Power Supply Applications Research Articles

Operational Limits of a Commercial Gate Turn-Off Thyristor for Inductive-Store Systems

This paper details the testing of a commercially available gate turn-off thyristor (GTO) for application in inductive-store power supplies. GTOs have been used as a component of inductive-store systems directly and as part of compound switches. These GTOs are generally available commercially and typically have extensive datasheets. However, the inductive-store application differs significantly from conventional switching applications, which significantly reduces the utility of the datasheets; GTOs are typically used at 100-1000 Hz in a fairly continuous manner, whereas in an inductive-store system, a GTO may be conducting for a relatively long time before doing a single turn off.

A novel DC-DC convertor using LTCC technology for magnetic integration application

A compact DC-DC convertor is proposed and fabricated in multilayer ferrite substrate using LTCC technology. The spiral conductors are buried into the ferrite substrate with a multilayer 3-D structure to reduce the volume of convertor. The passive integration of magnetic components and surface circuitry are achieved in a whole substrate and the size of module can be reduced markedly. The whole height of module is only 3mm, 1/3 of the height of conventional modules. Testing results indicate that the performance of the module is excellent in Point-of-Load (POL) field. The step-down DC-DC converter converts input voltage of 5V to output voltage of 3.3V. It is confirmed that the maximum conversion efficiency of 93.2% is sufficient for actual DC-DC converter application. Such a compact DC-DC convertor provides a compact, low cost and high reliability approach for power supply and magnetic integration application.

Flyback converter with novel active clamp control and secondary side post regulator for low standby power consumption under high-efficiency operation

Flyback converters are widely used in industrial and commercial products because of their advantages of simple structure and low cost. Energy and environmental conservation have prompted interest in high efficiency and low standby power consumption in switch mode power supply applications. However, it is difficult to satisfy both conditions simultaneously because of conflicting design considerations. A novel active clamp control method is proposed for improving power conversion efficiency and reducing standby power consumption in a flyback converter. In addition, an asynchronous-type secondary side post regulator is applied to the converter for minimising standby energy leakage and improving cross-regulation performance for a multiple output channel flyback converter. Operational principles, control schemes, switch stresses and power consumptions are analysed using a converter small signal model and mathematical equations of converter waveforms. The superiority of the proposed converter is verified using experimental results on 110 W prototype.

Ring-dot-shaped Multilayer Piezoelectric Step-down Transformers Using PZT-based Ceramics

In this study, multilayer piezo stack transformers for switching mode power supply (SMPS) application were manufactured using 0.01Pb(Ni1/3Nb2/3)O3 - 0.08Pb(Mn1/3Nb2/3)O3 0.91Pb(Zr0.505Ti0.495)O3 (PNN-PMN-PZT) ceramics. The voltage ratio of a multilayer piezo stack transformer showed a maximum at the resonance frequency of the input and then increased with increasing load resistance. The eciency of the multilayer piezo stack transformer showed its highest value at around the matching load. The output power increased with increasing input voltage. The temperature of the multilayer piezo stack transformer increased with increasing output power and load resistance. The manufactured multilayer piezo stack transformer could be used up to 5 W at a resonance frequency of 70.25 kHz for SMPS application because the temperature rise from room temperature is believed to about 20 C and because the transformer is electrically stable. The newly-developed ring-dot-type step-down multilayer piezo stack transformer shows possible applications as SMPS for electronic power sources with excellent input-to-output properties.

Power Quality Improvement in Switched Mode Power Supplies Using Autoconnected Transformer Based 9-Phase ac-dc Converters

Switched Mode Power Supplies (SMPS) of medium power ratings are extensively used in heating, welding and telecommunication power supply applications. Invariably, they use a 3-phase ac-dc converter at the front end. In this paper, different autoconnected transformer-based 9-phase ac-dc converter configurations are designed, modeled and simulated to feed such medium capacity SMPS for improving the power quality indices at the point of common coupling (PCC). The autoconnected transformer is designed suitable for producing 9-phase voltages of same magnitude and having equal phase shift. The proposed 9-phase ac-dc converters are found capable of suppressing up to 17th harmonic in the supply current along with the power factor improvement close to unity at varying loads. A set of power quality indices on input ac mains and magnetic ratings for various autoconnected transformer configurations for this SMPS are also presented so that the best converter configuration can be chosen according to the requirements for a particular application.

