An Integrated Nine-Switch Power Conditioner for Power Quality Enhancement and Voltage Sag Mitigation

Abstract

A nine-switch power converter having two sets of output terminals was recently proposed in place of the traditional back-to-back power converter that uses 12 switches in total. The nine-switch converter has already been proven to have certain advantages, in addition to its component saving topological feature. Despite these advantages, the nine-switch converter has so far found limited applications due to its many perceived performance tradeoffs like requiring an oversized dc-link capacitor, limited amplitude sharing, and constrained phase shift between its two sets of output terminals. Instead of accepting these tradeoffs as limitations, a nine-switch power conditioner is proposed here that virtually "converts" most of these topological short comings into interesting performance advantages. Aiming further to reduce its switching losses, an appropriate discontinuous modulation scheme is proposed and studied here in detail to doubly ensure that maximal reduction of commutations is achieved. With an appropriately designed control scheme then incorporated, the nine-switch converter is shown to favorably raise the overall power quality in experiment, hence justifying its role as a power conditioner at a reduced semiconductor cost.

Coordinated Control Strategies with and without Circulating Current in Unified Power Quality

“…The sum of the active power from the gird source, SC and PC is given by (16) which is just about the active power consumed by the loads. …”

“…Ignoring the power losses of the converters and lines, the SC capacity and the PC capacity can be obtained by (17) and (18) according to (6), (9) and (16). (19) Selecting a suitable angle  can optimize the capacity allocation of the SC and PC to realize a high economic benefit, a low investment cost and a small equipment capacity.…”

“…Meanwhile, the PC simultaneously fulfills reactive power compensation and harmonic elimination and is usually in heavy-load status. Nowadays, control strategy research on UPQC capacity allocation is usually limited to the case of voltage sags [16]- [19]. There are few references on the capacity allocation between the SC and the PC when the grid voltage is normal.…”

Optimal Control of a Compact Converter in an AC Microgrid

“…Therefore, several studies have been reported in the literature employing reduced switch count converters in different areas [5][6][7][8][9][10][11][12][13]. The reduced switch count has been employed in unified power quality conditioner (UPQC) using only ten switches in [5] and using nine-switches in [8].…”

Loss comparison of different nine-switch and twelve-switch energy conversion systems

“…Based on slightly different topological principles, a more recent example can be found almost simultaneously in [5] and [6], where the nine-switch converter is proposed to save three switches. The nine-switch converter has since been tested for single and dual motor drives [5] [7], uninterruptable power supplies [6] and unified power quality conditioners [8] with its performance noted to be not always satisfactory for some of them [7]. This is no doubt linked to performance constraints introduced by its reduced switch count, which are also experienced by other reduced-switch topologies.…”