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:
- Wednesday, September 21, 10:30AM-12:10PM Control for Photovoltaic Applications
- Photovoltaic Characterization and Modeling
- Utility Applications III
- Modeling, Analysis, and Control of Grid-Connected Converters II
- DC Microgrids II
| 9:45AM A Loosely Coupled Capacitive Power Transfer System with LC Compensation Circuit Topology [#48]
Hua Zhang, Fei Lu, Heath Hofmann, Weiguo Liu and Chris Mi, Northwestern Polytechnical University, China; University of Michigan, United States; San Diego State University, United States This paper proposes a double-sided LC compensated capacitive power transfer (CPT) system, which is the dual of the conventional series-series (SS) compensated inductive power transfer (IPT) system. Four metal plates are arranged as the capacitive coupler, and there are coupling capacitances between each pair of plates. At each side, a compensation capacitor is connected in parallel with the plates, and its value is usually much larger than the coupling capacitance between the plates, which results in a loosely coupled CPT system. In this paper, the fundamental harmonics approximation (FHA) method is used to analyze the circuit working principle. It shows that the system can work at constant current mode. An expression for the system output power is expressed, which is similar to that of the SS compensated IPT system. A 150W input power CPT system is therefore designed as an example to validate the compensation topology. The experimental results show that the dc to dc efficiency of the system is 66.67% when the air-gap distance is 180 mm and the switching frequency is 1.5 MHz. Wednesday, September 21, 10:30AM-12:10PM Control for Photovoltaic Applications Wednesday, September 21, 10:30AM-12:10PM, Room: 203AB, Chair: Martin Ordonez, Dezso Sera
10:30AM A Variable Step-Size MPPT for Sensorless Current Model Predictive Control for Photovoltaic Systems [#1613] Morcos Metry, Mohammad B. Shadmand, Robert S. Balog and Haitham Abu-Rub, Texas A and M University, United States; Texas A and M University at Qatar, Qatar Variability of the solar energy resources requires highly effective maximum power point tracking (MPPT) to ensure maximum energy harvesting from the photovoltaic (PV) modules. To accomplish this, a MPPT controller typically requires accurate knowledge of the voltage and current from the PV module, and must converge quickly with minimal hunting around the maximum power point (MPP). Conventional MPPT techniques use fixed step-size perturbation which need to be optimized for one of two objectives: reducing the convergence settling time, or reducing the steady state ripple. Also, the required sensors increase system cost and can cause reliability issues, particularly for the current sensors which can exhibit thermal drift and degrade over time. This paper presents a highly efficient, variable-step sensorless current MPPT controller using an observer-based model derived from the principles of model predictive control (MPC) to adaptively determine the perturbation step-size. The proposed variable step, sensorless current, model predictive control maximum power point tracking (VS-SC-MPC-MPPT) continuously adjusts the perturbation step size using the predicted dynamic model to enable fast convergence and small limit cycle, without the need of expensive measuring devices. The performance of the VS-SC-MPC-MPPT in this paper is compared to previously developed MPC-MPPT methods. The provided investigation aims to demonstrate higher system efficacy with lower cost. The feasibility of the proposed controller is verified though computer simulation and real time simulation using dSPACE DS1007. 10:55AM Study on the Unbalanced Current Injection Capability of Grid-Connected Photovoltaic Neutral-Point-Clamped Inverter [#1434]
Due to high penetration of distributed generation units in power system, fault ride through (FRT) capability is one of the new requirements of the medium-scale grid-tied photovoltaic power plants (PVPPs). This paper proposes and investigates a control strategy for the neutral-point-clamped (NPC) inverter in order to inject proper unbalanced reactive currents to the grid during unbalanced grid faults. The proper unbalanced current injection reduces negative sequence of grid voltages and currents. The current references are scaled up/down individually, based on the grid phase rms voltages and inverter nominal current. The performance of the implemented control algorithm is investigated on a 150-kVA PVPP connected to 12.47-kV medium-voltage grid simulation model under various voltage sag conditions. Results from an experimental setup of grid-tied NPC inverter are presented in order to demonstrate the effectiveness of the proposed unbalanced current injection algorithm. 11:20AM Adaptive Dc Link Voltage Control Scheme for Single Phase Inverters with Dynamic Power Decoupling [#1162]
