Keith Corzine

A New Family of Modular Multilevel Converter Based on Modified Flying-Capacitor Multicell Converters

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.

Analytical Determination of Conduction and Switching Power Losses in Flying-Capacitor-Based Active Neutral-Point-Clamped Multilevel Converter

Multilevel converters are mainly used in medium-voltage high-power applications. Active neutral-point-clamped (ANPC) flying capacitor multicell (FCM) converter is a well-known type of multilevel converters which is commercially available in high-power medium-voltage motor drive market. Since power loss investigation can be very advantageous in the design phase of multilevel converters, this paper presents an analytical approach to calculate and investigate the conduction and switching power loss in ANPC-FCM converter. First, the RMS and average currents of insulated-gate bipolar transistors (IGBTs) and antiparallel diodes are analytically calculated by considering the associated duty cycle of each IGBT and diode, converter modulation index, load current, and load power factor. Numerical results of the derived closed-form equations to calculate the RMS and average currents of IGBTs/diodes are compared with simulation results and experimental measurements. Numerical results match the simulation results and experimental measurements which validates the derived closed-form equations. Afterward, the obtained equations for RMS and average current computations are utilized to calculate the conduction power losses in a 12.1-MVA 6.6-kV nine-level (line-to-line) ANPC-FCM multilevel converter. For this purpose, a 4.5-kV 1.2-kA IGBT module from ABB is considered as a power switch and its parameters are employed in analytical computations and simulation of the ANPC-FCM multilevel converter for conduction power loss determination. Moreover, closed-form equations are derived for analytical determination of switching power losses for ANPC-FCM converter using Kapteyn (Fourier-Bessel) series. Based on the derived closed-form equations for conduction loss and switching loss calculation, a method is presented to determine the junction temperature in IGBTs and diodes for ANPC-FCM converter.

New Multilevel Converter Based on Cascade Connection of Double Flying Capacitor Multicell Converters and Its Improved Modulation Technique

This paper proposes a new multilevel converter based on the cascade connection of double flying capacitor multicell (DFCM) converters, as multilevel modules, to decrease the voltage diversity of the flying capacitors. Furthermore, a new switching pattern based on the phase-shifted pulse-width modulation technique is proposed to reduce the voltage ripple across the flying capacitors. Moreover, the proposed modulation technique reduces the rms value of the current flowing through flying capacitors. This results in an increase in the life time of flying capacitors and a decrease in the capacitance of the flying capacitors, to keep the same amount of the ripple, meaning a reduction in the physical size of the converter. In addition, this paper presents an analytical approach to calculate the average and rms currents of the insulated gate bipolar transistors (IGBTs)/diodes in the DFCM converter in a closed-form expression. The derived closed-form equations to calculate the average and rms currents of the IGBTs/diodes are utilized to investigate the conduction power losses in a DFCM converter and the proposed multilevel converter. Numerical results of the derived closed-form equations match the simulation results well, which validates the derived equations. Furthermore, simulation results and experimental measurements of the proposed multilevel power converter, configured by cascading two two-cell five-level DFCM converters, are presented to validate the performance of the proposed converter as well as the suggested modulation technique.

Modified Z-Source DC Circuit Breaker Topologies

The Z-source dc circuit breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified Z-source breaker design is introduced for the operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs, the respective design will allow for greater control of step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both the fault and step changes in load. Low-voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit.

Dc micro grid protection with the z-source breaker

Many components of a modern micro grid operate using a dc interface including solar panels, fuel cells, and battery energy storage. For this reason, a dc micro grid has been suggested and utilized in some power systems. With the absence of a zero-crossing in the current waveform, the dc breaker faces a unique challenge in that there is no natural method of extinguishing an arc that occurs during breaker operation. This is handled in practice by using over-sized ac breakers, using a solid-state breaker, or using a hybrid solid-state/mechanical breaker. A recently introduced z-source breaker is a unique form of the solid-state breaker that automatically reacts in real-time to system faults; not requiring the typical fault sensing and detection. It has the ability to clear the fault within microseconds. Furthermore, the source will not experience the fault current. In this paper, the theory behind the z-source breaker is reviewed and the breaker is studied in the context of several micro grid topological arrangements using non-real-time and real-time simulation.

