Table of contents monday, September 9, 1: 30pm-4: 00pm modular Multi-Level Converters, hvdc, and dc grids I 3

Modular Multilevel Converters (MMC) III

Thursday, September 22, 2:00PM-3:40PM, Room: 202B, Chair: Di Zhang, Jiangchao Qin

2:00PM Design and Implementation of Finite State Machine Decoders for Phase Disposition Pulse Width Modulation of Modular Multilevel Converters [#1384]
Carlos Teixeira, Yichao Sun, Grahame Holmes and Brendan McGrath, RMIT University, Australia; Southeast University, China

It is well known that level shifted phase disposition pulse width modulation (PD-PWM) achieves the best possible three-phase line-to-line output voltage spectrum for multilevel converters. However the strategy does require post modulation signal decoding to optimally select between redundant switched states and to achieve an even distribution of commutation events across all switching devices. For modular multilevel converters (MMCs), PD-PWM involves firstly scheduling the individual module switching events of both arms as an integrated process to achieve optimal harmonic performance, and then selecting between redundant states to balance the individual module capacitor voltages, and to also minimise the phase leg high frequency circulating currents. This paper discusses the design and implementation of finite state machine PD PWM post modulator decoders for MMCs to achieve these objectives. The proposed approach has been verified in simulation and then with experimental confirmation using a two module per arm MMC

2:25PM Control of the AC-AC Modular Multilevel Converter under Submodule Failure [#1531]
Yang Qichen and Saeedifard Maryam, Georgia Institute of Technology, United States

The family of Modular Multilevel Converter (MMC) has become one of the most promising converter topologies for medium/high-voltage applications because of its modularity and scalability. Specifically, the AC-AC MMC is a promising candidate for medium-voltage motor drive applications. As the AC-AC MMC is based on stacking a large number of Submodules (SMs), its operation is vulnerable to SM failure. To improve the reliability/availability of the AC-AC MMC, in this paper, a post-fault strategy is proposed to ensure stable operation and normal power transfer capability of the MMC subsequent to any SM failure. Besides, since proper operation of the AC-AC MMC necessitates that the magnitude of the SM capacitor voltage fluctuations need to be attenuated, SM capacitor voltage fluctuation mitigation strategies are also proposed. Performance and effectiveness of the proposed methods are verified based on simulation studies in the PSCAD/EMTDC software environment.

2:50PM Control of a Modular Multilevel Converter with Pulsed DC Load [#400]
Marija Jankovic, Alan Watson, Alessandro Costabeber and Jon Clare, University of Nottingham, United Kingdom

This paper focuses on a Modular Multilevel Converter grid interface for a klystron modulator system that behaves as a pulsed DC load. With such a load, and without mitigating control, the MMC suffers from cell capacitor voltage imbalance between the converter arms which leads to distortion (fluctuation) of the absorbed AC power. This paper proposes an augmented modulation strategy, with a tailored distribution of the modulation signals between the arms within a phase, to ensure low AC power fluctuation. The effectiveness of the method has been verified through simulation and has been experimentally proven on a 7kW MMC prototype operating with a 3 kA pulsed DC load.

3:15PM Short circuit output protection of MMC in Voltage Source Control Mode [#511]
Manfred Winkelnkemper, Lukas Schwager, Pawel Blaszczyk, Mischa Steurer and Dionne Soto, ABB Switzerland Ltd., Switzerland; ABB Poland Sp. z o.o., Poland; CAPS Florida State University, United States

The MMC operated in Current Source Mode (CSM) with branch current control shows excellent fault limiting capability. With proper design, the same capability is achieved in Voltage Source Mode (VSM). The key is combining the VSM and CSM controls and having same state variables. Seamless transition between CSM and VSM is ensured by the change of references triggered either by the user or by internal limiters. Experimental results in the full scale 1.25 MW demonstrator proved that the MMCs can limit short circuit currents without turning off even when it's shorted at its terminals.

