Power Loss Of Converter Research Articles

Comprehensive energy efficiency analysis of series hybrid electric vehicles with dual-phase-shift-controlled DC-DC converter

By considering converter fundamental operating principles, the paper first derives a complete set of analytic expressions of the overall power losses of a conventional Dual Active Bridge (DAB) bi-directional DC-DC converter under Dual Phase Shift (DPS) control. Expressions for conduction and switching losses in the electronic devices acting as the converter switches, and copper and core losses in the isolation transformer, are derived and accounted for in the DC-DC converter model. DPS control involves many more converter operating conditions, in comparison to the more common single-phase-shift (SPS) control, which makes the analytic power loss characterization of a DPS-controlled converter an arduous task. Subsequently and by employing the derived analytic converter power loss model with exemplary parameter values, the paper analyzes the efficiency of a high-fidelity full hybrid electric vehicle (HEV) model that includes a DAB DC-DC converter, under a wide range of realistic driving conditions and converter operation, including low- to high-speed driving, and converter DPS operation. Two popular hybrid powertrain energy management schemes, the Thermostat and Power Follower control strategies, are used to simulate the vehicle model to reinforce the range of realistic vehicle operating conditions. The results show that in series HEV applications more accurate modeling of DC-DC converter models than conventional constant efficiency models is required to predict converter losses, and also the fidelity in the characterization of converter losses can have a significant impact on the vehicle fuel consumption prediction.

Inverter Topology Selection for Photovoltaic Power Systems

This article is devoted to the task of selection of photovoltaic power system inverter that would comprehend to all of the demands that could be applied to it. The challenge of creating efficient and reliable converter for the renewable energy systems that implies solar panels as primary energy sources is well-known since the first day of their existence as a possible choice for the role of the only power source in the system. The great breakthrough in the field of photovoltaic power system converters design was achieved in late 80’s-early 90’s years of the 20th century due to the several positive circumstances that included rapid evolution of the semiconductor industry at whole which sums up in the development of a new generation of power switches that was capable to operate in higher voltage and current ranges which was unreachable for the prior generation switches and new microcontrollers that was able to maintain more complex control algorithms than ones that were used before which in general resulted in significant downsizing of the resulting device and made it possible to practically develop power inverters with complex topologies that was considered over sophisticated and unreliable before. These factors leaded to the development of numerous new topologies with the main goal of transformation losses reduction and power efficiency increase. The desired result was obtained either thru the fulfilling the demands invoked by the photovoltaic sources operation features (z-source topologies) or power system topology features and reduction of output voltage THD ratio (multilevel inverters). But consideration of only one type of factors has not allowed achieving the maximum result in power losses task. Thus solution of the determined task should be started from complete identification and broad consideration of the main factors that define set of demands that converter has to face. In this article parameters of THD ratio of the inverter’s output voltage, photovoltaic source’s operation features and power system topology specifics were considered as the most valuable parameters that affects the power conversion losses values and was discovered in details based on a survey of the existing publications in the field of the study, international and local standards of consumer voltage quality parameters and practical results of the most popular and widespread topologies simulation in order to obtain an output voltage THD ratio. The achieved results demonstrate that inverter topology that would be able to satisfy all of the requirements has to have modular structure to be able to maintain the proper THD ratio and connect to the most popular types of the photovoltaic power system topologies and be based on the z-source topologies to imply the photovoltaic sources operation features. Therefore as a conclusion a cascaded multilevel inverter with a separated input DC sources topology that is based on quasi-z-source modules was recommended as a solution that could also be used as a base for the further power converter development.

Switched Reluctance Generator for Low Voltage DC Microgrid Operation: Experimental Validation

This paper presents the control of a Switched Reluctance Generator (SRG) for low voltage DC grid with the objective of efficiency maximizing. Analysis of the energy conversion, including electrical machine losses (Joule, magnetic, mechanical) and power converter losses (switching and conduction), has shown that there is an optimal combination of control variables (turn-on and conduction angles, phase current reference), which maximizes the drive efficiency. The control variables are derived from a Finite Element Analysis and parametric optimization algorithm for all of the operating points in the torque-speed plane and stored in lookup tables. The performances are evaluated with intensive numerical simulations and experimental tests with a 8/6 SRG feeding a DC resistive load for different rotational speeds. The results show good performances of the output DC voltage control with low ripples, even in the presence of speed and load variations. Thanks to the optimization, simulation results show that beyond 1500 rpm, drive efficiency is higher than 60 % and almost reaches 70 % at nominal speed. The experimental results show that, for light loads and beyond rated speed, the drive efficiency lies in the range between 60 % and 80 % .

