CN102044883B - Maximum power point tracking (MPPT) optimization method for single-stage photovoltaic grid-connected inverter - Google Patents

Abstract

The invention relates to a maximum power point tracking (MPPT) process optimization method applied to a single-stage photovoltaic grid-connected generation system. The single-stage photovoltaic grid-connected generation system using the method comprises a solar photovoltaic array, a filter capacitor and a grid-connected inverter. In the MPPT process optimization method, on the basis of the power decoupling idea of the filter capacitor, the corresponding output power of the grid-connected inverter is quickly calculated and set according to the change of an energy relationship among the photovoltaic array, the filter capacitor and the grid-connected inverter and the voltage change of the filter capacitor when the output characteristic of the photovoltaic array is disturbed to eliminate the disturbance, so that the MPPT is quickly realized. The method can eliminate the influence of the change of the output characteristic of the photovoltaic array when illumination intensity, the temperature condition or other factors are changed on the MPPT process, and improves MPPT speed, the efficiency of the photovoltaic generation system and the stability and reliability of the system.

Description

A kind of optimization method of MPPT maximum power point tracking of stage photovoltaic single combining inverter

Technical field

The present invention relates to a kind of method that is applied to the optimization MPPT maximum power point tracking process of stage photovoltaic single combining inverter, belong to technical field of new energies, particularly solar energy power generating field.

Technical background

Solar energy has boundless application and development prospect as a kind of pollution-free, reproducible new forms of energy, along with socioeconomic development, utilize solar power generation to become a reliable approach that solves the productive life energy, improves problem of environmental pollution, can obtain huge economic benefit and social benefit.

The output of photovoltaic array is subject to the impact of the factors such as intensity of illumination, ambient temperature, presents nonlinear characteristic.Under certain intensity of illumination and ambient temperature, solar cell can be exported different voltage and currents, also can export different power, but only when a certain output voltage values, the power output of photovoltaic array can reach maximum, at this moment photovoltaic array is operated in the peak of power output voltage curve, is referred to as maximum power point (Maximum Power Point, MPP).

Grid-connected photovoltaic system generally comprises two-stage type and single stage type, while adopting single stage type mode, because electric energy only need to pass through linear transformation, therefore has the remarkable advantages such as conversion efficiency is high, solar array utilance is high, reliability is high.Single-stage photovoltaic grid-connected electricity generation system comprises photovoltaic array, filter capacitor and the combining inverter being linked in sequence, as shown in Figure 4.Because photovoltaic array power output is smooth direct current, and combining inverter power output presents periodically pulsing characteristic, so between photovoltaic array and combining inverter, need to be incorporated to the pulsation of the photovoltaic array power output that enough large electric capacity causes with level and smooth combining inverter.But the introducing as the electric capacity of energy-storage travelling wave tube has caused the Energy Coupling between photovoltaic array, combining inverter, electric capacity three, when the output characteristic of photovoltaic array changes, be photovoltaic array power output while changing, the variation of photovoltaic array power output can not embody at once in the power output of combining inverter.

In photovoltaic generating system, by the working point of real-time adjustment photovoltaic array, make it to always work near maximum power point, and then can improve the efficiency of whole photovoltaic generating system, this process is referred to as MPPT maximum power point tracking (Maximum Power Point Tracking, MPPT).The general power output that detects in real time photovoltaic array that adopts of MPPT strategy, remains near MPP power output by certain control algolithm.Existing MPPT method, generally by combining inverter power output is applied to little disturbance, by the variation tendency of certain algorithm judgement photovoltaic array power output, and then determines that next step applies the mode of disturbance.In fact, the above-mentioned MPPT method that applies small sample perturbations is to carry out under the stable prerequisite of photovoltaic array output characteristic.When illumination condition, temperature conditions or other unknowable external factor change and cause photovoltaic array output characteristic to change, while being also the power output generation acute variation of photovoltaic array, Energy Coupling effect due to electric capacity, the variation of photovoltaic array power output can not embody at once in the power output of combining inverter, therefore, MPPT method now can not guarantee the variation of the power output tracking photovoltaic array power output of combining inverter, also be that MPPT lost efficacy, when serious, can cause system crash.Traditional MPPT method generally takes the method that power output is applied to larger disturbance quantity to avoid system crash when there is above-mentioned situation as far as possible, but do not have clear and definite quantitative criteria for the size that should apply disturbance quantity, therefore be difficult to guarantee rapidity and the stability of MPPT tracing process, be also difficult to assurance system and can reenter rapidly stable state.Therefore when intensity of illumination, temperature condition and other factors change and cause photovoltaic array output characteristic to change constantly, system reenters stable state and realizes MPPT needs a longer transient process.