Piezoelectric Micro-power Generation to Charge Supercapacitor with Optimized Duty Cycle

Energy harvesting has been proved to be a novel solution to replace the batteries in remote power supply applications. Unfortunately, the limited capacity and low efficiency of output power constraint the practical applications of energy harvesting in daily life. After a systematic review of previous researches about energy harvesting in power management perspective, a circuit design, which focuses on low-frequency mechanical vibration, is introduced. With classical piezoelectric cantilever configuration, the maximum charging current of a supercapacitor can be obtained by optimizing the duty cycle of a buck regulator through software implemented pulse width modulation. The results of experiments prove the capacitive electric model of the piezo, the existence of maximum charging current of the supercapacitor, and the adaptive control of the designed circuits. With the duty cycle optimized to 2.17%, the maximum charging current of 17.36 mA is measured, which is approximately four times fold of previous researches in similar vibration conditions. An active RFID application is proposed to utilize the harvested power of 67.2 µW.

Conducted-Noise Characteristics of a Digitally-Controlled Randomly-Switched DC-DC Converter with an FPGA-Based Implementation

This paper investigates the conducted-noise characteristics of a digitally-controlled randomly-switched dc-dc converter. In order to investigate the effect of the suggested digital controller on the conducted-noise characteristics of a dc-dc converter, three factors have been studied: the field-programmable gate array (FPGA) clock speed, the randomization ratio percentage, and the effect of using a closed loop feedback controller. A field-programmable gate array is much more flexible than analog control circuits, has a lower cost, and can be used for power supply applications. A novel FPGA-based implementation has been suggested for obtaining the experimental validations and realizing the studied concepts. Furthermore, the experimental results have been discussed and design guidelines have been included.

Predicting effects of blood flow rate and size of vessels in a vasculature on hyperthermia treatments using computer simulation

BackgroundPennes Bio Heat Transfer Equation (PBHTE) has been widely used to approximate the overall temperature distribution in tissue using a perfusion parameter term in the equation during hyperthermia treatment. In the similar modeling, effective thermal conductivity (Keff) model uses thermal conductivity as a parameter to predict temperatures. However the equations do not describe the thermal contribution of blood vessels. A countercurrent vascular network model which represents a more fundamental approach to modeling temperatures in tissue than do the generally used approximate equations such as the Pennes BHTE or effective thermal conductivity equations was presented in 1996. This type of model is capable of calculating the blood temperature in vessels and describing a vasculature in the tissue regions.MethodsIn this paper, a countercurrent blood vessel network (CBVN) model for calculating tissue temperatures has been developed for studying hyperthermia cancer treatment. We use a systematic approach to reveal the impact of a vasculature of blood vessels against a single vessel which most studies have presented. A vasculature illustrates branching vessels at the periphery of the tumor volume. The general trends present in this vascular model are similar to those shown for physiological systems in Green and Whitmore. The 3-D temperature distributions are obtained by solving the conduction equation in the tissue and the convective energy equation with specified Nusselt number in the vessels.ResultsThis paper investigates effects of size of blood vessels in the CBVN model on total absorbed power in the treated region and blood flow rates (or perfusion rate) in the CBVN on temperature distributions during hyperthermia cancer treatment. Also, the same optimized power distribution during hyperthermia treatment is used to illustrate the differences between PBHTE and CBVN models. Keff (effective thermal conductivity model) delivers the same difference as compared to the CBVN model. The optimization used here is adjusting power based on the local temperature in the treated region in an attempt to reach the ideal therapeutic temperature of 43°C. The scheme can be used (or adapted) in a non-invasive power supply application such as high-intensity focused ultrasound (HIFU). Results show that, for low perfusion rates in CBVN model vessels, impacts on tissue temperature becomes insignificant. Uniform temperature in the treated region is obtained.ConclusionTherefore, any method that could decrease or prevent blood flow rates into the tumorous region is recommended as a pre-process to hyperthermia cancer treatment. Second, the size of vessels in vasculatures does not significantly affect on total power consumption during hyperthermia therapy when the total blood flow rate is constant. It is about 0.8% decreasing in total optimized absorbed power in the heated region as γ (the ratio of diameters of successive vessel generations) increases from 0.6 to 0.7, or from 0.7 to 0.8, or from 0.8 to 0.9. Last, in hyperthermia treatments, when the heated region consists of thermally significant vessels, much of absorbed power is required to heat the region and (provided that finer spatial power deposition exists) to heat vessels which could lead to higher blood temperatures than tissue temperatures when modeled them using PBHTE.

