Control Strategy for VSC-HVDC Power Quality Improvement under Unbalanced Grid Conditions

2011 ◽  
Vol 12 (6) ◽  
Author(s):  
Xiaoyun Wei ◽  
Hui Sun ◽  
Xiaoguang Wei ◽  
Qian Ma ◽  
Fengge Xu
Keyword(s):  
Power Quality ◽  
Control Strategy ◽  
Effective Control ◽  
Negative Sequence ◽  
Control Loops ◽  
Hvdc System ◽  
High Voltage Direct Current ◽  
Component Decomposition ◽  
Improved Performance ◽  
Unbalanced Grid

This paper presents a novel unified dynamic model and control strategy to improve the power quality for VSC based high voltage direct current transmission system (VSC-HVDC) under unbalanced grid conditions. The unified models present the dynamic behavior of VSC-HVDC in the unique positive synchronously rotating reference (dq-p) frame with respect to both the positive- and negative-sequence components. Based on the unified model, a strategy to either eliminate the dc-link ripple or achieve the balanced currents, along with a rather low level harmonics in each grid is introduced by resorting to the resonant integrator and filter based scheme in the two cascaded control loops. The resonant integrator and filter scheme enables effective control of the positive- and negative-sequence currents, and avoid the sequence component decomposition. The simulation studies in PSCAD/EMTDC verify the improved performance of VSC-HVDC system regarding the power quality and the ride-through capability.

Real power regulation design for multi-terminal VSC-HVDC systems

2013 ◽  
Vol 3 (2) ◽  
Author(s):  
Guo-Jie Li ◽  
Si-Ye Ruan ◽  
Tek Lie
Keyword(s):  
Control Strategy ◽  
Control Mode ◽  
Voltage Source ◽  
Voltage Source Converter ◽  
Real Power ◽  
The Real ◽  
Hvdc System ◽  
High Voltage Direct Current ◽  
Power Regulation ◽  
Regulation Functions

AbstractA multi-terminal voltage-source-converter (VSC) based high voltage direct current (HVDC) system is concerned for its flexibility and reliability. In this study, a control strategy for multiple VSCs is proposed to auto-share the real power variation without changing control mode, which is based on “dc voltage droop” power regulation functions. With the proposed power regulation design, the multiple VSCs automatically share the real power change and the VSC-HVDC system is stable even under loss of any one converter while there is no overloading for any individual converter. Simulation results show that it is effective to balance real power for power disturbance and thus improves operation reliability for the multi-terminal VSC-HVDC system by the proposed control strategy.

A Novel Control Strategy for DVR to Improve Voltage Profile in Wind Farm

2013 ◽  
Vol 768 ◽  
pp. 344-350 ◽  
Author(s):  
M. Naga Himaja ◽  
S. Premalatha ◽  
Subhransu Sekhar Dash ◽  
Paduchuri Chandra Babu
Keyword(s):  
Power Systems ◽  
Power Quality ◽  
Control Strategy ◽  
Wind Farm ◽  
High Stress ◽  
Wind Farms ◽  
Voltage Profile ◽  
Negative Sequence ◽  
The Stability ◽  
Custom Power

Power quality is one of major concerns in the present era. It has become important, especially, with the introduction of sophisticated devices, whose performance is very sensitive to the quality of power supply. To improve the power quality, custom power devices are used. The device considered in this work is DVR. This work presents a control strategy for a DVR to improve the stability in wind farms based on SCIG. The DVR controller is designed to work under unbalanced conditions, which allows overcoming most faults in the power grid. The proposed strategy is capable of balancing voltages at wind farm terminals obtaining several advantages. Firstly, negative-sequence currents are eliminated; thus, overheating, loss of performance, and decreasing of generator useful life are avoided. Secondly, by nullifying negative sequence voltages, 2ω pulsation in the mechanical torque is prevented, reducing high stress in the turbine mechanical system, especially in the gearbox. The power system, DVR converter, and controller were implemented in the Sim power Systems blockset of SIMULINK/MATLAB®.

