A portable multifunctional power box

In this study, we used a microcontroller to provide and control power to multiple sources using the highly efficient energy storage provided by the direct current (DC) bus of a lithium iron phosphate (LiFePO₄) battery. Through multiple loops, high-efficiency buck and boost conversion, and DC-to-alternating current (AC) conversion, the power box can quickly and simultaneously provide three sets of voltage outputs, 5-V DC, 19–22-V DC, and 110-V AC, to different electronic devices. Multiple sets of conversion output voltages were achieved using multiple sets of conversion circuits, in parallel to the DC bus. Compared with a single conversion output voltage, the multiple sets of conversion output voltages from the energy storage battery had a higher practicability. For a single output voltage, the battery provided a suitable voltage to different electric devices via a substage converter, thus lowering the overall conversion efficiency. For practical applications such as camping, blackouts, long journeys, emergencies, and rescues, the multiple sets of converted voltage outputs offer substantial functional convenience. For safety control, we used a single-chip controller to quickly detect various overcurrent situations.     

A new power standard for audio-frequency measurements

A thermal power comparator for audio-frequency measurements is presented. It is essentially a double-bridge-type multiplier that consists of two multijunction thermal converters that contain two heaters. Together with a precision inductive voltage divider and current transformer for extending the voltage and current range, the comparator ensured a high-precision power standard with an AC/DC transfer error of less than 15 p.p.m. in the audio-frequency range     

A grid-tie PV inverter with the ability to improve power quality under unbalanced and distorted source voltage conditions

ABSTRACT

This paper proposes a grid-tie PV inverter that is able to improve power quality under conditions of both distorted and unbalanced source voltage. The presented strategy is based on the instantaneous power theory and uses a second-order generalized integrator-quadrature signal generator (SOGI-QSG). The presented control strategy is aimed at compensating reactive power, eliminating current harmonics, load balancing, and enabling the PV to inject maximum power to the grid. The advantages of the control system are the use of SOGI-QSG adaptive filter and frequency-locked loop (FLL), and removing the low-pass filter and phase-locked loop (PLL). DC–DC and DC–AC converters are utilized for connecting the PV to the grid. The DC–DC and DC–AC converters are responsible for maximum PV power tracking and achieving the control aims, respectively. Using 4-leg converter structure for grid-tie inverter enables achieving the control objectives in 3-phase 4-wire distribution network without any transformer. The presented control strategy is applied to a 3-phase 4-wire distribution network and is simulated in MATLAB/SIMULINK environment. The results of this simulation are then compared with the conventional instantaneous power method in areas including load balancing, reactive power compensation and the elimination of current harmonics, under unbalanced and distorted source voltage conditions.     

Design and implementation of PV-based three-phase four-wire series hybrid active power filter for power quality improvement

This paper proposes a Photovoltaic (PV)-based three-phase four-wire Series Hybrid Active Power Filter (SHAPF), it comprises of a Series Active Power Filter (SAPF) and an LC shunt passive filter. The proposed system eliminates both the current and voltage harmonics and compensates reactive power, neutral current and voltage interruption. A SAPF demands a source of energy for compensating the voltage sag/swell. This system found a new topology for SHAPF which utilizes the PV with DC–DC boost converter as a source of DC power for the series active filter. The compensation current reference evaluation is based on the twin formulation of the vectorial theory of electrical power theorem with Fuzzy Logic Controller (FLC). The PV array/battery managed DC–DC boost converter is employed to step up the voltage to meet the DC bus voltage requirement of the three-leg Voltage Source Inverter (VSI). The foremost benefit of the proposed system is that, it will provide uninterrupted compensation for the whole day. This system utilizes the renewable energy; accordingly saves the energy and provides the uninterruptable power supply to critical/sensitive load, through the PV array/battery bank during both day time and night time. An experimental model was established and results were obtained, which indicated the capability of the proposed control scheme.     

