Voltage regulation and stabilization of DC/DC buck converter under constant power loading
01 Dec 2014-pp 1-6
TL;DR: In this article, a sliding mode controller is proposed which ensures supply of constant power demanded by the CPL and tight voltage regulation (error less than 0.1 V) of the output voltage.
Abstract: The low and medium voltage renewable energy based dc distribution systems are catching increased attention world-wide due to their inherent benefits over ac systems. Higher efficiency, simple control, more suitable for integration of the sources producing dc power, are some of the main benefits of the dc systems. However, these systems are prone to serious stability issues caused by the constant power load (CPL) nature of the point-of-load converters (POLs). This paper deals with the stabilization and voltage regulation of dc/dc buck converter feeding a combination of the constant voltage resistive load (CVL) and CPL in a dc micro-grid application. A sliding mode controller is proposed which ensures supply of constant power demanded by the CPL and tight voltage regulation (error less than 0.1 V) of the output voltage. The effectiveness of the controller is validated through simulation results under different operating conditions. It is shown that the controller is robust to the large changes in supply voltage and the load.
Citations
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TL;DR: In this paper, the authors present state-of-the-art and research needs in dc distributed power systems in one article, and a review of stability criteria used to study the stability of dc power systems are reviewed with their merits and limitations.
Abstract: The penetration of dc distributed power systems is increasing rapidly in electric power grids and other isolated systems to cater demand for cheap, clean, high quality, and uninterrupted power demand of modern society. DC systems are more efficient and suite better to integrate some of the renewable energy sources, storage units, and dc loads. A dc distributed power system usually consists of large number of power electronic converters connected in cascad0ed configuration to satisfy the power quality and voltage magnitude requirements of the sources and loads. Tightly-regulated power converters in the aforementioned settings exhibit negative incremental impedance and behave as constant power loads (CPLs), and tend to destabilize their feeder systems and upstream converters. The presence of CPLs reduces effective damping of the system leading to instability of the whole system and present significant challenge in the system operation and control. In-depth knowledge of the instability effects of constant power loads (CPLs), available stabilizing techniques and stability analysis methods, is imperious to the young researchers, system designers, system integrators, and practicing engineers working in the field of dc power systems and emerging applications of dc power. This paper is intended to fill this gape by documenting present state of the art and research needs in one article. Modeling, behaviour and effects of typical CPL are discussed and a review of stability criteria used to study the stability of dc power systems are reviewed with their merits and limitations. Furthermore, available literature is reviewed to summarize the techniques to compensate the CPL effect. Finally, discussion and recent challenges in the dc distribution systems.
160 citations
Cites background from "Voltage regulation and stabilizatio..."
...Authors in [92], have proposed a PWM based sliding mode control using a nonlinear switching function, to mitigate negative impedance instabilities in a dc/dc buck converter supplying mixed load (CPL and CVL)....
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TL;DR: In this paper, the authors provide a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I), and its dynamic behaviors on the μ-grid, and power system distribution.
Abstract: This paper provides a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I) and its dynamic behaviours on the μgrid, and power system distribution (PSD). In general, a μgrid is defined as a cluster of different types of electrical loads and renewable energy sources (distributed generations) under a unified controller within a certain local area. It is considered a perfect solution to integrate renewable energy sources with loads as well as with a traditional grid. In addition, it can operate with a conventional grid, for example, by energy sourcing or a controllable load, or it can operate alone as an islanding mode to feed required electric energy to a grid. Hence, one of the important issues regarding the μgrid is the constant power load that results from the tightly designed control when it is applied to power electronic converters. The effect of CPL is incremental negative resistance that impacts the power quality of a power system and makes it at negative damping. Also, in this paper, a comprehensive study on major control and compensation techniques for μgrid has been included to face the instability effects of constant power loads. Finally, the merits and limitations of the compensation techniques are discussed.
101 citations
Cites background from "Voltage regulation and stabilizatio..."
...In [77] the stable sliding surface (s), shown in Figure 13a, is designed to obtain system control law (u) is to meet the system stability requirements with reference values for the inductor current and capacitor voltage....
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TL;DR: An intelligent proportional-integral based on sliding mode (SM) observer to mitigate the destructive impedance instabilities of nonideal CPLs with time-varying nature in the ultralocal model sense is addressed.
