DC Load Research Articles

A Modular Multifunction Power Converter Based on a Multiwinding Flyback Transformer for EV Application

In this article, a revolutionary and novel single-stage, multiport power conversion block is proposed. The power conversion concept is based on a bidirectional flyback converter with four-quadrant switches that permit us to seamlessly control the direction of the energy flow and to select which ports are active. This approach, denominated as multicell multiport bidirectional flyback (M2BF), can be used as a modular and a multifunction building block interfacing ac and dc sources and loads in complex conversion systems like the one we can encounter in electric vehicle (EV) applications. The multiport property is obtained due to the multiwinding flyback transformer that interfaces different sources and loads in a simple and effective way. We present and analyze this concept in detail, focusing on different operation modes it can provide (multiport dc–dc conversion, ac–dc conversion, vehicle-to-grid, grid-to-vehicle, and so on) and their possible implementation in the energy distribution network of an EV, where this unique multifunction multiport converter could bring an important breakthrough. The operating principles of the M2BF for different operating modes are described and analyzed, placing emphasis on the modularity of the proposed concept. The overall concept is evaluated and quantified using a gallium nitride (GaN)-based prototype achieving efficiencies higher than 91% that additionally validates the proposed idea experimentally. The presented analysis and experimental results clearly identify the advantages and limitations of the presented concept leaving no doubt about its usefulness to the future EV distribution network.

Adaptive charging control using ANN-PID controllers on multiple DC loads with varying battery voltages

Various rechargeable electronic devices currently have batteries with different capacities and voltages, while the available chargers are generally fixed for one device. This is considered less effective because different types of electronic devices will require different battery chargers. Therefore, the adaptive power charge is needed to recharge batteries with different voltages and capacities through a single port by adjusting the type of load connected. This system uses buck converter with duty cycle settings through microcontrollers to lower the input voltage to variable output voltage. When the load is connected, the limit switch will be depressed and the system will start the duty cycle tracking process. The voltage will be increased gradually until the current is read at a certain value to identify the load. After the current reads the duty cycle stops tracking, then the current and voltage characteristics are used as input variables for the artificial neural network (ANN) algorithm to determine the target setpoint voltage to be executed by the proportional, integral and derivative (PID) controller. The designed adaptive power charge can identify the connected load accurately. The average ANN output error is 1.46e-4% and the average PID controller error is 6.4e-2%. The system can reach a steady state at 0.01 s.

Optimal design and decoupling control of series DC-link voltages for quadruple-active-bridge based UPQC

This study presents an optimal design and decoupling control scheme of the series DC-link voltages for a quadruple-active-bridge (QAB) based unified power quality conditioner (UPQC). Because of the advantages of more flexibility and higher power density for the UPQC-QAB, more DC ports are accessible for DC loads or renewable energy source (RES). Applying the QAB in the UPQC, the series and shunt converter do not share the same DC-link. Thus, the series DC-link voltages can be adaptively adjusted, while the shunt one remains stable. To improve the operation efficiency of the UPQC-QAB, an optimal operation scheme is presented by minimizing the total series DC-link voltages. However, due to the strong cross-coupling and nonlinear characteristic of the QAB, it is not easy to achieve good dynamic performance. To address this issue, the extended-state-observer based super-twisting algorithm (STA) is presented for the QAB. Finally, the simulation and experimental (OPAL-RT) results verify the correctness and effectiveness of the proposed scheme.

Hybrid SFLA MPPT design for multi-module partial shading photovoltaic energy systems

ABSTRACT Under partial shading conditions, the photovoltaic (PV) array will induce several local maximum power points, such that the traditional maximum power point tracking (MPPT) methods will trap in false maximum power points and reduce the energy conversion efficiency of the solar system. To solve this problem, this paper firstly introduces a multi-module solar energy system, where a master boost converter is used as a voltage regulator for the DC load, while other slave boost converters in parallel perform MPPT to support the load power as high as possible. Furthermore, a hybrid MPPT method is proposed by combining the shuffled frog leaping algorithm (SFLA) and the incremental conductance (In-Cond) method. The hybrid SFLA method can successfully and quickly find the maximum power region, while the exact MPP is achieved in the incremental conductance searching phase. As a result, trapping local maximum power points is avoided, while the computing complexity is reduced. Finally, simulation and experiments are carried out to verify the validity of the proposed MPPT method under partial shading conditions.

