【文章內(nèi)容簡(jiǎn)介】 eneration. This design enables to reach high efficiency over a wide range of water flows but using a plex operating mechanism, which is in consequence expensive and tends to be more affordable for largescale systems.This paper proposes an advanced structure of a MHPP based on a smaller, lighter, more robust and more efficient higherspeed turbine. The suggested design is much simpler and eliminates all mechanical adjustments through a novel electronic power conditioning system (PCS) to connect to the electric distribution grid, as depicted in Fig. 1. In this way, this topology allows obtaining higher reliability and lower cost of the power plant. A full detailed model of the MHPP is derived and a new threelevel control scheme is designed. The control consists of a multilevel hierarchical structure and incorporates a maximum power point tracker (MPPT) for better use of the hydro resource, in addition to reactive power pensation capabilities. The dynamic performance of the propose control schemes is validated through digital simulations in MATLAB/Simulink. Moreover, a 350 W MHPP experimental setup build at the Institute of Power Electronics and Electrical Drives of the University of Siegen (Germany) was implemented to demonstrate the accuracy of proposed models.2. Modeling of the proposed microhydro power plant The proposed hydropower station is a runofriver plant which consequently does not have any significant water reservoir such as large dams. Only a fraction of the available stream flow at a given time is used, this leading to a good agreement with the environment and permitting the utilization of low head water sources as DG. In order to allow extended control features when they are integrated into the electric power grid and also to provide the enough flexibility to adapt to the specific conditions of rivers with low water flow rate, a variablespeed turbine is proposed to be used in this work. Thus, by optimizing the turbine working point in order to extract the maximum power of the water flowing per second, superior efficiencies respect to traditional hydro turbines can be obtained. Moreover, by replacing mechanical controls with advance technologies in power electronic devices, higher reliability stations with better efficiencies can be reached. The modeling approach of the proposed microhydro power plant is based on the structure of Fig. 1. The MHPS consists of a variable speed microhydro turbine directly coupled to a permanent magnet synchronous generator (PMSG) and connected to the electric grid through anadvanced power conditioning system (PCS). The proposed PCS is posed of a threephase rectifier bridge, a DC/DC converter and a DC/AC power inverter.Fig. 1–Layout of the implemented MHPP. . Hydraulic turbine characteristics The proposed hydro power is a basic reaction turbomachine well suited for low water heads and low water flow rates. This hydraulic turbine is a propeller type, modified from a Kaplan turbine with neither blade pitch control nor upstream guide vane one. In addition, the turbine does not implement a gear box for coupling to the generator which yields a simple and robust design. Fig. 2 shows a puteraided design (CAD) of the implemented propeller hydraulic turbine. The turbine is a vertical axis machine with a spiral case and a radial guide vane configuration.Fig. 2 – CAD of the proposed propeller hydraulic turbine.The hydraulic turbine characterized in the laboratory is a 350 W rated power one designed for an average m head and a water flow rate of 35 L/s , which is shown in the photograph of Fig. 1 (right side). The hydraulic turbine model is obtained from its steadystate characteristics, assuming water to be inpressible. The output hydraulic power available from the hydraulic turbine is given as [4]: = beingthe specific density of water (1000 kg/m3at approximately 4 C), the acceleration due to gravity ( ), H the water net head (m) and Q the water flow rate or discharge (). The potential energy in water is converted into mechanical energy in the turbine as a result of the water pressure which applies a force on the runner blades and then decreases as it passes through the reaction turbine. The relation between the mechanical and the hydraulic powers can be obtained by using the hydraulic turbine efficiency , as expressed in Eq. (2). Since the proposed hydraulic turbine operates over near all the range of rotor speeds, the assumption of linear torque versus speed characteristic (at given operating conditions) cannot be used, as usually considered in the literature. As a result, the mechanical power characteristic could not be considered simply a parabola (as typically) [4,5]. Indeed, the hydraulic turbine efficiency that yieldsis highly dependent of the turbine design and operating conditions (Q, H, and the angular speed of the turbine rotor u), and thus is very plex to be analytically determined. Consequently, numerical approximations have been developed in this work to calculate the mechanical power characteristic of the implemented hydraulic turbine and an expression of as a function of Q and u has been proposed and validated in the laboratory. being R the radius of the hydraulic turbine blades (m) and A the area swept by the rotor blades (㎡). ； Fig. 3–Mechanical power versus rotor speed curves measurements and simulations at various water flow Rates for the studied hydraulic turbine. Fig. 3 illustrates the steadystate mechanical power characteristic function Pmversus the rotatingspeed of the hydraulic turbine u at various constant water flow rates Q, with H fixed at m. The point of optimal efficiency is designed to be at rated water flow rate and head, where the turbine captures the maximum power. It can be observed that, for each water flow rate, there