High Voltage Side Research Articles

A Nonintrusive Power Supply Design for Self-Powered Sensor Networks in the Smart Grid by Scavenging Energy From AC Power Line

An advanced metering and monitoring system based on autonomous, ubiquitous and maintenance-free wireless sensor networks is of great significance to the smart grid. However, the power supply for sensor nodes (especially those installed on high-voltage side) remains one of the most challenging issues. To date, miniaturized, reliable, low-cost and flexible designs catering the massive application of self-powered sensor nodes in the smart grid are still limited. This paper presents a nonintrusive design of power supply to support the sensor network applied in the smart grid. Using a cantilever-structured magnetoelectric (ME) composite, the energy harvester is able to scavenge energy from the power-frequency (50 Hz) magnetic field distributed around the transmission line. Design considerations for this specific type of scavenger have been discussed, and optimized energy harvester prototypes have been fabricated, which are further tested on a power line platform. Experimental results show that the single-cell and double-cell energy harvesters are capable of producing 0.62 mW and 1.12 mW at 10 A, respectively, while corresponding power outputs are enhanced to 4.11 mW and 9.40 mW at 40 A. The good energy harvesting ability of this particular ME composite indicates its great potential to make a nonintrusive, miniaturized, flexible and cost-effective power supply, which possesses great application prospects in the smart grid.

Novel High-Conversion-Ratio High-Efficiency Isolated Bidirectional DC–DC Converter

This paper proposes a novel high-conversion-ratio high-efficiency isolated bidirectional dc-dc converter. The proposed converter is operated in the step-down stage. The dc-blocking capacitor in the high-voltage side is used to reduce the voltage on the transformer, and the current-doubler circuits are used in the low-voltage side to reduce the output current ripple. The energy stored in the leakage inductance is recycled to the dc-blocking capacitor. When the proposed converter is operated with a step-up function, dual current-fed circuits on the low-voltage side are used to reduce the current ripples and conduction losses of the switches in the low-voltage side. The voltage-doubler circuit in the high-voltage side increases the conversion ratio. The proposed converter can achieve high conversion with high efficiency. Experimental results based on a prototype implemented in the laboratory with a high voltage of 200 V, low voltage of 24 V, and output power of 200 W verify the performance of the proposed converter. The peak efficiency of the proposed converter in the high-step-down and high-step-up stages is 96.3% and 95.6%, respectively.

A Four-Phase High Voltage Conversion Ratio Bidirectional DC-DC Converter for Battery Applications

This study presents a four-phase interleaved high voltage conversion ratio bidirectional DC-DC converter circuit based on coupled inductors and switched capacitors, which can eliminate the defects of conventional high voltage conversion ratio bidirectional DC-DC converters in terms of high-voltage/current stress, less efficiency and low-power limitation. Parallel channels are used to reduce current stress at the low-voltage side and series connected switched capacitors are used to enlarge voltage conversion ratio, reduce voltage stress and achieve auto current sharing. This paper proposes the operation principle, feature analysis and optimization design considerations. On this basis the objectives of high voltage conversion ratio, low voltage/current stress, high power density, high efficiency and high-power applications can be achieved. Some experimental results based on a 500 W prototype converter (24 V to 48 V at low-voltage side, 400 V at high-voltage side) are given to verify the theoretical analysis and the effectiveness of the proposed converter.

Bidirectional Semiconductor Transformer using high frequency resonant converter

This paper describes a prototype of modularized 3-phase semiconductor transformer which was developed in the lab for feasibility study. The developed prototype is composed of three units of single-phase semiconductor transformer coupled in Y-connection. Each single-phase unit has multiple units of high-voltage high-frequency resonant AC-DC converter, a low-voltage hybrid-switching DC-DC converter, and a low-voltage hybrid-switching DC-AC inverter. Also each single-phase unit has two DSP boards to control converter operation and to acquire monitoring data. Monitoring system was developed based on LabView by using CAN communication between the DSP board and the PC. Through diverse experimental analyses it was verified that the prototype operates with proper performance under normal and sag condition. The developed prototype confirms a possibility to fabricate a commercial high-voltage high-power semiconductor transformer by increasing the number of series-connected converter modules in high-voltage side and improving the system efficiency with a new switching device such as SiC device.