The Z-source breaker for fault protection in ship power systems

The z-source breaker is a new kind of breaker which is designed specifically for dc power systems. Without a zero crossing, interrupted dc currents produce arcing and hence ac breakers would not be applicable. The z-source breaker resolves this problem because it is designed to turn off as soon as it experiences a sharp transient in current. In this paper a new design for the z-source breaker is considered so that load transients are not identified as faults. The design is also modified to accommodate bi-directionality which is required in mediumvoltage dc ship power systems. A higher-level coordinated control scheme is discussed which enables multiple breakers to coordinate and isolate the fault in a simple medium-voltage dc ship power system architecture with a central control unit.

Modified z-source DC circuit breaker topologies

The z-source breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified z-source breaker design is introduced for operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs the respective design will allow for step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both fault and step changes in load. Low voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit.

New Flying-Capacitor-Based Multilevel Converter With Optimized Number of Switches and Capacitors for Renewable Energy Integration

The flying-capacitor-based multilevel converter is one of the well-known breeds of the multilevel power converters. This paper proposes a new flying-capacitor-based multilevel converter to minimize the number of flying capacitors (FCs) and power switches. The advantage of the proposed FC-based multilevel converter in comparison with the conventional flying-capacitor multicell converter is that it needs fewer FCs. Also, in comparison with the stacked multicell converter, the proposed multilevel converter requires fewer semiconductor switches. In order to balance the voltage of the FCs in proposed multilevel converter, a new active voltage balancing method which is fully implemented using logic-form equations is presented. The proposed voltage balancing method measures output current and FC voltages to generate switching states to produce the required output voltage level, as well as balance the FCs voltages at their reference values. The output voltage of the proposed multilevel converter controlled with suggested active voltage balancing method can be modulated with any pulse-width-modulation (PWM) method, such as phase-shifted-carrier PWM or level-shifted-carrier PWM. Simulation results and experimental measurements of proposed FC-based multilevel converter are presented to verify the performance of the proposed converter, and its novel switching and modulation strategy, which is based on the active voltage balancing method.

A New Breed of Optimized Symmetrical and Asymmetrical Cascaded Multilevel Power Converters

Multilevel voltage source power converters are the state-of-the-art and key elements for medium-voltage (MV) high-power applications. The cascaded multicell (CM) topologies reach higher output voltage and power levels, and also retain higher reliability due to their modular and fault-tolerant features. This paper initially proposes an optimized topology for symmetrical CM (SCM) multilevel converters. The superiority of the proposed SCM, as compared with the conventional CM converter structure, is that the number of required high-frequency power switches is reduced. Next, a new topology of an asymmetrical CM (ACM) converter, which is formed based on the proposed optimized modules of an SCM converter, is suggested. The advantage of the proposed new ACM converter in comparison with the traditional ACM topology is that the variety of the dc links with different voltage ratings reduces, which makes the proposed topology more modular. The simulation results and the experimental measurements taken from the laboratory prototypes are presented for the proposed converters in order to validate the effectiveness and the advantages of these converters as well as their control strategy.

A New-Coupled-Inductor Circuit Breaker for DC Applications

In order to eliminate power conversion steps, future microgrids with renewable energy sources are being visualized as dc power systems. System components such as sources (solar panels, fuels cells, etc.) loads, and power conversion have been identified and are readily available. However, when it comes to dc circuit breakers, many designs are still in the experimental phase. The main limitation is that interrupting a current which does not have a zero crossing will sustain an arc. This paper introduces a new type of dc circuit breaker. It uses a short conduction path between the breaker and load as well as mutual coupling to automatically and rapidly switch Off in response to a fault. The proposed breaker also can have a crowbar type switch at the output so that it can be used as a dc switch. Mathematical analysis, detailed simulation, and laboratory measurements of the new dc switch are included.