Hybrid AC/DC hub for integrating onshore wind power and interconnecting onshore and offshore DC networks

A hybrid AC/DC hub is proposed in this study, where a modular multilevel converter and a line-commutated converter are paralleled at the AC side to integrate onshore wind power, and connected in series at the DC sides to interconnect two DC networks with different voltages. The hybrid AC/DC hub facilitates wind power integration and DC network interconnection with reduced converter ratings and power losses when compared with the ‘conventional’ approach using DC–DC converters. To investigate the design requirement and performance of the hybrid AC/DC hub, power flow analysis is assessed to evaluate the converter power rating requirement. To ride through DC faults at either side of the interconnected DC networks, a coordinated DC fault protection for the hybrid AC/DC hub is proposed and studied. Simulation results in PSCAD/EMTDC verify the feasibility and effectiveness of the proposed control and protection of the hybrid AC/DC hub under power flow change, AC and DC fault conditions.

Current Control of the Coupled-Inductor Buck–Boost DC–DC Switching Converter Using a Model Predictive Control Approach

Coupled-inductor buck–boost dc–dc switching converter has emerged as an alternative to manage power in several hybrid system architectures. This is due to features such as a noninverting voltage step-up and step-down characteristic, high efficiency, wide bandwidth, and the possibility to regulate its input or output currents as has been reported in previous works. All of them are based on a small-signal linearized model around an operating point. In this article, a model predictive control strategy is proposed to increase the operation point domain. The proposal consists in the use of the mathematical model of the system in discrete time to obtain the optimal switching state to be applied in the converter based on a cost function optimization, which simultaneously improves the current tracking and reduces the converter power losses. Experimental results validate the proposal demonstrating that this is a good alternative for the control of this kind of power converters.

Research of electric drive systems with real time software configurable control

Subject of Research. The paper discusses design principles of educational laboratory bench for practical research of electric drive control systems. The laboratory bench provides training opportunities for students in “Control of Electrical Drives” course and is used to increase the efficiency of material acquisition. Method. The proposed solution was based on the method of mutual loading of electric machines powered by the power converters with a common direct current link. At that, one electric machine can be used as a tested one, and the other as a load one, and vice versa. The flow of power from a machine operating in generator mode to a machine operating in motor mode was ensured, which provides an energy-saving mode of operation when power is consumed only from the network to cover losses in power converters and the machine unit. To study the various structures of control systems for direct and alternating current motors, a method for software creation with a freely configurable structure was proposed. Main Results. The paper describes laboratory stands that contain a two-machine unit, where each electric motor receives power from its power semiconductor converter controlled by a real-time microcontroller control system. The software has been implemented for the synthesis of the control researched structure using the control system settings. The system setting is performed by a number of freely configurable control elements, which are then compiled into a control algorithm for the microcontroller. To ensure the safe execution of the experiment, the control algorithm works in conjunction with the main on-line software. Thus, protection for electric motors and power converters is provided. Thanks to the built-in protection software, it has become possible to achieve reliable operation of electric drives with the power of 1.5 kW, as well as to realize characteristics close to industrial ones. The paper describes in detail the features of laboratory equipment and software for the system of an induction motor field-oriented control. This example demonstrates the setting of control systems, compiling of executable code, an experiment procedure and evaluation of results. Practical Relevance. The considered approaches to the educational equipment creation can be used in the design of similar educational equipment in related disciplines. The results are applicable for scientific and research-pedagogical staff during the course of specialist training in the field of electric drive control systems. The presented equipment has been actively used for more than 5 years and can be of practical value in the educational process.