DC-DC: Isolated Convertes

Thursday, September 22, 2:00PM-3:40PM, Room: 102C, Chair: Sudip Mazumder, Jason Stauth

2:00PM An Isolated Three-Port DC-DC Converter with High Power Density in 10 cm X 5 cm X 0.8 cm Card Size for Flexible Automotive Systems [#594]
Shuntaro Inoue, Kenichi Itoh, Masanori Ishigaki, Takahide Sugiyama and Masaru Sugai, TOYOTA CENTRAL R and D LABS., INC., Japan

A credit-card sized three-port dc-dc converter (TPC) has been designed and constructed. The TPC has three DC ports in one circuit, and DC power can be transferred without interference mutually. A dual active bridge converter (DAB) and a non-isolated bi-directional dc-dc converter (NBC) are integrated in the TPC by using a technique known as magnetic coupling inductor. Both thermal and soft-switching analysis are conducted to realize a high energy density of prototype, where a 750 W, 375 kHz, 18 W/cc is achieved. The efficiency and total losses have been measured in order to verify the validity of the proposed converter, and efficiency over 90% in wide range of output power is achieved by using Si MOSFETs.

2:25PM Auxiliary power supply based on a modular ISOP Flyback configuration with very high input voltage [#555]
Alberto Rodriguez, Maria R. Rogina, Mariam Saeed, Diego G. Lamar, Manuel Arias, Mario Lopez and Fernando Briz, University of Oviedo, Spain

This paper proposes a Flyback-based Input-Series Output-Parallel (ISOP) Auxiliary Power Supply (APS), intended to feed the control system of the cells of a Solid-State Transformer (SST). The SST topology is based on a modular Multiport Multilevel Converter (MMC). Energization of the cells auxiliary circuitry is not trivial due to the high voltages involved (tens of kV for the electric power distribution system), most of the commercially available control and driving circuitry not being usable due to the isolation requirements. It is possible to energize the control circuitry from an APS, connected to the cell capacitor voltage. However, in the SST under consideration, cells target DC voltage is in the range of 1.5kV to 2.5kV. Design of an APS capable of feeding the auxiliary circuitry from such high voltage and the required isolation is not trivial. A modular APS using autonomous Flyback converters in Continuous Conduction Mode (CCM) and based on commercial AC adapters is proposed in this paper. The solution is scalable and therefore applicable to cells with larger DC voltages.

2:50PM Design Considerations for Series Resonant Converters with Constant Current Input [#707]
Hongjie Wang, Tarak Saha and Regan Zane, Utah State University, United States

Applications such as under-sea power prefer dc current distribution in a series cable connection instead of dc voltage distribution due to the long distance and cable loss. Power converter modules employed in these scenarios have a constant current input. In this paper, steady state analysis and unique design considerations are presented for the series resonant converter topology with constant current input. Constraints on the resonant tank component selection and operating frequency are developed to achieve the desired load range for the given input current. Hardware results are provided based on an under-sea dc distribution scenario to verify the benefits of the analysis and design considerations for a 400 kHz, 500 W SRC with 1 A input current and 330 mA output current.

3:15PM Galvanically Isolated Switched-Boost-Based DC-DC Converter [#123]
Saman A. Gorji, Mehran Ektesabi, Trung N. Nguyen and Jinchuan Zheng, Swinburne University of Technology, Australia

A new galvanically isolated DC-DC converter has been presented in this paper. The proposed topology is based on the quasi-switched-boost impedance network. It not only includes all positive characteristics of previous converters including continuous input current, high boost ability and high efficiency, but also has the prominent features of less passive elements utilization, small size and light weight. The proposed converter has been analyzed and inspected in the steady state. Furthermore, other possible galvanically isolated switched boost dc-dc topologies have been obtained by altering the switching network. Theoretical analysis has been verified by simulations as well as the experiments.

