Additional DC-DC Converter Research Articles

Three-Leg DC–DC Converter for Efficient Inductive Power Transfer of Electric Vehicles for Wide-Range Battery Applications

The design of an inductive power transfer system for different electric vehicle (EV) models with widely varied battery pack voltages has been a challenging task. The majority of modern EV models are equipped with 400 V or 800 V battery packs. To charge both batteries efficiently, an additional DC-DC converter on the receiver side is employed, which reduces the overall system efficiency and also increases the cost. This article proposes a reduced switch count novel converter to charge distinct EV models without degrading the efficiency of the system. The proposed converter has two operating modes, a voltage doubler mode to charge an 800 V battery and a current doubler mode to charge a 400 V battery at the same power level. MATLAB/Simulink simulations have been carried out to verify the performance of the 3-leg converter for both 400 V and 800 V batteries at 7.2 kW. Furthermore, a laboratory prototype of the proposed converter for 500 W has been built using the SiC devices, and the results obtained are provided.

A novel controller for PV-fed water pumping optimization system driven by an 8/6 pole SRM with asymmetrical converter

A locally installed photovoltaic (PV)-powered motor pump is a viable solution for a water pumping system (WPS) in rural locations. In this study, a single-stage, PV-fed, SRM-powered WPS was investigated and realized using a speed sensorless sliding mode controller (SMC)-based direct torque control (DTC). As a result, no additional DC-DC converter was required for maximum power absorption from the PV source. By utilizing a novel high-side switch asymmetric converter with a hybrid Perturb and Observe–Grey Wolf optimization (POGWO) method integrated with a DC-link voltage controller, an efficient single-stage conversion was achieved. The robustness of the proposed integrated control is presented by comparing it with a Genetic Algorithm and Particle Swarm Optimization (PSO). Extensive results using MATLAB SIMULINK are shown to validate the proposed system in both steady-state and transient conditions for various partial shading conditions.

Integration of a lithium-ion battery in a micro-photovoltaic system: Passive versus active coupling architectures

A balcony photovoltaic (PV) system, also known as a micro-PV system, is a small PV system consisting of one or two solar modules with an output of 100–600 Wp and a corresponding inverter that uses standard plugs to feed the renewable energy into the house grid. In the present study we demonstrate the integration of a commercial lithium-ion battery into a commercial micro-PV system. We firstly show simulations over one year with one second time resolution which we use to assess the influence of battery and PV size on self-consumption, self-sufficiency and the annual cost savings. We then develop and operate experimental setups using two different architectures for integrating the battery into the micro-PV system. In the passive hybrid architecture, the battery is in parallel electrical connection to the PV module. In the active hybrid architecture, an additional DC-DC converter is used. Both architectures include measures to avoid maximum power point tracking of the battery by the module inverter. Resulting PV/battery/inverter systems with 300 Wp PV and 555 Wh battery were tested in continuous operation over three days under real solar irradiance conditions. Both architectures were able to maintain stable operation and demonstrate the shift of PV energy from the day into the night. System efficiencies were observed comparable to a reference system without battery. This study therefore demonstrates the feasibility of both active and passive coupling architectures.

Robust Parity-Time-Symmetric WPT System With Reduced Switching-Frequency and Improved Step-Down Conversion Ratio

In this paper, combining the phase synchronization method (PSM) and high harmonic operation (HHO), a novel parity-time(PT)-symmetric wireless power transfer (WPT) system with reduced switching frequency and improved step-down conversion ratio is proposed, where the power transferred to receiver side is carried by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic. We demonstrate that constant current (CC) and constant voltage (CV) independent of coupling coefficient and load resistance can also be obtained without wireless communication and additional dc-dc converters. Here, a new implementation of a negative resistor based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic operation is proposed, which is a necessary condition of a PT-based system. In contrast to the standard PT-based system with the same resonant frequency, the switching frequency is reduced to 1/n due to the use of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> th harmonic, thereby realizing low switching losses and high system efficiency. Besides, an inherently improved step-down conversion ratio can be obtained. A prototype with a 6 A charging current and a 36 V charging voltage is built to verify the feasibility of the proposed method.

