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:
- Modelling, Analysis, and Control of Grid-Connected Converters
- DC-DC Converters: Switched Capacitor
- Multi-Phase Rectifiers
| 1:30PM Energy Storage Opportunities and Capabilities in a Type 3 Wind Turbine Generator [#152] Eduard Muljadi, Vahan Gevorgian and Anderson Hoke, National Renewable Energy Laboratory, United States Wind power plants and other renewable power plants with power electronic interfaces are capable of delivering frequency response (both governor and/or inertial response) to the grid by a control action; thus, the reduction of available online inertia as conventional power plants are retired can be compensated by designing renewable power plant controls to include frequency response. The source of energy to be delivered as inertial response is determined by the type of generation and control strategy chosen. The cost of energy storage drops over time, and global research activities on energy storage are very active, funded both by the private industry and governments. Different industry sectors (e.g., transportation, energy) are the major drivers of the recent storage research and development. This work investigates the opportunities and capabilities of deploying energy storage in renewable power plants. In particular, we focus on wind power plants with doubly-fed induction generators, or Type 3 wind turbine generator (WTGs). We find that the total output power of a system with Type 3 WTGs with energy storage can deliver a power boost during inertial response that is up to 45% higher than one without energy storage without affecting the torque limit, thus enabling an effective delivery of ancillary services to the grid. 1:55PM Assessment of System Frequency Support Effect of a PMSG-WTG Using Torque-Limit Based Inertial Control [#281]
The presented method aims to improve the frequency support capability considering the maximum torque restriction of a permanent magnet synchronous generator. The advantages of the proposed method are improved frequency nadir in the event of an under-frequency disturbance; and avoidance of over- deceleration and a second frequency dip during the inertial response. The system frequency response is different, with different slope values in the power-speed plane when the inertial response is performed. The proposed method is evaluated in a modified three-machine, nine-bus system. The simulation results show that there is a trade-off between the recovery time and FN, such that a gradual slope tends to improve the FN and restrict the rate of change of frequency aggressively while causing an extension of the recovery time. These results provide insight into how to properly design such kinds of inertial control strategies for practical applications. 2:20PM Improved Efficiency of Local EPS through Variable Switching Frequency Control of Distributed Resources [#1128]
This contribution explores the possibility of improving the global efficiency of three-phase inverter-based distributed resources (DR) embedded in low- voltage (LV) distribution feeders, by the adaptation of their switching frequency (SF) to the operation point of both the converter and local loads. The core of this proposal lies on the fact that in a good number of applications, in both services and residential sectors, the owner of the DR is also in charge of the losses caused in the local electric power system (EPS). This fact leaves room for a global optimization of the power losses, i.e, converter losses will be considered together with those losses caused by the current harmonics injected into the local grid. A dynamic adaptive SF frame of the DR is considered in this proposal to allow its operation beyond its rated frequency at light loads, subjected to the thermal constraints of the device. Simulation results obtained using PLECS software as well as an experimental validation of the method are included. 2:45PM Smart EV Charging System for Maximising Power Delivery from Renewable Sources [#1207]
The design of a smart EV charging system that provides maximum power delivery from renewable energy (PV) sources is described, through the application of control strategies which ensure that system power converters are operated in regions of high efficiency. Using the proposed approach, system level models predict power efficiency improvements of up to 6% for a 6.5 kW PV installation with four EV charging points. The implementation of a complete small-scale demonstrator system designed as a test bed for validation and investigation of other smart control algorithms is described, including a PV source, power converters, a smart controller and Li-ion battery loads. 3:10PM Instantaneous Frequency Regulation of Microgrids via Power Shedding of Smart Load and Power Limiting of Renewable Generation [#1284]
