Switched Capacitor Concept Research Articles

Fault-Tolerant Operation Strategy for Reliability Improvement of a Switched-Capacitor Multilevel Inverter

The necessity of using several components in multilevel inverters jeopardizes the reliability of their operation. Hence, the aim of this article is to propose a novel single-phase fault-tolerant topology based on a switched-capacitor concept to ensure the robustness of the converter in the occurrence of a fault. The proposed single-source converter steps up the input voltage seven times with a simple control strategy. Fault tolerance of the converter is achieved by considering multiple fault cases and providing several redundant switching schemes concerning the type and location of failure. Each switching scheme is designed in a way to ensure the tolerability to both single and multiple open-/short-circuit failures. Also, self-voltage balancing of the capacitors, as well as the same amount of voltage levels and amplitude in the output, is guaranteed. Experimental analysis is carried out, and the results confirm the viability of the proposed inverter under normal and postfault operating modes.

A Repetitive Bipolar Pulsed Power Generator Based on Switched-capacitor Concept

This paper presents a pulsed-power generator that can produce a high voltage bipolar pulse from a relatively low-voltage input source, based on the switched-capacitor concept. The circuit boosts the input voltage by storing energy in several capacitors in a predefined pattern and simultaneously releasing it to the load. It is worth noting that the structure can short-circuit its output terminal while charging the capacitors without using any switches across the load. This topology is mainly suitable for applications requiring a high voltage pulse and only having access to low voltage input sources. Moreover, thee structure can generate a combination of wide and narrow pulses by alteranting its output voltage between two different values. Precise calculation and employment of capacitors ensure that the structure can properly generate the intended output pulses with an acceptable ever-so-slight voltage drop. Finally, MATLAB Simulink was used to evaluate the circuit’s operation, and experimental tests were conducted on a laboratory setup, where the results confirmed the proper performance of the circuit.

High Voltage Gain Switched-Z-Source Bidirectional DC-DC Converter

The DC-DC converters are the essential modules in electric vehicles, grid interface of renewable energy sources and DC power supplies. This paper presents a novel high gain bidirectional switched Z-source DC-DC converter. The proposed bidirectional converter utilizes switched-capacitor concept with inductors for high voltage gain. The proposed bidirectional converter presents wide operating range of operation in both boost and buck mode of operation. The proposed converter has common ground between input and output, and uses only 5 active switches and 4 passive elements with reduce switch voltage stress. The current drawn from the low voltage side input source is continuous with reduced ripple. The operating principle, circuit analysis, design, mathematical model and closed loop operation of the proposed converter are presented. The proposed converter is verified through computer simulation and laboratory experiments. The simulation and experimental results are presented.

A Dumbbell Type (D-Type) multilevel inverter based on switched capacitor concept

ABSTRACT In this paper, a new single-phase seven level inverter with reduced device count is introduced. The structure can boost the input voltage by synthesising the capacitors’ voltages in predetermined current paths. A single DC voltage source is utilised to generate the output AC staircase waveform, which is facilitated via Nearest Level Control. Self-voltage balancing ability, less number of semiconductor devices, high efficiency and control simplicity are the most significant inherent attributes of the proposed circuit. It is also noticeable that in this configuration neither bulky transformer/inductor nor filters are applied. Power loss calculation and required capacitance of the proposed inverter are investigated and theoretical efficiency of 93.31% was reached. Moreover, the proposed converter operates under various load conditions with lower Total Harmonic Distortion compared to recent topologies. Ultimately, operating principles of the proposed D-Type seven-level Inverter and simulation results in MATLAB SIMULINK environment are validated by experimental ones obtained from the laboratory prototype.

Single-Phase Hybrid Switched-Capacitor Interleaved AC-DC Boost Converter

In this paper a single-phase boost PFC multilevel interleaved high-voltage gain based on the hybrid switched-capacitor concept is presented. The proposed converter merges interphase transformers and switched-capacitor cells to obtain current sharing and high voltage gain. These features allow for both the reduction of voltage and current stresses on the semiconductors. Furthermore, the interleaving method allows for obtaining multilevel voltages at AC terminals, thereby reducing the weight and bulk of the input inductor. PFC operation is guaranteed through both input current control and output voltage control. Both steady-state and dynamic analyses were conducted. Experimental results for a 1.25 kW, 127 V to 800 V laboratory prototype are presented and discussed.

A new enhanced‐boost switched‐capacitor quasi Z‐source network

This paper proposes a new enhanced-boost non-transformer-based impedance source network. The strong boosting ability of the proposed topology is realized by making use of the switched capacitor concept in the formerly introduced enhanced-boost quasi Z-source network (EB-qZSN) without any additional active switch. Meanwhile, the advantages of the EB-qZSN such as input current continuity and shared ground between the input and the output are maintained. In addition to the lower shoot-through requirement to obtain high voltage gains, the proposed impedance network takes advantage of a smaller size of passive components along with a lower input current ripple to achieve higher power density and higher efficiency. Moreover, the lower total rating of the switching elements, defined by switching device power, directly translates to lower cost for the proposed method. The operation principles and the design guideline of components are explained in detail and a thorough comparison with other ZSN is presented. A 240W DC–DC prototype converter was built to validate the performance principles and properties of the proposed impedance network.