A Mode-Switching-Based Phase Shift Control for Optimized Efficiency and Wide ZVS Operations in Wireless Power Transfer Systems

This paper proposes a mode-switching based phase shift control (MS-PSC) for wireless power transfer (WPT) systems, which is able to achieve power regulation, load matching, and wide ZVS operations simultaneously without using additional dc-dc converters. Based on the mode transitions between the full-bridge, mixed-bridge, and half-bridge modes of both the inverter and the rectifier, the MS-PSC method guarantees a wide-range ZVS with minimized circulation of reactive power. Therefore, the system efficiency is improved over a wider power range compared to the conventional triple-phase-shift (TPS) control and the existing hybrid modulation control. The principles of different operating modes are analysed. Then, the implementation of the proposed MS-PSC method and the mode selection strategy are presented. Finally, the effectiveness of the proposed MS-PSC method is validated in a WPT prototype. Experimental results show that the proposed MS-PSC method can achieve a high overall efficiency in a wide power range. Compared with the conventional TPS control, the MS-PSC method further optimizes the efficiency in 10%-63% of the rated power, with efficiency improvements ranging from 1.5% to 6%. As a result, the system efficiency remains at 93.5%-96.1% in the power range of 1-10 kW, with the transformer coupling coefficient k=0.19.

Variable DC-Link Voltage Regulation of Single-Phase MMC Battery Energy-Storage System for Reducing Additional Charge Throughput

Battery energy-storage system (BESS) based on the modular multilevel converter (MMC) can flexibly manage the battery packs integrated into submodules, where the battery pack can directly or through a small capacitor connect to the rear-end half-bridge circuit for reducing cost and volume caused by an additional dc-dc converter. But the alternating current ripples will cause substantial additional charge throughput for battery packs and, consequently, reduce the battery lifetime in theory. Therefore, this article proposes a variable dc-link voltage regulation method for a single-phase MMC-BESS. In specific, the phase disposition (PD) modulation scheme is improved to properly bypass the gating signals with unnecessary conduction during operation and the modified gating signals will be rearranged for balancing the states-of-charge and states-of-health. Doing so, the additional charge throughput could be significantly reduced compared with the traditional phase-shift modulation and PD modulation. Even comparing with the ideal dc current charging/discharging, the proposed method will only increase slight additional charge throughput and nearly negligible capacity loss. The experimental results of a 6.6 kW/6.6 kWh single-phase MMC-BESS prototype verified the performance of the proposed method.

MSVM ‐based hybrid energy‐fed quasi‐Z‐source cascaded H‐bridge inverter for grid‐connected system

Hybrid energy sources are much needed to meet the power demand for various real-time applications, and the desired output level is attained with the help of various advanced power converter topologies. Here, the hybrid energy source-fed quasi-Z-source cascaded H-bridge inverter (QZS-CHI) is implemented for a grid-connected system. The conventional multilevel inverter topologies are suitable for voltage buck operation, but this proposed system includes quasi-Z-source inverter network, which leads voltage buck-boost operation without any additional dc-dc converter. Modified space vector modulation (MSVM) technique is developed to control the QZS-CHI system, which leads to reduced total harmonic distortion(THD), reduced common-mode voltage (CMV), controlled output current, and improved output voltage. The proposed system QZS-CHI is energized using a hybrid energy source with a photovoltaic (PV) system and wind energy conversion system (WECS). With the help of shoot through mode in QZS, the output voltage is boosted without an additional converter and CMV is minimized by the proper utilization of medium and small switching state vectors. To assess the proposed technique, a laboratory prototype model is built and analyzed under different cases. From the obtained results, it is observed that the proposed method reduces THD to 2.15% for output voltage and 2.99% for output current, and common-mode voltage is reduced to Vdc/6 times of applied dc voltage.

Dual-Mode Supply Modulator IC With an Adaptive Quiescent Current Controller for Its Linear Amplifier in LTE Mobile Power Amplifier

This article presents a hybrid envelope tracking (ET) supply modulator (SM) integrated circuit (IC) based on a Class-AB linear amplifier (LA) with supply voltage and temperature insensitive quiescent current. For ET mode, to further improve efficiency of the ET-SM, the supply voltage of the LA can be modulated using an additional dc-dc converter according to the average output power. An adaptive quiescent current controller for the LA of the ET-SM is proposed to maintain its quiescent current for large variations in voltage and temperature. Due to the insensitive quiescent current over the voltage of the LA, the supply voltage to the LA can be controlled in a wider range for the average output power, which allows the power amplifier (PA) in the ET mode to have a greater improvement in efficiency. The size of the output stage of the LA is also discretely reconfigured using 3-bit digital control to reduce the power consumption of the LA according to the output power level. For the low average output power levels, the operation mode is changed to APT mode, which supplies a reduced dc voltage according to the reduced average output power to the PA. The proposed SM, dc/dc converter and PA ICs were designed and implemented using CMOS processes for 0.9 GHz LTE application. Using an LTE uplink signal with a signal bandwidth of 5 MHz and a PAPR of 7.5 dB, a PAE of 38.4% at an average output power of 24.0 dBm was obtained under an ACLR of −30.0 dBc for the overall ET-PA. At a 6 dB back-off for the average output power, a PAE of 24.6% was achieved using the ET mode. A maximum PAE improvement of 8.0% point using the proposed SM IC was achieved compared to the stand-alone PA.

