Direct Converter Research Articles

Performance Analysis of LLC Resonant and Pulse Width Modulation Direct Current- Direct Current Converters for Buck and Boost Operation

Performance Analysis of LLC Resonant and Pulse Width Modulation Direct Current- Direct Current Converters for Buck and Boost Operation

Design and implementation of an innovative single-phase direct AC-AC bipolar voltage buck converter with enhanced control topology

Direct AC–AC converters are strong candidates in the power converting system to regulate grid voltage against the perturbation in the line voltage and to acquire frequency regulation at discrete step levels in variable speed drivers for industrial systems. All such applications require the inverted and non-inverted form of the input voltage across the output with voltage-regulating capabilities. The required value of the output frequency is gained with the proper arrangement of the number of positive and negative pulses of the input voltage across the output terminals. The period of each such pulse for low-frequency operation is almost the same as the half period of the input grid or utility voltage. These output pulses are generated by converting the positive and negative input half cycles in noninverting and inverting forms as per requirement. There is no control complication to generate control signals used to adjust the load frequency as the operating period of the switching devices is normally greater than the period of the source voltage. However, high-frequency pulse width modulated (PWM) control signals are used to regulate the output voltage. The size of the inductor and capacitor is inversely related to the value of the switching frequency. Similarly, the ripple contents of voltage and currents in these filtering components are also inversely linked with PWM frequency. These constraints motivate the circuit designer to select high PWM frequency. However, the alignment of the high-frequency control input with the variation in the input source voltage is a big challenge for a design engineer as the switching period of a high-frequency signal normally lies in the microsecond. It is also required to operate some high-frequency devices for various half cycles of the source voltage, creating control complications as the polarities of the half cycles are continuously changing. This requires at least the generation of two high-frequency signals for different intervals. The interruption of the filtering inductor current is a big source of high voltage surges in circuits where the high-frequency transistors operate in a complementary way. This may be due to internal defects in the switching transistors or some unnecessary inherent delay in their control signals. In this research work, a simplified AC–AC converter is developed that does not need alignment of high-frequency control with the polarity of the source voltage. With this approach, high-frequency signals can be generated with the help of any analog or digital control system. By applying this technique, only one high-frequency control signal is generated and applied in AC circuits, as in a DC converter, without applying a highly sensitive polarity sensing circuit. So, controlling complications is drastically simplified. The circuit and configuration always avoid the current interruption problem of filtering the inductor. The proposed control and circuit topology are tested both in computer-based simulation and practically developed circuits. The results obtained from these platforms endorse the effectiveness and validation of the proposed work.

К выбору параметров регулятора непосредственного понижающего преобразователя с одноконтурной системой управления с учетом динамических нелинейностей

The article is devoted to the issues of choosing the parameters of a proportional-integral-differentiating regulator of a single loop control system with a buck converter taking into account dynamic nonlinearities This problem arises when it is necessary to design pulsed voltage conver¬ters with increased performance, when it is necessary to increase the cutoff frequency of an open-loop control loop without the possibility of increasing the carrier frequency of pulse width modulation due to limitations of the element base, which in some cases leads to the appearance of nonlinear effects. This must be taken into account when choosing both the open-loop cutoff frequency and the stability margin. The article proposes a nonlinear dynamic model of a direct buck converter with a proportional-integral-differentiating regulator both in the form of a piecewise smooth system of differential equations and in the form of a Poincaré map. A method for selecting controller parameters is proposed for a given open-loop cutoff frequency, and a given stability margin, as well as for given ranges of input voltage and load resistance based on the use of numerical methods for solving systems of nonlinear equations with given restrictions. The nonlinear dynamics of the system was studied for various sets of controller parameters. It is shown that with an increase in the cutoff frequency and small stability margins, undesirable dynamic modes may arise in the system when the filter capacitance drops within the calculated values, while linear dynamic models show the stability of the system. To eliminate the possibility of the emergence of undesirable modes, it is necessary to increase the stability margin with subsequent monitoring of the results using a nonlinear dynamic model. The proposed method for selecting the cutoff frequency of an open loop and the phase stability margin, based on the analysis of nonlinear dyna¬mics, allows you to design power supplies with increased performance.