Summary of the invention

The present invention is directed to the deficiency that in background technology, existing MPPT method is applied to exist in Single-Stage Grid Connected Solar Inverter System, propose a kind of method that is applied to the optimization MPPT maximum power point tracking process of Single-Stage Grid Connected Solar Inverter System.

Below in conjunction with accompanying drawing 1 explanation concrete scheme of the present invention, the method that is applied to the optimization MPPT maximum power point tracking process of Single-Stage Grid Connected Solar Inverter System of the present invention, as the optimization method of traditional MPPT method, is used jointly with traditional MPPT method.Above-mentioned application Single-Stage Grid Connected Solar Inverter System of the present invention comprises: photovoltaic array, filter capacitor, combining inverter, wherein the output of photovoltaic array is directly connected with the two ends of filter capacitor and two inputs of combining inverter, as shown in Figure 1.The method of the described optimization MPPT maximum power point tracking process that is applied to Single-Stage Grid Connected Solar Inverter System is disturbed and causes photovoltaic array power output and combining inverter power output when unequal according to system, photovoltaic array, filter capacitor, the variation of the energy relationship between combining inverter three and filter capacitor voltage, calculate rapidly combining inverter power output given, make the rapid tracking photovoltaic array power output of combining inverter power output, in a power cycle, remove the Energy Coupling relation between filter capacitor and combining inverter and photovoltaic array, avoid the dynamic tracking time of the system crash that causes due to above-mentioned factor or MPPT long.

The method that is applied to the optimization MPPT maximum power point tracking process of Single-Stage Grid Connected Solar Inverter System of the present invention is characterised in that:

1) the method judges the instantaneous relation of combining inverter power output and photovoltaic array power output according to the variation tendency of the voltage of the filter capacitor between photovoltaic array and combining inverter, also: if capacitance voltage declines, combining inverter power output is greater than the output power from photovoltaic cells, if capacitance voltage rises, combining inverter power output is less than photovoltaic array power output, and the moment that capacitance voltage variation tendency changes is exactly the moment that combining inverter power output equals photovoltaic array power output.

2) the method comprises the following steps successively:

Step 1: use microprocessor as controller, Detection capacitance voltage u _c, line voltage v _o, combining inverter output current i _o;

Step 2: deduct the capacitance voltage of a upper control cycle sampling with current capacitance voltage, obtain the difference DELTA u of double sampling;

Step 3: the capacitance voltage difference calculating according to a upper control cycle and the current capacitance voltage difference calculating judge whether the variation tendency of capacitance voltage changes:

Be: the v that record ought sine table be last time counted and sampled _oand i _o,

If: Δ u, by just becoming negative, calculates power output p corresponding to this moment ₁, and record is corresponding to the sinusoidal tabular value sin α of current time ₁;

: calculate power output p corresponding to this moment ₂, and record is corresponding to the sinusoidal tabular value sin α of current time ₂;

No: to continue execution step 4;

Step 4: whether determining program has moved the civil power cycle half:

Be: judgement sin ²α ₁+ sin ²α ₂whether equal 1:

Be: finish;

No: the given p of power output of combining inverter _mbe adjusted into p ₁sin ²α ₁+ p ₂sin ²α ₂, finish;

No: to finish;

The great advantage of the method for the invention is: when the factors such as intensity of illumination change suddenly, cause photovoltaic array power output and combining inverter power output when unequal; can remove rapidly the Energy Coupling effect of filter capacitor; make the rapid tracking photovoltaic array power output of combining inverter power output, avoid the dynamic tracking time of system crash or MPPT long.

Accompanying drawing explanation

Fig. 1 is that single-stage photovoltaic grid-connected electricity generation system forms schematic diagram.

Fig. 2 is combining inverter power output and photovoltaic array power output relationship analysis schematic diagram.

Fig. 3 is the principle analysis schematic diagram of the method for the present invention's optimization MPPT maximum power point tracking process of being applied to Single-Stage Grid Connected Solar Inverter System.

Control program flow chart during method that Fig. 4 is the application optimization MPPT maximum power point tracking process that is applied to Single-Stage Grid Connected Solar Inverter System of the present invention.

