An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Use of multilevel inverters is becoming popular in recent years for high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in literature. Trends in power semiconductor technology indicate a trade-off in the selection of power devices in terms of switching frequency and voltage sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCT) and insulated gate bipolar transistors (IGBT) operating in synergism. This paper is devoted to the investigation of a hybrid multilevel power conversion system typically suitable for high performance, high power applications. This system designed for 4.16 kV, /spl ges/100 hp load comprises of a hybrid seven-level inverter, a diode bridge rectifier and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low voltage converter and as a harmonic compensator for the high voltage converter. The hybrid seven-level inverter on the load side consists of a high voltage, slow switching IGCT inverter and a low voltage, fast switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is included. In addition, performance of a multilevel current regulated delta modulator as applied to the single phase full bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper. <s> BIB001 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The authors have developed a new control technique which allows paralleled inverters to share linear or nonlinear load in a distributed AC power supply system. This technique does not require control interconnections and automatically compensates for inverter parameter variations and line impedance imbalances. Experimental results are provided in the paper to prove the concept. <s> BIB002 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Three-phase pulsewidth-modulated (PWM) boost-buck rectifiers with power-regenerating capability are investigated. The converters under consideration are capable of: (1) both voltage step-up and step-down; (2) bidirectional power processing; and (3) almost unity-power-factor operation with nearly sinusoidal AC current. Expected advantages are: (1) applicability to lower voltage applications, e.g., direct retrofit to replace diode or thyristor rectifiers; (2) switching loss reduction in the inverter load; (3) low-order harmonic control in the inverter load output voltage; (4) blanking time effect mitigation in the inverter load; and (5) a modest level of voltage sag/swell compensation. In this paper, firstly, a step-by-step power stage derivation process is described. Then, taking the Cuk-Cuk realization as an example, its operating principle and modulation scheme are described. A steady-state model and dynamic model for controller design are also described. Representative results of circuit simulations and hardware experiments are presented. Through these procedures, the feasibility of the presented three-phase PWM boost-buck rectifier with power-regenerating capability is demonstrated. <s> BIB003 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper presents an impedance-source (or impedance-fed) power converter (abbreviated as Z-source converter) and its control method for implementing DC-to-AC, AC-to-DC, AC-to-AC, and DC-to-DC power conversion. The Z-source converter employs a unique impedance network (or circuit) to couple the converter main circuit to the power source, thus providing unique features that cannot be obtained in the traditional voltage-source (or voltage-fed) and current-source (or current-fed) converters where a capacitor and inductor are used respectively. The Z-source converter overcomes the conceptual and theoretical barriers and limitations of the traditional voltage-source converter (abbreviated as V-source converter) and current-source converter (abbreviated as I-source converter) and provides a novel power conversion concept. The Z-source concept can be applied to all DC-to-AC, AC-to-DC, AC-to-AC, and DC-to-DC power conversion. To describe the operating principle and control, this paper focuses on an example: a Z-source inverter for DC-AC power conversion needed in fuel cell applications. Simulation and experimental results are presented to demonstrate the new features. <s> BIB004 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> In this paper, a general structure for cascaded power converters is presented in which any number of H-bridge cells having any number of voltage levels are series connected to form an inverter phase leg. Equations are introduced for determining an optimal voltage ratio of DC voltages for the H-bridge cells which will maximize the number of voltage levels obtainable resulting in high power quality. Special cases of the generalized inverter are presented including novel 11-level and 15-level inverters. Laboratory measurements demonstrate the proposed inverter performance. <s> BIB005 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper describes a multilevel inverter for delivering power to a set of frequency selectable induction heating targets for stimulating temperature sensitive polymer actuators. The proposed inverter topology overcomes the capacitor voltage balancing issue common to traditional multilevel inverters. This inverter is suitable for sustained real power transfer. <s> BIB006 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Recent research in flying capacitor multilevel inverters (FCMIs) has shown that the number of voltage levels can be extended by changing the ratio of the capacitor voltages. For the three-cell FCMI, four levels of operation are expected if the traditional ratio of the capacitor voltages is 1:2:3. However, by altering the