| Micro hydropower is a kind of clean and renewable energy that generates electricity through taking advantage of the micro water resources in the vicinity of power load,operating off-grid and supplying directly for users which has provided electricity for people especially for those who far away from the power grid and has promoted the development of rural agriculture and reduction of disaster losses while protecting the ecological environment.The development of micro hydropower is taken as one of the key development projects of "Thirteen Five-Year Plan" and the "energy development plan" and an important way to solve the contradiction between the rural environment and resources.However the system is of poor stability and power quality owing to the characteristic of micro hydropower operating stand-alone and directly supplying customers.Since the AC excited generator(ACEG)using rotor excitation control technology which has a oobvious advantage over load changing and variable speed constant frequency(VSCF)power generation system,therefore this paper uses ACEG and makes off-grid micro hydropower for the studied,according to the issues of poor quality and poor stability and so on,making research on the excitation control of ACEG of off-grid micro hydropower,then the control strategy and control schemes for the ACEG of stand-alone micro hydropower are presented.Firstly,this paper describes the development situation and trends of the micro hydropower system in turbine,generator and excitation and other sectors at home and abroad.According to the problem that the low utilization in the low head and small water of the micro turbine,the model of the variable volume and offset distance type of micro hydropower based on the energy conservation principle is proposed,and then the structure and working principle of micro-turbine are described.At the basis of the analysis of AC excited generation system for off-grid micro hydropower structure and operation principle,according to the issues for which the difficult in voltage regulator or low voltage rate by using conventional generator in stand alone micro hydropower,AC excited generator and the dual PWM excitation converter are used,morever at the hand of coordinate transformation,its mathematical model are derived in detail.Establish the equivalent circuit and give the power transmission characteristics of the different modes of ACEG.Based on topology of the dual PWM excitation converter,according to problem of off-grid micro hydro output voltage and frequency which caused by balance load mutation,worthwhile a control scheme of the stand-alone microhydropower system is proposed under the balanced load condition which contains the vector control strategies for the rotor-side converter(RSC)and the stator side converter(SSC).Simulation and experimental results verify the effectiveness of the proposed control scheme.According to the fact that the vector control technology using conventional encoder speed sensor for off-grid micro hydro excitation control system brings the system cost and power quality problems,based on the current hysteresis control and direct voltage control(DVC)technique,a control scheme to suppress the load disturbance and speed changes which includes an excitation control strategy of the stator rotor side converter(RSC)by tracking RMS voltage to control the rotor current controlling the output voltage and a vector control strategy for the stator side converter(SSC)which using establish dual closed loop containing load current inner loop and intermediate DC voltage outer is proposed.Simulation and experimental results verify the effectiveness of the proposed control scheme.To realize the AC excitation control system for the off grid micro hydropower,using the chip DSP-TMSF2812 as the system controller,through dual PWM excitation converter,the off-grid micro hydropower ACEG excitation control system hardware is designed,and then the specific process of RSC and the SSC control implementation are given. |
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