The control of a doubly-fed induction machine (DFM) with and without the use of a rotor position encoder is examined. First, a stator flux linkage oriented control scheme for power and speed control with a position encoder, shows the high performance control capabilities of this control arrangement and serves as foundation for the sensorless scheme. The power-control method is then applied to a sensorless method, based on a previous control arrangement. This method is then extended to derive a sensorless speed-control mechanism for the DFM. All control schemes are implemented and performed on an experimental test system, comprising two 80C167 microcontrollers and a 2.25 kW wound rotor induction machine.

Stator-flux-oriented control of a doubly-fed induction machine with and without position encoder

A different circuit configuration for the slip-power recovery system is presented in this paper. A boost chopper is used to connect the diode rectifier to the DC-link voltage, which is composed of a capacitor and a voltage-source inverter (VSI). The diode rectifier gives rise to mains current harmonies of variable frequency, which can present subharmonics, harmonics, and interharmonics that can lead to flicker in the mains. Two simple solutions to this drawback are studied. In the first solution, additional inductances were connected on the AC side of the rotor circuits to increase the overlap angle. In the second solution, the stator current harmonics are compensated by a VSI that can work simultaneously as an inverter and as an active power filter. This system represents a very interesting and useful application for active power filters. The merits of the configuration presented are cost, control simplicity, the possibility of reactive power control over a wide range, and quasi-optimum exploitation of the electrical machine. The characteristics of the proposed system and its control are presented in this paper. It is concluded that, although the system proposed is much simpler than others, it has interesting performance.

A simple slip-power recovery system with a DC voltage intermediate circuit and reduced harmonics on the mains

Flux-oriented control has given a great attention because of its high performances in AC variable speed drives. This paper deals with the implementation of the stator-flux-oriented control in a doubly-fed synchronous machine (DFSM). Compensation of the control system is detailed according to DFSM parameters. It has been found that an adaptive control has to be performed when the load torque is a function of DFSM speed. Simulation works show that the DFSM is no longer an unstable machine when driven by a stator-flux-oriented control system. Moreover, the drive acquires a high dynamic which makes the DFSM one of the most attractive features in the slip recovery system domain.

On the stator‐flux‐oriented control of a doubly‐fed synchronous machine

This paper analyses the operation of a power unit with a doubly fed machine. A novel vector control method is presented which enables independent control of both positive- and negative-sequence components of stator currents. Also, operation of the system under the condition of unbalanced voltage supply applied to the stator is discussed.

Independent control of positive- and negative-sequence current components in a doubly fed machine

This paper deals with the control of a variable speed drive made up of a doubly-fed motor (DFM) and a rotor converter including two current-regulated voltage inverters separated by a DC link: the rotor-side inverter and the line-side one. Both inverters are controlled by vector control strategies using electrical variables expressed in the frame held by the DFM stator flux. High transient and steady-state performances of the DFM have been gained with the implementation of the stator flux oriented control in the rotor-side inverter, while a unity overall power factor operation has been achieved with the implementation of a (P,Q) vector control strategy in the line-side inverter.

On the dynamic and steady state performances of a vector controlled DFM drive

This paper deals with the energy balance of the doubly fed synchronous machine (DFSM). The proposed method is based on the principle which consider that the electro–mechanical conversion takes place between stator circuits and the machine shaft, so that the electrical power applied to rotor circuits is taken as a command. From this point of view, the study stresses are: Stability, A low ratio of the rotor command referred to the converted energy, High efficiency. Results are presented in the rms value of rotor applied voltage (V2a) – angle between the stator and the rotor voltages vectors (5) plane. We have found, when we vary the slip (s), that the high efficiency areas move in such way that the ratio of s over V2a remains constant (which means a constant rotor flux).

A. Masmoudi

Papers

Power flow analysis and efficiency optimization of a doubly fed synchronous machine

On the stator‐flux‐oriented control of a doubly‐fed synchronous machine