High Voltage Side Research Articles

Implementation and Control of an AC/DC/AC Converter for Double Wound Flywheel Application

An all-electric driveline based on a double wound flywheel, connected in series between main energy storage and a wheel motor, is presented. The flywheel works as a power buffer, allowing the battery to deliver optimized power. It also separates electrically the system in two sides, with the battery connected to the low voltage side and the wheel motor connected to the high voltage side. This paper presents the implementation and control of the AC/DC/AC converter, used to connect the flywheel high voltage windings to the wheel motor. The converter general operation and the adopted control strategy are discussed. The implementation of the AC/DC/AC converter has been described from a practical perspective. Results from experimental tests performed in the full-system prototype are presented. The prototype system is running with satisfactory stability during acceleration mode. Good efficiency and unity power factor could be achieved, based on vector control and space vector modulation.

Analysis on 2nd Main Transformer Trip Accident of a Certain Substation of the West Inner Mongolia Power Grid

This paper mainly analyzes the causes of a 10KV line and 2nd transformer circuit breaker tripping, also analyzes the action mechanism of the relay protection. Because of the permanent phase fault at the head of the line, instantaneous over-current protection(SegmentⅠ) as its main protection of the phase fault made the 921 breaker triping, the action was selective.And the permanence of this fault led to the failure of the reclosing; Reversed the TA(current transformer) for measuring with the TA for differential protection in high voltage side of the transformer, this fault can also make the TA of the differential protection circuit quickly saturated when the external short-circuit current flowing through the TA. When the above saturation happens, a big differential current generating from differential circuit will lead to sampling error. This is the direct cause of the mal-operation of the differential protection which resulting in the 2nd transformer tripping. In response to this accident, put forward specific prevention measures.

Multiblock Soft-Switched Bidirectional AC–AC Converter Using a Single Loss-Less Active Snubber Block

A multiblock soft-switched bidirectional ac-ac converter using an active snubber is proposed in this paper. The snubber provides zero-voltage switching (ZVS) for the main switches of the entire power converter blocks in the entire input voltages and polarities. To achieve ZVS operation, the snubber block extracts the energy of the main switch drain-source capacitors and delivers it to the high-voltage side. Moreover, the snubber switches have zero-current switching (ZCS) turn-on and ZVS turn-off transitions. The performance of the proposed converter system is evaluated on a prototype including two converter blocks of 500 W working at 150 kHz with an input-voltage range of 110 V (-30% to +20%) and output of 175 V. Experimental results confirm that the proposed snubber improves the efficiency by 3% (4%) at half (full) load power for the entire input-voltage range.

Design and Performance of a Bidirectional Isolated DC–DC Converter for a Battery Energy Storage System

This paper describes the design and performance of a 6-kW, full-bridge, bidirectional isolated dc-dc converter using a 20-kHz transformer for a 53.2-V, 2-kWh lithium-ion (Li-ion) battery energy storage system. The dc voltage at the high-voltage side is controlled from 305 to 355 V, as the battery voltage at the low-voltage side (LVS) varies from 50 to 59 V. The maximal efficiency of the dc-dc converter is measured to be 96.0% during battery charging, and 96.9% during battery discharging. Moreover, this paper analyzes the effect of unavoidable dc-bias currents on the magnetic-flux saturation of the transformer. Finally, it provides the dc-dc converter loss breakdown with more focus on the LVS converter.

Study on a New Program of Passive Fiber Optic Current Sensor

With the raise of the grade of voltage and current in the transmission line, the traditional current transformer based on electromagnetism theory can no longer satisfy the requirement of actual measurement in recent years. Therefore a new method of fiber optic current sensor is presented in this paper. Taking the iron-core coil with air gap as current transformer in high-voltage side, the system loads the weak current signal created by mutual inductance into thin film resistor. And the strength of electric current can be known indirectly by measuring the temperature of thin film resistor. On the basis of its structure and testing conditions, supporting with finite element software ANSYS, a three dimensions model about thin film resistor is developed and thermal analysis on it is done. The temperature characteristics of the device obtained by ANSYS can provide a basis for the analysis on the current transformer.

