Comparisons between CRM and CCM PFC

The paper presents detailed comparisons between CRM (critical conduction mode) and CCM (continuous conduction mode) control schemes used for Boost PFC converter. The two schemes are analyzed and compared under the chips of L6561 and UC 3854 which are commonly used for CRM and CCM respectively. Both schemes are based on multiplier; however, the CCM is more complex and needs more periphery components which increase the cost. The Boost PFC under CRM is easier to be implemented. Nevertheless, the variable switch frequency makes the system (including the power-stage inductor and capacitor) hard to design. It seems that the CRM PFC is more attractive in low power applications which only need to meet IEC61000-3-2 D standard. Some experiment results are also presented for the comparison

A high power factor rectifier based on buck converter operating in discontinuous inductor current mode

By adding a suitable LC filter to the input of a Buck converter, a high-power-factor buck converter is proposed. The converter can operate in the discontinuous-output-current mode operation. A Buck converter in this operation mode features simple control as the constant duty cycle PWM used. The operation condition of the converter is studied. The validity of analysis is verified by Simulation and Experimental results

A single phase current source PFC converter based on UC3854

A novel high-power-factor Buck type converter with average current control based on UC 3854 is proposed. The input current is directly controlled by average current control scheme to deliver sinusoidal input current and to gain a high power factor. The practical results, which illustrate the proposed control philosophy, were obtained from a 120 W AC/DC Buck type converter. The power factor can reach 0.97

Analysis and modeling of buck converter in discontinuous-output-inductor-current mode operation

The Buck converter with LC input filter operating in discontinuous output current mode has a high power factor with a constant duty cycle. A Buck converter in this operation mode can reduce the reverse recovery loss of the freewheeling diode thus increase the efficiency. The operation, power factor analysis and modeling of the converter are studied in this paper. Experimental results are presented to verify the theoretical predictions

Design and modelling of permanent magnet fault current limiter For electrical power applications

As the electrical power grids are extending in capacity with connection of distributed generations, the fault current level is increasing and approaching the capacity limits of the circuit breakers. In this paper, a saturated inductor fault current limiter (FCL) based on permanent magnet biasing has been developed to overcome the inherent disadvantages associated with many previous technologies such as superconducting based techniques. A 3D Finite Element Modeling (FEM) is used to develop and validate the proposed design and compared it with air-cored inductor. A lab-scale prototype was built to verify the design. Furthermore, a scaled up model which could be introduced to 11 kV network is introduced and its electromagnetic performance is evaluate

Impact of distributed PV generation on relay coordination and power quality

Distributed generation (DG) has gained popularity among electricity end users who are determined to contribute to a cleaner environment by conforming to green and sustainable energy sources for various daily needs. The power system impact of such trends (e.g. roof-top solar-PV) need thorough investigation, such as impact on fault current levels on the distribution network. Varying fault current levels could adversely affect the operation of protection relays, which may lead to localized blackouts. Therefore, it is imperative to avoid localised blackouts due to mal-operation of protective relays under high penetration of DGs in distribution network. The focus of this research is to study the importance and implications of protective relays and over-current protection in the presence of distributed generation; where the impact of distributed generation on distribution network is identified. Relay coordination is observed to determine their operation characteristics to avoid mal-operation with the presence of DGs (e.g. solar-PV). This paper uses the UK generic distribution network model to simulate different scenarios in DIgSILENT Power Factory. The resulting power quality measures, such as voltage levels, short-circuit current levels and frequency are presented and discussed in the paper. The research highlights that small-scale DG penetration allows for existing protection infrastructure to continue operation and expensive upgrades for overall network are not required as fault levels remain the same

A Low Power Single-stage LED Driver Operating between Discontinuous Conduction Mode and Critical Conduction Mode

A novel single-stage single-switch (S4) LED driver is proposed in this paper. The paper focuses on the operation principles of the power stage circuit with an operation switched between Critical Conduction Mode (CRM) and Discontinuous Conduction Mode (DCM), including steady state analysis, simulation and backed up by experimental results. The results verify that this proposed LED driver can obtain a high power factor (PF) and the dc output is relatively stable

Automated quantification system for vision through polymer‐dispersed liquid crystal double‐glazed windows: circuit implementation

Polymer‐dispersed liquid crystal automated quantification system for vision through polymer‐dispersed liquid crystal double‐glazed windows: Circuit implementation (PDLC)‐windows played an essential role in providing a visual comfort for occupants in commercial buildings recently. PDLC windows adjust the visible transparency of the glazing to control the daylight accessed to internal environments. A former study proposed an algorithm to quantify the vision through the PDLC glazing in terms of image contrast. The quantification algorithm determines the minimum level of transparency that maintains a comfortable vision through the window. This study introduced the implementation of a real‐time automated system that achieves the vision quantification process. Firstly, system on‐chip was utilised to realise the quantification algorithm, including contrast estimation. Secondly, the contrast determination action was re‐implemented using MATLAB, Cortex‐A9 microcontroller, and Cyclone V field programmable gate array field programmable gate array‐chip. The implemented systems were evaluated based on the latency, throughput, power consumption, and cost

Quantifying of vision through polymer dispersed liquid crystal double-glazed window

The visual linking of a building’s occupants with the outside views is a basic property of windows. However, vision through windows is not yet a metricized factor. The previous research employs a human survey methods to assess the vision through conventional windows. The recently fabricated smart films add a changeable visual transparency feature to the windows. The varied operating transparency challenges the evaluation of vision. Therefore, surveying human preferences is no longer a feasible approach for smart windows. This paper proposes an image-processing-based approach to quantify the vision quality through smart windows. The proposed method was experimentally applied to a polymer dispersed liquid crystal (PDLC) double-glazed window. The system instantaneously determines the available contrast band of the scenes seen through the window. The system adjusts the excitation of the PDLC film to maintain a desired vision level within the determined vision band. A preferred vision ratio (PVR) is proposed to meet the requirements of occupant comfort. The impact of the PVR on vision quality, solar heat gain, and daylight performance was investigated experimentally. The results show that the system can determine the available vision comfort band during daytime considering different occupant requirements

Thermal Loss Reduction Using a Ventilated Double-Glazed Window for Commercial Buildings in Average-Climate Environments

The power consumption of buildings is exacerbated in modern societies. The most effective load in buildings is heating and cooling systems. Numerous studies have been done on energy saving for buildings recently. Windows are one of the most thermal loads that cause the loss of heat from inside to outside a room during winter. This paper demonstrates an alternative insight into the use of double glazed windows in average climate environments. The proposed system uses an air inject system to impact the heat transfer properties of the window considering the trade-off between the heating load energy saving and air injection power consumption. The theoretical analysis showed a reduction of 52 % in the thermal loss of the window, in addition to a declination in the heat transfer coefficient of the window from 3.5 to 1.8 W/m2K. Consequently, an energy saving of 19 % in the heating capacity has been achieved