Parallel Buck Converters Research Articles

Voltage Drop Compensation Technology for High-Voltage and High-Power DC Energy Storage Power Supply System

This paper presents an output voltage drop compensation technology for high-voltage and high-power DC energy storage system (DC-ESS). This technology is used to improve the output voltage stability of high-voltage high-power DC-ESS in high rate discharge. The proposed output voltage drop compensation technology includes an ESS architecture and a corresponding control method. The proposed ESS architecture adopts DC dynamic voltage regulator (DC-DVR) to compensate for output voltage drop. DC-DVR adopts 6-phase interleaved parallel buck converter. This architecture not only maintains the system output voltage stability, but also reduces the system cost. Moreover, the proposed ESS architecture does not change the original energy storage capacity. The dynamic power flow of the proposed ESS architecture is analyzed and a direct power control method based on full response power compensation is proposed. The steady-state power and dynamic power of the proposed ESS architecture are compensated respectively, so that the input power can quickly track the change of the output power. The proposed control method improves the stability and dynamic response speed in the system dynamic process. Simulation and experiment verify the effectiveness of the proposed ESS architecture and control method.

A Sliding Mode Controller with Signal Transmission Delay Compensation for the Parallel DC/DC Converter’s Network Control System

The network control system (NCS) of the parallel DC/DC converter is always affected by the signal transmission delay, and the ideal output performance is lost. In this paper, a typical parallel buck converter is taken as the research object. Firstly, a sliding mode controller (SMC) in the discrete domain is designed to enhance the robustness of the system. On this basis, the effects of different delays on the stability of the converter’s NCS are analyzed, and the actual effects of long/short delays on the converter’s NCS are obtained. To further solve the problem of damage to transmitted signals of the NCS by long delay, the SM controller designed in this paper is improved by incorporating a multi-step prediction method. This enhancement enables effective prediction and compensation of the delay signals lost by the NCS, ensuring the output performance of the parallel buck converter. Finally, the superiority of the proposed method is verified by designing simulations and experiments.

Power and signal dual modulation‐based bidirectional communication between intrinsically safe converters

AbstractIn harsh operating environments such as mines and gas stations, intrinsically safe power converters are required for electronics devices. Reliable communication is the key ensuring good performance of monitoring and coordinated control for intrinsically safe converters. This paper proposes a power and signal dual modulation (PSDM)‐based communication method for intrinsically safe parallel‐connected Buck converters. The bidirectional communication between two parallel Buck converters is realized by combining the frequency shift keying (FSK) and phase shift keying (PSK) methods. In addition, switching frequencies are employed to identify the signals received from the power converters interfacing different sources. According to the intrinsic safety requirement, inductors and capacitors are redesigned based on the modulated voltage ripples during communication. Simulations and prototype experiments are performed to verify the feasibility of the proposed bidirectional communication for intrinsically safe converters. The amplitude of voltage ripples modulated for carrying data is restricted to less than 1.5% of the bus voltage. The transmission speed can be achieved from 0.5 to 2kbps depending on the adopted switching frequencies. The demodulation delay is less than 5% duration of one bit of transmitted data.

Fault- Tolerant DC-DC Converter with Zero Interruption Time Using Capacitor Health Prognosis

A high-end critical electronic system is expected to have hundreds of electronic subsystems, which rely on the Power Management Unit (PMU) to be energized. Having an efficient PMU is crucial and it requires reliable and well-structured voltage buck converters to translate the supplied voltage levels. The buck converters employed in PMU are expected to be fault tolerant and supply uninterrupted power while serving critical subsystems. Active redundant parallel buck converters employed in PMU to achieve fault tolerance increases overhead in terms of area, cost and power dissipation. In this paper, a DC-DC converter is designed for the PMU by combining two legs of buck converters with an effective output of 3.3 V. A simple yet effective technique is proposed to design a fault-tolerant buck DC-DC converter by bypassing a faulty converter leg. The proposed system utilizes an online signal processing-based method for prognostic fault detection. Ripple content in the voltage of the output Aluminum Electrolytic Capacitor (AEC) is monitored and used as a primary health indicator for the primary buck converter leg. Increase in the output ripple due to degradation is used for the prognosis of primary converter failure. The secondary buck converter leg is activated only upon the confirmed prognosis of a faulty primary converter leg to avoid false triggering. The timely prognosis of primary converter failure and activation of secondary converter facilitates uninterrupted power supply. An experimental setup is built and tested in the laboratory. Experimental results indicate a smooth transition from the primary converter leg to the secondary demonstrating an uninterrupted power supply along with the simplicity and effectiveness of the proposed solution

