output of this inverter and insert electrical network.

Based on the control method of above-mentioned division induction three-level photovoltaic grid-connected inverter, comprise following content:

I. the stagnant ring width of the change of inverter side inductive current control frequently surely

Become hysteresis band h by line voltage u _gWith the DC power supply output voltage U _PvInstantaneous value calculate in real time;

At line voltage u _gPositive half cycle adopt first division inductive current i _L1Become the ring width hysteresis current control frequently surely that stagnates, first power switch pipe is pressed the action of PWM mode high frequency, and the second power switch pipe range is logical, and the 3rd power switch pipe and the 4th power switch pipe range are disconnected;

At line voltage u _gNegative half period adopt the second division inductive current i _L2Become the ring width hysteresis current control frequently surely that stagnates, the 4th power switch pipe is pressed the action of PWM mode high frequency, and the 3rd power switch pipe range is logical, and first power switch pipe and the second power switch pipe range are disconnected;

II. the HF switch drive signal closes in advance

At line voltage u _gPositive half cycle, the high-frequency driving signal of first power switch pipe is at line voltage u _gClose before the zero passage;

At line voltage u _gNegative half period, the high-frequency driving signal of the 4th power switch pipe is at line voltage u _gClose before the zero passage.

The present invention is the basis with the semi-bridge type non-isolated grid-connected inverter, in the good leakage current characteristic that keeps the semi-bridge type circuit structure, introduces dual buck half bridge inverter and prevents the structural advantage that leads directly to, has realized the simplification and the high reliability of circuit structure; Through adopting closing in advance of hysteresis current control technology and high-frequency switching signal, guaranteed the fail safe that current path switches; Adopt the change hysteresis band to control frequently surely and can the harmonic current spectrum concentration be helped the design of further filtering measure; Phase structure of the present invention can extend to the three-phase four-wire system three-phase grid-connected inverter structure of band center line easily, and has same high reliability and low leakage characteristic.In sum, technique effect of the present invention is: do not produce high-frequency leakage current when 1) converter is worked under the single-polarity PWM modulation system, be fit to non-isolated grid-connected inverter and use; 2) do not exist bridge arm direct pass dangerous, significantly improve the reliability of converter; 3) voltage stress of all power switch pipes and diode is equal to or half the less than input voltage.

Description of drawings

Fig. 1 is the phase structure circuit theory diagrams of inverter of the present invention, and among the figure: A is a power circuit; B, C are respectively the first and second inversion branch roads; PV is a DC power supply; U _PvBe the DC power supply output voltage; C _Dc1, C _Dc2Be respectively the first and second dividing potential drop electric capacity; S ₁, S ₂, S ₃, S ₄Be respectively first to fourth power switch pipe; D ₅, D ₆Be respectively first and second power diodes; L ₁, L ₂Be respectively the first and second division inductance; i _L1, i _L2Be respectively the first and second division inductive currents; i _L12Be the network access electric current; u _gBe line voltage.

Fig. 2 is the three-phase structure circuit theory diagrams of inverter of the present invention.

Fig. 3 is inverter control mode of the present invention and driving signal of power switching tube sequential chart, among the figure: i _RefBe inverter inductance reference current; u ₁₃Be voltage between the inverter bridge mid point 1 and 3 among Fig. 1; u ₂₃Be voltage between the inverter bridge mid point 2 and 3 among Fig. 1.

Fig. 4 is operation mode equivalent circuit theory figure during for inverter stable state of the present invention, wherein: (a) the positive half cycle of line voltage, power delivery stage; (b) the positive half cycle of line voltage, the afterflow stage; (c) line voltage negative half period, the power delivery stage; (d) line voltage negative half period, the afterflow stage.

Fig. 5 (a) is the voltage oscillogram of inverter brachium pontis mid point of the present invention to dc power cathode; Fig. 5 (b) is the oscillogram of the first and second division inductive currents in the inverter of the present invention.

Fig. 6 (a) is the half the experimental waveform figure of power input voltage for the first power switch pipe operating voltage stress in the inverter of the present invention; Fig. 6 (b) is the experimental waveform figure of line voltage (less than power input voltage half the) for the second power switch pipe operating voltage stress in the inverter of the present invention.

