CN106602999A - Super-capacitor-based hybrid cascade photovoltaic inverter and control method - Google Patents

Abstract

The invention relates to a super-capacitor-based hybrid cascade photovoltaic inverter and control method. The inverter comprises a super capacitor, photovoltaic cells, an ordinary filtering capacitor, an H bridge. The super capacitor, the plurality of photovoltaic cells and the ordinary filtering capacitor in parallel connection with the photovoltaic cells are connected with the direct current side of the H bridge and are then connected in series at the alternating current side of the H bridge to develop relatively high voltage output so as to absorb the power of the photovoltaic cells during the power generation peak of the photovoltaic cells and compensate the deficiency of the output power at the ebb of power generation from the photovoltaic cells. In this way, the power fluctuation of photovoltaic power generation is reduced. The super-capacitor is provided with a certain saving capacity as well as the advantage of fast power charging and discharging, therefore, making the inverter able to suppress power fluctuation and overcome the drop in voltage of a power grid.

Description

A kind of Mixed cascading type photovoltaic inverter and control based on super capacitor energy-storage Method

Technical field

The achievement in research of the present invention is applied to distributed photovoltaic power generation system, and the photovoltaic that also may extend to large centralised is sent out Electric system, more particularly to a kind of Mixed cascading type photovoltaic inverter and control method based on super capacitor energy-storage.

Background technology

Distributed photovoltaic power generation system with energy storage link, conventional structure is that photovoltaic cell is passed through into DC-to-dc (DC/DC) changer and energy-storage travelling wave tube parallel connection, or both on dc bus passes through respectively DC-AC (DC/AC) inverter It is in parallel in AC.A kind of existing band stored energy distribution formula photovoltaic power generation system structure is as shown in Figure 2.

This existing structure is that multiple photovoltaic cells are directly together in series, and is then entered through unified DC transfer circuit The overall maximum power control of row, then directly and is connected in the DC side of inverter and carries out unifying inversion output with super capacitor. For New Cascading type structure proposed by the present invention, overall structure is more simple, control strategy for this existing structure Relatively easily, but considerable problem is there is also, specifically there are these points：

(1) series connection of several photovoltaic cells is got up, although this mode is simple, is detrimental to carrying for overall generating efficiency It is high.Since when sunshine is uneven or battery behavior is uneven or has the masking photovoltaic battery panel such as local shades or broken gravel, photovoltaic electric The overall output power of pond group will be reduced, it is impossible to reach the peak power of single battery plate.Also, it is if any in series connection One cell malfunctions, then whole set of cells will fail.

(2) because photovoltaic system is through single grid-connected inverters or powers to the load, DC side voltage of converter ratio Higher, the voltage stress of corresponding each power device is also high.

(3) for super capacitor, monomer voltage ratio is relatively low, generally only several volts, so being applied to photovoltaic system Need series connection.More series of connecting are accomplished by when DC bus-bar voltage is higher, equivalent electric capacity is which reduces, or Need additional DC-to-dc (DC/DC) translation circuit.

(4) the output level number of single two level or three-level inverter is few, and harmonic content is high, needs relatively large volume Output filter.

On the whole, the problems of this existing band energy storage photovoltaic power generation system structure, can be attributed to light Problem produced by volt battery and the mismatch between the low-voltage and high line voltage of energy-storage travelling wave tube.If photovoltaic generating system The independent load to low-voltage or electrical network is powered, and this contradiction is easy for alleviating, and this will change multiple photovoltaic cells The structure of the single inverter outputs of Jing after plate series connection.

The content of the invention

From improving photovoltaic efficiency, reducing from the aspect of electricity generation system volume, reduces cost etc., the present invention proposes a kind of The photovoltaic DC-to-AC converter structure of new Mixed cascading type, photovoltaic is constituted by photovoltaic cell and super capacitor by the way of the cascade of H bridges Electricity generation system.This structure can be used with single-phase, it is also possible to constitute three-phase structure.The low-voltage device cost that this structure is used It is cheap, and small volume, using maturation, and the volume of output filter can be substantially reduced, increase sending out for single photovoltaic cell Electrical efficiency, reliability is high.