X-Type Step-Up Multi-Level Inverter with Reduced Component Count Based on Switched-Capacitor Concept

This paper aims to present a novel switched-capacitor multi-level inverter. The presented structure generates a staircase near sinusoidal AC voltage by using a single DC source and a few capacitors to step-up the input voltage. The nearest level control (NLC) strategy is used to control the operation of the converter. These switching states are designed in a way that they always ensure the self-voltage balancing of the capacitors. Low switching frequency, simple control, and inherent bipolar output are some of the advantages of the presented inverter. Compared to other existing topologies, the structure requires fewer circuit elements. Bi-directional power flow ability of the proposed topology, facilitates the operation of the circuit under wide range of load behaviors which makes it applicable in most industries. Besides, a 13-level laboratory prototype is implemented to realize and affirm the efficacy of the MATLAB Simulink model under different load conditions. The simulation and experimental results accredit the appropriate performance of the converter. Finally, a theoretical efficiency of 92.73% is reached.

Circuit Configuration and Modulation of a Seven-Level Switched-Capacitor Inverter

In this article, a step-up seven-level inverter supplied by a single dc source suitable for renewable energy application is presented. Forming the desired output is realized by charging capacitors and synthesizing them based on a switched-capacitor concept. This structure is praised for the ability of sensorless voltage balancing of the capacitors, reducing control complexity to produce a bipolar staircase waveform. It also benefits from regenerative performance, avoiding unwanted capacitors overvoltage. A phase disposition pulsewidth modulation (PD-PWM) technique is utilized to control the circuit operation. Furthermore, a comparison with other recent topologies reveals that losses, number of semiconductor devices, and gate driver circuits are reduced. Theoretical analysis is verified through a laboratory prototype implementation. Experimental results under various types of loads approve the performance of the proposed inverter and validity of the design. Finally, maximum experimental efficiency of 94.3% (115 V, 250 W load) was reached.

Reduced switch count‐based N ‐level boost inverter topology for higher voltage gain

This study proposes a new boost inverter based on a switched-capacitor concept with reduced switch count. The basic unit is a five-level topology, which inherently generates the AC output voltage with the self-voltage balancing of the capacitors. A conventional carrier-based sinusoidal modulation technique has been designed to maintain the capacitor voltage up to the input source voltage. The N -level structure of the proposed basic unit is also presented, which has the additional advantage of higher voltage gain with a single input. A detailed comparison with other similar topologies has been carried out. A laboratory prototype has been used to test the workability of the proposed basic unit and its extension for seven-level through several results.

Reduced Switch Count Based Single Source 7L Boost Inverter Topology

The new inverter topologies based on switched capacitor concept with voltage boosting ability are attractive for the low voltage applications. Such low voltage requirements allow a single-stage dc-ac power conversion, improving overall system performance, reliability and power density. This brief proposes a new multilevel inverter topology based on the switched-capacitor (SC) with a single source of dc voltage. The proposed topology is ideal for low voltage renewable energy applications. Seven-level (7L) output voltage is accomplished with triple voltage gain using two switched capacitors and 10 switches. Other major features of the proposed topology are self-voltage balancing of capacitor voltages, reduced number of switches with lower voltage stress and generation of negative voltage levels without using backend H-bridge. To show the advantages of the proposed topology, a detailed comparison with other similar topologies with seven-level single-source configuration has been accomplished in this brief. The proposed topology has been tested using the traditional level-shifted sinusoidal pulse width modulation (LS-PWM) technique. This brief includes various experimental results with different operating conditions to prove the performance of the proposed topology.

Transformerless UPS System Based on the Half-Bridge Hybrid Switched-Capacitor Operating as AC–DC and DC–DC Converter

A single-phase transformerless online uninterruptible power supply (UPS) is proposed in this article. This UPS is based on the new half-bridge doubler-boost with switched-capacitor operation. It is capable of operating with ac and dc input sources. The proposed converter provides a high power factor and improves power efficiency for line voltage applications. The switched capacitor concept allows a natural balance of the dc bus capacitor voltages, both in the ac–dc mode and the dc–dc mode. It presents a common point between the line voltage source, load, and batteries. This characteristic makes it possible to eliminate the common mode current, reducing problems with electromagnetic interferences and allowing the use of a simple bypass system. The feasibility of the proposed UPS is verified by experimental results from a 2.5-kW prototype with an efficiency of up to 94.9% and unity power factor.

