Kevin Gaughan

A 12-kVA DSP-Controlled Laboratory Prototype UPQC Capable of Mitigating Unbalance in Source Voltage and Load Current

This paper reports the development of a laboratory prototype of a fully digital DSP-controlled 12-kVA unified power quality conditioner (UPQC), capable of compensating for both the supply voltage and the load current imperfections. A fully digital controller based on the TMS320F2812 DSP platform is implemented for the reference generation as well as control purposes. The delay problem in the digital controller is overcome by application of a fast DSP, a compact control technique and proper flow of control steps in the DSP software. A phase-locked loop-less software grid synchronization method has been implemented for the effective operation of the UPQC under conditions of grid frequency variation. A sequence-based compensation strategy has been developed to compensate for balanced and unbalanced sags while accommodating the fact that the voltage injection capability of the UPQC is limited. The prototype UPQC power circuit, control features, and control algorithm along with experimental results are presented in this paper.

A discussion of anti-islanding protection schemes incorporated in a inverter based DG

The discussion in this paper is about the local anti-islanding protection techniques that are incorporated in a inverter based DG. The most widely used passive and active techniques along with their suitability to reduce the Non-detection zone (NDZ) are explained here. The most recent work using wavelet transform which actually reduces the NDZ to zero is also introduced in the last section of the paper.

Optimising the Rating of the UPQC for Applying to the Fault Ride Through Enhancement of Wind Generation

The unified power quality conditioner (UPQC) is a combination of a shunt and a series compensator cascaded via a DC link capacitor which works on the combined principle of active filtering and dynamic voltage restoration. Therefore, the UPQC can be a potential solution to the grid integration problems associated with fixed speed wind generators including reactive power compensation and fault ride through capability. The hardware design of the UPQC can be made more cost effective by proper selection of the rating of the individual compensators of the UPQC. It is shown in the paper that the application of a fixed capacitor can lower the cost of the UPQC further, without compromising the performance. The fixed capacitor shares the reactive power load with the shunt compensator and the overall rating of the UPQC is reduced. The proposed scheme also helps in reducing the power loss occurring in the power electronic switches as current conduction of the switches is reduced. Simulation results are provided in the paper to support the theory.

Sequence analysis based DSP controller for Dynamic Voltage Restorer (DVR)

The paper examines the behaviour of a dynamic voltage restorer (DVR) under balanced/unbalanced supply voltage sag condition, and restricted DVR injection capability (e.g. limited to 50% of the supply voltage injection). Sequence components of the supply voltage are extracted to generate the reference injected voltage for the DVR. The control determines the maximum possible positive sequence injection within the capacity of the compensator to achieve balanced voltage conditions at the load terminals. The control is verified through simulation and experimentation. The control algorithm has been implemented in a TI320F2812 fixed point DSP and the effectiveness of the controller is verified in a three-phase, 10kVA DVR laboratory prototype. In a three-phase, 240 V system, balanced sag and sag with magnitude and phase unbalance have been created, which is successfully compensated by the DVR with the proposed controller.

Investigation of Wave Farm Electrical Network Configurations

Wave Energy Converters (WECs) have been in development for a number of decades and some devices are now close to becoming a commercial reality. As such, pilot projects are being developed, particularly in the UK and Ireland, to deploy WECs on a pre-commercial array scale. There is little experience in the wave energy or utility industry of designing and installing electrical networks for WEC arrays with the closest comparison being offshore wind farms. There are some key features of WECs which will ultimately dictate that the electrical configuration differs from that of offshore wind farms. This paper investigates the potential representative electrical network configurations for small (10MW), medium (40MW) and large scale (150MW) ‘wave farms’ in order to establish a development path for such projects. The configurations are evaluated for efficiency (power loss), redundancy and short circuit levels. Key interfaces in the electrical infrastructure are identified and discussed. This paper also identifies the key differences between offshore wind farm electrical networks.

Performance comparison of a left shunt UPQC and a right shunt UPQC applied to enhance fault-ride-through capability of a fixed speed wind generator

The enhancement of voltage-ride through capability of a fixed speed induction generator (FSIG) with the help of a unified power quality conditioner (UPQC) is examined. The performance of the left-shunt (LS) and right-shunt (RS) UPQC are compared under both full and partial voltage restoration. From the comparative study, the rating of the UPQCs is determined.

A new configuration and control of doubly fed induction generator (UPQC-WG)

The paper presents detailed simulation based analysis and investigation on grid code compliance of a new configuration of a 2 MW doubly fed induction generator. The converters of DFIG are connected and controlled to function like a unified power quality conditioner (UPQC). One of the converters is connected in series with the stator terminals and acts to maintain the stator voltage at a predetermined value. It can also transfer power to or from the rotor side converter through the common DC link. The other converter is connected to the rotor like a conventional DFIG and is controlled to maintain appropriate rotor currents to establish the operating point based on the input mechanical torque and reactive power set point at the grid connection. The generator performs satisfactorily under steady state and grid fault condition both in the super and sub synchronous speed range. The newly designed machine is Irish grid code compliant.

Development of laboratory prototype of a 12kVA digital shunt active filter

The paper reports the development of a laboratory prototype of a fully digital DSP controlled 12 kVA shunt active filter (ShAF) capable of compensating for non-linear, unbalanced load and reactive power. A fully digital controller is implemented for the reference generation and the current control purposes. The delay problem in digital current controller is overcome by application of a fast DSP, a compact controller and proper flow of control steps in the DSP software. A phase locked loop (PLL)-less software grid synchronization method has been proposed for the effective operation of the ShAF under the grid frequency variation. The source current THD has been improved from 15.8% to 4.45%. The control features, experimental setup, and results are presented in the paper.