Long-Horizon Sequential FCS-MPC Approaches for Modular Multilevel Matrix Converters

The Modular multilevel matrix converter (M3C) is a direct ac-ac power converter that presents several features such as scalable and flexible structure, high efficiency, fault-tolerant capability, and high power quality. However, this converter requires a complex control strategy to govern the cluster currents and balance the internal floating capacitor voltages among clusters and cells. To fulfill these requirements, this work proposes a long-horizon sequential finite-control-set model predictive control (sFCS-MPC). The resulting predictive strategy is formulated to perform both the local cell balancing control and to regulate cluster currents of the M3C in a unified control algorithm, considering the nonlinear and coupled dynamic model of each cluster. Additionally, the total available combinations and the average cell switching frequency are reduced. The proposed sFCS-MPC is implanted for a prediction horizon from one to four, and compared with some previous FCS-MPC approaches. Experimental results on a 3 kW prototype are provided to demonstrate the effectiveness and high-quality performance of the proposed strategy.

The hybrid solar energized back-to-back high voltage direct current modular converter for distributed networks

The hybrid solar energized back-to-back high voltage direct current modular converter for distributed networks

A Bidirectional Direct AC-AC Resonant SCC

A direct ac-ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant voltage regulator (CVR), and constant current regulator (CCR). Zero voltage switching (ZVS) and zero current switching (ZCS) operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference (EMI) noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

Emulator of electrocardiographically biopotentials based on a sliding mode controlled buck power converter

The primary objective of this research is to present the design of an artificial signal generation system of electrocardiography continuous signals based on the application of a buck power converter. A first-order sliding mode control application for a buck direct current–direct current power converter induces the generation of continuous variations of a direct current voltage as the response of a power converter. The output voltage reproduces the required electrocardiography signals corresponding to the regular or pathological variants. The equivalent control method permits introducing a novel design of a kind of cascade-like sliding mode controller that can regulate both current and voltage operative loops simultaneously, which force the controlled tracking of the reference bioinspired voltages at the output of the buck power converter. For the developed control design, the current regulation is enforced as the primary outcome of the sliding mode controller. Consequently, the required voltage from the buck converter is produced, regulating the switching operation in the electrical power system. The suggested control operates robustly concerning the internal uncertainties and perturbations for both input and voltage signals. Furthermore, the variation of the needed gain for the designed sliding mode controller is developed by studying the online amplitude of the electrocardiography electrophysiological signals used as references and their time derivatives over time. Two reference signals were developed to validate the controllers with the same quality at the numerical simulation and using some experimental validations. The proposed signals used as references were successfully generated in both evaluated cases.

Analytical Benchmarking of Direct Hybrid Switched-Capacitor DC-DC Converters

Analytical Benchmarking of Direct Hybrid Switched-Capacitor DC-DC Converters

An Intelligence-Based Controller for Improved Frequency Regulation in Deregulated Power Environment

A methodology for designing and assessing an optimal controller to regulate frequency in a two-area interconnected power system with Renewable Energy Sources (RES) is demonstrated in this paper. The Load Frequency Control (LFC) system makes it possible to restore both system frequency and scheduled tie-line power to their nominal values in a deregulated environment. The introduction of an advanced controller has the potential to improve the LFC mechanism's performance. The present article employs the Inertia Emulation Technique (IET) to demonstrate the potential influence of the novel High Voltage Direct Current (HVDC) tie-line model and converter capacitors. The Integral Time-weighted Absolute Error (ITAE) has been taken as an objective function for the proposed controller. This investigation proposes a novel adaptive control strategy i.e., ANN-based (PIλf + PIλDN) controller for the anticipated LFC mechanism. The modified Quasi-Opposition-learning-based Volleyball Premier League (QOVPL) method is utilized to assess the optimal control parameters with the highest efficacy. The effectiveness of the proposed LFC framework has been evaluated through the implementation of established methodologies for managing step and random load perturbations. The supremacy and effectiveness of the proposed control scheme are validated over recently published work.

Neural Dielet 2.0: A 128-Channel 2mm×2mm Battery-Free Neural Dielet Merging Simultaneous Multi-Channel Transmission through Multi-Carrier Orthogonal Backscatter.

