Power Loss Of Converter Research Articles

Optimization of Hybrid Energy Storage Systems for Vehicles with Dynamic On-Off Power Loads Using a Nested Formulation

In this paper, identification of an appropriate hybrid energy storage system (HESS) architecture, introduction of a comprehensive and accurate HESS model, as well as HESS design optimization using a nested, dual-level optimization formulation and suitable optimization algorithms for both levels of searches have been presented. At the bottom level, design optimization focuses on the minimization of power loss in batteries, converter, and ultracapacitors (UCs), as well as the impact of battery depth of discharge (DOD) to its operation life, using a dynamic programming (DP)-based optimal energy management strategy (EMS). At the top level, HESS optimization of component size and battery DOD is carried out to achieve the minimum life-cycle cost (LCC) of the HESS for given power profiles and performance requirements as an outer loop. The complex and challenging optimization problem is solved using an advanced Multi-Start Space Reduction (MSSR) search method developed for computation-intensive, black-box global optimization problems. An example of load-haul-dump (LHD) vehicles is employed to verify the proposed HESS design optimization method and MSSR leads to superior optimization results and dramatically reduces computation time. This research forms the foundation for the design optimization of HESS, hybridization of vehicles with dynamic on-off power loads, and applications of the advanced global optimization method.

Techno-economic analysis of DC power distribution in commercial buildings

Improvements in building end-use efficiency have significantly reduced the energy intensity of new buildings, but diminishing returns make it a challenge to build very-low energy buildings cost-effectively. A largely untapped efficiency strategy is to improve the efficiency of power distribution within buildings. Direct current (DC) distribution with modern power electronics has the potential to eliminate much of the power conversion loss in alternating current (AC) building distribution networks that include photovoltaics and DC end uses. Previous literature suggests up to 15% energy savings from DC power distribution in very energy efficient buildings with onsite generation and battery storage. This paper extends prior energy modeling of DC versus AC distribution in buildings, to consider the cost of implementing DC systems on a life-cycle basis.A techno-economic analysis framework based on commercially available products that evaluates the cost-effectiveness of DC systems is presented. The analysis is conducted for three commercial building types in two California climate zones and for various PV and battery storage capacities. Monte Carlo simulation is used to compute the payback period and lifecycle cost savings of DC versus AC distribution systems. A future-market scenario is also examined, which evaluates how future efficiency improvements in power converters and changes in electricity tariffs may affect cost savings. This analysis shows that DC systems can be cost-effective in all scenarios that include large capacities of battery storage and onsite solar, whereas for systems without storage, DC distribution is generally not cost-effective.

Delta-Channel Modular Multilevel Converter for a Variable-Speed Motor Drive Application

Delta-channel modular multilevel converter (MMC) proved successful for zero/low-fundamental-frequency operation without injecting common-mode voltage. However, its application in a medium-voltage variable-speed motor drive is not verified. This paper develops a variable-speed motor drive system based on a delta-channel MMC. The converter power losses together with the compensation strategies are analyzed, and accordingly the submodule capacitor voltage controls are elaborated. The converter controls cascaded with the advanced motor control form the entire control scheme for the drive system. The system performances are tested based on a 4160-V 1-MW simulation model and 208-V 5-kW experimental setup. The results show that the delta-channel MMC along with the proposed control algorithm performs satisfactorily in a driving motor from standstill to a rated speed even under rated torque condition.

An improved topology for high power soft-switched power converters

The push to higher switching frequencies and a desire for lower losses in high power converters requires that switching losses be significantly reduced. Resonant, soft-switching technologies such as the ARCP (Auxiliary Resonant Commutated Pole) attempt to minimize power converter losses by switching the semiconductors at zero voltage or zero current. Deficiencies, however, exist in current ARCP topologies. A novel configuration has been demonstrated that achieves better performance than a conventional ARCP while maintaining essentially the same efficiency and nearly the same power density. This paper describes our new approach and gives simulation and experimental results. A 10 kW, 3-phase inverter, used primarily for driving induction motors, has been constructed and used to experimentally verify the concept.