Design of DC Magnet Power Supply System for ITER Static Magnetic Field Test Facility

International Thermonuclear Experimental Reactor (ITER) static magnetic field (SMF) test facility requires a dc power supply with low voltage, high current, and low harmonics under high power density. Due to the limitation of switching loss, there is a contradiction between the output current capability and the output ripple. Large output current usually leads to low switching frequency, and low switching frequency will generate a large number of harmonics. To solve the problems, a topology based on the interleaving parallel buck converter is used and tested in this article. Moreover, the topology is realized with only a small number of switching metal–oxide–semiconductor field-effect transistors (MOSFETs). This article introduces the system design scheme and control method in detail. The analysis of harmonic and simulation is carried out. The validity of the proposed scheme and control strategy was confirmed by experiments, and the power supply system can supply a large current of 12.23 kA and has the ability of low ripple.

Stabilization of Constant Power Loads in DC Microgrid Systems Using an Adaptive Continuous Control Set Model Predictive Control

This paper represents an adaptive continuous control set model predictive control (CCS-MPC) to solve the disturbance-caused instability problems in a DC microgrid consisting of symmetrical parallel buck converters, constant voltage loads (CVL), and constant power loads (CPL). The symmetric model of the system is founded at first to describe and analyze the disturbance-caused instability problem. To mitigate the instability by taking the disturbances into consideration, the proposed adaptive controller is made from a double loop feedback controller and a feedforward estimation algorithm. In the voltage loop of the double loop controller, a capacitor dynamic-based voltage controller is developed, while in the current loop, a CCS-MPC algorithm is modified and applied. Meanwhile, a feedforward algorithm is developed to estimate the disturbance information and send it to the double loop controller to improve its robustness, so the composite controller can maintain the bus voltage fixed at its reference and the symmetrical equal current sharing. Finally, comparative MATLAB simulations and OPAL-RT hardware-in-the-loop experiments are conducted to verify the effectiveness and dynamic performance of the proposed algorithm towards other previous nonlinear controllers.

Intermittent subharmonic and chaos in parallel Buck converters with coupled interference signal

This paper studies intermittent instabilities in parallel power system. Taking parallel buck converters with coupled interference signals as an example, model and actual system are established. By numerical simulation, the nonlinear behaviours are captured under some conditions. Characteristics and mechanism of intermittency are depicted by nonlinear theory. In this paper, mappings time to parameter are established and discrete iterative mappings for nonlinear systems are derived. All the simulation results are consistent with the theoretical analysis results. The research method adopted in the paper is applicable for the other parallel powersystems. The conclusion can provide a reference for the parallel converters to maintain stable operation and serves as a theoretical basis for further optimization design and system control.

An Extended Stability Analysis Method for Paralleled DC-DC Converters System With Considering the Periodic Disturbance Based on Floquet Theory

Paralleled DC-DC converters system normally is operated with current-sharing control to achieve equal current distribution among the converters connected in parallel. However, the added current-sharing control might make the paralleled DC-DC converters system suffer from potential degradation of stability and dynamic performances. Hence, the stability analysis of paralleled DC-DC converters system is a hot issue. In order to analyze the stability of paralleled DC-DC converters system accurately and effectively, an extended stability analysis method based on Floquet theory is proposed for paralleled DC-DC converters system in this paper with considering the periodic disturbance. And, a paralleled buck converters system with average current-mode control is taken as an analysis object. The extended stability criterion of paralleled buck converters system based on Floquet theory is derived. Finally, the simulation and experimental results verify the correctness and effectiveness of the proposed stability criterion with considering the periodic disturbance. This paper provides a new choice for the stability analysis of paralleled DC-DC converters system.

Mitigation of circulating currents for proportional current sharing and voltage stability of isolated DC microgrid

Droop control is commonly adopted method for sharing load current among parallel-operated DC–DC converters in DC microgrid. However, when different power ratings converters are parallel connected, it gives rise to circulating currents, which deteriorates current sharing. This paper proposes consensus-based distributed secondary control for voltage regulation and current sharing with different rating converters connected. A modified droop control is presented by employing average circulating current control strategy for mitigation of circulating currents. Moreover, to compensate the voltage deviation caused by droop control, a dynamic consensus-based average voltage control is designed. The proposed algorithms can achieve proper current sharing ratio among converters and also guarantee low voltage regulation. The effect of line resistance and communication delay is also considered and better performance is achieved. Simulation and experimental tests on two DC–DC parallel buck converters based microgrid systems show the effectiveness of the proposed method.

