Showing papers on "Converters published in 2004"

Cascaded DC-DC converter connection of photovoltaic modules

Abstract: New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single dc-ac inverter connected to a series string of pv panels, or many small dc-ac inverters which connect one or two panels directly to the ac grid. This paper proposes an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter. This offers the advantages of a "converter-per-panel" approach without the cost or efficiency penalties of individual dc-ac grid connected inverters. Buck, boost, buck-boost, and Cu/spl acute/k converters are considered as possible dc-dc converters that can be cascaded. Matlab simulations are used to compare the efficiency of each topology as well as evaluating the benefits of increasing cost and complexity. The buck and then boost converters are shown to be the most efficient topologies for a given cost, with the buck best suited for long strings and the boost for short strings. While flexible in voltage ranges, buck-boost, and Cu/spl acute/k converters are always at an efficiency or alternatively cost disadvantage.

A new ZVS bidirectional DC-DC converter for fuel cell and battery application

Abstract: This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented.

Impact of digital control in power electronics

Abstract: In this paper, we discuss the impact of digital control in high-frequency switched-mode power supplies (SMPS), including point-of-load and isolated DC-DC converters, microprocessor power supplies, power-factor-correction rectifiers, electronic ballasts, etc., where switching frequencies are typically in the hundreds of kHz to MHz range, and where high efficiency, static and dynamic regulation, low size and weight, as well as low controller complexity and cost are very important. To meet these application requirements, a digital SMPS controller may include fast, small analog-to-digital converters, hardware-accelerated programmable compensators, programmable digital modulators with very fine time resolution, and a standard microcontroller core to perform programming, monitoring and other system interface tasks. Based on recent advances in circuit and control techniques, together with rapid advances in digital VLSI technology, we conclude that high-performance digital controller solutions are both feasible and practical, leading to much enhanced system integration and performance gains. Examples of experimentally demonstrated results are presented, together with pointers to areas of current and future research and development.

Semiconductor losses in voltage source and current source IGBT converters based on analytical derivation

Abstract: A crucial criterion for the dimensioning of three phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation in the semiconductors at certain operating points and its maximum. Methods for the calculation and simulation of semiconductor losses in the most common voltage source and current source three phase PWM converters are well known. Here a complete analytical calculation of the power semiconductor losses for both converter types is presented, most parts are already known, some parts are developed here, as far as the authors know. Conduction losses as well as switching losses are included in the calculation using a simplified model, based on power semiconductor data sheet information. This approach should benefit the prediction and further investigations of the performance of power semiconductor losses for both kinds of converters. Results of the calculation are shown. Dependencies of the semiconductor power losses on the type of converter, the operating point and the pulse width modulation are pointed out, showing the general behaviour of power losses for both converter types.