To reach above-mentioned purpose, the present invention is adopted the following technical scheme that：

A kind of Mixed cascading type photovoltaic inverter based on super capacitor energy-storage, it is characterised in that super including one Electric capacity C_sWith several dc-link capacitances, respectively dc-link capacitance C₁, dc-link capacitance C₂... dc-link capacitance C_n；And inverter bridge H₀, inverter bridge H₁... inverter bridge H_n；Inverter bridge H₁To H_nRespectively with corresponding dc-link capacitance C₁, dc-link capacitance C₂... dc-link capacitance C_nIt is joined directly together；It is sequentially connected in series between n+1 inverter bridge, also including one Super capacitor C_sWith inverter bridge H₀It is joined directly together, it is described；N+1 inverter bridge is straight with 1 super capacitor and n again after being sequentially connected in series The photovoltaic DC-to-AC converter of the H bridge cascade systems that stream bus capacitor is constituted after being joined directly together with scattered photovoltaic cell.

In a kind of above-mentioned Mixed cascading type photovoltaic inverter based on super capacitor energy-storage, the switching tube of H bridges is constituted There are multiple choices, using Metal-Oxide Semiconductor field-effect transistor (MOSFET) or edge grid bipolar transistor (IGBT)。

A kind of Mixed cascading type photovoltaic DC-to-AC converter control method based on super capacitor energy-storage, it is characterised in that：

Step 1, photovoltaic cell control：Direct current is determined using maximal power tracing (MPPT) control method conductance increment method Bus capacitor C₁To C_nVoltage-target, by inverter bridge H₁To H_nControl cause dc-link capacitance C₁To C_nVoltage Desired value is reached, makes photovoltaic cell keep maximum power output, wherein conductance increment method principle is instantaneous in relatively photovoltaic cell Differentiate photovoltaic cell present operating point location on the basis of the variable quantity of the conductance and conductance of voltage and output, The control of peak power is realized so as to adjust quiescent potential.

Step 2, super capacitor C_sControl：Due to the fluctuation of intensity of illumination, super capacitor should be in photovoltaic cell output work Rate increases active output when being less than rated output power, and absorbing when the output power from photovoltaic cells is higher than rated output power has Work(, reduces inverter active output, so as to reduce the fluctuation of photovoltaic DC-to-AC converter output；Super capacitor simultaneously can be according to need Reactive power is adjusted, on the one hand the reactive power that the inductance being connected with electrical network is consumed can be provided, on the other hand also can be inhaled Reactive power or provide reactive power to electrical network that receipts send from electrical network.

Wherein, with super capacitor C_sConnected H₀The phase place of the output voltage of bridge, amplitude, and be connected with photovoltaic cell it is inverse Become bridge H₁To H_nThe phase place of output voltage, amplitude it is different, control super capacitor C by controlling the difference of the two_sCharging With the switching of discharge condition, to keep super capacitor C_sVoltage stabilization.

In a kind of above-mentioned Mixed cascading type photovoltaic inversion control method based on super capacitor energy-storage, all and photovoltaic electric Connected inverter bridge H in pond₁To H_nOutput voltage phase place it is identical, and the amplitude of output voltage is with the voltage of dc-link capacitance Change, amplitude is variable.

In a kind of above-mentioned Mixed cascading type photovoltaic inversion control method based on super capacitor energy-storage, with photovoltaic cell phase Inverter bridge H even₁To H_nThe amplitude of output voltage, the determination method of phase place be：

Step 1, detects amplitude Vs and phase place of line voltage, makes H₁To H_nOutput voltage phase place and line voltage phase Position is identical, and H₁To H_nOutput voltage amplitude summation Vp2 it is identical with amplitude Vs of line voltage, i.e.,

V_p2=V_s (1)

