Table of contents monday, September 9, 1: 30pm-4: 00pm modular Multi-Level Converters, hvdc, and dc grids I 3
Modeling and Control of DC-DC Converters II
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- Bu səhifədəki naviqasiya:
- Modulation Techniques II
- Modeling, Control and Stability of Modular Multilevel Converters
- Reluctance Machines II
- PM Machines I
| Modeling and Control of DC-DC Converters II
Wednesday, September 21, 8:30AM-10:10AM, Room: 102C, Chair: Reza Sabzehgar, Liuchen Chang 8:30AM A New High-Frequency Simulation Model for Multi-Winding Transformers used in Switched-Mode Power Supplies [#165] Ripunjoy Phukan, Lakshmi Ravi, Amirhossein Shahirinia and Rangarajan Tallam, Georgia Institute of Technology, Atlanta GA, United States; Rockwell Automation, Mequon WI, United States; Alfred University, Alfred NY, United States In this paper, a new high-frequency simulation model for multi-winding transformers used in switched-mode power supplies (SMPS) is presented. The model can be constructed from simple impedance measurements on a transformer and using information that can typically be found on component datasheets. The model can be applied to the design of an SMPS to determine peak voltage and current stress on the switching device, and to predict conducted emissions for electro-magnetic compatibility (EMC). The model can be implemented through any commercially available circuit simulation package. Simulation and experimental results obtained on a high-voltage one-switch and two-switch Flyback SMPS are provided to validate the modeling method. 8:55AM Multi-Phase Sliding Mode Control for Chattering Suppression in a DC-DC Converter [#1476]
This paper presents a Multi-Phase Sliding Mode(MPSM) Control Strategy for solving chattering issues inherently existing in DC-DC converters. The main idea of the proposed methodology is to implement a MPSM Control for geometrically nullifying the amplitude of ripple currents yielded by the switching patterns. The benefits of the proposed Multi-Phase Sliding Mode Control strategy involve low-switching frequency contributing to reduce switching power loss and leading to simplification of circuit topology. Throughout the experimental implementation, the concepts of control strategies were validated and the advantages of the proposed strategy were confirmed such as low-switching power loss, and simple circuit structure compared to traditional multi-phase SMC implementations. 9:20AM Gradient-reference-current Control of Tri-state Buck Converter to Improve Dynamic Response over Wide Load Range [#361]
Gradient-reference-current (GRC) control strategy is proposed to achieve better dynamic response for tri-state buck converter over a wide load variety without additional hardware. By designing the logical current comparing element without load current detection, the conduction mode of tri-state buck converter under GRC control could be switched between discontinuous conduction mode (DCM) and pseudo continuous conduction mode (PCCM) adaptively to avoid large ripple voltage when converter operates over wide load range. As it operates in load condition within a comparatively small range, the converter stays operating in PCCM and the reference current could be changed in the same trend with load current among the pre-set values to improve the efficiency of tri-state buck converter in light load condition and the dynamic performance of it in heavy load condition. Simulation results verify the effectiveness of GRC control strategy. 9:45AM A Control Strategy for Paralleled Bi-Directional DC-DC Converters Used in Energy Storage Systems [#212]
According to the control requirements of modular power used in energy storage systems, a parallel control strategy for bi-directional DC-DC converter is proposed and applied to the bi-directional DC-DC converter combined by current-fed half bridge and voltage- fed half bridge. While converters operate in parallel, the master-slave control based on digital communications can solve the problem of unequal current distribution caused by different parasitic parameters between parallel modules, and the strategy is with strong anti-interference ability. When running, each slave module will modify the reference of its own internal current loop by comparing its bus side current with the master module's bus side current via its current-sharing loop, so that the current sharing at the DC bus side can be achieved. Meanwhile, with the auto-master-selected strategy, a new master module will arise immediately when the former master module fails, which solves the problem of system failure when master module breaks down with traditional master-salve control. The simulation and experimental results prove the validity of the parallel control strategy. Modulation Techniques II Wednesday, September 21, 8:30AM-10:10AM, Room: 102E, Chair: Madhu Sudhan Chinthavali, Sufei Li 8:30AM Steady-State Analysis of the Phase Shift Modulated LLC Resonant Converter [#269] Wei Liu, Binbin Wang, Wenxi Yao, Zhengyu Lu and Xiaoyi Xu, Zhejiang University, China; State Grid Nantong Supply Company, China In many applications, phase shift modulation (PSM) has been proven to be a promising supplement of pulse frequency modulation (PFM) in LLC resonant converter. However, steady-state analysis of PSM LLC converter is not thoroughly studied yet. This paper presents a generalized PSM LLC model which can provide accurate prediction on resonant voltage and current behavior, dc gain and all the other steady-state information. Then, operation modes, mode boundaries and distribution are discussed with three cases according to the relationship between switching frequency and resonant frequency. Meanwhile, dc voltage gain and zero-voltage switching characteristics of each operation mode are briefly analyzed. Simulation results verify the accuracy of proposed analysis. 8:55AM Practical Implementation of Global Synchronous Pulse Width Modulation with Time Delay Compensation and Distributed Calculation Capabilities [#934]