HVDC and FACTS Controllers: Applications of Static Converters in Power Systems

Abstract: Preface. Acronyms. 1: Introduction to HVDC Transmission. 1.1. Introduction. 1.2. Comparison of AC-DC Transmission. 1.3. Types of HVDC Systems. 1.4. References. 2: Types of Converters. 2.1. Introduction. 2.2. Current Source Converters (CSC). 2.3. Voltage Source Converters (VSC). 2.4. Closing Remarks. 2.5. References. 3: Synchronization Techniques for Power Converters. 3.1. Introduction. 3.2. Review of GFUs. 3.3. GFUs - Design And Analysis. 3.4. Tests On GFUs. 3.5. EMTP Simulation Of A Test System. 3.6. Conclusions. 3.7. Acknowledgement. 3.8. References. 4: HVDC Controls. 4.1. Historical Background. 4.2. Functions of HVDC Controls. 4.3. Control Basics for a Two-terminal DC Link. 4.4. Current Margin Control Method. 4.5. Current Control at the Rectifier. 4.6. Inverter Extinction Angle Control. 4.7. Hierarchy of Controls. 4.8. Action By Controls After a Disturbance. 4.9. References. 5: Forced Commutated HVDC Converters. 5.1. Introduction. 5.2. Commutation Techniques for HVDC Converters. 5.3. Examples of FC Converters for HVDC Transmission. 5.4. References. 6: Capacitor Commutated Converters for HVDC Systems. 6.1. Capacitor Commutated Converters (CCC). 6.2. Controlled Series Capacitor Converter (CSCC). 6.3. Comparison of CCC and CSCC. 6.4. Garabi Interconnection between Argentina-Brazil. 6.5. Closing Remarks. 6.6. Acknowledgement. 6.7. References. 7: Static Compensators: STATCOM Based on Chain-Link Converters. 7.1. Introduction. 7.2. The Chainlink Converter. 7.3. Advantages of the Chain Circuit STATCOM. 7.4. Design for Production. 7.5. Acknowledgement. 7.6. References. 8: HVDC Systems Using Voltage Source Converters. 8.1. Introduction. 8.2. Basic Elements of HVDC using VSCs. 8.3. Voltage Source Converter. 8.4. Applications. 8.5. Tjaereborg Windpower Project in Denmark. 8.6. Power Supply to Remote Locations (i.e. Islands). 8.7. Asynchronous Inter-Connections. 8.8. Concluding Remarks. 8.9. Acknowledgement. 8.10. References. 9: Active Filters. 9.1. Introduction. 9.2. DC Filters. 9.3. AC Filters. 9.4. Concluding Remarks. 9.5. Acknowledgement. 9.6. References. 10: Typical Disturbances in HVDC Systems. 10.1. Introduction. 10.2. CIGRE Benchmark Model for HVDC Control Studies. 10.3. Details of Control Systems Used. 10.4. Results. 10.5. Closing Remarks. 10.6. Acknowledgement. 10.7. References. 11: Advanced Controllers. 11.1. Introduction. 11.2. Application of an Advanced VDCL Unit. 11.3. Conclusions. 11.4. Acknowledgement. 11.5. References. 12: Measurement/Monitoring Aspects. 12.1. Introduction.

Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

Abstract: This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.

Positive output cascade boost converters

Abstract: The voltage lift technique has been successfully employed in the design of DC/DC converters, eg three-series Luo-converters, in which the output voltage increases stage-by-stage in arithmetic progression The super-lift technique considerably increases the voltage transfer stage-by-stage gain in geometric progression However, their circuits are complex An approach, positive output cascade boost converters, that implements the output voltage increasing in geometric progression with a simple structure is introduced These converters also effectively enhance the voltage transfer gain in power-law terms

Theory and applications of incremental /spl Delta//spl Sigma/ converters

Abstract: Analog-Digital (A/D) converters used in instrumentation and measurements often require high absolute accuracy, including very high linearity and negligible dc offset. The realization of high-resolution Nyquist-rate converters becomes very expensive when the resolution exceeds 16 bits. The conventional delta-sigma (/spl Delta//spl Sigma/) structures used in telecommunication and audio applications usually cannot satisfy the requirements of high absolute accuracy and very small offset. The incremental (or integrating) converter provides a solution for such measurement applications, as it has most advantages of the /spl Delta//spl Sigma/ converter, yet is capable of offset-free and accurate conversion. In this paper, theoretical and practical aspects of higher order incremental converters are discussed. The operating principles, topologies, specialized digital filter design methods, and circuit level issues are all addressed. It is shown how speed, resolution, and A/D complexity can be optimized for a given design, and how with some special digital filters improved speed/resolution ratio can be achieved. The theoretical results are verified by showing design examples and simulation results.

Prototype of multiphase modular-multilevel-converter with 2 MW power rating and 17-level-output-voltage

Abstract: A versatile prototype converter system of the new modular-multilevel converter (M/sup 2/LC) family is introduced. The new concept stands out due to its stringent modular construction as well as its extremely good control characteristics. This new M/sup 2/LC concept is well suitable for a wide range of high voltage applications. The basic working principle as well as the static and dynamic behaviour is explained in detail on a single-phase AC/AC-converter enabling four-quadrant operation. The M/sup 2/LC-family has already been introduced and examined for applications like traction converters, operating directly on the power line, and network interties [Marquardt, R et al., 2003 and Lesnicar, A et al., 2002]. With this prototype converter system, the characteristics of various different M/sup 2/LC-topologies can be investigated, including single or three phase DC/AC converters as well as multiphase AC/AC converters. The prototype converter has been designed in such a way that its configuration can be quickly changed between wide ranges of topologies. A flexible control system has been implemented, which is capable of controlling up to 32 IGBTs per converter arm, independently. Next to the presentation of the converter and its control system, measurement results are presented including converter operation.

