<p class="Abstract">This paper introduces a new method, called IB-SMC method, to control DC/DC boost converters in systems exploiting photovoltaic power generation. This method combines the sliding mode control technique and iterative-bisectional technique in the maximum power point tracker to change operations modes of photovoltaic power generation. The IB-SMC controller uses voltage sliding surface to evaluate the relation of instantaneous voltage at the input converter and instantaneous voltage at the maximum power point. Using information about the power of electromagnetic radiation from a pyranometer and temperature from a temperature sensor, the sliding surface and hyteresis band are changed by practically operational conditions that help improving energy efficiency of the process exploiting PVg. Simulations are carried out by Matlab/Simulink that show the ability to ensure dynamic stability by tracking instaneous maximum power point at any time whenever having any change of the operational condition, static stability by maintaining the operation point at maximum power point whenever not have any change of the operational condition and help to bring out approximately absolute energy efficiency.</p>
Abstract:A grid-connetected control system is proposed in this paper to regulate three-phase bidirectional DC/AC converters in distribution grid exploiting photovoltaic power generation and not having energy storage at the DC side. To interact power flow at two its sides, statbilize voltage at the DCbus and synchronize with the grid, it includes an inner current controller and an outer voltage controller in a cascaded structure. Using small signal modeling and information about voltage at the point of common coupling and DCbus, control parameters for controllers are determined to balance power between photovoltaic system side and grid side. Simulation results show that the grid-connected control system helps the three-phase bidirectional DC/AC converter meet all requirements very well due to the balance of power at its sides to hold voltage at DC side at a fixed value, grid synchronization and low harmonic distortion total for current and voltage waveforms. They also represents the capability to exploit maximum available power of photovoltaic power generation under any operational condition.
This paper focuses on the effect of transformer parameters and a line reactor on distribution of power flows in a high-voltage substation and transmission lines. Four case studies that have different values of transformer parameters including rated power, short-circuit impedance and reactance/resistance ratio are supposed in this research. Basing on power flows on transformers in case of the parallel operation, load factor of each transformer and operating parameters are considered in above case studies. Moreover, a line reactor is proposed in this paper to regulate power flows in a system having two power sources. Four operating modes of the proposed line reactor are defined by changing on/off states of switches in this device to modify the value of impedance. The effect of the line reactor on power received from sources and power flows on transmission lines is evaluated in its all modes. Research results are carried out by the ETAP 16.0 software and present high accuracy and reliability for the proposed problems. Research contributions help dispatchers understand the essence of power transmission process, solve real problems and give out effective solutions to operate high-voltage systems.
This paper proposes a new method to determine optimal energy storage sizing in photovoltaic and wind hybrid power generation systems. These generations are placed in a scheme of three blocks to forecast, measure, and dispatch/control and distribute power flows in whole system to meet requirements of the demandside management program in Viet Nam. Data about electric load power, power of solar irradiance, ambient temperature, wind speed and other weather conditions must be forecasted in a high accuracy. An algorithm to determine the optimal sizing is designed basing on forecasting data, constraints, the relation of quantities in whole system and the capability to charge/discharge energy of energy storage. The optimal sizing in this research helps to rearrange load diagrams that compensate deficient energy completely in stages having high and medium price levels. It can be applied at each bus to reduce cost for buying electricity from electric power system. The new proposal is illustrated by simulation results in a case study carried out by MATLAB 2017a.
-This paper introduces a method to determine optimal sizing and location of shunt capacitors in medium voltage Underground Power Cables or in distribution system. To execute this method, two models of standard branch and the Newton-Raphson method are also mentioned to analyze and determine values of bus voltage and currents going through lines in whole system. The EN 50160 standard is introduced to evaluate all operational parameters and propose solutions to reduce risks. In additionally, the cost function method is introduced basing on cost of purchasing compensative device, power loss in own compensators and whole system after compensating. By considering partial derivative of cost function with respect to variables, optimal sizing and location of shunt capacitors can be determined for all buses in the system. Analyzing the system by using the Newton-Raphson method in stable mode, all operational parameters are evaluated to see the benefit of placing capacitors in some criterions: reduce the current going through all lines and increase value of bus voltage in whole system. Theory research is verified by simulation results carried out in Matlab 2016 software.
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