A power-flow control method for hybrid active front-end converters

The hybrid active front-end converter, which is composed of a capacitor and a voltage source converter in series connection, has been presented recently. Compared with grid-connected converter, the hybrid converter could be operated with reduced dc voltage as well as small-sized passive filters due to series-connected capacitor. This paper presents a power flow control method for a hybrid active front-end converter. Real power of the converter is controlled by the output voltage vector perpendicular to the grid voltage, whereas reactive power of the converter is determined by the output voltage vector parallel to the grid voltage. By dynamically adjusting voltage vector, power conversion between low-voltage dc side, such as PVs or batteries, and high-voltage grid side could be accomplished with no low-frequency transformer required. In addition, a harmonic resistance is emulated in the proposed method to avoid inrush current flowing into the converter due to unintentional voltage spike coming from the power system. Operation principles are explained in detail, followed by both computer simulations and experimental results validating effectiveness.

Study on Optimization Strategy for Voltage and Reactive Power Control of Wind Farm

A method for calculating reactive power limit of wind farm comprised of doubly-fed induction generators (DFIG) is proposed. The reactive power limit of wind farm is the sum of reactive power limit of DFIGs which is calculated by the method considering static stability margin. Based on this, reactive power control of wind farm is discussed and proposed. The proposed reactive power control is divided into different control modes according to power factor of high voltage side in wind farm substation and voltage of low voltage side in point of interconnection(POI). In different control modes, different control objects are applied on reactive power regulation. After reactive power regulation is finished, some reactive power of wind farm should be released. At last, numerical test system is established, the result shows that the proposed method is effective to support voltage of POI

Isolated Winding-Coupled Bidirectional ZVS Converter With PWM Plus Phase-Shift (PPS) Control Strategy

A novel winding-coupled bidirectional dc/dc converter with zero-voltage-switching (ZVS) performance is proposed in this paper. In the low-voltage side, the parallel configuration is employed to share the large current and reduce the current ripple. In the high-voltage side, the series structure is adopted to sustain the high bus voltage and achieve large voltage ratio conversion. There are only two coupled inductors in the proposed interleaved bidirectional converter and their secondary windings are in series to serve as winding-coupled inductors. Furthermore, the two winding-coupled inductors can be integrated into a magnetic core to reduce the passive component numbers and improve the power density. Moreover, ZVS soft-switching operation is implemented for all the power switches to minimize the switching losses by introducing the active clamp scheme. In addition, the pulsewidth modulation plus phase-shift control strategy is employed to reduce the power MOSFET peak current and diminish the circulating losses. The duty cycle is applied to balance the voltages of both sides. The phase-shift angle is introduced to realize the power flow regulation. This decoupling control strategy is advantageous for bidirectional dc/dc conversion to realize high efficiency. Finally, a 1-kW prototype is built to verify the effectiveness of the proposed circuit.

Multivariate Analysis of Transformer Resonant Overvoltages in Power Stations

In this paper, cable-transformer resonant overvoltages are studied on the low-voltage (LV) side of a 410-MVA generator step-up (main) transformer, due to ground fault and energization. The transformer is placed in a network configuration often found in Norwegian hydropower stations. The overvoltages are calculated when systematically varying the length of the high-voltage (HV) side cable and that of the cable between the main transformer LV side and the station transformer. This multivariate analysis is performed efficiently, using frequency-domain calculations and the inverse Numerical Laplace Transform. Time-domain simulations are used for analyzing the critical cases in detail. Both types of calculations make use of a blackbox, wideband model of the transformer, and novel procedures are introduced for initializing computations from correct 50-Hz initial conditions. Among the findings are that extreme overvoltages can occur on the station transformer if current-limiting reactors are placed in series with the cable between the main transformer LV side and the station transformer.

Real-Time Database System Implementation of Railway Signal Power Source Remote Monitoring

Railway signal is a key technology for high-speed railway，which is the foundation to keep the high-speed train line. Railway signal power is the automatic blocking of railway lines and 10kV lines transform into 380V power through after the power supply for railway signals. Signal power as the railway traffic signal of the power supply, it belongs to the first level of power system load. Its 10kV high voltage side stik up by the major of electric, 380V low voltage side maintenance by the signal major. When the signal power failure, often occur shirk responsibilities between the different majors, in order to define the responsibilities of the accident better, which need automation remote monitoring for main railway lines of the railway signal power and scheduling control as soon as possible[1-3].

