Active Power Supply Research Articles

Identification of the refrigerant pressure in split-type air conditioners based on harmonic analysis of electricity supply current

An analysis is presented of the interdependence between power supply characteristics of single phase split-type air conditioners and pressure of the operating fluid (refrigerant) within the air conditioner system. On the basis of the tests performed by a real air conditioner the corresponding correlations have been established. Of special interest is the influence of refrigerant pressure on the level of the second harmonic of the supply current and active input power of air conditioner. The established correlations allow that by processing the input current and voltage of an air conditioner one can make a diagnosis of the state of refrigerant pressure within the system which is a fast, comfortable, and ecologically better approach compared to the classic direct measurement on the operating fluid by a pressure gauge.

Effective active power control of a high penetration wind diesel system with a Ni–Cd battery energy storage

High penetration (HP) Wind Diesel Hybrid Systems (WDHS) have three modes of operation: Diesel Only (DO), Wind Diesel (WD) and Wind Only (WO). The HP-WDHS presented in this article consists of a Wind Turbine Generator (WTG), a Diesel Generator (DG), the consumer Load, a Ni–Cd Battery based Energy Storage System (BESS), a discrete Dump Load (DL) and a Distributed Control System (DCS). The DG includes a friction clutch which allows the Diesel Engine (DE) to be engaged (DO and WD modes)/disengaged (WO mode) to the Synchronous Machine (SM). The DCS consists of a sensor node which measures the SM speed and active power, calculates the reference active power PREF necessary to balance the active power in the WDHS and communicates this PREF value through a message to the BESS and DL actuator nodes. In the WD mode both the DG and WTG supply active power to the system and the DE speed governor regulates the system frequency. However in an HP-WDHS the power produced by the WTG (PT) can be greater than the one consumed by the load (PL). This situation means a negative power in the DG (power inversion) with its speed governor unable to regulate frequency. To avoid this situation, the DCS must order coordinated power consumption to the BESS and DL in order to keep the DG produced power positive. In this article it is shown by simulation how the DCS manages both a temporary power inversion and a permanent one with the mandatory transition from WD to WO mode. The presented graphs for frequency, voltage, active powers of the system elements and battery voltage/current show the effectiveness of the designed control.

Islanding detection of inverter-based distributed generation

An active islanding detection technique for an inverter-based distributed generator (DG) is presented. Two control strategies are studied: one in which the DG only supplies active power and one in which the DG supplies both active and reactive power to improve the power factor. The nondetection zone (NDZ) of the over/under voltage and frequency protection (OVP/UVP and OFP/UFP) method for each control strategy is determined. For the presented interface control, it is observed that the NDZ of the OVP/UVP and OFP/UFP is larger when the DG interface is designed to improve the power factor. In order to decrease the NDZ, an islanding detection method is designed that is based on creating a mismatch between the load and DG reactive power, thus forcing the frequency to deviate outside the OFP/UFP limits. It is shown that the proposed islanding detection technique is robust and has a negligible NDZ.

Flying capacitor multilevel PWM converter based UPFC

A unified power flow controller (UPFC) based on the flying capacitor (FC) multilevel voltage-source converter (VSC) topology with phase-shifted sinusoidal pulse-width modulation (PWM) control is presented. This converter allows higher power handling, potentially lower power loss, lower harmonic distortion and hence less filtering requirements when compared with the typical two-level counterpart. The series converter injects a voltage with controlled magnitude and phase, to control the active/reactive power flow in a transmission line. The shunt converter absorbs/ supplies active power demanded by the series converter to maintain a constant DC link voltage, also providing independent reactive support to the network. A complete model of the proposed UPFC system is shown and control circuits are described in the synchronous d-q frame. Finally, simulation results are provided to confirm the robustness of the proposed system.