Table of contents monday, September 9, 1: 30pm-4: 00pm modular Multi-Level Converters, hvdc, and dc grids I 3
Distribution-System Utility Interface Topics
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- Bu səhifədəki naviqasiya:
- Thursday, September 22, 8:30AM-10:10AM Converter Topologies for Wind Power Systems
- Energy Storage Systems
- Power Quality I
- AC Microgrids I: Modelling and Stability
| Distribution-System Utility Interface Topics
Wednesday, September 21, 3:30PM-5:10PM, Room: 102A, Chair: Tsorng-Juu Liang, Deepak Divan 3:30PM Unbalanced Voltage Compensation in LV Residential AC Grids [#898] Ionut Trintis, Philip Douglass and Stig Munk-Nielsen, Aalborg University, Denmark; Danish Energy Association, Denmark This paper describes the design and test of a control algorithm for active front-end rectifiers that draw power from a residential AC grid to feed heat pump loads. The control algorithm is able to control the phase to neutral or phase to phase RMS voltages at the point of common coupling. The voltage control was evaluated with either active or reactive independent phase load current control. The control performance in field operation in a residential grid situated in Bornholm, Denmark was investigated for different use cases. 3:55PM The Hierarchical Energy Management Control for Residential Energy Harvesting System [#1468]
A hierarchical energy management system (EMS) for a residential power router is proposed to further reduce costs and stabilize the voltage of a load. There are ten modes of the EMS including three grid-connected modes and seven islanding modes. The state machine diagram shows the transition into and out of these modes. These transitions are based on switching criteria, over generation conditions, and under generation conditions. In comparison to previously published EMS, the proposed EMS could effectively minimize the expense on residential electrical utilities for daily cycling and stabilize the voltage of load when off-grid. The operations of the EMS are based on the local information such as current and voltage without needing the prediction of load and solar illumination. Simulation results reported in this paper verify the functionality of the proposed EMS for the system. 4:20PM Reactive Power Distribution Strategy using Power Factor Correction Converters for Smart Home Application [#1246]
Multiple unit of PFC converters can be utilized for better power quality in the residential applications. It is important to set proper amount of reactive power contribution from each unit of PFC converter to reduce power loss and increase stability. To set the referenced amount of reactive power contribution for each PFC converter, a dynamic supervisory controller is necessary. In this paper, a wireless based supervisory controller is introduced to mitigate the problem. Multiple unit of unidirectional bridgeless ac-dc boost PFC converters were used as reactive power resources in a smart home application. The supervisory controller is comprised of a discrete Proportional- Integral controller and distributor which sets the reactive power references for each PFC converter. The controller was designed based on the systems identification method. The controller was designed and simulated considering different communication delays. In the ideal condition, the system had no communication delay. However, actual practical system had some reasonable delay. The effect of the use of supervisory controller was observed for dynamic load changing conditions. The simulation was done by using SIMULINK. Reactive power consumption from grid becomes 0VAR within 0.25 second for ideal condition. However, for the actual condition this become 9.35 seconds. 4:45PM Active Voltage Balancing Control for Multi HV-IGBTs in Series Connection [#986]
The series connection of insulated gate bipolar transistors (IGBTs) allows the operation at voltage levels higher than the rated voltage of one IGBT. However, the technology has not been widely applied due to transient voltage unbalance. Asynchronous gate drive signals, which cause series-connected IGBTs not to turn-on and turn-off at the same time, result in serious unbalanced voltage sharing. This paper presents an active voltage balancing control for multi series connected HV-IGBTs including the active voltage balancing control (AVBC) circuit integrated in the gate driver and the control for multi series connected IGBTs. The effectiveness of the control has been experimentally validated in a 10 kV dc-link voltage converter using four 4.5 kV HV-IGBTs in series connection. Thursday, September 22, 8:30AM-10:10AM Converter Topologies for Wind Power Systems Thursday, September 22, 8:30AM-10:10AM, Room: 203AB, Chair: Akshay Kumar Rathore, Yilmaz Sozer
8:30AM The DOE Next-Generation Drivetrain for Wind Turbine Applications: Gearbox, Generator, and Advanced Si/SiC Hybrid Inverter System [#44] William Erdman and Jonathan Keller, Cinch, Inc., United States; National Renewable Energy Laboratory, United States This paper reports on the design and testing results from the U.S. Department of Energy Next-Generation Wind Turbine Drivetrain Project. The drivetrain design reduces the cost of energy by increasing energy capture through drivetrain efficiency improvements; by reducing operation and maintenance costs through reducing gearbox failures; and by lowering capital costs through weight reduction and a series of mechanical and electronic innovations. The paper provides an overview of the drivetrain gearbox and generator and provides a deeper look into the power converter system. The power converter has a number of innovations including the use of hybrid silicon (Si)/silicon carbide (SiC) isolated baseplate switching modules. Switching energies are compared between SiC and Si PIN diodes. The efficiency improvement by use of the SiC diode in a three-level converter is also described. Finally, a brief discussion covering utility interconnect requirements for turbines is provided with a particular focus on utility events that lead to high transient torque loads on drivetrain mechanical elements. 8:55AM Inductorless Boost Rectifier for Small Power Wind Energy Converters [#1606]