New Framework for Optimal Current Sharing of Nonidentical Parallel Buck Converters

In this brief, parallel interconnection of buck (step-down) converters is considered. Classical control of such a topology uniformly distributes load current over branches. Yet, whenever nonidentical converters (having distinct characteristics) are considered, this brief demonstrates, both theoretically and experimentally, that minimizing overall losses requires nonuniform and even load-depend current distribution. In this context, a novel highly modular hierarchical control framework is proposed for arbitrary number of buck converters. Solutions for the two related design steps are given, which lead to a control law minimizing total losses as well as correcting voltage deviation for any operating point and without knowledge about load magnitude. Experimental results support our discussions.

New framework for parallel interconnection of buck converters: Application to optimal current-sharing with constraints and unknown load

In this paper, heterogeneous set of parallel buck converters, feeding an unknown resistive load via a common DC bus, is considered. When addressing control design problem of this interconnected power converter, one has to accommodate competing objectives of (i) voltage regulation and (ii) power distribution among branches, also called current-sharing in this context. Related dynamics being coupled, classical solution resorts to frequency separation to prevent undesirable interaction between them. In stark contrast with this approach, this paper proposes a novel framework which completely separate voltage regulation from current distribution dynamics without frequency separation, hence offering tractability without sacrificing performance. Such a reformulation is performed on the open-loop model so that control law candidates are not confined in some particular class. Arbitrary large set of heterogeneous converters can be handled. Remarkably, voltage regulation boils down to the control of a single virtual buck converter. Controller design example exploiting the new structure is provided. In the context of unknown resistive load, this controller achieves voltage regulation and minimizes overall power losses at the steady-state while taking current limits of each branch into account. Those results are supported by formal statements and proofs, and assessed through experimental results.

An Implementation of Parallel Buck Converters for Common Load Sharing in DC Microgrid

The increase in demand for clean, safe, and environmentally friendly renewable energy sources faces several challenges such as system design and reliable operations. DC microgrid (MG) is a promising system due to higher efficiency and natural interface to renewable sources. In the hierarchical control of DC Microgrid, the V-I droop control is deployed usually in primary control level for common load sharing between converters. However, conventional droop control causes improper current sharing, voltage variations, and circulating current regulation due to the presence of droop and line resistance between converters. The aim of this paper is to presents the primary control level design of buck converters in current mode control according to the concepts of time constant and time delay, and secondary control design for parallel operations in distributed manners by combining methods, namely, low bandwidth communication (LBC), circulating current minimization techniques, and average voltage/current control. Moreover, different time delays are used for two converters to testify the effects of communication delays on current sharing and voltage restoration. The simulation is done for 2 × 2.5 KWdc parallel buck converters in PLECS (a Simulation software used for high speed simulation for power electronics) environment which shows excellent results in minimizing circulation currents, enhancing proportional current sharing, and restoring the grid voltage.

Modeling and Analysis of Four-phase Interleaved Synchronous Rectifier

Because of the efficiency and heating problem, the single-phase BUCK converter cannot be applied to the situation of low voltage and large current. Under the same stress conditions, the multiphase parallel BUCK converter cannot only reduce the output ripple, improve the converter efficiency, but also reduce the volume of the converter. The four-phase interleaved synchronization BUCK converter is used as the research object, and the corresponding mathematical model was established to describe the instantaneous ripple of the converter. Finally, the model was built with Simulink to verify the simulation. The simulation results show that the four phase synchronous rectifier improves the output current and reduces ripple compared with single-phase.

A zero-voltage-switched three-phase interleaved buck converter

ABSTRACTThis paper proposes a three-phase interleaved buck converter which is composed of three identical paralleled buck converters. The proposed solution has three shunt inductors connected between each other of three basic buck conversion units. With the help of the shunt inductors, the MOSFET parasitic capacitances will resonate to achieve zero-voltage-switching. Furthermore, the decreasing rate of the current through the free-wheeling diodes is limited, and therefore, their reverse-recovery losses can be minimised. The active power switches are controlled by interleaved pulse-width modulation signals to reduce the input and output current ripples. Therefore, the filtering capacitances on the input and output sides can be reduced. The power efficiency is measured to be as high as 98% in experiment with a prototype circuit.

