Power quality improvement using a dual unified power quality conditioner/uninterruptible power supply in three‐phase four‐wire systems

Abstract

Using a dual compensation strategy, this study proposes the analysis and implementation of active power quality conditioners (PQCs), which are applied for power quality improvement in three-phase four-wire (3P4W) systems. By means of similar control strategy use, the topology employed to implement the PQCs can operate as unified PQC (UPQC), or, through some circuit modifications, as uninterruptible power supply (UPS) system. Considering 3P4W systems, the use of the dual compensation strategy into the PQCs comprised of two four-leg (4-Leg) converters is the main contribution of this study. Different from the conventional strategies, in the dual compensation strategy, the 4-Leg converter connected in parallel with the load is controlled to operate as a sinusoidal voltage source, whereas the 4-Leg converter connected in series between the grid and the load is controlled to operate as a sinusoidal current source. Both the voltage and current controllers are implemented into the synchronous rotating reference frame, and the converters use the three-dimensional space vector modulation technique. Experimental tests, based on a digital signal processor, are performed in order to validate the theoretical development and to verify both static and dynamic performance of the PQC operating as UPQC, as well as UPS system.

Three‐phase four‐wire unified power quality conditioner structure with independent grid current control and reduced dc‐bus voltage operating with inverted/dual compensating strategy

“…To overcome the most problems related to PQ, single‐phase and three‐phase series‐parallel active power‐line conditioners, known as unified power quality conditioners (UPQC), have been employed in there‐phase three‐ and four‐wire systems (3P3W and 3P4W) by means of different configurations and control strategies.…”

“…Usually UPQC topologies applied 3P4W systems are composed of either three‐leg split‐capacitor (3‐Leg‐SC) or four‐leg (4‐Leg) converter topologies performing the parallel and the series conditioning. The main drawback of the 3‐Leg‐SC inverter topology, which uses two capacitors in the dc‐bus, is associated to its higher dc‐bus voltage level when compared to the four‐leg (4‐Leg) topology.…”

“…As a result, this dc‐bus voltage level is enough high to guarantee properly the operation of the S‐APF prevent oversizing in the voltage rate. Thus, the proposed UPQC requires lower dc‐bus voltage when compared to the UPQC that uses two 3‐Leg‐SC topologies, and requires reduced number of power switches when compared to the UPQC the uses two 4‐Leg topologies …”

A 3D-Space Vector Modulation Algorithm for Three Phase Four Wire Neutral Point Clamped Inverter Systems as Power Quality Compensator

“…A three phase four wire inverter system [5] can be used for numerous applications like distributed generation, Static synchronous Compensator (STATCOM), Uninteruptable Power Supply (UPS), Dynamic Voltage Restorer, UPQC to improve the power quality. Conventional 2-level three phase 4-leg inverters have been reported [6,7].…”

Advance Technology in Application of Four Leg Inverters to UPQC

“…Also, it was proved to apply the same scheme to regulate the DC-link capacitor voltage without utilising additional controller. It seems the system to be most robust and powerful for unbalanced conditions.In [7], a dual compensation strategy was implemented to control the nonsinusoidalquantites, which consectively helps in reducing the complexity of algorithms. These current and voltage controllers are implemented into the synchronous reference frame [21]- [23], their control references are continuous, decreasing the steady-state errors when traditional proportional-integral controllers are employed.…”