ratio, the inverter can operate as a five-, six-, seven-, or eight-level inverter. According to previous research, the eight-level case is referred to as maximally distended (or full binary combination schema) since it utilizes all possible transistor switching states. However, this case does not have enough per-phase redundancy to ensure capacitor voltage balancing under all modes of operation. In this paper, redundancy involving all phases is used along with per-phase redundancy to improve capacitor voltage balancing. It is shown that the four- and five-level cases are suitable for motor drive operation and can maintain capacitor voltage balance under a wide range of power factors and modulation indices. The six-, seven-, and eight-level cases are suitable for reactive power transfer in applications such as static var compensation. Simulation and laboratory measurements verify the proposed joint-phase redundancy control. <s> BIB007 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> With the popularity of micro-processors, digital controllers are widely used in uninterruptible power supply (UPS) inverters. These digital control systems of UPS inverters require a time interval for sampling and computation, which sometimes affects the performance of inverters. In this paper, the problem of time delay in digital control of a UPS inverter is discussed. Then two novel pulsewidth modulation (PWM) methods, the two-polarity PWM method and the asymmetric PWM method, are proposed to handle the time-delay problem. Both of these PWM methods can achieve a wide range of duty ratio between 0.05-0.95, which is independent of inverter model. Furthermore, they are easy to implement using a digital micro-controller. Experimental results are presented in the paper to verify feasibility of the proposed PWM methods. <s> BIB008 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The use of a multiple-input buck-boost converter for budgeting power between different energy sources is discussed. It is shown mathematically that the idealized converter can accommodate arbitrary power commands for each input source while maintaining a prescribed output voltage. Power budgeting is demonstrated experimentally for a real converter under various circumstances, including a two-input (solar and line-powered) system. A closed-loop control example involving simultaneous tracking of output voltage and set-point tracking of the solar array shows that an autonomous system is realizable. <s> BIB009 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> In this paper a low cost electronic ballast for high pressure sodium vapor lamps (HPS) is presented. The proposed ballast is a two-stage circuit that requires only one switch and one inductor for each stage. The power factor correction (PFC) stage is a buck DC-to-DC converter operating in discontinuous conduction mode (DCM) to meet with the IEC-1000-3-2 Class C requirements. The inverter stage is a very low cost non-resonant topology, based on a buck-boost inverter controlled by means of a specific current mode control implementation. Besides, a novel and simple circuit, compatible with the presented inverter is proposed to ignite the lamp. Furthermore, this circuit implementation provides a protection against broken lamp. <s> BIB010 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The photovoltaic (PV) generator exhibits a nonlinear i-v characteristic and its maximum power (MP) point varies with solar insolation. In this paper, a V2-based MP point tracking (MPPT) scheme is developed using a buck-boost transformation topology. Although several buck-boost transformation topologies are available we have considered here a coupled inductor SEPIC converter for experimentation. To achieve almost ripple-free array current we have used ripple steering phenomena with the help of integrated inductor. This integrated inductor not only reduces the magnetic core requirements but also improves converter performance. Mathematical models are formulated and tracking algorithm is evolved. A combined PV system simulation model is developed in the SIMULINK. For a given solar insolation, the tracking algorithm changes the duty ratio of the converter such that the solar cell array (SCA) voltage equals the voltage corresponding to the MP point. This is done by the tracking algorithm, which mainly computes the power proportional to square of terminal voltage and changes the duty ratio of the converter so that this power is maximum. The proposed algorithm is implemented in real-time with the help of Analog Device ADMC-401 DSP evaluation module. The tracking program is developed to perform experimental investigations using analog-to-digital converter (ADC) interrupt. Using this processor we are able to track the MP within 200 ms. The proposed peak power tracking effectiveness is demonstrated through simulation and experimental results. <s> BIB011 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper focuses on the fault-tolerance potential of multilevel inverters with redundant switching states such as the cascaded multilevel inverters and capacitor self-voltage balancing inverters. The failure situations of the multilevel inverters are classified into two types according to the relationship between output voltage levels and switching states. The gate signals can be reconfigured according to the failure modes when some of the power devices fail. The reconfiguration method is discussed for phase disposition PWM strategy (PDPWM) and phase shifted PWM strategy (PSPWM) in the paper and it can be extended for other carrier-based PWM strategies easily. Balanced