INDUCTION HEATING TOPOLOGY WITH ASSYMETRICAL SWITCHING SCHEME

Domestic induction appliances require power converters that feature high efficiency and accurate power control in a wide range of operating conditions. To achieve this, modulation techniques play a key role to optimize the power converter operation. A softswitching high-frequency resonant inverter for induction heating applications is used here. Three switches are used in this topology, one switch in the high voltage side and two switches in the low voltage side. The working of the circuit is illustrated by adopting the operating principle of the high frequency resonant inverter in periodic switching equivalent circuit mode. The topology is advantageous compared to full bridge topology since the number of switches is reduced in this topology. The switching stresses are also reduced due to the soft switching operation of the circuit.

Comparative Analysis of Modified Isolated Resonant Converters for Photovoltaic Application using Bidirectional Switch

paper represents a comparative study of isolated resonant topologies for photovoltaic application such as half bridge, full bridge and push pull topology. The performance of these topologies is analyzed with the help of Pulse Width Modulation (PWM) technique. The stressful behavior of the switches is reduced by soft switching technique. So, the primary side switches utilize zero voltage switching (ZVS) and output diodes utilize zero current switching (ZCS). A bidirectional switch is used at the high voltage side to provide voltage regulation over fixed frequency PWM control. Simulation results are performed by using a MATLAB- SIMULINK.

New zero voltage switching DC converter with flying capacitors

A new soft switching converter is presented for medium power applications. Two full-bridge converters are connected in series at high voltage side in order to limit the voltage stress of power switches at Vin/2. Therefore, power metal–oxide–semiconductor field-effect transistors (MOSFETs) with 600 V voltage rating can be adopted for 1200 V input voltage applications. In order to balance two input split capacitor voltages in every switching cycle, two flying capacitors are connected on the AC side of two full-bridge converters. Phase-shift pulse-width modulation (PS-PWM) is adopted to regulate the output voltage. Based on the resonant behaviour by the output capacitance of MOSFETs and the resonant inductance, active MOSFETs can be turned on under zero voltage switching (ZVS) during the transition interval. Thus, the switching losses of power MOSFETs are reduced. Two full-bridge converters are used in the proposed circuit to share load current and reduce the current stress of passive and active components. The circuit analysis and design example of the prototype circuit are provided in detail and the performance of the proposed converter is verified by the experiments.

Influence of the winding design of wind turbine transformers for resonant overvoltage vulnerability

Switching transients and earth faults may lead to resonant overvoltages at wind turbine transformer terminals as well as inside High Voltage (HV) and Low Voltage (LV) windings. The winding design in a transformer could strongly influence the internal voltage distribution as function of frequency, and this has a great impact on risk of insulation failure. In this paper, resonant overvoltages in three winding designs; layer, disc and pancake, are investigated and analyzed for the application in offshore wind farm. To achieve this, a prototype 500 kVA transformer with the three winding types on the HV side and taps for voltage measurements is designed and produced. The measurements show that a HV winding of layer type gives the highest transferred voltage to the LV terminal and that this happens at 1.6 MHz which could be excited for close-up earth faults. Although disc winding seems the least vulnerable when measuring the transferred voltage to the LV terminal, it has higher potential of internal resonances in the HV winding compared to the two other types both voltage-to-ground and voltage drops. Pancake and layer windings have less vulnerability in the case of internal resonances. Pancake windings have modular design characteristic. This advantage eases the repair for offshore wind applications.