In this paper, a collaborative control scheme is proposed to improve the stability of the microgrid with intermittent renewable energy sources. Different from other cooperative control schemes targeting mostly on regulating the generation side, the proposed operating scheme utilizes all controllable resources in the microgrid, including renewable energy sources (RESs), storage devices, and controllable loads. A modified maximum power point tracking (MPPT) scheme is proposed for RESs in limiting its power output when frequency surges over its upper limit. The adaptive/smart load enabled by the electric spring (ES) reduces the power demand when the frequency falls below the lower limit. Both operating schemes for RES and adaptive/smart load can be activated when the storage system fails to respond to disturbances. The proposed collaborative scheme can be enacted in an instantaneous manner and is easy to implement by simply modifying the control of RES and adaptive/smart load. Simulation results have confirmed that the proposed scheme is efficient in reducing the frequency oscillation in a microgrid. 3:35PM Modeling and identification of harmonic instability problems in wind farms [#1039]
In power electronics based power systems like wind farms, the interactions between the inner control systems of the power converters and the passive components may lead to high frequency oscillations, which can be called harmonic instability. In this paper, a simple methodology is presented to identify harmonic instability problems in wind farms, where many wind turbines, cables, transformers, capacitor banks, shunt reactors, etc, typically are located. This methodology introduces the wind farm as a Multi-Input Multi-Output (MIMO) control system, where the linearized models of fast inner control loops of the grid-side converters are considered. Therefore, instability problems of the whole wind farm are predicted based on the poles of the introduced MIMO system. In order to confirm the effectiveness of the proposed analytical approach, time- domain simulations are performed in the PSCAD/EMTDC software environment for a 400-MW wind farm. The proposed analytical analysis method and time-domain simulation results show that both dynamics of the power electronic converter and the parameters of the passive component can effect on the wind farm stability. Modelling, Analysis, and Control of Grid-Connected Converters Monday, September 19, 1:30PM-4:00PM, Room: 202A, Chair: Behrooz Mirafzal, Fariba Fateh 1:30PM A Method for Improving Stability of LCL-Type Grid-Tied Inverters in Weak Grid with Resonant Feed forward Control [#186] Yu Tang, Liuliu Huang and Guoshu Zhao, NUAA, China; Jinling Institute of Technology, China Weak grid is commonly seen as a voltage source which contains the gird impedance and background harmonics. The grid current closed-loop control and the grid voltage feed forward control are coupled with each other because of the grid impedance. The proportion feed forward control strategy introduces a positive feedback loop, which affects the grid current quality and the system stability. This paper establishes the model of LCL-type grid-tied inverter, and elaborates the formation mechanism of resonant current under weak grid condition. The resonant feed forward control (RFC) is proposed to attenuate the response of grid impedance during the resonant frequency band, and also to improve the phase margin and decrease the injected current steady state error. A 3kW single-phase grid-tied inverter prototype is designed in the lab, and the proposed RFC strategy is verified by experiments. 1:55PM Passivity Enhancement in RES Based Power Plant with Paralleled Grid-Connected Inverters [#621]
Harmonic instability is threatening the operation of power plants with multiple grid connected converters in parallel. To analyze and improve the stability of the grid connected converters, the passivity of the output admittance converters is first analyzed in this paper. It is shown that the non-passivity of the output admittance of the converters will make the system un-stable under certain grid conditions. Based on the stability analysis, this paper proposes a new method to cancel the non-passivity of the power plant by using inverters with different power rating and control strategies. Three specific cases, where the LCL parameters, sampling frequency and current control strategies of the paralleled inverters are different, are studied. The results suggest that the grid connected converters with different power ratings and control strategies improve the stability of the power plant as a whole. 2:20PM Voltage Stability Analysis Using A Complete Model of Grid-Connected Voltage-Source Converters [#653]
Due to the increasing popularity of renewable energies, a significant share of the power generation in future microgrids is expected to originate from converter-interfaced Distributed Energy Resources (DERs). Traditionally, idealized device models are used to conduct grid stability studies. For instance, a DER interfaced via a Voltage-Source Converter (VSC) would be modeled as an ideal current or power source (depending on the control schemes), ignoring non-ideal behavior like the response of the converter synchronization. However, such a simplification may lead to misjudging the stability, in particular for weak microgrids. To address this issue, ZIP models of grid-interfaced VSCs, which take into account both the control scheme and the synchronization, are developed in this paper. The influence of the synchronization response on the stability of a weak microgrid system is demonstrated using a benchmark system simulated in MATLAB/Simulink. It is shown that the idealized models normally used for static stability analysis do underestimate the voltage stability issue in the investigated microgrid system. 2:45PM Resonant Control for Power Converters Connected to Weak and Micro Grid Systems with Variant Frequency [#701]