This paper analyzes a cost-effective modification of the rectifier plus boost converter power topology which is commonly found in small wind turbine systems. The paper proposes removing the input capacitor after the rectifier and the boost converter inductance. This will be done without adding any LC filter between the permanent magnet generator and the passive rectifier. This paper discusses both the power topology and the control strategy as well as a performance comparison with the usual topology. Simulation and experimental results are presented to demonstrate the technical viability of this proposal. 9:20AM High-frequency Isolated DC-DC Converter for Offshore Wind Energy Systems [#1205]
This paper presents a novel three-phase high-frequency isolated DC-DC converter topology for offshore wind energy systems. The primary side of the converter consists of three half-bridge legs connected to three single-phase star-connected transformers. Each transformer secondary has a full-bridge rectifier and their outputs are connected in series. Constant frequency phase- shift modulation scheme is used for converter control. Leakage inductance of transformers and resonant capacitors, along with the modulation scheme provide zero current switching for converter switches. Modularity, high-gain and high- frequency isolation make the proposed converter a suitable candidate for offshore wind energy conversion systems with high voltage DC transmission. Simulation and experimental results are presented to validate the operation of proposed converter. 9:45AM A New Three-phase AC/DC High Power Factor Soft-switched Step-up Converter with High Gain Rectifier Modules for Medium Voltage Grid in Wind Systems [#855]
This paper presents a new single-stage AC/DC step-up soft-switched converter for medium voltage (MV) DC grid for wind energy systems. To achieve close-to-unity power factor, stepping up the voltage and reduce the number of conversion stages, a three-phase boost AC/DC rectifier and a high frequency step-up resonant converter with high gain rectifier modules are combined into a single-stage step-up converter. As a result, the proposed converter is capable to achieve very high voltage gain efficiently without using bulky high turns ratio step-up transformer. Soft switching operation is achieved by using multiple resonant circuit modules. The voltage stress of each power switch is also reduced to half of the DC-link voltage by using a series connection of two strings of switch pairs. In addition, the proposed converter is capable to regulate the output MV grid voltage by utilizing a combination of duty cycle and variable switching frequency control. Results are given on a 1.5MW, 690Vac/40kV system to highlight the merits of the proposed converter. Energy Storage Systems Thursday, September 22, 8:30AM-10:10AM, Room: 203C, Chair: Adel Nasiri, Tsai-Fu Wu 8:30AM A Comparison of Broadband Impedance Measurement Techniques for Lithium-Ion Batteries [#240] Alfred Waligo and Paul Barendse, University of Cape Town, South Africa Electrochemical impedance spectroscopy (EIS) is a well-known technique that has been employed on various electrochemical cells in order to obtain their impedance spectra.Lithium-ion cells are some of these cells to which it has been applied. The impedance spectra obtained from EIS can be used to estimate various battery state of health (SOH) and state of charge (SOC) characteristics. The lengthy acquisition time associated with standard EIS makes it unsuitable for rapid on-line impedance measurements. Alternative methods that take a shorter time have therefore been proposed. This paper compares the spectra obtained by Harmonic Compensated Synchronous Detection (HCSD) broadband signal technique with EIS and a custom Broadband Impedance Spectroscopy (BIS) technique at different DC bias currents which mimic a real time load. The test cells are industry standard Nickel-Cobalt and Manganese Oxide (NCM) lithium-ion cells. The BIS technique is similar to HSCD in the selection of frequencies however the amplitude of the excitation broadband signal is varied to match the impedance magnitude response of the cell. Also, parameter extraction is performed on both EIS and BIS for fault detection purposes. 8:55AM Evaluation of Lithium-ion Battery Second Life Performance and Degradation [#411]
Reusing electric vehicle batteries once they have been retired from the automotive application is stated as one of the possible solutions to reduce electric vehicle costs. Many publications in the literature have analyzed the economic viability of such a solution, and some car manufacturers have recently started running several projects to demonstrate the technical viability of the so-called battery second life. Nevertheless, the performance and degradation of second life batteries remain an unknown topic and one of the biggest gaps in the literature. The present work aims at evaluating the effects of lithium-ion (Li-ion) battery State of Health (SOH) and ageing history over the second life performance on two different applications: a residential demand management application and a power smoothing renewable integration application. The performance and degradation of second life batteries are assessed both at the cell level and at stack level. Homogeneous and heterogeneous stacks are analyzed in order to evaluate the impact of cell-to-cell history and SOH differences over the stack level battery cell performance and degradation behaviour. 9:20AM A Distributed ESO based Cooperative Current-Sharing Strategy for Parallel Charging Systems Under Disturbances [#506]
