CN103218006A - Novel maximum power point tracking (MPPT) control method based on Boost-type convertor - Google Patents

Abstract

The invention provides a novel maximum power point tracking (MPPT) control method based on a Boost-type convertor. According to the novel MPPT control method, the relationship between voltage gains of the Boost-type convertor and the duty ratio is used for deducing the relationship between the input voltage, at the maximum power point, of the Boost-type convertor and the duty ratio, and the maximum power point output by a photovoltaic cell is tracked on the basis of the relationship between the input voltage, at the maximum power point, of the Boost-type convertor and the duty ratio. Compared with a traditional MPPT method, a current sampling circuit is eliminated in the novel MPPT control method, tracking is faster and more stable, and therefore photovoltaic power generation efficiency can be effectively improved, and complexity and cost of a system can also be lowered.

Description

A kind of novel MPPT control method based on the Boost quasi-converter

Technical field

The present invention relates to a kind of maximum power point tracing method, belong to technical field of new energies, particularly the solar energy generation technology field based on the Boost quasi-converter.

Background technology

Photovoltaic generating system partly is made up of photovoltaic cell, photovoltaic charger, accumulator etc.By the photovoltaic cell Output Characteristic as can be known, the output of photovoltaic cell is a kind of nonlinear direct supply, and its I-V curve is non-linear, and can change along with the variation of extraneous natural conditions (temperature, intensity of illumination).When the operating voltage of photovoltaic cell changed, its output power also can change.If will improve the energy conversion efficiency of photovoltaic generating system, just must grasp the characteristic of this non-linear power, under the certain situation of temperature and intensity of illumination, there is maximum power point (mpp) in photovoltaic cell, seek the maximum power point of photovoltaic cell, output power just must adopt MPPT maximum power point tracking (MPPT) technology to greatest extent.

Study at present and use more MPPT maximum power point tracking algorithm thanks for your hospitality moving observation method (Perturb﹠Observe, P﹠O) and the conductance increment method (Incremental Conductance, INC).All there is the shortcoming of oneself in these two kinds of methods: disturbance can not stop after adopting the disturbance observation method to reach the maximum power point place, therefore has oscillatory occurences, and tracing step can not be taken into account speed and precision simultaneously, and it is disconnected that erroneous judgement may take place when illumination changes; There is the contradiction of speed and precision in the conductance increment method, and algorithm is had relatively high expectations to the sampling hardware circuit.These two kinds of methods all need current sampling circuit, have increased the complexity of the cost and the algorithm of system.

Because boosting and the load regulation effect of Boost quasi-converter is adapted at carrying out in the photovoltaic generating system maximal power tracing, therefore the Boost quasi-converter is used widely in photovoltaic generating system.At the voltage gain of Boost quasi-converter and the relation of dutycycle, the present invention proposes a kind of new maximal power tracing algorithm, this method only need be sampled to Boost quasi-converter input voltage, saved current sampling circuit, sample circuit is simple, and tracking velocity is fast, stability is high.

Summary of the invention

The present invention is on the basis of traditional MPPT maximum power point tracking algorithm, relation in conjunction with Boost quasi-converter voltage gain and dutycycle, a kind of novel MPPT control method based on the Boost quasi-converter is proposed, this method only need be sampled to Boost quasi-converter input voltage, saved current sampling circuit, sample circuit is simple.Fast, the stable height of this method tracking velocity, good reliability, good economy performance.

The novel MPPT control method that the present invention proposes based on the Boost quasi-converter, the controlled step feature of this technical method is as follows:

Step 1: twice Boost quasi-converter input terminal voltage calculates its difference DELTA v before and after the sampling _p, obtain double sampling transducer dutycycle constantly from DSP simultaneously and calculate its duty ratio Δ D.

Step 2: calculate $Q=\frac{\mathrm{\Δ}{v}_p}{\mathrm{\ΔD}}+\frac{v_p\left(k\right)}{1-D\left(k\right)}$ Value.

Step 3: determine the change direction of dutycycle according to the value of Q, when Q＞0, dutycycle increases Δ d; When Q＜0, dutycycle reduces Δ d.

Description of drawings

Fig. 1 is an algorithm flow chart of the present invention.

Fig. 2 is the photovoltaic cell output characteristic curve.

Fig. 3 is the control structure figure of system of no current sensor of the present invention.

V among Fig. 1 _p(k), D (k) is respectively input voltage, the dutycycle of current sampling instant Boost quasi-converter, v _p(k-1), D (k-1) is respectively input voltage, the dutycycle of previous sampling instant Boost quasi-converter, D (k+1) is the dutycycle after upgrading; P among Fig. 2 _Pv, V _PvBe respectively the output power and the output voltage of photovoltaic cell, MPP is a maximum power point, P _m, V _mBe respectively the output power and the output voltage of maximum power point place photovoltaic cell.PV is a photovoltaic cell among Fig. 3, v _pIt is the input of Boost quasi-converter.

Embodiment

The output power of Boost quasi-converter:

P _oBe the output power of Boost quasi-converter, V _oBe the output voltage of Boost quasi-converter, R is the outgoing side load.When system reaches maximum power point.According to Fig. 2 dP as can be known _Pv/ dV _Pv=0, can derive at the transducer outgoing side also has dP _o/ dV _o=0.Promptly the rate of change of locating output power at maximum power point (MPP) is tending towards 0.To formula dP _o/ dV _o=0 carries out conversion, and both sides are with multiply by (dV _o/ dt), just can obtain formula (2).

Formula (1) and formula (2) are carried out simultaneous, can solve

Because at maximum power point R and V _oAll be not equal to 0, so formula (3) just can abbreviation be

The voltage gain of common Boost transducer is:

The voltage gain of high-gain crisscross parallel Boost transducer is:

Formula (5) and formula (6) difference substitution formula (4) can be got:

Can get by formula (7) and formula (8):

Formula (9) just is based on the basis for estimation of Boost quasi-converter MPPT maximum power point tracking.When the photovoltaic cell duty was in maximum power point output, Boost quasi-converter input voltage and dutycycle satisfied the mathematical relation of formula (9), and Q＞0 when photovoltaic cell is operated in the maximum power point left side needs to increase duty and recently follows the tracks of maximum power point; Q when photovoltaic cell is operated in the maximum power point right side＜0 need reduce duty and recently follow the tracks of maximum power point.

Claims (1)

1. novel MPPT control method based on the Boost quasi-converter, it is characterized in that utilizing the relation derivation of Boost quasi-converter voltage gain and dutycycle to go out the relation of maximum power point Boost quasi-converter input voltage and dutycycle, this algorithm only need be to the output voltage v of photovoltaic cell _pSample, calculate v then _pIncrement Delta v _pWith the increment Delta D of dutycycle, calculate then Value, if Q＞0, dutycycle increases Δ d, if Q＜0 o'clock, dutycycle reduces Δ d, so circulation is carried out, and reaches the purpose of following the tracks of maximum power point.

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