Anshuman Tripathi

Decoupled DQ-PLL with positive sequence voltage normalization for wind turbine LVRT control

The behavior of PLL under usual and nonstandard operational circumstances is a vital facet, as the RES is anticipated to function to meet grid code requirement. This paper proposes a positive sequence voltage normalization method to be applied in conventional dq-PLL which is normally used as the last stage of positive-negative sequence voltage decoupled PLL scheme. The benefit of this solution is that it helps to eliminate the effect of positive voltage amplitude in PLL control loop bandwidth. Therefore, the dynamic functionality of the decoupled PLL scheme can be improved in grid voltage dip conditions. The proposed solution has been studied in DDSRF-NOM-PLL (decoupled double synchronous reference frame normalized PLL) scheme. Simulation results show that DDSRF-NOM-PLL has less frequency overshoot compared to DDSRF-PLL scheme and has identical dynamic performance as DHRF-PLL. The suggested solution can also be readily implemented to improve the dynamic response of MCCF-NOM-PLL scheme (Multiple Complex coefficient filters PLL with positive sequence normalization) or other positive-negative sequence decoupling schemes with conventional dq-PLL as its last stage for frequency and phase estimation.

Multi-area model predictive load frequency control: A decentralized approach

Increasing power consumption requires engineers to find better control techniques to increase energy efficiency. Advancements in technology allows us to use more complex control algorithms to pursue this goal. Load frequency control (LFC) is one of the vital points in power system control and a state of art control method must be used to ensure power quality of the grid. In this work, decentralized model predictive controller (MPC) with state and generation rate constraints is used to handle LFC problem of four area interconnected system. It is seen that the decentralized MPC is successfully achieved the given control scenario for the system. The presented results indicate that decentralized MPC is feasible for frequency control of power systems.

Li-ion battery cell equalization by modules with chain structure switched capacitors

In electric vehicles (EVs), Li-ion battery has been applied as the main power source. To give enough power and energy to the system, single Li-ion battery cells will be connected in series and parallel to make a battery pack. Thus, cell equalization for battery pack has been an important topic in battery management system (BMS). Recently, researches have proposed different topologies and control strategies to achieve cell equalization. In this paper, a modularization strategy is proposed based on the chain structure switched capacitor method. Simulation results in Matlab/Simulink have shown good cell equalization performance for the proposed method.

Modular DAB DC-DC converter low voltage side dc link capacitor two-stage charging-up control for solid state transformer application

This paper presents an effective two stage DAB charging-up control method for modular DC-DC converters with low voltage side common DC bus voltage starting from zero. In 1st stage of charging, the DAB controller is modified to allow variable duty cycle control of medium voltage side DAB converter. In this stage, a constant charging-up current is applied so that low voltage side DC link voltage is charged up linearly. In the 2nd stage of charging control, the normal dual voltage and current control loops are applied. At the end of 2nd charging up stage, the DAB controller is ready for normal power regulation. The proposed DAB charging control method is applicable for modular SST start-up application for both grid tied and standalone application. The important advantage of the proposed DAB charging control method is that the DC-DC converter performance is robust to DC-DC converter circuit parameter variation and operation condition variation among DAB modules. Another attractive advantage is that the proposed solution is purely DAB control algorithm change without requiring extra circuit component in start-up charging process.

Control of active front-end rectifier of the solid-state transformer with improved dynamic performance during precharging

The control of the active front-end rectifier of the three-stage solid-state transformer (SST) system is addressed in this paper. A comprehensive precharging sequence is introduced for the active front-end rectifier of the SST to limit the inrush current during the start-up process to its nominal current. The proposed precharging algorithm consists of two phases, passive and active precharging. The precharging resistor limits the current during the passive precharging, while a ramp increase of the voltage reference is used in the controller during the active precharging to prevent large inrush currents. Additionally, a feedforward voltage compensator is added to the voltage reference of the controller to improve the dynamic response at the beginning of the active precharging. The proposed algorithm is detailed and simulation results on a 4-kW active front-end converter are presented to validate its performance. The simulation results under various operation conditions show the ability of the proposed algorithm to limit the converter current to its nominal value during the precharging as well as to control the dc-link voltage under different load changes.