Active voltage clamp in flyback converters operating in CCM mode under wide load variation

Abstract: Active clamp topologies of low power dissipation have become a very attractive solution in order to limit overvoltages in flyback converters. Although many suitable topologies have been introduced for the case of discontinuous conduction mode (DCM), where the duty cycle value depends on the load level, in continuous conduction mode (CCM) it is more difficult to appropriately design such topologies so as to "sense" load changes-due to the small duty cycle divergence under wide load variation. Taking for granted that in order to achieve high power-factor correction in these converters, CCM is a more attractive mode of operation, a drastic solution for this case that will manage to eliminate voltage stresses under wide load changes has become very essential. For this purpose, this paper presents an active clamp topology with small power dissipation, suitable for flyback converters operating in CCM mode. Its main idea is the use of a load-dependent current source, consisting of an auxiliary converter operating in DCM mode. Experimental results highlight the effectiveness of the proposed topology under wide load changes, establishing it as an appropriate solution in order to develop flyback converters, even at the power range of 500 W.

H/sup /spl infin// repetitive control of DC-AC converters in microgrids

Abstract: This paper proposes a voltage controller design method for DC-AC converters supplying power to a microgrid, which is also connected to the power grid. This converter is meant to operate in conjunction with a small power generating unit. The design of the output voltage controller is based on H/sup /spl infin// and repetitive control techniques. This leads to a very low harmonic distortion of the output voltage, even in the presence of nonlinear loads and/or grid distortions. The output voltage controller contains an infinite-dimensional internal model, which enables it to reject all periodic disturbances which have the same period as the grid voltage, and whose highest frequency components are up to approximately 1.5 kHz.

An innovative digital control architecture for low-Voltage, high-current DC-DC converters with tight voltage regulation

Abstract: This paper describes an innovative digital control architecture for low-voltage, high-current dc-dc converters, based on a combination of current-programmed control and variable frequency operation. The key feature of the proposed architecture is the low complexity: only two digital-to-analog converters (DACs) with low resolution (7-b) are used for control. An original control algorithm is used to reduce quantization effects to negligible levels, in spite of the low resolution of the DACs. Thanks to this algorithm, both static and dynamic output voltage regulation are improved with respect to traditional digital solutions. Adaptive voltage positioning and active current sharing are inherently provided by the new architecture. A detailed description of the control strategy is given with reference to a single-phase buck converter. Extension to multiphase converters is straightforward. The digital control architecture is experimentally verified on a FPGA-based four-phase prototype buck converter operating at 350 kHz/phase. Output voltage tolerance within /spl plusmn/0.5% is experimentally demonstrated, along with negligible quantization effects and fast transient response. The features and the performance of the proposed architecture make it a valuable candidate for the control of next generation voltage regulator modules.

Small-signal z-domain analysis of digitally controlled converters

Abstract: As the performance of digital signal processors has increased rapidly during the last decade, there is a growing interest to replace the analog controllers in low power switching converters by more complicated and flexible digital control algorithms. Compared to high power converters, the control loop bandwidths for converters in the lower power range are generally much higher. Because of this, the dynamic properties of the uniformly-sampled pulse-width modulators used in low power applications become an important restriction to the maximum achievable bandwidth of control loops. Though frequency- and Laplace-domain models for uniformly-sampled pulse-width modulators are very valuable as they improve the general perception of the dynamic behavior of these modulators, the direct discrete design of the digital compensator requires a z-domain model for the combination modulator and converter For this purpose a new exact small-signal z-domain model is derived. In accordance with the zero-order-hold equivalent commonly used for 'regular' digital control systems, this z-domain model gives rise to the development of a uniformly-sampled pulse-width-modulator equivalent of the converter. This z-domain model is characterized by its capability to quantify the different dynamics of the converter for different modulators, its ease of use and its ability to predict the values of the control variables at the true sampling instants of the real system.