line-to-line voltage will be achieved with the proposed method when device failure occurs. Furthermore, the circuit structures can be the same as the general ones and the voltage stress of the devices does not increase. Simulation and experimental results are included in the paper to verify the proposed method. <s> BIB012 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper presents a simple carrier symmetric method for the voltage balance of flying capacitors in flying-capacitor multilevel inverters. The carrier-redistribution pulsewidth-modulation (CRPWM) method was reported as a solution for the voltage balance but it has a drawback at the transition of voltage level. To achieve the voltage balance of flying capacitors, the utilization of each carrier must be balanced during a half-cycle of the switching period such as phase-shifted PWM. However, the CRPWM method causes the fluctuation of flying-capacitor voltages because the balanced utilization of carriers is not achieved. Moreover, it does not consider that the load current change has an influence on flying-capacitor voltages by assuming that the current flows into the load. Therefore, the charging and discharging quantities of flying-capacitor voltages do not become zero during the switching period. To overcome the drawbacks of CRPWM, it is modified by the technique where carriers of each band are disposed of symmetrically at every fundamental period. Firstly, the CRPWM method is reviewed and the theory on voltage balance of flying capacitors is analyzed. The proposed method is introduced and is verified through simulation and experimental results. <s> BIB013 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> It is known that the optimal carrier based approach for modulating a multilevel converter is to use a phase disposition (PD) carrier arrangement with a common mode offset added to the reference waveforms to centre the implicitly selected space vectors. However, this strategy does not fully utilize all available voltage levels at lower modulation depths, with an odd level system only using odd voltage levels and an even level system only using even voltage levels as the modulation depth varies. Recent work has suggested that this is not the harmonically optimal approach at reduced modulation depths. This paper shows how up to a 40% reduction in harmonic distortion can be achieved if all available voltage levels are used throughout the linear modulation range. The improvement is achieved by adding a simple (1/2) carrier magnitude common mode dc offset in key modulation regions, which allows the converter to use all available voltage levels. The paper uses analytical spectral decomposition and harmonic flux trajectory analysis to propose a theoretical basis for this improvement, and to determine the precise points at which the (1/2) carrier magnitude offset should be added to achieve the harmonic improvement. <s> BIB014 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The three-level diode-clamped multilevel converter commonly called the neutral-point-clamped converter has become established to be a preferred topology for high-power motor drive applications operating at several kilovolts. Although solutions to the problem of maintaining a stable neutral-point voltage in the converter continue to be the topic of research, a simple solution based on a design-oriented dynamic model of the system is not widely known. This paper presents the design, analysis, and implementation of a simple neutral-point voltage regulator for a three-level diode-clamped multilevel inverter, which uses a multiple-carrier sine-triangle modulator in conjunction with a closed-loop controller for neutral-point regulation. Redundant state choices are controlled via a continuous offset voltage that regulates the dc injection into the midpoint of the dc bus. A small-signal transfer function is developed in closed form, for neutral-point regulation, with the voltage offset as the control variable. Besides maintaining dc-bus voltage balance, the use of the approach leads to a significant reduction in the voltage distortion at the neutral point, allowing a definitive reduction in the required dc bus capacitance. Analytical, computer simulation, and experimental results verifying the approach are presented in this paper. <s> BIB015 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper discusses a repetitive-based controller for an uninterruptible power supply (UPS) inverter. It is shown that a bank of resonant filters, used as a refinement term for harmonic compensation in earlier works, is equivalent to a repetitive scheme with a particular structure. The latter is implemented using a simple feedback array with a delay line, thus making the implementation relatively easy. More precisely, the repetitive scheme takes a negative feedback structure plus a feedforward path whenever the odd harmonics are considered for compensation only. The repetitive scheme, equivalent to the bank of resonant filters, acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS inverter to deliver an almost pure sinusoidal balanced voltage. Experimental results in a 1.5 KVA three-phase inverter are included to show the performance of the proposed controller <s> BIB016 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper presents a detailed analysis of the impact of a hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are first discussed from the load point of view. This paper also proposes a new modulation strategy for hybrid multilevel inverters which can be used with asymmetrical multipulse connection of uncontrolled rectifiers