Control System for Multi-Inverter Parallel Operation in Uninterruptible Power Systems

Abstract

This paper proposes a network communication system applied in a control strategy for parallel-connected multi-inverters, which is based on a distributed control system and a redundant communication system. The control system is produced by a Phased-Locked Loop (PLL) synchronism algorithm, a voltage controller and a parallelism controller. All control systems are based on instantaneous values and in the parallelism control the inverters share a single voltage reference signal. The communication system, which is the main focus of the paper, is based on two buses: one analog, which is a measurement taken from the electrical grid; and one digital, comprised of a Controller Area Network (CAN). The former allows the reference voltage of all inverters to be in synchronism and the latter keeps the reference voltage in synchronism even during a grid power outage. There is a PLL algorithm in each Voltage Source Inverter (VSI), which ensures the synchronism between the internal reference and external signal received from the grid or from the CAN. The proposed networked control system was verified in three 5 kVA three-phase VSIs operating in parallel. Experimental results with static and dynamic tests and with electrical grid interruption and return, were obtained. The networked control system is redundant and it provides increased reliability, thus it can be applied in the parallel operation of an on-line Uninterruptible Power Supply (UPS).

Unraveling Bidirectional Converter Capabilities: a Didactic Platform for Proving Dual-Direction Operation Based on Current Injection

“…This procedure, commonly referred to as "disturb and linearize" [25], involves representing all state space variables (x(t)) as a combination of static gains (X, V L , and D) and small time-varying disturbances ( x(t), vL (t), and d(t)). This transformation is demonstrated in (8)(9)(10). Following the disturb and linearize process, the nonlinear terms can be disregarded, and the Laplace transform can then be applied to derive the linear transfer functions.…”

“…In the context of uninterruptible power sources, bidirectional converters are used to provide continuous and reliable power during electricity outages [8], [9]. They allow the energy stored in storage systems, such as batteries or capacitor banks, to be converted and made available to power critical devices during grid disruptions.…”

D-Transform Based Control of Power Converters

“…The design of non-conventional methods for solving power electronics and control problems is an emerging area [1], [2]. There are many reasons to use non-classical techniques, such as energy savings, cost reductions and, obviously, the increase of dynamic performance, large stability margin, and high robustness [3], [4], [5]. Therefore, this paper presents a new perspective regarding the control of static power converters that play a key role in several emerging applications including power systems [6], transformers [7], dc micro-grids [8] - [9], electric vehicles and aircrafts [10] - [11]], integrated energy systems [12], photovoltaic systems [13] l, cyber-physical systems [2], inverters [14], etc.…”