LC-StatCom with symmetrical I-V characteristic: Total Harmonic Distortion Study

In this paper, the effect of capacitor voltage ripple on current quality in a cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) with symmetrical I-V characteristics is investigated. Total harmonic distortion of the synthesized ac voltage of an H-bridge converter operating with different capacitor voltage ripples is evaluated for both inductive and capacitive operating modes. Simulation-based analyses on a 350-VA three-cell CHB LC-StatCom system are provided to demonstrate LC-StatComs effectiveness to provide high quality current compared to a conventional StatCom.

Study of electric vehicles penetration in Singapore and its potential impact on distribution grid

The various schemes of electric vehicle (EV) charging and the related impacts on electrical generation, transmission and distribution systems has been the subject of intense research over the past decade. The major problems have been narrowed down more to the distribution side of the electricity network. With this background, it becomes critical for a place like Singapore with heavy reliance on electricity as the prime mover for its industrial and domestic growth, to be well positioned to the ever-increasing potential demand that the electric vehicle market brings to table at the present growth rate and also the potential increase and growth that EV segment will bring in the next few decades. In this context it becomes necessary to understand the capability requirements of the distribution sectors in different areas of Singapore and upgrade to meet the challenges of 2050 where required. The present study is aimed to give a consolidated understanding of the typical problems on the distribution side and also analyze the capacity based on a projected EV increase of the passenger vehicle sector and calculate and predict the overloading on the distribution transformer requirements in particular under the different EV penetration scenarios mentioned in the Electromobility roadmap study for Singapore. Analysis will also focus on the impact of type of charging levels like single phase, three phase and fast DC charging.

State of art survey for design of medium frequency high power transformer

Medium and high frequency, high power transformers play an important role in footprint reduction along with their functions of galvanic isolation, and voltage transformation in all high power converters typically used in traction power systems, offshore wind plant power converters, and solid state transformer based distribution system grids. This state of art report analysis the various materials and design tradeoffs that govern the electromagnetic behavior and loss mechanisms of the medium frequency transformer applications. Typical winding and core geometries that have been reported extensively in the literature are described, and some design procedures and flow charts are analyzed including specific optimization routines. Estimation of core loss at high frequency using Steinmetz method and other modified methods are shown in detail. Thermal modelling including static and dynamic methods available in literature are put forward with references to thermal management methods. FEM analysis for electromagnetic behavior is described and couple of commercially available tools and their limitations are analyzed. Different challenges of relevance are included in different sections and brief comparisons are drawn. Design tools which are available is given a preview and limitations are drawn. A comprehensive literature survey was done and included in the paper in the reference section.

Hybrid energy storage power allocation and motor control for electric forklifts

Enhancing transportation efficiency is the preeminent place to start efforts to minimize emissions of carbon dioxide which is a crucial malefactor in global warming. Due to awe-inspiring advantages over vehicles with internal combustion engines, use of electric vehicles (EVs) finds application in a variety of areas. However, energy storage system (ESS) of the EV plays an important role in EVs performance and can be a limiting factor in its utilization. To mitigate problems arise from ESSs, different storage equipment can be combined into an integrated hybrid energy storage system (HESS). In this paper, the effectiveness of a HESS comprising lithium-ion battery pack and supercapacitors, has been tested by simulating a simple power splitting scheme in an electric forklift application considering a real world drive cycle. With the purpose of numerical investigation, battery and supercapacitor models in Simulink SimPowerSystems are used, induction motor parameters are estimated using data sheet values and field oriented control (FOC) technique is adopted to drive motors. Simulation results have shown that HESS could reduce stress on the battery by limiting peak and surge power demands.