to improve the input harmonic performance of adjustable-speed drives at every operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes it possible to eliminate undesirable low-frequency harmonics from input currents in all operating ranges, even when the series-connected cells process distinct active power levels <s> BIB017 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The issue of voltage imbalance remains a challenge for the flying capacitor multilevel converter. The phase-shifted pulsewidth modulation (PS-PWM) method has a certain degree of self-balancing properties. However, the method alone is not sufficient to maintain balanced capacitor voltages in practical applications. The paper proposes a closed-loop modified PS-PWM control method by incorporating a novel balancing algorithm. The algorithm takes advantage of switching redundancies to adjust the switching times of selected switching states and thus maintaining the capacitor voltages balanced without adversely affecting the system's performance. Key techniques of the proposed control method, including selection of switching states, calculation of adjusting times for the selected states, and determination of new switching instants of the modified PS-PWM are described and analyzed. Simulation and experimental results are presented to confirm the feasibility of the proposed method <s> BIB018 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Abstract Electrical energy storage technologies for stationary applications are reviewed. Particular attention is paid to pumped hydroelectric storage, compressed air energy storage, battery, flow battery, fuel cell, solar fuel, superconducting magnetic energy storage, flywheel, capacitor/supercapacitor, and thermal energy storage. Comparison is made among these technologies in terms of technical characteristics, applications and deployment status. <s> BIB019 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> In this paper a control method for cascaded H-bridge multilevel converters for grid connection of photovoltaic systems is analyzed. The use of the multilevel converter introduces a series of advantages: improved power quality (lower current ripple), smaller filters, reduced switching frequency, no need of boost dc-dc stage and possible elimination of step-up transformer, all of which have a positive impact on the system efficiency. However it requires a more sophisticated control method specially due to dc-link voltage drifts produced by circulating power in the converter. The proposed control method is based on traditional voltage oriented control with a cascaded dc-link voltage control and grid current control loop. Two extra stages are added to this traditional control scheme, one to introduce maximum power point tracking for each module or string, and another to control the dc-link voltages drift due to circulating power in the converter. The latter is performed by the addition of a simple feedforward control strategy directly in the modulation stage. The proposed control method is modular and easy to adapt for any number of converters in series. Simulation results are presented to support the theoretical analysis. <s> BIB020 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Power electronic converters are commonly used for interfacing distributed generation systems to the electrical power network. This paper deals with a single-phase inverter for distributed generation systems requiring power quality features, such as harmonic and reactive power compensation for grid-connected operation. The idea is to integrate the DG unit functions with shunt active power filter capabilities. With the proposed approach, the inverter controls the active power flow from the renewable energy source to the grid and also performs the non-linear load current harmonic compensation keeping the grid current almost sinusoidal. The control scheme employs a current reference generator based on Sinusoidal Signal Integrator (SSI) and Instantaneous Reactive Power (IRP) theory together with a repetitive current controller. Experimental results obtained on a 4 kVA inverter prototype demonstrate the feasibility of the proposed solution. <s> BIB021 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Neutral-point-clamped (NPC) inverters are the most widely used topology of multilevel inverters in high-power applications (several megawatts). This paper presents in a very simple way the basic operation and the most used modulation and control techniques developed to date. Special attention is paid to the loss distribution in semiconductors, and an active NPC inverter is presented to overcome this problem. This paper discusses the main fields of application and presents some technological problems such as capacitor balance and losses. <s> BIB022 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper presents a comparison of three topologies of multilevel inverters applied to drive an induction motor of 500 kVA/4.16 kV rating. The multilevel inverters analyzed are the following: a neutral-point-clamped inverter, a symmetrical cascaded multilevel inverter, and a hybrid asymmetrical cascaded multilevel inverter. The performance indexes used in the comparison are total harmonic distortion, first-order distortion factor, second-order distortion factor, common-mode voltage, semiconductor power loss distribution, and heat-sink volume. The multilevel inverters are designed to present 99% efficiency at the nominal operating point, and the aforementioned performance indexes are compared for distinct values of amplitude modulation depth. <s> BIB023 