Joint Research Projects

Study In Vietnam

Stability Analysis Of A Hybrid Renewable-energy System Fed To A Multi-Machine Power System Using A Static Compensator Integrated With A Flow Battery

Keyword:

Author/Institute

 

Introduction

This study presents stability-improvement results of a DC microgrid (MG) with a wind farm (WF) and an oceanic wave farm (WAF) fed to a multimachine power system (MMPS) using a static compensator (STATCOM) integrated with a vanadium redox flow battery (VRFB)-based energy-storage system (ESS). The AC outputs of the WF and the WAF are connected to the DC MG through individual aggregated equivalent voltage-source converters (VSCs) while the DC MG is connected to the MMPS through an aggregated equivalent voltage-source inverter (VSI). A damping controller for the bidirectional DC-DC converter of the VFRB-based ESS is designed by using phase-compensation method. Root-loci plots under different values of wind speed and wave force and both dynamic and transient responses of the studied system are also analyzed. The simulation results show that the STATCOM integrated with the designed PODC at the bidirectional DC-DC converter of the VRFB-based ESS can offer adequate damping to improve the damping of the dominant mode of studied MMPS. Fig. 1 shows the configuration of an MPSS connected with an integrated wind/oceanic wave farm-based DC MG.

Fig. 1.  Configuration of the studied system.

 

Methods

Fig. 2 plots the control block diagram of the bidirectional DC-DC converter of the proposed VRFB-based ESS, where DS is the duty ratio of two power semiconductor switches inside the bidirectional DC-DC converter. Fig. 3 shows the control block diagram of the DC-DC converter for the proposed VRFB-based ESS including the designed power oscillation damping controller (PODC), where the reference value of the output active power (PVRFB_ref) of the proposed VRFB-based ESS is shown in Fig. 4. The transfer function H(s) of the designed PODC in s domain shown in Fig. 3 is given by

(1)

The designed results for the PODC using phase-compensation method under the wind speed of 11 m/s for the WF and the wave force of 0.9 MN for the WAF are: 1,2 = -0.524  j7.046 rad/s (pre-specified eigenvalue), KSTA = 0.67, TW = 0.45 s, T1 = 0.1448 s, and T2 = 0.0282 s (parameters of the designed PODC).

Fig. 2. Schematic diagram of the employed bidirectional DC-DC converter.

Fig. 3. Control block diagram of the bidirectional DC-DC converter for the proposed VRFB-based ESS including the designed power oscillation damping controller (PODC).

Fig. 4. Control block diagram of the reference value of the output active power (PVRFB_ref) of the proposed VRFB-based ESS shown in Fig. 3.

 

Results

Fig. 5 draws the root-loci plots of the selected modes of the studied system when the wind speed VW is kept at 10 m/s, the wave force of WAF is kept at 0.9 MN, and the moving speed uZ of the floater of the AWS is changed from 0.3 m/s to -0.3 m/s.

Fig. 6 shows the dynamic responses of the studied system when SG3 of the MMPS subject to a torque disturbance of 0.1 p.u. at t = 1 s and lasting for 0.1 s. Figs. 9(a) and 9(b) plot the dynamic responses of the wind speed of the WF and the wave force of the WAF of the studied system, respectively. The corresponding output active powers of the WF and the WAF of the studied system are shown in Figs. 9(c) and 9(d), respectively.

Fig. 5. Root-loci plots of the selected modes when the wind speed VW is kept at 10 m/s, the wave force of WAF is kept at 0.9 MN, and the moving speed uZ of the floater of the AWS is increased from 0.3 m/s to -0.3 m/s.

Fig. 6. Dynamic responses of the studied system when SG3 of the MMPS subject to a torque disturbance of 0.1 p.u. at t = 1 s and lasting for 0.1 s.

 

Discussion

The use of the proposed STATCOM joined with the VRFB-based ESS plus the designed PODC can have the best damping characteristics on the first and third electromechanical (EM) modes of the four SGs (SG1-SG4) of the MMPS and the mode of the VSI and DC link under different wind speeds of WF and various wave forces of WAF. The second EM mode can have the best damping characteristics when the studied system is without the STATCOM joined with the VRFB-based ESS.

It is clearly observed from the comparative dynamic responses that the proposed STATCOM joined with the VRFB-based ESS plus the designed PODC can have the smallest and smoothest responses on the active powers of SG2, SG3, and SG4 than ones without STATCOM. The proposed STATCOM joined with the VRFB-based ESS plus the designed PODC can render the best damping effects to effectively decrease the large output active-power variations of the studied SGs of the MMPS due to the applied three-phase fault.