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Impact of component losses on the voltage boost properties and efficiency of the QZS-converter family
Abstract
Purpose
This paper is devoted to the quasi‐Z‐source (qZS) converter family. Recently, the qZS‐converters have attracted high attention because of their specific properties of voltage boost and buck functions with a single switching stage. As main representatives of the qZS‐converter family, this paper aims to discuss the traditional quasi‐Z‐source inverter as well as two novel extended boost quasi‐Z‐source inverters.
Design/methodology/approach
Steady state analysis of the investigated topologies operating in the continuous conduction mode is presented. Input voltage boost properties of converters are compared for an ideal case. Mathematical models of converters considering losses in components are derived. Practical boost properties of converters are compared to idealized ones and the impact of losses on the voltage boost properties of each topology is justified. Finally, the impact of losses in the components on the boost conversion efficiency is analyzed.
Findings
To demonstrate the impact of component losses on the overall efficiency of the qZS‐converter, a number of experiments were performed. The impact of inductor winding resistance was compared with the forward voltage drop of qZS‐network diodes. It was found that the forward voltage drop of diodes has the highest effect on the efficiency. If the diodes are replaced with high‐power Schottky rectifiers with a low forward voltage drop (UD=0.6 V), the effective efficiency rise by at least 5 percent could be expected for all three qZS‐converter topologies. For the same operating parameters and component values, the traditional qZS‐converter had the highest efficiency of the qZS‐converter family. The boost converter was compared with the traditional qZS converter in terms of efficiency. It was found that the boost converter has an efficiency 2 percent higher in the boost operation mode and approximately the same efficiency in the non‐boost operation.
Practical implications
The paper provides a good theoretical background for further practical studies. qZS‐converters have voltage boost and buck functions with a single switching stage, which could be especially advantageous in renewable energy applications.
Originality/value
The paper presents a detailed study of the qZS‐converter family. Mathematical models of converters considering losses in components are derived. It is the first time the boost converter is compared with the qZS converter.
... The conception of extending the qZSI boost capability without increasing the number of active switches has been recently proposed by several authors [5][6][7][8][9][10][11][12]. These new converters are known as cascaded (or extended boost) qZSIs and are generally classified as capacitor assisted and diode assisted. ...
... Since each of these three topologies has a different number of passive components in the qZS-networks, a detailed analysis of component losses and their impact on a converter's operating properties is especially topical to obtain higher energy efficiencies. In [12] it was stated that for the same operating parameters and component values the twofold boost of the input voltage could be realized at the efficiency of 93.9 %, 89.2 % and 89.3 % for the traditional, CAEB and DAEB qZS-converters, respectively. This paper is devoted to further investigation of the properties of the qZS-converter family and will provide a mathematical representation of the lossless dynamic models in order to study the transient stability of the presented topologies. ...
... As in the previous case the ratios of currents and voltages were determined from the static model [12]. The state space model is described by the differential Eqs. ...
This paper is devoted to the quasi-Z-source (qZS) converter family.
Recently, the qZS-converters have attracted attention because of their
specific properties of voltage boost and buck functions with a single
switching stage, which could be especially beneficial in renewable
energy applications. As main representatives of the qZS-converter
family, the traditional quasi-Z-source inverter as well as two novel
extended boost quasi-Z-source inverters are discussed. Lossless dynamic
models of these topologies are presented and analyzed.
... Voltage-source converters commonly used as step-down and current-source as step-up converters. Impedance-source converters are more versatile, but they consist of larger number of components [4]. Another notable property is that in the full-bridge voltage-source converter, the transistors are in the open state less than a half of the switching period. ...
... It is seen from Fig. 13 that for the threefold input voltage regulation range, the shoot-through duty cycle should vary in the range from 0 to 0.33. However, in real systems, the practical voltage gain in the boost mode could be seriously affected by the losses in the primary side of the converter where the major part is formed by the conduction losses of semiconductors [25]. ...
