Table of contents monday, September 9, 1: 30pm-4: 00pm modular Multi-Level Converters, hvdc, and dc grids I 3
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- Bu səhifədəki naviqasiya:
- Modeling, Analysis, and Control of Grid-Connected Converters I
- Utility Applications II
- DC Microgrids I
- Transportation Electrification I
Min-Kwon Yang, Seung-Jae Lee, Jun Heo and Woo-Young Choi, Chonbuk National University, Korea (South) The two-level single-ended primary-inductor converter (SEPIC) has been used for grid-tied photovoltaic (PV) systems. However, it has high switching losses because of high voltage stresses. To reduce the switching losses, a three-level SEPIC is suggested in this paper. The three-level SEPIC has low switching losses by reducing the switch voltage stress. It improves power efficiency by using a lower-voltage-rated switch compared to the switch in the two-level SEPIC. The capacitor voltage balance control is presented with a maximum power point tracking (MPPT). Experimental results for a 1.0 kW prototype system are discussed with a grid-tied transformerless H6 inverter. 9:45AM A Novel Zero-voltage-switched Multi-resonant DC-DC Converter [#1570]
This paper proposes a novel zero-voltage-switched multi-resonant DC-DC converter. With the resonance between the resonant inductor and the resonant capacitors paralleled with the main switch and rectifier diode, the proposed converter achieves zero- voltage-switching (ZVS) operation of the semiconductors. The resonance components absorb all parasitic components, including the transformer leakage inductance, switch output capacitance and diode junction capacitance. The topological modes, operation principles and dc characteristics are presented in detail. A prototype based on the proposed topology was built in the lab to verify the theoretical analysis. Modeling, Analysis, and Control of Grid-Connected Converters I Wednesday, September 21, 8:30AM-10:10AM, Room: 202D, Chair: fred wang, Paolo Mattavelli 8:30AM Seamless Transfer Strategy Considering Power Balance in Parallel Operation [#121] Chee Seung-Jun, Lee Younggi, Son Young-Kwang, Sul Seung-Ki, Lim Changjin and Huh Sungjae, Seoul National University, Korea (South); LG Electronics, Korea (South) This paper presents a power reference modifier for seamless transfer considering the power balance in the parallel operation. When the PCS (Power Conditioning System) is disconnected from the grid, the PCS should operate in the stand-alone mode to supply energy to the critical loads. If multiple PCSs work as one PCS, slave PCSs maintain the current control mode even if master PCS change its control mode from the current control to the voltage control. If the power references of slave PCSs are not changed properly based on the load condition, the power balance condition may not be met. In that case, the voltage applied to the critical loads might be beyond or below the rated voltage. To avoid this phenomenon, the power values absorbed into the loads should be monitored consistently and the power references of the slave PCSs should be modified properly based on them. But the master PCS which transfers the power references to the slave PCSs and works as voltage source in stand- alone mode can obtain it indirectly by calculating its own power values without monitoring the power consumed by critical loads. Using those, simple controller for modifying the power references of the slave PCSs can be configured. The effectiveness of the proposed power reference modifier has been verified through the experimental results. By applying the proposed method, the transition from the grid-connected mode to the stand-alone mode works satisfying Computer Business Equipment Manufacturers Association (CBEMA) curve. 8:55AM Robust Control for Parallel Operated L-Inverters with Uncertainty and Disturbance Estimator [#229]
In conventional droop control, accurate proportional load sharing could not be achieved among parallel operated inverters due to the mismatch of output impedance and system disturbances. In this paper, an uncertainty and disturbance estimator (UDE)-based robust droop control strategy is proposed for accurate proportional load sharing, particularly reactive power sharing, among parallel operated L- inverters. The reactive power dynamics is derived from power delivery equation passed by a low-pass filter, while the reactive power reference is designed with the feedback of load voltage. , and tThe reactive power control is developed based on UDE-based method. The model nonlinearity and uncertainty (e.g., power angle), and system operation disturbances (e.g., change of output impedance, and load change), can be estimated and compensated by this UDE-based robust droop control. Experimental validation is provided to show the effectiveness of the proposed method. 9:20AM Active and Reactive Power Operational Region for Grid-Interactive Cascaded H-Bridge Multilevel Converters [#1062]
Cascaded h-bridge (CHB) multilevel converters are being considered as a promising option for interfacing renewable energy resources with the grid, due to their modularity, scalability, and increased efficiency when compared to traditionally used two-level inverters. When used as grid interfaces, CHB converters should be capable of controlling the injected active and reactive power while also satisfying operating criteria such as grid standards, e.g. IEEE 519. This paper aims to identify practically available operating points in the PQ plane when using a grid-interactive CHB converter, and to determine the factors which prevent utilization of other operating points. This work (i) provides distribution engineers with information regarding the active and reactive power which can feasibly be generated by a grid-interactive CHB converter, (ii) creates a framework for assessing operating point trajectories when altering the steady-state operation of grid-tied CHB converters, and (iii) provides a basis for selecting and modifying steady-state PWM generation techniques in order to meet desired performance criteria. Simulation data are presented to verify the findings of this work. 9:45AM Harmonic Stability Analysis and Controller Parameter Design of Three-Phase Inverter-Based Multi-Bus Ac Systems Based on Sequence Impedances [#1331]