LVDC Bipolar Balance Control of I-M2C in Urban AC/DC Hybrid Distribution System

With the high proportional renewable energy integration and rapid increase in the DC loads, such as the electric vehicle and distributed energy storage, the DC distribution system becomes a prospective solution for the urban power grid enhancement for its high-efficiency and eco-friendly nature. In most DC distribution systems, power interfaces are applied to connect low-voltage DC (LVDC) distribution systems with multiple medium-voltage (MV) systems in order to improve the operating reliability and economy. Compared to other types of multiports power interfaces, the three-port-isolated modular multilevel converter (I-M2C) has shown many advantages, including low cost, high power density, and low control complexity. However, the I-M2C cannot handle the power imbalance at the bipolar LVDC port like the other MMC-based three-port power interfaces, which limits the operating range and decreases the stability of the I-M2C in bipolar LVDC application. In order to solve the bipolar imbalance problems, a novel balance control method is proposed in this article. The proposed balance control method is based on symmetrical decomposition. By decoupling the MV power control and the LV bipolar power compensation control, the proposed method can eliminate the bipolar voltage deviation under different working conditions. The simulation results prove the validity and good control performance of the proposed method.

High-Precision Low-Temperature Drift LDO Regulator Tailored for Time-Domain Temperature Sensors.

This paper proposes a high-precision LDO with low-temperature drift suitable for sensitive time-domain temperature sensors. Its topology is based on multiple feedback loops and a novel approach to frequency compensation, that allows the LDO to maintain a large DC gain while handling capacitive loads that vary over a wide range. The key design constraints are derived by using a simplified, yet intuitive and effective, small-signal analysis devised for LDOs with multiple feedback loops. Simulation and measurement results are presented for implementation in a standard 130 nm CMOS process: the LDO outputs a stable 1 V voltage, when the input voltage varies between 1.25 V to 1.5 V, the load current between 0 and 100 mA, and the load capacitor between zero and 400 pF. It exhibits a DC load regulation of 1 µV/mA, a 288 µV output offset with a standard deviation of 9.5 mV. A key feature for the envisaged application is the very low thermal drift of the output offset: only 14.4 mV across the temperature range of −40 °C to +150 °C. Overall, the LDO output voltage stays within +/−3.5% of the nominal DC value over the entire line voltage, load, and temperature ranges, without trimming. The LDO requires only 1.4µA quiescent current, yet it provides excellent responses to load transients. The output voltage undershoot and overshoot caused by the load current jumping between 0 and 100 mA in 1 µs are: 10%/22% for CL = 0 and 12%/16% for CL = 400 pF, respectively. A comparative analysis against seven LDOs published in the last decade, designed for similar levels of supply voltage and output voltage and current, shows that the LDO presented here is the best option for supplying sensitive time-domain temperature sensors. The smallest thermal drift of the output offset, smaller than +/−15 mV, that is, 6.7 times smaller than its closest competitor, and the best overall performance when PSR up to 1 kHz, was considered.

A Transistor-Based Dual-Band High-Efficiency Rectifier With Dual-Polarity Modes

This letter proposes a dual-band high-efficiency rectifier using a GaN transistor. Positive polarity and negative polarity modes are set at $f_{1}$ , and $f_{2}$ , respectively. Then, the rectifier operation at $f_{1}$ and $f_{2}$ is realized upon adjusting only the phase of the corresponding feedback loop. This releases the limitation that the original power amplifier (PA) must be dual-band operation. In addition, class-F harmonic control theory is used to enhance efficiency. Moreover, the proposed technique has no frequency dependence and can be used to achieve arbitrary frequency ratios. To verify the effectiveness of the proposed method, a high-efficiency rectifier operating at 1.9 and 2.4 GHz is designed and fabricated using a CGH40010F GaN HEMT. Measurements illustrate that the implemented rectifier can realize an efficiency of over 75% at 1.9 GHz and 2.4 GHz when an input power of 40 dBm is applied and the dc load is 70 Ω . Also, the size of circuit is only 4.7 cm x 3.4 cm.