Miniaturization of wireless neural-recording systems enables minimally-invasive surgery and alleviates the rejection reactions for implanted brain-computer interface (BCI) applications. Simultaneous massive-channel recording capability is essential to investigate the behaviors and inter-connections in billions of neurons. In recent years, battery-free techniques based on wireless power transfer (WPT) and backscatter communication have reduced the sizes of neural-recording implants by battery eliminating and antenna sharing. However, the existing battery-free chips realize the multi-channel merging in the signal-acquisition circuits, which leads to large chip area, signal attenuation, insufficient channel number or low bandwidth, etc. In this work, we demonstrate a 2mm×2mm battery-free neural dielet, which merges 128 channels in the wireless part. The neural dielet is fabricated with 65nm CMOS process, and measured results show that: 1) The proposed multi-carrier orthogonal backscatter technique achieves a high data rate of 20.16Mb/s and an energy efficiency of 0.8pJ/bit. 2) A self-calibrated direct digital converter (SC-DDC) is proposed to fit the 128 channels in the 2mm×2mm die, and then the all-digital implementation achieves 0.02mm2 area and 9.87μW power per channel.

Comparison of Different Optimization Techniques for Model-Based Design of a Buck Zero Voltage Switching Quasi-Resonant Direct Current to Direct Current Converter

The present paper provides a comparison of different optimization techniques applied to the model-based design of a Buck Zero Voltage Switching (ZVS) Quasi-Resonant DC-DC Converter. The comparison was made both on the basis of the duration of the optimization procedures and in terms of guaranteeing the performance of the power electronic device. The main task of the paper is to present various techniques based on the use of mathematical software for the optimal design of Quasi-Resonant DC-DC converters. These topologies were chosen because in them, the design is carried out according to computational procedures, in which several iterations are often necessary for the successful completion of the process. An optimization procedure with a target function reference curve of the output voltage was used. In this way, the optimization is performed without the need for a complete design of the device but only by using base ratios, design constraints, and past experience to determine initial values and intervals of change in circuit parameters. This is also the main advantage of the used optimization of the reference curve type of the output, compared to applying other objective functions, such as achieving minimum losses or maximum efficiency of the device.

A bridgeless configured asymmetrical alternating current–direct current converter‐based isolated single‐stage electric vehicle battery charger with supply side power factor enhancement

AbstractAn approach is presented to employ two different types of converters in bridgeless configuration for supply side power factor enhancement of the system. The isolated single‐stage electric vehicle battery charger uses two different converters in a bridgeless configuration to extract the advantages of both converters for supply‐side power factor enhancement. For the negative and positive semi‐cycles of the supply voltage, the power factor‐enhanced asymmetrical alternating current–direct current converter utilises a fourth order single‐ended primary‐inductor converter and a second order buck‐boost converter, respectively. The use of single‐ended primary‐inductor converter and buck‐boost converter in bridgeless configuration reduces the net order of the system with respect to conventional bridgeless‐single‐ended primary‐inductor converter schemes. The buck‐boost converter also needs the supply‐side filter to eradicate the unwanted harmonics in the supply current which increases the order of the system. The usage of both converters presents many benefits like input inductance of the single‐ended primary‐inductor converter can be utilised as a filtering element with a capacitor for the buck‐boost converter. The anti‐parallel diode conduction operation of both switches facilitates the elimination of extra reverse feed diodes (generally used in bridgeless schemes). The single‐stage charger itself comes with the benefit of elimination of extra stages and thus the losses associated with it. The presented charger also witnesses the elimination of the rectifier due to usage of bridgeless configuration. The isolated single‐stage electric vehicle battery charger is also garnished with electrical isolation which adds to the safety standard of the system. To attain power factor enhancement, the asymmetrical alternating current–direct current converter functions in discontinuous current conduction mode in the present work. The elimination of extra‐stages (with respect to two stage charger), a filter, a rectifier, two extra reverse‐feeding diodes, one voltage sensor, one current sensor (with respect to continuous current conduction mode), and electrical isolation not only makes the system compact and safer but also makes the system cheaper. Elaborated mathematical modelling and stability analysis of the presented alternating current–direct current converter using a pole‐zero map and bode plot have been included in the article. The prototype and MATLAB/Simulink model of isolated single‐stage electric vehicle battery charger system with discontinuous current conduction mode control has been built and results of both prototype and MATLAB/Simulink are deployed to verify isolated single‐stage electric vehicle battery charger system's performance during dynamic and steady‐state conditions.