Power density and efficiency are important metrics for power converters in many applications including renewable energy interface. Combined with the desire to replace the bulky, unreliable electrolytic dc link capacitors with film or ceramic capacitors due to reliability concerns, this has led to the trend of allowing increasingly higher double line frequency dc link voltage ripple. This paper discusses a scheme to improve the system overall efficiency by implementing an adaptive dc link voltage control scheme under different operating conditions for a recently introduced class of single phase inverter topologies that operate with very large dc link voltage ripple. The relationship between the minimum necessary dc link voltage for different input voltage, apparent power and power factor are analyzed and the optimal dc link voltage average value are derived analytically. The analysis and benefits of the proposed scheme are validated on a single-phase inverter hardware prototype employing SiC MOSFETs and DSP28335 for control implementation. The scheme can decrease the dc link voltage average value by 24.1% while decreasing the total loss of the inverter by around 20% compared to a design that does not use the adaptive dc link approach. 11:45AM ZVS Analysis and Power Flow Control for Three Limb Transformer Enabled SiC Mosfet Based Three Port DAB Integrating PV and Energy Storage(ES) [#1684]
Multi-port dc-dc converters are the modular power electronic building blocks for integration of PV and Energy Storages(ES). The work in this paper focuses on ZVS characteristics for independent power flow control of three port DAB converter integrating PV and Energy Storage(ES), using three limb high frequency transformer. The independent power flow control discussed here, focuses on ES charging scenario for the converter using two different modulation techniques. ZVS scenario variations for two different modulation control technique for two different designs of three limb transformers, are discussed in the paper. A laboratory scale prototype using 1200V and 1700V SiC Mosfets has been made and preliminary results have been obtained for experimental validation of the ZVS scenarios. Photovoltaic Characterization and Modeling Wednesday, September 21, 10:30AM-12:10PM, Room: 203C, Chair: Tirthajyoti Sarkar, Ahmed Elasser 10:30AM A Rapid I-V Curve Generation for PV Model-based Solar Array Simulators [#437] Young-Tae Seo, Jun-Young Park and Sung-Jin Choi, University of Ulsan, Korea, Republic of Photovoltaic (PV) model can be a viable alternative to the conventional look-up- table as an accurate and versatile solar array simulator (SAS) engine. In PV model-based SAS, PV model has a critical role to generate appropriate I-V characteristic of the PV panel under rapidly varying temperature and irradiation, and its calculation speed as well as accuracy are key performances. In this paper, a novel algorithm that is suitable for such a SAS engine is proposed. The suggested method adopts conjugate gradient optimization to extract PV model parameters from the changing conditions and to reconstruct the exact I-V curve very rapidly. For the verification, the proposed algorithm is compared with conventional ones which have been widely used in the PV model extraction. As a result, the proposed model shows superior calculation speed with good accuracy. 10:55AM Photovoltaic Panel Simulation Based on Individual Cell Condition [#463]
The maximum power generated by a photovoltaic (PV) system depends on the intensity and uniformity of the irradiation over panels. The Maximum Power Point Tracking (MPPT) is a control technique used to adjust the operating voltage of PV panels in order to continuously harvest the maximum power available. Modeling of PV panel characteristic curves are useful for the evolution of MPPT control algorithms. However, most of simulation models are not capable of completely handling non-uniform irradiation, since they do not consider PV cells individually, and use simplified uniform approaches instead. This paper explains mislead estimation of maximum power point (MPP) caused by simplified approaches and proposes a new perspective to model PV panels based on individual cells' irradiation condition. The testing of shadow patterns demonstrates the importance of modeling cells individually in order to performan accurate MPP analysis. During the passing of shadows, the MPP voltage variation range can be over 39 times wider than the range predicted by simplified approaches. The proposed PV model is feasible and capable of provide a set of characteristic curves suitable for evaluating the MPPT algorithm efficiency. 11:20AM Development and implementation of a PV performance monitoring system based on inverter measurements [#960]
Performance monitoring and fault detection systems are becoming more common in large photovoltaic (PV) plants as they can contribute to decreasing operation and maintenance costs, as well as for maximizing plant yield and lifetime. However, in case of residential and smaller commercial PV system applications the cost of the performance monitoring hardware and implementation is still high. Therefore, we present the practical development and implementation of a low-cost PV performance monitoring system for residential and commercial PV applications, based on the inverter's own monitoring and communication capabilities. The proposed monitoring system supervises the PV array maximum power and inverter energy production using performance models of the system, and is able to detect PV array and inverter level power loss and faults. 11:45AM Characterization of Silicon Based Photovoltaic Cells Using Broadband Impedance Spectroscopy [#43]