Van der Pol oscillator based on NbO2 volatile memristor: A simulation analysis

Nature positively embodies a rich yet complex array of nonlinear phenomena. To date, it has remained unclear how to exploit these phenomena to solve a wide range of problems. The Van der Pol oscillator is one of the nonlinear dynamical systems that hold tremendous promise for a broad range of important applications from a circuit performance booster to hard problem solving to mapping the biological nonlinear dynamics. Here, we theoretically build a Van der Pol oscillator circuit using a NbO2 volatile memristor to perform a systematic analysis of the complex nonlinear dynamic behavior. Three types of oscillation phenomena including period doubling, quasi-period, and chaos are obtained by varying the parallel capacitance and futher distinguished by mathematical analysis, such as fast Fourier transform, Poincaré plots, and plane trajectories of voltage on the memristor. The frequency locking phenomenon of the system is presented to enable a programmable frequency demultiplication. Moreover, the other critical circuit parameters such as DC voltage amplitude, load resistance, and AC driving frequency are also modulated to understand the nonlinear dynamic behavior of the system. All these analyses provide a viable platform to understand and implement nonlinear systems for a broad range of multifunctional oscillatory devices.

Frequency-Watt and Volt-Var Control by Self-commutated Converter Connected Controllable DC Load

The promotion of renewable energy is accelerated in the world however frequency and voltage profile in the power system may become worse by the generation of renewable energy varied depend on weather conditions. To stabilize the power system, a controllable DC load such as hydrogen supplying equipment connected by self-commutated converter, which can regulate active and reactive power, has attracted much attention as one of the alternative regulating resources. The authors focus on Frequency-Watt and Volt-Var control by self-commutated converter connected controllable DC load. This paper proposes an effective and cooperative system on converter and load to regulate active and reactive power. Moreover, this paper reveals the verification and control ability in the proposed system through simulations, in which frequency and voltage in the power system fluctuate independently.

5kV급 MV-LVDC 독립형 마이크로그리드의 보호협조 운용방안에 관한 연구

Recently, demands on MVDC distribution system is being significantly increased due to interconnection of renewable energy sources, expansion of DC load and high quality and reliability of the power supply system etc., while commercialization of facilities for MVDC is yet in early stage. Accordingly, demonstration projects on applying existing AC devices and cables to MVDC distribution system are being carried out. However, the protection on high-cost facilities such as converters and cables may not be reliable in the event of fault, and then operation method of protection coordination for MV-LVDC micro grid(MG) system is being required. For the purpose of stable operation of the 5kV MV-LVDC micro-grid, this paper proposes operation methods of protection devices depending on scenarios, such as faults on the MVDC line, LVDC line, or customer load. And also, a modeling of 5kV MV-LVDC MG system, which is composed of PV system, ESS, MVDC cable, DC/DC converter, DC/AC inverter, protection devices etc., is performed using PSCAD/EMTDC S/W. From the simulation results based on the proposed modeling and operation method of protection devices, it is confirmed that this paper is useful tool to perform the proper protection coordination.

Wireless power transfer self‐adaptive to incident power density

Inspired by the envision of space solar power satellite, microwave-based wireless power transfer has been intensively studied. To date, while significant progresses have been achieved, bottlenecks still exist. Among them, the deterioration of the radiofrequency (RF)-to-direct current (DC) efficiency due to the variation of incident microwave power is a major problem. It prevents this technology from many practical applications. In this work, based on the dependence between the incident power density and the resistive DC load, we propose a self-adaptive approach to mitigate this deterioration by introducing a continuous DC load modulation. Experiments based on a complex-conjugate rectifying surface showed effective improvements of the RF-to-DC efficiency for the incident power density varied in a wide range.

Direct Sliding Mode Control for Dynamic Instabilities in DC-Link Voltage of Standalone Photovoltaic Systems with a Small Capacitor

Large electrolytic capacitors used in grid-connected and stand-alone photovoltaic (PV) applications for power decoupling purposes are unreliable because of their short lifetime. Film capacitors can be used instead of electrolytic capacitors if the energy storage requirement of the power conditioning units (PCUs) is reduced, since they offer better reliability and have a longer lifetime. Film capacitors have a lower capacitance than electrolytic capacitors, causing enormous frequency ripples on the DC-link voltage and affecting the standalone photovoltaic system’s dynamic performance. This research provided novel direct sliding mode controllers (DSMCs) for minimizing DC-link capacitor, regulating various components of the PV/BES system that assists to manage the DC-link voltage with a small capacitor. DSMCs were combined with the perturb and observe (P&O) method for DC boost converters to increase the photovoltaic system’s dynamic performance, and regulate the battery’s bidirectional converter (BDC) to overcome the DC-link voltage instabilities caused via a lower DC-link capacitor. The system is intended to power both AC and DC loads in places without grid connection. The system’s functions are divided into four modes, dependent on energy supply and demand, and the battery’s state of charge. The findings illustrate the controllers’ durability and the system’s outstanding performance. The testing was carried out on the MT real-time control platform NI PXIE-1071 utilizing Hardware-In-The-Loop experiments and MATLAB/Simulink.