Modular Snubberless Bidirectional Soft-Switching Current-Fed Dual 6-Pack (CFD6P) DC/DC Converter

This letter presents a modular naturally clamped snubberless bidirectional soft-switching current-fed dual 6-pack (CFD6P) dc/dc converter to interface two dc buses of large voltage difference such as 24 V and 380 V. It is therefore suitable for energy storage, uninterruptible power system, renewable energy system, vehicle, and micro-grid applications. The proposed novel secondary modulation technique forces the currents through the primary-side (low-voltage side) devices to reverse its direction resulting in zero-current switching (ZCS) or natural commutation of current-fed low-voltage side devices. Secondary-side (high-voltage side) devices are turned-on with zero-voltage switching (ZVS). In addition, the resonance between the device parasitic capacitance and transformer leakage inductance achieves ZVS turn-on of the primary-side devices. Thus, the converter maintains a zero-voltage zero-current switching of the current-fed devices and ZVS of high-voltage devices. High-current applications needs short-circuit protection and that is built-in the converter inherently. It limits the peak current and circulating current through the devices resulting in low kVA rating devices. Steady-state operation, analysis, and design of the proposed converter have been studied and explained. Experimental results for 1-kW laboratory prototype have been demonstrated as a proof of concept to validate the claims.

The Design of a Low Power Consumption High-voltage Side for Current Transducer

Traditional current transformer (CT) has more and more problems in the process of development, and a new hybrid current transformer (HOCT) obvious advantages, still need to focus on one of the core problems is the problem of high voltage side processing system power. The greater the power consumption of high end processing system, power link the more complex the cost is higher; Reduce the power consumption of the high pressure end processing system can well solve the problem. The low power design of high pressure end processing system are introduced, the main measures are given, and mainly introduces the program design. After data results confirmed that the design in this paper, high pressure processing system can greatly reduce power consumption.

A Non-Isolated Bidirectional Soft Switching Current fed LCL Resonant DC/DC Converter to Interface Energy Storage in DC Microgrid

This paper proposes a current-fed non-isolated soft-switching bidirectional dc/dc converter for interfacing energy storage to dc microgrid. The proposed converter employs a current-fed half-bridge boost converter at front-end followed by an LCL resonant circuit to aid in soft-switching of semiconductor devices. A voltage doubler at output is selected to enhance the gain by $2 \times $ . The LCL resonant circuit also adds a suitable voltage gain. Therefore, the topology offers overall high voltage gain without transformer or large number of multiplier circuits. For buck operation, high side voltage is first divided by half with capacitor divider to gain higher stepdown ratio. Converter operates at high switching frequency to realize merits of reduced magnetics and filters. Zero voltage turn-on is achieved for all switches and zero current turn-on and turn-off is achieved for all diodes for both buck/boost operation. Voltage across switches and diode is clamped naturally without any external snubber circuit. Detailed analysis and design have been proposed. A proof-of-concept experimental prototype rated at 350 W has been designed, developed, and tested in the laboratory to demonstrate the performance and validate the claims of the converter for wide load variation.

Naturally Clamped Snubberless Soft-Switching Bidirectional Current-Fed Three-Phase Push-Pull DC/DC Converter for DC Micro-Grid Application

A current-fed three-phase push-pull bidirectional dc-dc converter is proposed with unique features of natural zero current commutation and natural device voltage clamping. The proposed topology is suitable for uninterruptible power supply, storage, renewable energy sources, and interfacing two dc buses of 48- and 380-V dc buses in a dc microgrid. The proposed converter implements a novel and innovative modulation that results in natural commutation with zero current switching (ZCS) and device voltage clamping of low voltage side (LVS) current-fed devices, and zero voltage switching (ZVS) turn-on of high voltage side (HVS) voltage-fed devices. It eliminates the use of passive/active clamp circuits to mitigate the turnoff voltage spike across the devices, a traditional problem associated with current-fed topologies. Additionally, the higher ripple frequency reduces the volume of the transformer and the input inductor, making it suitable for high-power applications. The detailed modulation scheme, steady-state operation, and analysis, design, and soft-switching conditions have been explained. Simulation results obtained using PSIM 9.3 have been illustrated to verify the modulation, analysis, and proposed design. Experimental results have been demonstrated for full load (1 kW), half-load (500 W), and 20% load conditions on a proof-of-concept hardware prototype to validate the claims and performance. The efficiency is plotted against various load conditions for a wide range of battery voltage variation (40-59 V). Peak efficiencies of 95.8% and 93.8% are obtained at half-load condition for an input voltage of 59 V and nominal voltage (48 V), respectively. The experimental results for battery charging (reverse direction) using dual phase-shift plus pulsewidth modulation are given. The ZVS of HVS switches and the synchronous rectification of LVS active switches are shown through experimental results.