Introduction to fuel cells and hydrogen technology

Whereas the 19th century was the century of the steam engine and the 20th century was the century of the internal combustion engine, it is likely that the 21st century will be the century of the fuel cell. Full cells are now on the verge of being introduced commercially, revolutionising the way we presently produce power. Fuel cells can use hydrogen as a fuel, offering the prospect of supplying the world with clean, sustainable electrical power. The article discusses the history of fuel cells, fuel cells for NASA, alkaline fuel cells for terrestrial applications and PEM fuel cells. Fuel cell applications in transportation, distributed power generation, residential and portable power are discussed. The science of the PEM fuel cell and the direct methanol fuel cell are discussed. Benefits of fuel cells and obstacles to their widespread introduction are briefly outlined.     

Feedforward simple control technique for on-chip all-digital three-phase AC/DC power-MOSFET converter with least components

A novel simple control technique for on-chip all-digital three-phase alternating current to direct current (AC/DC) power-metal oxide semiconductor field-effect transistors (MOSFET) converter with least components, which is employed to obtain small current and DC output voltage ripples as well as excellent performance, and using a feedforward simple control method for DC output voltage regulation is proposed. The proposed all-digital feedforward controller has the features of low cost, simple control, fast response, independence of load parameters and the switching frequency, it has no need for compensation, and high stability characteristics; moreover, the proposed controller consists of three operation amplifiers and few digital logic gates that are directly applied to the three-phase converter. The power-MOSFETs are also known as power switches, whose control signals are derived from the proposed all-digital feedforward controller. Instead of thyristors or diodes, the application of power-MOSFETs can reduce the loss of AC/DC converter that is proper to the power supply system. The input stage of an AC/DC converter functions as a rectifier and the output stage is a low pass inductor capacitor (LC) filter. The input AC sources may originate from miniature three-phase AC generator or low-power three-phase DC/AC inverter. The maximum output loading current is 0.8 A and the maximum DC output ripple is less than 200 mV. The prototype of the proposed AC/DC converter has been fabricated with Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 2P4M complementary MOS (CMOS) processes. The total chip area is 2.333 1.960 mm². The proposed AC/DC converter is suitable for the following three power systems with the low power, DC/DC converter, low-dropout linear regulator and switch capacitor. Finally, the theoretical analysis is verified to be correct by simulations and experiments.     

敏感用户高品质交-直流级联供电方案研究

工业过程中大量使用的变频器(variable frequency drive,VFD)在采用传统交流供电时易受到电压暂降影响,传统治理方式存在检测延时、控制复杂等问题。为此,该文从敏感负荷变频器在电网扰动工况下的供电需求量化出发,围绕供电拓扑设计、DC/DC变换器的控制策略及储能单元容量配置等方面,构建一种实用化工业用交-直流级联供电方案。该文利用电压暂降过程中直流供电回路与敏感负荷间的压差自感应控制,实现交-直流供电回路无扰动切换,提高电压暂降治理响应的快速性;采用两相交错并联DC/DC变换器接入集中式储能,减少储能系统纹波系数,并给出两相均流控制方法。最后,通过Matlab/Simulink中的建模仿真与样机的实验测试,验证所提方案能够在交流系统发生不同严重程度电压暂降过程中为各类敏感负荷提供稳定的连续供电,为解决工业敏感用户高品质供电问题提供可实用的新思路。     

A single-stage AC/DC converter based on zero voltage switching LLC resonant topology

A zero voltage switching based on LLC resonant topology is proposed to implement a single-stage AC/DC converter which performs both input-current harmonics reduction and power factor correction (PFC). By integrating a boost-PFC cell and an LLC resonant DC/DC cell into a single power conversion stage, the power losses in the secondary rectifier diodes and the primary switches can be significantly reduced. The proposed architecture exhibits extreme simplicity and lower cost while providing nearly unity power factor and well-regulated output; hence, the proposed converter is very suitable for low power level applications. The operating principles and design procedures for the proposed converter are analysed and discussed. Simulation and experimental results from a 125 W laboratory prototype are provided to verify the feasibility.     

