Priyesh J. Chauhan

A novel non-fragile single-loop voltage and frequency controller for induction generator based isolated renewable energy conversion system

Poor voltage and frequency regulation under source and load perturbations limit the use of self excited induction generator (SEIG) in isolated and dispersed generation, which can exploit wind/microhydro type renewable energy sources. In the present work, a Generalized Impedance Controller (GIC), which is a pulse-width-modulated voltage-source-inverter with a dc-link battery, is used to regulate both, amplitude and frequency of the SEIG terminal voltage using only PI controller in voltage feedback loop. The important aspect of the present work is to show the dependence and sensitivity of the dynamic response of both amplitude and frequency of the SEIG terminal voltage, following source and load perturbations, on the PI controller gain settings of the voltage feedback loop. For non-fragile system operation, optimum gain settings of the voltage-loop controller are selected within a stabilizing range to minimize the frequency disturbances caused by the source/load perturbations.

Synchronized Operation of DSP-Based Generalized Impedance Controller With Variable-Speed Isolated SEIG for Novel Voltage and Frequency Control

In this paper, the performance of a novel two-loop control strategy for a three-phase self-excited induction generator (SEIG), used in wind/microhydro/biogas-based isolated generation schemes, is presented. The implementation of the grid-interactive synchronization of the generalized impedance controller (GIC), an impedance-controlled operation of pulse width modulation (PWM) voltage-source converter, with SEIG is described. The SEIG frequency is tracked using digital phase-locked loop implemented on a dSpace DSP platform. The open-loop SEIG-GIC system is experimentally analyzed for the sensitivity of the SEIG voltage and frequency to GIC modulation index m and phase angle δ. Based on this, a simple and practical control strategy with proportional-integral (PI)-based voltage and frequency feedback loops is evolved for the regulation of the SEIG voltage and frequency. A novel design procedure for both the PI controllers for stable closed-loop operation is presented. The performance of the proposed closed-loop system is experimentally tested under speed and load perturbations.

Single-loop vs two-loop voltage and frequency control of isolated SEIG based RECS

Present investigation deals with the comparison of performance of a Generalized Impedance Controller (GIC) based 3-phase self excited induction generator (SEIG) terminal voltage and frequency regulator, having single and two-loop control, in an isolated wind/microhydro type renewable energy conversion system (RECS). Where, GIC is a PWM voltage source converter with dc-bus battery, having controlled four-quadrant equivalent impedance. Amplitude and frequency regulation of SEIG terminal voltage under source and load perturbations, are accomplished by controlling modulation index m of the GIC and phase angle δ of fundamental component of GIC terminal voltage with respect to SEIG terminal voltage. These m and δ control are achieved by operating the GIC in closed loop with, (i) only voltage feedback, and (ii) voltage and frequency feedbacks. The PI-controllers in both the schemes are designed for non-fragile system operation with optimized transient response of both amplitude and frequency of SEIG terminal voltage. The integrated SEIG-GIC closed loop system with single and two-loop control schemes are modeled and simulated in MATLAB/Simulink to highlight the superior performance of single-loop control scheme in transient and steady states.

Fuel efficiency improvement by optimal scheduling of diesel generators using PSO in offshore support vessel with DC power system architecture

This paper presents optimal generation scheduling for minimization of fuel consumption (FC) in a typical offshore support vessel with DC power system architecture employing four identical diesel generator (DG) sets. FC is analyzed for (i) equal load sharing among DGs in AC architecture, (ii) equal load sharing among DGs in DC architecture and (iii) optimal load sharing among DGs in DC architecture using Particle Swarm Optimization (PSO). Due to the presence of non-linearity in Specific FC (SFC) curves of the diesel engines, the PSO algorithm is used. The SFC-vs-load relationship obtained from Brake SFC (BSFC) map of the diesel engines is characterized using a Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) interpolation. A solution to problem has been attained by comparing yearly fuel consumption in the three cases for the load profile of target vessel. This method can be applied to any vessel equipped with multiple generation units having DC power system architecture.

Shaft input adaptive source current compensation based novel voltage and frequency control of autonomous induction generator

In this paper a novel scheme for regulation of amplitude and frequency of an autonomous self-excited induction generator (SEIG) terminal voltage under perturbations in shaft speed and connected load has been presented, which does not require voltage and frequency feedback. In this technique, compensation of active and reactive component of SEIG stator phase current using a generalized impedance controller (GIC) provides the regulation of SEIG output. The stator current compensation is different from standard hysteresis current compensation technique. The GIC is a voltage controlled PWM voltage source converter, offering controlled bidirectional flow of active and reactive power, while connected at the PCC via coupling reactance. For wide range of shaft input to the given generator, the relationship between the shaft input and reference amplitude of active and reactive component of SEIG stator phase current, at rated PCC voltage and frequency, is pre-established for proper GIC based compensation. A mathematical model of SEIG-GIC-load integrated system has been developed and simulated in MATLAB/Simulink to demonstrate capability of the generating system to provide voltage and frequency regulated supply, under variety of source and load perturbations.