Modeling and Control of DC-AC converters II

Thursday, September 22, 2:00PM-3:40PM, Room: 202D, Chair: Thomas Jahns, Jon Are Suul

2:00PM A Triangle Phase-Shift Control Strategy for Interleaved Critical-Mode Power Converters [#541]
Lanhua Zhang, Rachael Born, Qingqing Ma, Yu Wei, Xiaonan Zhao and Jih-Sheng Lai, Virginia Polytechnic Institute and State Univers, United States

Due to its high conversion efficiency and high power density, interleaved critical-mode converter is widely employed by modern power converters. This topology is utilized in ac-dc, dc-dc, and dc-ac converters. Because of the variable switching-frequency operation, phase-shift control is a challenge in the design of critical-mode power converters. This paper presents a triangle phase-shift control strategy for interleaved critical-mode power converters. Based on circuit parameters of the topology and current information of the master phase, a control ramp is derived to control the current phase of slave phase. Based on the proposed control ramp, triangle phase-shift control is proposed. The proposed control strategy is experimentally verified on a dual- phase interleaved dc-dc converter.

2:25PM Seamless Transition Control between Motoring and Generating Modes of a Bidirectional Multi-Port Power Converter Used in Automotive SRM Drive [#1173]
Fan Yi, Wen Cai and Babak Fahimi, The University of Texas at Dallas, United States

In this paper, a control strategy providing seamless transition between motoring and generating modes within a bidirectional integrated multi-port power converter (IMPC) used in switched reluctance machine (SRM) drive is presented. The IMPC offers capacitance reduction in the dc bus while maintaining a very small ripple on the input current from or output current to the dc source under both modes of operation. This facilitates a direct connection to the battery pack in an electric propulsion system. In addition, the braking torque can be controlled even under high speed thanks to the adjustable dc bus voltage. Model of the SRM drive system incorporating the converter and SRM is established for both motoring and generating modes. Accordingly, the seamless transition strategy is developed based on IMPC. Finally, the effectiveness of the proposed system is validated by simulation and experimental results.

2:50PM Three-Phase Inverter Modeling using Multifrequency Averaging with Third Harmonic Injection [#500]
Xiao Liu and Aaron Cramer, University of Kentucky, United States

Models of converters based on averaging have been used widely with numerous benefits. Multifrequency averaging (MFA) model can predict both the fundamental and switching behavior of converters and has the faster simulation run times associated with average-value models. Third harmonic injection is commonly used in the modulation signal for three-phase inverters to increase the inverter maximum output voltage while avoiding overmodulation. Herein, an MFA model for three-phase pulse width modulation inverters with third harmonic injection is proposed. The quasi-Fourier-series representation of the switching functions with third harmonic injection is necessary for constructing three-phase inverter MFA model. The third harmonic injection does not change the fundamental and third harmonic components of the state variables in a balanced three-phase system, but it changes the higher-order harmonics. As a result, the quasi-Fourier-series representation of the switching functions for three-phase inverters with third harmonic injection must include the third harmonics. The proposed MFA model is demonstrated in simulation, and the simulation results show that this model has high accuracy (including the switching behavior) and fast run times.

3:15PM Transformation Based Tracking Controller for a GaN Microinverter [#978]
Ankit Gupta, Harshit Soni, Sudip Mazumder, Shirish Raizada, Debanjan Chatterjee, Paromita Mazumder and Parijat Bhattacharjee, University of Illinois, United States; Tagore Tech, United States; NextWatt LLC, United States

Differential mode cuk inverter (DMCI) represents a class of single-stage inverter with low device count, modular symmetry, and topological simplicity. Recently, discontinuous modulation scheme (DMS) has been proposed for the DMCI. This paper extends the modular nature of the power stage to the control architecture and proposes a transformation based tracking controller using adaptive control algorithm for the same. A key challenge in designing a controller for DMS based DMCI is to take into account the inherent converter nonlinearity and startup transient at the start of every line cycle. Experimental results are provided for startup, steady state, load transition, and total harmonic distortion (THD) using GaN FET based DMCI, which validate the efficacy of the implemented modular transformation-based tracking controller.