The growth in photovoltaic installations makes characterization and condition monitoring essential. In this paper, broadband impedance spectroscopy is implemented for characterization and performance monitoring of silicon solar cells for near real-time operation. An optimized quasi-logarithmic broadband signal is designed to estimate the impedance response of the cells. Electrochemical equivalent circuits of the frequency response are then modelled from the obtained Nyquist plots and the cell parameters are extracted using complex nonlinear least squares. This procedure can be applied for direct estimation of the internal parameters of the silicon solar cells/module at different operating points. Results show that the implemented broadband characterization yields good correlation to the conventional electrochemical impedance spectroscopy at significantly reduced procedural time and equipment cost. Utility Applications III Wednesday, September 21, 10:30AM-12:10PM, Room: 202A, Chair: Srdjan Lukic, Deepak Divan 10:30AM DC Solid State Transformer Based on Input-Series-Output-Parallel Dual-Active-Bridge for MVDC Power Distribution [#719] Biao Zhao, Qiang Song, Jianguo Li and Wenhua Liu, Tsinghua University, China; Tsinghua Univesity, China Dc power transmission and distribution are becoming research hotspot all around the world, this paper presents dc solid state transformer (DCSST) will be the key device for dc power distribution to achieve flexible control and fast management of voltage and power between the medium/high voltage dc distribution grid and low voltage dc micro-grid. This discusses a high-frequency-link (HFL) isolated bidirectional DCSST scheme based on input-series-output- parallel dual-active bridge (DAB), and the topology, operation principle, control strategy, and experiments are present and analyzed. The proposed DCSST has the similar transmission power model with DAB. The series voltage balance and parallel power balance of DCSST can be achieved just by controlling series voltage balance. The experimental results verify the validity and effectiveness of proposed solution for MVDC power distribution. 10:55AM Six-Leg Single-Phase to Three-Phase Converter [#1088]
This paper investigates the utilization of two different six-leg configurations of single-phase to three-phase converters. One of the topologies is transformerless and the other is transformer-based. The drive systems provide both bidirectional power flow and power factor control. Pulsewidth modulation techniques for the converter control are discussed. Simulation and experimental results are provided to illustrate and compare the operation of the systems. 11:20AM Flexible Transformers for Distribution Grid Control [#1398]
This paper presents a novel device for distribution grid control. The proposed device, called flexible transformer, consists of a fractionally-rated converter and a slightly modified medium voltage (MV) distribution transformer with additional taps. The converter can be wired to either the primary or the secondary side of the transformer, resulting two different configurations. The proposed device successfully meets the requirements of great performance, long lifetime, high efficiency, and low cost for typical utility assets. This paper presents the concept of the flexible transformer as well as the schematic and operating principle of both configurations. Simulation and experimental results of the proposed device rated at 7.2 kV / 50 kVA is also provided. 11:45AM Comparative Analysis of Modular Multiport Power Electronic Transformer Topologies [#1601]
Conventional line-frequency transformers are a key element in the current power transmission system. Although they are a relatively cheap and well established technology, they are not able to provide new functionalities demanded by the power system operator. Solid State Transformers (SSTs), also called Power Electronic Transformers (PETs) are power electronics-based arrangements able to provide, in addition to the basic functions of a conventional transformer, new functionalities like harmonics, reactive power and imbalance compensation, and power flow control. This paper addresses a comparative analysis of modular PET topologies, including the popular CHB-based approach and MMC-based topologies. Criteria for the evaluation will include aspects like the number of cells required, ratings of the power devices, number and type of the PET ports and design requirements for passive elements. Modeling, Analysis, and Control of Grid-Connected Converters II Wednesday, September 21, 10:30AM-12:10PM, Room: 202D, Chair: Frede Blaabjerg, Rajendra Prasad Kandula 10:30AM Advanced Control of a High Power Converter Connected to Weak Grids [#984] Shahparasti Mahdi, Catalan Pedro, Luna Alvaro, Candela Jose Ignacio and Rodriguez Pedro, Technical University of Catalonia, Spain; Ingeteam Power Technology, Spain This paper addresses the stability problems of a high power converter connected to a weak grid. The wide range values that grid impedance can take, challenges the stability and the performance of the controllers, which are responsible of regulating the current injection in such converters. In this work, a control strategy based on stationary reference frame controllers is selected and implemented using a proportional resonant (PR) controller, with capacitor voltage feedforward and a phase shifter. As it will be demonstrated in this paper, although the feedforward contributes to enhance the transient response of the converter, it may cause also deep unstable dynamics near to the medium frequency and decreases the phase margin in low frequency ranges. Therefore, it can be used to damp the unstable dynamics near to resonance frequency range and the LCL-filter can be adopted for the high frequency one. In order to improve the controller performance, a new phase shifter is added to the control scheme to enhance the phase margin at low frequency ranges. Simulation and experimental results considering weak grid conditions are shown to validate the proposed method. 10:55AM A Power Density Optimization Method for a Power Pulsation Decoupling Buffer in Single-Phase DC-AC Converters [#1497]