The distributed inverters are integrated into grid without coordinated PWM and the switching ripples of inverters are randomly accumulated at point of common coupling (PCC). Global synchronous pulse width modulation (GSPWM) can attenuate the accumulated switching ripples. This paper proposes time compensation method which compensates the time delay of synchronization signals for inverters in distance. Then, this paper proposes distributed calculation method for optimal phase shift and synchronization frequency in large-scale application. This new method is much faster than before. Finally, Matlab simulations and experimental results are presents to verify the performance of proposed methods. 9:20AM Research on Zero-Sequence Circulating Currents in Parallel Three-Level Grid-Tied Photovoltaic inverters [#185]
This paper proposes a parallel-connected system where two three-phase three-level T-Type photovoltaic inverters with common ac and dc sides to improve the power rating. However, zero-sequence circulating currents (ZSCCs) will occur, which will distort currents, decrease efficiency, and increase loss. In this paper, the fundamental mechanism of ZSCCs based on the derived model of ZSCCs is analyzed in details including the dead time effects. It is can be seen that the ZSCCs generated in three-level case are more complex than parallel two-level inverters due to existing more space vectors. Then, a synchroniz-ing starting small vector control method with PI controller and feedforward control method is proposed to suppress the ZSCCs. As a result, a good circulating current suppression performance can be obtained. The effectiveness of the analysis and proposed method is validated by experimental results. 9:45AM Modified Pulse Energy Modulation Technique of a Three-Switch Buck-Boost Inverter [#26]
This paper proposed a modified pulse energy modulation (PEM) technique for a single-phase single-stage three-switch buck-boost inverter, solving the issue existed in practical applications that the requirement for sampling circuits is too high to achieve. The three-switch buck-boost inverter was investigated for both standalone and grid-connected operations. Simulation and experimental results verified that the newly proposed PEM technique enables the buck-boost inverter to transfer the demanded energy from a DC source to AC side and achieve a sinusoidal output current with low total harmonic distortion (THD). Therefore, it can be concluded that the proposed modified PEM technique is suited for buck-boost inverters in distributed generation systems, with lower requirement for the sampling circuits. The new contributions presented in this paper include advancing the PEM concept as an alternative to PWM for inverter modulations; and applying the proposed PEM technique to a low component-count inverter in standalone and grid-connected applications. Modeling, Control and Stability of Modular Multilevel Converters Wednesday, September 21, 8:30AM-10:10AM, Room: 202E, Chair: Rik De Doncker, Pragasen Pillay 8:30AM MMC-HVDC: Simulation and Control Strategy [#808] Suman Debnath and Madhusudhan Chinthavali, Oak Ridge National Laboratory, United States Simulation of modular multilevel converter (MMC) based high-voltage direct current (HVDC) systems assumes significance due to their growing popularity. It could assist with the design of hardware, control systems of MMC and HVDC networks, and power system topology. However, simulation of MMC-HVDC using existing software takes a long time due to the presence of a large number of states and non-linear devices. This paper presents an ultra-fast single- or multi-CPU simulation algorithm to simulate the MMC-HVDC system based on state-space models and using hybrid discretization algorithm with a relaxation technique that reduces the imposed computational burden. Using the developed simulation algorithm, a control system is developed for an MMC-HVDC system that reduces the switching losses in the system. 8:55AM Hybrid Railway Power Conditioner Based on Half-Bridge Modular Multilevel Converter [#416]
Hybrid railway power conditioner (HRPC) has been applied to compensating negative-sequence current, reactive power and harmonics in a traction power supply system. Single-phase back-to-back converter is used to implement power conditioning in a HRPC. Its operational voltage is lower than a conventional RPC since it is coupled to 25 kV feeder via a LC branch. However, multilevel converter was not used which is necessary if the HRPC is coupled to the feeder without transformer. A HRPC based on single-phase half-bridge back-to-back modular multilevel converter (MMC) is proposed in this paper. The center-split point of the DC bus is connected to one phase and provides compensating current. Since direct current tracking with hysteresis PWM is not applicable to MMC, proportional-integral (PI) current controller is selected to generate voltage reference. The circulating current is analyzed in detail and parameter design of the MMC is presented. The cell voltage balancing and dc bus voltage balancing of the MMC are studied. Simulation results are provided to verify the effectiveness of the proposed HRPC with its control method. 9:20AM A PWM Method Reducing Harmonics of Two Interleaved Converters [#926]