Leakage current waveform and spectrogram when Fig. 7 (a) uses for single-phase inverter of the present invention; Fig. 7 (b) is leakage current waveform and the spectrograms of conventional single-phase three level combining inverters when using.

Among Fig. 5～Fig. 7: u _1NVoltage for 1 pair of power cathode of inverter bridge mid point among Fig. 1; u _2NVoltage for 2 pairs of power cathodes of inverter bridge mid point among Fig. 1; u _3NVoltage for 3 pairs of power cathodes of dividing potential drop electric capacity mid point among Fig. 1; i _LeakageBe leakage current; I _50HzBe the low-frequency component in the leakage current; I _18kHzHigh frequency action generation for the photovoltaic dummy source; I _20kHzThe leakage current composition that produces for the action of the high frequency of combining inverter; u _{GS (S1)}Be the first power switch tube drives voltage; u _{DS (S1)}It is the first power switch tube drives drain-source terminal voltage; u _{GS (S2)}Be the second power switch tube drives voltage; u _{DS (S2)}It is the second power switch tube drives drain-source terminal voltage.

Embodiment

Inverter one-phase structure of the present invention is as shown in Figure 1, comprises power circuit A, the first inversion branch road B and the second inversion branch road C, and wherein: power circuit A comprises DC power supply PV, the first dividing potential drop capacitor C _Dc1With the second dividing potential drop capacitor C _Dc2, the positive pole of DC power supply PV connects the first dividing potential drop capacitor C _Dc1Anode, the negative pole of DC power supply PV connects the second dividing potential drop capacitor C _Dc2Negative terminal, the first dividing potential drop capacitor C _Dc1Negative terminal connect the second dividing potential drop capacitor C _Dc2Anode and ground connection; The first inversion branch road B comprises first power switch tube S ₁, second power switch tube S ₂, the first power diode D ₅With the first division inductance L ₁, first power switch tube S ₁Drain electrode connect the first dividing potential drop capacitor C _Dc1Anode, first power switch tube S ₁Source electrode connect second power switch tube S respectively ₂The drain electrode and the first power diode D ₅Negative electrode, second power switch tube S ₂Source electrode connect the first division inductance L ₁An end; The second inversion branch road C comprises the 3rd power switch tube S ₃, the 4th power switch tube S ₄, the second power diode D ₆With the second division inductance L ₂, the 4th power switch tube S ₄Source electrode connect the second dividing potential drop capacitor C _Dc2Negative terminal, the 4th power switch tube S ₄Drain electrode connect the 3rd power switch tube S respectively ₃The source electrode and the second power diode D ₆Anode, the 3rd power switch tube S ₃Drain electrode connect the second division inductance L ₂An end, the second power diode D ₆Negative electrode connect the first power diode D respectively ₅Anode, the first dividing potential drop capacitor C _Dc1The negative terminal and the second dividing potential drop capacitor C _Dc2Anode and ground connection, second the division inductance L ₂The other end and first division inductance L ₁The other end connect and compose the output of this inverter and insert electrical network after ground connection; To photovoltaic generating system, said DC power supply PV is photovoltaic array (solar panel).

For being applicable to the three phase network structure; The three-phase structure of inverter expansion of the present invention is as shown in Figure 2; Its shared power circuit; Inverter circuit is made up of the parallel connection of three groups of single-phase inversion branch roads, and the inductance output end of each group inversion branch road connects an input of three phase network respectively, and the electrical network center line connects the earth point of power circuit.The principle of this structure is identical with phase structure.

As shown in Figure 3 is inverter control mode of the present invention and driving signal of power switching tube sequential chart.At line voltage u _gPositive half cycle, first power switch tube S ₁Press the action of PWM mode high frequency, second power switch tube S ₂Long logical, the 3rd power switch tube S ₃With the 4th power switch tube S ₄Long disconnected; At line voltage u _gNegative half period, the 4th power switch tube S ₄Press the action of PWM mode high frequency, the 3rd power switch tube S ₃Long logical, first power switch tube S ₁With second power switch tube S ₂Long disconnected.For the fail safe that guarantees that current path switches, in conjunction with Fig. 3, at line voltage u _gPositive half cycle, first power switch tube S ₁High-frequency driving signal at line voltage u _gX π before the zero passage closes constantly; At line voltage u _gNegative half period, the 4th power switch tube S ₄High-frequency driving signal at line voltage u _g(1+x) π before the zero passage closes constantly.

