Constant power loads: A solution using sliding mode control
01 Oct 2014-pp 1989-1995
TL;DR: A sliding-mode controller with a non-linear sliding surface to mitigate negative impedance instabilities caused by the CPLs in dc distribution systems (dc Micro-grids) and ensures stable operation of dc micro-grid system under various disturbances is proposed.
Abstract: Rapidly increasing penetration of renewable energy sources into conventional power distribution systems has led to the rise in power electronic converter dominated power distribution systems. However, it has been a well established that the presence of tightly regulated point-of-load (POL) converters in the power distribution system, which act as Constant Power Loads (CPLs), cause serious stability challenge in spite of ensuring stability of individual converters. In this paper, we propose a sliding-mode controller with a non-linear sliding surface to mitigate negative impedance instabilities caused by the CPLs in dc distribution systems (dc Micro-grids). The stability of proposed surface and existence of sliding modes are proved. A simplified structure of a dc micro-grid system with dc/dc boost converter and CPL is used for the implementation of the proposed controller. Proposed controller is able to mitigate negative impedance instabilities and ensures stable operation of dc micro-grid system under various disturbances. The performance of the proposed controller, under steady state, line and load variations are validated through simulations in MATLAB Simulink environment.
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 or methods from "Constant power loads: A solution us..."
...Mitigation of CPL induced instabilities in a dc/dc boost converter with a pure CPL has been presented in [93,79] using a nonlinear switching function based sliding mode controller....
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...The major drawbacks of this approach are its noise sensitivity due to the presence of differentiator and slower transient response compared to techniques which handle CPL nonlinearity directly, such as sliding mode control and synergetic control [79,80]....
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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
TL;DR: A comprehensive review is presented on accomplished research work on stabilization of dc and ac microgrid system stabilization techniques, which can basically be classified as compensation done at feeder side; by adding intermediate circuitry; and at load side.
Abstract: Microgrid, because of its advantages over conventional utility grids, is a prudent approach to implement renewable resource-based electricity generation. Despite its advantages, microgrid has to operate with a significant proportion of constant power loads that exhibit negative incremental impedance and thus cause serious instability in the system. In this paper, a comprehensive review is presented on accomplished research work on stabilization of dc and ac microgrid. After reviewing these, microgrid system stabilization techniques are classified with required discussions. As found out in this paper, the stabilization techniques can basically be classified as compensation done: 1) at feeder side; 2) by adding intermediate circuitry; and 3) at load side. Finally, after analyzing the merits and drawbacks of each generalized technique, several infographics are presented to highlight the key findings of this paper.
82 citations
Cites methods from "Constant power loads: A solution us..."
...By using a sliding mode controller, a sliding surface has been established to stabilize the voltage of the entire system [34]....
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TL;DR: In this paper, the cascade connection of two dc-dc switching converters for constant power supply was studied. But the source converter is of boost type while the load converter was of buck type.
Abstract: The cascade connection of two dc-dc switching converters for constant power supply is studied. The source converter is of boost type while the load converter is of buck type. The natural unstable behaviour of the cascade connection for both on and off states of the boost converter is counteracted by a sliding-mode control strategy that combines unstable trajectories to generate a stable one for the regulated boost converter dynamics. Experimental results using an electronic load to emulate a buck converter-based constant power load are in good agreement with the theoretical predictions. A similar agreement is later obtained when a buck converter with a dynamic behaviour close to an instantaneous constant power load is employed instead of the electronic load.
51 citations
TL;DR: A robust pulse-width modulation-based type-II fuzzy controller for a dc/dc boost converter feeding the CPL in a dc MG and the experimental results demonstrate that the proposed intelligent controller has a faster and more robust response in comparison to the previously suggested control techniques.
Abstract: The negative impedance characteristic of the constant power loads (CPLs) causes instability in dc/dc converters in the dc microgrids (MGs). To improve the stability of the dc/dc converter feeding CPLs, a robust and fast controller is required. This brief presents a robust pulse-width modulation-based type-II fuzzy controller for a dc/dc boost converter feeding the CPL in a dc MG. Theoretical analysis and real-time simulation are presented to demonstrate the effectiveness of the proposed non-integer intelligent controller. Finally, the experimental results demonstrate that the proposed intelligent controller for the dc/dc converter has a faster and more robust response in comparison to the previously suggested control techniques.