This paper presents the high-performance quasi-Zsource series resonant dc-dc converter as a candidate topology for the photovoltaic module-level power electronics applications. The converter features a wide input voltage and load regulation range thanks to the multimode operation, i.e., when the shoot-through pulse width modulation and phase-shift modulation are combined in a single switching stage to realize the boost and buck operating modes, respectively. Our experiments confirmed that the proposed converter is capable of ensuring ripple-free 400 V output voltage within the sixfold variation of the input voltage (from 10 to 60 V). The converter prototype assembled achieved a maximum efficiency of 97.4%, which includes the auxiliary power and control system losses.
... From one side the topology features such benefits as continuous input current, low start up inrush current, converterless integration of short-term energy storages, soft switching of transistors during active states and the inherent "shoot-circuit immunity" caused by the properties of the qZS-network. From another side, the converter suffers from the lack of efficiency at the high shoot-through duty cycle values, which is mostly caused by the increased power dissipation in the qZS diode D (Fig. 1a) [5]. The implementation of module integrated freewheeling diodes as rectifiers described in [6] could also decrease the efficiency and affect the performance of the qZS DC-DC converter, especially in the applications with bidirectional power flow. ...
This paper discusses the performance improvement method of the recently popular galvanically isolated quasi-Z-source DC-DC converter. In order to decrease the conduction losses in the quasi-Z-source network and voltage doubler rectifier the replacement of diodes by the N-channel MOSFETs was analyzed. The proposed approach was validated by the computer simulations in PSIM environment with accurate models of the semiconductors based on the device datasheet values. Finally, the power losses and resulting efficiency of the proposed quasi-Z-source DC-DC converter with synchronous rectification were compared to those of the traditional topology.
... The proposed approach was validated by the computer simulations in the PSIM environment. In the qZS based topologies, the properties of semiconductors have direct impact on the step-up performance of the converter [9], therefore we used accurate models of the semiconductors based on the device datasheet values. To simplify the analysis, the ideal models of passive components (inductors, capacitors and isolation transformer) were used. ...
This paper presents a novel quasi-Z-source halfbridge galvanically isolated DC-DC converter intended for the photovoltaic applications. The topology could be envisioned as an alternative to the boost half-bridge DC-DC converter but the benefit of its symmetric structure reduces the threat of transformer saturation due to the dc flux. The proposed converter features the continuous input current and could be used either with one or two input voltage sources.
... In order to facilitate the impact of the component losses on the output power of the qZS based DAB, the mathematical models were derived based on the steady state analysis of the qZS inverter [7] and DAB [8]. Selected circuit parameters are shown in Table 1. ...
The paper analyzes the impact of the component losses on the efficiency of the novel DC/DC converter. The converter is a combination of the quazi-Z-source (qZS) network and dual active bridge (DAB). In the analysis the mathematical loss models of the proposed DC/DC converter are derived and efficiency is estimated. Eventually the efficiency is verified experimentally.
... Another issue of the qZSC family is the power conversion efficiency at the high input voltage gain due to the power losses in the semiconductors. It was found in [6] that 50% reduction of the forward voltage drop of the qZS diode D will follow to the efficiency rise of at least 3% at the twofold input voltage gain. ...
This paper addresses an approach to improve the efficiency of the quasi-Z-source (qZS) converters. By replacing the qZS diode by the n-channel MOSFET, the power loss over a diode can be reduced in a qZS network. The paper presents operation basics of the approach, analysis and comparison of the power losses of the traditional and proposed designs and experimental validation of the theoretical assumptions.
In this paper, a new single‐phase seven‐level quasi‐Z‐source (qZs) inverter with reduced switch count for multistring photovoltaic applications is proposed, which is capable of supplying both direct current (dc) and alternating current (ac) loads simultaneously. The proposed configuration is derived from a combination of qZs networks and asymmetrical seven‐level inverter. The front‐end qZs converter boosts the input voltage obtained from the dc sources to the desired value, whereas the asymmetrical seven‐level inverter performs dc‐ac conversion with reduced switch count and provides better efficiency. The steady‐state performance of the model is evaluated in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of operation. In addition, the dynamic performance of the model is tested for the load as well as input voltage changes. A simple proportional‐integral (PI) controller is implemented in FPGA Spartan‐6 Processor using Xilinx system generator blocks. An experimental prototype is also developed to validate the feasibility of the proposed topology. Finally, a brief comparative assessment is formulated with other topologies to show the merits of the proposed structure. A new structure of quasi‐Z‐source–based MLI is proposed for multistring PV applications. The proposed topology has the merits of reduced switch count, simple control, modularity, and high efficiency. The performance of the model is evaluated in CCM and DCM modes for different loads under steady state. The dynamic response of the system is verified through simulation and a prototype model using Xilinx FPGA‐based control signals in a real‐time environment.
