Series-parallel Converter Research Articles

Design and Implementation of a Modular Multilevel Series-Parallel Converter for Second-Life Battery Energy Storage Systems

Battery Energy Storage Systems (BESS) offer scalable energy storage solutions, especially valuable for remote, off-grid applications. However, traditional battery packs with fixed series-parallel configurations lack reconfigurability and are limited by the weakest cell, hindering their application for second-life batteries. The Modular Multilevel Series-Parallel Converter (MMSPC) addresses these limitations by enabling dynamic reconfiguration, optimizing cell balancing, and enhancing energy control. This paper experimentally evaluates a single-phase BESS based on the MMSPC with an output power equivalent to 2 kW and two battery units (155V), demonstrating stable output and reduced internal losses across varied battery parameters.

Design Considerations for Power-Efficient Fully Integrated 3:1 Switched Capacitor DC-DC Converter for PV Modules

This article presents a power-efficient DC-DC converter based on a switched-capacitor (SC) cell in power management systems supplied for fully integrated photovoltaic (PV) modules. These modules shall provide high-performance point-of-load voltage regulation. The primary objective of this study is to better utilize capacitance and switches by selecting a proper SC topology in order to improve the power efficiency of SC converters. A general steady-state performance model is investigated to optimize and compare a variety of SC DC-DC topologies. The investigation method relies on a charge-multiplier approach and considers the impact of area constraint on capacitors. To identify the most suitable topology for a given conversion ratio, the performance-limit metrics of SC converters are calculated. The analysis provides framework to determine optimum switch size and switching frequency for a two-phase 3:1 series–parallel converter for a target load current of 10 mA implemented on a 22 nm process technology. The results shows that a minimum of 250 MHz switching frequency is desirable for achieving a target efficiency greater than 85% while maintaining the minimum output voltage of 0.34 V. The analysis results are verified through MATLAB and PSpice-based simulations.

Optimal Switching Method Using Variable Additional On-Time Control for CRM-Operated Multicell Series-Parallel Converter

Unlike the conventional boost-derived power-factor-correction (PFC) converter, the multi-cell series-parallel (MCSP) converter can step-up/step-down the output voltage. Its modular concept has a flexibility to select the voltage rating of switches depending on the number of cells. Based on its high degree-of-freedom (DOF) in combination of switching states, this paper proposes an optimal switching method that can suppress the amplitudes of switch currents while improving converter efficiency by synthesizing pentagonal inductor current waveform in critical conduction mode (CRM) control. In addition, a total harmonic distortion of input current (iTHD) is improved with variable additional on-time control. Thanks to an inherent capacitor voltage balancing feature of the MCSP converter, it does not require additional balancing control. The feasibility of the proposed control is verified by experiments in the 300 W prototype.

Degradation-Conscious Multiobjective Optimal Control of Reconfigurable Li-Ion Battery Energy Storage Systems

Lithium-ion battery energy storage systems are made from sets of battery packs that are connected in series and parallel combinations depending on the application’s needs for power. To achieve optimal control, advanced battery management systems (ABMSs) with health-conscious optimal control are required for highly dynamic applications where safe operation, extended battery life, and maximum performance are critical requirements. The majority of earlier research assumed that the battery cells in these energy storage systems were identical and would vary uniformly over time in terms of cell characteristics. However, in real-world situations, the battery cells might behave differently for a number of reasons. Overcharging and over-discharging are caused by an electrical imbalance that results from the cells’ differences in properties and capacity. Therefore in this study, a stratified real-time control scheme was developed for the dual purposes of minimizing the capacity fade and the energy losses of a battery pack. Each of the cells in the pack is represented by a degradation-conscious physics-based reduced-order equivalent circuit model. In view of the inconsistencies between cells, the proposed control scheme uses a state estimator such that the parametric values of the circuit elements in the cell model are determined and updated in a decentralized manner. The minimization of the capacity fade and energy losses is then formulated as a multiobjective optimization problem, from which the resulting optimal control strategy is realized through the switching actions of a modular multilevel series-parallel converter which interconnects the battery pack to an external AC system. A centralized controller ensures optimal switching sequence of the converter leading to the maximum utilization of the capacity of the battery pack. Both simulation and experimental results are used to verify the proposed methodologies which aim at minimizing the battery degradation by reconfiguring the battery cells dynamically in accordance with the state of health (SOH) of the pack.