Abstract: The nonlinearities and unmodeled dynamics inevitably degrade the quality and reliability of power conversion, and as a result, pose big challenges on higher-performance voltage stabilization of dc–dc buck converters. The stability of such power electronic equipment is further threatened when feeding the nonideal constant power loads (CPLs) because of the induced negative impedance specifications. In response to these challenges, the advanced regulatory and technological mechanisms associated with the converters require to be developed to efficiently implement these interface systems in the microgrid configuration. This article addresses an intelligent proportional-integral based on sliding mode (SM) observer to mitigate the destructive impedance instabilities of nonideal CPLs with time-varying nature in the ultralocal model sense. In particular, in the current article, an auxiliary deep deterministic policy gradient (DDPG) controller is adaptively developed to decrease the observer estimation error and further ameliorate the dynamic characteristics of dc–dc buck converters. The design of the DDPG is realized in two parts: (i) an actor-network which generates the policy commands, while (ii) a critic-network evaluates the quality of the policy command generated by the actor. The suggested strategy establishes the DDPG-based control to handle for what the iPI-based SM observer is unable to compensate. In this application, the weight coefficients of the actor and critic networks are trained based on the reward feedback of the voltage error, by using the gradient descent scheme. Finally, to investigate the merits and implementation feasibility of the suggested method, some experimental results on a laboratory prototype of the dc–dc buck converter, which feeds a time-varying CPL, are presented.
62 citations
Cites background from "Voltage regulation and stabilizatio..."
...The readers can refer to [39], [40] to acquire more information about the modeling of dc–dc power Buck converters feeding CPLs....
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TL;DR: It is found that the proposed control scheme ensures desired operation of the DC micro-grid under various operating modes and maintains system stability with CPL under variations in the primary resource and load demand.
Abstract: In recent years DC micro-grid has been widely accepted as one of the promising solutions to integrate renewable energy sources and to supply power to critical loads such as data centres, remote villages and communication stations However, DC micro-grid has a fundamental stability challenge due to constant power load (CPL) characteristics of point-of-load converters, which introduce destabilising effect in the system This study presents a sliding mode control based non-linear control scheme for a solar photo-voltaic based DC micro-grid in the presence of CPLs The objective of the proposed control scheme is to tightly regulate the DC bus voltage and mitigate the destabilising effects of CPLs The stability of the system is analytically established and a limit of CPL is obtained Furthermore, a charging/discharging algorithm is implemented for battery bank interfacing bidirectional converter which facilitates three modes charging namely constant current, constant voltage, and float mode, to enhance the battery life The validation of the effectiveness of the proposed scheme is done through simulation and experimental results It is found that the proposed control scheme ensures desired operation of the DC micro-grid under various operating modes and maintains system stability with CPL under variations in the primary resource and load demand
36 citations
01 Nov 2017
TL;DR: The fuzzy logic controller is design to ensure the stabilization of buck converter under change the constant power load and tight voltage regulation after transient response by choosing the proper duty cycle for each cycle.
Abstract: Load converter is the second stage of multiconverter electronic power system. Under tight control, the converter acts as constant power load (CPL). The CPL has innate incremental negative resistance properties (INR). The INR influence the power quality of system. In this paper, the proposed fuzzy logic controller aims to regulate the voltage of dc-dc buck converter which is feeding the CPL and the resistive load. The fuzzy logic controller is design to ensure the stabilization of buck converter under change the constant power load and tight voltage regulation after transient response by choosing the proper duty cycle for each cycle. The fuzzy logic controller is validated by simulation in MATLAB/Simulink.
29 citations
References
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21 Nov 2011
TL;DR: In this article, a typical structure of multi-stage converters present in direct current (dc) distribution systems is examined, and an analysis of the open loop dynamic behavior of the line regulating converter feeding CPLs is performed.
Abstract: This paper examines a typical structure of multi-stage converters present in direct current (dc) distribution systems. In such electric power distribution systems, point-of-load converters behave as a constant power load (CPL). Such loads may result in destabilizing nonlinear effects to their supply bus voltage. An analysis of the open loop dynamic behavior of the line regulating converter feeding CPLs is performed. This analysis gives the background to understand the proposed washout sliding mode controller to regulate the dc bus voltage under constant impedance load (CIL) and CPL changes. Also, the operating limits of the controlled system are determined in terms of the maximum power drained by CPL and CIL connected to the bus. The theoretical analysis is validated through simulation results.
20 citations
"Voltage regulation and stabilizatio..." refers methods in this paper
...In [14], authors have proposed sliding mode controller using a washout filter for dc/dc buck converter and bidirectional dc/dc converter [13], [15] feeding a combination of resistive and CPL in a dc micro-grid....
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11 Sep 2014
TL;DR: In this article, a sliding-mode controller with a non-linear sliding surface is proposed to ensure large signal stability in DC micro-grid, which is able to mitigate CPL effect of tightly regulated POLs and ensure stable operation of DC microgrid under various disturbances.