Three-phase inverter-based multi-bus ac systems could suffer from the small- signal instability issue due to the dynamic interaction among inverters and passive components in the systems. To address this issue, this paper proposes two harmonic stability analysis methods and an inverter controller parameter design approach for stable system operation. The proposed sequence-impedance-based harmonic stability analysis methods can reduce the computation effort by avoiding the calculation of right-half-plane poles of impedance ratios, as compared with the impedance-based analysis method using Nyquist stability criterion. Therefore, the controller parameters can be designed in the forms of stability regions in the parameter space, by repetitively applying the proposed stability analysis methods. In addition, the proposed stability analysis methods enable the system stability by using only measured component impedances. Experimental results of an inverter- based two-area system validate the effectiveness of the proposed stability analysis methods and parameter design approach. Utility Applications II Wednesday, September 21, 8:30AM-10:10AM, Room: 202A, Chair: Deepak Divan, Alireza Nami 8:30AM Full-ZVS Modulation for All-SiC ISOP-Type Isolated Front End (IFE) Solid-State Transformer [#583] Jonas E. Huber, Daniel Rothmund, Li Wang and Johann W. Kolar, Power Electronic Systems Lab, ETH Zurich, Switzerland; FREEDM Systems Center, NC State University, United States Thanks to their comparatively low system complexity, SSTs based on an isolated front end (IFE) approach are suitable for space and weight-constrained medium voltage (MV) AC to low voltage (LV) DC power supply applications, e. g., in future traction, naval, subsea or aerospace systems. The IFE approach connects series resonant isolation stages operating in the half-cycle discontinuous- conduction-mode (HC-DCM) directly to the MV AC grid in an input-series, output- parallel (ISOP) configuration, but the entire control, i.e., the shaping of the grid current for unity power factor and output voltage regulation, is carried out by a second, non-isolated conversion stage on the LV side. However, since the isolation stages do not operate with a DC but with an AC or rectified AC input voltage, the transformer magnetizing current available for ZVS as well as the voltage to be switched vary over the grid period. Taking into account also component tolerances among the cascaded converter cells, this paper provides an in-depth analysis of the ZVS behavior under these conditions, and of the associated losses and EMI considerations, presenting a loss-optimal choice of the magnetizing inductance value and of the dead time (interlock time) of the isolation stages' bridge legs. A time-dependent variation of the latter to achieve ZVS over the entire grid period without an increase of the isolation stage losses is proposed. The considerations are verified at the example of the Swiss SST (S3T), an all-SiC 25 kW, 6.6 kV MVAC to 400 V LVDC converter system, using a detailed simulation model, including non-linear MOSFET capacitances. 8:55AM Stability issues in reverse power flow limitation in a Smart Transformer-fed distribution grid [#666]
The increasing implementation of Distributed Generation (DG) in the distribution grids creates new challenges in controlling the voltage profile. If the DG production exceeds the load consumption, the power flow reverses through the MV/LV substations. The reverse power flow impacts mainly on the voltage profile, increasing further the voltage in LV and MV grids. At this regard the Smart Transformer offers a new possibility to avoid the reverse power flow in the MV grids. The ST can adapt the voltage waveform modifying the frequency in order to interact with the local DG: the DG PLL notices the frequency change and the generators, equipped with droop controllers, decrease their power output. This paper deals specifically with the stability issues of the DG PLL when a fast change in the frequency is applied for avoiding the reverse power flow in MV grid. If the PLL in the DG is tuned with a low bandwidth, it could result in oscillatory phenomena in the current controller of the DG. The evaluation of the stability analysis has been performed analytically and validated by means of Control-Hardware-In- Loop (CHIL). 9:20AM Smart Transformer-Based Hybrid Grid Loads Support in Partial Disconnection of MV/HV Power System [#774]