In this paper, a distributed extended state observer (ESO) based cooperative control is proposed to achieve current-sharing for parallel chargers under disturbances in energy storage type light rail vehicle systems. By treating the parallel charging system as a nonlinear and non-identical multi-agent system, the current-sharing objective is converted as a distributed leader-follower consensus problem. A distributed ESO is designed to observe total disturbances with the known information from the established mathematical model of subchargers. A tracking differentiator (TD) is established to provide a transitional process for the reference signal to increase the dynamical performance and robustness. Based on ESO and TD, a distributed cooperative control protocol is proposed. Simulation and experimental results are provided to verify the disturbance rejection ability, feasibility and practicability of the proposed distributed current-sharing control method. 9:45AM A Comprehensive Study on the Degradation of Lithium-Ion Batteries during Calendar Ageing: The Internal Resistance Increase [#1259]
Lithium-ion batteries are regarded as the key energy storage technology for both e-mobility and stationary renewable energy storage applications. Nevertheless, the Lithium-ion batteries are complex energy storage devices, which are characterized by a complex degradation behavior, which affects both their capacity and internal resistance. This paper investigates, based on extended laboratory calendar ageing tests, the degradation of the internal resistance of a Lithium-ion battery. The dependence of the internal resistance increase on the temperature and state-of-charge level have been extensive studied and quantified. Based on the obtained laboratory results, an accurate semi-empirical lifetime model, which is able to predict with high accuracy the internal resistance increase of the Lithium-ion battery over a wide temperature range and for all state-of-charge levels was proposed and validated. Power Quality I Thursday, September 22, 8:30AM-10:10AM, Room: 101B, Chair: Jonathan Kimball, Dao Zhou 8:30AM Enhanced Power Quality and Minimized Peak Current Control in An Inverter based Microgrid under Unbalanced Grid Faults [#138] Wenzhao Liu, Xiaoqiang Guo, Giorgio Sulligoi, Yajuan Guan, Xin Zhao, Baoze Wei, Mehdi Savaghebi and Josep M Guerrero, Aalborg University, Denmark; Yanshan University, China; University of Trieste, Italy The microgrid inverter experiences the power oscillations and current harmonics in case of the unbalanced grid voltage faults. However, there is a trade-off between power oscillations and current harmonics should be considered in three phase three wire inverter systems during the conventional fault ride through control. In order to solve this problem, a novel control strategy is proposed to enhance the output current quality while mitigating the active and reactive output power oscillations. Moreover, a simple current- limited control strategy can be achieved without the necessity of the voltage/current positive/negative sequence extraction. Finally, the simulation tests of the conventional and proposed control solutions are carried out. The results verify the effectiveness of the proposed strategy 8:55AM Parallel Interfacing Converters under Unbalanced Voltage: Active Power Oscillation Cancellation with Peak Current Sharing [#166]
Unbalanced voltage has adverse effects on power electronic interfacing converters (IFCs) operation such as output power oscillations, DC link voltage oscillations and peak current increase. These adverse effects can be aggregated in parallel IFCs with common DC and AC link, which are commonly used to connect AC and DC subsystems in hybrid AC/DC microgrid or to interface high-power distributed generations/storage elements to AC subsystem. In this paper, two novel control strategies for parallel IFCs operation under unbalanced voltage are proposed, which are focusing on active power oscillation cancellation and sharing of collective peak current of parallel IFCs among IFCs considering their power ratings. In the first proposed control strategy, IFCs power coefficient factors are controlled for cancellation of active power oscillation and collective peak current sharing of parallel IFCs. In the second proposed control strategy, IFCs peak currents are controlled for controlling targets. In this paper, individual and parallel IFCs peak currents are thoroughly studied, and their relationship with active power oscillation cancellation are analyzed. Based on analysis, it is proven that collective peak current of parallel IFCs is constant under zero active power oscillation in the fixed average active powers output. Both proposed control strategies ensure the peak currents of individual IFCs to be approximately in-phase with collective peak current of parallel IFCs, which provide minimum peak currents summation of IFCs. 9:20AM The Reverse Zero-Sequence Current Compensation Strategy for Back-to-Back Active Power Conditioners [#205]