Belt-Driven Integrated Starter and Generator Using Planetary Gears for Micro Hybrid Electric Vehicles

This paper presents a 12 V mechanical torque converting belt-driven integrated starter and generator (BSG) system without a DC-DC converter. A micro hybrid electric vehicle (micro HEV) typically uses a 12 V battery with a 12/48 V bidirectional DC-DC converter to satisfy its high starting torque and wide operating speed for generating the required power. In contrast, the proposed BSG consists of a wound field synchronous machine (WFSM), planetary gears, and a belt-type pulley, which does not require an additional bidirectional DC-DC converter. Owing to the mechanical torque converter, the proposed BSG system produces a high starting torque in starter-mode with a 12:1 gear ratio, and it operates in generator-mode with a 1:2 gear ratio to satisfy the required target specifications. To verify that the proposed BSG system meets the required target design specifications, simulations using MATLAB/Simulink 2018b and ANSYS electromagnetic 19.0 were performed. Additionally, the experimental results verify that this proposed BSG meets the required starter and generator modes specifications. Based on an analysis of the cost and vehicle environment conditions, the proposed BSG provides an efficient solution to the high cost issue incurred by a micro-HEV that requires a DC-DC converter system.

An Active Switched-Capacitor Half-Wave Receiver With High Efficiency and Reduced Components in WPT System

There is an increasing attention on wireless power transfer (WPT) technology in many applications. However, for WPT systems, the changing coils distance and variable load make the output power fluctuant. In this article, a switched-capacitor-based half-wave rectifier with active impedance matching ability is proposed in the WPT system to solve the issue. Different from typical half-wave rectifier, the conducting time of the diode in the proposed topology becomes adjustable, making the equivalent impedance controllable. Compared with the universal methods, where an additional dc-dc converter located at the end of the rectifier for power adjustment, fewer components are employed and soft-switching is achieved for the rectifier switch in the proposed topology, leading to lower cost, higher power density, and higher efficiency. In the theoretical analysis, the operation principle is given and the relationship between the diode conducting time and the equivalent load is obtained. A prototype was built to verify the performance of the proposed topology, the experiments agree with the calculation well.

Quasi-Z Source T-Type Power Converter for PV Based Commercial and Industrial Nanogrids with Active Functions Strategy

Since most power electronics used in photovoltaic (PV) inverters at commercial and industrial facilities exhibit behavior as non-linear loads from the grid side, these high-power demand installations are expected to have a major impact on the network’s power quality. In an attempt to facilitate their integration into the distribution grid, this paper presents a comprehensive control strategy for Quasi-Z Source T-Type PV inverters inside a facility, which performs active and reactive power control, and harmonic and imbalance compensation at expenses of the spare inverter power capacity. Unlike other approaches, the one proposed here operates properly under distorted and unbalanced grid voltages. The electrical network structure inside a commercial and industrial facility is considered, analyzing the operation of the proposed strategy on three-phase PV inverters. The power topology used has voltage boosting ability, which eliminates the requirement for both an additional DC-DC converter and/or a step-up transformer commonly used in PV inverter systems. The proposed strategy performance is demonstrated on a 50 kW converter model under a disturbed grid environment and changing load conditions.

Flexible Converters for Meshed HVDC Grids: From Flexible AC Transmission Systems (FACTS) to Flexible DC Grids

Flexible Alternating Current Transmission Systems (FACTS) have achieved to enhance the flexibility of modern AC power systems, by providing fast, reliable and controllable solutions to steer the power flows and voltages in the network. The proliferation of High Voltage Direct Current (HVDC) transmission systems is leading to the opportunity of interconnecting several HVDC systems forming HVDC Supergrids. Such grids can eventually evolve to meshed systems which interconnect a number of different AC power systems and large scale offshore wind (or other renewable sources) power plants and clusters. While such heavily meshed systems can be considered futuristic and will not certainly happen in the near future, the sector is witnessing initial steps in this direction. In order to ensure the flexibility and controllability of meshed DC grids, the shunt connected AC-DC converters can be combined with additional simple and flexible DC-DC converters which can directly control current and power through the lines. The proposed DC-DC converters can provide a range of services to the HVDC grid, including power flow control capability, ancillary services for the HVDC grid or adjacent grids, stability improvement, oscillation damping, pole balancing and voltage control. The present paper presents relevant developments from industry and academia in the direction of the development of these converters, considering technical concepts, converter functionalities and possible integration with other existing systems. The paper explores a possible vision on the development of future meshed HVDC grids and discusses the role of the proposed converters in such grids.

