Fangming Zhu

Bio: Fangming Zhu is an academic researcher from Hangzhou Normal University. The author has contributed to research in topics: Time-domain reflectometer & Maximum power principle. The author has an hindex of 1, co-authored 2 publications receiving 16 citations.

An Improved Particle Swarm Optimization Algorithm Suitable for Photovoltaic Power Tracking Under Partial Shading Conditions

Abstract: The partial shading of a photovoltaic array repeatedly occurs in the natural environment, which can cause a failure of a conventional maximum power point tracking (MPPT) algorithm. In this paper, the convergence conditions of the standard particle swarm optimization (PSO) algorithm are deduced by the functional analysis, and then the influence of the random variables and inertia factor of the algorithm on the trajectory in the particle swarm optimization is analyzed. Based on the analysis results, an improved particle swarm optimization (IPSO) algorithm, which adopts both global and local modes to locate the maximum power point, is proposed. Compared to the standard PSO algorithm, in the improved PSO algorithm, many random and interfered variables are removed, and the structure is optimized significantly. The proposed algorithm is first simulated in MATLAB to ensure its capability. The feasibility of the approach is validated through physical implementation and experimentation. Results demonstrate that the proposed algorithm has the capability to track the global maximum power point within 3.3 s with an accuracy of 99%. Compared with five recently developed Global MPPT algorithms, the proposed IPSO algorithm achieved better performance in the maximum power tracking in the partial shading conditions.

Circuit Model of Parallel Corrugated Transmission Lines for Differential Signal Propagating in Microwave Band

Abstract: A viable wide-band circuit model of parallel corrugated differential transmission line is established. By solving for the even- and odd-modes in this structured differential transmission line, the equivalent capacitance, inductance, resistance, and conductance per unit length are calculated, then the characteristic impedances of differential and common signals are obtained. The ${S}$ -parameters obtained from the equivalent circuit model agree well with the full-wave simulation results with a deviation of only about 0.036 dB in the frequency range of 10 GHz. Experimentally, the characteristic impedances are measured for the differential and common signals using a time domain reflectometer (TDR). The deviation between the experimental and theoretical results was less than 1.05%. Based on the equivalent circuit model, it is feasible to implement this type of structured differential line directly into real circuits.

A Novel Bat Algorithm Strategy for Maximum Power Point Tracker of Photovoltaic Energy Systems Under Dynamic Partial Shading

Abstract: Power versus voltage curves of partial shading photovoltaic (PV) systems contain several local peaks (LPs) and one global peak (GP). Most conventional maximum power point tracker (MPPT) techniques may not follow the GP under partial shading conditions (PSC). The use of metaheuristic techniques such as the bat algorithm (BA) and particle swarm optimization (PSO) can overcome these obstacles. All problems inherent in the using of BA as MPPT of PV systems has been discussed and solved in this paper. The first problem is the random initial values of bats that may cause premature convergence. Therefore, the initial values of bats were modified to be close to the anticipated positions of peaks to reduce the convergence time and improve the chance of capturing the GP. The second problem occurs when shading pattern changes the value and position of the GP which is not configurable because all bats are concentrated at the previous GP; this can be resolved by BA re-initialization. The the third problem is the GP memorized in the execution of the BA code forces the PV system to work at the duty ratio of the highest GP ever seen, which may not be the real GP. This problem is solved by updating the memorized GP. This paper also proposes a new criterion for selecting the optimal swarm size against number of peaks to reduce the convergence time and improve the chance of capturing the GP. To the authors' knowledge, most of these problems inherent in the BA have hitherto not been addressed in the literature. The simulation and experimental results obtained from the proposed modified BA (MBA) with re-initialization have been compared to the PSO and grey wolf optimization (GWO) techniques which show the superiority of using MBA strategy in the MPPT of partial shading PV systems.

Identification of Partial Shading Conditions for Photovoltaic Strings

Abstract: Under partial shading conditions (PSC), the power-voltage (P-V) characteristic curve of photovoltaic (PV) strings exhibits multiple peaks. Such mismatching phenomenon brings challenges in controlling the output power. To analyze the electrical characteristics of PV strings in complex environments, a quantitative analysis method is required to characterize the PSC. This paper introduces the shading matrix to describe the shading rate and shading strength information. The proposed shading matrix would provide maximum power point tracking (MPPT) controllers with the essential environmental information to improve the global maximum power point (GMPP) tracking performance. A modified Tabu search (MTS) based identification method is proposed to estimate the shading matrix. The proposed modified method involves a preselection process of updating the Tabu list to optimize the searching efficiency. The accuracy and efficiency of the proposed analytical estimation expression are validated through simulations and experiments. By comparing with binary search (BS), golden-section search (GS) and Tabu search (TS) algorithms, the proposed MTS algorithm is demonstrated to perceive the shading information at least 18.75% faster.

A Modified INC Method for PV String Under Uniform Irradiance and Partially Shaded Conditions

Abstract: Due to the bypass diodes, the partially shaded photovoltaic (PV) string exhibits multiple peaks in the P-V curve. And the conventional Maximum Power Point Tracking (MPPT) methods are not capable of tracking the global peak (GP) under partially shaded condition (PSC). In order to track the GP fast and efficiently under uniform irradiance condition (UIC) and PSC, a modified incremental conductance (INC) method is proposed in this paper. This method can not only detect the occurrence of PSC, but also determine if the other peaks need to be tracked under PSC by using the relationship between the minimum current at other peaks and the short circuit current to enhance the tracking speed. In order to improve efficiency, the converter duty cycle will be regulated slightly to ensure that the operating point reaches in the vicinity of GP, after the approximate GP is located. The Matlab simulation results show that the proposed method is faster and more efficient than other methods. It only requires 3 and 11 sampling cycles to locate the GP under UIC and PSC, respectively. Its overall tracking efficiency is increased by 13.61%, 4.28% and 0.42% under UIC, PSC and one-day irradiance profile respectively, compared to the conventional INC method.