Comparative study of semiconductor power losses between CSI-based STATCOM and VSI-based STATCOM, both used for unbalance compensation

In this paper, we present a detailed procedure to determine the semiconductor losses for both structures of a shunt STATCOM (Static Compensator), STATCOM based on Current Source Inverter (CSI) and STATCOM based on Voltage Source Inverter (VSI), both used for voltage unbalance compensation. As a first step, we study the VSI-based STATCOM and the CSI-based STATCOM used in high speed railway substations. Then we analyze the design and the sizing of the unbalance compensator in order to obtain an unbalance factor that does not exceed the limits imposed by the standards or by the energy provider. Following that, we compare the performances obtained with both structures VSI-STATCOM and CSI-STATCOM, after calculating the semiconductor power losses in the STATCOM converters. Finally, we validate our approach by simulation over real data of unbalance compensation caused by the new high-speed railway in Morocco. We use the tools MATLAB / Simulink/Simpowersys for performing our simulations.

Enhanced robustness with damping interval widening strategy of LCL-type converter under weak grid condition

Active damping methods are widely adopted to present a damping effect on the resonance phenomenon without the power loss of LCL-type converters connected to a grid. However, extra sensors are used to implement the damping strategy. In this paper, a sensorless damping strategy where only the grid current is sampled has been proposed. Furthermore, the inner relationship between the tradition capacitor current feedback strategy and the proposed strategy has been clarified. Considering the digital delay and a weak grid, a robust method that uses unit delay feedback to mitigate the phase lag and to widen the effective damping interval has been developed. With this simple measure, stability is enhanced during the Nyquist frequency and robustness is improved when the LCL parameters vary and grid impedance exists. Finally, simulation and experimental results are presented to verify the feasibility and engineering significance of the proposed strategy.

The Impact of Multi-MHz Switching Frequencies on Dynamic On-Resistance in GaN-on-Si HEMTs

Dynamic on-resistance ( ${\text{d}R_\text{on}}$ ), where the on-resistance immediately after turn-on is higher than the DC resistance, increases the conduction losses in power converters with gallium nitride high-electron-mobility transistors (GaN HEMTs). There exist no direct ${\text{d}R_\text{on}}$ measurements in the literature above ${1}\,\text{MHz}$ , leaving designers unable to predict conduction losses in emerging multi-MHz applications. We address this literature gap by collecting the first on-state voltage ${\text{d}R_\text{on}}$ measurements at multi-MHz frequencies, with a focus on the zero-voltage-switching conditions that are predominantly employed at high frequency. On the selected commercially-available HEMT with a breakdown voltage below ${200}\,\text{V}$ , the dynamic contribution asymptotes above $\approx {2}\,\text{MHz}$ , a finding predicted by the slow time constants of the traps that cause ${\text{d}R_\text{on}}$ . For the tested HEMT, we find a maximum ${\text{d}R_\text{on}}$ increase over the DC resistance of 2 $\times $ in a multi-MHz, zero-voltage-switched application.

Wielopoziomowe przekształtniki energoelektroniczne – topologie, zasada działania, metody modulacji

In this paper selected issues concerning topological structure, operation and control as well as modulation methods used in multilevel converters are presented. There is reviewed general topologies of multilevel converters, which include Diode-Clamped Converters, Capacitor-Clamped Converters, Cascade Converters and Hybrid Converters. The general structure of a multilevel converter consisting of several stages depending on its application and topology is described. In the structure of operation, the stages of Outer Control Loop, Inner Control Loop, DC voltage stabilization and modulation are specified. Next, the division of modulation methods used in multilevel converters is presented and a detailed description of selected modulation methods is made. In the further part of the article the modulation methods were described in detail, i.e. the Level-Shifted Carrier Modulation Technique and Phase-Shifted Carrier Modulation Technique were used to present the analysis of power losses in multilevel converters.

Analysis and Design of 4-to-1 Capacitor-Stacking Balancer for Stacked Voltage Domain

This paper presents an alternative method for achieving more efficient and reliable DC-DC conversion and balancing operations for low-power applications in a stacked voltage domain. This work comprehensively analyzes the operating principles and power conversion loss of a proposed capacitor-stacking balancing circuit at the system level. The analysis and design of the capacitor-stacking balancing circuit in the stacked voltage domain, including the time-domain operation, voltage equation, and dead-time effect, are explored and implemented. This study provides an opportunity to achieve a highly optimized system with high efficiency. A comprehensive analysis of efficiency at the system level shows the advantages and limitations according to each stacking method under a given system condition. Considering the redundancy issues of the previous method at system-level analysis, the capacitor-stacking balancing method is a preferable choice for low-power, high-reliability, and high-efficiency applications under light load conditions. This study also provides an analytical efficiency model under current imbalance, which is a notable difference from previous research and case studies concerning power converters. Prototype board with lithium-ion battery power and a core voltage of 0.825 V-a low-power application-was built to verify the proposed model and analysis. The experimental efficiency reached 94.9% at 20% of the maximum workload.

