scholarly journals A Virtual Impedance Control Strategy for Improving the Stability and Dynamic Performance of VSC–HVDC Operation in Bidirectional Power Flow Mode

2019 ◽  
Vol 9 (15) ◽  
pp. 3184 ◽  
Author(s):  
Yuye Li ◽  
Kaipei Liu ◽  
Xiaobing Liao ◽  
Shu Zhu ◽  
Qing Huai
Keyword(s):  
Control Strategy ◽  
Impedance Control ◽  
Dynamic Performance ◽  
Flow Mode ◽  
Transmission Power ◽  
Output Impedance ◽  
Dc Voltage ◽  
The Stability ◽  
Bidirectional Power Flow ◽  
Virtual Impedance

It is a common practice that one converter controls DC voltage and the other controls power in two-terminal voltage source converter (VSC)–based high voltage DC (HVDC) systems for AC gird interconnection. The maximum transmission power from a DC-voltage-controlled converter to a power-controlled converter is less than that of the opposite transmission direction. In order to increase the transmission power from a DC-voltage-controlled converter to a power-controlled converter, an improved virtual impedance control strategy is proposed in this paper. Based on the proposed control strategy, the DC impedance model of the VSC–HVDC system is built, including the output impedance of two converters and DC cable impedance. The stability of the system with an improved virtual impedance control is analyzed in Nyquist stability criterion. The proposed control strategy can improve the transmission capacity of the system by changing the DC output impedance of the DC voltage-controlled converter. The effectiveness of the proposed control strategy is verified by simulation. The simulation results show that the proposed control strategy has better dynamic performance than traditional control strategies.

Separated-PI Control Strategy and Stability Analysis of a Single-Phase Inverter Connected to the Grid with a LCL Filter

2013 ◽  
Vol 291-294 ◽  
pp. 2464-2469
Author(s):  
Dian Li Hou ◽  
Qing Fan Zhang ◽  
Xiao Liu
Keyword(s):  
Control Strategy ◽  
Single Phase ◽  
Dynamic Performance ◽  
Structural Features ◽  
Lcl Filter ◽  
Phase Inverter ◽  
Hurwitz Stability ◽  
Single Phase Inverter ◽  
Grid Connected Inverter ◽  
The Stability

Because of the powerful filtering ability the third-order LCL filters has been widely used in grid-connected inverters, but there are some problems to be solved on systems stability and control accuracy. A separated-PID control strategy has been proposed according to the PID characteristics and the structural features of a single-phase inverter connected to the grid with a LCL filter. This control strategy has some advantages as a strong dynamic tacking stability, and the system output has a small steady state error. A detailed description is presented on this control strategy applied in the single-phase grid inverter with a LCL filter. According to the Routh-Hurwitz stability criterion, the stability of a grid-connected inverter system based on the proposed control strategy has been analyzed. Finally, waveforms of this inverter have been presented through a simulation to show the steady and dynamic performance of the proposed scheme.

Source-Side Series-Virtual-Impedance Control to Improve the Cascaded System Stability and the Dynamic Performance of Its Source Converter

2019 ◽  
Vol 34 (6) ◽  
pp. 5854-5866 ◽  
Author(s):  
Xin Zhang ◽  
Qing-Chang Zhong ◽  
Visakan Kadirkamanathan ◽  
Jinsong He ◽  
Jingjing Huang
Keyword(s):  
Impedance Control ◽  
Dynamic Performance ◽  
System Stability ◽  
Virtual Impedance ◽  
Cascaded System

scholarly journals Decentralized Virtual Impedance-based Circulating Current Suppression Control for Islanded Microgrids

2021 ◽  
Vol 11 (1) ◽  
pp. 6734-6739
Author(s):  
A. Abu Bakar ◽  
E. Pathan ◽  
M. K. Khan ◽  
M. A. Sadiq ◽  
M. I. Rabani ◽  
...  
Keyword(s):  
Power Distribution ◽  
Voltage Drop ◽  
Impedance Control ◽  
Negative Resistance ◽  
Power Sharing ◽  
Control Technique ◽  
Droop Control ◽  
Output Impedance ◽  
Circulating Current ◽  
Virtual Impedance