Design and Implementation for the High Voltage DC-DC Converter of the Subsea Observation Network

The subsea observation network has become an indispensable means of ocean exploration worldwide. However, the scale of the subsea observation network is limited by the power supply voltage and power level. Hence, to promote the development of a subsea observation network, this paper investigates the underwater high voltage DC-DC converter (HVC), which greatly improves the voltage and power level of the subsea observation network. The traditional series-parallel converter based on multi-module is faced with many technical problems, such as difficult transformer isolation, many fault points, low power density under higher input voltage level, and higher output power. The subsea HVC of this paper adopts a modular multilevel resonant DC-DC converter. The main circuit of HVC is designed in detail, including a module circuit, a resonant circuit, and a control scheme. Through the combination of the sub-module removal voltage regulation and closed-loop control, the converter can still output a stable voltage of 375 V when the input voltage changes. The modular sub-module and centralized transformer structure enables the converter to isolate high voltage easily, small volume, and high power density. The simulation and experiment results show the proposed HVC meets the design requirements and has good application prospects. It can be applied to submarine power transmission and distribution needs because of its wide range, large transformation ratio, and high efficiency.

High-Gain Switched-Capacitor DC-DC Converter With Low Count of Switches and Low Voltage Stress of Switches

This paper presents a novel concept of a high-voltage-gain DC-DC converter. The converter is made up of switched capacitors and passive resonant branches. A significant reduction in the count of switches and low voltage stress on the switches is achieved in this proposed converter topology, in comparison to that of a classical SC series-parallel converter. It is essential from the cost, volume, and efficiency of the converter standpoint. The reduction in the count of switches is threefold. The highest voltage stress on the switches depends on the output voltage and is decreased in the proposed converter as well, as the output voltage is divided into two series-connected capacitors. The presented results demonstrate the operation of the converter with the use of resonant branches, its switching strategies, voltage stresses of switches, efficiency, voltage gain, and output voltage regulation as well as the zero-voltage switching (ZVS) operation. The paper also presents novel issues related to analytical loss modeling, extended concepts of topology, converter start-up, and operation during transient states. The demonstrated concept of the converter, the analytical discussion and its design, as well as the experimental setup and results clearly demonstrate the optimization achievements.

Design of a dual-input cross-connected charge pump utilizing scavenged energy

This paper presents a novel dual-input cross-connected charge pump utilizing scavenged energy. The proposed converter has two input sources: a battery input and a scavenged energy input. Unlike existing charge pumps, the proposed converter alleviates the energy consumed in a battery source by utilizing the scavenged energy. Therefore, the proposed converter can extend the lifetime of a battery source. Furthermore, the cross-connected structure offers not only higher voltage gain but also faster response speed than existing charge pumps. Through theoretical analysis and simulation program with integrated circuit emphasis (SPICE) simulation, the proposed converter demonstrates high power efficiency and high output voltage, where the proposed converter is compared with series–parallel converter, traditional charge pump, and Fibonacci converter. Concretely, about 90% power efficiency can be achieved by the proposed converter when the output power is 15 μW, and the settling time is less than 19 μS when the output load is 500kΩ. Furthermore, the feasibility of the proposed converter is confirmed by breadboard experiments, where the experimental circuit is built with commercially available ICs.

Control of Modular Multilevel Converter With Parallel Connectivity—Application to Battery Systems

This paper presents a multiobjective real-time controller for a modular multilevel converter capable of parallel module connectivity, the so-called modular multilevel series parallel converter (MMSPC). The MMSPC topology allows the batteries to be dynamically rewired in various series–parallel configurations, generating a wide range of output voltage levels. The novel control method parallelizes the modules to balance their voltages without the need for individual module voltage monitoring. Additionally, the controller optimizes across the large number of feasible system configurations to minimize switching and conduction losses. Finally, the controller efficiently encodes the system configuration with module interconnection states rather than the module switch states, which substantially simplifies control. Furthermore, this work experimentally validates the MMSPC topology and concept. In the prototype, the parallel mode reduced the system losses at 5 kW output power by 18% and 24% for load power factors of 1.0 and 0.8, respectively. Sensorless balancing via parallelization maintained well-matched module voltages (standard deviation = 0.045 V) over a 5-h battery discharge with highly variable load current. The reduced conduction losses and simple balancing capability of the MMSPC can enable new applications at medium and low voltages that benefit from its high-quality output, elimination of filtering magnetics, fast response, and modularity.