Reliability 'H' scheme of HV/MV substations

Substations (HV/MV) connect transmission and distribution systems with consumers of electric energy. The selective search method was used for calculation of substation reliability, where all arrangement elements were grouped into blocks. Subject of the analysis was H-arrangements comprising air-insulated switchgears on the high voltage side of HV/MV substations with different number of feeder and transformer bays and diverse scope of the installed switching equipment. Failure rate and duration were used as main HV/MV substation equipment reliability indices. A large number of arrangements were classified into groups, and within a group the arrangements were ranked with the use of multiple criteria. It is shown that the reliability of the electricity transit depends on the equipment of field for the transit of electricity, which favors poorly equipped field. On the other hand, the reliability of transformation of the full power depends mostly on the equipment in coupling field. It is essential that in the coupling field, there are at least two disconnectors. Installation of the switch in the coupling field is meaningful only with appropriate protection, because it further improves reliability. Conclusions are drawn for phased construction and expansion of the single pole diagram with an additional field for the transmission line.

Battery Energy Storage System for PV Output Power Leveling

Fluctuating photovoltaic (PV) output power reduces the reliability in power system when there is a massive penetration of PV generators. Energy storage systems that are connected to the PV generators using bidirectional isolated dc-dc converter can be utilized for compensating the fluctuating PV power. This paper presents a grid connected energy storage system based on a 2 kW full-bridge bidirectional isolated dc-dc converter and a PWM converter for PV output power leveling. This paper proposes two controllers: a current controller using the d-q synchronous reference and a phase-shift controller. The main function of the current controller is to regulate the voltage at the high-side dc, so that the voltage ratio of the high-voltage side (HVS) with low-voltage side (LVS) is equal to the transformer turns ratio. The phase-shift controller is employed to manage the charging and discharging modes of the battery based on PV output power and battery voltage. With the proposed system, unity power factor and efficient active power injection are achieved. The feasibility of the proposed control system is investigated using PSCAD simulation.

Comparative Analysis of the Calculation Results of Online Short-Circuit Current Based on PSASP and Fault Wave Recording

In daily operation process,the results of online short-circuit current calculation and fault wave recording is different, the differences between the two results affected the dispatcher’s decision. In-depth analysis of the calculation process and finding the possible causes of the differences should be done. The on-line PSASP short-circuit current calculation based on power flow and scheme was studied. The boundary conditions and calculation models of two methods were studied, the influence of the modeling scope and equivalent circuits to the short-circuit current was also studied. Fault wave recording calculated short-circuit current through forward calculation, the middle to both sides calculation and backward calculation, and the differences of the three calculation mode were also analyzed. Through the above analysis and comparison, online data equivalent to 220kV high voltage side of the transformer greatly impacts short-circuit current, but effective value calculation method of fault wave recording has a little impact on the short-circuit current, mainly in the following reasons, the first one is that non-dispatching power plant is equivalent to a load, the second one is that several different types of load is equivalent to a load using one load model, the third one is that all devices connecting to low voltage side of the 220kV transformers are equivalent to 220kV. Conclusions of the analysis can provide the basis for the practical work of online short-circuit current calculation.

Practical Implementation of Coordinated Q-V Control in a Multi-Machine Power Plant

This paper presents details of the practical implementation of a coordinated reactive power-voltage controller (CQVC) developed for a multi-machine steam power plant. The CQVC performs optimal coordination of the synchronous generators' reactive power outputs in order to maintain the total reactive power delivered by a steam power plant (SPP) or the voltage at a steam power plant HV busbar. This is required to achieve slow preventive control of generated reactive powers in order to maximize reactive power reserves along with slow high side voltage control. The CQVC is designed to act through existing automatic voltage regulator inputs, thus no modification of an existing excitation system was made. In order to increase the robustness to changes in operating conditions and to achieve the desired shape of the reactive power response, the two-step predictor corrector method is implemented. A newly developed algorithm for steady state detection ensures non-interference of reactive power voltage control with excitation system response. The paper also presents practical design solutions to overcome limitations posed by application to a real system. Acceptance and functional tests carried out during the commissioning of the CQVC are also discussed in this paper.