Abstract: It has been an established fact that the presence of Constant Power Load (CPL) in DC micro-grid causes instability as it has negative impedance characteristic. This poses a serious challenge for the stability of the DC micro-grid in spite of ensuring stability of individual converters. Some efforts are made by the community to address the issue. In this paper, we have proposed a sliding-mode controller with a non-linear sliding surface to ensure large signal stability. The proposed non-linear surface ensures that constant power is maintained by the converter. The proposed controller is able to mitigate CPL effect of tightly regulated POLs and ensures stable operation of DC micro-grid under various disturbances. Proposed controller is implemented on a typical DC micro-grid feeding a CPL. The theoretical development is verified through simulations in MATLAB Simulink environment.
15 citations
"Voltage regulation and stabilizatio..." refers methods in this paper
...Sliding mode control approach have also been applied to stabilize dc/dc converters against CPL induced instabilities [1], [2], [7], [10]–[15]....
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TL;DR: A delayed feedback controller that can converge the bus voltage exactly on an unstable operating point without accurate information and can track it using tiny control energy even when a system parameter is slowly varied demonstrate that delayed feedback control can be considered a strong candidate for solving the destabilizing problem.
Abstract: This paper tackles a destabilizing problem of a direct-current (dc) bus system with constant power loads, which can be considered a fundamental problem of dc power grid networks. The present paper clarifies scenarios of the destabilization and applies the well-known delayed-feedback control to the stabilization of the destabilized bus system on the basis of nonlinear science. Further, we propose a systematic procedure for designing the delayed feedback controller. This controller can converge the bus voltage exactly on an unstable operating point without accurate information and can track it using tiny control energy even when a system parameter, such as the power consumption of the load, is slowly varied. These features demonstrate that delayed feedback control can be considered a strong candidate for solving the destabilizing problem.
14 citations
"Voltage regulation and stabilizatio..." refers methods in this paper
...Some of the techniques among many others, proposed in the literature for the stabilization of the CPL induced instabilities are power shaping based Brayton-Mayer’s mixed potential function [3], coupling induced open loop stabilization [5], [6], and sliding mode control....
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01 Nov 2013
TL;DR: A nonlinear sliding mode controller based on a proportional-integral controller is proposed to regulate the bus voltage under unknown load variations and the proposed methodology is validated trough simulation and experimental results.
Abstract: In this work, a typical structure of cascaded converters present in DC microgrids is analyzed. From the control point of view, converters acting as loads add a nonlinear effect to the supply bus, caused by its constant power load behavior. A realistic analysis of the equivalent load is presented. The open loop dynamics of the system is discussed, taking into account the equivalent load profile. A nonlinear sliding mode controller based on a proportional-integral controller is proposed to regulate the bus voltage under unknown load variations. The proposed methodology is validated trough simulation and experimental results.
13 citations
"Voltage regulation and stabilizatio..." refers methods in this paper
...In [14], authors have proposed sliding mode controller using a washout filter for dc/dc buck converter and bidirectional dc/dc converter [13], [15] feeding a combination of resistive and CPL in a dc micro-grid....
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...Sliding mode control approach have also been applied to stabilize dc/dc converters against CPL induced instabilities [1], [2], [7], [10]–[15]....
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01 Dec 2014
TL;DR: In this article, a PWM-based sliding mode controller for negative impedance stabilization of dc-dc converters in a dc micro-grid is presented, and simulated response validates the effectiveness of the proposed controller with variations in input voltage and the load.
Abstract: DC micro-grids are getting increased attention around the world due to the paradigm shift in electricity generation and changing nature of the modern electrical loads. However, one of the major issues with dc micro-grids and other multi-converter systems is stabilization of the system against negative impedance instabilities caused by negative incremental resistance behavior of tightly regulated point-of-load converters. This paper presents a PWM based sliding mode controller for negative impedance stabilization of dc-dc converters in a dc micro-grid. The existence of sliding modes is proved. The proposed controller and simplified dc micro-grid are modeled in MATLAB SIMULINK and simulated response is studied to check the suitability of the proposed controller. Simulated response validates the effectiveness of the proposed controller with variations in the input voltage and the load.
3 citations
"Voltage regulation and stabilizatio..." refers background or methods in this paper
...The non-linear switching function proposed in [11], [12] is used to design SMC for a buck converter system of Fig....
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...In this paper, we present discontinuous SMC based on the surface proposed in [11], [12] for the voltage regulation and stabilization of a dc/dc buck converter against CPL induced instabilities in a dc micro-grid scenario....
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...In [11], [12] have proposed nonlinear surface based discontinuous and PWM SMC for a boost converter feeding a purely constant power load....
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