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:
- Tuesday, September 20, 8:30AM-11:00AM Photovoltaic Converters I
- Modular Multi-Level Converters, HVDC, and DC Grids II
- Renewable Energy II
| P1706 Modeling and Investigation of 4-Coil Wireless Power Transfer System with Varying Spatial Scales [#734]
Lu Chen, Fuxin Liu, Xinbo Ruan and Xuling Chen, Nanjing Univ. of Aeronautics and Astronautics, China As a mid-range wireless power transfer (WPT) technology, magnetically coupled resonant (MCR) WPT has become a reseach focus in recent years. In this paper, an equivalent circuit model of 4-coil MCR WPT system was presented, along with the formulas of the output power and transmission efficiency. Besides, to comfirm whether spatial misalignments will influence the transmission characteristics of the system, the relationship between the mutual inductance and the spatial misalignments of the coils was analyzed, and the transmission characteristics under various spatial scales was revealed. An experiment circuit was designed and experimental results were well consistent with the theoretical analysis. P1707 Vehicular Integration of Wireless Power Transfer Systems and Hardware Interoperability Case Studies [#1356]
Several wireless charging methods are under development or available as an aftermarket option in the light-duty automotive market. However, there are not a sufficient number of studies detailing the vehicle integration methods, particularly a complete vehicle integration with higher power levels. This paper presents the design, development, implementation, and vehicle integration of wireless power transfer (WPT)-based electric vehicle (EV) charging systems for various test vehicles. Before having the standards effective, it is expected that WPT technology first will be integrated as an aftermarket retrofitting approach. Inclusion of this technology on production vehicles is contingent upon the release of the international standards. The power stages of the system are introduced with the design specifications and control systems including the active front-end rectifier with power factor correction, high frequency power inverter, high frequency isolation transformer, coupling coils, vehicle side full-bridge rectifier and filter, and the vehicle battery. The operating principles of the control, and communications, systems are presented. Aftermarket conversion approaches including the WPT on-board charger (OBC) integration, WPT CHAdeMO integration, and WPT direct battery connection scenarios are described. The experiments are carried out using the integrated vehicles and the results obtained to demonstrate the system performance including the stage-by-stage efficiencies. Tuesday, September 20, 8:30AM-11:00AM Photovoltaic Converters I Tuesday, September 20, 8:30AM-11:00AM, Room: 203AB, Chair: Francisco Canales, Liming Liu
8:30AM Low Power Factor Operation of the PV Inverter with Power Decoupling Function [#293] Yusuke Seta and Toshihisa Shimizu, Tokyo Metropolitan University, Japan A novel power conditioner with a power decoupling circuit is proposed in this paper. The proposed power conditioner can generate reactive power for the utility lines. Therefore, the proposed circuit must operate under very low power factors to meet the anti-islanding and fault-ride-through (FRT) functionalities required. In addition, by applying the power decoupling circuit, the current ripple of the DC input side capacitor can be reduced. Therefore, a film capacitor can be used instead of an electrolytic capacitor. The influence of the maximum power point tracking (MPPT) control can be reduced as well. The operating principle, theoretical analysis, and circuit/characteristic simulations of the proposed circuit are described. In addition, the hardware is implemented with a 100-V DC input and a 50-V AC/100-W output to demonstrate its feasibility. 8:55AM Stand-Alone Photovoltaic Asymmetrical Cascade Converter [#1115]
This paper presents a stand-alone photovoltaic (PV) generation system based on an asymmetric cascade H-bridge (ACHB) converter. The system is composed of two H- bridge converters (A and B) series connected, supplying an ac load. To maximize the number of voltage levels, the dc-link voltage ratio is 3:1. The higher dc- link voltage (converter A) is connected to PV panels, and two options are presented for the lower dc-link voltage (converter B): a battery cluster or a floating capacitor. In addition, two pulsewidth modulation (PWM) strategies are proposed: one is based on phase-shifted carrier (PSC) disposition and the other is based on level-shifted carrier (LSC) disposition. The regulation of the dc-link voltage of converter B is performed with the proposed PWM techniques by changing the power distribution between converters A and B, whereas the dc-link voltage of converter A can be regulated by a feedback controller. Finally, simulation and experimental results are shown for validation purposes. 9:20AM Ground Leakage Current Suppression in a 50 kW 5-level T-type Transformerless PV Inverter [#459]