냉음극 형광램프의 광 전파

The light propagation along a long positive column has been observed in a cold cathode fluorescent lamp. The optical signals are observed with the DC and AC voltage power during lamp operation. The light propagating is observed in the operation with the DC-rippled voltage as well as the AC-voltage. The optical signals propagate from the high voltage side to the ground. These signals show two kinds of features according to the before and after Townsend breakdown. At the dark current before Townsend breakdown, the optical intensity is damped and the propagation velocity is . At the high current of normal glow after Townsend breakdown, the propagation velocity is 1 without damping.

Design and research of fiber optically powered Rogowski coil current transformer

By the two-fiber way to power for the probe in high voltage side and convey the pulse signal, the Rogowski coil photoelectric current transformer is constructed, solving the problem of electrical insulation between high and low voltage sides. The photoelectric conversion efficiency of optical fiber power supply may reach 50%, which can meet the demand of electricity utilization steadily. The digital signal processing method of V/F conversion makes the signal transmission has a strong anti-interference ability, and the experimental results show that this method for maximum error is 2% in the input range of 0∼50A.

Optimal voltage support mechanism in distribution networks

Optimal scheduling of voltage regulators (VRs), fixed and switched capacitors and voltage on customer side of transformer (VCT) along with the optimal allocation of VRs and capacitors are performed using a hybrid optimisation method based on discrete particle swarm optimisation and genetic algorithm. Direct optimisation of the tap position is not appropriate since in general the high voltage (HV) side voltage is not known. Therefore, the tap setting can be determined given the optimal VCT once the HV side voltage is known. The objective function is composed of the distribution line loss cost, the peak power loss cost and capacitors' and VRs' capital, operation and maintenance costs. The constraints are limits on bus voltage and feeder current along with VR taps. The bus voltage should be maintained within the standard level and the feeder current should not exceed the feeder-rated current. The taps are to adjust the output voltage of VRs between 90 and 110% of their input voltages. For validation of the proposed method, the 18-bus IEEE system is used. The results are compared with prior publications to illustrate the benefit of the employed technique. The results also show that the lowest cost planning for voltage profile will be achieved if a combination of capacitors, VRs and VCTs is considered.

Fault ride through capability enhancement for self-excited induction generator-based wind parks by installing fault current limiters

This study presents a new technique for improving the fault ride through (FRT) capability of self-excited induction generator (SEIG)-based wind parks by implementing fault current limiters (FCLs) using the electromagnetic transient program simulation program (PSCAD/EMTDC). A non-inductive high-temperature superconducting coil of an FCL is developed comprising its major components, operation control algorithm, sequence of events and fault detection techniques. The test system is adopted with an integrated 80 MW SEIG-based wind park that comprises a static synchronous compensator (STATCOM) at each wind turbine. A novel damping voltage control algorithm for the STATCOM is presented for improving the FRT and damping the power system oscillation. FCLs are installed in series with the high voltage (HV) side of the substation transformers of the wind park. The operation of the FCLs is tested in the proposed system to demonstrate its superior performance for reducing the high fault currents and improving the FRT capability. The system performance is tested in steady-state operation and in response to system contingencies, taking into account the impact of the short circuit ratios on the transient stability margin with and without FCLs. Thereafter, the simulation results are presented to demonstrate the effectiveness of installing the FCLs for improving the FRT and transient stability margin of the wind park.

Design of 33kV Transformer Bushing Insulator from NR and HDPE

Abstract This research presents a design of transformer bushing insulation at high-voltage wire connection side. The bushing insulator is made from composite materials between natural rubber (NR) and high-density polyethylene (HDPE). The HDPE has been utilized to increase a weather resistance property of natural rubber, such as ultraviolet resistance, temperature, heat resistance, and so on. The blend ratio of materials depends on NR 60% and HDPE 40%. To study properties of insulator material, it is tested by using ASTM D2240, ASTM D412, ASTM D257-99 and ASTM D149-05 standard. The test results shown that the composite material has a tensile strength equal to 4.28 ± 5.4 MPa, volume resistivity more than 2.14 × 1016 Ω-cm and surface resistivity about 5.56 × 1016 Ω/square. This insulation material can be withstanding a maximum AC power frequency voltage about 19.7 kV/mm. In additional to design, the electric field distribution around the bushing insulator is analyzed by using a finite element method (FEM). The highest electric field strength occurs at wire connector and equal to 0.95 kV/mm. Finally, the developed bushing insulator has been installed on 33 kV distribution systems at Saraburi province.