Symbol description in accompanying drawing: 10 is single-stage photovoltaic grid-connected electricity generation system; 101 is photovoltaic array; 102 is combining inverter; C _mfor filter capacitor; p _pVfor the power output of photovoltaic array, p _cfor flowing into the power of filter capacitor, p _opower output for combining inverter; u _cfor capacitance voltage; S _iand S _iIrepresent area; T, t ₁, t ₂, t ₃, t ₄represent the time; T _prepresent a power cycle; α ₁and α ₂represent angle; ω represents line voltage angular speed.

Embodiment

Below in conjunction with accompanying drawing explanation the specific embodiment of the present invention.As shown in Figure 1, the single-stage photovoltaic grid-connected electricity generation system of described application maximum power tracking method of the present invention comprises: photovoltaic array, filter capacitor and combining inverter.Wherein the output of photovoltaic array is directly connected with the two ends of filter capacitor and the input of combining inverter.

The method of the invention and traditional MPPT maximum power point tracking (MPPT) method are used jointly, for not restriction of MPPT method used.

As shown in Figure 1, do not consider the power loss of combining inverter, the input power of combining inverter equals power output, by law of conservation of energy, can know the instantaneous power relation between photovoltaic array, filter capacitor, combining inverter three: p _pV=p _c+ p _o, wherein, p _pVfor the power output of photovoltaic array, p _cfor flowing into the power of filter capacitor, p _opower output for combining inverter.

Combining inverter injects sinusoidal current with unity power factor to electrical network, p _othere is following form $p_o={\hat{p}}_o{\sin }^2\mathrm{\ωt},$ ω=100 π wherein, for the peak value of combining inverter power output, the frequency of combining inverter power output is the twice of line voltage frequency.No matter p _pVhave which kind of functional form, a power output, in the cycle, combining inverter output power curve and photovoltaic array output power curve must have and only have two intersection points, suppose p _pVwith p _otime corresponding to intersection point be t ₁, t ₂, t ₃, t ₄..., as shown in Figure 2, can obtain as drawn a conclusion:

1. at interval (t ₁, t ₂), (t ₃, t ₄) ... upper capacitor discharge, filter capacitor magnitude of voltage u _cdullness reduces;

2. at interval (t ₂, t ₃), (t ₄, t ₅) ... upper capacitor charging, filter capacitor magnitude of voltage u _cmonotone increasing;

3.p _pVwith p _ointersection point be constantly the moment that filter capacitor change in voltage trend changes;

4. if p in figure _pVwith p _othe area S that curve surrounds _i=S _iI, showing in a power cycle (100Hz), the net power flow of electric capacity is zero, in one-period,,, in a power cycle, between filter capacitor and photovoltaic array and combining inverter, there is not Energy Coupling in PV power output and inverter power output balance.

During steady operation, electric capacity average power stream in a power cycle is zero, is equivalent to electric capacity the coupling of low frequency power (100 hertz) is eliminated.When system is subject to the disturbance of extraneous factor, while changing suddenly such as intensity of illumination, power output moment of photovoltaic array changes, impact due to filter capacitor, combining inverter power output is the variation of tracking photovoltaic array power output at once, unpredictability due to disturbance, can cause normal MPPT process to be affected, in serious situation, can cause system crash, even if system is not collapsed, from photovoltaic array output characteristic changes constantly, Energy Coupling effect to filter capacitor is eliminated completely, it is the transient process that is equivalent to the step response of a second order link that system is transitioned into the process that combining inverter power output equals photovoltaic array power output, from cybernatic basic principle, easily know, when damping coefficient is less than 1, this process must be vibrated, damping coefficient is greater than 1 and means that transient process increases.In fact said process is the process of the passive releasing filter capacitor of system self Energy Coupling, is referred to as passive decoupling zero process.Method of the present invention is the active decoupling zero process for above-mentioned situation, guarantee combining inverter power output tracking photovoltaic array power output in a power cycle, avoid concussion and transient process, avoid system to collapse simultaneously, guarantee the validity of MPPT, thereby improve greatly dynamic characteristic and the stability of system.