Parallel connected inverters in islanded mode, are getting momentous attention due to their ability to increase the power distribution and reliability of a power system. When there are different ratings of Distributed Generation (DG) units, they will operate in parallel connection due to different output voltages, impedance mismatch, or different phase that can cause current to flow between DG units. The magnitude of this circulating current sometimes can be very large and damage the DG inverters and also cause power losses that affect power-sharing accuracy, power quality, and the efficiency of the Microgrid (MG) system. Droop control, improved droop control, and virtual impedance control techniques and modifications in the virtual impedance control technique are widely used to suppress the circulating current. However, the addition of the virtual impedance to each inverter to compensate the output impedance is resistive or inductive in nature. The resistive nature of the output impedance always causes a certain voltage drop, whereas the inductive nature of the output impedance causes phase delay for the output voltage. Both problems are addressed by the proposed control mechanism in this paper. Negative resistance, along with virtual impedance, is utilized in the proposed control strategy. The output impedance is to be maintained as inductive in nature to achieve good load sharing in droop control MGs. The simulation results validate the proposed control scheme.

scholarly journals Virtual Impedance-based Decentralized Power Sharing Control of an Islanded AC Microgrid

2021 ◽  
Vol 11 (1) ◽  
pp. 6620-6625 ◽  
Author(s):  
E. Pathan ◽  
M. H. Khan ◽  
H. Arshad ◽  
M. K. Aslam ◽  
D. Jahangir ◽  
...  
Keyword(s):  
Power Systems ◽  
Decentralized Control ◽  
Control Strategy ◽  
Impedance Control ◽  
Power Sharing ◽  
Voltage Source ◽  
Renewable Energy Resources ◽  
Circulating Current ◽  
Distribution Generation ◽  
Virtual Impedance

The future of power systems depends on the microgrid (MG) which includes distribution generators utilizing Renewable Energy Resources (RERs) and storage facilities. Decentralized control techniques are more reliable and stable in comparison with centralized controlled techniques. In this paper, a decentralized control strategy is presented for an islanded AC MG system. The control strategy includes improved droop control and virtual impedance. Control strategy with PI controllers to control the voltage and current is implemented to two Voltage Source Inverter (VSI) distribution generation units connected in parallel through a Point of Common Coupling (PCC). Circulating current and power-sharing deviations caused by the mismatched line impedance were taken into account. The proposed control scheme was tested in MATLAB/Simulink. Power-sharing accuracy and circulating current suppression were obtained by implementing the proposed virtual impedance-based decentralized control strategy.

Augmented predictive functional control for missile autopilot design

2016 ◽  
Vol 231 (10) ◽  
pp. 1794-1803 ◽  
Author(s):  
Jianguo Guo ◽  
Guoqing Wang ◽  
Zongyi Guo ◽  
Jun Zhou
Keyword(s):  
Control Strategy ◽  
Closed Loop ◽  
Dynamic Performance ◽  
Reference Trajectory ◽  
Input Constraints ◽  
Control Approach ◽  
Predictive Functional Control ◽  
State Dependent ◽  
Functional Control ◽  
The Stability

In this paper, an augmented predictive functional control approach is investigated to design a missile autopilot system, which can be expressed as a linear model with state-dependent coefficient matrices. A novel performance index depending on the reference trajectory, the output prediction and the set-point is proposed to improve the closed-loop dynamic performance. An augmented predictive functional control strategy is designed based on the proposed index and the stability is proven by using the Z-transform. In order to demonstrate the performance of the proposed approach, numerical simulations comparing the predictive functional control in the missile autopilot system are performed. Finally, results from comprehensive simulations are presented to evaluate the proposed approach in the presence of input constraints and abrupt disturbances.

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