Present-day small hydropower plants (SHPs) have a large development potential because of the increasing interest in renewable resources and distributed energy generation; however, the variable hydrological conditions that are found in run-of-the-river projects require operations over a wide range of water flow and head variations. Special control methods and system topologies are needed to maintain the high efficiency of energy conversion systems.This paper presents a complete SHP solution based on an innovative generation unit (hydro-set): a propeller turbine is integrated with a permanent magnet synchronous generator working at a variable speed in a grid-connected system that utilises an ac/dc/ac converter. The main elements of this energy conversion system are described. A dedicated control strategy is proposed and verified. All of the results presented here originate from an actual 150-kW SHP that contains two innovative hydro-sets working in parallel on the same river.

In this paper, a small hydropower plant (SHP) working at variable speed is analysed. The energy conversion system contains a propeller turbine, which is coupled directly to a permanent magnet synchronous generator (PMSG) that is connected with a power system through a power electronic converter (PEC). The PEC that consists of a diode bridge rectifier and a DPC-SVM controlled inverter is described using the average value modelling method. The presented analysis considers only the fundamental harmonic component of ac currents and voltages. The system components are structured in the form of equivalent circuits that also include the power losses. The turbine model consists of the discharge and torque characteristics, which are approximated by analytical formulas based on the turbine hill diagram. The dynamic features represent the speed limiter of the guide vane governor and the mass of water, which fills the turbine chamber and the inlet and outlet pipes. The model is verified on a prototype hydropower plant of nominal power of 150 kW by the steady state characteristic and a transient performance comparison. Such approach is found to minimise the necessary measurement, simplify the description and provide satisfactory accuracy of the hydro-set model.

The paper presents the control system of a small hydropower plant (SHP) working at variable speed operation (VSO). In general, VSO increases the turbine operating discharge and gives higher efficiency over a wide operating range. It is particularly advantageous under conditions different from the original design conditions. Changing of the hydrological conditions requires adjustments to the control system; therefore, the new maximum efficiency point tracking (MEPT) algorithm is proposed. The MEPT algorithm implemented in the load controller employs the gradient method. The water level governor based on the PI controller combined with the adaptive load controller is analyzed. The troublesome measurement of the turbine discharge is replaced by the neural-network-based estimator. The correlation analysis of the system parameters was performed by using principal component analysis. The proposed algorithm was implemented in the programmable logic controller and tested on a real low-head SHP of 150 kW power with two single-regulated propeller turbines.

In recent times, much attention has been paid to small hydropower plants (SHPs) with variable speed operation and different control techniques. Control complexity in SHPs is mainly caused by specific steady-state features of the water turbine, the long time constants of the hydraulic system and significant seasonal and/or aging-related deterioration in the system performance. This paper presents the most important features of the turbine model from a control point of view. It classifies control techniques for SHPs with variable speed operation in terms of the turbine type and SHP function (run-of-the-river and reservoir). Furthermore, various control methods are analysed taking into account the complexity of the method, dynamics, adaptability and applicability. The novelty of this study is the proposal of a simple, universal analytical formula, which, based on the basic dimensions of the turbine, determines the optimal operating curve. The proposed formula is verified on a real SHP 150 kW by comparison with measurements in the form of operational characteristics. The analysis of the annual energy production confirms the effectiveness of the approximation precision, yielding only 1% production losses, and shows an advantage of variable speed over constant speed in annual energy production of 16%.

This article focuses on modeling of an Axial Flux Permanent Magnet Generator (AFPMG). The authors analyzed selected variants of disk generators, including coreless stator constructions and with iron core ones, also taking into account the Permanent Magnet (PM) arrangement in order to show the way to obtain the optimal machine characteristics based on analytical equations. In addition to the full model, which takes into account the higher harmonics of the magnetic field distribution, the paper presents a simplified mathematical model developed for generator operation cases such as standalone, connected to a 3-phase power grid and loaded with a diode rectifier. The analytical and finite-element method (FEM) calculations were performed as well as laboratory tests to confirm the correctness of presented model assumptions.