Flexible solar cells and modules

Flexible photovoltaic (PV) modules enable a wealth of applications in architecture, clothing integration, or other mobile power supplies. Moreover, a simple and cost-effective roll-to-roll manufacturing of thin film PV modules could in the long run compete with large area glass plate processing for the PV power market. Based upon the optimisation of amorphous, nano and protocrystalline silicon thin films, flexible solar cells grown at temperatures between 40°C and 110°C are described with power conversion efficiency up to 5%. A novel in situ series connection technique establishes monolithic integration of such cells into a PV module by locally masking thin film deposition, without any laser patterning or breaking of the continuous production flow. The first flexible modules from a non-optimised, single junction n-i-p structure demonstrate the function of the in situ series connection, and exhibit a total area efficiency of 3%, resulting from an average single cell efficiency of 3.3% and a total interconnection loss of only 15% over the 40 cm2 module area.

High Resistance Grounding—Avoiding Unnecessary Pitfalls

The high resistance grounding (HRG) of 480-4160-V industrial power systems increases service continuity, enhances personnel safety, and reduces equipment damage when a ground fault occurs. HRG allows maintenance personnel to quickly and safely locate a ground fault while avoiding unscheduled downtime. An abundance of literature has been published on HRG practices since the mid-1970s. Recent years have seen increased application and misapplication of transient voltage surge suppressors and uninterruptible power supplies in HRG power systems. These misapplications and their solutions are discussed. Additionally, engineering oversights in the design of HRG systems are addressed, as well as operations and maintenance issues associated with an HRG system.

High-Voltage IGBT Switching Arrays

Under a Navy SBIR, Diversified Technologies, Inc. (DTI) will design and demonstrate scalable solid state switches in support of future U.S. Navy needs related to power supplies and inverters. One switch approach being developed consists of a massive series-parallel array of high-voltage insulated gate bipolar transistors that are switched synchronously in order to achieve high peak currents. DTI is evolving its technology in high-voltage switching to include very high peak currents. As an objective of the SBIR effort, DTI will utilize these high-power switches to build a power converter. From a practical viewpoint, high-voltage switches that can operate reliably at large currents have potential applications in missile launchers, high-power actuators, and radar power supplies. The massive series-parallel switch array approach has the potential to provide a compact, reliable, and effective switching solution to converting sufficient electrical energy to kinetic energy that could meet a variety of Navy applications. In this paper, DTI reviews current switch requirements and recent SBIR progress toward the goal of demonstrating massive series-parallel high-voltage switching that meets the Navy SBIR requirements.