Stability Analysis of Multi-Phase Synchronization in Paralleled Buck Converters With Winner-Take-All and Loser-Take-All Switching Rules

This paper studies paralleled systems of buck converters with two kinds of switching rules. First, the system is controlled by the winner-take-all and current threshold switching rules. The system can generate stable multi-phase synchronization of inductor currents. As parameters vary, the multi-phase synchronization loses stability and the system exhibits a chaotic phenomenon in which unstable multi-phase synchronization is embedded. Second, the system is controlled by winner-take-all and loser-take-all switching rules. The system can generate stable multi-phase synchronization in a wide range of parameters: it is suitable to realize current-sharing and ripple reduction for low-voltage-high-current capabilities. In order to analyze the dynamics, we present simple piecewise linear models. Using the piecewise exact solutions, we prove stability of the synchronization phenomena and give a condition of parameters for the stability. We can also investigate the ripple characteristics precisely. Presenting simple test circuits, the stable synchronization phenomena are confirmed experimentally.

Control and Design of a Arc Power Supply for KSTAR's the Neutral Beam Injection

The neutral beam injection generate ultra-high temperature energy in the tokamak of nuclear fusion. The neutral beam injection make up arc power supply, filament power supply and acceleration & deceleration power supply. The arc power supply has characteristics of low voltage and high current. Arc power supply generate arc through constant output of voltage and current. So this paper proposed suitable buck converter for low voltage and high current. The proposed buck converter used parallel switch because it can be increased capacity and decrease conduction loss. When an arc generated, the neutral beam injection chamber occur high voltage. And it will break output capacitor of buck converter. Therefore the output capacitor was removed in the proposed converter. Thus the proposed converter should be designed for the characteristics of low voltage and high current. Also, the arc power supply should be guaranteed for system stability. The proposed parallel buck converter enables the system stability of the divided low output voltage and high current. The proposed converter with constant output be the most important design of the output inductor. In this paper, designed arc power supply verified operation of system and stability through simulation and prototype. After it is applied to the 288[kW] arc power supply for neutral beam injection.

An Experimental Approach for Locating the Current Distribution in Multiphase Buck Converters

The objective of this paper is to present a methodology for identifying the current flow in the capacitors of a multiphase buck converter by synchronously measuring the capacitor currents. A multiphase buck converter uses multiple parallel buck converters with different switching times to source a large amount of current. Currents in the primary capacitors of a multiphase buck converter are drawn by all phases of the converter; however, the phases switch asynchronously. Synchronizing to the switching of a specific phase reveals how the current from that phase is distributed among the capacitors throughout a circuit board. The proposed measurement method is illustrated by comparing an initial printed circuit board design to a new design to show the effect of better capacitor placement and the addition of a ground plane. The new design confines the phase currents to the capacitors close to the field effect transistors of the specific phase.

Non‐linear intermittent instabilities and their control in an interleaved DC/DC converter

The undesirable intermittent instabilities in periodically driven parallel power converter are caused due to periodic interferences in input voltage. This is a more common problem in power electronic circuit design and such operations are usually avoided by controlling the circuit parameters. In this study, the mechanism and conditions for the emergence of intermittent instabilities and remerging chaotic band attractors (or Feigenbaum sequences) in a master-slave controlled parallel buck converter are investigated. It is found that sinusoidal-type interference in input voltage at frequencies near the switching frequency or its rational multiples of this circuit results typically in period-bubbling, chaos and intermittency. It is also shown that an optimal, phase-shifted sinusoidal interference added to the reference voltage controls the period-bubbling behaviour and significantly extends the parameter range of desirable period-1 operation. The dynamics of this converter has been first investigated with suitable numerical simulations. The ordered and the chaotic dynamics of this system have been further mathematically described and analysed with a simple discrete map and experimental means. Experimental observations are found to be in good agreement with the analytical and simulation results.

Predicting Converter Utilization Convergence under Various Dynamic Loading Conditions of Paralleled Converters

In this paper, converter utilization equalization under various dynamic loading conditions experienced by parallel buck converters were observed. Equalization of converter utilization is ensured by using fuzzy logic control while output voltage regulation and current sharing between converters is maintained by employing sliding mode control. This research work has also contributed the derivation of the working equation in determining the converter's utilization point of equalization even in dynamic loading. Simulation results have confirmed that the value solved from the working equations are correct and equal to the value of the utilizations each of the converters converged under a given dynamic load. 

Applications of the generalized state-space averaging method to modelling of DC–DC power converters

Power converter models are time varying because of the switching action of power electronic devices. To find time-invariant models, this tutorial article presents the applications of the generalized state-space averaging method to the modelling of a zeta converter feeding a resistive load and paralleled buck converters driving a DC motor. Simulations using the proposed models with MATLAB coding agree well with the results of PSIM™ and SimPowerSystem™ of SIMULINK. Beside, simulations using the proposed model reduce the simulation time by 64% as an average in comparison with the available software packages.