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper presents a model predictive current control algorithm that is suitable for multilevel converters and its application to a three-phase cascaded H-bridge inverter. This control method uses a discrete-time model of the system to predict the future value of the current for all voltage vectors, and selects the vector which minimizes a cost function. Due to the large number of voltage vectors available in a multilevel inverter, a large number of calculations are needed, making difficult the implementation of this control in a standard control platform. A modified control strategy that considerably reduces the amount of calculations without affecting the system's performance is proposed. Experimental results for five- and nine-level inverters validate the proposed control algorithm. <s> BIB024 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Despite the rapid growth of self-commutated inverter technology, the well-known current source inverter (CSI) has not achieved significant practical application so far. This raised the question regarding the fundamental criteria that could either prevent or promote the use of such inverters, especially considering emerging fields of application such as grid integration of renewable sources. This paper will, thus, focus on a systematic comparison between circuits based on the CSI and voltage source inverter (VSI). For such purpose, dimensionless benchmark factors were derived. The pulse width-modulated CSI with its inherent step-up capability alongside the indirect CSI (ICSI) with only two high-frequency switches features very interesting characteristics in terms of low switching losses and high inductor power density. However, both topologies show constraints with respect to the provision of reactive power. Two experimental setups have been implemented demonstrating the technical feasibility of different CSI solutions as a grid interface. <s> BIB025 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The five-level active neutral-point (NP)-clamped (ANPC) converter is a newly emerging topology which can overcome the drawbacks of traditional NP-clamped and flying-capacitor multilevel converters. This paper presents a comprehensive theoretical analysis of the NP potential balancing issue and demonstrates that the NP potential can be naturally balanced under ideal and steady conditions. An NP potential balancing method based on zero-sequence voltage injection is presented. By calculating the average NP currents of all key zero-sequence voltages, the most appropriate zero-sequence voltage is selected to generate the demanded NP current, which can also limit the switching frequency of the series-connected insulated-gate bipolar transistors to the fundamental frequency. A three-phase five-level ANPC inverter prototype is built up, and both steady and dynamic experimental results are presented to verify the validity of this method. <s> BIB026 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> This paper mainly deals with three different topologies of cascaded H-Bridge multilevel inverter. The Existing Topology is a general type of multilevel inverter and has two DC sources for each phase. In Proposed Topology-I the number of DC sources has been reduced to one for all the three phases and the usage of transformers comes into picture. Proposed Topology-II has also only one DC source for all the three phases and the number of switches has been reduced than compare to all other proposed topologies of Cascaded H-bridge multilevel inverter. MATLAB simulations has been carried out for all three Topologies and compared with each other. <s> BIB027 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Multilevel flying capacitor (FC) converters provide natural capacitor voltage balance under phase-shifted pulse width modulation (PS-PWM). However, natural balancing may not be robust enough to maintain the voltages at the reference values, especially under certain transient conditions. Furthermore, natural balancing dynamics depend on the load and it may be very slow in some practical applications. Therefore, a more robust balancing mechanism of maintaining the FC voltages at the desired values is required. This paper proposes a new closed-loop voltage-balancing method for the multilevel FC converters using PS-PWM. The proposed method balances the voltages of the FCs by modifying the duty cycle of each switch of the FC converter using a proportional controller. The crossed effect between FC currents and duty cycles is considered and is used for optimal FC voltage balancing. Simulation and experimental results verify that the proposed voltage-balancing method is very robust to different operating conditions, such as load transients, linear/nonlinear and unbalanced loads. <s> BIB028 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Modular multilevel converters (MMCs) are one of the next-generation multilevel converters intended for medium/high-voltage high-power market. This paper initially studies a modified topology for flying-capacitor multicell converters (FCMCs) as a modular submultilevel module. The main advantage of the modified FCMC, in comparison with the conventional one, is that the number and voltage rating of the required dc voltage sources are halved. Afterward, the MMC that comprises the series connection of the modified FCMCs used as submultilevel modules is proposed. Simulation results and experimental measurements taken from the four-cell-five-level laboratory prototype system of the modified FCMC as a modular submultilevel module are presented in order to validate its