A coordinated control of PMSG based wind turbine generator to improve fault-ride-through performance and transient stability

Dey, P 2018, A coordinated control of PMSG based wind turbine generator to improve fault-ride-through performance and transient stability, Doctor of Philosophy (PhD), Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title A coordinated control of PMSG based wind turbine generator to improve fault-ride-through performance and transient stability
Author(s) Dey, P
Year 2018
Abstract With the high penetration of wind power into the medium and low voltage power grid, ensuring power quality and transient stability following the utility grid codes become challenging nowadays. Wind power fluctuates with the variation of wind speed which leads to the voltage regulation and frequency control problems in the power grid.

Among the issues wind power systems are facing, grid fault is a major one. According to the utility grid codes, wind turbine generators (WTGs) need to have enough fault ride through (FRT) capability. Different configurations of power converters and control techniques have been developed to address this issue. However, a coordinated controller which is capable of the grid voltage regulation, frequency control, and DC link overvoltage minimisation altogether at the time of grid faults is yet to be reported in any literature. This PhD research is focused on developing such a coordinated control method for a permanent magnet synchronous generator (PMSG) based WTG. This coordinated control combines a pitch angle control, a flux weakening control and a reactive power control to enhance the low voltage ride through (LVRT) capability of the PMSG based variable speed wind energy conversion system (WECS). The design process of the controller parameters and the stability of proposed control strategy have been analysed. Here, the pitch angle controller is modified to adjust the pitch for wind power smoothing as well as LVRT enhancement during variable wind speeds and grid fault respectively. The flux weakening controller is used to reduce the flux linkages of PMSG by supplying negative field regulating current to reduce the DC link overvoltage during grid voltage dips. Additionally, static compensator (STATCOM) or grid side converter (GSC) is used to provide reactive power support during the grid faults. Extensive simulations of the proposed method have been carried out under different cases. The proposed control method is compared with the braking chopper (BC) and the battery energy storage system (BESS) based conventional controls via simulations results and are verified to perform better in providing FRT.

Frequency stability of the grid connected WECS after the fault recovery is also an important issue which needs to be solved. If the frequency fluctuation goes beyond the safe limit, the power system will collapse creating a cascaded failure that was seen in the South Australian Power System in 2016. Therefore, it is essential to provide primary frequency control support for a stable operation of the power system. Two control methods are considered in this PhD research to provide the grid frequency stability.

A simultaneous controller is developed based on the inertia support from the wind turbine and the DC-link capacitor energy to provide the primary frequency control from a PMSG based variable speed WECS. Another approach is developed based on the PMSG flux linkage controller with a Superconducting Magnetic Energy Storage (SMES). The SMES is considered here due to its higher efficiency over other energy storage devices. In this approach, the PMSG flux increases or decreases according to the frequency variation. Similarly, SMES also absorbs or injects some amount of real power when the system frequency is increased or decreased.

Both strategies are verified with the WTGS connected to the single and multi-machine power systems under different wind speeds, load demand variations, and grid faults. Time series simulation results illustrate that a significant enhancement of frequency regulation is achieved with both proposed controllers.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Engineering
Subjects Control Systems, Robotics and Automation
Renewable Power and Energy Systems Engineering (excl. Solar Cells)
Circuits and Systems
Keyword(s) Wind energy
Fault ride through
DC voltage
Frequency control
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Created: Thu, 17 Jan 2019, 14:51:11 EST by Keely Chapman
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