Carrier-based sinusoidal pulse-width modulation techniques for flying capacitor modular multi-level cascaded converter

Carrier-based sinusoidal pulse-width modulation (PWM) techniques, such as phase disposoed PWM(PD-PWM) and phase shifted PWM (PS-PWM), are widely applied to control the modular multilevel cascaded converters (MMCC) having full H-bridge as sub-modules. This paper evaluates these PWM techniques when controlling a variant of the H-bridge MMCC, i.e. the MMCC five-level flying capacitor converter as sub-modules. This MMCC poses an extra challenge to PWM schemes; namely maintaining two inner floating capacitor voltage balancing. Two novel PWM techniques known as the swapped carrier PWM techniques are introduced for the control of this converter. The paper compares them with the two conventional ones using a performance metrics composed of voltage waveform performance, capability in natural flying capacitor voltage balancing, converter power loss, and switch utilisation. The results show that the proposed new PWM schemes outperform both conventional methods in both switching and conduction power losses and achieve similar performance like the PS-PWM under the three other metrics.

INTERCONNECTED DC MICROGRID FOR EFFICIENT USE OF RENEWABLE ENERGY SOURCES

The use of a dc micro-grid with the interconnection of the main ac power supply, which is provided from renewable energy sources such as the sun, wind, and other sources, was investigated in this article. Micro-grids will play a significant role in the future development of the energy sector, but the generation phase may differ. In this article, we show that when we use green energy sources for dc applications such as smartphone chargers, laptop chargers, and LEDs, the performance of the dc micro-grid device improves by up to 40%. This is due to the reduction of ac to dc and back to ac, which results in excessive power conversion losses in the current system. The PIC16F73 microcontroller is used to power the micro-grid device and solar tracker, increasing the model's performance. When this sort of device is attached to a specific load, it uses more power during off-grid renewable generation, resulting in more pulse width modulation (PWM) waveform generation, demonstrating the system's failure compared to renewable energy sources.

A simple and effective design strategy to increase power conversion efficiency of linear charge pumps

SummaryThis paper introduces a simple design strategy to increase the power efficiency of linear charge pumps. The technique exploits a voltage amplitude of the clock signal lower than the supply voltage to reduce the power conversion losses. The nominal output voltage is maintained unaltered by increasing the number of stages.

Energy efficient control of a stand-alone wind energy conversion system with AC current harmonics compensation

This paper presents a new energy-efficient control strategy for a variable-speed wind energy conversion system (WECS). The considered WECS is designed for dc load supply and battery charging in stand-alone applications. The batteries are charged through a three-phase full-bridge power converter. The WECS contains a vector-controlled self-excited induction generator (SEIG) coupled to a wind turbine (WT) for electric power generation on the ac side. The control algorithm proposed in this paper includes three separate optimizations: two fuzzy-logic-based optimizations, which ensure that maximum energy is extracted from both the WT and the SEIG, respectively, at all operating conditions, and also the optimization of phase current harmonics through adaptive hysteresis control. In addition, a recently developed algorithm for real-time loss calculation of a hysteresis-driven power converter is utilized to quantitatively assess the power converter losses with respect to different hysteresis bandwidth settings. The performance of the proposed control algorithm is experimentally evaluated and compared with two competing algorithms which do not involve current harmonics compensation, whereas one of them also does not involve optimization of the SEIG output power. This enables evaluation of the gain in system performance due to the introduced optimizations. The evaluation and comparison are made over a wide range of wind speeds, both in steady state and under transient conditions, by using a 1.5 kW experimental setup with the DS1103 controller board (dSPACE).

Analytical Switching Loss Model for GaN-Based Control Switch and Synchronous Rectifier in Low-Voltage Buck Converters

In this paper, an analytical switching loss model for a gallium nitride (GaN) based control switch (CS) and synchronous rectifier (SR) in low-voltage buck converters is proposed. Based on the consideration of parasitic inductances, SR reverse conduction voltage drop, and overshoot current effect caused by output capacitance of SR, the total switching loss is modeled with regard to both CS and SR, which can lead to more accurate prediction of power loss and system efficiency in low-voltage buck converters. The modeling results show that the percentage of SR switching loss in total switching loss is 25.4% in the 12–1.2-V converter, which is far larger than the 6.3% in the 48–5-V converter, and this verifies the necessity of including SR into the model for low-voltage converters. Experiment results exhibit an average increase of 52.3% and 66.1% in the accuracy of predicted system efficiency and converter power loss through the proposed model with SR than conventional models from 400 kHz to 1 MHz.