Luminescent Properties of RE-Doped Mullite (Al6Si2O13) Phosphors for Energy Conversion from UV to Visible Rays

Introduction Leveraging of solar energy is a key issue in the world. The world’s energy consumption is increasing year by year due to rise in population and improvement of living quality. For the realization of sustainable development, utilizing alternative energy sources rather than fossil fuels is of critical importance. Using solar cells, such as silicon (Si), is the most popular way for harvesting solar energy. However, light absorbing materials have their intrinsic band gaps, and therefore, the energy range that cells can harvest is limited, which brings power conversion loss. To overcome the problem, combining a solar cell and a phosphor, which is a wavelength conversion material, is important. Here we report UV-excitable mullite (Al6Si2O13) phosphors doped with REs. Luminescence spectra can be tailored from 390 to 620 nm by changing doping rare-earth ions. Experimental Mullite samples were synthesized via a sol-gel process. Al(NO3)3•9H2O, tetraethylorthosilicate (TEOS) and a RE source (or sources) in a form of nitrate or oxide were dissolved in ethanol. Then the pH of the solution was increased to 10 by adding NH3 aq. The precipitate was filtered off by suction filtration and treated at 1400 °C for 6h. For Ce3+, Tb3+ and Eu2+ phosphors, the samples were heat-treated in 5% H2/Ar atmosphere for the reduction of the luminescent centres. For Eu3+ phosphor, the sample was treated in air. Results ＆ discussions Fig. 1 shows the emission spectra of the mullite phosphors doped with Ce3+, Eu2+, Ce3+-Tb3+ or Eu3+. Ce3+ and Eu2+ in mullite show relatively broad peaks around 380 and 410 nm, respectively. These peaks are typically assigned to the 5d-4f transitions in Ce3+ and Eu2+. The Ce3+-Tb3+ phosphor shows green emission with the sharp peaks attributed to the Tb3+ 4f-4f transitions. Absence of an emission peak of Ce3+ indicates the energy transfer from Ce3+ to Tb3+. Red luminescence with the sharp peaks in mullite are attributed to the 4f-4f transitions of Eu3+. Fig. 2 shows the thermal quenching properties of the mullite phosphors compared with commercially available YAG:Ce3+ and SrSiO4:Eu2+ phosphors [2]. The mullite phosphors maintain more than 50% of the initial intensities even at 200 °C. Conclusions We have successfully synthesized red, green and blue phosphors with mullite doped with Ce3+, Eu2+, Ce3+-Tb3+ and Eu3+. They all show good thermal quenching properties, which are comparable with the commercially available phosphors of YAG:Ce3+ and SrSiO4:Eu2+. Figure 1

Hierarchical and decentralized optimization method based on multi-agent system for multiple AC/DC hybrid microgrids

AC/DC hybrid microgrids (MGs) have been developed rapidly in recent years due to their efficient integration and management of large-scale distributed energy resources. How to achieve the optimal operation and coordinated control of AC/DC hybrid MGs has become crucial. A multi-agent system (MAS) based hierarchical and decentralized method for coordination operation of multiple AC/DC hybrid MGs is proposed. First, a structure of AC/DC hybrid MGs including wind turbines, photovoltaics, micro-hydro, and biogas generators is designed, which aims at reducing the power conversion loss. Second, a three-level MAS including distribution network (DN) level, MG level, and distributed generation (DG) level is presented. At the DG level, the DG agents obtain the optimal results from the MG agent. At the MG level, the independent optimization is implemented based on the mixed integer linear programming, and the consensus algorithm is utilized to realize the coordination of MG with adjacent MGs through the communication among MG agents when there is imbalance power. At the DN level, the DN agent performs power exchange with AC/DC hybrid MGs to balance the load demand when needed. Finally, the distributed energy management platform is developed by the Java Agent Development Framework platform to simulate the optimal operation of AC/DC hybrid MGs. The results show the rationality and availability of the proposed optimization method.