Unified analysis of switched-capacitor resonant converters

Abstract: A family of switched-capacitor resonant circuits using only two transistors is presented. The circuit operates under zero-current switching and, therefore, the switching loss is zero. It also offers a wide choice of voltage conversions including fractional as well as multiple and inverted voltage conversion ratios.

Multiphase voltage-mode hysteretic controlled DC-DC converter with novel current sharing

Abstract: Today's on-board high-density, low-output-voltage, high-output-current, fast transient point-of-load (POL) dc-dc converters design requirements for the new generation of integrated circuits, digital signal processors, and microprocessors are increasingly becoming stricter than ever. This is due to the demand for high dynamic performance dc-dc conversion with tight dynamic tolerances for supply voltages coupled with very high power density. In this paper, a multiphase voltage-mode hysteretic controlled POL dc-dc converter with new current sharing is presented. Theoretical analysis is provided for multiphase and interleaved dc-dc converters with new current sharing method. The simulation and experimental results are compared based on a specific design example.

Parasitic ringing and design issues of digitally controlled high power interleaved boost converters

Abstract: High power boost converter has become the essential part of the distributed power system that enables energy to be fully utilized in fuel cell powered electric vehicles and stationary power systems. This paper presents analysis and design of a high-power multileg interleaved boost converter with a digital signal processor (DSP) based controller. A 20-kW converter was designed with coupled inductors to allow core-loss reduction and designed with high frequency switching to minimize the component size and eliminate the switching losses under discontinuous conducting mode operation. A dual-loop average current mode current control method implemented in DSP is employed to achieve the fast transient response. It was found through circuit analysis, simulation and experiment that the boost inductor interacted with the device parasitic capacitor and created unnecessary oscillating current whenever it reached zero current. Two high-power devices were used in both simulation and experiment to verify the analysis and design for a wide load range. Simulation and experiment results of the 20-kW boost converter under startup condition and load transient condition are also presented. Different anti-windup schemes for a typical PI-controller are evaluated. The results show that this typical controller with proper anti-windup scheme achieves better transient performance than without anti-windup scheme.

A new ZVT-ZCT-PWM DC-DC converter

Abstract: In this paper, a new active snubber cell is proposed to contrive a new family of pulse width modulated (PWM) converters. This snubber cell provides zero voltage transition (ZVT) turn on and zero current transition (ZCT) turn off together for the main switch of a converter. Also, the snubber cell is implemented by using only one quasi resonant circuit without an important increase in the cost and complexity of the converter. New ZVT-ZCT-PWM converter equipped with the proposed snubber cell provides most the desirable features of both ZVT and ZCT converters presented previously, and overcomes most the drawbacks of these converters. Subsequently, the new converter can operate with soft switching successfully at very wide line and load ranges and at considerably high frequencies. Moreover, all semiconductor devices operate under soft switching, the main devices do not have any additional voltage and current stresses, and the stresses on the auxiliary devices are at low levels. Also, the new converter has a simple structure, low cost and ease of control. In this study, a detailed steady state analysis of the new converter is presented, and this theoretical analysis is verified exactly by a prototype of a 1-kW and 100-kHz boost converter.

Modeling characteristics of harmonic currents generated by high-speed railway traction drive converters

Abstract: This paper presents a study for modeling harmonic currents injected by three-level pulse-width-modulated (PWM) converters of the high-speed railway traction drive in steady-state motoring mode. An analytical solution for converter harmonics based on the double Fourier series theory is described. The time-domain simulation results obtained by the use of PSpice are then compared with those obtained by the proposed model. It is shown that the harmonic currents determined according to the proposed model agree well with those results obtained by using the time-domain simulation tool.

