Athanasios Mesemanolis

High-Efficiency Control for a Wind Energy Conversion System With Induction Generator

In this paper, an improved efficiency control scheme for wind energy conversion systems (WECSs) with squirrel cage induction generators is proposed. Thus, the power harvesting from the WECS is increased and additionally expansion of the exploitable wind speed region toward the lower speed range is accomplished. The generator is connected to the power grid by means of two space-vector-controlled back-to-back converters. A minimum ohmic loss (MOL) controller is introduced in order to minimize the generator resistive loss that is accomplished by adjusting the d-axis stator current according to torque conditions. The implementation of the proposed controller is easy and cost effective because neither additional control signals nor the knowledge of the generator loss model is required. The effectiveness of MOL controller and its successful cooperation with two types of maximum power point tracking (MPPT) controllers, which are employed to maximize the wind turbine output power, are experimentally verified. The MPPT controller is implemented by using an adaptive search control and a fuzzy-logic-based control technique, since both are independent of wind turbine characteristics and widely used. Selective experimental results are presented to demonstrate the resulting improvements of the suggested control scheme.

Optimal Efficiency Control Strategy in Wind Energy Conversion System With Induction Generator

This paper presents an optimal efficiency control strategy for wind energy conversion systems (WECSs) with squirrel cage induction generators (SCIGs). The developed control scheme provides an optimal efficiency of the induction generator and maximum power extraction from the wind turbine. Thus, maximum power harvesting from the whole WECS is achieved and additionally expansion of the exploitable wind speed region toward the lower speed range is accomplished. A minimum electric loss (MEL) controller is introduced to minimize the generator electric loss and a maximum power point tracking (MPPT) controller is used to maximize the wind turbine output power. Common input to the two optimal controllers is only the generator speed, while the measurement of the wind speed is not required. The controllers determine the optimal d- and q-axis stator current components of the SCIG through optimal conditions and, therefore, fast dynamic response of the WECS is accomplished. An experimental procedure is proposed to determine the MEL and MPPT controller parameters. Therefore, neither the knowledge of SCIG loss model, nor the characteristic curves of the wind turbine are required. The effectiveness and the operational improvements of the suggested optimal control scheme have been verified experimentally.

Maximum electrical energy production of a variable speed Wind Energy Conversion System

This paper proposes a control strategy for Wind Energy Conversion Systems (WECSs) aiming in both maximum power harvesting from the wind turbine and minimum power loss of the electrical generator. Thus, maximum efficiency along the whole wind energy conversion process is achieved and additionally expansion of the exploitable wind speed region towards the lower-speed range is accomplished. A squirrel cage induction generator connected to the power grid by means of two back-to-back converters is used. Field oriented control is applied and a system of two Search Controllers (SCs) is introduced for the control of the d- and q-axis stator current components of the generator. The maximum power at the wind turbine is achieved through the one SC by adjusting the q-axis current and through this, the generator speed. Another SC is introduced in order to maximize the efficiency of the electrical generator by controlling its flux-linkage. The dynamic performance of the system is improved by introducing control loops that compensate the delayed response of the flux-linkage to the d-axis current component and provide improved torque control operation. Several experimental results are presented to demonstrate the effectiveness and operational improvements of the proposed control system.

Self-tuning maximum power point tracking control for wind generation systems

In this paper, a new Maximum Power Point Tracking (MPPT) control scheme for wind generation systems is proposed. A new procedure based on an adaptive neuro-fuzzy training technique is proposed for the self-tuning of the MPPT controller parameters in order to compensate for the unmodeled nonlinearities and degradation due to mechanical aging of various parts of the wind turbine. The suggested control scheme can be easily implemented because neither the measurement of the wind speed nor the knowledge of the wind turbine characteristics are required. Moreover, it has fast dynamic response and thus it can follow the fast dynamics of the wind. The effectiveness and fast dynamic performance of the proposed control scheme has been verified experimentally.