Hybrid Control Scheme for Photovoltaic Microinverter With Adaptive Inductor

This paper studies the two-stage photovoltaic microinverter. Its prestage is a full-bridge dc–dc converter with an adaptive inductor whose inductance can be regulated by a controlled current source. The aim of the adaptive inductor is to realize current boundary continuous mode (BCM) operation with constant frequency and decrease the current stress of the switches in the prestage converter. The structure and operational principle of the proposed adaptive inductor are introduced. The mathematical model has been established for achieving the proper inductance of the adaptive inductor for BCM operation and for verifying the operational condition of the core. The current stress of switches and power loss of the prestage converter with the adaptive inductor or the fixed inductor are analyzed. A hybrid control strategy, which includes an adaptive inductor regulating controller, discontinuous conduction mode operation, and BCM selection in different power ranges, is proposed according to the derived mathematical model. The experimental results are presented to verify the analysis.

Electrothermal Cosimulation for Predicting the Power Loss and Temperature of SiC MOSFET Dies Assembled in a Power Module

The electrothermal cosimulation proposed in this paper accurately reproduces the power loss and the temperature of the silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor ( mosfet ) dies assembled in a power module comprising a buck converter. The current–voltage characteristic of the body diode embedded in a SiC mosfet is not like that of an ideal diode because this characteristic depends on the negative gate–source voltage of the transistor. Our device model was, therefore, created to reflect this unique feature and the temperature dependence of the drain current for predicting the power loss of the mosfet . The simulation uses a look-up table to reduce the computation time. This yields accurate results for the power loss in a buck converter operating at switching frequencies ( f sw) ranging from 50 to 350 kHz. The f sw-dependent steady-state temperature of the SiC mosfet was reproduced well; it ranged from 60 °C to 140 °C. The maximum deviation between the measured and the simulated results was less than 3.0 W and 8 °C, respectively, for the power loss and the temperature of the dies.

Investigation of Nonlinear Droop Control in DC Power Distribution Systems: Load Sharing, Voltage Regulation, Efficiency, and Stability

Linear droop faces the design tradeoff between voltage regulation and load sharing due to cable resistances and sensing errors. Using a larger droop resistance improves load sharing, but requires a wider droop voltage range. In the nonlinear droop, droop resistance is a function of the converter's output current, and its value increases when the output current increases. As a result, the impacts from sensors and cables are reduced. In this paper, the design of nonlinear droop in dc power distribution systems is studied with special emphasis on load sharing, voltage regulation, system efficiency, and stability. After discussing the piecewise linear and nonlinear droop control, a generic polynomial expression is presented to unify different droop equations. The impact of droop on dc system efficiency is analyzed by evaluating cable and power converter losses. The converter's output impedance using nonlinear droop is modeled to analyze the system stability with constant power loads. The selection and design guidelines of nonlinear droop are summarized, considering both the static performance and interaction with load systems. The analysis is verified in 400-V multi-source dc systems. The nonlinear droop is fully distributed as it only needs local information.

LED Driver Achieves Electrolytic Capacitor-Less and Flicker-Free Operation With an Energy Buffer Unit

Electrolytic capacitors are often needed to provide the high-density energy storage required by ac-powered LED drivers; however, they are also well known for their short lifespans. Eliminating electrolytic capacitors in ac–dc LED driver design has become a very important target to improve LED driver technology. In this paper, a cycle-by-cycle energy buffering LED driver has been proposed to achieve electrolytic capacitor-less flicker-free operation. An energy buffering unit, with high-voltage film capacitors being the energy storage device, is introduced in the design to buffer the imbalanced energy in every switching cycle. The switching current can be controlled to meet high power factor correction requirement, while maintaining dc LED output current at the same time. Compared to previous electrolytic capacitor-less designs, this technology can reduce circulating power and, therefore, power conversion loss. A 15-W experimental prototype had been built and tested to verify the proposed LED driving method.