A Control Strategy for the Grid-Side Converter of the Directly-Driven Wind Turbine with PM Synchronous Generator under Unbalanced Grid Voltage

2013 ◽  
Vol 816-817 ◽  
pp. 669-677
Author(s):  
Wei Cai ◽  
Hui Min He ◽  
Jian Wei Wang ◽  
Shao Ze Su
Keyword(s):  
Control Strategy ◽  
Synchronous Generator ◽  
Active Power ◽  
Current Control ◽  
Frequency Oscillation ◽  
Dc Voltage ◽  
Negative Sequence ◽  
Double Frequency ◽  
Grid Side ◽  
Unbalanced Grid

A mathematical model of the full power grid-connecting converter at grid side for permanent magnet synchronous generator (PMSG) under unbalanced grid conditions is built, double-frequency oscillation mechanism on DC voltage is analyzed, and the influence of active power ripple of grid-connecting impedance on dual current control is discussed. To suppress the double-frequency oscillation on DC voltage, and take the grid-connected impedance on active power into account, a dual current control strategy, which based on respectively orientating positive-and negative-sequence voltages,is proposed, and introduced the correction value of active power ripple of grid-connecting impedance to correct reference current of proposed control strategy. Simulation results show that the proposed control strategy can effectively control positive and negative-sequence currents,eliminate the DC voltage double-frequency oscillation,and improve harmonic characteristic of grid-connected current.

scholarly journals DC Voltage Adaptive Droop Control Strategy for a Hybrid Multi-Terminal HVDC System

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 380 ◽  
Author(s):  
Yingpei Liu ◽  
La Zhang ◽  
Haiping Liang
Keyword(s):  
High Voltage ◽  
Direct Current ◽  
Control Strategy ◽  
Power Flow ◽  
Influence Factor ◽  
Current System ◽  
Droop Control ◽  
Dc Voltage ◽  
Hvdc System ◽  
High Voltage Direct Current

To solve the problems of DC voltage control and power allocation in the hybrid multi-terminal high voltage direct current system effectively, a DC voltage adaptive droop control strategy based on DC voltage-current characteristics is proposed. Based on adjustment of the droop coefficient of the converter station, the proposed control strategy introduces the influence factor of the droop coefficient, which considers the dynamic power margin of the converter station according to the direction of DC current variation in the converter station. When changes in the hybrid multi-terminal high voltage direct current system power flow occur, the droop coefficient of the converter station can be adjusted by the influence factor of the droop coefficient, so that the converter station can participate in power regulation according to its own power regulating ability. Consequently, the proposed control strategy can reasonably allocate the active power and minimize the deviation of the DC voltage. Besides, the stability analysis of the proposed control strategy is also carried out. Simulation results have verified the feasibility and effectiveness of the proposed control strategy.

scholarly journals Advanced Fault Ride-through Strategy by an MMC HVDC Transmission for Off-Shore Wind Farm Interconnection

2019 ◽  
Vol 9 (12) ◽  
pp. 2522
Author(s):  
Lee ◽  
Yoo ◽  
Yoon ◽  
Jang
Keyword(s):  
Control Strategy ◽  
Power Plants ◽  
Wind Farm ◽  
Dc Voltage ◽  
Hvdc System ◽  
Hvdc Transmission ◽  
High Voltage Direct Current ◽  
Fault Ride Through ◽  
Doubly Fed ◽  
Grid Side

In order to solve the problems brought upon by off-shore wind-power plants, it is important to improve fault ride-through capability when an on-shore fault occurs in order to prevent DC overvoltage. In this paper, a coordinated control strategy is implemented for a doubly-fed induction generator (DFIG)-based off-shore wind farm, which connects to on-shore land by a modular multilevel converter (MMC)-based high voltage direct current (HVDC) transmission system during an on-shore fault. The proposed control strategy adjusts the DC voltage of the off-shore converter to ride through fault condition, simultaneously varying off-shore AC frequency. The grid-side converter detects the frequency difference, and the rotor-side converter curtails the output power of the DFIG. The surplus energy will be accumulated at the rotor by accelerating the rotor speed and DC link by rising DC voltage. By the time the fault ends, energy stored in the rotor and energy stored in the DC capacitor will be released to the on-shore side to restore the normal transmission state. Based on the control strategy, the off-shore wind farm will ride through an on-shore fault with minimum rotor stress. To verify the validity of the proposed control strategy, a DFIG-based wind farm connecting to the on-shore side by an MMC HVDC system is simulated by PSCAD with an on-shore Point of Common Coupling side fault scenario.

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