Double circuit lines are common for transmitting the electrical power in high voltage (HV) and/or medium voltage (MV) power system. During the faults in one of the lines or transformers of the double circuit lines, one line is disconnected from the system and the healthy line is utilized for supplying the entire load. In that case, the transformer supplying the entire load could be overloaded. For the safe operation of the transformer, it is needed to disconnect some of the loads. This partial disconnection of MV/HV power system can severally effect the performance of critical loads. Recently, power electronic based transformer equipped with effective control and communication called smart transformer (ST) has been proposed for installation in the distribution system in place of conventional transformer. One of the most important feature of ST is to allow for connection of ac and dc grid forming hybrid grid which allow easy integration of renewable energy sources and storage. Considering these feature of ST, this paper proposes a new functionality of the ST where it provides continuous power to a section of the loads during the partial disconnection of MV/HV power system and improves the performance of power system. This new feature of ST has been proved through power system computer aided design (PSCAD) software based simulation results. Power hardware in loop (PHIL) and control hardware in loop (CHIL) is under development to test the idea. 9:45AM Soft-Switching Solid State Transformer (S4T) [#1354]
This paper presents a new topology for a fully bidirectional soft-switching solid state transformer (S4T). The minimal topology, featuring 12 main devices and a high-frequency transformer, does not use an intermediate DC voltage link, and provides sinusoidal input and output voltages. The S4T can be configured to interface with two- or multi-terminal DC, single- or multi-phase AC systems. An auxiliary resonant circuit creates zero-voltage-switching (ZVS) conditions for main devices from no-load to full-load, and helps manage interactions with circuit parasitic elements. The modularized structure allows series and/or parallel stacking of converter cells for high-voltage and high- power applications. DC Microgrids I Wednesday, September 21, 8:30AM-10:10AM, Room: 203DE, Chair: Giovanna Oriti, Babak Parkhideh 8:30AM Hierarchical Coordination of a Hybrid AC/DC SmartGrid with Central/Distributed Energy Storage [#1518] Pablo Arboleya, Cristina Gonzalez-Moran, Pablo Garcia, Jorge Garcia and Bassam Mohamed, University of Oviedo, Spain This work describes a hybrid AC/DC Smart Grid distribution scheme installed at LEMUR microgrid laboratory. The control of the microgrid is carried out according to a hierarchical coordination considering the high level control. The configuration includes a microgrid (uG) connected to the main utility grid (MUG) by means of a solid state transformer (STT). The uG is formed by several nanogrids (nGs). All (nGs) are based on four wire configurations, as they are usually employed in AC distribution systems. However, the scheme is considered as a hybrid Smart Grid because the connection among different nanogrids and with the SST are DC connections. The SST is also equipped with a third port connected to a central energy storage system (CESS). The coordination between the different involved in the systems: the installed dispersed generators at nanogrid level, the nanogrids, the SST and the CESS has been implemented using a bottom-up hierarchical approach. Several configurations at nanogrid and microgrid levels are shown and analyzed. For making the coordination of the different elements of the microgrid, a fast power flow algorithm for estimating the state of the microgrid in real time was developed. In this paper the proposed structure is described paying special attention to the power flow algorithm. The results obtained with the power flow algorithm in simulations were validated at laboratory level. 8:55AM Dynamic Optimal Power Flow for DC Microgrids with Distributed Battery Energy Storage Systems [#23]
This paper proposes a model predictive control strategy for power flow optimisation between battery energy storage systems distributed in a DC Microgrid. The proposed control strategy uses a new convex formulation of the DC microgrid dynamic optimal power flow problem, based on a static voltage-current model and linear power flow approximations. Unlike optimisation strategies based on a single bus model, line losses and line voltage drops are included in the optimisation. The availability of fast and robust solvers for convex optimisation problems makes this a scalable solution for a real-time model predictive control implementation. To verify the performance of the proposed control strategy, real-time simulations were carried out for a DC microgrid with distributed lead-acid batteries and intermittent photovoltaic generation. The simulations were completed on an RTDS Technologies real-time digital simulator, using switching converter models and non-linear battery models. 9:20AM DC Electric Springs with Modified Droop Control for Storage Reduction in DC Microgrids [#282]
Series DC electric springs (series ESs) can be a cost-effective technology to tackle the intermittency of the renewable generations in DC distribution grids. When multiple series ESs are connected to differently rated non-critical loads (NCLs) and are operated to regulate the voltages at their respective points of common coupling, the charging and discharging characteristics among the ESs are different. In this paper, a modified droop controller, which is designed to reduce the total storage capacity of the series ES, is proposed to coordinate the operation of multiple series ESs. The power curves of series ESs with light, medium, and heavy NCLs are compared and analyzed. Experimental results on a 60 V DC grid have confirmed that the proposed controller can effectively reduce the total storage capacity with good coordination among multiple series ESs. 9:45AM Optimal Droop Surface Control of Dc Microgrids Based on Battery State of Charge [#53]