Stability in Power Converters II

Thursday, September 22, 2:00PM-3:40PM, Room: 102E, Chair: Dusan Borojevic, Leila Parsa

2:00PM Source-side Series-virtual-impedance Control Strategy to Stabilize the Cascaded System with Improved Performance [#547]
Xin Zhang, Qing-Chang Zhong and Wen-Long Ming, The University of Sheffield, United Kingdom; Illinois Institute of Technology, United States

For cascaded system, interactions among individually designed power subsystems may cause the instability of the whole system. It has been shown recently that the series-virtual-impedance (SVI) control strategy can stabilize the cascaded system via shaping the load input impedance in a very small frequency to minimize its impact on the original load converter. In this paper, a further investigation of the SVI control strategy is carried out by two-port network analysis. Firstly, it is pointed out that, though the impact of the SVI control strategy is limited in a very small frequency, it still deteriorates the performance of the original load converter. In order to overcome this drawback, this paper proposes source-side series-virtual-impedance (SSVI) control strategy, which move the series-virtual- impedance of the traditional SVI control strategy from load side to source side by changing the control of the source converter instead of the load converter. With the proposed SSVI control strategy, the cascaded system not only can solve its instability problem, but also can improve the performance of its source converter. Finally, a 100W 48V-32V-24V experimental system is fabricated to validate the SSVI control strategy.

2:25PM Bifurcation Analysis of Photovoltaic-Battery Hybrid Power System with Constant Power Load [#939]
Meng Huang, Lijun Wei, Yi Liu, Jianjun Sun and Xiaoming Zha, Wuhan University, China

The photovoltaic-battery hybrid power system is a kind of flexible renewable power generation system, which is composed of a photovoltaic array and a battery connected to an output DC bus via power converters. The system can work with multiple structures and multiple operating modes due to the source and load states. Particularly, the nonlinear nature of the constant power load will destablize the system under different operating modes. In this paper, the bifurcation phenomena are identifed in this kind of system when the local load working as a constant power load. It is obersed that the loading has a nonlinear impact on the system and leads to low-frequency Hopf bifurcation and catastrophic bifuration which is an irreversible instability in the system. Based on the averaged model, the two bifurcation is analyzed and the stability boundaries are located. Finally, the instability phenomena are verified by experimental measurements in a practical PBHPS of 200 W.

2:50PM Measurement technique to determine the impedance of automotive energy nets for stability analysis purpose based on a floating capacitor H-bridge converter [#505]
Matthias Hiermeier, Michael Muerken, Thomas Hackner and Johannes Pforr, Technische Hochschule Ingolstadt, Germany; Audi AG Ingolstadt, Germany

The complexity of electrical energy nets in modern cars is increasing rapidly due to the rising number of dc-dc converters and motor controllers. Multi-converter systems may lead to negative impedance instability that must be avoided in the automotive energy net under all circumstances, including faulty conditions such as a failure of batteries or other energy storage devices. Many stability criteria that have been developed during the last years for multi-converter systems are impedance based stability criteria. Impedance measurements therefore play an important role when investigating stability issues of multi-converter systems. In this paper a floating capacitor H-bridge converter is proposed as a simple measurement device for impedance measurements in automotive energy nets. The device can be easily implemented, provides small size and weight and is able to cope with the high dc currents required by the loads. A full-size prototype converter was built and tested to prove the performance for the given application. Theoretical predictions are in good correlation with experimental results.

3:15PM Harmonic Suppression and Stability Improvement for Aggregated Current-Controlled Inverters [#39]
Qiang Qian, Shaojun Xie, Jinming Xu and Lin Ji, Nanjing University of Aero. and Astronautics, China

For LCL-filtered grid-connected inverters, classical control methods such as the proportional grid voltage feed-forward, the harmonic quasi resonant (HQR) control etc., are widely utilized to achieve low current distortion. However, the system stability is easily challenged by the grid impedance and the increased number of the paralleled inverters. Therefore, this paper orients to guarantee the harmonic suppression and the system stability, simultaneously. The impedance-based approach is employed for modeling the multiple-inverter system. The control strategy which consists of the proportional weighted grid voltage feed-forward and HQR with phase compensation is proposed. Moreover, the relationship between the proportional weighted value and the number of the improved HQR controllers is clearly clarified. With the help of the proposed control strategy, the magnitude of the inverter output impedance is maximized as much as possible and the phase across -90 degree is avoided to improve the system stability. The effectiveness of the method is verified with experimental results on a two-inverter-parallel system