This paper proposes a PWM method reducing harmonics of two interleaved converters at twice the switching frequency region. If harmonics at twice the switching frequency region can be reduced by the PWM method, the size of filter interfacing the grid and converter would be reduced. Based on Fourier series of phase voltage in every switching period, offset voltage for PWM minimizing harmonics at twice the switching frequency region can be calculated in real time. With the proposed PWM, the size and volume of inductive filters of two interleaved parallel converters can be shrunken conspicuously. Effectiveness of the proposed method is verified by the computer simulation and experimental results. The maximum harmonic at twice the switching frequency region has been reduced by 58% at modulation index 0.8. 9:45AM DC Impedance Modeling and Stability Analysis of Modular Multilevel Converter for MVDC Application [#833]
Modular multilevel converter (MMC) is a promising converter topology to be applied in medium-voltage dc (MVDC) system due to its advantages of superior fault response, high quality output voltage and high efficiency. This paper is focused on the analysis of the features of MMC dc impedance in MVDC system and its influence on MVDC system stability. First, the closed-loop terminal impedance of a MMC at the dc output side is derived and verified by compared with that measured through a circuit-based model. It is also found that the capacitor size and dynamic will not affect the MMC impedance if the capacitor is designed to limit up to 20% voltage ripple, which will simplify the stability analysis. A shipboard MVDC system consisting of a MMC and other load converters has been established. All the impedance characteristics of load converters and their mutual interactions with the MMC are explored. With the developed MMC dc impedance and stability analysis method, the MVDC system stability characteristics can be predicted, which can be used for system design to maintain stability. The simulation results are consistent with the analysis. Reluctance Machines II Wednesday, September 21, 8:30AM-10:10AM, Room: 102B, Chair: Babak Fahimi, Sufei Li 8:30AM Segmented Rotor Design of Concentrated Wound Switched Reluctance Motor (SRM) for Torque Ripple Minimization [#464] Md Ashfanoor Kabir and Iqbal Husain, North Carolina State University, United States; North Carolina State Unievrsity, United States Torque ripple minimization of concentrated wound segmented rotor SRM is achieved through rotor segment designs. Compared to existing ripple minimization techniques the proposed method does not require current profiling, controller complexity or additional converter components. First, an FEA based semi-numerical machine model is developed to identify the torque ripple sources. Next, a new design of rotor segment is presented with segmented dip to effectively minimize torque ripple. Effect of different rotor design parameters on machine performance are studied. Both one factor at a time and multi-dimensional, multi-objective optimization of design parameters are performed to evaluate their performances. The optimized design can reduce torque ripple by 29 percent which is a significant improvement considering the simplicity of this method. 8:55AM Extending the Speed Range of A Switched Reluctance Motor using a Fast Demagnetizing Technique [#1267]
In this paper, a switched reluctance motor (SRM) with an auto-transformer like winding in each phase is presented. The new winding structure allows for fast demagnetization, which enhances the machine performance at high speeds. During demagnetization, the DC bus voltage is applied across a portion of the phase winding and accordingly, a higher negative demagnetization voltage/turn is applied, which leads to an increment in the discharge rate for the phase excitation currents. The proposed concept is verified through Finite Element Analysis (FEA) circuit simulations on a case study motor. The power electronic converters that can be used with the proposed winding configuration and its associated control have been investigated. 9:20AM Development and Analysis of U-core Switched Reluctance Machine [#395]
Switched reluctance machines (SRMs) have seen a lot of interest due to their rugged and fault tolerant construction as well as their high efficiency over a wide speed range. The technology however suffers from torque ripple, acoustic noise and low torque density. Many concepts to address these disadvantages have been presented, but not all of them have been demonstrated practically. This paper presents a practical demonstration and assessment of a segmented U-core SRM, which copes with some of the disadvantages of the regular SRM. The U-core SRM has a segmented stator, with a short flux path and reduced flux reversal, reducing core losses. Due to an increased number of poles, torque density is increased and torque ripple reduced. A prototype is built and through a number of tests, the machine is mapped and all loss components are analysed. As a result of the analysis, an assessment is presented, which addresses the shortcomings of the U-core technology, as well as general considerations for SRMs. This allows for further development and improvement of the technology, and also contributes to improve the development and modelling of conventional SRMs. 9:45AM Torque Ripple and Acoustic Noise of Current Modulations of a Pseudo-Sinusoidal Switched Reluctance Motor [#1282]