Adaptive Nonlinear Control of Generator Load VSC-HVDC Association

This paper studies the problem of controlling a long distance transmission system for huge amounts of electrical energy (Generator-Load VSC-HVDC). An adaptive controller is designed to meet two controller objectives: (i) regulating the continuous voltage at the end of the HVDC cable; and (ii) ensuring a perfect power quality and system stability, which can be achieved by continuously adjusting the active and reactive powers independently. The controller's robustness is addressed by considering various parameter uncertainties, such as DC cable parameter variations. Furthermore, since the DC load is usually located at great distances from the control unit, a high gain observer is designed to estimate the DC cable states, as well the current in the load. Thus, the output voltage and current of the VSC are the only accessible measurements. The theoretical analysis results are approved by numerical simulation within MATLAB/SIMULINK environment.

Impact of MV Standards on Shipboard DC Cable System Size

There is rising interest in medium-voltage direct current (MVDC) power systems for several reasons, including compatibility with DC loads and avoidance of alternating current (AC) frequency synchronization issues when combining multiple source outputs [1]. However, few MVDC systems are currently in operation, and there is relatively little experience compared to the knowledge available for medium-voltage alternating current (MVAC) systems. Presently, IEEE Std. 1709 is the only standard that provides guidance for MVDC systems [2]. This work’s objective is to harmonize the information within MVAC standards to produce prospective design and test values for shipboard MVDC cables and evaluate their impact on cable system sizes. Standards for MVAC cable design and test parameters including Basic Lightning Impulse Insulation Level, Withstand Voltage, and cable insulation thickness are compiled to understand the range of parameter values deemed acceptable for MVAC cables. Based on existing shipboard MVAC standards and IEEE Std. 1709, this study produces prospective design and test values for a shipboard MVDC system with a 12 kV Nominal System Voltage. Additionally, a tradeoff was identified with the thickness of cable insulation where a small reduction in cable system size can be achieved but at the expense of substantially greater electric stresses within the insulation.

Study on Stability of Hand-in-hand Structure of Multi-terminal DC Hydrogen Production System

Multi-terminal DC (MTDC) hydrogen production systems are becoming one of the important forms of power distribution systems with the increasing growth of distributed renewable energy sources (such as PV and wind turbines), energy storage devices, and DC loads. To explore the key factors in stability analysis, the circuit diagram of MTDC hydrogen production system in hand-in-hand structure composed of voltage source converters (VSCs), DC lines, renewable energy and DC hydrogen production load was established in this paper. The overall state space model of the system was put forward, taking the master-slave converter control strategy into consideration. Then, the small-signal stability analysis of the MTDC hydrogen production system was carried out by comparing and analyzing the moving trajectories of the dominant eigenvalues in different system parameters. The key factor affecting the stability of the system such as DC capacitance of the converter and the electrolyzer power in the DC bus are determined. On this basis, a simulation model of the low-voltage MTDC hydrogen production system was built based on MATLAB/Simulink to verify the correctness of the theoretical analysis.

Small scale wind & solar photovoltaic energy conversion system for DC microgrid applications

The rise in demand for electrical energy throughout the globe gives a significant rise in new power generating sources. The Wind and Solar Photovoltaic energy sources are the most propitious power generating sources among them. Nowadays, these sources play an important role to form a Micro Grid with the incorporation of conventional grid and energy storage facilities. This article comprises of the simulations analysis for Wind Energy Conversion System and Photovoltaic Energy System incorporated with DC load for the applications of DC Microgrid. The mathematical model of the WECS and PVES are incorporated and proposed with the Gain Scheduled Proportional Integral controller is proposed in the paper. The WECS and PVES are simulated with interfacing units for the DC load. The results are obtained for Ahmedabad, Gujarat, India for the input solar insolation and wind speed data. The materials used in small wind energy conversion systems and photovoltaic energy systems are discussed for microgrid applications. The performance for the WECS and PVES is analyzed for change in wind speed and change in solar insolation. The incorporation of GSPI controller provides stable results to maintain the voltage regulation. The results are stable over an extensive range under the unpredictable atmospheric conditions the dynamic scheduling is proposed.