Energy Neutral Sensor System With Micro-scale Photovoltaic and Thermoelectric Energy Harvesting

Minimizing power conversion losses is critical for energy neutral operation of micro-scale energy harvested sensor nodes. These small form-factor sensor nodes rely on miniature harvesters with low output voltages that must be boosted with large conversion ratios to recharge batteries or super-capacitors. Selective Direct Operation (SDO), a technique to selectively avoid power conversion and thereby eliminate conversion loss in energy harvested systems has been demonstrated as an effective technique for light harvesters. This paper extends SDO to thermoelectric generators (TEGs). SDO exploits the ultra-low circuit functional voltages, enabling sensor systems to effectively harvest energy from cm-scale TEGs which output few 10’s of mW but at low output voltages (100’s of mV). PV cell construction from prior-work, TEG characterization and field measurements are presented in this paper to demonstrate the effectiveness of SDO and co-designing energy harvesters, power conversion circuits and digital sub-systems.

An optimal power flow algorithm for AC/DC hybrid power systems with VSC‐based MTDC considering converter power losses and voltage‐droop control strategy

This paper presents an optimal power flow algorithm of AC/DC hybrid power systems with voltage source converter‐multiterminal high‐voltage direct current (VSC‐MTDC) networks, considering precise converter power losses and voltage‐droop control strategy. Based on the generalized model of VSC stations accounting for the converter power losses, the optimal power flow model of AC/DC power system with VSC‐MTDC networks is developed. The effects of control strategies of VSC stations on the settings of optimal variables and equality constraints are discussed. To deal with the ‘coupling relationship’ between the AC power injection and the power loss of converters with droop control, an iterative algorithm to calculate the AC active power of voltage‐droop converters is proposed. Moreover, by analyzing the construction of Jacobian matrix, the step‐controlled primal–dual interior point method is used to solve the optimal power flow model. Finally, case studies are performed with the modified IEEE 30‐bus test system to evaluate the effectiveness of the proposed optimal power flow algorithm. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Status and Trends in Epitaxy and Defects

SiC-powered devices which reduce the power loss, size, and weight of power converters are gradually appearing in the power electronics market. From now on, cost reduction and quality improvement of SiC epitaxial wafers is required to further increase their popularity. This paper describes the state of development of mass production of the epi-wafer at Showa Denko K. K.

Single-Phase Boost Inverter-Based Electric Vehicle Charger With Integrated Vehicle to Grid Reactive Power Compensation

Vehicle to grid (V2G) reactive power compensation using electric vehicle (EV) onboard chargers helps to ensure grid power quality by achieving unity power factor operation. However, the use of EVs for V2G reactive power compensation increases the second-order harmonic ripple current component at the DC-side of the charger. For single-phase, single-stage EV chargers, the ripple current component has to be supplied by the EV battery, unless a ripple compensation method is employed. Additionally, continuous usage of EV chargers for reactive power compensation, when the EV battery is not charging from the grid, exposes the EV battery to these undesirable ripple current components for a longer period and discharges the battery due to power conversion losses. This paper presents a way to provide V2G reactive power compensation through a boost inverter-based single stage EV charger and a DC-side capacitor without adversely affecting the EV battery. The operation of the boost inverter-based EV charger with second-order harmonic and switching frequency ripple current reduction, the dynamic behavior of the system, the transition between different operating modes, the DC-side capacitor voltage control above a minimum allowed voltage, and the DC-side capacitor sizing are extensively analyzed. The performance of the proposed system is verified using an experimental prototype, and presented results demonstrate the ability of the system to provide V2G reactive power compensation both with and without the EV battery.

Improved solar system with maximum power point tracking

This study presents an improved solar system with maximum power point tracking (MPPT). A digital signal processor is used to control the converter with the proposed control; thus, the system can implement MPPT independently for each solar panel whether it is under shading, various irradiation conditions or with faulty solar cells. A modified MPPT method is designed to reduce the power oscillation significantly, thus the power loss is reduced. With the proposed scheme, most of the solar panel available output power is delivered to the load only through a diode, reducing the converter power loss. In addition, the converter only handles part of the solar panel output power. Therefore, the system cost is reduced due to the low-power rating converter. A laboratory prototype is constructed and tested to evaluate the effectiveness of the proposed system. The proposed photovoltaic (PV) system and the PV balancer are compared through simulations and experiments under various shading conditions. The experimental results show that the proposed PV system can produce more output power with high efficiency.