Torque ripple and acoustic noise are two major drawbacks to switched reluctance motors. The abrupt change of phase current is main cause of acoustic noise, while both commutation and current wave shape are two major factors contributing to high torque ripple. In order to simultaneously reduce torque ripple and noise, a specific current modulation based on real inductance profile can be employed to recently proposed pseudo-sinusoidal switched reluctance motor (PSSRM). Performance comparison including torque ripple, acoustic noise and efficiency with conventional square and half-sine current modulations are investigated. The performance of the specific current modulation is verified by simulations and experiments with a 12/16, three phase 0.4-hp PSSRM. The results show torque ripple and acoustic noise can be simultaneously reduced with a comparable efficiency by the proposed current modulation method. PM Machines I Wednesday, September 21, 8:30AM-10:10AM, Room: 101A, Chair: Ayman El-Refaie, Ali Bazzi 8:30AM Proposal of Electrically Reversal Magnetic Pole Type Variable Magnetic Flux PM Motor [#606] Masahiro Aoyama, Kazukiyo Nakajima and Toshihiko Noguchi, SUZUKI Motor Corporation, Japan; Shizuoka University, Japan This paper describes a variable magnetic flux PM motor in which space harmonic power is utilized for the magnetic flux weakening, automatically. The stator has a toroidally-concentrated winding structure, and the torque generation surfaces are composed of three air-gaps which are single radial-gap and double axial-gaps. The radial-gap rotor is a consist-magnetized PM rotor and the axial- gap rotors are self-excited wound-field rotor. The axial-gap rotor can retrieve a space harmonic power, which is inevitabley generated by a concentrated winding structure, for magnetomotive force. A mechanical design of the prototype is revealed, and the operation principle of the automated-magnetic flux weakening is clarified through the FE-analysis. In addition, actual prototype machine is introduced, and preliminary experimental test for the verification of self-exitation is demonstrated. Consequently, the effect of automated-armature line voltage decrease is investigated with respect to rotation speed increase. 8:55AM Torque and Core Loss Characterization of a Variable-Flux Permanent-Magnet Machine [#1433]
An appropriate torque-angle selection can improve the torque-to-current ratio of a machine, the size of the converter, and provide an optimal operation of the motor. An accurate determination of the core loss will lead to a better machine design and efficiency estimation. This paper presents the torque-angle and core loss characterization of a variable-flux permanent-magnet machine. Torque-angle curves and core losses are measured and simulated for a 7.5 hp variable-flux machine. The core losses are also obtained using an analytical method. The experimental results for torque-angle and core losses are found to be in good agreement with the simulations and the core losses are also in correlation with analytical data. 9:20AM Examination to Enhance Efficiency of V-shaped IPMSM Using Concentrated Winding Structure at High Speed and High Torque Area [#1513]
IPMSMs used for industrial applications generally require high efficiency operation in a certain operating point or area in addition to constant torque operation. In this research, the examined motor demands high efficiency operation at high speed and high torque area. In this case, the current phase angle is small and it is difficult to use reluctance torque effectively. Furthermore, concentrated winding structure has been adopted to cut manufacturing cost and to use limited space effectively. In general, IPMSMs using concentrated winding structure have a difficulty of generating reluctance torque from the perspective of getting q-axis armature reaction magnetic flux. In this paper, to enhance the efficiency of V-shaped IPMSM using concentrated winding structure at high speed and high torque area, the rotor structures which effectively use permanent magnet torque have been examined. Analysis result of 2D-FEA shows that the examined rotor structure, which arranges disproportional gap and large flux barrier on the q-axis magnetic flux path, can enhance the efficiency at high speed and high torque by suppressing the q-axis magnetic flux and by concentrating the field magnetic flux of PMs on the d-axis. 9:45AM Advanced High Torque Density Non-overlapping Winding PM Vernier Machines [#263]
In recent years, permanent magnet (PM) vernier machines have gained more and more attentions due to their high torque density and simple mechanical structure. However, vernier PM machines with lap windings always suffer from long end winding length, and regular non-overlapping winding may result in torque reduction for PM vernier (PMV) machines. In this paper, an advanced PM vernier (APMV) machine topology with multi working permeance harmonics is proposed. This topology is equipped with non- overlapping winding, i.e. short end winding length, and could achieve 20% higher torque density than that of regular non-overlapping winding PMV machine, with the same magnet usage. Furthermore, both the theoretical analysis and finite element algorithm (FEA) are used to study the performances of this topology, such as back EMF, output torque as well as structure parameter effect. Finally, analysis results are verified by experimental test on a 21Nm prototype, which is designed to have similar volume and weight with a 14Nm regular commercial PM machine. |