A Double Wound Flywheel System under Standard Drive Cycles: Simulations and Experiments

Flywheel systems are attractive for use in electric vehicles, being able to efficiently handle the large power needed for acceleration and regenerative braking. A double wound flywheel machine, divided in two different voltage levels by the windings, acting like a rotating transformer, is studied.The flywheel stator windings have two sides: a low voltage side connected to the battery and a high voltage side connected to the wheel motor. The load variations on the high voltage side have minimal affect on the low voltage side of the system, in which the speed control of the machine is performed.In this paper the functionality of the system is investigated by means of simulations and experiments. Different standard drive cycles are applied on the high voltage side to assess the effect of load variations in the system as a whole and particularly in the speed control. The response of the speed control system is investigated with computer simulations and experimental verification. The energy storage in the flywheel allows a steady power supply from the battery via the inverter, proving the functionality of the system.

Isolated Bidirectional Full-Bridge DC–DC Converter With a Flyback Snubber

An isolated bidirectional full-bridge dc-dc converter with high conversion ratio, high output power, and soft start-up capability is proposed in this paper. The use of a capacitor, a diode, and a flyback converter can clamp the voltage spike caused by the current difference between the current-fed inductor and leakage inductance of the isolation transformer, and can reduce the current flowing through the active switches at the current-fed side. Operational principle of the proposed converter is first described, and then, the design equation is derived. A 1.5-kW prototype with low-side voltage of 48 V and high-side voltage of 360 V has been implemented, from which experimental results have verified its feasibility.

Three-Level Bidirectional Converter for Fuel-Cell/Battery Hybrid Power System

A novel three-level (3L) bidirectional converter (BDC) is proposed in this paper. Compared with the traditional BDC, the inductor of the 3L BDC can be reduced significantly so that the dynamic response is greatly improved. Hence, the proposed converter is very suitable for fuel-cell/battery hybrid power systems. In addition, the voltage stress on the switch of the proposed converter is only half of the voltage on the high-voltage side, so it is also suitable for high-voltage applications. The operation principle and the implementation of the control circuit are presented in detail. This paper also proposes a novel bidirectional soft-start control strategy for the BDC. A 1-kW prototype converter is built to verify the theoretical analysis.

Study of Transformer Resonant Overvoltages Caused by Cable-Transformer High-Frequency Interaction

Power transformers can fail from dielectric stresses caused by electromagnetic transients. In this paper, we focus on a special phenomenon where excessive overvoltages arise due to resonance. This situation can take place when a transformer on the high-voltage side is connected to a cable and the low-voltage side is unloaded. Very high overvoltages can then result on the low-voltage side from transient events that cause a weakly attenuated overvoltage on the cable with a dominant frequency matching a resonance peak in the transformer voltage ratio. Laboratory tests on a 11-kV/230 V distribution transformer show that a step voltage excitation on a 27-m cable produces 24-p.u. overvoltage on the open low-voltage side. The voltage waveforms are accurately reproduced by a black-box model obtained from frequency sweep measurements. Simulations show that overvoltages as high as 43 p.u. could occur with the most unfavorable cable length. It is further shown that the following situations can lead to high overvoltages on an unloaded transformer low-voltage side: 1) ground fault initiation at the far cable end, 2) cable energization from a busbar with several other cables connected, 3) cable energization from another cable with the same length, and 4) capacitor bank energization at the far cable end.

Implementation of Full-Bridge Current-Fed Resonant Boost Converter using PIC microcontroller

This paper presents a current-fed full-bridge boost DC-AC-DC converter with transformer isolation operating without switching power dissipation. The output voltage is regulated by dc-ac converter whose frequency changes with a constant turn-off time of transistors. The proposed converter is devoid of parasitic oscillations, as all of the parasitic capacitances and inductances are included in a resonant tank circuit. The main advantage of such systems is that they include a capacitive output filter, which is preferred in higher voltage applications. Moreover, it achieves ZCS for all active switches and zero-voltage switching (ZVS) operation for all diodes on high voltage side, which is an additional benefit. In this paper, the system operation is first explained, then a mathematical description that is useful for its design is provided, and finally, a report on the implementation of a laboratory prototype with 125W power is presented.