C. Rivetta

Bio: C. Rivetta is an academic researcher from Illinois Institute of Technology. The author has contributed to research in topics: Buck converter & Converters. The author has an hindex of 6, co-authored 6 publications receiving 989 citations.

Constant power loads and negative impedance instability in automotive systems: definition, modeling, stability, and control of power electronic converters and motor drives

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

Analysis and control of a buck DC-DC converter operating with constant power load in sea and undersea vehicles

Abstract: Power-electronics-based zonal direct current (dc) power distribution systems are being considered for sea and undersea vehicles. The stability of the dc power-electronics-based power distribution systems is a significant design consideration because of the potential for negative-impedance-induced instabilities. In this paper, the dynamic properties and control of a buck converter feeding a downstream dc-dc converter are studied. The controller in this system combines an instantaneous current feedback loop using hysteresis with a proportional-integral (PI) algorithm to regulate the output voltage of the converter. Based on a large-signal-averaged model of the converter, the stability-in-large around the operation point is presented. The complete analysis is carried out considering a buck dc-dc converter operating with a constant power load (CPL). Simulations and experimental results are provided to verify the analysis.

Constant power loads and negative impedance instability in sea and undersea vehicles: statement of the problem and comprehensive large-signal solution

Abstract: Power electronic converters are usually loaded by passive loads or combinations of passive elements and voltage and current sources. However, there is an emerging vehicular system configuration where converters are loaded by power converters and a better model for the load is a constant power model. This converter operation appears in multi-converter applications such as advanced sea and undersea vehicles where a main converter has as loads a set of converters operating in closed-loop with tight output voltage regulation. This set of converters present at the input terminals a dynamic behavior similar to a constant power load (CPL) for a range of input voltages and a frequency span that ranges from DC up to the bandwidth of the converters. The primary goal of this paper is the development and extension of a technique for large-signal analysis of power electronic converters operating with constant power loads in sea and undersea vehicles using a phase plane analysis. This proposed approach could be used to present advantages and limitations of different controllers and, based on that analysis, define the selection and synthesis of controllers to achieve the required performance and robustness of the system.

Large-signal analysis of a DC-DC buck power converter operating with constant power load

Abstract: The dynamic properties of the buck converter operating with a constant power load are studied in this paper This configuration is present in DC-DC converters feeding power converters tightly regulated in multi-converter power electronics systems The dynamic behavior of converters loaded by constant power loads differs from the behavior of converters loaded by resistors or current generators The purpose of this paper is to address the closed-loop behavior of the buck converter feeding a constant power load Based on a comprehensive large-signal analysis of the converter, the basin of attraction of the equilibrium point is defined This region, in general, excludes the low range of the output voltage affecting the transient stability, forcing proper coordination between the converter and loads during start-up

Large-signal analysis and control of buck converters loaded by DC-DC converters

Abstract: The dynamic behavior of the buck converter feeding downstream DC-DC converters is studied in this paper. DC-DC converters acting as a load are modeled as constant power loads except at low voltage, where the behavior of the start-up circuitry is included. A comprehensive large-signal analysis of a buck converter including over-current protection and feeding the described load is performed. This paper addresses the transient process of the converter's start-up and turn on/off of loads consisting of DC-DC converters and gives design considerations to assess performance and stability robustness of a simple proportional-derivative controller.

DC Microgrids—Part I: A Review of Control Strategies and Stabilization Techniques

Abstract: This paper presents a review of control strategies, stability analysis, and stabilization techniques for dc microgrids (MGs). Overall control is systematically classified into local and coordinated control levels according to respective functionalities in each level. As opposed to local control, which relies only on local measurements, some line of communication between units needs to be made available in order to achieve the coordinated control. Depending on the communication method, three basic coordinated control strategies can be distinguished, i.e., decentralized, centralized, and distributed control. Decentralized control can be regarded as an extension of the local control since it is also based exclusively on local measurements. In contrast, centralized and distributed control strategies rely on digital communication technologies. A number of approaches using these three coordinated control strategies to achieve various control objectives are reviewed in this paper. Moreover, properties of dc MG dynamics and stability are discussed. This paper illustrates that tightly regulated point-of-load converters tend to reduce the stability margins of the system since they introduce negative impedances, which can potentially oscillate with lightly damped power supply input filters. It is also demonstrated that how the stability of the whole system is defined by the relationship of the source and load impedances, referred to as the minor loop gain. Several prominent specifications for the minor loop gain are reviewed. Finally, a number of active stabilization techniques are presented.

Eliminate Reactive Power and Increase System Efficiency of Isolated Bidirectional Dual-Active-Bridge DC–DC Converters Using Novel Dual-Phase-Shift Control

Abstract: This paper proposes a novel dual-phase-shift (DPS) control strategy for a dual-active-bridge isolated bidirectional DC-DC converter. The proposed DPS control consists of a phase shift between the primary and secondary voltages of the isolation transformer, and a phase shift between the gate signals of the diagonal switches of each H-bridge. Simulation on a 600-V/5-kW prototype shows that the DPS control has excellent dynamic and static performance compared to the traditional phase-shift control (single phase shift). In this paper, the concept of ldquoreactive powerrdquo is defined, and the corresponding equations are derived for isolated bidirectional DC-DC converters. It is shown that the reactive power in traditional phase-shift control is inherent, and is the main factor contributing to large peak current and large system loss. The DPS control can eliminate reactive power in isolated bidirectional DC-DC converters. In addition, the DPS control can decrease the peak inrush current and steady-state current, improve system efficiency, increase system power capability (by 33%), and minimize the output capacitance as compared to the traditional phase-shift control. The soft-switching range and the influence of short-time-scale factors, such as deadband and system-level safe operation area, are also discussed in detail. Under certain operation conditions, deadband compensation can be implemented easily in the DPS control without a current sensor.

Constant power loads and negative impedance instability in automotive systems: definition, modeling, stability, and control of power electronic converters and motor drives

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

Dynamic Behavior and Stabilization of DC Microgrids With Instantaneous Constant-Power Loads

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.

Review on Control of DC Microgrids and Multiple Microgrid Clusters

Abstract: This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors’ point of view, are also provided in the final concluding part.