Research on Critical SVG Technology for Low Voltage High Power Load

impact loads, such as submerged arc furnace, are often used in the smelting industry, their features include high power, low voltage, high current, rated power is from several MVA to tens of MVA, rated voltage is less than 200V. Reactive and harmonic compensation scheme for such load is generally centralized compensation on high voltage side of the power grid, facts have proved that, the effect of such compensation mode is not satisfactory to customers. Therefore, people have designed a special low voltage high power SVG, which is installed on the low voltage side for compensation, it could perform reactive power compensation, and filter out harmonic, protect against grid voltage fluctuation and flicker caused by submerged arc furnace in different production periods effectively.Compared with common SVG project, how to guarantee safe and stable operation of the equipment under high current conditions is critical technical issue in the design. This paper takes an example of an actual project, designs water-cooled copper pipe bus as connecting bus of low voltage high power SVG. Rationality and feasibility of this design has been proved in actual equipment operation.

Corona generated Radio Interference of the 750 kV AC Bundle Conductors in Sandy and Dusty Weather Condition in the High Altitude Area

Sandy and dusty weather condition often occurs in the high altitude areas of China, which may greatly influence the corona generated radio interference (RI) characteristics of the bundle conductors of 750 kV AC power transmission lines. Corona generated RI of the conductors of the 750 kV AC power transmission lines used in practice is measured by EMI receiver with a coupling circuit and a coupling capacitor connected between the high voltage side and the earth side in fine and sandy and dusty condition. The measuring frequency is 0.5 MHz, and the quasi-peak detection is used. RI excitation function is calculated based on the corona RI current measured by the EMI receiver. Corona generated RI characteristics were analyzed from sand concentration and sand particle size. The test result shows that the corona generated RI excitation function is influenced by the sandy and dusty condition. Corona discharge of the conductors is more serious in sandy and dusty condition with an ultraviolet (UV) detector. Corona generated RI excitation function increases with the increase of sand concentration and also increases with the increase of particle size.

Analysis of an Interleaved Resonant Converter for High Voltage and High Current Applications

This paper presents an interleaved resonant converter to reduce the voltage stress of power MOSFETs and achieve high circuit efficiency. Two half-bridge converters are connected in series at high voltage side to limit MOSFETs at <TEX>$V_{in}/2$</TEX> voltage stress. Flying capacitor is used between two series half-bridge converters to balance two input capacitor voltages in each switching cycle. Variable switching frequency scheme is used to control the output voltage. The resonant circuit is operated at the inductive load. Thus, the input current of the resonant circuit is lagging to the fundamental input voltage. Power MOSFETs can be turn on under zero voltage switching. Two resonant circuits are connected in parallel to reduce the current stress of transformer windings and rectifier diodes at low voltage side. Interleaved pulse-width modulation is adopted to decrease the output ripple current. Finally, experiments are presented to demonstrate the performance of the proposed converter.

Traceability of DC high voltage measurements using the Josephson voltage standard

This paper introduces a new methodology for obtaining high voltage DC measurements traceability to the International System of Units (SI) at the Egyptian National Institute for Standards (NIS). The traceability has been achieved via the NIS automated 10 V DC Josephson Voltage Standard (JVS). A 100kV DC voltage divider with a nominal voltage ratio of 10,000:1 is being used with its display in parallel with a high sensitive digital voltmeter. The traceability has been realized by calibrating this digital voltmeter via the JVS system and then it has been used to calibrate the divider display readings. Moreover, the divider ratio has been accurately calibrated using a traceable calibrator source on its high voltage side and the calibrated digital voltmeter on its low voltage side. Accurate and traceable high voltage values have been obtained associated with their expanded uncertainties. Highly improved uncertainties have been achieved using this new calibration technique.