Negative Sequence Voltage Compensation Research Articles

Positive and Negative Sequence Voltage Compensation Using Statcom at Wind Farm

The study of shunt connected FACTS devices is a connected field with the problem of positive and negative voltage compensation and better mitigation of instability problems in today’s world. In this project, the shunt operation of FACTS controller is studied, the STATCOM, and how it helps in the better utilization of a network operating under normal conditions. First literature review of many papers related to FACTS and STATCOM is carried out, along with positive and negative voltage compensation. The study of STATCOM and its principles of operation and control, including phase angle control and PWM techniques, are carried out. The study of shunt connected devices is a shunt connected field positive and negative sequence voltage compensation and better mitigation of transmission related world. Statcom is a FACTS device whose capacitive or inductive current can be controlled independent of system ac voltage. Whenever an asymmetrical fault occurs in a system, power loss and voltage instability can occur in that system. So to increase the life time of generator drives and to reduce that voltage instability, Statcom can be used. Statcom can compensate positive sequence voltage for improving voltage stability and for reducing torque ripples negative sequence voltage has to be compensated. Statcom can perform co-ordinated action regarding positive and negative voltage compensation. In this thesis, review of positive and negative voltage compensation and results for positive sequence voltage compensation and negative voltage compensation using MATLAB simulation is shown.

Hybrid one-cycle control scheme for fault-tolerant modular multilevel rectifiers

ABSTRACTThis paper customises the classic one-cycle control (OCC) scheme for modular multilevel rectifiers (MMRs) and overcomes the inherent defect of the OCC. To be specific, a hybrid one-cycle control scheme is proposed combining the OCC and the virtual loop mapping (VLM). First, on the basis of the classic OCC and the volt-second equivalence principle, the relationships between the MMR arm equivalent duty cycle and the sub-module (SM) duty cycle are derived. Then, by making use of VLM methods, the switching frequency of the SM is reduced and the dynamic capacitor voltage balance is obtained as well. Further, to achieve the single-line-to-ground fault-tolerance capability and eliminate the second harmonic ripple in the DC voltage, the constant power control is presented using the negative-sequence voltage compensation. Specifically, the whole control scheme only needs one proportional integration controller, which greatly reduces the complexity of system control and the system cost. The validity of the proposed scheme is verified through simulation and experimental studies.

StatCom control at wind farms with fixed-speed induction generators under asymmetrical grid faults

The stability of fixed-speed induction generator (FSIG)-based wind turbines can be improved by a StatCom, which is well known and documented in the literature for balanced grid voltage dips. Under unbalanced grid voltage dips, the negative-sequence voltage causes heavy generator torque oscillations that reduce the lifetime of the drive train. In this paper, investigations on an FSIG-based wind farm in combination with a StatCom under unbalanced grid voltage fault are carried out by means of theory, simulations, and measurements. A StatCom control structure with the capability to coordinate the control between the positive and the negative sequence of the grid voltage is proposed. The results clarify the effect of the positive- and the negative-sequence voltage compensation by a StatCom on the operation of the FSIG-based wind farm. With first priority, the StatCom ensures the maximum fault-ride-through enhancement of the wind farm by compensating the positive-sequence voltage. The remaining StatCom current capability of the StatCom is controlled to compensate the negative-sequence voltage, in order to reduce the torque oscillations. The theoretical analyses are verified by simulations and measurement results on a 22-kW laboratory setup.