Control techniques with system efficiency comparison for micro-wind turbines

This paper presents the implementation of a sensorless speed controller and active rectification in a micro-wind turbine intended for battery charging. The controller was tested in a wind turbine emulator test rig using real wind data available from British bases in Antarctica. The control algorithm was successfully tested up to 14 m/s wind speed. Beyond this point the electrical unbalance in the turbine generator compromised the stability and performance of the system. Also, a system efficiency comparison of different control algorithms is given to demonstrate the advantages of using active rectification instead of passive diode rectifiers in microwind turbines. This comparison was done between the sensorless control plus active rectifier, a DC-DC converter regulator and the direct connection between the turbine and battery by means of a diode rectifier. The turbine with an active rectifier and sensorless control achieved the highest power coefficient over the range of wind speeds showing that this technique is an attractive and relatively low cost solution for maintaining good performance of micro-wind turbines at low and moderate wind speeds

Modelling, control and sensorless speed estimation of micro-wind turbines for deployment in Antarctica

This paper presents the modelling, control and sensorless speed estimation of two micro-wind turbines deployed by the British Antarctic Survey (BAS) in Antarctica. Mathematical models for the generators attached to an Ampair 100 and Rutland 913 wind turbines and their experimental validation are given. Also, a model for the wind turbines, particularly taking into account the power coefficient Cp versus tip speed ratio λ relationship was proposed and successfully evaluated on a wind turbine emulator test rig. This paper describes an analogue speed estimator board and a Kalman filter for estimating the shaft speed. These estimators use only DC side measurements to match the characteristics of the current version of the turbine control board. The wind turbine control and speed estimators were tested on the emulator test rig using real wind data from BAS research bases in Antarctica. Using only DC side measurements leads to low computation requirements to execute the algorithms in comparison to commonly used schemes that rely on AC measurements. In addition, the estimation algorithms are based on the model of a PM generator connected to a diode rectifier, as they can be used in a wider range of applications, including DC to DC converters with MPPT algorithms based on speed measurements

Control and efficiency analysis for a Lundell-alternator/active-rectifier system in automotive applications

This paper presents a control strategy for a conventional Lundell alternator and an active-rectifier. The control scheme focuses on the minimisation of the stator copper losses of the alternator in an effort to maximise its efficiency. The modulation scheme of the active-rectifier is being investigated with the introduction of three different modulation techniques in order to quantify the effect they have on the alternator’s efficiency. Steady-state results from experimental measurements of the alternator rectifier system are compared against a standard passive rectifier. The comparison indicates that the modulation scheme of the active-rectifier is significant to the alternator’s efficiency as well as to the overall system efficiency

Efficiency improvement and power loss breakdown for a Lundell-alternator/active-rectifier system in automotive applications

A control strategy for a conventional Lundell alternator and an active-rectifier using different modulation schemes was proposed in previous work. The modulation techniques examined indicated that the system could operate more efficiently than a passive rectifier over a certain speed and power range. This paper extends the modulation scheme analysis using a SVM scheme with six commutations per switching cycle, giving better electrical and overall efficiency. Furthermore, a power loss breakdown is performed for the active-rectifier with the assistance of experimental and simulation results of double pulse tests. Switching loss estimation curves are produced allowing the loss examination of the active-rectifier. Switching losses account only for a minor portion of the total rectifier losses in comparison to conduction losses. Finally, a higher dc-link voltage of 14.5 V was introduced using SVM scheme, giving better efficiency, in order to exploit further the rectifier loss distribution

Torque observer and extended H filter for sensorless control of permanent magnet generators tested on a wind turbine emulator

This paper presents a discrete time torque observer and an extended H∞ filter to estimate the rotor speed and position in a permanent magnet machine. Those estimated variables are key components of a robust sensorless controller for the machine when it is associated with a wind turbine emulator test-rig. In addition, an iterative maximum power point tracking algorithm is proposed for maximum efficiency of the device. Experimental verification on the laboratory setup is given to demonstrate the correct integration of all the control algorithms

Maximum power point tracking and sensorless control for permanent magnet generators tested on a wind turbine emulator

This paper presents a maximum power point tracking algorithm (MPPT) and sensorless control for permanent magnet generators associated with small scale wind turbines. The basis for the wind energy conversion is presented to model the wind turbine emulator test-rig and support the proposed MPPT algorithm. The maximum power point tracking algorithm is based on estimations of the load torque and shaft speed. The shaft speed and position are estimated with an extended Kalman filter. The load torque is estimated with a discrete time observer. A sliding mode controller in the rotor reference frame drives the generator in speed control mode. A minimum number of sensors is required for this implementation: one voltage sensor for the DC link and two current sensors for the phase currents. Experimental implementation on the wind emulator test-rig is given. The proposed estimators, sensorless controller and MPPT algorithm were shown to be well integrated and work properly. The sensorless controller was able to track a speed reference calculated by the MPPT algorithm and based on the speed and load torque estimations

Sensorless control for permanent magnet generators associated with a wind turbine emulator test-rig

This paper presents a robust sensorless control scheme to control a permanent magnet generator associated with a wind turbine emulator test-rig. A Sliding mode controller was used for speed tracking regardless the wind speed profile used in the emulator. Two sensorless estimation algorithms, Sliding mode observer and extended Kalman filter, were implemented to calculate the rotor position and speed. This sensorless control is perfectly suited for high performance and low cost small scale wind turbines. Simulation and experimental verification on the emulator test-rig are given. Also, a discrete time observer was demonstrated to estimate the wind torque

Single phase grid integration of permanent magnet generators associated with a wind turbine emulator test-rig

This paper presents low computation algorithms for single phase integration of permanent magnet generators associated with a wind turbine emulator test-rig. The grid synchronisation and grid side control are performed by Second Order Generalised Integrators (SOGI). A SOGI-FLL (frequency locked loop) was used for robust, accurate and low computation single phase grid synchronisation. Proportional-Resonant and Harmonics compensator controllers (PR+HC) were used to drive a grid tied inverter. Easy implementation, robustness and good current harmonic attenuation are the highlights of these control algorithms. Experimental verification on the wind turbine emulator test-rig, to include the generator side dynamics, is given