Inverter reactive power control for the integration of distributed generation

Thesis

This thesis sets out to answer the following question:

To what extent can inverter reactive power control, combined with voltage regulators, increase network effciency and hosting capacity of distributed generation?

The first part of this thesis is concerned with analytic methods for studying this question; therefore, a two-bus network model is used. Two aspects of the problem are considered using this model. Firstly, the maximum power transfer capabilities of distributed generation are considered. This bounds the maximum generation of a network, even if the marginal costs of both real and reactive power are zero. It is shown that losses caused by the reactive power and generation result in maximum power transfer before stability limits, in networks with high impedance (R=X) ratios.

Secondly, analytic bounds on a proposed 'relative energy loss fraction' are derived in closed form, using the LinDistFlow approximate solution. The bounds are validated by comparison with both the exact solution of the two-bus equations, and on a set of unbalanced distribution networks. The relative energy loss fraction was found to be as high as 30%, with the approximate bounds able to estimate the true bounds to within 5%.

The next part of this thesis studies how reactive power and taps can be used to increase hosting capacity under uncertainty in the locations and sizes of domestic generation. A linear method is proposed that is shown to reduce the computing runtime by as much as 1000 times. A proposed hosting capacity sensitivity is shown empirically to correlate well with the error caused by linearization. Centralised control of taps and regulators are shown to increase hosting capacity by as much as 70%.

Finally, an optimization is proposed to study the impact of taps and domestic inverter control on the feeder total power draw. The use of regulator control in isolation results in benefits of up to a 5% reduction in feeder power; the use of inverter reactive power control further reduces the feeder power by up to 0.5% of the load. A control scheme is proposed with a reduced communications overhead, which can obtain up to 97% of the potential benefits of full inverter control.

Authors: Deakin, M

• DOI: 10.5287/ora-zoyyr80qx
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English