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The purpose of this paper is to compare three power-feedback maximum power point tracking (MPPT) algorithms used in photovoltaic systems. The Matlab/Simulink is used in this paper to establish a model of photovoltaic system with MPPT function. This system is developed by combining the models of established PV module and DC-DC boost converter with the power-feedback MPPT algorithms of perturbation and observation, incremental conductance and hill climbing, respectively. The system will be simulated under different weather conditions and MPPT algorithms. According to the comparisons of the simulation results, it can be observed that the photovoltaic simulation system can track the maximum power accurately using the three MPPT algorithms discussed in this paper. HC algorithm possesses fast dynamic response, but P&O algorithm is well regulated PV output voltage and power than HC algorithm. The tracking time spent by INC algorithm is a little longer than the other two algorithms. The HC algorithm is suitable for the cases of battery charging which doesn't need extremely stable voltage, and the P&O algorithm is more suitable for the system with precision electric instruments. Furthermore, the INC algorithm is adaptable to the cases of fast changing weather conditions owing to its advantage of no misjudgment.

Due to the structure of underground cables, the frequency dependence of shunt admittances is more important to underground cables than to overhead lines. The main purpose of this paper is to establish a frequency-dependent underground cable model for advanced research and analysis regarding the influences of frequency-dependent shunt admittances on underground cable systems. The model will be more practical by adding the frequency dependence of shunt admittances into mathematical models and transferring them to the corresponding programming codes. In the cable Electromagnetic Transient Program (EMTP) models, the frequency dependence of shunt admittances could be represented by a set of equivalent circuits with constant parameters that can be determined by observing the characteristics of shunt admittances, then synthesizing them with a rational function approximation for discrete-time EMTP solutions. A number of simulation cases are presented in this paper to show that the frequency dependence of shunt admittances for underground cable systems leads to magnitude attenuation and strong traveling time reduction in a transient period of voltages. Also, the influences of frequency-dependent capacitances on cable systems are comparatively more impressive than those of frequency-dependent conductances. The conclusions are supported by numerical simulation results.

A major difficulty in multiphase cable modeling with traditional electromagnetic transient program like the EMTP is the synthesis of the frequency-dependent transformation matrix which relates modal and phase domain variables. This paper presents a new model (zCable) to represent the frequency-dependence of cable parameters directly in phase coordinates thus avoiding the problems related to frequency-dependent transformation matrices. The cable model is split into two parts: a constant ideal line section and a frequency-dependent loss section. A pi-correction is proposed to solve the problem of different traveling times in the ideal line section. The main advantage of the proposed model as compared to existing frequency-dependent transformation matrix models is the model's absolute numerical stability for strongly asymmetrical cable configurations and for arbitrary fault conditions. In addition, the model parameters are easy to obtain with robust algorithms and the model can be efficiently implemented in the context of a real-time PC-cluster simulator.