Shousun Chen

Application of unified power flow controller in interconnected power systems-modeling, interface, control strategy, and case study

In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its DC link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC-network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly.

A novel hysteresis current control for active power filter with constant frequency

Abstract In this paper a novel hysteresis current control for active power filter (APF) is suggested which is based on optimal voltage vector and in the meantime with constant switching frequency. In the method the location region of the reference voltage vector is detected quickly by a set of hysteresis comparators through one try-and-error process. Two appropriate switches are then selected to control the corresponding two line-to-line currents independently with constant switching frequency. The new method has the advantages of fast allocation of reference voltage space vector, good current tracking accuracy, and constant switching frequency. Therefore, it is efficient and safe in operation. Computer simulation results show that the new current control method can improve APF performance noticeably.

Discussion of "Application of unified power flow controller in interconnected power systems-modeling, interface, control strategy, and case study" [and reply]

E. Uzunovic et al. comment on the paper by Z. Huang et al. (see ibid., vol.15, no.2, p.817-24, 2000). They point out the importance of adequately representing inverter losses in the model. The original authors reply to the comments.

A novel hysteresis current controller for active power filter with constant switching frequency

A novel hysteresis current controller for active power filter (APF) is suggested which is based on optimal voltage vectors and in the meantime with constant switching frequency. In this controller, the location region of the reference voltage vector is detected quickly by a set of hysteresis comparators through one trial-and-error process. Two appropriate switches are then selected to control the corresponding two line to line currents independently with constant switching frequency. The new method has the advantages of quick response, good current tracking accuracy, and constant switching frequency. Therefore it is very efficient and secure in operation. Computer simulation results show that the new current control method can improve APF performance noticeably.

Incorporating UPFC model into the power system toolbox of the MATLAB for transient stability study

In this paper, power frequency model for unified power flow controller (UPFC) is presented with its DC link capacitor dynamics included. A novel interface of UPFC to AC network for transient stability study is then suggested and realised using Power System Toolbox (PST) of MATLAB. The control strategies for UPFC shunt and series elements are also discussed. Computer results on a 4-generator interconnected test power system show that the convergence and accuracy of the suggested interface are challenging and the suggested interface makes it very easy to incorporate the UPFC model into the conventional transient stability programme. The results also show that the UPFC control strategy had strong impacts on the performance of UPFC.

A novel current controller for active power filter based on optimal voltage space vector

In this paper, a novel hysteresis current controller for active power filter based on the optimal voltage space vectors is suggested. The controller jointly utilizes two sets of inter-phase current difference comparators to determine the location region of the reference voltage space vector and the current error space vector respectively. When the system reference voltage space vector is changing rapidly and randomly which makes its location region difficult to be estimated, the novel controller can quickly detect its correct location region by one trial-and-error process which is essential to the performance improvement of the active power filter. The related concept and formulation are presented. Computer simulation is conducted on a test system and the results show that the controller can quickly determine the optimal voltage space vector, therefore current tracking error is reduced effectively. So the voltage source inverter (VSI) switching frequency can be reduced and the efficiency of active power filter (APF) can be improved apparently under the same control accuracy.

UPFC Power Frequency Model for Power System Stability Analysis

Abstract In this paper a power frequency model is derived for unified power flow controller (UPFC). The UPFC capacitor charging dynamics is considered. Its shunt part control is to keep constant the UPFC terminal bus voltage magnitude and the UPFC capacitor voltage respectively. Its series part control is to keep constant real and reactive power flow of the UPFC-installed line or to act as a series compensator. The integrated UPFC model has been incorporated into power system transient stability program with a novel interface. Computer tests on a 4-generator power system show that the suggested UPFC model and the UPFC-network interface method work very well in transient stability analysis. The tests also show that the different control strategies might have distinct effects on system stability performance.

Modified selective modal analysis method and its application in the analysis of power system dynamics

The selective modal analysis (SMA) method is modified which is especially efficient in analyzing and stabilizing power oscillation of multi-machine power systems. All the formulas necessary for forming the reduced system matrix, calculating eigenvalues and eigenvectors, and performing the sensitivity analysis of eigenvalues are presented. A computer program has been developed and tested on a three-machine AC/DC system and a thirteen-machine AC/DC system with DC control represented as a first-order model. The results are very good. >