Design Optimization of Power Converters

Thursday, September 22, 2:00PM-3:40PM, Room: 202C, Chair: Suman Debnath, Pericle Zanchetta

2:00PM Efficiency-wise Optimal Design Methodology of LCLC Converter for Wide Input Voltage Range Applications [#101]
Yang Chen, Hongliang Wang, Zhiyuan Hu, Yan-fei Liu, Jahangir Afsharian and Zhihua (Alex) Yang, Queen's University, Canada; Murata Power Solutions, Canada

LCLC converter is an LLC-based, four-element resonant topology, which has been proved to achieve high voltage gain and high efficiency. Such trait makes LCLC converter specifically suitable for wide-input-voltage-range DC/DC applications. Currently, LCLC converter lacks a design method targeting at optimal efficiency over a wide input voltage range. In fact, due to the complexity, efficiency itself is seldom used as optimization criterion even for LLC designs. In this paper, a systematic methodology is proposed to optimize the efficiency at different input voltage levels for LCLC converter. Three mathematical programs (developed in MATLAB) are employed respectively to find all resonant parameter combinations that critically achieve the required voltage gain; precisely analyze the current stress in time domain; and comprehensively calculate the losses in the power circuit including magnetic components. The programs will automatically generate the optimal parameter design with highest weighted efficiency at desired input voltage levels, as well as the magnetic components construction with specified types and sizes of core and conductor. Besides, this method can be extended to other topologies for wide voltage range applications. To verify the effectiveness of the proposed optimal design method, the function of the mathematical tools will be carefully explained in this paper; and a step-by-step design will be demonstrated as an example. Simulation will be included to verify the accuracy of the method.

2:25PM Reliability-Oriented Design of LC Filter in Buck DC-DC Converter with Multi-Objective Optimization [#598]
Yi Liu, Meng Huang, Yuexia Liu and Xiaoming Zha, School of Electrical Engineering, Wuhan Universi, China

Reliability-oriented design has been proved to be a kind of effective design methodology for power electronic equipment. This paper proposes a design method to obtain the value of inductance and capacitance sets that obtain high capability, power density, high reliability of an LC filter in buck converters through a multi-objective optimization way. The cut-off frequency, lifetime of capacitor and total volume of LC filter are set as objectives in the optimization procedure. The relationship of design objectives and parameters are analyzed. The distribution of these objects and corresponding parameters as well as the Pareto front of the objectives are presented. Simulation and experiment results are presented and verified the theoretical analysis.

2:50PM Optimal Design of Output LC Filter and Cooling for Three-Phase Voltage-Source Inverters Using Teaching-Learning-Based Optimization [#880]
Hamzeh Jamal, Saher Albatran and Issam Smadi, Jordan University of Science and Technology, Jordan

Three-phase voltage-source inverters are becoming widely used in grid applications, due to the increased utilization of renewable energy resources such as photovoltaic (PV) systems. The connection of the inverter to the grid must not deteriorate the voltage quality at the point of the common coupling (PCC). Therefore, the injected current harmonics must not exceed certain level. Reduction of the injected harmonics can be achieved by increasing the filter size and/or increasing the switching frequency. However, increasing the switching frequency will increase the losses in the inverter due to the switching actions. On the other hand, increasing the filter size will increase the cost of the filter. In this paper, an optimal simultaneous design method which aims to minimize the output LC filter cost and the cooling cost with the switching frequency being the main design parameter is proposed. The cooling and filtering components are expressed in terms of the switching frequency. An optimization problem was formulated to find the minimum cost design, constrained by thermal and harmonic limits in addition to another constraints related to the design of the filter. The optimization problem is solved by means of Teaching-Learning-Based Optimization (TLBO) algorithm. The importance of the proposed design method is that the selection of the switching frequency is based on mathematical formulation rather than relying solely on the experience of the designer.