Modeling of quantization effects in digitally controlled DC-DC converters

Abstract: In digitally controlled DC-DC converters with a single voltage feedback loop, the two quantizers, namely the A/D converter and the digital pulse-width modulator (DPWM), can cause undesirable limit-cycle oscillations. In this paper, static and dynamic models that include the quantization effects are derived and used to explain the origins of limit-cycle oscillations. In the static model, existence of DC solution, which is a necessary no-limit-cycle condition, is examined using a graphical method. A concept of amplitude and offset dependent gain is introduced to extend the describing function method and derive the dynamic system model. From the static and dynamic models, no-limit-cycle conditions associated with A/D, DPWM and compensator design criteria are derived. The conclusions are illustrated by simulation and experimental examples.

Operation of a prototype microgrid system based on micro-sources quipped with fast-acting power electronics interfaces

Abstract: The paper presents experimental results from the operation of a prototype microgrid system, installed in the National Technical University of Athens, which comprises a PV generator, battery energy storage, local load and a controlled interconnection to the LV grid. Both the battery unit and the PV generator are connected to the AC grid via fast-acting DC/AC power converters. The converters are suitably controlled to permit the operation of the system either interconnected to the LV network, or in stand-alone (island) mode, with a seamless transfer from the one mode to the other. The paper provides a technical description of the system components and the control concept implemented, along with extensive measurement results which demonstrate its capability to operate in the aforementioned way.

Synergetic control of power converters for pulse current charging of advanced batteries from a fuel cell power source

Abstract: This paper presents a synergetic controller for pulse current charging of advanced batteries from a fuel cell power source. Pulse current charging protocol that has been shown to have many advantages over the traditional constant current/constant voltage protocol is applied in a fuel cell powered battery-charging station to reduce the total charging time. Strong nonlinearity and dynamics exist in such systems. In this paper, the synergetic control approach is applied to regulate the buck converters that control the pulse charging currents to the many batteries. A practical synergetic controller to coordinate pulse current charging of the battery is synthesized and discussed. It provides asymptotic stability with respect to the required operating modes, invariance to load variations, and robustness to variation of the input and converter parameters. The synergetic controller is then implemented in Simulink. The dynamic characteristics of the synergetic controller are studied and compared with PI controller by conducting system simulation and experimental tests. Simulation and experiment results show the synergetic controller is robust for such nonlinear dynamic system and achieves better performance than the standard PI controller.

Study of the multilevel converters in DC-DC applications

Abstract: Multilevel converters have been demonstrated to have many advantages such as low harmonic, low voltage stress, and high power capability. However, most of the researches are focused on high power AC-DC and DC-AC applications. This paper presents several multilevel DC-DC converters, which can be used in automotive applications as well as in high power applications. Based on the diode-clamp, flying-capacitor, and cascaded multilevel inverters, their correlative DC-DC converters are derived. A 1 kW prototype of four-level flying-capacitor DC-DC converter used in automotive systems was built as an example to demonstrate the advantages.

Proportional-Resonant Controllers. A New Breed of Controllers Suitable for Grid-Connected Voltage-Source Converters

Abstract: -This paper is describing the recently introduced proportional-resonant (PR) controllers and their suitability for grid-connected converters current control. It is shown that the known shortcomings associated with PI controllers like steady-state error for single-phase converters and the need of decoupling for three-phase converters can be alleviated. Additionally, selective harmonic compensation is also possible with PR controllers. Suggested control-diagrams for three-phase grid converters and active filters are also presented. A practical application of PR current control for a photovoltaic (PV) inverter is also described. Index Terms current controller, grid converters, photovoltaic inverter

Power conversion system and method of converting power

Abstract: A power conversion system includes a first converter having a DC side and an AC side and a second converter having a DC side and an AC side. The DC sides of the converters are connected in series with a battery connected in parallel across the DC side of the first converter. The AC sides of the converters are connected in parallel across an AC voltage grid. A DC generating power source is coupled across the DC sides of both converters. The first converter is bi-directional with the second converter being either an inverter providing DC to AC conversion or alternately a bi-directional inverter.