A Unidirectional DC-DC Autotransformer for DC Grid Application

Conventional unidirectional DC-DC converters for DC grid application employ DC-AC-DC two-stage conversion technology and suffer from high converter cost and power loss. To solve these issues, a unidirectional step-up DC-DC autotransformer (UUDAT) and a unidirectional step-down DC-DC autotransformer (DUDAT) are studied. The UUDAT and DUDAT are composed of a series connection of diode bridges and voltage source converters. Topologies of UUDAT and DUDAT are detailed. The harmonic and un-controllability issues are discussed. Control and possible application scenarios for UUDAT and DUDAT are depicted. DC fault isolation mechanism and the methods of dimensioning the voltage and power ratings of the components in UUDAT and DUDAT are studied. Extensive simulations on power system level and experiments on a UUDAT and DUDAT prototype verified their technical feasibility.

Improved Voltage Control Strategy for Multi-terminal Flexible DC System

This paper presents an improved Voltage Droop control strategy, which updates the reference of DC link voltage by adding the difference between reference and actual voltage, which also adopts a dynamic P-V droop coefficient to improve the DC voltage level. By applying this method, we can eliminate the steady-state deviation of DC link voltage caused by ignoring the power loss in converter. In this paper, in order to demonstrate the reduction of deviation of DC link voltage, an improved control strategy is implemented for a three-terminal flexible DC power system modelled in PSCAD/EMTDC.

Design and development of high efficiency five stage battery charge controller with improved MPPT performance for Solar PV Systems

This paper presents the design and development of a novel highly efficient synchronous buck converter operating both as a battery charge controller with five stage charging method and also as improved Maximum Power Point Tracker (MPPT) for operation in Solar Photovoltaic (PV) Systems. The algorithm regulates the duty cycle of the switching devices of the converter following a variable step size perturb and observe (P&O) MPPT technique. At the same time it provides precise control on the battery charging voltage and current according to five charging stages which is desirable for protection of battery health and maximizing charging rate. Thus the algorithm developed provides a combined solution for maximizing the transfer of solar electricity generated by the PV module(s) and also ensuring a long battery lifetime. Both these aspects, which are generally investigated separately earlier, are treated in an integrated fashion in this work. The work analyses in detail about the converter power loss as well as describes the development of MPPT technique and battery charging method used in the controller. A prototype of 1500W MPPT Charge Controller based on this algorithm has been designed, fabricated and tested. It shows satisfactory performance of the MPPT charge controller in terms of performance parameters i.e. converter efficiency, MPP tracking efficiency, MPP tracking time, fluctuation of PV operating point around MPP, input operating voltage range of the controller, independency of battery type as well as provision of temperature compensation.

Fuzzy PI controller for bidirectional power flow applications with harmonic current mitigation under unbalanced scenario

The depletion of fossil fuels and environmental concern forces the extraction of power from low carbon fuels causes generation problem due to intermittent solar-wind renewable energy sources and power electronic applications. Furthermore, the significant amount of non-linear loads in the system causes power quality problems. Nowadays, the more and more DC loads like LED lights to save energy consumption are connected to the AC distribution system. These DC loads are connected at DC grid side in order to avoid the extra AC/DC power conversion loss. In this paper, the proposed d-q reference current method applied for shunt active power filter based 3-phase 4-leg bidirectional interfacing converter with fuzzy PI controller to achieve the real power transfer between DC grid side and AC grid side with current harmonics compensation at common connecting point simultaneously under balanced and unbalanced distorted grid and non-linear load conditions. The hysteresis current control comparator without PLL is used to compare actual grid current with reference filter current and generate the switching pulses for driving the bidirectional interfacing converter. The DC grid shunt connected intermittent hybrid solar-wind energy sources are integrating with AC grid utility through bidirectional interfacing converter has been into consideration for simulation studies. The MATLAB/SIMULINK tool is used to yield the improved grid current THD with fuzzy logic controller over PI controller.