The shut-in time that shifts to an earlier date of HF switch drive signal is satisfied following formula:

$\frac{{\∫}_{\mathrm{x\π}}^{\mathrm{\π}}[U_g\·\sin \left(\mathrm{\ωt}\right)+U_D\left(\mathrm{on}\right)+U_S\left(\mathrm{on}\right)}{L}\≥I_{\mathrm{ref}}\·\sin \left(\mathrm{x\π}\right)+\frac{h}{2}---\left(1\right)$

In the formula: U _g, I _RefBe respectively u _g, i _RefAmplitude; L is division inductance value, L=L ₁=L ₂U _D(on), U _S(on) be respectively the conduction voltage drop of power diode and power switch pipe; H is the electrorheological hysteresis band.

Fig. 4 is operation mode equivalent circuit theory figure during for inverter stable state of the present invention.Analyze for ease, do following hypothesis: 1) all power switch pipes and diode are desirable device, do not consider switching time and conduction voltage drop; 2) all inductance and electric capacity are ideal element, and C _Dc1=C _Dc2, L ₁=L ₂=L; 3) invertor operation is in unity power factor, i.e. the network access current i _L12With line voltage u _gComplete same-phase.Be the operation mode of example labor inverter with the positive half cycle of line voltage (Fig. 4 (a) (b)) below, line voltage negative half period (Fig. 4 (c) (d)) is similar with it.

Mode 1, shown in Fig. 4 (a):

Power switch tube S ₁And S ₂Open-minded, S ₃And S ₄Turn-off.Output voltage is a capacitor C between brachium pontis _Dc1Last voltage, promptly

This stage inductive current i _L1Linear increasing.

$L=\frac{{\mathrm{di}}_{L1}}{\mathrm{dt}}=\frac{1}{2}{U}_{\mathrm{pv}}-u_g---\left(2\right)$

Mode 2, shown in Fig. 4 (b):

Power switch tube S ₁Shutoff, S ₂Open-minded, S ₃And S ₄Still turn-off.S ₁Terminal voltage by diode D ₅Half of clamp to input voltage, output voltage is zero between brachium pontis, i.e. u ₁₃=0, this stage inductive current i _L1Be in the afterflow stage, linear decline.

$L\frac{{\mathrm{di}}_{L1}}{\mathrm{dt}}=0-u_g---\left(3\right)$

Thus it is clear that, line voltage u _gPositive half cycle brachium pontis output voltage does

With 0 level, similarly, do at negative half period brachium pontis output voltage

With 0 level, it is only to compare dual buck half bridge inverter (DBHBI)

With

Level, the present invention can significantly reduce filter inductance current pulsation amount, helps reducing inductance value.

Can get by formula (2) and formula (3):

$h=\frac{u_g(U_{\mathrm{Pv}}-2\·u_g)}{U_{\mathrm{Pv}}\·L\·f},$ F is switching frequency (4)

In service at inverter is according to line voltage u _gAnd electric power output voltage U _PvInstantaneous value calculate in real time and become hysteresis band h, can realize deciding the hysteresis current control of switching frequency.

A concrete experiment embodiment of the present invention is following:

Parameter is in the circuit: DC power supply (cell panel) output voltage U _Pv=800V, line voltage U _Grid=240VRMS, mains frequency f _Grid=50Hz, rated power P _N=1kW, dc bus (dividing potential drop) capacitor C _Dc1=C _Dc2=235 μ F, filtering division inductance L ₁=L ₂=4mH, cell panel be parasitic capacitance C over the ground _Pv1=C _Pv2=0.1 μ F, switching frequency f=20kHZ.

Fig. 5～7 are the experimental waveform figure of this instance, and wherein: Fig. 5 (a) is brachium pontis output voltage u of the present invention _1N, u _2N, u _3NExperimental waveform figure, Fig. 5 (b) is first, second division inductive current i among the present invention _L1, i _L2Experimental waveform figure; Fig. 6 (a) is first power switch tube S among the present invention ₁Operating voltage stress is the half the experimental waveform figure (the battery input voltage is 800V) of battery input voltage, and Fig. 6 (b) is second power switch tube S among the present invention ₂Operating voltage stress is the experimental waveform figure (the line voltage peak value is 339V, less than the battery input voltage half the) of line voltage; Fig. 7 (a) is single-phase inverter of the present invention leakage current waveform and a spectrogram when using, and Fig. 7 (b) is leakage current waveform and the spectrograms of conventional single-phase three level combining inverters when using.

