An Improved Perturb and Observe Algorithm for Photovoltaic Motion Carriers

An improved perturbation and observation algorithm for photovoltaic motion carriers is proposed in this paper. The model of the proposed algorithm is given by using Lambert W function and tangent error method. Moreover, by using matlab and experiment of photovoltaic system, the tracking performance of the proposed algorithm is tested. And the results demonstrate that the improved algorithm has fast tracking speed and high efficiency. Furthermore, the energy conversion efficiency by the improved method has increased by nearly 8.2%.


Introduction
Photovoltaic (PV) generation system is one of the important renewable energy, which has been widely used in motion carriers such as UAV, bike sharing and internet of things [1]. However, the maximum power point of PV module changes with different solar irradiance and temperature [2]. Therefore, it is necessary to use the maximum power point tracking (MPPT) technique in PV system to to obatin high power.
During the past decade, the method of maximum power point tracking technique has developed in a variety of directions, and the typical algorithms are as follows: fraction open circuit voltage/short circuit current [3], incremental conductance (IC) [4], artificial neural network (ANN) [5], perturb and observe (P&O) [6], particle swarm optimization (PSO) [7], genetic algorithm (GA) [8], teaching-learning based optimization(TLBO) [9], fuzzy logic controller (FLC) [10] and sliding-mode controller [11]. Moreover, in low cost practical PV system, perturb and observe is the most used in all these algorithms. Howerer, conventional perturb and observe algorithm has two obvious drawbacks in the case of moving carriers. One is near the maximum power point of PV module, the operating point of PV system is forced to go back and forth around maximum power point [12], results in loss power. The other is that perturb and observe is easy to lose the direction, when the environment is varying [13]. Therefore, the traditional perturb and observe is not is not suitable for photovoltaic motion carriers.
To obtain high power of PV system, an improved perturbation and observation algorithm is proposed in this paper. The output characteristics of the proposed method are test in simulation and experiment. Moreover, it is found that the energy conversion efficiency of the proposed algorithm has increased by approximately 8.2%.

The proposed P&O Algorithm
According to the characteristics analysis of the conventional perturbation and observation algorithm [14], it is found that three parameters and sig play a key role in perturbation and observation algorithm, which is depicted in Eq.(1).
And the estimation of initial voltage can be given by: The step size pv V ∆ can be calculated by using tangent error method, as shown in Eq. (5), Eq. (6) and under different irradiance levels. By using Lambert W function [15], the disturbance power P ∆ can be given by: Where Z 1 =V mp −U. According to the Eq. (7), it can be seen that when pv V converges to the maximum power point, . In summary, the proposed algorithm for photovoltaic motion carriers is illustrated in Fig.3, in which the black boxes are added parts with respect to the traditional perturb and observe algorithm.

Results and Discussion
In this section, simulation and experimental results of the proposed MPPT algorithm are provided to validate the tracking performance in a common platform [16]. Fig.4 shows the simulation diagram of 1234567890''""

SAMSE
IOP Publishing IOP Conf. Series: Materials Science and Engineering 322 (2018) 072028 doi:10.1088/1757-899X/322/7/072028 photovoltaic motion carrier system. And the specifications for the PV system are listed in Table1.Moreover, the simulation results with different methods of the PV system are depicted in Fig.5. Besides, experimental results of PV system under varying environment is given in Fig.6 and Table 2.
With the Fig.5, it is easy to see that the proposed perturb and observe algorithm is closest to the theoretical values, which has perfect tracking effect. Compared with the traditional algorithm, it also can be concluded that the proposed method not only has low oscillating power at the stable condition, but also never loses its tracking direction under the fast and slow changing irradiance levels.   Simulation results of PV system with different methods. Fig.6 shows the experimental results obtained from prototype PV system under varying environment. with traditional perturb and observe and proposed method. It is easy to find that the proposed MPPT algorithm not only has higher efficiency but also has faster speed. Moreover, Table 2

Conclusions
This paper proposes an improved perturbation and observation algorithm for photovoltaic motion carriers. By using tangent error method and Lambert W function, a novel technique is proposed to improve the tracking speed and efficiency. Moeover, the tracking performance of the proposed method is evaluated by using simulation and experiment. Comparing with conventional perturb and observe, the proposed method has the best tracking performance, which can be used for motion carriers.