Controlled Power Converters are extensively used in industrial applications as they can adapt the electrical energy as required by the application. However, these devices must be properly commutated in order to control voltages and currents. Indeed, power converters are known to be multivariable, coupled, and nonlinear systems; therefore, the control technique needs to be chosen carefully. There are several control techniques reported in the literature for power converters and one of them is the Resonant Control (RC) mainly used on ac based systems. Advantageously, RC guarantees zero steady state error for a sinusoidal reference with a constant frequency and, in addition, it does not need a stationary to rotating reference frame transformation. However, the conventional RC approach requires the exact ac mains frequency value to ensure zero steady state error, being a significant drawback for applications where variable frequency environments are expected. This paper proposes an enhanced RC scheme capable to work under variable frequency scenarios, as in weak and micro grid systems while guaranteeing zero steady state error. The scheme results in a simple algorithm based upon discrete mathematics whose parameters become independent of the ac grid frequency. Results show the feasibility of the proposed approach even under severe ac frequency variations (over 100%) while featuring a stable control loop operation and zero steady state error. 3:10PM Extended-Horizon Finite-Control-Set Predictive Control of a Multilevel Inverter for Grid-Tie Photovoltaic Systems [#702]
This paper proposes a control scheme composed by a linear control and a predictive algorithm with extended horizon for a three-level neutral-point-clamped (NPC) inverter topology for grid- tie photovoltaic applications. The proposed strategy is capable to balance the capacitor voltages at the DC link and to generate a sinusoidal current at the grid side with a unitary power factor. Differently to other approaches, the proposed scheme is easy to digitally implement, and does not need to retune the controller cost function weighting parameters, and reduces the computational effort. These advantages are added to the capability to operate photovoltaic modules at the maximum power point (MPP). Results validate the proposed control methods and the mathematical analysis 3:35PM A Novel Seamless Transfer Control Strategy For Wide Range Load [#406]
This paper proposes a novel seamless transfer control strategy of three-phase grid-connected inverter between grid-connected (GC) and stand-alone (SA) modes w which can cover from no load to full load, even in non linear (NL) loads. The three-phase grid-connected inverter which uses in distributed generation (DG) s system can be operated in both GC and SA control modes, especially for energy s storage systems. The current and the voltage is controlled by the inverter in G GC and SA mode respectively. In other words, the control methods are d differently applied to each mode. When the grid outage, the inverter changes its operation mode. During the mode transition from GC to SA, undesired phenomena such as a voltage spike and a current spike are occurred. With the proposed method, the seamless transfer can be achieved. In addition, proposed algorithm is considered the non detection zone (NDZ) condition which the inverter cannot recognize changes such as magnitude and frequency variation of critical load. The proposed control method is verified by the experimental results. DC-DC Converters: Switched Capacitor Monday, September 19, 1:30PM-4:00PM, Room: 102D, Chair: Alireza Khaligh, Nasser Badawi 1:30PM Hybrid Switched-Capacitor Quadratic Boost Converters with Very High DC Gain and Low Voltage Stress On Their Semiconductor Devices [#21] Manxin Chen, Jiefeng Hu, Li Kerui and Adrian Ioinovici, Sun Yat-sen University, China; Holon Institute of Technology, Israel By inserting a simple cell formed by a capacitor and diode into quadratic boost structures, new converters are obtained. They feature: a larger dc gain compared with that of quadratic boost converters and a smaller voltage stress on the switch and output diode, non-pulsating input current, as required for the use in conjunction with the environmental-friendly energy cells, easiness of the transistor driving, line-to-load common ground. The proposed cell can be easily generalized for enhancing the dc gain. The new converters compare favorably with available ones with the same reactive elements count. Simulations and experimental results confirm the theoretical analysis of the proposed converter. 1:55PM Mixed Switched-Capacitor Based High Conversion Ratio Converter and Generalization for Renewable Energy Applications [#24]
A mixed switched-capacitor cell is proposed by integrating a voltage divider with a voltage multiplier. It is inserted in a boost stage for achieving a converter with high conversion ratio, low voltage stress on switches, non- pulsating input current as required as front-end to electrical grids supplied by renewable energy sources. The generalization of the proposed cell allows to achieve an ultra-high dc conversion ratio. Analysis and experimental data show the superiority of the proposed converter over other hybrid converters with similar complexity: higher dc voltage gain and less voltage stress on the switches. 2:20PM A High Step-Up DC-DC Converter with Switched-Capacitor and ZVS Realization [#570]