In this paper, a novel reverse zero-sequence current (RZSC) compensation strategy for three-phase four-wire back-to-back active power conditioner (APC) is proposed. The objective of the APC is to achieve the active and reactive power compensation between two micro-grids. However, for the unbalanced voltage sag micro-grid system, the double- line frequency oscillation exists in the output active/reactive power of the APC. In order to eliminate these power oscillation, the zero-sequence current control must be utilized, but it will produce the line frequency ripple voltage on the split capacitors of the dc-bus. The capacitor ripple voltage will speed up the aging process and reduce its life-time. Therefore, the RZSC strategy is proposed to compensate the impact of the ripple voltage to the split capacitors. The circuit configuration and control block diagram of the APC will be introduced. The operation principle of the proposed RZSC strategy will be presented. Both computer simulations and hardware experimental results are presented to verify the performance of the proposed RZSC. 9:45AM Harmonic Mitigation in Interphase Power Controllers Using Passive Filter-Based Phase Shifting Transformer [#108]
A novel, genetic-algorithm based, design method of the passive filter-based phase shifting transformers is presented. The method improves the reliability, effectiveness, and accuracy of the filter. The filter is employed in an interphase power controller (IPC), a FACTS device unique in its power- transmitting properties. The paper demonstrates how the implementation of the proposed filter in the IPC structure significantly reduces the total harmonic distortion without affecting the IPC characteristics. AC Microgrids I: Modelling and Stability Thursday, September 22, 8:30AM-10:10AM, Room: 203DE, Chair: Adel Nasiri, Reza Ahmadi 8:30AM Modeling and Stability Analysis of the Small-AC-Signal Droop Based Secondary Control for Islanded Microgrids [#1412] Teng Wu, Zeng Liu, Jinjun Liu, Baojin Liu and Shike Wang, Xian Jiaotong University, China The recently proposed small-AC-signal droop based secondary control is very attractive for microgrids to restore the voltage and frequency of overall system and to share the output power between paralleled distributed generations (DGs). However, the previous work has not discussed the system stability of the novel secondary control method. This paper presents a small-signal model for the microgrids regulated by the novel secondary control method. Then the system stability is analyzed by accessing the eigenvalues of the proposed model. Finally, the correctness of theoretical analysis is verified by both simulation and experimental results. 8:55AM A Small-AC-Signal Injection Based Harmonic Power Sharing Method for Islanded Microgrids [#61]
This paper proposes a novel control method for harmonic power sharing in an islanded microgrid, without employing any control interconnections between the distributed generation (DG) units. The fundamental real and reactive power is shared by implementing conventional P-f and Q-V droop control. A virtual negative output impedance at harmonic frequency is introduced to control the distribution of harmonic power. Moreover, a small-AC-signal is injected in each DG unit for dynamically regulating the magnitude of its virtual negative harmonic output impedance to realize evenly sharing of harmonic power among all DG units according to their available harmonic power capacities. This novel method can also provide improved load voltage quality and does not need information about line impedance. Simulation results on PSCAD are offered to validate the proposed method. 9:20AM Improvement of Transient Stability in Inverter-Based AC Microgrid via Adaptive Virtual Inertia [#520]
Unlike centralized synchronous generator (SG) in conventional power system, distributed microsources are parallel connected to neighbors by inverters, which are less inertia. To improve the transient stability, inverter based distributed generators (DG) can draw an analogy between the storage and rotor rotational kinetic energy of SG in inertia function. Instead of emulating a fixed virtual inertia, this study proposes adaptive virtual inertia to alleviate the frequency response. In the transient process, a large inertia is implemented when the frequency will deviate from the normal value, and a low inertia is adopted when it is necessary to recover the frequency. The proposed method can enhance the anti interference and overload capacity, so that frequency stability is strengthened. Lyapunov stability analysis is utilized to prove the convergence. Simulation results are presented to verify the effectiveness of the method. 9:45AM Frequency Support Properties of the Synchronous Power Control for Grid-Connected Converters [#1109]
Grid-connected converters with primary frequency control and inertia emulation have emerged and are promising for future renewable generation plants because of the contribution in power system stabilization. This paper gives a synchronous active power control solution for grid-connected converters. As design considerations, the virtual angle stability and transient response are both analyzed, and the detailed implementation structure is also given without entailing any difficulty in practice. The analysis and validation of frequency support characteristics are particularly addressed. The 10 kW simulation and experimental frequency sweep tests on a regenerative source test bed present good performance of the proposed control in terms of showing inertia and droop characteristics, and the controllable transient response is also demonstrated. |