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 Novel MPPT Control Method Based on Boost Converter

technical field

The invention relates to a maximum power point tracking method based on a Boost converter, which belongs to the technical field of new energy sources, in particular to the technical field of solar power generation.

Background technique

Photovoltaic power generation system consists of photovoltaic cells, photovoltaic chargers, batteries and other parts. From the analysis of the output characteristics of photovoltaic cells, it can be known that the output of photovoltaic cells is a nonlinear DC power supply, and its I-V curve is nonlinear and will change with the external natural conditions (temperature, light intensity). When the working voltage of the photovoltaic cell changes, its output power will also change. To improve the energy conversion efficiency of the photovoltaic power generation system, it is necessary to master the characteristics of this nonlinear power supply. When the temperature and light intensity are constant, there is a maximum power output point of the photovoltaic cell. Find the maximum power point of the photovoltaic cell and maximize the output. power, it is necessary to use the maximum power point tracking (MPPT) technology.

At present, the most researched and applied maximum power point tracking algorithms include Perturb&Observe (P&O) and Incremental Conductance (INC). These two methods have their own shortcomings: the disturbance will not stop after the maximum power point is reached by the disturbance observation method, so there is oscillation phenomenon, and the tracking step size cannot take into account both speed and accuracy, and misjudgment may occur when the illumination changes; There is a contradiction between speed and precision in the incremental method, and the algorithm has higher requirements on the sampling hardware circuit. Both of these methods require a current sampling circuit, which increases the cost of the system and the complexity of the algorithm.

Due to the boost and load regulation functions of Boost converters, they are suitable for maximum power tracking in photovoltaic power generation systems, so Boost converters are widely used in photovoltaic power generation systems. Aiming at the relationship between the voltage gain and the duty cycle of the Boost converter, the present invention proposes a new maximum power tracking algorithm, which only needs to sample the input voltage of the Boost converter, eliminating the need for a current sampling circuit and sampling The circuit is simple, and the tracking speed is fast and the stability is high.

Contents of the invention

On the basis of the traditional maximum power point tracking algorithm, the present invention proposes a novel MPPT control method based on the Boost converter in combination with the relationship between the voltage gain and the duty cycle of the Boost converter. The input voltage of the device is sampled, the current sampling circuit is omitted, and the sampling circuit is simple. The method has the advantages of fast tracking speed, high stability, strong reliability and good economy.

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

Step 1: Calculate the difference Δv _p of the input voltage of the boost converter twice before and after sampling, and at the same time obtain the duty cycle of the converter at the two sampling moments from the DSP to calculate the duty cycle difference ΔD.

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

Step 3: Determine the changing direction of the duty cycle according to the value of Q. When Q>0, the duty cycle increases by Δd; when Q<0, the duty cycle decreases by Δd.

Description of drawings

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

Figure 2 is a photovoltaic cell output characteristic curve.

Fig. 3 is a system control structure diagram of the currentless sensor according to the present invention.

In Figure 1, v _p (k) and D(k) are the input voltage and duty cycle of the Boost converter at the current sampling time respectively, and v _p (k-1) and D(k-1) are the previous sampling time The input voltage and duty cycle of the Boost converter, D(k+1) is the updated duty cycle; P _pv and V _pv in Figure 2 are the output power and output voltage of the photovoltaic cell, respectively, and MPP is the maximum power point , P _m , V _m are the output power and output voltage of the photovoltaic cell at the maximum power point, respectively. In Fig. 3, PV is a photovoltaic cell, and v _p is the input of a Boost converter.

Detailed ways

Output power of Boost converter:

P _o is the output power of the Boost converter, V _o is the output voltage of the Boost converter, and R is the load on the output side. when the system reaches its maximum power point. According to Fig. 2, it can be seen that dP _pv /dV _pv =0, and it can be deduced that dP _o /dV _o =0 at the output side of the converter. That is, the rate of change of output power tends to zero at the maximum power point (MPP). Transform the formula dP _o /dV _o =0, and multiply both sides by (dV _o /dt) to get formula (2).

Combining formula (1) and formula (2), we can get

Since both R and V _o are not equal to 0 at the maximum power point, formula (3) can be simplified as

The voltage gain of an ordinary Boost converter is:

The voltage gain of the high-gain interleaved parallel Boost converter is:

Substituting formula (5) and formula (6) into formula (4) respectively, we can get:

From formula (7) and formula (8) can get:

Equation (9) is the judgment basis based on the maximum power point tracking of Boost converters. When the photovoltaic cell is working at the maximum power point output, the input voltage and duty cycle of the Boost converter satisfy the mathematical relationship of formula (9). When the photovoltaic cell is operating at the left side of the maximum power point, Q>0, it is necessary to increase the duty cycle To track the maximum power point; when the photovoltaic cell works on the right side of the maximum power point, Q<0, it is necessary to reduce the duty cycle to track the 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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