In this paper ground leakage current suppression in a 50 kW 5-level T-type transformerless PV inverter has been presented. Compared to a 3-level T-type PV inverter, this topology allows a simple modulation method such as carrier- based (CB) PWM can be used to suppress the leakage current without the penalty of the traditional methods. Phase disposition (PD) and phase opposition disposition (POD) based CB PWM method has been applied to this 5-level topology. The spectrum analysis has demonstrated that PD and POD will generate the same phase voltage spectrum. In addition, the common-mode (CM) voltage of a 5-level T-type PV inverter has been derived and the CM choke has been designed. The value of the CM choke is a 73% reduction compared to that of a 3-level T-type PV inverter. The simulation and experimental verification have been provided. 9:45AM A High Performance T-type Single Phase Double Grounded Transformer-less Photovoltaic Inverter with Active Power Decoupling [#1360]
Transformer-less PV inverters are gaining widespread applications with lower cost, reduced footprint, and improved efficiency. This paper proposes a topology that can eliminate the common mode leakage current which is a major challenge in transformer-less PV inverters. In addition, an active power decoupling strategy is implemented in this topology instead of using large energy storage element for double line frequency power decoupling, thus achieving a smaller volume. A constant input voltage with negligible double line frequency ripple component ensuring high MPPT efficiency is achieved in this topology. Compared to the previously proposed topology, a T-type branch is added as an improvement to fully take advantage of the inherent three level structure resulting in much reduced switching loss and inductor current ripple. A 1 kW, 100 kHz single-phase prototype with 200 V DC input and 120 V/60 Hz AC output using SiC MOSFETs has been built to validate the theoretical analysis. The control strategy and modulation scheme are implemented in DSP TMS320F28335 resulting in 24% reduction in the total loss and 50% reduction in the inductor current ripple. 10:10AM Low Leakage Current Transformerless Three-Phase Photovoltaic Inverter [#1503]
In a transformerless inversion system, the suppression of common mode leakage current is one of the most important issues concerned. Several single phase full bridge PV inverters have been proposed to eliminate the leakage current. However, in the three phase applications of the PV inverters, few attentions have been paid on the improvement of leakage current from a topological point of view. This paper focuses on the reduction of common mode voltage in three phase transformerless inverter. Firstly, the common mode characteristic of the three phase inverter is analyzed. Then, a kind of novel three phase topology is proposed to suppress the common mode voltage. Also, the NPC circuit can be added to the novel topology in order to further reduce the common mode voltage. The novel topology has the advantages of fewer device cost and lower conduction losses compared to the traditional three phase NPC topologies. Finally, the simulation and experimental results illustrated the theoretical findings. 10:35AM Operation of Dual-Input Central Capacitor Photovoltaic Inverter under Unbalanced Grid Voltage Condition [#647]
To date, a family of series-connected boost converter (SCBC) with enhanced efficiency has been presented as the front-end dc/dc stage of distributed photovoltaic (PV) inverter, which suffers the severe PV voltage/power oscillation when operated under unbalanced grid voltage condition. This paper proposes an operational scheme to enhance the performance of one type SCBC, namely the dual- input central capacitor (DICC) converter, under unbalanced grid voltage condition. The PV voltage/power oscillation is eliminated using the propose scheme, resulting in the maximum PV energy harvest and enhanced grid current quality even under severe unbalanced condition. Also the overall dc-link voltage oscillation amplitude is minimized. The analytical representation of double line-frequency current along with the DICC circuitry model are studied, so that the DICC circuitry parameters could be designed accordingly. This paper further proposes the control strategy of DICC-PV inverter under unbalanced grid voltage condition. All the theoretical findings and the control method proposed can be derived to other type SCBCs. Finally, the theoretical findings were verified through both Matlab simulation and an experimental prototype. Modular Multi-Level Converters, HVDC, and DC Grids II Tuesday, September 20, 8:30AM-11:00AM, Room: 203DE, Chair: Rajib Datta, Ali Mehrizi-Sani 8:30AM Impact on Small-Signal dynamics of Using Circulating Currents Instead of AC-Currents to Control the DC Voltage in MMC HVDC Terminals [#1009] Gilbert Bergna, Jon Are Suul and Salvatore D'Arco, SINTEF Energy Research, Norway; NTNU / SINTEF Energy Research, Norway The traditional approach for controlling the dc-voltage in Voltage Source Converter (VSC) HVDC terminals is to act on the reference for the active current or active power on the ac-side. For a Modular Multilevel Converter (MMC) with explicit control of the internally stored energy, this implies that the total energy sum must be controlled by acting on the dc-components of the circulating currents. However, the internal energy storage of an MMC acts as a buffer between the transient dynamics on the ac- and dc-sides. Thus, the dynamic response of the dc-voltage will depend on the closed loop dynamics of the internal energy control. Different system characteristics can be obtained if the reference signals from the dc-voltage control and the sum energy control are interchanged. As a result, the dc-voltage controller can provide the reference value for the dc-components of the circulating current, while the sum energy controller will provide the ac-side active current reference. In this paper, it will be demonstrated by time domain simulations and eigenvalue analysis that dc-voltage control by acting on the circulating current reference introduces a decoupling between the dynamics of the ac- and dc-side interfaces. This decoupling will also make the system dynamics less sensitive with respect to the operating conditions, which enables improved dynamic performances and less strict tuning requirements for the dc-voltage and sum energy controllers. 8:55AM Control of VSC-HVDC with Electromechanical Characteristics and Unified Primary Strategy [#1169]