The goal of this work is to develop an analytical method to determine the optimum size of an active decoupling buffer in single phase DC-AC converters for the highest power density. The conventional method for active twice line frequency power pulsation decoupling is a structure commonly known as the full ripple port architecture. However, its high voltage stress and correspondingly large inductor volume become a bottleneck to improve its power density, and the large amount of power processed in the active converter increases the power losses, leading to large heat removal solutions. recently proposed series-stacked buffer architecture provides a way to reduce the buffer converter voltage stress, reduce the power conversion losses and balance the volume of passive components to achieve very high power density. This paper presents a design procedure of the series-stacked buffer architecture that optimizes the power density through mathematical derivations and numerical design examples. The design procedure is based on calculating the energy storage of the passive components as the optimization objective and analyzing the operation of the buffer converter that forms certain optimization constraints. A set of optimal design parameters is found by the method of Lagrange multipliers. A hardware prototype is developed under the guidance of this optimization and the high power density has been experimentally verified. 11:20AM Control Design in $$-Synthesis Framework for Grid-Connected Inverters with Higher Order Filters [#1568]
In this paper, a robust controller is designed based on $\mu$-synthesis method for grid-connected inverters. The performance of the controller is made robust against realistic uncertainties including the time delay and parameter changes, while the resonant oscillations are actively damped. The designed controller only relies on output feedback eliminating the need for extra feedback sensors that are normally used in full or partial state feedback systems. Simulation and experimental results confirm the satisfactory performance and robustness of the designed controller in both cases of a nominal system and a system with parameter variations. 11:45AM Sensorless Current Model Predictive Control for Maximum Power Point Tracking of Single-Phase subMultilevel Inverter for Photovoltaic Systems [#1618]
Stochastic dynamic behavior of solar energy necessitates the use of robust controllers for photovoltaic (PV) power electronics interfaces to maximize the energy harvest by continuous operation at maximum power point (MPP). This paper proposes a sensorless current model predictive control maximum power point tracking (SC-MPC-MPPT) algorithm. By predicting the future behavior of the power conversion stage, the proposed controller features fast and stable performance under dynamic ambient condition and negligible oscillation around MPP at steady state. Moreover, it does not require expensive sensing and communication equipment and networks to directly measure the changing solar insolation level. The power conversion stage includes an upstream boost dc/dc power conversion to a dc-link capacitor, and a downstream seven-level sub-Multilevel Inverter (sMI) from the dc-link capacitor to the grid. The sMI is using three power arms cascaded with an H-bridge inverter. This topology brings considerable benefits such as reduced number of power switches and their gate drivers when compared to the traditional multilevel inverters. Model Predictive Control (MPC) is employed for current regulation of the sMI, thus eliminating the need of cascaded classical control loops and modulator. The proposed SC-MPC-MPPT technique for a boost converter is implemented experimentally using the dSPACE DS1007 platform. DC Microgrids II Wednesday, September 21, 10:30AM-12:10PM, Room: 203DE, Chair: Josep M. Guerrero, Ali Davoudi 10:30AM An Adaptive Power Distributed Control Method to Ensure Proportional Load Power Sharing in DC Microgrid Considering Equivalent Line Impedances [#824] Duy-Hung Dam and Hong-Hee Lee, University of Ulsan, Korea (South) This paper proposed a distributed control method for dc microgrid to ensure the proportional load sharing by taking into account the different line impedance. In the proposed method, the operation point of each DG is effectively defined based on the power rating and the instantaneous power of the DG to achieve the proportional load power sharing. A low bandwidth communication is used to transmit the data required to determine the power reference for all DGs. In order to balance the power per unit requirement, the output voltage of each DG is controlled by a power controller to adjust the desired operating point. Therefore, all DGs can operate at the balanced operating point on the droop curve to ensure the proportional load power sharing. This paper also considers the load shedding to prevent the dc microgrid from operating under overload condition. The effectiveness of the proposed method is verified by simulation and experiment which are carried out with 2.8kW prototype dc microgrid.
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