A New Structure for PMG-Based WECSs With Battery Storage Systems

Abstract

This paper develops and tests the performance of a new structure for grid-connected permanent magnet generator (PMG)-based wind energy conversion systems (WECSs) that have battery storage units (BSUs). The new structure is called the split dc-bus, and it is designed to reduce the pulsations in PMG developed torque and fluctuations in the power delivered to the grid. The reduction in PMG torque pulsations is achieved by employing a 5-level ac-dc power electronic converter (PEC) as the generator-PEC, whose dc outputs are processed by a two-port active dc-link. This active dc-link charges the BSUs and supplies the discharging PEC. The reduction of fluctuations in the delivered power is achieved by discharging the BSUs at point-of-common-coupling (PCC). The generator-side PEC, dc-link, grid-side PEC, and discharging PEC, are operated by a supervisor droop controller. The split-dc bus PMG-based WECS is implemented for performance testing under different wind speeds and levels of power delivery. Test results demonstrate reductions in PMG torque pulsations, along with reductions in the power delivered to the grid. These features of the split-dc bus PMG-based WECS are found to be complimented with a minor sensitivity to the changes in wind speed and changes in the power delivered to the grid. INDEX TERMS Battery storage systems, wind energy conversion systems, permanent magnet generators, torque pulsations, and frequency variations. I. INTRODUCTION A. GENERAL

Parameter Adjustment for the Droop Control Operating a Discharge PEC in PMG-Based WECSs With Generator-Charged Battery Units

“…These previous remarks imply that input dc voltages for the GS-PEC and DS-PEC can be regulated independently from the droop controllers operating these two PECs [2].…”

“…In general, grid-connected power electronic converters (PECs) are operated by nested control loops, which are an inner current control loop and an outer voltage control loop. The reference voltage for the outer control loop is generated by a droop controller, while the reference current vector is generated by voltage controller [2]- [4]. The reference current is typically limited based on the power ratings of the PEC, in order to avoid saturation of the current control loop.…”

“…A small signal state space model of a gridconnected PEC has been developed, and has been used to design various current/voltage controllers without employing droop FIGURE 1. A schematic diagram for a grid-connected PMG-based WECS with generator-charged battery units [2]. The notation MCHB denotes modified cascaded H-bridge.…”

“…1), the PCC is fed by the gridside dc-ac PEC (GS-PEC) and the battery discharge dc-ac PEC (DS-PEC). These two parallel connected PECs are operated by droop controllers with features similar to those discussed in the previous section [2], [4], [21], [22]. For a PMG-based WECS with a structure similar to that in Fig.…”

“…These energy storage systems have modular structure, high efficiency, fast response, and high energy density. Features of BSSs have made them good candidates for applications in WECSs [2], [5]. In order to employ the capabilities of BSSs, accurate, reliable, and dynamic controls are required for the PMG-based WECS and its BSS.…”