Impedance-source networks are an increasingly popular solution in power converter applications, especially in single-stage buck-boost power conversion to avoid additional front-end dc-dc power converters. In the survey papers published, no analytical comparisons of different topologies have been described, which makes it difficult to choose the best option. Thus, the aim of this paper is to present a comprehensive analytical comparison of the impedance-source-based buck-boost inverters in terms of passive component count and semiconductor stress. Based on the waveform of the input current, i.e., with or without a transformer, and with or without inductor coupling, the impedance-source converters are classified. The main criterion in our comprehensive comparison is the energy stored in the passive elements, which is considered both under constant and predefined high frequency current ripple in the inductors and the voltage ripple across the capacitors. Two-level and multilevel solutions are described. The conclusions provide a 'one-stop' information source and a selection guide of impedance-source-based buck-boost inverters for different applications.
This paper describes novel single-phase solutions with increased inverter voltage levels derived by means of a non-standard inverter configuration and impedance source networks. Operation principles based on special modulation techniques are presented. Detailed component design guidelines along with simulation and experimental verification are also provided. Possible application fields are discussed, as well as advantages and disadvantages. Finally, future studies are addressed for the new solutions.
The paper analyzes the impact of the component losses on the efficiency of the novel DC/DC converter. The converter is a combination of the quazi-Z-source (qZS) network and dual active bridge (DAB). In the analysis the mathematical loss models of the proposed DC/DC converter are derived and efficiency is estimated. Eventually the efficiency is verified experimentally. © IFIP International Federation for Information Processing 2013.
This paper describes a novel family of modified
quasi-Z-source buck-boost multilevel inverters with reduced
switch count. The inverters are derived by means of the
modified inverter configuration with quasi-Z-source networks.
The main benefits of the proposed solutions lie in the increased
amount of levels with all possible sequences: reduced THD,
reduced voltage stress on the transistors and size of the output
filter. Also their modulation techniques are proposed and
described. Simulation results have confirmed all theoretical
predictions. The pros and cons are discussed in the
conclusions.
This paper presents original test results using GaAs and SiC based diode structures instead of Si based fast recovery diode structures to be applied in a new voltage fed step-up DC/DC converter. Overall test results show that the GaAs diodes behave similarly to fast recovery silicon diodes assuming equal operating and cooling conditions. As expected, SiC Schottky diode was found to show a clear advantage in terms of reverse-recovery characteristics. The positive temperature coefficient of the on-state voltage drop of GaAs and SiC diodes could provide significant application advantage in high-power applications, where the parallel connection of devices is necessary.
Focus is on the stability analysis of the quasi-Z-Source (qZS) DC/DC converter based on a small signal model. Control system of the converter is described and its transfer function for the small signal model is presented. The stability estimation was carried out. The results of the analytical analysis, simulation and experimental investigation showed that a DC/DC converter based on the qZS-network has limited but predictable stability margin.
The aims of the latest research on new power electronics topologies and systems are to obtain maximum efficiency to improve control properties and to extend the range of application. Authors propose new topologies of cascaded quasi-Z-source inverters to improve the range of operatea voltages particularly in renewaoie source applications.
The Z-source inverter has gained popularity as a single-stage buck-boost inverter topology among many researchers. However, its boosting capability could be limited and therefore it may not be suitable for some applications requiring very high boost demanding of cascading other dc-dc boost converters. This could lose the efficiency and demand more sensing for controlling the added new stages. This paper is proposing a new family of extended boost quasi ZSI to fill the research gap left in the development of ZSI. These new topologies can be operated with same modulation methods that were developed for original ZSI. Also they have the same number of active switches as original ZSI preserving the singlestage nature of ZSI. Proposed topologies are analyzed in the steady state and their performances are validated using simulated results obtained in Matlab/Simulink. Furthermore they are experimentally validated with results obtained from a prototype developed in the laboratory.
