Wind Generator Impedance Matching in Small-Scale Passive Wind Energy Systems

Abstract

In this paper, the improved turbine power matching of passive wind energy systems for dcconnected battery storage applications with an impedance matching method is investigated. The passive system uses a direct-drive permanent magnet synchronous generator and is directly connected via a diode rectifier to the dc fixed-voltage battery storage. To improve power matching, an external inductance is added to the passive system between the generator and the diode rectifier. A static finite element based solution method is proposed to accurately calculate the necessary external inductance to achieve near maximum power point matching. It is shown that the proposed finite element based calculation method is computationally efficient and excellently suited for generator design optimization, which is critical for this application. It is also shown that by rewinding existing machines for the correct cut-in speed and adding the external inductance for improved power matching, existing machines can be effectively recycled for passive wind energy systems. The proposed static finite element solution method's accuracy and improved power matching are confirmed with measured results on a sub 5 kW power level.

On the Design and Topology Selection of Permanent Magnet Synchronous Generators for Natural Impedance Matching in Small-Scale Uncontrolled Passive Wind Generator Systems

“…The required reactance at base speed is X d = X q = 2.73/2.91 = 0.94 pu, whereas surface-mounted PMSGs with non-overlapping windings have per-unit reactance values that are typically between 0.2 pu and 0.4 pu. Therefore, it is often necessary to add an external inductance, L ext , between the PMSG and the diode rectifier [18]. With external impedance matching, the dq-equations in (1) are then:…”

“…In [10], an analytical model was used to design the PMSG for a passive wind generator system; however, substantial errors of 17% and 26% were reported for the generated torque and back-EMF. Furthermore, in [18], it was also shown that using analytical calculations for the synchronous inductance resulted in a significant error in power matching with the wind turbine. The results in [10,18] confirmed that it is better to use finite-element analysis (FEA) for PMSGs in passive wind generator systems.…”

“…In [18], a method of external impedance matching was used to match the wind generator's power with the wind turbine, whereby an external inductance impedance was connected between the generator and the diode rectifier, shown in Figure 1. Although this method can be used effectively, as was done in [18,19], the additional external inductor is an unwanted component to the system.…”

“…In [18], a method of external impedance matching was used to match the wind generator's power with the wind turbine, whereby an external inductance impedance was connected between the generator and the diode rectifier, shown in Figure 1. Although this method can be used effectively, as was done in [18,19], the additional external inductor is an unwanted component to the system. This incentivised the investigation performed in [20], which was to design PMSGs for a natural impedance matching the wind turbine, i.e., where the internal synchronous inductance of the PMSG alone was sufficient for good power matching.…”

“…This incentivised the investigation performed in [20], which was to design PMSGs for a natural impedance matching the wind turbine, i.e., where the internal synchronous inductance of the PMSG alone was sufficient for good power matching. Hence, this paper is an extension of the work performed in [18,20] and forms part of an overarching study on PMSGs for passive wind generator systems.…”