A fuzzy-logic based control strategy for maximum efficiency of a Wind Energy Conversion System

In this paper, a control method for a Wind Energy Conversion System (WECS) utilizing a Squirrel Cage Induction Generator (SCIG) is presented. Aims of the control are both maximum wind power harvesting and minimization of the SCIG power loss, thus achieving maximum power production on any wind speed. The SCIG is connected to the utility grid through two back-to-back converters. The first converter uses Field Oriented Control to regulate the speed and the excitation of the SCIG. The proposed control system uses two Fuzzy-Logic Controllers that regulate the speed and excitation of the SCIG, implementing Maximum Power Point Tracking (MPPT) and Loss Minimization by regulating the speed of the generator and the excitation respectively. Thus, maximum power is extracted by the wind and additionally, power output is increased by reducing the core loss of the generator. In order to improve the slow response time of the flux-linkage to the d-axis current an additional control loop has been introduced that improves the response time of the flux-linkage. Several experimental results are displayed that validate the operational improvements of the proposed control scheme.

Performance study of start-up control techniques in a Wind Energy Conversion System with induction generator

This paper studies the performance of a Wind Energy Conversion System (WECS) with an induction generator under various start-up control techniques. The capability of self-excitation of the induction generator using three control techniques is examined. The generator is connected to the power grid by means of a fully controlled frequency converter which consists of a pulse-width modulation (PWM) rectifier, an intermediate dc-link circuit and a PWM inverter. Field oriented control is applied and Maximum Power Point Tracking (MPPT) of the wind turbine is achieved by using the Perturb & Observe (P&O) control technique. A squirrel cage induction generator is considered in this paper. The control system has been simulated using the Matlab/Simulink software and several simulation results are presented in order to demonstrate the performance of the WECS under the examined start-up control techniques.

Copper loss minimization in combination with MPPT control in a wind energy conversion system with induction generator

In this paper, a control scheme for wind energy conversion systems (WECS) with induction generator is presented that is composed of a copper loss minimization (CLM) controller and a maximum power point tracking (MPPT) controller. The CLM is accomplished by controlling the excitation current of the induction generator and the MPPT control is attained by controlling the rotational speed of the wind turbine. The suggested control scheme can be easily implemented because, neither the measurement of the wind speed nor the knowledge of the wind turbine characteristics are required. Moreover, it exhibits fast dynamic response and thus, it can follow the fast dynamics of the wind. The generator is connected to the power grid by means of two vector controlled back-to-back converters. Experimental results are presented to validate the cooperation of the CLM controller with the MPPT controller.

On-line estimation of induction generator parameters using adaptive neuro-fuzzy inference systems for wind energy conversion systems

This paper proposes a new method for online estimation of the induction generator parameters by means of adaptive neuro-fuzzy inference systems (ANFIS). The suggested technique can be applied to induction generators that are used in wind energy conversion systems (WECS). The WECS structure comprises a wind turbine, a three-phase induction generator and two back-to-back power converters. The WECS provides electric energy to the utility grid through an LCL filter. The selfadjustment of the induction generator parameters provides accuracy in the implementation of the field oriented control and therefore accomplishes optimal operation on the WECS. The proposed method is simple and, since it does not require time consuming off-line laboratory experiments, it can be easily applied to any wind energy system that is already in operation. Several simulation results will be presented in order to validate the theoretical considerations and demonstrate the operational improvements of the proposed system.

A new modulation technique for reduced harmonic distortion of current in PV inverters

This paper deals with the modeling of a single-phase PV inverter using current control. Two control methods are described; the hysteresis band and the zero-tolerance control. A study for the optimization of the Total Harmonic Distortion (THD) of the output current and for the minimization of the switching losses is being conducted. A new modulation method is also presented, defined as mixed modulation, which is a combination of the unipolar and bipolar modulation. The mixed modulation is applied both to the hysteresis band and to the zero-tolerance control. It is proved, by simulation, that this method produces the best results, since it combines the advantages of the other two modulation methods. A comparison between the modulation methods is conducted, using as criteria the THD of the output current of the inverter and the efficiency of the inverters.