performance and advantages. Moreover, simulation results and experimental measurements of three cascaded two-cell-three-level modules (ultimately seven-level proposed MMC) and four cascaded two-cell-three-level modules (ultimately nine-level proposed MMC) are presented in order to validate its viability, merits and the proposed control strategy. <s> BIB029 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> renewable energy conversion transmission and storage is available in our book collection an online access to it is set as public so you can get it instantly. Our digital library saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the renewable energy conversion transmission and storage is universally compatible with any devices to read. <s> BIB030 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The standard single-phase three-level voltage source inverter (VSI) for uninterruptible power supply systems consist of a pulse width modulation (PWM) modulator, an H-bridge, and an output inductance/capacitance filter. The design of most control systems requires the inverter small-signal model. Two approaches for the discrete modelling of the VSI can be considered. The first is based on solving the state space equations during the switching period, which yields a discrete model that depends on the single-edge or double-edge type of PWM model. The second approach is the based on the continuous model of the inverter, which is derived from measurements of the real inverter and its discretisation. Both models should regard the increase in the real value of the equivalent coil series resistance and changes in the filter coil inductance with the frequency and amplitude of the magnetising current. The design of the control system requires experimental estimation of the additional delays, which are outside of the models during the measurements and modelling. Both models are validated by comparing the closed-loop systems with the simple instantaneous controllers in the experimental model. <s> BIB031 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> In this paper, a control strategy for the parallel operation of three-phase inverters forming an online uninterruptible power system (UPS) is presented. The UPS system consists of a cluster of paralleled inverters with LC filters directly connected to an ac critical bus and an ac/dc forming a dc bus. The proposed control scheme comprises two layers: 1) a local layer that contains a “reactive power-to-phase droop” in order to synchronize the phase angle of each inverter and a virtual resistance loop that guarantees equal power sharing among inverters; and 2) a central controller that guarantees synchronization with an external real/fictitious utility, and critical bus voltage amplitude restoration. Improved transient and steady-state frequency, active, reactive, and harmonic power sharing, and global phase-locked loop resynchronization capability are achieved. Detailed system topology and control architecture are presented in this paper. Furthermore, a mathematical model was derived in order to analyze critical parameters effects on system stability. The proposed control approach has been validated by means of experimental results obtained for several case-study scenarios. <s> BIB032 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application. <s> BIB033 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> The ordinary Voltage source inverter (VSI) has two output levels +V DC /2 and -V DC /2. For medium and high power applications, multi-stage VSI (series and/or parallel combinations) with suitable filter (for obtaining near sinusoidal waveform at the output) may be a solution but there are problems in matching of different stages, selection of bulky transformer and proper filter. The quality of both the output voltage and current waveforms with minimum ripple is obtained using high frequency switching along with various PWM techniques. These conventional two level inverters have some limitations in operating at high frequencies mainly due to switching losses and constraints in device rating. The problem is resolved by means of multilevel inverters (MLIs) which utilize lower switching frequencies and give high voltages with improved total harmonic distortion (THD) without use of filter. This paper gives a brief review on different MLI techniques with advantages and disadvantages of each technique. The main disadvantages of MLI are requirement for isolated power supplies, design complexity and switching control circuits for proper elimination of lower order harmonics. <s> BIB034 </s> An Overview of Carrier-based Modulation Methods for Z-Source Inverter <s>  <s> Generally, single-stage buck–boost inverters consist of distinct circuits operating individually in buck/boost or positive/negative modes, the latter definitely leading to crossover distortion in the output current. This paper proposes a switching strategy that changes the bimodal operation of a single-stage buck–boost topology to a single-mode inverter. This is due to the consequent voltage gain that ensures that the output voltage polarity, apart from its magnitude, is an exclusive function of the duty ratio. Operational principle and salient hardware design are explained with the help of equivalent circuits. Details about the dynamic model are presented, based on which controller design is carried out for both stand-alone and grid-connected operation. Experimental results obtained from a 300-W, 110-V laboratory prototype are presented to validate the performance of the proposed switching strategy. <s> BIB035