As generally acknowledged, the high step-up DC-DC converter is widely used in the sustainable energy system as the front-end stage of the DC-AC converter. Therefore, a novel high step-up DC-DC converter is proposed in this paper. The proposed converter with network of switched-inductor and switched-capacitor can achieve high voltage gain under low duty cycle. Meanwhile, the active switches and diodes suffer from low voltage stress compared with conventional step-up DC-DC converter. More importantly, the presented converter employs an auxiliary resonant circuit to realize zero-voltage switching (ZVS) turn-on and ZVS turn-off for the active switches, resulting in high conversion efficiency. Firstly, the operation principle and steady-state performance are discussed in detail. Then, prototype with power rating of 200W is built to verify the performance of the proposed converter. The maximum efficiency of the prototype can be up to 96.3%, and the experimental results agree with the theoretical analysis and the simulation results well. 2:45PM A Flying Capacitor Multilevel Converter with Sampled Valley-Current Detection for Multi-Mode Operation and Capacitor Voltage Balancing [#1338]
Multi-level hybrid converters have been shown to be a promising class of DC-DC converters. One member of this class is the Flying Capacitor Multilevel (FCML) Converter, which is explored in this work. The multi-mode approach is discussed as a tool to affect high efficiency and power-density across a wide load range, provide variable regulation, and as a general framework to conceptualize the advantages and opportunities of the approach compared to more traditional DC-DC converters. Sampled valley-current detection is explored as a robust control approach for multi-mode regulation. Furthermore, a theoretical framework is developed to show that flying capacitor voltages can be balanced through valley current balancing. Experimental results from a 4-level FCML converter are presented to verify the findings. 3:10PM Resonant Switched Capacitor Stacked Topology Enabling High DC-DC Voltage Conversion Ratios and Efficient Wide Range Regulation [#265]
This paper presents a stacked-topology resonant switched-capacitor (ResSC) dc-dc converter to achieve a high voltage conversion ratio. The topology can be generalized to any N-to-1 dc-dc conversion application with only a single inductor. Multiphase interleaving can be further employed to improve the ripple cancellation and reduce requirement for bypass capacitors. To enable a wide output range while maintaining high efficiency, a phase shift operation is adopted. The regulation is maintained with frequency modulation. The controller is designed with the aid of current phase compensation in addition to voltage mode control. A prototype of a nominal 4-to-1 two phase interleaved resonant switched capacitor converter has been built and tested. The control and regulation of the output voltage are verified through the experiment. Burst mode is further introduced to improve efficiency at the light load condition. 3:35PM Bi-Directional Bridge Modular Switched-Capacitor-Based DC-DC Converter with Phase-Shift Control [#1321]
This paper presents a bi-directional bridge modular switched-capacitor-based resonant DC-DC converter,and the corresponding phase-shift control strategy is proposed for it. Under this control method, bi-directional flow of energy can be realized between the high and low voltage sides. Meanwhile, the output voltage regulation can be achieved 0.15-0.44 times voltage conversion ratio at the step- down mode and above 2.5 times at the step-up mode. In additional, zero-voltage switching (ZVS) operation can be obtained for switches, which improves the system efficiency further. Meanwhile, the working principle of the converter is discussed and the operation parameters are calculated in detail in the converter's optimal working condition. At last, the prototype of proposed converter was built and the experimental results has verified the feasibility and the high efficiency of the proposed converter. Multi-Phase Rectifiers Monday, September 19, 1:30PM-4:00PM, Room: 202E, Chair: Luca Zarri, Mahshid Amirabadi 1:30PM A Review of Electronic Inductor Technique for Power Factor Correction in Three-Phase Adjustable Speed Drives [#1025] Pooya Davari, Yongheng Yang, Firuz Zare and Frede Blaabjerg, Aalborg University, Denmark; The University of Queensland, Australia Electronic Inductor (EI) techniques are promising approaches for improving the grid-side current quality, and they are suitable for motor drive applications. In this paper, different EI topologies are investigated from the efficiency perspective, including the effect of employing Silicon Carbide (SiC) power devices. Moreover, the influence of partial loading on component sizing in Adjustable Speed Drives (ASDs) is studied. Finally the analytical loss modelling of power switches is utilized for efficiency measurement. The theoretical analyses are verified by experimental benchmarking in an ASD system.
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