Fuel cell power system and high power DC-DC converter

Abstract: This paper discusses the principle and electrical characteristics of the fuel cell, designs an innovative hybrid power system, and proposes a new DC/DC converter scheme to combine the fuel cell with the storage system. An effective converter scheme for the fuel cell is obtained by analyzing the high efficient topology as well as the phase shifted pulse-width modulation. Through comparing several different control modes of converters, a 75-kW prototype system is constructed, moreover, which steady-state operating characteristics are illustrated and discussed in detail. At last, experimental results are also shown to verify the proposed scheme.

Improving power system dynamic behavior through doubly fed induction machines controlled by static converter using fuzzy control

Abstract: This work presents a control strategy applied to a doubly fed induction machine (DFIM) for wind generation in a medium power system. In order to control the active power and reactive power exchange between the machine and the grid, the rotor is fed by a link of AC-DC-AC converters modeled as voltage and controlled current sources, respectively. The control of the rotor-side converter is realized by fuzzy controllers whose performances are compared with that of conventional Proportional-Integral controllers. The control of the grid-side converter is carried out by a control block based on the instantaneous power theory and it is controlled to maintain the DC link voltage constant and to improve the power factor of the system. Some design considerations of the control schemes are discussed. A multimachine model is used in digital simulations to assess the dynamic behavior of the power system control scheme proposed in this work.

Small-signal Laplace-domain analysis of uniformly-sampled pulse-width modulators

Abstract: As the performance of digital signal processors has increased rapidly during the last decade, there is a growing interest to replace the analog controllers in low power switching converters by more complicated and flexible digital control algorithms. Compared to high power converters, the control loop bandwidths for converters in the lower power range are generally much higher. Because of this, the dynamic properties of the uniformly-sampled pulse-width modulators used in low power applications become an important restriction for the maximum achievable bandwidth of control loops. After the discussion of the most commonly used uniformly-sampled pulse-width modulators, small-signal frequency- and Laplace-domain models for the different types of uniformly-sampled pulse-width modulators are derived theoretically. The results obtained are verified by means of experimental data retrieved from a test setup.

Limits of the neutral-point balance in back-to-back-connected three-level converters

Abstract: This paper explores the limits of neutral-point current control in back-to-back connected three-level converters. The theoretical analysis used is based on a mathematical neutral-point current model, which can be extended to apply to converters with higher numbers of levels. The low-frequency ripple, which appears in the neutral-point voltage for some operation conditions, can be removed for an extended operating area when two converters are connected back to back to the same dc bus. As a consequence, a lower voltage is applied to the devices, and the value of the capacitors can also be significantly reduced. Some practical graphics are given to represent the design according to the specifications of the application.

Analysis, design and experimentation of a high voltage power supply for ozone generation based on the current-fed parallel-resonant push-pull inverter

Abstract: The use of supply frequencies above 50-60 Hz allows for an increase in the power density applied to the ozonizer electrode surface and an increase in ozone production for a given surface area, while decreasing the necessary peak voltage. Parallel-resonant converters are well suited for supplying the high capacitive load of ozonizers. Therefore, in this paper the current-fed parallel-resonant push-pull inverter is proposed as a good option to implement high-voltage high-frequency power supplies for ozone generators. The proposed converter is analyzed and some important characteristics are obtained. The design and implementation of the complete power supply are also shown. The UC3872 integrated circuit is proposed in order to operate the converter at resonance, allowing us to maintain a good response disregarding the changes in electric parameters of the transformer-ozonizer pair. Experimental results for a 50-W prototype are also provided.

Comparative evaluation of modulation algorithms for neutral point clamped converters

Abstract: Neutral-point-clamped converters are increasingly applied in industrial drive systems as they allow the use of lower voltage devices in higher voltage applications, provide reduced output voltage total harmonic distortion (THD), and can develop low common mode voltage. Several distinct modulation strategies have been proposed in the past for eliminating the common mode voltage, providing low THD output voltage or reducing the neutral point current ripple. However, each of these strategies improves the performance of the converter on one metric while trading off performance in other metrics. Nearest three vector, radial state, and zero-common-mode types of space-vector modulation techniques are compared using metrics that clearly elucidate the performance tradeoffs. Analytical models, computer simulation results, and experimental verification are presented.