Bidirectional controller supported inductively coupled dual buck converter based DSTATCOM with passive filterfor PQ improvement

This research paper explains about the bidirectional controller (BC) supported inductively coupled dual buck converter (IC-DBC) based distributed static compensator (DSTATCOM) with passive filter (PF) for 3-ф 3-wire (3P3W) power distribution system (PDS). The most significant concern in the PDS is power quality (PQ) control. Hence, innovative approach is proposed by considering concept and benefits of BC, inductive coupled filtering transformer (IFCT), passive filter and dual buck converter. Equivalent circuit for IC-DBC based DSTATCOM is realized in view of impedance of transformer and direct coupled dual buck converter (DC-DBC) based DSTATCOM to disclose the filtering mechanism. The supremacy of the proposed DSTATCOM is introduced by comparing its simulation outcomes with DC-DBC based DSTATCOM and IC-DBC based DSTATCOM in terms of better harmonics curtailment, power factor advancement, load balancing &amp;amp; reduced DC link voltage compared to other approaches as per IEEE standard.

Multi‐objective optimization method for control parameters of flexible direct current transmission converters based on intelligent algorithms

AbstractIn order to meet the current needs of power transmission, people have turned their attention to direct current (DC) transmission. When the alternating current(AC) power grid (PG) fails, it is easy to cause commutation failure in the DC system, thereby increasing the fault scope of the system. Therefore, this article adopts a flexible DC transmission system. Flexible DC converters have many control parameters, and there are mutual influences and conflicts between these parameters. By applying intelligent algorithms to multi‐objective optimization (MOP), these complex MOP problems can be effectively solved and an optimal set of control parameter combinations can be found. This method has an important contribution and novelty for optimizing the converter control parameters of flexible DC transmission systems. This article achieves fast and accurate MOP of the control parameters of flexible DC transmission converters by continuously detecting the similarities between antibodies and maintaining the diversity of the population. The research results show that the average DC side current is about 405A in the first 20 seconds, and the DC side current fluctuates regularly after 20 seconds. This article lays the foundation for establishing a real‐time simulation model of flexible DC transmission systems suitable for real‐time simulation systems.

Passivity-Based Control of Three-Phase PWM AC-DC Converters with Close to Unity Power Factor and RL Load

In the present work, a strategy is proposed to control the pulse width modulation signals of the power devices of high switching of a three-phase alternating current to direct current converter as well as the current of a load type RL guaranteeing that the power factor of the supply be the unity, which is achieved by taking advantage of the properties that the complete mathematical model has in the two-phase synchronous frame of reference. Likewise, a formal stability analysis of the complete closed-loop system is presented, thereby demonstrating that the proposed scheme guarantees global asymptotic stability with all bounded internal signals.

Fuzzy logic-based controller of the bidirectional direct current to direct current converter in microgrid

Microgrids are small-scale power networks that include renewable energy sources, load, energy storage systems, and energy management systems (EMS). Lithium-ion batteries are the most used battery for energy storage in microgrids due to their advantages over other types of batteries. However, to protect the battery from the explosion and to manage to charge and discharge based on state-of-charge (SoC) value, this type of battery requires the use of an energy management system. The main objective of this paper is to propose an intelligent control strategy for energy management in the microgrid to control the charge and discharge of Li-ion batteries to stabilize the system and reduce the cost of electricity due to the high cost of grid electricity. The proposed technique is based on a fuzzy logic controller (FLC) for voltage control. The FLC is based on the measured voltage of the direct current (DC) bus and the fixed reference voltage to generate buck/boost converter signal control. The proposed technique has been simulated and tested using MATLAB/Simulink software which illustrates the tracking of desired power and DC bus voltage regulation. The simulation results confirm that the proposed systems can diminish the deviations of the system's voltage.

A Direct AC–AC Switched-Capacitor Converter With Input-Series Output-Parallel and In-Phase/Out-of-Phase Capabilities

In this paper, a bidirectional transformerless multi-level direct ac-ac switched-capacitor converter (SCC) is proposed with both in-phase and out-of-phase output voltage capabilities. This converter can be used for series compensator applications, such as dynamic voltage restorers (DVRs), to compensate grid voltage sag and swell phenomena by incorporating its input-output common ground. Its input-series output-parallel capabilities reduce voltage and current stresses of the converter components in multi-level configurations, which lead to higher efficiency and lower manufacturing costs for high-power applications. Furthermore, proper utilization of an interleaving control scheme can provide lower input and output currents ripples values and smaller filter sizes. The proposed SCC operation principle and its mathematical analyses are given, in detail. Additionally, its switching patterns have been developed with a safe-commutation strategy to obtain various output voltages. Subsequently, both single- and two-level SCC prototypes are implemented as series compensators for DVR applications. Moreover, experimental results are given to generate in-phase and out-of-phase regulated output voltages. The experimental results at 2 kW show that the output voltage changes are less than 3% under the steady-state conditions, despite the large input voltage changes from 140 to 300V. The converter maximum efficiency value is equal to 95.4% at maximum output power value.

