Automated and scalable optimal control of three-phase embedded power grids including PLL

Abstract

Embedded grids have been increasingly adopted into applications such as More Electric Aircraft where different power converters are interconnected to each other. Interactions between the grid components poses the risk of instability to the system, more so when in the presence of reduced passive filters. An approach of automated and scalable tuning of such embedded grids with consideration for the dynamics introduced by a PLL is presented in this paper. A structured state feedback optimal control approach is proposed which enables a controller to be synthesised is such a way that maximum performance of the grid can be achieved, whilst guaranteeing power converter synchronisation to the grid, and avoiding instability due to converter interaction, and PLL dynamics.

Decentralised Optimal Controller Design of Variable Frequency Three-Phase Power Electronic Networks Accounting for Sub-System Interactions

“…In doing this an individual three-phase converter can be remodelled as two coupled DC systems. Therefore, DC-based controls, which in general are simpler to design and better understood can be employed [20].…”

“…The superscript P defines terms as observed on the PLL dq frame, and shall be further explained in Section II-C. The non-linear system described in (5)-(7) contains two equilibrium points as defined in (8)-(10) [20]:…”

“…3. The PLL is well discussed in the literature [20], [26] and therefore shall not be described here, however since it is part of the whole global system, its dynamics must be incorporated into the optimisation, and therefore its state-space model must be derived.…”

“…H 2 control had therefore been used, which is less conservative than H ∞ , at the cost of reduced robustness. It was shown in [20], [21] that H 2 does allow for an optimal, and fully decentralised control for the power network. In addition, since the H 2 optimisation uses the whole system model for the development of decentralised controllers, each independent controller is optimised with the knowledge of every other converters closed loop dynamics, and crosscoupled interactive effects.…”

“…Secondly, this paper presents a methodology for optimising a single converter to a wider pre-designed network. In the studies presented in [20] it was assumed that all parameters of the grid were known and accessible. However, in industrial settings, this is not a likely occurrence.…”