A Scalar Resonant-Filter-Bank-Based Output-Voltage Control Method and a Scalar Minimum-Switching-Loss Discontinuous PWM Method for the Four-Leg-Inverter-Based Three-Phase Four-Wire Power Supply

An all-scalar-control and pulsewidth-modulation (PWM) approach for the four-leg-inverter (FLI)-based three-phase transformerless four-wire power supply (PS) is proposed. The output voltage of each phase is controlled independently, and its controller is formed by a stationary-frame resonant-filter bank accompanied with proportional-control and output-capacitor current-based active-damping loops. The simple and easy to implement scalar-control method exhibits superior overall steady-state and dynamic performance in the PS applications involving loads with high crest factor and/or significant load imbalance. Utilizing the inverter zero-state partitioning, a generalized form of scalar PWM for the FLI is developed. A novel minimum loss discontinuous PWM method, which provides minimum switching losses under all loading conditions (including load imbalance), is derived. This simple scalar method provides superior performance, and unlike the vector methods, it is easy to implement. The controller and modulator design and implementation details for the system are given. Linear and nonlinear loads for balanced and imbalanced load operating conditions are considered. The scalar-control and PWM methods are proven by means of theory, simulations, and thorough laboratory experiments of a 5-kVA PS.

Fabrication of organic solar array for applications in microelectromechanical systems

We have developed an innovative way to fabricate organic solar arrays for application in dc power supplies for electrostatic microelectromechanical systems devices. A solar array with 20 miniature cells interconnected in series was fabricated and characterized. Photolithography was used to isolate the individual cells and output contacts of the array, whereas the thermal-vacuum deposition is employed to make the series connections of the array. With 1mm2 for single cell and a total device area of 2.2cm2, the organic solar array based on bulk heterojunction structure of π-conjugated polymers and C60 derivative [6,6]-phenyl C61 butyric acid methyl ester produced an open-circuit voltage of 7.8V and a short-circuit current of 55μA under simulated air mass (AM) 1.5 illumination with an intensity of 132mW/cm2. The procedure described here has the full potential for use in future fabrication of microarray with the size as small as 0.01mm2.

Slow-Scale and Fast-Scale Instabilities in Voltage-Mode Controlled Full-Bridge Inverter

This paper discusses the slow-scale and fast-scale instabilities of a voltage-mode controlled full-bridge inverter which is widely used in AC power supply applications. The main results are illustrated by exact cycle-by-cycle simulations. It is shown that the slow-scale instability is a type of low-frequency instability which manifests itself as a Hopf-type low-frequency oscillation in the whole line cycle, whereas the fast-scale instability is a type of local instability which manifests itself as a period-doubling bifurcation in some intervals of a line cycle. An averaged model and an improved discrete-time model are used to theoretically analyze the slow-scale and fast-scale instabilities, respectively. Finally, experimental results are presented to verify the results from simulations and analysis. Our work has revealed more instabilities which are likely to occur in the inverter, and has provided a convenient means of predicting stability boundaries to facilitate the design of the inverter.

A Direct PWM Technique for a Single-Phase Full-Bridge Inverter Through Controlled Capacitor Charging

The controlled-capacitor-charging (CCC) technique is utilized in this paper to synthesize a sinusoidal voltage at the output from the unregulated dc at the input. The method is based on the controlled charging/discharging of a capacitor to realize the desired voltage waveform. A capacitor that is connected across the load is charged/discharged through an inductor by applying high-frequency pulses. The applied pulses could be of either positive or negative polarity, depending on the error signal in the controller. The controller senses the output voltage and current and operates to maintain zero-current switching at every turn-on while keeping the output voltage close to the reference waveform by a tracking-control algorithm, enforcing limits in maximum switching frequency and voltage ripples. This paper presents a direct method of implementing the pulsewidth modulation for the single-phase full-bridge inverter, using the CCC technique. A simple procedure to design such an inverter is also discussed. The proposed controller is simulated in a personal computer simulation program with integrated circuit emphasis. Supporting results from an experimental prototype confirm the usefulness of the proposed controller. The inverter may be used in uninterruptible power supply and many other applications.