Peformance Analysis of LLC-LC Resonant Converter Fed PMDC Motor

In this paper, a modified form of the most efficient resonant LLC series parallel converter configuration (SPRC) is proposed. The proposed system comprises of an additional LC circuit synchronized along with the existing resonant tank of LLC configuration (LLC-LC configuration). With the development of power electronics devices, resonant converters have been proved to be more efficient than conventional converters as they employ soft switching technique. Among the three basic configurations of resonant converter, Series Resonant Converter (SRC), Parallel Resonant Converter (PRC) and Series Parallel Resonant Converter, the LLC configuration under SPRC is proved to be most efficient providing narrow switching frequency range for wide range of load variation, improved efficiency and providing ZVS capability even at no load. The modified LLC configuration i.e., LLC-LC configuration offers better efficiency as well as better output voltage and gain. The efficiency tends to increase with increase in input voltage and hence these are suitable for high input voltage operation. In this paper, LLC topology of SPRC and a modified LLC topology (LLC-LC) of SPRC for the closed loop control of a BLDC motor are simulated and their performances are compared and analyzed.

Design and control of an LCL series parallel resonant converters using bacterial foraging optimisation

The paper introduces a design technique for robust PID controllers for inductance capacitance inductance-T network (LCL-T) series parallel resonant converts. AC analysis and stability analysis for LCL-T series parallel converter are premeditated. The converter controllers' designs are based on bacterial foraging optimisation (BFO). A BFO algorithm is utilised in order to obtain the controller parameters and guarantee superior step response performance criterion. Simulation results of the designed controllers are compared with that of conventional controllers whose parameters are tuned by using will known Ziegler-Nichols technique. Results imply the perfection of the proposed technique over the conventional method. Experimental measurements of system performance validate the proposed technique and emphasise its feasibility.

Combined deadbeat control of a series-parallel converter combination used as a universal power filter

This paper presents the notion of combined control of a system of interconnected power electronic converters. The concept is demonstrated using a three-phase series-parallel active power filter as an example. The described active power filter consists of a series-parallel combination of two full bridge VSIs capable of arbitrarily controlling the input current and output voltage. The proposed control scheme treats the converter combination as a single unit and uses the inverse system model to generate deadbeat control response for both input current and output voltage. A full-order predictive state observer is used to reduce the number of sensors. Simulation results show better disturbance rejection characteristics of the proposed control when compared to the separately controlled converter scheme.

Energy based closed form solution of ZCS multiresonant series-parallel converters

Under-resonant operation of an ideal multi-resonant series-parallel power converter (MRSPC) with a capacitive output filter is modeled in this paper. This operation allows zero current switching (ZCS), which is convenient for bipolar devices. The capacitive output filtering reduces the recovery effect of the rectifier diodes and is suitable for high output voltage applications. A closed-form solution is found for this power converter, based on state space analysis using energy concepts. This approach simplifies the mathematical operations and gives better physical insight of the system variables. Based on the model, the steady-state characteristics of this power converter are derived by a simulation program, which are discussed and compared with the series resonant half-bridge power converter (SRHC). The optimum power converter parameters are found for given design requirements using computerized optimization routines. Several design examples are presented and compared with SRHC. The validity of the model is verified by SPICE simulations.

A comparison of half-bridge resonant converter topologies

The half-bridge series-resonant, parallel-resonant, and combination series-parallel resonant converters are compared for use in low-output-voltage power supply applications. It is shown that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, avoids the main disadvantages of each of them. Analyses and breadboard results show that the combination converter can run over a large input voltage range and a large load range (no load to full load) while maintaining excellent efficiency. A useful analysis technique based on classical AC complex analysis is introduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>