Integrated power management circuit for piezoelectronic generator in wireless monitoring system of orthopaedic implants

Piezoelectric (PZT) materials are capable of converting the mechanical energy of compression into electrical energy. With the recent advent of extremely low-power electrical devices, PZT generators have become attractive in many kinds of applications, especially for biomedical applications. Piezoelectronic generators are used in a wireless monitoring system of orthopaedic implants. Due to their poor source characteristics, the efficiency of PZT generator is low. A hybrid direct current (DC)?DC, comprising a switched capacitor (SC) DC?DC converter and a low dropout (LDO) linear voltage regulator, is presented to improve conversion efficiency. A bandgap reference (BGR) circuit which works in sub-threshold region is also presented. Because SC DC?DC converter works in the highest voltage region in this system, small power supply current, including supply current through BGR and other auxiliary modules, means low power consumption. BGR?s power supply voltage can be varied from 3 to 16 V. Its supply current is only 3.2 μA at 125 C and its temperature coefficient is 46 ppm. Stacked switches technique is proposed to reduce leakage current in switching process of SC converter. Simulation results show that the efficiency of SC?s converter can reach 88%, that of LDO can reach 80% and that of the overall system can reach 66%, including power consumption of all auxiliary components, which is far higher than previous work.     

Novel zero voltage switching dual-switch forward converter with ripple current cancellation

A zero voltage switching (ZVS) dual-switch forward converter with ripple current cancellation is presented. In the proposed converter, active clamp circuit is used to clamp the voltage stresses and to realise ZVS of all switching devices. Active clamp boost converter with power factor correction is used in the front stage of the proposed converter to draw a sinusoidal line current from the AC source and to maintain a constant voltage at the DC bus. The second stage of the proposed converter is a dual-switch forward converter with current doubler rectifier to obtain the isolated low output voltage. Active clamp circuit used in the DC/DC converter can recycle the energy stored in the leakage inductor and magnetising inductor so that the voltage stresses on the switches are limited and the ZVS feature is realised. The current doubler rectifier offers the ripple current cancellation at the output capacitor and reduces the current stress of the transformer secondary winding. The circuit configuration and principle of operation are analysed and discussed in detail. Experimental results with a laboratory prototype based on a 90-260 V_rms input and 12 V/30 A output were provided to verify the effectiveness of the proposed converter.     

The relationship between microsystem technology and metrology

Microsystem technology (MST) has enabled silicon sensors to evolve from simple transduction elements to microsystems (micro-instruments) that include readout circuits, self-test, and auto-zeroing facilities. This paper discusses the impact of MST in the instrumentation and measurement (I&M) field. In metrology, in particular, the development of electrical reference standards by using microtechnology has opened a wide variety of potential applications, such as the Josephson junction array (DC voltage reference) and thin-film multijunction thermal converters (AC voltage and AC current reference). It is shown that MST has even more to offer to the I&M field. Two devices that have highly benefited from MST. thermal and capacitive RMS-to-DC converters are discussed in historical perspective., Subsequently, a recently developed microdevice, the pull-in voltage reference, which may have a huge impact in I&M applications, is outlined. Finally, it is demonstrated that recent developments in electrical and nonelectrical metrology system concepts offer special opportunities for on-chip cointegrated silicon microsystem realizations     

Dynamics on a ZCZVT soft-switching DC/DC boost converter

The non-floating switches, zero-current–zero-voltage-transition (ZCZVT) soft-switching DC/DC boost power converter is proposed in this article. The AC small-signal mathematical model for the ZCZVT boost converter is then derived. It shows that the ZCZVT boost converter exhibits better dynamical behavior than the conventional PWM boost converter. The accuracy of theoretical results is verified by experiments and simulations. In addition, a classical and a modified integral variable structure controllers are designed to achieve output voltage regulation. They are used to eliminate the effect of the variations of input voltage and load on the output voltage. The performances of the proposed converter with these controllers are also validated by experimental results.     