Evaluation of synchronized operation of isolated induction generator with DSP based Generalized Impedance Controller

Performance evaluation of an isolated wind/hydro electric generation scheme having variable speed 3-phase Self Excited Induction Generator (SEIG) operating in synchronism with a Generalized Impedance Controller (GIC) has been presented in this paper. The GIC is an impedance controlled operation of Pulse-width-modulated voltage source inverter (PWM-VSI). The performance of the SEIG-GIC integrated synchronized operation under open loop condition, with fixed excitation and balanced isolated load, has been analyzed in detail for variations in modulation index ‘m’ of the GIC and relative phase angle ‘δ’ between the fundamental components of the GIC and the SEIG terminal voltages. The GIC operation is controlled by implementing Space Vector Pulse Width Modulation (SVPWM) technique. Detailed experimental studies have been undertaken on a laboratory prototype of the SEIG-GIC system for steady state operation. The effects of variations in ‘m’ and ‘δ’ on the amplitude and frequency of the SEIG terminal voltage and active and reactive power flow between the SEIG and the GIC are presented here.

An exercise to qualify LVAC and LVDC power system architectures for a Platform Supply Vessel

This paper attempts an investigation on low voltage AC (LVAC) and low voltage DC (LVDC) architectures with supply voltage of 690 V AC, 60 Hz and 1000 V DC respectively for a Platform Supply Vessel (PSV ). Quantitative evaluation of performance of both the architectures is exercised for a PSV based on fuel consumption (FC), weight, volume, gas emissions and reliability. The PSV has four identical Diesel Generators (DG) of 8000 kW total capacity. A methodology to assess the performance of each parameter is presented. The annual fuel consumption is assessed for equal load sharing among the DGs based on the PSV load profile. Accurate specific fuel consumption (SFC) -vs- load relationship is obtained from the brake specific fuel consumption (BSFC) chart of the diesel engines. The weight, volume and reliability are assessed based on the parameters of individual components like cables, circuit breakers, switchboards, DGs, propulsion motors and power converters. The emissions are assessed for NOx, SO2 and CO2 gases based on their emission factors. The proposed methodology can be applied with a reasonable confidence to make critical assessment of any power system architecture for marine vessel application.

A fault tolerant control approach for a three-stage cascaded multilevel solid state transformer

A solid state transformer (SST) is going to be a vital part of the future grid due to its attractive features such as step-up/step-down of grid voltage, provision for an intermediate DC bus to interface renewable energy source and energy storage, controlled bidirectional power flow between two girds etc. Even though the reliability of the SST is questioned due to high switching device count, redundant modules can be integrated into the SST architecture to ensure uninterrupted operation. Unlike the high short circuit current withstanding capability of the passive copper windings in a conventional iron-and-copper based transformer, an SST can fail in the event of any fault due to the limited over current rating of the switching devices. Several fault identification and isolation techniques for the power converters have been researched, but the power converter operation during the time frame between fault isolation and post fault restoration was neglected. In this paper, the grid current and sub-module capacitor voltage deviations are analysed during the time frame between fault isolation and post-fault restoration. A new control approach is proposed to improve the fault tolerance of the SST by identifying a short circuit fault and limit the short circuit current before a healthy module is brought into operation i.e., post-fault restoration. In the proposed method, the control is designed to switch from the conventional control to a fault tolerant control scheme in the event of fault. The proposed control method is validated using the PLECS real time (RT) hardware-in-loop (HIL) platform and results are presented.

Battery energy storage in standalone microgrid: Synchronization and transfer between operating modes

This paper presents control scheme for a standalone microgrid having a non-dispatchable fixed-pitch variable-speed wind turbine generator (WTG) and a battery energy storage (BES). The WTG is directly interfaced at a point of common coupling (PCC) and the BES is interfaced at the PCC via a bidirectional DC-AC converter. The unique aspect of the control strategy is that the BES not only regulates voltage and frequency at the PCC by active-reactive power compensation, but also ensures proper synchronization and disconnection of WTG during the wind velocity variations for seamless transfer between these operating modes with and without WTG, while providing an uninterruptible supply to critical load. Performance under each operating mode and transitions is tested through modeling and implementation of control algorithm in MATLAB/Simulink environment to demonstrate the capability of the scheme.

Optimal scheduling of diesel generators in offshore support vessels to minimize fuel consumption

This paper presents optimal generation scheduling for minimization of fuel consumption (FC) in an offshore support vessel with a dynamic positioning system and diesel generator (DG) sets of 8000 kW total capacity. FC is analyzed for equal load sharing among equal capacity DGs, optimal load sharing among equal capacity DGs, and optimal load sharing among unequal capacity DGs. Due to nonlinear specific FC (SFC) curves of the diesel engines, a Genetic Algorithm is used for optimal load sharing. The SFC-vs-load relationship obtained from Brake SFC (BSFC) map of the diesel engines is characterized using a cubic spline interpolation. A solution to the problem is attained by comparing yearly fuel consumption in the three cases for the load profile of target vessel. This method can be applied to any vessel equipped with multiple generating units. A vessel with proper selection of DG capacities and closed bus-tie can achieve maximum fuel savings; however, when deciding the DG capacity and load scheduling, it is necessary to consider fuel consumption alongside concerns such as optimizing exhaust emissions after-treatment, ensuring adequate power availability for essential services, and scheduling engine maintenance.