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Über dieses Buch

This book focuses on the mitigation of the destabilizing effects introduced by constant power loads (CPLs) in various non-isolated DC/DC converters and island DC microgrids using a robust non-linear sliding mode control (SMC) approach. This book validates theoretical concepts using real-time simulation studies and hardware implementations. Novel sliding mode controllers are proposed to mitigate negative impedance instabilities in DC/DC boost, buck, buck-boost, bidirectional buck-boost converters, and islanded DC microgrids. In each case, the condition for the large-signal stability of the converter feeding a CPL is established. An SMC-based nonlinear control scheme for an islanded DC microgrid feeding CPL dominated load is proposed so as to mitigate the destabilizing effect of CPL and to ensure system stability under various operating conditions. A limit on CPL power is also established to ensure system stability. For all proposed solutions, simulation studies and hardware implementations are provided to validate the effectiveness of the proposed sliding mode controllers.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

In this an introduction to DC distributed power systems, Constant Power Loads (CPLs) and its behaviour is presented. Analysis of small-signal stability of generalised and converter based DC systems with CPL is also presented in this chapter. Furthermore, a brief review of major techniques to mitigate CPL induced instabilities is presented, followed by motivation and organization of the book.
Deepak Kumar Fulwani, Suresh Singh

Chapter 2. Stabilization of a Buck Converter Feeding a Mixed Load Using SMC

A buck converter is usually used in a dc distribution system to step-down the dc voltage, either to extend the primary distribution for low voltage applications or to meet a specific low voltage requirement of a load. This chapter presents stabilization of CPL induced destabilizing effects in DC/DC buck converter with CPL and a resistive load using Sliding Mode Control (SMC) approach. Nonlinear switching function based discontinuous and PWM based SMCs are proposed. The existence of sliding mode and stability of switching surface are established. The proposed theory is validated through simulation studies and experimentations. The proposed controllers are robust with respect to the sufficiently large variations in the input voltage and load. However, it was found from experimental results that PWM based SMC is sensitive to the slow variations in the supply.
Deepak Kumar Fulwani, Suresh Singh

Chapter 3. Mitigation of Destabilizing Effects of CPL in a Boost Converter Feeding Total CPL

In dc microgrids, a dc/dc boost converter is usually required to interface renewable energy sources (solar PV, fuel cells etc.) to the dc bus or to meet the high voltage requirement of certain loads. In such situations, due to tight regulation of downstream power converter and the presence of other electronic loads, the equivalent load to the boost converter may exhibit CPL behaviour. In this chapter, the mitigation of CPL induced instabilities in a boost converter is addressed using a robust SMC designed using novel nonlinear switching functions. A PWM based SMC is presented to mitigate the destabilizing effects of CPL in a boost converter supplying a CPL. The existence of sliding mode and large-signal stability of the system are proved. The effectiveness of the controller is validated through simulation studies and experimental results under different operating conditions. Furthermore, a modified nonlinear switching function is proposed which incorporates tight voltage regulation capability. The modified nonlinear switching function, having inherent characteristics to ensure supply of constant power to CPL and output voltage regulation, is then used to design a discontinuous sliding mode controller. The existence of sliding mode and stability of the switching function are proved. A limit on the CPL power is established to ensure system stability under different operating conditions. The performance of the proposed controller is validated through real-time simulation results under sufficiently wide variations in the input voltage and the load.
Deepak Kumar Fulwani, Suresh Singh

Chapter 4. Compensation of CPL Effects in a Bidirectional Buck-Boost Converter

The compensation of CPL induced destabilizing effects in a bidirectional dc/dc converter (BDC), interfacing a storage unit in a typical isolated dc microgrid is presented in this chapter. The net CPL power (aggregate of power produced from RESs operating in MPPT mode and exhibiting constant power source characteristics, and CPL) is used to select the operating mode of the BDC. A robust sliding mode controller for BDC is proposed to ensure tight regulation of dc bus voltage and system stability in different operating modes. The existence of sliding mode and system stability are established analytically. The effectiveness of the controller is validated through real-time simulation studies using Opal-RT Digital Simulator. The controller demonstrates the dc bus regulation within tight limits and robustness with respect to the sufficiently large variations in the net power demand.
Deepak Kumar Fulwani, Suresh Singh

Chapter 5. Robust Control of an Islanded DC Microgrid in Presence of CPL

This chapter presents robust control of an islanded DC microgrid in the presence of CPL using sliding mode control. A robust sliding mode control scheme is proposed to ensure system stability in the presence of CPL and the desired DC bus voltage regulation. Furthermore, a charging/discharging algorithm is implemented in the control loops of BDC to facilitate three mode charging of the battery bank. The test system consists of solar PV arrays interfaced to dc bus through dc/dc boost converters, energy storage system (lead-acid batteries) interfaced through a BDC, and a mixed load (Resistive, voltage regulator and a speed controlled drive). Tightly regulated voltage regulator and a speed controlled dc/dc drive, both represent CPLs in the system. The proposed theory is validated through simulation studies and experimental results. It is shown through simulation studies and experimental results that the proposed control scheme ensures stabilized dc bus voltage, i.e. it does not show any destabilizing effect of CPLs, under different operating conditions. It has been found that the proposed control ensures voltage regulation of less than 5 % and is robust to changes in the load.
Deepak Kumar Fulwani, Suresh Singh

Backmatter

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