Offshore wind farm with centralised power conversion and DC interconnection

The study of a hypothetical large offshore wind farm based on centralised power conversion and interconnected to the grid using a multiterminal parallel high voltage direct current (HVDC) link is presented. The 300 MW wind farm consists of 60 squirrel-cage based 5 MW generators connected to a common DC bus using ten voltage source converters (VSCs). The transmission system converters provide variable speed generator control, and therefore individual converters are not required for each wind generator, implying savings in wind farm costs. The paper studies the technical and economical benefits of the proposed topology, as well as the selection of the main components. A detailed analysis of the control circuits for both generator and grid facing converters, with respect to primary control functions, is also given. PSCAD/EMTDC simulation of the proposed concept is presented for realistic wind signals. The results confirm operation at an average optimum coefficient of performance at each respective generator group, as well as satisfactory stability even for severe wind speed changes. The proposed concept reduces the costs associated with DC interconnection and may simplify integration of large offshore wind farms at substantial distances.     

A simplified time-domain design and implementation of cascaded PI-sliding mode controller for dc–dc converters used in off-grid photovoltaic applications with field test results

A time-domain design methodology for voltage regulation control of dc–dc boost and buck-boost converters based on a multi-loop controller with PI regulator for the outer loop and an inner loop with sliding mode current controller has been developed for renewable energy applications such as photovoltaic (PV)-fed dc–dc converters. This paper proposes a new method for the design of PI regulators in such multi-loop control scheme. The proposed design presents a simple analytical method for selecting controller gains and has been validated by simulation as well as hardware implementation. Also, this paper presents an illustrative example based on the proposed design for the voltage regulation control of PV-fed boost converters for off-grid applications. The simulation results for varying irradiation, temperature and load along with stability analysis have been presented in this paper. The proposed controller is implemented in hardware for a 1.1 kW PV-array-fed boost converter. Performance analysis based on field test results using real-time weather data validates the proposed design. Therefore the proposed controller could be considered as an attractive solution for off-grid renewable energy applications like PV- or fuel-cell-fed dc–dc converter, where the variations are stochastic in nature.     

Low voltage surface transverse wave oscillators for the next generation CMOS technology

The design and performance of voltage controlled surface transverse wave oscillators (VCSTWO) in the lower gigahertz frequency range, operating on supply and tuning voltages in the 1.2 to 3.3 V range, and suitable for direct interfacing with the next generation CMOS circuits are presented. By applying the "boost" principle, as used in direct current (DC)-DC converters, to the design of the sustaining amplifier, the VCSTWO outputs are switched between 0 V and a positive peak value, exceeding the supply voltage Us, to provide safe CMOS-circuit switching while keeping the radio frequency (RF)/DC efficiency to a maximum for low DC power consumption. The investigated 1.0 and 2.5 GHz VCSTWO are varactor tuned feedback-loop oscillators stabilized with two-port surface transverse wave (STW) resonators. Each VCSTWO has a DC-coupled, high-impedance switched output to drive the CMOS circuit directly, and an additional sinusoidal 50 ohmz high-power reference output available for other low-noise system applications. Phase noise levels in the -103 to -115 dBc/Hz range at 1 kHz carrier offset are achieved with 1.0 GHz VCSTWO at a RF/DC efficiency in the 21 to 29% range. The 2.5 GHz prototypes demonstrate phase noise levels in the -97 to -102 dBc/Hz range at 1 kHz carrier offset, and efficiencies range between 8 and 15%.     

Transient response analysis of a Rosen-type piezoelectric transformer and its applications

This paper investigates the characteristics of voltage transient response, such as the maximum voltage, direct current (DC) time constant, alternating current (AC) time constant and oscillation frequency, and their applications for a Rosen-type piezoelectric transformer (PT). The transient response is induced immediately after an AC voltage connected to the PT is switched off. For the applications, the maximum voltage is used to elucidate how to cause an electrical shock for users of the PT under open-circuit operation. The DC time constant and the AC time constant are used to estimate the equivalent resistance of the mechanical loss and the dielectric resistance of the dielectric loss, respectively. Also, the AC time constant is used to estimate the quality factor of the PT. Additionally, the oscillation frequency is used as an antiresonant frequency of the PT. In order to verify the above characteristics and applications, both an equivalent circuit with initial conditions and a drive system with a control switch interposed between the PT and its AC voltage source are adopted to derive the transient response and measure its characteristics. Effects of the load resistance of the PT and the switching-off time of the voltage source on the transient response are measured and discussed.     