For a microgrid with a high penetration level of renewable energy, energy storage use becomes more integral to the system performance due to the stochastic nature of most renewable energy sources. This paper examines the use of droop control of an energy storage source in dc microgrids in order to optimize a global cost function. The approach involves using a multidimensional surface to determine the optimal droop parameters based on load and state of charge. The optimal surface is determined using knowledge of the system architecture and can be implemented with fully decentralized source controllers. The optimal surface control of the system is presented. Derivation of a cost function along with the implementation of the optimal control are included. Results were verified using a hardware-in-the-loop system. Transportation Electrification I Wednesday, September 21, 8:30AM-10:10AM, Room: 102D, Chair: Bulent Sarlioglu, Tim Burress 8:30AM A Modified Z-source Converter based Single Phase PV/Grid Inter-connected DC Charging Converter for Future Transportation Electrification [#1015] Siddhartha A. Singh, Giampaolo Carli, Najath A. Azeez and Sheldon S. Williamson, University of Ontario Institute of Technology, Canada; EMD Technologies - Heico Corporation., Canada Use of renewable sources of energy for charging of electric vehicle(EV) batteries have generated tremendous interest. The use of off-board DC chargers to reduce the weight and increase space inside an electric vehicles has been an important area of interest. Harvesting solar energy to charge electric vehicle batteries can result in large inefficient systems when multiple power conversion stages are present. On the other hand,integration of renewable sources of energy with the grid can reduce the dependency on the AC grid while charging an Electric Vehicle(EV) and also the use of fossil fuels to generate more energy. In this paper, a single stage PV grid integrated modified z source inverter is presented. The component sizing, modeling and different modes of operation have been presented. 8:55AM Comprehensive design comparison of using different order harmonics as the power carrier in wireless power transfer for PHEV and EV Wireless Charging [#561]
A series resonant converter (SRC) with third harmonic as the power carrier has been verified with the benefit of reducing the resonant components to one third. With proper design, it can have competitive efficiency with that using fundamental power, while the siaze and weight are much smaller. However, there is a trade-off between using a highter order harmonic and the larger current stress on the primary side. In this paper, a comprehensive design comparison of using different order harmonics as the power carrier in wireless power transfer for plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) wireless charging is presented. The comparison mainly focuses on overall efficiency and each component's stress. A guideline for choosing the optimal order or harmonic as power carrier is discussed after the comparison. A 1-kW prototype with 20-cm air gap using harmonic power is built to verify the proposed method. 9:20AM A New Inductive Wireless Power Transfer Topology Using Current-Fed Half-Bridge CLC Transmitter LC Receiver Configuration [#608]
A new current-fed topology for wireless inductive power transfer (IPT) application using half-bridge circuit is proposed and analyzed. Conventional IPT circuits employ parallel L-C resonant tank/compensation network to transfer power effectively through air-gap. However, in medium power application, this topology suffers from a major drawback that the voltage stress across the inverter switches are considerably high due to high reactive power consumed by the loosely coupled coil. In the proposed topology, his is mitigated by adding a properly designed capacitor in series with the coils. During grid-to-vehicle (G2V) operation, the power flow is controlled through variable switching frequency modulation to achieve extended ZVS of the inverter switches. For G2V operation, the converter circuit is analyzed and simulated using PSIM 9.3. Analytical and simulation results are verified through experimental results obtained by testing a 1.2kW lab-prototype. 9:45AM Reduction on Radiation Noise Level for Inductive Power Transfer Systems with Spread Spectrum focusing on Combined Impedance of Coils and Capacitors [#308]
Two reduction methods on radiation noise of inductive power transfer (IPT) systems are proposed and experimentally demonstrated. In the IPT systems for electrical vehicles (EVs) or plug-in hybrid electrical vehicles (PHEVs), noise reduction technologies are strongly required because the radiation noise from the IPT system for EVs or PHEVs must not exceeds the limits on standards; for example the regulation by CISPR is well-known regulation. The proposed method suppresses the radiation noise using spread spectrum technique. The radiation noise from the transmission coils of the IPT system is spread in a frequency domain by changing the output frequency of an inverter at random. The output frequency is selected according to pseudo random numbers. The first proposed method; a spread spectrum with a uniform distribution (SSUD), evenly selects the output frequency within 80 kHz to 90 kHz. Another method; a spread spectrum with a biased distribution (SSBD) is focusing on the output current of the inverter. The possibility for the select of output frequency is biased in proportion to a combined impedance of the transmission coil and the resonance capacitors. In the experiments with an output power of 3 kW, the fundamental components are suppressed by 42.6% and 72.1% by applying the SSUD and the SSBD in comparison with the conventional system, which operates the inverter at a fixed frequency. Yüklə 2,78 Mb. Dostları ilə paylaş:
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