Improving the quality of the stabilization of the output current of the pulse dc converter operating on a plasma arc

Purpose. Improving the quality indicators of control processes for pulsed DC converters operating on an arc load, based on the construction of procedures for the synthesis of robust systems. Methodology. A method of improving the quality of stabilization of the output current of a pulsed direct current converter based on a combination of disturbance control with control of the output current deviation from a given value (localization method) is considered. Findings. The article deals with the solution of the optimization problems of the output current stabilization system of the pulsed direct current converter feeding the plasma arc under, among other things , stochastic external influences in connection with the problems of non-roughness and strict implementation of optimal regulators and the solution of optimization problems according to the quality of invariance. Methods for constructing optimal controllers are considered and the possibility of solving the optimization problem by the invariance property is established. Examples of solving deterministic and stochastic optimization tasks are given, taking into account the properties of roughness, structural and strict implementation of the stabilizing regulator. Better accuracy of arc current stabilization in statics and dynamics is provided, which is confirmed by simulation modeling. The quality of arc current stabilization is achieved when using control systems based on the quality of invariance and solving optimization problems in the class of "good" regulators built on the basis of the localization method. Regulators calculated on the basis of the correlations of the localization method provide the required quality of the processes and have the property of roughness (robustness) in relation to the deviation of the object parameters from the nominal values in a wide range. If the object contains non-stationary parameters or its properties are not fully known, in this case it is better to use the localization method to calculate the controller. Originality. We received further development of the procedure for the synthesis of optimal regulators and methods of solving optimization problems by the property of invariance. Practical value. On the basis of the method of combined control and the concepts of localization, the optimal laws of control of free and forced movements of a one-dimensional system are synthesized. The latter, however, has the property of rudeness. The efficiency of the synthesized algorithms is illustrated by the results of mathematical modeling.

Three-Level Isolated Direct AC–AC Converter and its Closed-Loop Control Strategy

The isolated direct AC-AC converter has the advantages of high power density and long life time, however, suffering from the high cost and relatively low efficiency. In this paper, a three-level isolated direct resonant AC-AC converter is proposed, thus the voltage stress of power switches reduce to half of the input voltage amplitude and as a result, the voltage rating of the power switches is reduced. A hybrid modulation strategy for the proposed converter is proposed to realize the AC-AC conversion and reduce the switching power loss. Furthermore, in order to obtain a good control of the output voltage based on the proposed converter, the closed-loop control strategy of the output voltage combining a linear controller with the repetitive controller is proposed and the detailed parameters design rule is discussed. The proposed control strategy not only realizes the sinusoidal output voltage waveforms and good dynamic performance, but also effectively eliminates the effect of input voltage harmonics. The corresponding proposed topology, modulation and closed-loop control strategy are all verified by the detailed experimental results.

A self-powered synchronous magnetic flux extraction interface for electromagnetic energy harvesting

In this work, a self-powered synchronous magnetic flux extraction (SP-SMFE) circuit is proposed for electromagnetic energy harvesting. It's a bridgeless direct ac-dc converter, that uses a large-value external inductor L to store and transfer energy. By comparing the voltage across L, SP-SMFE achieves the peak detection of the inductor current Iem without an external power supply and transfers the energy to the load when Iem reaches the peak value, which can maximize the energy extraction from the electromagnetic transducer. Simulation results show that the output power of SP-SMFE is much higher than that of the voltage doubler circuit under the load range of 1–100 kΩ and the frequency range of 20–140 Hz. The input ac voltage with 4 V amplitude is rectified and stepped up to 59 V dc by SP-SMFE at the load of 100 kΩ and the frequency of 40 Hz. Experiment results verify the effectiveness of the SP-SMFE circuit in power harvesting at low frequencies and large loads.