Step 2, according to conductance increment method the dc-link capacitance C that k-th photovoltaic cell is directly connected is determined_kElectricity Pressure desired value Vdck, k=1,2 ... ... n.Vdck is amplitude partition coefficient with the ratio of n dc-link capacitance voltage sum Mk, i.e.,

Step 3, H₁To H_nThe amplitude of output voltage be respectively defined as U1 to Un, then the width of the output voltage of k-th H bridge Value Uk is determined by following formula：

U_k=V_p2×M_k (3)

6. a kind of Mixed cascading type photovoltaic inversion method based on super capacitor energy-storage according to claim 3, its It is characterised by, described and super capacitor C_sConnected inverter bridge H₀The phase place of output voltage, the concrete determination method of amplitude be：

Step 1, using phaselocked loop the phase place of line voltage is detected, makes H₀Output voltage phase place be ahead of line voltage 90 degree of phase place；If super capacitor C_sDC voltage be less than rated value, then H₀Output voltage phase place be ahead of line voltage Phase place is (90+ α) degree；If super capacitor C_sDC voltage be higher than rated value, then H₀Output voltage phase place be ahead of electrical network The phase place of voltage is (90- α) degree；α is more than zero and the adjustable angle value of size.

Step 2, measures average anode current value Idck of each photovoltaic cell, k=1,2 ... ... n.N is calculated according to following formula Individual the output power from photovoltaic cells summation is

Then H₀Amplitude Vp1 of output voltage determined that wherein L is the filter inductance between inverter and electrical network by following formula Inductance value, f is the frequency of electrical network：

Therefore, the invention has the advantages that：The knot that super capacitor Jing H bridges are cascaded with the H bridges of photovoltaic cell in AC Structure, for comparing the photovoltaic DC-to-AC converter of photovoltaic cell H bridges cascade, further increases the quantity of the H bridges of AC cascade, thus The level quantity of synthesising output voltage is increased, output is reduce further than the photovoltaic DC-to-AC converter of photovoltaic cell H bridges cascade humorous Ripple.Common filter capacitor carries out in parallel with photovoltaic cell, is connected with H bridges while strobing.The present invention is cascaded using H bridges Type grid-connected inverters, its advantage can be to save output transformator, be directly synthesized high voltage output, and this structure is used Low-voltage device it is with low cost, and small volume, using maturation, can be substantially reduced output filter volume in addition, increase single The generating efficiency of photovoltaic cell, improves reliability, therefore application prospect is fine.

Description of the drawings

Fig. 1 is the system phase structure figure of the present invention.

Fig. 2 photovoltaic cells and super capacitor are in dc bus system architecture diagram in parallel.

Fig. 3 is the one phase equivalent circuit figure of mixed cell cascade structure.

Fig. 4 is the phasor diagram of photovoltaic generating system active power of output.

Fig. 5 is photovoltaic generating system active power of output, the phasor diagram of absorbing reactive power.

Fig. 6 is photovoltaic generating system active power of output, the phasor diagram of output reactive power.

Specific embodiment

The feasibility of the present invention is described below in detail, the example is shown in the drawings, wherein identical from start to finish or class As label represent same or similar element or the element with same or like function.It is presented herein below by reference to Description of Drawings Exemplary, it is only used for explaining the present invention, and be not considered as limiting the invention.

In figure：1-Cs- super capacitors, 2-PV- photovoltaic cells, 3- conventional capacitives, 4-H bridges, 5-L- inductance, the super electricity of Vp1- Hold unit output voltage, Vp2- photovoltaic cell output voltages, Isp- flows through inductive current, Vs- electrical network phase voltages, on Vsl- inductance The sum of voltage, Zl- equivalent loads, Vp- supercapacitive cells output voltage and photovoltaic cell output voltage.

First, the circuit topology and basic control principle of the present invention are introduced first.

A kind of Mixed cascading inverter structure with super capacitor energy-storage, including photovoltaic cell (2) series connection with it is super Electric capacity (1), the H bridges (4) being also joined directly together with every unit photovoltaic cell (2) and super capacitor (1), it is characterised in that：Will be super Level electric capacity (1) constitutes photovoltaic DC-to-AC converter with scattered photovoltaic cell (2) by the way of the cascade of H bridges.