As shown in Figure 3, the combining inverter power output of take equals the initial time that moment of 0 is a power cycle, p in a power cycle _pVwith p _otwo angles corresponding to the moment of answering that occur to intersect are designated as respectively α ₁and α ₂, the power output of the combining inverter in corresponding two moment is respectively p ₁and p ₂, suppose that photovoltaic array power output is smooth direct current.P in figure _pVwith p _otwo areas that curve surrounds are respectively S _iand S _iI, as photovoltaic array power output p _pVchange or power output p _owhile being subject to causing when other factors disturbance changes the mean value of combining inverter power output and the mean value of photovoltaic array power output unequal, be also S _iand S _iIactive decoupling zero process when unequal is obtains new combining inverter power output set-point, and the mean value of combining inverter power output is equated with the mean value of photovoltaic array power output, is also S in Fig. 3 _iand S _iIarea equate.This problem is converted into a mathematical problem, i.e. α in figure ₁, α ₂and p ₁and p ₂known asking make S _i=S _iI.

First, quadrature:

${\∫\hat{p}}_o{\sin }^2\mathrm{\ωtd}\left(\mathrm{\ωt}\right)={\hat{p}}_o\∫\frac{1-\cos 2\mathrm{\ωt}}{2}d\left(\mathrm{\ωt}\right)={\hat{p}}_o\frac{\mathrm{\ωt}-\frac{\sin 2\mathrm{\ωt}}{2}}{2}$

Then, quadrature:

$S_I={\hat{p}}_o(\frac{{\mathrm{\α}}_2}{2}-\frac{\sin 2{\mathrm{\α}}_2}{4})-{\hat{p}}_o(\frac{{\mathrm{\α}}_1}{2}-\frac{\sin 2{\mathrm{\α}}_1}{4})-\frac{{\mathrm{\α}}_2}{2}\·{\hat{p}}_o({\sin }^2{\mathrm{\α}}_2+\mathrm{si}{n}^2{\mathrm{\α}}_1)$

$={\hat{p}}_o\frac{{\mathrm{\α}}_2-{\mathrm{\α}}_1}{2}-{\hat{p}}_o\frac{\sin 2{\mathrm{\α}}_2-\sin 2{\mathrm{\α}}_1}{4}-\frac{{\mathrm{\α}}_2-{\mathrm{\α}}_1}{2}{\hat{p}}_o({\sin }^2{\mathrm{\α}}_2+\mathrm{si}{n}^2{\mathrm{\α}}_1)$

$S_{\mathrm{II}}=\frac{\mathrm{\π}-({\mathrm{\α}}_2-{\mathrm{\α}}_1)}{2}\·{\hat{p}}_o({\sin }^2{\mathrm{\α}}_2+s{\mathrm{in}}^2{\mathrm{\α}}_1)-(\frac{{\mathrm{\α}}_2}{2}+\frac{\sin 2{\mathrm{\α}}_2}{4}+\frac{\mathrm{\π}+{\mathrm{\α}}_1}{2}-\frac{\sin 2{\mathrm{\α}}_1}{4})$

$=\frac{\mathrm{\π}-({\mathrm{\α}}_2-{\mathrm{\α}}_1)}{2}\·{\hat{p}}_o({\sin }^2{\mathrm{\α}}_2+{\sin }^2{\mathrm{\α}}_1)-{\hat{p}}_o(\frac{\mathrm{\π}-({\mathrm{\α}}_2-{\mathrm{\α}}_1)}{2}+\frac{\sin 2{\mathrm{\α}}_2-\sin 2{\mathrm{\α}}_1}{4})$

Make S _i=S _iI:

${\hat{p}}_0\frac{{\mathrm{\α}}_2-{\mathrm{\α}}_1}{2}={\hat{p}}_0\frac{\mathrm{\π}}{2}({\sin }^2{\mathrm{\α}}_2+{\sin }^2{\mathrm{\α}}_1)-{\hat{p}}_0\frac{\mathrm{\π}-({\mathrm{\α}}_2-{\mathrm{\α}}_1)}{2}$

Abbreviation obtains:

sin ²α ₂+sin ²α ₁＝1

Therefore, above-mentioned formula becomes the foundation that judges whether combining inverter power output equates with photovoltaic array power output.If combining inverter power output equates with photovoltaic array power output, the power output of combining inverter is given, and has following relation:

${\mathrm{\α}}_m=\frac{{\mathrm{\α}}_2+{\mathrm{\α}}_1}{2}=\frac{\mathrm{\π}}{2},$ $p_m={\hat{p}}_0\frac{{\sin }^2{\mathrm{\α}}_2+{\sin }^2{\mathrm{\α}}_1}{2}=\frac{{\hat{p}}_0}{2}$

If system is in couple state (nonequilibrium condition), S _i≠ S _iI.According to shifting onto above, we provide a kind of approximation method to reach quick decoupling zero.

