Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> B. ELECTRICAL GENERATORS CONTROL CLASSIFICATIONS <s> The paper describes the engineering and design of a doubly fed induction generator (DFIG), using back-to-back PWM voltage-source converters in the rotor circuit. A vector-control scheme for the supply-side PWM converter results in independent control of active and reactive power drawn the supply, while ensuring sinusoidal supply currents. Vector control of the rotor-connected converter provides for wide speed-range operation; the vector scheme is embedded in control loops which enable optimal speed tracking for maximum energy capture from the wind. An experimental rig, which represents a 7.5 kW variable speed wind-energy generation system is described, and experimental results are given that illustrate the excellent performance characteristics of the system. The paper considers a grid-connected system; a further paper will describe a stand-alone system. <s> BIB001 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> B. ELECTRICAL GENERATORS CONTROL CLASSIFICATIONS <s> This paper presents the simulation results of a grid-connected wind driven doubly fed induction machine (DFIM) together with some real machine performance results. The modeling of the machine considers operating conditions below and above synchronous speed, which are actually achieved by means of a double-sided PWM converter joining the machine rotor to the grid. In order to decouple the active and reactive powers generated by the machine, stator-flux-oriented vector control is applied. The wind generator mathematical model developed in this paper is used to show how such a control strategy offers the possibility of controlling the power factor of the energy to be generated. <s> BIB002
There are many control classifications for AC machines in general. The most common control methods are vector or field oriented control (VC) and direct control which is further divided to direct power and direct torque control BIB002 . In the vector control scheme, the machine is controlled in a synchronous rotating dq frame with the d-axis oriented with the flux. The current components can independently control the active and reactive powers. For example, if the reference frame is oriented with the stator flux, the d-axis and q-axis current components control the stator reactive and active powers respectively BIB001 . The direct power control (DPC) scheme is based on a direct control of active and reactive powers of the stator. It is performed by injecting directly current/voltage vectors. The direct torque control (DTC) scheme is established by direct control of two magnitudes of the doubly fed induction machine which are the rotor flux and the electromagnetic torque. It is based on a space vector representation of the achievable output of AC voltages of the converter. This space vector representation is used as a lookup table for the converter output voltage. The DTC directly creates the pulses for the converter without using modulation schemes such as pulse width modulation (PWM).