A Family of Switched-Resonant Converters With Wide Conversion Ratio and Controlled Sourcing Features for Volume-Sensitive Applications

In this paper, a family of switched-resonant converters with high efficiency over a wide conversion ratio range is introduced. Inspired by the gyrator resonant switched-capacitor concept, the new topology provides high efficiency over wide and continuous range of conversion ratios using a single resonator. This is enabled by new modes of operation (switching sequences) developed and analyzed in this paper that modify the charge balance of the flying capacitor. By that, the sourcing as well as the efficiency characteristics of the converter can be shaped to peak at various conversion ratios. A generalized methodology is presented to describe resonant converters with multiple operation modes as a two port which is then used to analyze several operational modes of the presented topology. Experimental results validate the developed theoretical model and demonstrate the superiority of the concept in terms of efficiency (over 10%) and current-sourcing capabilities (over 80%) using a compact 5-W prototype.

High Step-Up Transformerless Inverter for AC Module Applications With Active Power Decoupling

This paper explores a power-conversion system for single-phase transformerless ac module application. A nonisolated high-gain dc–dc stage is coupled with a doubly grounded dynamic dc-link inverter to implement the microinverter topology. The front-end boost stage steps up the single-module voltage to a higher dc voltage, typically to 200 or 400 V as required for the following inverter stage. It is a hybrid of an interleaved boost and switched capacitor concept capable of achieving high gain while simultaneously maintaining reduced voltage and current stress, and thus lowering switching and conduction loss for most of the switches. By directly connecting the grid neutral to the photovoltaic (PV) negative, the doubly grounded voltage swing inverter has the advantage of zero capacitive-coupled common-mode ground currents, critical for transformerless PV inverters. The two dc links of the inverter stage share the double-line frequency power decoupling with a combination of higher value of mean voltage and relatively large 120-Hz ripple component–the dynamic dc-link approach. Through an optimization algorithm, the decoupling capacitance is minimized enabling an all-film capacitor implementation while satisfying the converter's operating constraints over a wide range of power factors. The simulation as well as experimental results from a GaN-based hardware prototype validate the converter's performance.

Single-Phase Hybrid Switched-Capacitor Voltage-Doubler SEPIC PFC Rectifiers

In this paper, the switched-capacitor concept is extended to the voltage-doubler discontinuous conduction mode SEPIC rectifier. As a result, a set of single-phase hybrid SEPIC power factor correction rectifiers able to provide lower voltage stress on the semiconductors and/or higher static gain, which can be easily increased with additional switched-capacitor cells, is proposed. Hence, these rectifiers could be employed in applications that require higher output voltage. In addition, the converters provide a high power factor and a reduced total harmonic distortion in the input current. The topology employs a three-state switch, and three different implementations are described, two being bridgeless versions, which can provide gains in relation to efficiency. The structures and the topological states, a theoretical analysis in steady state, a dynamic model for control, and a design example are reported herein. Furthermore, a prototype with specifications of 1000-W output power, 220-V input voltage, 800-V output voltage, and 50-kHz switching frequency was designed in order to verify the theoretical analysis.

A Three-Phase Multilevel Hybrid Switched-Capacitor PWM PFC Rectifier for High-Voltage-Gain Applications

In this paper, a three-phase multilevel power factor correction rectifier using the hybrid switched-capacitor concept is proposed. The converter is suitable for high-voltage-gain applications from conventional three-phase low-voltage sources. The three-level voltage operation reduces the weight and bulk of the magnetic devices. The main advantages of the proposed converter are low number of active switches, high voltage gain, sinusoidal currents, low voltage stress across all components, and simple control. Both steady-state and dynamic analyses are investigated. Experimental results for a 7500-W/220-V-to-1600-V laboratory prototype with maximum efficiency of 97.78% are presented and discussed.

Linear Fluid Resistance Using Switching Valves and a Tank

An active linear fluid resistance is demonstrated using the switched capacitor concept from electronics. For the analogous fluid component, this requires using switching valves to alternately fill and empty a tank. Analysis shows that the equivalent linear resistance is directly proportional to the switching period and inversely proportional to the tank capacitance. For fluid components, the linearity is restricted to those cases where complete filling and emptying is achieved. The time period required to insure linearity is derived in terms of fluid circuit variables. As a result, there is a lower limit on the magnitude of resistance that can be obtained for a given fluid circuit. This magnitude depends on circuit component values, as well as on the desired operating pressure range. However, the net result is that we may construct a linear fluid resistance that has no dependence on orifice sizes, discharge coefficients, or Reynolds number. The experimental fluid circuit contains a source volume in addition to the switching values and tank required for the resistance component. The source volume filters the transients and permits steady state measurements. Experiments are performed for resistances with different switching periods and tank volumes. The experimental resistance values are always within 5 percent of the theoretical predictions. The switched capacitor concept may prove useful in the design of mass flowmeters, frequency-to-analog converters, electric-to-pneumatic transducers, and temperature sensors.