High voltage dc (HVDC) systems act as the prevailed solution for transmitting offshore wind energy to onshore main grids. Control of the voltage source converters (VSC) in HVDC systems is decisive for the performance. This paper proposes the control of VSC-HVDC with electromechanical characteristics and unified primary strategy, as a reaction to the updated requirements of the ac grid transmission system operators. As two important aspects of VSC-HVDC control, converter control and primary control are both designed in detail. Electromechanical characteristics make the VSC capable of providing inertia to the ac networks as well as simplicity in island operation. Besides, unified primary control is given as a universal primary strategy for VSC stations, and especially takes into account frequency support and control mode transition. The proposed converter control is validated in scaled-down 10 kW laboratory setups, while the proposed primary control is endorsed by the simulation tests on a CIGRE multi-terminal HVDC model. 9:20AM A Novel Interline DC Power Flow Controller for Meshed HVDC Grids [#36]
Power flow control ability of meshed high voltage direct current (HVDC) grids can be improved by inserting DC power flow controller into the grids. Based on the study of existing DC power flow controllers, this paper proposes a novel interline DC power flow controller (IDCPFC) which has the benefit of less active switching devices, simpler control, little side effect on meshed grids, no external power source needed and wide application occasions. The performance of the IDCPFC is validated by simulation and experiment tests. The results show that the proposed IDCPFC can achieve stable power flow control in different conditions. 9:45AM Impedance-based and Eigenvalue based Stability Assessment Compared in VSC-HVDC System [#650]
This paper presents the comparison between the impedance-based and eigenvalue-based stability analysis methods for a VSC-based HVDC system. In order to apply the impedancebased method, an impedance model for the VSCs is analytically derived and the derived model is validated by comparing the frequency responses of the analytical impedance and the impedance measured in a detailed switching model of the VSC-HVDC system. To determine the stability from the eigenvalue based method, an analytical state-space small-signal model is developed and the model is validated by time domain simulations. It is shown that both stability analysis methods can effectively determine the stability of the system. In the case of the impedance- based method, a low phase-margin in the Nyquist plot of impedance ratio indicates that the system can have harmonic oscillation; however the system still operates stably. A weakness of the impedance method is that the stability determined by this method is not a global stability assessment; and it is therefore necessary to investigate the stability at all possible sub/systems. On the other hand, the eigenvalue based method can determine the stability of the entire system; but it cannot predict harmonic oscillations caused by a PWM inverter operating in a stable point. A two terminal VSC-HVDC system has been developed analytically and the frequency domain stability analysis based on impedance and eigenvalues has been carried out. The theoretical analysis has been further validated by simulation and experiments 10:10AM Performance Analysis of a Triple-Active Bridge Converter for Interconnection of Future DC-Grids [#942]
Dc-dc converters are a promising technology for interconnection of future dc grids. Besides the relatively low volume and space requirements, dc-dc gonverters provide good controllability of the power flow. This is particularly important with regard to a more decentralized energy generation, where a fully bidirectional power flow - even between grids of equal voltage levels - is desired to increase overall grid efficiency and stability. This paper analyzes the performance of a three-phase triple-active bridge converter (3ph-TAB) which interconnects a 5 kV medium-voltage dc grid and two low-voltage dc grids with nominal voltages of 380V and 760V, respectively. First, the modulation strategy of the converter is described. The different cases of operation are analyzed and a method is developed which significantly simplifies the theoretical analysis of the converter. The design specifications for the leakage inductances of the transformer and the dc-link capacitors are derived and analyzed. Furthermore, the soft-switching boundaries are derived analytically. The theoretical assessment is supported by a semiconductor loss simulation for the whole operating range. 10:35AM Dc Fault Protection of Multi-Terminal VSC-HVDC System with Hybrid Dc Circuit Breaker [#1038]