(1) for photovoltaic cell control, using classical maximal power tracing (MPPT) control method, such as conductance increment Method, make photovoltaic cell keep maximum power output, wherein conductance increment method principle be relatively photovoltaic cell instantaneous voltage with it is defeated Go out on the basis of the conductance of power and the variable quantity of conductance to differentiate photovoltaic cell present operating point location, so as to adjust Quiescent potential is realizing the control of peak power.Preferably, comparing other method conductance increment methods has higher precision It is simultaneously easy to operate.Preferably, this structure realizes that per unit photovoltaic cell independent control can be accomplished raising system is integrally sent out Electrical efficiency.

(2) for super capacitor, its energy density is little, power density is big, efficiency for charge-discharge is high, speed is fast and uses the longevity Life length.Preferably, for the control of super capacitor and coupled H bridges, by photovoltaic cell (group) and coupled The output voltage of H bridges, the output voltage of super capacitor and coupled H bridges, this three's phase relation of line voltage and The control of amplitude size, is capable of achieving the quick drop to make up the output power from photovoltaic cells by super capacitor fast charging and discharging Or the unnecessary part of the output power from photovoltaic cells is absorbed, reduce the amplitude of photovoltaic cell capable of generating power power swing.Preferably, this In structure control super capacitor charge, electric discharge while, the coupled H bridges of control can be passed through and be connected with photovoltaic cell The purpose of the phase contrast of the output voltage of H bridges, realization absorption or compensation network reactive power, and photovoltaic cell and its connected H Bridge is active power of output.

After photovoltaic cell is connected respectively with super capacitor with H bridges AC cascade structure, due to by illumination, Unmatched impact between temperature and photovoltaic cell, the output characteristics of batteries at different levels in cascade multilevel photovoltaic grid-connected inverter Difference, its peak power output is also different.The requirement that controls according to MPPT when photovoltaic cell and operate in respective peak power When at point, DC bus-bar voltages at different levels can occur variation because photovoltaic generation power is unbalanced, and no longer be consistent. Because the present invention will ensure the maximum power output of photovoltaic cells at different levels, therefore, for photovoltaic cell and super capacitor respectively with H The structure of bridge cascade, the control strategy of the present invention should be in the control of Traditional DC busbar voltage summation, power network current double-closed-loop control Basis on, the requirement controlled according to the MPPT of each photovoltaic cell determines the d-c bus voltage value of each H bridges, rather than as Some cascade connection type photovoltaic DC-to-AC converters force like that the DC bus-bar voltage of each H bridges to be consistent as far as possible.

In the structure of AC cascade after being connected with H bridges respectively with super capacitor for photovoltaic cell, due to photovoltaic electric Also there is a DC parallel electric capacity between pond and H bridges, thus each H bridge can output reactive power and active power.Its control Mode processed flexibly, is adapted to different demands.Such as, the H bridge active power of output of (1) photovoltaic cell, the H bridges of super capacitor Reactive power required for the inductance that is connected with electrical network of output, now super capacitor neither charge, nor discharge, whole inverter Active power is only conveyed to electrical network；(2) the H bridge active power of output of photovoltaic cell, the H bridges active power of output of super capacitor and Reactive power, now super capacitor electric discharge, whole inverter to electrical network conveys active power and reactive power；(3) photovoltaic cell H bridge active power of output, the H bridge active power of output of super capacitor, absorbing reactive power, now super capacitor electric discharge, it is whole Individual inverter is to electrical network conveying active power, absorbing reactive power；(4) the H bridges of photovoltaic cell, the H bridges of super capacitor are all exported Quantity not wait active power and reactive power, now super capacitor electric discharge, whole inverter to electrical network conveying active power and Reactive power；(5) the H bridges active power of output and reactive power of photovoltaic cell, the H bridges of super capacitor absorb active power, defeated Go out reactive power, now super capacitor charges, whole inverter to electrical network conveys active power and reactive power.