A Novel Solid-State Transformer With Loosely Coupled Resonant Dual-Active-Bridge Converters

Solid-state transformers (SSTs) utilize multiple isolated dual-active-bridge (DAB) converters to deliver power from a medium-voltage ac or dc grid to low-voltage dc or ac loads. The DAB converter is a key component of SSTs. This study proposes a novel SST with loosely coupled resonant DABs (LCR-DAB) utilizing loosely coupled inductive power transfer (IPT) coils instead of high-frequency (HF) transformers. Unlike HF transformers, the large air gap between the primary and secondary coils enables easier packaging and high-voltage insulation of the proposed LCR-SST system. Series–series compensated symmetric resonant tanks are selected for the proposed IPT system. The impact of the phase-shift angle and the circuit parameters on the input impedance, efficiency, and power transfer direction of the proposed LCR-DAB is investigated. By performing theoretical analyses, a circuit parameter design method for LCR-DAB is proposed. In addition, a new design approach for low-loss coils of the LCR-DAB is investigated using finite-element analysis results. The proposed LCR-DAB and SST topologies are evaluated using the experimental results. The coil-to-coil and dc-to-dc efficiencies of a single LCR-DAB were 97.4% and 96.7%, respectively, over an air gap of 3 cm. The dc-to-dc efficiency of the three-level LCR-SST was 95.2% at 2.4 kW.

Design methodology for digital active disturbance rejection control of the DC motor drive

Digital active disturbance rejection controllers (DADRC) have a wide scope as they have inherent advantages such as: easy hardware implementation, the entire system's mathematical model it is not necessary, is a linear controller dealing with uncertainty and is intended to ensure that energy savings are achieved. This document provides a procedure for designing a DADRC for a dc motor drive from the perspective of a Generalized Proportional Integral observer and differential flatness. The angular speed of a dc motor drive is the main purpose of the controller. The proposed DADRC was implemented using floating point operations on a field programmable gate array Artix-7™ using a Nexys 4 board. The system is subject to current demands, parameter variations, dc power supply changes and external load torque variations. The coupling of buck converter and dc motor resulting in external and internal disturbances that are actively counteracts the linear controller, as shown in the results.

Common Mode Power Control of Three-Phase Inverter for Auxiliary Load Without Access to Neutral Point

The purpose of this article is to investigate the potential of obtaining an auxiliary dc output from the common-mode switching harmonics of a three-phase inverter without access to the neutral point of the ac load. To achieve this, the control of common-mode (CM) switching harmonics with space vector modulation is proposed. With this control, CM switching harmonics can be regulated independently from the differential mode power flow to the main three-phase load. To physically implement the CM power flow, a harmonic extraction circuit is placed in parallel with the main three-phase load. The extraction circuit is formed by series-connected inductance and capacitance. Due to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonance and the mutual coupling of the inductance, only common-mode switching harmonics can pass through the extraction circuit. The extracted harmonics are then rectified and delivered to the auxiliary dc output. The control and topology are verified in both simulations and experiments. In the end, it is shown in experiments that there is no significant difference of the inverter efficiency after the auxiliary dc load is connected. This method can be used for instance to drive an ac machine while charging a low voltage battery or powering a compressor simultaneously.

A power balance control strategy for stand alone wind energy conversion systems

Supplying off-grid areas with stand-alone wind energy conversion systems required a battery charge controller for energy storage. Furthermore, to cope with the stochastic wind nature, the frequent variations of the load demand, together with ensuring a proper battery charging process, based on the available wind power, the battery status, and the load power demand, a multi-mode control strategy is proposed, which can instantly balance the wind power flow delivered to the DC load and the battery. The control system entails three operating modes, namely, maximum power point tracking (MPPT) charging mode, constant current (CC) charging mode, constant voltage (CV) charging mode. Thereafter, a new battery energy management algorithm is also developed, to ensure a smooth switching from one operating mode to another. The controller performances are theoretically analyzed, then are tested through MATLAB/SIMULINK/SIMPOWER environment. The obtained simulation results prove that the proposed controller meets its objectives under various weather conditions and load demand.