Get ${\mathrm{\β}}_m=\frac{{\mathrm{\β}}_1+{\mathrm{\β}}_2}{2},$ By (0, β _m) do perpendicular to L ₁intersect at M:

$p_m=\frac{p_1+p_2}{2}={\hat{p}}_0\frac{{\sin }^2{\mathrm{\β}}_2+{\sin }^2{\mathrm{\β}}_1}{2}$

Order ${\hat{p}}_0^{\′}=2p_m=p_1\·\mathrm{si}{n}^2{\mathrm{\α}}_1+p_2\·{\sin }^2{\mathrm{\α}}_2,$ New output is given ${p_0}^{\′}={{\hat{p}}_0}^{\′}{\sin }^2\mathrm{\ωt}$ Can be similar to and reach capacitive energy decoupling zero.

Therefore, application the method for the invention specifically comprises following steps:

Step 1: use microprocessor as controller, Detection capacitance voltage u _c, line voltage v _o, combining inverter output current i _o;

Step 2: deduct the capacitance voltage of a upper control cycle sampling with current capacitance voltage, obtain the difference DELTA u of double sampling;

Step 3: the capacitance voltage difference calculating according to a upper control cycle and the current capacitance voltage difference calculating judge whether the variation tendency of capacitance voltage changes:

Be: the v that record ought sine table be last time counted and sampled _oand i _o,

If: Δ u, by just becoming negative, calculates power output p corresponding to this moment ₁, and record is corresponding to the sinusoidal tabular value sin α of current time ₁;

: calculate power output p corresponding to this moment ₂, and record is corresponding to the sinusoidal tabular value sin α of current time ₂;

No: to continue execution step 4;

Step 4: whether determining program has moved the civil power cycle half:

Be: judgement sin ²α ₁+ sin ²α ₂whether equal 1:

Be: finish;

No: the given p of power output of combining inverter _mbe adjusted into p ₁sin ²α ₁+ p ₂sin ²α ₂, finish;

No: to finish;

Accompanying drawing 4 has provided the program flow diagram of the method for the optimization MPPT maximum power point tracking process that is applied to Single-Stage Grid Connected Solar Inverter System of the present invention.

Claims (2)

1. a method that is applied to the optimization MPPT maximum power point tracking process of Single-Stage Grid Connected Solar Inverter System, it is characterized in that, the method is utilized photovoltaic array, coupled relation between filter capacitor and combining inverter three, if that is: capacitance voltage declines, combining inverter power output is greater than the output power from photovoltaic cells, if capacitance voltage rises, combining inverter power output is less than photovoltaic array power output, the moment that capacitance voltage variation tendency changes is the moment that combining inverter power output equals photovoltaic array power output, only according to the variation of filter capacitor voltage, accurately provide the given p of power output of the next power cycle of combining inverter _m, in a power cycle, remove the Energy Coupling relation between filter capacitor and combining inverter and photovoltaic module, optimize the dynamic process of MPPT.

2. a kind of method that is applied to the optimization MPPT maximum power point tracking process of Single-Stage Grid Connected Solar Inverter System as claimed in claim 1, is characterized in that the method comprises the following steps successively:

Step 1: use microprocessor as controller, Detection capacitance voltage u _c, line voltage u ₀, combining inverter output current i ₀;

Step 2: deduct the capacitance voltage of a upper control cycle sampling with current capacitance voltage, obtain the difference DELTA u of double sampling;

Step 3: the capacitance voltage difference calculating according to a upper control cycle and the current capacitance voltage difference calculating judge whether the variation tendency of capacitance voltage changes:

Be: if Δ u is by just becoming negative, record the power output p that current time is corresponding ₁sinusoidal tabular value sin α with current time ₁, execution step 4; If Δ u does not change, record the power output p that current time is corresponding ₂sinusoidal tabular value sin α with current time ₂, execution step 4;

Step 4: whether determining program has moved the civil power cycle half;

Be: execution step 5;

No: to finish;

Step 5: judgement sin ²α ₁+ sin ²α ₂whether equal 1;

Be: finish;

No: the given p of power output of combining inverter _mbe adjusted into p ₁sin ²α ₁+ p ₂sin ²α ₂, finish.