2nd, specific control case is illustrated below in conjunction with the accompanying drawings.

Shown in Fig. 1, the Mixed cascading type photovoltaic inverter of super capacitor energy-storage of the present invention, including：Photovoltaic cell (2), Filter capacitor (3), super capacitor (1), H bridges (4) and inductance (5).

Shown in Fig. 2, this is a kind of photovoltaic power generation system structure having been proposed that.

It is the one phase equivalent circuit figure of mixed cell cascade structure shown in Fig. 3, super capacitor output voltage V_p1And photovoltaic electric Pond output voltage V_p2It is connected with electrical network or load after series connection, V_slIt is the voltage drop on inductance L, the electric current I of inductance L_sp, its vector Analysis is as shown in Figure 4.

Fig. 4 is the vector that the Mixed cascading type photovoltaic inverter of super capacitor energy-storage of the present invention only sends active power Figure.Due to super capacitor output voltage V_p1With photovoltaic cell output voltage V_p2Sum V_pIt is ahead of line voltage V_s, active power Electrical network is flowed to from inverter.Assume that photovoltaic cells only export active, the output voltage V of photovoltaic cells_p2(Fig. 4 middle conductor AO) direction With line voltage V_sSame phase, amplitude size and V_sIt is identical.Supercapacitive cell output voltage V_pl(Fig. 4 middle conductor DA) phase place surpasses It is front in line voltage V_s90 degree, voltage V in amplitude and inductance L_slSize is identical.The now electric current I of inductance L_spDirection and electrical network electricity Pressure V_sDifference 180 degree.Understand, the supercapacitive cell reactive power that now an outputting inductance L is consumed.If photovoltaic cells output electricity Pressure amplitude value declines (such as Fig. 4 middle conductor CO), then supercapacitive cell output voltage V_p1It is ahead of line voltage V_sPhase angle be less than 90 degree (such as Fig. 4 middle conductor DC), and its amplitude increase, now super capacitor electric discharge；If otherwise photovoltaic cells output voltage amplitude Raise (such as Fig. 4 middle conductor BO), then supercapacitive cell output voltage V_p1It is ahead of line voltage V_sPhase angle more than 90 degree and Less than 180 degree (such as Fig. 4 middle conductor DB), and its amplitude increase, now super capacitor charging.Meanwhile, by controlling V_pWith V_sBetween Phase relation and amplitude, it is possible to while controlling the active power that conveys to electrical network of photovoltaic generating system and reactive power.

Fig. 5 is the vectogram of absorbing reactive power while photovoltaic system sends active.Due to V_pIt is ahead of line voltage Vs, active power flows to electrical network from inverter.V_pAmplitude is less than line voltage V_sAmplitude, now inductive current I_spDirection it is stagnant After line voltage V_sAngle more than 90 degree and less than 180 degree.Assume that photovoltaic cells only export active, the output of photovoltaic cells Voltage V_p2(such as the line segment OA of Fig. 5) and I_spAngle be 180 degree, then supercapacitive cell output voltage V_p1Lag behind V_p290 degree (such as the line segment AD of Fig. 5).Supercapacitive cell is now from electrical network absorbing reactive power.If photovoltaic cells output voltage amplitude declines (such as the line segment OC of Fig. 5), then supercapacitive cell output voltage V_p1Lag behind V_p2Angle less than 90 degree (such as the line segment of Fig. 5 CD), now super capacitor electric discharge；Otherwise if photovoltaic cells output voltage amplitude is raised (such as the line segment OB of Fig. 5), super capacitor Unit output voltage V_p1Lag behind V_p2Angle more than 90 degree and less than 180 degree (such as the line segment BD of Fig. 5), now super capacitor Charge.