, renewable system interface (Carrasco et al., 2006; Panwar et al., 2011; BIB030 , distributed power generation BIB021 Mohamed and El-Saadany, 2008; BIB002 Xue et al., 2004) , energy storage systems BIB019 ) and uninterruptible power sources BIB008 BIB016 BIB031 BIB032 requires power converters with two-level and multilevel configurations. Fig. 1 demonstrates the outline configuration of energy conversion by renewable energy sources. The power converters are classified into Voltage Source Inverters (VSIs) and Current Source Inverters (CSIs) based on their power flow directions. The number of switches remains identical for both the converters. However, the difference is observed in the construction of the switches and the diode combination. VSI has an anti-parallel diode connected to each switch to provide bidirectional current flow and unidirectional voltage blocking characteristics  . CSI has a diode connected in series with each switch to provide unidirectional current flow and bidirectional voltage blocking BIB025 . The dc input voltage needs to be greater than the ac output voltage in VSI, and ac output voltage should be greater than the dc input voltage in CSI. In order to operate the inverters efficiently, an additional boost or buck converter should be incorporated prior to the inverter. This mode of energy conversion involves a dc-dc conversion followed by a dc-ac inversion, hence named as twostage energy conversion. Alternatively, energy conversions without employing boost or buck converter have been utilized in the research field. These inverters perform a direct conversion from dc to ac, and thereby this mode of energy conversion is referred to as single-stage energy conversion BIB009 BIB035 BIB010 Walker and Sernia, 2004) . As mentioned earlier, the traditional VSI and CSI require a dc-dc conversion interface, which increases the system cost and lowers efficiency. When compared to the normal six-switch converter, boost converter has one additional switch. Inclusion of this additional switch, its corresponding driving circuits and other passive components, has rendered the boost converter with multiple components. Additionally, dead time protection must be provided in VSI to avoid Shoot Through (ST; gating 'on' of all the switches in the same phase leg). Safe current commutation in CSI is achieved by introducing overlap time (gating 'on' of one of the upper and one of the lower switches) to avoid open circuit of the dc inductor. The ST problem in VSI and the open circuit problem in CSI, which are caused by electromagnetic interference, highly affect the reliability of the converter. Furthermore, LC filter at the output of VSI causes additional power loss and adds to the complexity. Traditionally, two-stage energy converters operate in eight switching states and provide either buck or boost operation. Therefore, the output voltage range is limited to the input voltage. The limitations of the traditional VSI and CSI can be amended by implementing a single-stage energy conversion. Some of the single-stage converters proposed in the literature include Cuk-derived buck-boost BIB003 , Single-Ended Primary-Inductor Converter (SEPIC)-derived buck-boost BIB011 and Z-Source Inverter (ZSI; BIB004 . Among these inverters, ZSI is an emerging topology for dc-ac conversion. The advantages of ZSI over other converters are discussed in Section 2. Hence with primary focus being ZSI, a review on the carrier-based modulation methods for the ZSI is provided in this article. Two-level inverters are highly preferred for induction motor applications due to their fast switching characteristics. Some applications require two-level inverters to operate at high switching frequency, in order to eliminate low-order harmonic  , which may reduce the filter size. However, high voltage stresses are introduced across the switches. Therefore, for high-power applications, additional switches are required to improve the voltage rating of the inverter. As a solution to this problem, Multilevel Inverters (MLIs) are proposed  BIB033 BIB012 Peng, 2000; BIB006  . Due to the advantages BIB034 BIB001 BIB014 BIB017 of the MLIs, these inverters are used for high-power applications. Some of the advantages include: • MLI can be operated at both higher switching frequencies and lower switching frequencies • Lower switching frequency indicates lower switching losses as the number of levels in the output voltage increases • Total Harmonic Distortion (THD) reduces with the increase in the output voltage levels. • MLI can draw input current with low distortion • Selective harmonic elimination technique along with MLI topology results in low THD in the output waveform without using any filter circuit • For high-and low-power inverter applications, low-rated semiconductor devices can be used due to low conduction loss Among all the MLI topologies available, diode-clamped inverter BIB015 BIB022 BIB026 BIB023 , flying capacitor inverter BIB029 BIB018 BIB028 BIB007 BIB013 and cascaded H-bridge inverter BIB024 BIB005 BIB020 BIB027 are the most common topologies. Integrating these topologies to provide single-stage energy conversion remains a highly preferred area of research. The remainder of this review is structured as follows. It begins with a review on the single-stage energy converters in Section 2, followed by the description of the concepts of ZSI operation and their topologies in Section 3. A review of the multiple carrier-based modulation methods that can be implemented to insert the additional ST state to the traditional inverter operation is presented in Section 4. Finally, the concluding remarks are given in Section 5.