This paper presents the MPPT (maximum power point tracking) and PCC (point of common coupling) current control strategy for photovoltaic (PV) grid-connected generating system using the quasi-Z-source inverter (QZSI). At first, in order to explain the above controllers, the characteristic of QZSI is analyzed. And then, the MPPT control technique with a modified P&O method, the PCC current control one for the regulation of DC-link capacitor voltage, and the PWM methods for the proposed system are explained. The feasibility of the propose algorithm is verified through the simulation and experiment with 3 kW system.
This paper presents a quasi-Z-source inverter (qZSI) that is a new topology derived from the traditional Z-source inverter (ZSI). The qZSI inherits all the advantages of the ZSI, which can realize buck/boost, inversion and power conditioning in a single stage with improved reliability. In addition, the proposed qZSI has the unique advantages of lower component ratings and constant dc current from the source. All of the boost control methods that have been developed for the ZSI can be used by the qZSI. The qZSI features a wide range of voltage gain which is suitable for applications in photovoltaic (PV) systems, due to the fact that the PV cell's output varies widely with temperature and solar irradiation. Theoretical analysis of voltage boost, control methods and a system design guide for the qZSI in PV systems are investigated in this paper. A prototype has been built in the laboratory. Both simulations and experiments are presented to verify the proposed concept and theoretical analysis.
In this paper, theoretical results are shown for several novel inverters. These inverters are similar to the Z-source inverters presented in previous works, but have several advantages, including in some combination; lower component ratings, reduced source stress, reduced component count and simplified control strategies. Like the Z-source inverter, these inverters are particularly suited for applications which require a large range of gain, such as in motor controllers or renewable energy. Simulation and experimental results are shown for one topology to verify the analysis. Also, a back-to-back inverter system featuring bidirectionality on both inverters, as well as secondary energy storage with only a single additional switch, is shown.
The quasi-Z-source inverter is a very attractive topology because of its unique capability of voltage boost and buck functions in a single stage. But its voltage boost property could be a limiting feature in some applications where very high input voltage gain is required. The input voltage gain could be extended by the implementation of the cascaded quasi-impedance network. This paper discusses two novel extended boost quasi-Z-source inverters. Steady state analysis of topologies operating in continuous conduction mode is presented. Performances of topologies were compared and experimentally validated.
This paper proposes the performance improvement method for the voltage-fed continuous input current quasi-impedance source inverter (qZSI) by the introduction of the two-stage quasi-Z-source network (qZS-network). The two-stage qZS is derived by the adding of one diode, one inductor and two capacitors to the traditional qZSI. The proposed two-stage qZSI inherits all the advantages of traditional solution (voltage boost and buck functions in a single stage, continuous input current and improved reliability). Moreover, the proposed solution features over the 30% shoot-through duty cycle reduction for the same voltage boost factor and component stresses as compared to conventional qZSI. Theoretical analysis of the two-stage qZSI in shoot-through and non-shoot-through operating modes is presented. The design guidelines for the two-stage qZS-network based step-up DC/DC converter are provided. A prototype has been built to verify the theoretical assumptions. The simulation and experimental results are presented and discussed.
This paper proposes a new extended boost quasi Z-source inverter (ZSI) and a simple modulation and control method based on one-cycle control for controlling a grid connected PEM fuel cell energy system. ZSIs are gaining popularity. Similarly one-cycle controllers are becoming popular due to their simplicity, ease of implementation and fast response. However, this control method has not been developed for controlling three-phase ZSIs. Therefore, introducing and developing modulation and controllers based on one-cycle controller design for ZSIs would enable many applications to take advantage of the recently proposed ZSI. The proposed controller can be used with all voltage source type ZSIs. Contributions of this paper are introducing and applying one-cycle control to ZSI and developing a novel PWM method based saw-tooth waveform and a simple shoot-through method, where the new method eliminates the increasing of switchings per carrier cycle in the original simple shoot-through method. Also this paper proposes a closed loop controller to control the dc side of the extended boost qZSI. The proposed topology and control method are extensively simulated in Matlab/Simulink.
Cascaded Quasi-ZSource Inverters for Renewable Energy Generation Systems
- M Adamowicz
- R Strzelecki
- D Vinnikov