Dc fault protection is a main challenge in voltage source converter (VSC) based multi-terminal high voltage direct current (HVDC) systems. This paper develops a systematic dc fault protection strategy for systems utilizing hybrid dc circuit breakers as the main protection devices. A two-step fault detection method to accommodate the proactive hybrid dc circuit breaker has been simulated and demonstrated with both fast speed and selectivity. The necessities of temporary blocking HVDC converters for both pole-to-pole and pole-to-ground faults have been evaluated, and the corresponding criteria have been established. In order to achieve fast system recovery after the fault clearance, voltage margin control is proposed to simplify the restart sequence for different converters and reduces the dc voltage variation during the process. The overall protection strategy is demonstrated in a 4-terminal HVDC simulation platform, showing a total dc fault recovery time of around 200 ms. Renewable Energy II Tuesday, September 20, 8:30AM-11:00AM, Room: 203C, Chair: Alex.Q Huang, Xueguang Zhang 8:30AM Partial Power DC-DC Converter for Photovoltaic String Inverters [#768] Alexander Morrison, Jaime Zapata, Samir Kouro, Marcelo Perez, Thierry Meynard and Hugues Renaudineau, Universidad Tecnica Federico Santa Maria, Chile; University of Toulouse, France In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string, a wider range of operation, higher energy yield and, when required for grid connection, the possibility of voltage regulation. However, the conversion efficiency is lower than configurations with a single stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the surplus power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance. 8:55AM On Reactive Power Injection Control of Distributed Grid-tied AC-stacked PV Inverter Architecture [#1502]
In this paper, two different Reactive Power Injection (RPI) methods for a fully distributed PV inverter architecture are investigated. RPI methods are parts of ancillary service requirements for modern PV systems to play a more active role in grid regulation and control in future high penetrated PV generation networks. The main objective of this paper is to demonstrate and test RPI methods on a panel-level AC-stacked PV-inverter string which is controlled with distributed control scheme with minimum communication requirements and propose a combined RPI method. Effectiveness and feasibility of distributed control architecture and RPI methods are verified by experimental results during normal operation and voltage disturbance conditions using a lab-scale PV inverter string setup. 9:20AM A Cost-Effective Power Ramp-Rate Control Strategy for Single-Phase Two-Stage Grid-Connected Photovoltaic Systems [#600]
In the case of a wide-scale adoption of grid-connected Photovoltaic (PV) systems, more fluctuated power will be injected into the grid due to the intermittency of solar PV energy. A sudden change in the PV power can potentially induce grid voltage fluctuations, and thus challenge the stability of the grid. Hence, this sudden active power change resulting in a large power ramp-rate should be avoided in practice. In fact, some grid regulations also released strict rules on active power ramp-rates for PV systems. This paper proposes a cost-effective control strategy to limit the power ramp-rate for two- stage grid-connected PV systems. The main concept of the proposed scheme is to modify the maximum power point tracking algorithm in such a way to regulate the PV power at the left side of the maximum power point curve. As a consequence, the power ramp-rate can be controlled according to the set-point. Experiments conducted on a 3-kW single-phase two-stage grid-connected PV system have verified that the proposed solution can accomplish fast dynamics, high accuracy, and high robustness in the power ramp-rate control for PV systems. 9:45AM Delta Power Control Strategy for Multi-String Grid-Connected PV Inverters [#601]
With a still increasing penetration level of grid-connected PV systems, more advanced active power control functionalities have been introduced in certain grid regulations. A delta power constraint, where a portion of the active power from the PV panels is reserved during operation, is required for grid support (e.g., during frequency deviation). In this paper, a cost-effective solution to realize delta power control for grid-connected PV systems is presented, where the residential/commercial multi-string PV inverter configuration is adopted. This control strategy is a combination of Maximum Power Point Tracking (MPPT) and Constant Power Generation (CPG) modes. In this control scheme, one PV string operating in the MPPT mode estimates the available power, while the other PV strings regulate the total PV power by the CPG control strategy in such a way that the delta power constraint for the entire PV system is achieved. Simulations and experiments have been performed on a 3-kW single-phase grid- connected PV system. The results have confirmed the effectiveness of the delta power control strategy, where the power reserve according to the delta power constraint is achieved under several operating conditions.
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