Fig. 6 is the vectogram that reactive power is sent while photovoltaic system sends active power.Inverter output voltage V_p It is ahead of line voltage V_s, and V_pAmplitude is higher than line voltage V_s, now inductive current I_spDirection be ahead of line voltage V_s's Angle more than 90 degree and flows to electrical network less than 180 degree, active power and reactive power from inverter.Assume that photovoltaic cells were both exported Active power, sends reactive power, the output voltage V of photovoltaic cells again_p2It is ahead of line voltage V_sAngle be less than 90 degree, together When lag behind V_p(such as Fig. 6 middle conductor OA), then supercapacitive cell output voltage V_p1It is ahead of line voltage V_sAngle be less than 180 degree and it is ahead of I_sp90 degree of phase angle (such as Fig. 6 middle conductor AD).Now supercapacitive cell output reactive power.If photovoltaic Unit output voltage amplitude declines (such as Fig. 6 middle conductor OC), then supercapacitive cell output voltage V_p1It is ahead of line voltage V_s Angle reduce (such as Fig. 6 middle conductor CD), amplitude increase, now super capacitor electric discharge；If otherwise photovoltaic cells output voltage width Value is raised (such as Fig. 6 middle conductor OB), then supercapacitive cell output voltage V_p1It is ahead of line voltage V_sAngle increase (as scheme 6 middle conductor BD), now super capacitor charges.

By above phasor analysis, this Mixed cascading system can be to control and super while completing generation current The charge and discharge control of electric capacity.

There are some to research and propose and adopted H bridges cascaded inverter simultaneously in the photovoltaic plant of large centralised ground Net, its advantage can be to save output transformator, be directly synthesized high voltage output grid-connected.In distributed photovoltaic system, due to Existing power device can reach line voltage grade, thus seem more simple direct using single inverter, using level Connection formula structure seems that complex structure, components and parts are more.But the low-voltage device that for the present invention, this structure is used its into This is very cheap, and small volume, using maturation, the volume of output filter can be substantially reduced in addition, increases single photovoltaic cell Generating efficiency, improve reliability, therefore the structure and its control method of the present invention have obvious advantage, are worthy to be popularized.

Specific embodiment described herein is only explanation for example spiritual to the present invention.Technology neck belonging to of the invention The technical staff in domain can be made various modifications to described specific embodiment or supplement or replaced using similar mode Generation, but without departing from the spiritual of the present invention or surmount scope defined in appended claims.

Claims (6)

1. a kind of Mixed cascading type photovoltaic inverter based on super capacitor energy-storage, it is characterised in that including a super electricity Hold C_sWith several dc-link capacitances, respectively dc-link capacitance C₁, dc-link capacitance C₂... dc-link capacitance C_n；And inverter bridge H₀, inverter bridge H₁... inverter bridge H_n；Inverter bridge H₁To H_nRespectively with corresponding dc-link capacitance C₁, dc-link capacitance C₂... dc-link capacitance C_nIt is joined directly together；It is sequentially connected in series between n+1 inverter bridge, also including one Super capacitor C_sWith inverter bridge H₀It is joined directly together, it is described；N+1 inverter bridge is straight with 1 super capacitor and n again after being sequentially connected in series The photovoltaic DC-to-AC converter of the H bridge cascade systems that stream bus capacitor is constituted after being joined directly together with scattered photovoltaic cell.

2. a kind of Mixed cascading type photovoltaic inverter based on super capacitor energy-storage according to claim 1, its feature It is to constitute the switching tube of H bridges to have multiple choices, it is ambipolar using Metal-Oxide Semiconductor field-effect transistor or edge grid Transistor.