Claims (3)

1. a division induction three-level photovoltaic grid-connected inverter comprises power circuit (A), and this power circuit (A) comprises DC power supply (PV), the first dividing potential drop electric capacity (C _Dc1) and the second dividing potential drop electric capacity (C _Dc2), the positive pole of DC power supply (PV) connects the first dividing potential drop electric capacity (C _Dc1) anode, the negative pole of DC power supply (PV) connects the second dividing potential drop electric capacity (C _Dc2) negative terminal, the first dividing potential drop electric capacity (C _Dc1) negative terminal connect the second dividing potential drop electric capacity (C _Dc2) anode and ground connection, it is characterized in that: also comprise the first inversion branch road (B) and the second inversion branch road (C), wherein: the first inversion branch road (B) comprises the first power switch pipe (S ₁), the second power switch pipe (S ₂), the first power diode (D ₅) and first division inductance (L ₁), the first power switch pipe (S ₁) drain electrode connect the first dividing potential drop electric capacity (C _Dc1) anode, the first power switch pipe (S ₁) source electrode connect the second power switch pipe (S respectively ₂) the drain electrode and the first power diode (D ₅) negative electrode, the second power switch pipe (S ₂) source electrode connect first division inductance (L ₁) an end; The second inversion branch road (C) comprises the 3rd power switch pipe (S ₃), the 4th power switch pipe (S ₄), the second power diode (D ₆) and the second division inductance (L ₂), the 4th power switch pipe (S ₄) source electrode connect the second dividing potential drop electric capacity (C _Dc2) negative terminal, the 4th power switch pipe (S ₄) drain electrode connect the 3rd power switch pipe (S respectively ₃) the source electrode and the second power diode (D ₆) anode, the 3rd power switch pipe (S ₃) drain electrode connect the second division inductance (L ₂) an end, the second power diode (D ₆) negative electrode connect the first power diode (D respectively ₅) anode, the first dividing potential drop electric capacity (C _Dc1) the negative terminal and the second dividing potential drop electric capacity (C _Dc2) anode and ground connection, the second division inductance (L ₂) the other end and first division inductance (L ₁) the other end connect and compose the output of this inverter and insert electrical network after ground connection.

2. division induction three-level photovoltaic grid-connected inverter according to claim 1 is characterized in that: said DC power supply (PV) is a photovoltaic array.

3. control method based on the described division induction three-level photovoltaic grid-connected inverter of claim 1 is characterized in that comprising following content:

I. the stagnant ring width of the change of inverter side inductive current control frequently surely

Become hysteresis band h by line voltage u _gWith the DC power supply output voltage U _PvInstantaneous value calculate in real time, computing formula is following:

$h=\frac{u_g(U_{\mathrm{pv}}-2\·u_g)}{U_{\mathrm{pv}}\·L\·f}$

In the formula: u _gBe line voltage, U _PvBe the DC power supply output voltage, L is the division inductance value, and f is a switching frequency;

At line voltage u _gPositive half cycle adopt first division inductive current i _L1Become the ring width hysteresis current control frequently surely that stagnates, the first power switch pipe (S ₁) press PWM mode high frequency action, the second power switch pipe (S ₂) long logical, the 3rd power switch pipe (S ₃) and the 4th power switch pipe (S ₄) long disconnected;

At line voltage u _gNegative half period adopt the second division inductive current i _L2Become the ring width hysteresis current control frequently surely that stagnates, the 4th power switch pipe (S ₄) press PWM mode high frequency action, the 3rd power switch pipe (S ₃) long logical, the first power switch pipe (S ₁) and the second power switch pipe (S ₂) long disconnected;

II. the HF switch drive signal closes in advance

At line voltage u _gPositive half cycle, the first power switch pipe (S ₁) high-frequency driving signal at line voltage u _gClose before the zero passage;

At line voltage u _gNegative half period, the 4th power switch pipe (S ₄) high-frequency driving signal at line voltage u _gClose before the zero passage.

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