Single-stage unity power factor based electronic ballast

This paper deals with the design, modeling, analysis and implementation of unity power factor (UPF) based electronic ballast for a fluorescent lamp (FL). The proposed electronic ballast uses a boost AC–DC converter as a power factor corrector (PFC) to improve the power quality at the input ac mains. In this single-stage UPF based electronic ballast, boost PFC converter and a half bridge series resonant inverter (HBSRI) share a common power switch. Thus one power switch is reduced as compared to the conventional two-stage approach. The design, modeling, analysis and implementation of this topology were carried out in MATLAB-Simulink environment for a T8 36 W, 220 V, 50 Hz fluorescent lamp. The switching frequency was kept more than the resonant frequency of the inverter, to ensure the zero voltage switching (ZVS) operation of both power switches. This resulted in reduction of high frequency switching losses. The power quality parameters such as displacement power factor (DPF), distortion factor (DF), power factor (PF), crest factor (CF) and total harmonic distortion of ac mains current (THD_i) were evaluated to analyze the performance of proposed electronic ballast. Test results on a developed prototype of PFC electronic ballast were included to validate the design and simulated results.     

Automation and Evaluation of Two Different Techniques to Calibrate Precision Calibrators for Low Frequency Voltage Using Thermal Devices

Low frequency (LF) voltage and current are important parameters in electrical metrology. The standards for LF voltage and current are established by assigning AC–DC transfer difference to thermal devices, i.e. thermal converters or thermal transfer standard along with current shunts. Automated calibration systems have been developed based on Null method and measurement technique developed by Budovsky for calibration of precision calibrator in LF voltage and current against thermal devices. The technique based on the Algorithm developed by Dr. Ilya Budovsky (National Metrology Institute (NMI), Australia) has been compared with the conventional null technique. Indigenously developed software has been used to calibrate the precision calibrator in the entire LF voltage and current range using Holt thermal converters and current shunts. Calibration results at 1 V, 10 V in the frequency range from 10 Hz to 1 MHz as well as calibration results of 1 A in the frequency range from 40 Hz to 10 kHz are presented in this paper. These result shows that the measurement technique developed by Budovsky has reduced the complexity of AC–DC transfer measurements, measurement time and the uncertainty in measurement.     

Analysis of thyristor DC chopper power converters including nonlinear commutating reactors

Dc chopper power converters are used to control the power supplied to a dc load from a dc source. In a battery-powered vehicle, for example, a dc chopper can control the dc series traction motor. Thyristors are favored for the switching element in high power applications. The particular circuit described here can be used as a voltage step-down converter or a voltage step-up converter and uses two auxiliary thyristors to turn off the main power thyristor. The behavior of the step-up circuit is described by exactly the same equations as the step-down circuit when the input voltage is replaced by the load voltage and the load current is replaced by the input current. The analysis treats the general case where saturating reactors are used to soften the commutation of current in the power semiconductors. The nonlinear characteristics of these reactors are approximated by two linear segments when molybdenum-Permalloy powder cores are used. Linear or square-loop cores are included by the theory as special cases. A design synthesis based on the analytical equations is best performed with the aid of a computer.     

Soft-switching flyback inverter with enhanced power decoupling for photovoltaic applications

A novel single-phase flyback inverter for photovoltaic applications is proposed to achieve low-frequency ripple current reduction on the DC busbar and to draw sinusoidal current into the AC grid. Based on capacitive idling techniques, the proposed circuit topology is derived from a single-ended primary-inductance converter and two-switch flyback inverter to obtain soft-switching operation for all of the active switches. Compared with a buck-boost inverter and other flyback inverter topologies for AC photovoltaic module systems, no extra active switches are used in the proposed inverter to realise both soft-switching and enhanced power decoupling with only four active switches. Peak-current mode control method is employed in the control schemes to ensure pure sinusoidal current with unity power factor on the AC grid. Laboratory experimental results based on a 500 W prototype are provided to verify the effectiveness of the proposed inverter