Active Rectification For the Optimal Command of Bidirectional Resonant Wireless Power Transfer Robust to Severe Circuit Parameters Deviations

In this article, a method resorting to active rectification for the optimal control of a bidirectional resonant wireless power transfer system is proposed. Benefiting from a dual active bridge topology and without requiring any additional dc-dc converter, the real and the imaginary parts of the equivalent load impedance are modulated simultaneously and independently, for achieving optimal operating conditions despite circuit parameters deviations. Based on a first harmonic analysis, the methodology and its beneficial impacts against variations in the windings mutual inductance or against mistuned resonant capacitor are presented and illustrated. By an argued discussion, the proposed method extent is enlarged to changes in any circuit parameters. Time-domain simulations of the converters topology and command demonstrates the method effectiveness by achieving the system maximum efficiency. Controllability restrictions preventing the compensation of the most severe parameters variations are highlighted. Associated with the limited voltage producible by conventional full-bridge converters, the latter restrictions are surmounted with success by considering Z-source topologies for the front-end and back-end converters.

Efficiency and performance analysis of DTC‐based IM drivetrain using variable dc‐link voltage for electric vehicle applications

In recent times, there has been a surge in R&D activities in the area of electric vehicles (EVs). This surge is fuelled by various governmental policies that aim at increasing the penetration of EVs on roads. This work aims at developing and analyzing drivetrain configurations for city commute vehicles. Since city commute involves frequent start stops, it is necessary to focus on the dynamic performance as well as the system efficiency. Here two drivetrain configurations are considered. The first has a battery pack, an inverter, and an induction motor while the second configuration has an additional dc-dc converter. A detailed control strategy for each drivetrain is presented. Moreover, an experimental setup is developed that mimics the behavior of a scaled-down vehicle. Both the configurations are subjected to extensive experimentation using the developed setup and it is found that despite the use of an additional dc-dc converter, the second configuration has better overall system efficiency in city driving conditions. To explain the results, detailed efficiency maps of the individual subsystem and the overall system are also presented. Furthermore, the drive cycle response and energy consumption analysis, for both the drivetrains for NYCC and city part-NEDC are presented.

A Novel PV Microinverter With Coupled Inductors and Double-Boost Topology

A coupled-inductor double-boost inverter (CIDBI) is proposed for microinverter photovoltaic (PV) module system, and the control strategy applied to it is analyzed. Also, the operation principle of the proposed inverter is discussed and the gain from dc to ac is deduced in detail. The main attribute of the CIDBI topology is the fact that it generates an ac output voltage larger than the dc input one, depending on the instantaneous duty cycle and turns ratio of the coupled inductor as well. This paper points out that the gain is proportional to the duty cycle approximately when the duty cycle is around 0.5 and the synchronized pulsewidth modulation can be applicable to this novel inverter. Finally, the proposed inverter servers as a grid inverter in the grid-connected PV system and the experimental results show that the CIDBI can implement the single-stage PV-grid-connected power generation competently and be of small volume and high efficiency by leaving out the transformer or the additional dc-dc converter.

An Ultrahigh-Speed, Low Power Electrical Drive System

New emerging applications in the areas of portable power generation, small turbocompressors and spindles require the development of ultrahigh-speed, low power electrical drives. A 500 000 r/min, 100 W electrical drive system is presented. Because of the ultrahigh-speed requirements, standard machine design and power electronic topology choices no longer apply and the complete drive system has to be considered. A permanent magnet machine with a slotless litz-wire winding is used, which results in a low motor inductance and a high fundamental machine frequency. Three different combinations of power electronic topologies and commutation strategies have been experimentally investigated. A voltage source inverter with block commutation and an additional dc-dc converter is selected as the most optimal choice for the power electronics interface as it results in the lowest volume of the entire drive system due to lower switching losses, no heat sink cooling required, a small number of semiconductor devices, and relatively simple control implementation in a low cost digital signal processor.

Compact, reliable efficiency

The work presents a multiphase DC-DC converter aimed to equip a C segment, next generation car having a 42/14 V automotive dual-voltage electric power system. The inverted power flow can be obtained by an additional DC-DC converter working in step-up mode or by using electronic interface based on a bilateral converter topology. The experimental result show that proposed solution has greater efficiency over the entire input voltage range.