System Efficiency Improvement for Electric Vehicles Adopting a Permanent Magnet Synchronous Motor Direct Drive System

To improve the endurance mileage of electric vehicles (EVs), it is important to decrease the energy consumption of the Permanent Magnet Synchronous Motor (PMSM) drive system. This paper proposes a novel loss optimization control strategy named system efficiency improvement control which can optimize both inverter and motor losses. A nonlinear power converter loss model is built to fit the nonlinear characteristics of power devices. This paper uses double Fourier integral analysis to analytically calculate the fundamental and harmonic components of motor current by which the fundamental motor loss and harmonic motor loss can be accurately analyzed. From these loss models, a whole-frequency-domain system loss model is derived and presented. Based on the system loss model, the system efficiency improvement control method applies the genetic algorithm to adjust the motor current and PWM frequency together to optimize the inverter and motor losses by which the system efficiency can be significantly improved without seriously influence on the system stability over the whole operation range of EVs. The optimal effects of system efficiency is verified by the experimental results in both Si-IGBT-based PMSM system and SiC-MOSFET-based system.

DSCC-MMC STATCOM Main Circuit Parameters Design Considering Positive and Negative Sequence Compensation

The double-star chopper cell modular multilevel converter (DSCC-MMC) has been employed in several applications as HVDC, energy storage, renewable energy, electrical drives and STATCOMs. Generally, the DSCC-MMC main circuit parameter design presented in literature considers balanced currents flowing through the converter. Nevertheless, in STATCOM application, the converter can compensate negative sequence components and unbalanced currents flow through the DSCC-MMC, resulting in different stresses in the converter phases. Therefore, this work presents a detailed design methodology of the DSCC-MMC main circuit parameters, considering both positive and negative sequence current compensations. The dc-link voltage, number of submodules, power semiconductor thermal stresses, submodule capacitance and arm inductances are designed. Expressions for the energy storage requirements are derived when negative sequence is compensated. A case study considering a 15-MVA STATCOM is presented, and simulation results validate the proposed design methodology. Finally, the converter power losses and thermal stresses in the power semiconductors are evaluated.

Automatic tuning of the switching frequency for efficiency maximization in an ESS-PV hybrid PCS

An automatic switching frequency tuning algorithm (ASTA) for a real-time condition is proposed. The primary aim is to maximize the power efficiency of a power electronic system. The power loss of a hard-switched power converter is determined by the power loss in power semiconductor devices, magnetic devices, capacitors, etc. Switching frequency of a power converter is one of the parameters which influence the power loss. The parameters which determine the maximum-efficiency point can vary with the ageing of devices and the change in environmental conditions. In this paper, a PWM-carrier frequency is utilized for efficiency maximization of a power conversion system. By varying the PWM-carrier frequency from the minimum to maximum value to search for the switching frequency associated with the point of maximum efficiency, this algorithm is designed for a hybrid-energy power conversion system which consists of DC/DC converters and a DC/AC inverter. For the realization of this algorithm, real-time power metering for efficiency calculations is realized by software, which requires no cost increase as the method shares the voltage-and-current sensing circuits with the converter control unit. The metering algorithm has tolerance of less than 1% over a wide load range. The experimental results present efficiency data captured during the operation of the ASTA algorithm in wide ranges of switching frequencies.

Triple-Mode, Hybrid-Storage, Energy Harvesting Power Management Unit: Achieving High Efficiency Against Harvesting and Load Power Variabilities

This paper presents a triple-mode, hybrid storage, energy-harvesting power management unit (EH PMU) that interfaces a photovoltaic cell, a regulated load, and a rechargeable battery. The objective is to maximize the end-to-end conversion efficiency of the EH PMU against temporal mismatch and variabilities of harvesting and load power. To minimize the involvement (charging or discharging) of a battery in the voltage conversion process, the proposed hybrid energy storage employs both battery and capacitor, which increases transient energy buffering capability and reduces the overall power conversion loss. Measurement results with 65-nm test chips show that the proposed EH PMU can achieve up to 2.2 $\times $ higher end-to-end conversion efficiency than the conventional dual-mode architectures under testing cases emulating realistic load and harvesting power variabilities. We also devised a framework for the system design to guide capacitor sizing, buffering voltage range selection, and end-to-end efficiency tradeoffs.

On the impact of current generation commercial gallium nitride power transistors on power converter loss

The enormous potential benefits of gallium nitride based power switching devices, only commercially available very recently, in terms of power switching device loss are highlighted. This is first demonstrated through a simulated prediction of loss in multilevel converters, followed by experimental validation. While the simulations focus on losses in multilevel converters, the observations made are relevant in a broad range of applications.