3. a kind of Mixed cascading type photovoltaic DC-to-AC converter control method based on super capacitor energy-storage, it is characterised in that：

Step 1, photovoltaic cell control：Dc-link capacitance C is determined using maximum power tracking and controlling method conductance increment method₁ To C_nVoltage-target, by inverter bridge H₁To H_nControl cause dc-link capacitance C₁To C_nVoltage reach target Value, make photovoltaic cell keep maximum power output, wherein conductance increment method principle be relatively photovoltaic cell instantaneous voltage with it is defeated Go out on the basis of the conductance of power and the variable quantity of conductance to differentiate photovoltaic cell present operating point location, so as to adjust Quiescent potential is realizing the control of peak power；

Step 2, super capacitor C_sControl：Due to the fluctuation of intensity of illumination, super capacitor should be less than in the output power from photovoltaic cells Increase active output during rated output power, absorb active when the output power from photovoltaic cells is higher than rated output power, reduce Inverter active is exported, so as to reduce the fluctuation of photovoltaic DC-to-AC converter output；Super capacitor can be adjusted as needed simultaneously Reactive power, on the one hand can provide the reactive power that the inductance being connected with electrical network is consumed, and on the other hand also can absorb from electricity Reactive power or provide reactive power to electrical network that net sends；

Wherein, with super capacitor C_sConnected H₀The phase place of the output voltage of bridge, amplitude, and the inverter bridge being connected with photovoltaic cell H₁To H_nThe phase place of output voltage, amplitude it is different, control super capacitor C by controlling the difference of the two_sCharging and put The switching of electricity condition, to keep super capacitor C_sVoltage stabilization.

4. a kind of Mixed cascading type photovoltaic inversion control method based on super capacitor energy-storage according to claim 3, its It is characterised by, all inverter bridges H being connected with photovoltaic cell₁To H_nOutput voltage phase place it is identical, and the amplitude of output voltage With the change in voltage of dc-link capacitance, amplitude is variable.

5. a kind of Mixed cascading type photovoltaic inversion control method based on super capacitor energy-storage according to claim 3, its It is characterised by, inverter bridge H being connected with photovoltaic cell₁To H_nThe amplitude of output voltage, the determination method of phase place be：

Step 1, detects amplitude V of line voltage_sAnd phase place, make H₁To H_nOutput voltage phase place and electric network voltage phase phase Together, H₁To H_nOutput voltage amplitude summation V_p2With amplitude V of line voltage_sIt is identical, i.e.,

V_p2=V_s (1)

Step 2, according to conductance increment method the dc-link capacitance C that k-th photovoltaic cell is directly connected is determined_kVoltage mesh Scale value V_dck, k=1,2 ... ... n；V_dckIt is amplitude partition coefficient M with the ratio of n dc-link capacitance voltage sum_k, i.e.,

$M_k=\frac{V_{dck}}{\underset{i=1}{\overset{n}{\Σ}}{V}_{dci}}---\left(2\right)$

Step 3, H₁To H_nThe amplitude of output voltage be respectively defined as U₁To U_n, then amplitude U of the output voltage of k-th H bridge_kBy Following formula determines：

U_k=V_p2×M_k (3)。

6. a kind of Mixed cascading type photovoltaic inversion method based on super capacitor energy-storage according to claim 3, its feature It is, described and super capacitor C_sConnected inverter bridge H₀The phase place of output voltage, the concrete determination method of amplitude be：

Step 1, using phaselocked loop the phase place of line voltage is detected, makes H₀Output voltage phase place be ahead of the phase place of line voltage 90 degree；If super capacitor C_sDC voltage be less than rated value, then H₀Output voltage phase place be ahead of the phase place of line voltage For (90+ α) degree；If super capacitor C_sDC voltage be higher than rated value, then H₀Output voltage phase place be ahead of line voltage Phase place be (90- α) degree；α is more than zero and the adjustable angle value of size；

Step 2, measures average anode current value I of each photovoltaic cell_dck, k=1,2 ... ... n；N light is calculated according to following formula Lying prostrate cell output summation is

$P_{sum}=\underset{k=1}{\overset{n}{\Σ}}{V}_{dck}\×I_{dck}---\left(4\right)$

Then H₀Output voltage amplitude V_p1Determined by following formula, wherein L is the inductance of the filter inductance between inverter and electrical network Amount, f is the frequency of electrical network：

$V_{p1}=\frac{P_{sum}}{V_{p2}}\×2\mathrm{\π}f\×L---\left(5\right).$