50 citations
Cites background from "Constant power loads: A solution us..."
...In [7], a comprehensive comparison of the linear and boundary controllers was presented....
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References
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TL;DR: Sliding-mode and feedback linearization techniques along with large-signal phase plane analysis are presented as methods to analyze, control, and stabilize automotive converters/systems operating with CPLs.
Abstract: Power electronic converters and electric motor drives are being put into use at an increasingly rapid rate in advanced automobiles. However, the new advanced automotive electrical systems employ multivoltage level hybrid ac and dc as well as electromechanical systems that have unique characteristics, dynamics, and stability problems that are not well understood due to the nonlinearity and time dependency of converters and because of their constant power characteristics. The purpose of this paper is to present an assessment of the negative impedance instability concept of the constant power loads (CPLs) in automotive power systems. The main focus of this paper is to analyze and propose design criteria of controllers for automotive converters/systems operating with CPLs. The proposed method is to devise a new comprehensive approach to the applications of power electronic converters and motor drives in advanced automotive systems. Sliding-mode and feedback linearization techniques along with large-signal phase plane analysis are presented as methods to analyze, control, and stabilize automotive converters/systems with CPLs
813 citations
TL;DR: In this article, stability issues in dc microgrids with instantaneous constant-power loads (CPLs) are explored and mitigation strategies such as load shedding, adding resistive loads, filters, or energy storage directly connected to the main bus, and control methods are investigated.
Abstract: This paper explores stability issues in dc microgrids with instantaneous constant-power loads (CPLs). DC microgrids typically have distributed power architectures in which point-of-load converters behave as instantaneous CPLs to line regulating converters located upstream. Constant-power loads introduce a destabilizing effect in dc microgrids that may cause their main bus voltages to show significant oscillations or to collapse. This paper also discusses stabilization strategies to prevent these undesired behaviors from occurring. Mitigating strategies such as load shedding, addition of resistive loads, filters, or energy storage directly connected to the main bus, and control methods are investigated. Advantages and disadvantages of these methods are discussed and recommendations are made. The analysis is verified with simulations and hardware-based experiments.
538 citations
TL;DR: The implementation of novel active-damping techniques on dc/dc converters has been shown and the proposed active- damping method is used to overcome the negative impedance instability problem caused by the CPLs.
Abstract: Multi-converter power electronic systems exist in land, sea, air, and space vehicles. In these systems, load converters exhibit constant power load (CPL) behavior for the feeder converters and tend to destabilize the system. In this paper, the implementation of novel active-damping techniques on dc/dc converters has been shown. Moreover, the proposed active-damping method is used to overcome the negative impedance instability problem caused by the CPLs. The effectiveness of the new proposed approach has been verified by PSpice simulations and experimental results.
422 citations
01 Jan 2001
301 citations
Additional excerpts
...as x1,x2 ∈Ω, ∃ k∗ 1 and k∗ 2 such that for some β1m > 0 [24], [25]:...
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...as x1,x2 ∈Ω, ∃ k̄∗ 1 and k̄∗ 2 such that for some β2m > 0 [24], [25]: β2 x1r(k̄∗ 1 k̄ ∗ 2) (1− k̄∗ 2) < β2m (27)...
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TL;DR: In this paper, the authors present tools allowing large signal stability analysis of a dc power system, which allows estimation of the domain of attraction of the system operating point, and the impact of the load dynamics on stability is also studied.
Abstract: Electric motor drives and power electronic converters have become increasingly common in advanced power systems. Passive LC filters are used in these systems to reduce the power ripples. These filters are usually poorly damped for reducing the losses as well as the size/weight and the cost of the system. This leads to instability phenomena if the load power exceeds a power limit depending on the filter parameters. The purpose of this paper is to present tools allowing large signal stability analysis of a dc power system. These tools allow estimation of the domain of attraction of the system operating point. It will be shown that this large signal stability analysis gives useful hints on the design of the system to optimize the stability criteria for constant and variable power loads. The impact of the load dynamics on stability is also studied. An electric drive connected to a dc power supply through a poorly damped LC filter is used as a case study. The simulations and the experimentations confirm the analytical results.
283 citations