Control of High-Speed Solid-Rotor Synchronous Reluctance Motor/Generator for Flywheel-Based Uninterruptible Power Supplies

A hybrid controller, consisting of a model-based feedforward controller and a proportional-integral feedback compensator, for a solid-rotor synchronous reluctance motor/generator in a high-speed flywheel-based uninterruptible power supply application is proposed in this paper. The feedforward controller takes most of the control output of the current regulator based on the machine model, and the PI controllers compensate the possible inaccuracies of the model to improve the performance and robustness of the complete control system. The machine current tracking error caused by parameter inaccuracy in the model-based controller is mathematically analyzed and utilized to dynamically compensate the estimated flux linkage to eliminate the steady-state error in current regulation. Stability analysis is also presented, and it can be seen that the regulation performance and robustness of the system are improved by the proposed hybrid controller. Simulation and experimental results consisting of a flywheel energy storage system validates the performance of the controller.

Active power flow control in a distribution system using discontinuous voltage controller

This paper proposes a hybrid discontinuous control methodology for a voltage source converter (VSC), which is used in an uninterrupted power supply (UPS) application. The UPS controls the voltage at the point of common coupling (PCC). An LC filter is connected at the output of the VSC to bypass switching harmonics. With the help of both filter inductor current and filter capacitor voltage control, the voltage across the filter capacitor is controlled. Based on the voltage error, the control is switched between current and voltage control modes. In this scheme, an extra diode state is used that makes the VSC output current discontinuous. This diode state reduces the switching losses. The UPS controls the active power it supplies to a three-phase, four-wire distribution system. This gives a full flexibility to the grid to buy power from the UPS system depending on its cost and load requirement at any given time. The scheme is validated through simulation using PSCAD.

A Three-Phase UPS That Complies With the Standard IEC 62040-3

This paper proposes a down-sampled discrete-time internal-model-based controller in the synchronous reference frame with a reduced number of poles. This controller is suitable for three-phase pulsewidth modulation inverters with output transformer for double-conversion uninterruptible power supply applications. It is demonstrated that the use of a down-sampled rate and fewer poles in the internal model results in a number of benefits, among which are the following: 1) improvement of the transient response; 2) increase of the stability margin of the closed-loop system; 3) a straightforward implementation in fixed-point digital signal processor (DSP) and microcontroller implementation as well as a reduction of the required memory space; and 4) a simple solution for the saturation of the output transformer. As a result, it is possible to obtain output voltages with reduced total harmonic distortion while ensuring good transient performance for both linear and nonlinear loads. To confirm the advantages claimed for the proposed synchronous reference dq frame internal-model-based controller and to demonstrate the steady-state and transient performance under the test conditions of the International electrotechnical commission standard 62040-3, the experimental results from a 10-kVA space-vector-modulated three-phase inverter, which is fully controlled by a DSP TMS320F241, are presented.

A New Model for Sigma-Delta Modulator Oriented to Digitally Controlled DC/DC Converter

Recent research activities have shown the feasibility and advantages of using digital controller ICs specifically developed for high-frequency switching converters, highlighting a challenging future trend in Switched-mode power supplies (SMPS) applications. Up to a few years ago, the application of digital control for SMPS was impractical due to the high cost and low performance of DSP and microcontroller systems, even if the advantages that digital controllers offer were well known, such as immunity to analog component variations and ability to implement sophisticated control schemes and system diagnostics. Digital controller ICs potentially offer other advantages from the integrated design point of view, such as faster design process, ease of integration with other digital systems, and lower silicon area and power consumption than standard analog ICs. Digital control is also used for implementation of sophisticated control techniques and adaptive control. This paper presents a new modelling methodology of sigma-delta modulator, based on representing the nonlinear quantizer with a linear factor. Its use in DC/DC power converter systems permits implementation of a complete digital control. The digital control is implemented in a field-programmable gate array (FPGA) using a hardware description language (VHDL), providing flexibility and technology independence. Results of an investigation from a buck converter prototype, in terms of simulated and experimental performances, confirm the properties of the proposed approach.

A NEW MODEL FOR SIGMA-DELTA MODULATOR ORIENTED TO DIGITALLY CONTROLLED DC/DC CONVERTER

Recent research activities have shown the feasibility and advan-tages of using digital controller ICs specifically developed for high-frequency switching converters, highlighting a challenging futuretrend in Switched-mode power supplies (SMPS) applications.