Instantaneous Constant Power Loads Research Articles

On Existence of Equilibria of Multi-Port Linear AC Networks With Constant-Power Loads

In this paper we give an answer to the following question. Given a multi-port, linear ac network with instantaneous constant-power loads identify a set of active and reactive load powers for which there is no steady-state operating condition of the network—in this case, we say that the power load is inadmissible . The identification is given in terms of feasibility of simple linear matrix inequalities, and hence it can be easily verified with existing software. For one- or two-port networks, the proposed feasibility test is necessary and sufficient for load power admissibility with the test for the former case depending only on the network data. Two benchmark numerical examples illustrate our results.

An Active Damping Method Based on a Supercapacitor Energy Storage System to Overcome the Destabilizing Effect of Instantaneous Constant Power Loads in DC Microgrids

This paper presents a novel active damping method to overcome instability problems of dc microgrids (MGs) caused by constant power loads (CPLs). This method is implemented based on the existing energy storage system (ESS) in the dc MGs. As an indispensable part in the dc MGs, the ESS in this paper is used for more than just compensating the conventional power unbalance in the system, it has taken an additional responsibility and is used for adjusting the system damping to deal with the instability problems induced by the CPLs as well. First, the stability criteria of a simplified dc MG are analyzed. Based on this, an active damping method that aims at virtually reshaping the loads in the dc MG is introduced. With the proposed method, which is realized by a supercapacitor ESS in this paper, the CPLs in the system are virtually reduced and the resistive loads are virtually increased. Therefore, the destabilizing effect of the CPLs in the dc MG is eliminated. Simulations and experiments are conducted and the effectiveness of the proposed method is verified. This method is suitable to be applied in the dc MG with various elements and variable operation modes.

Nonlinear Analysis of Interconnected Power Converters: A Case Study

In this paper the nonlinear dynamics of interconnected power converters in an islanded direct current (DC) microgrid is analyzed. By using a simplified scheme based on two cascaded converters we analyze the dynamical behavior that can arise from the interconnection of these devices on a common DC bus. Furthermore, in order to address the bus voltage control problem, we propose a Sliding Mode Controller for a DC-DC bidirectional power converter to control the DC bus voltage under instantaneous constant power loads. This class of loads introduces a destabilizing nonlinear effect on the converter through an inverse voltage term that can lead to significant oscillations in the DC bus voltage. Simulation results are shown to illustrate the nonlinear analysis.

Amplitude Death Solutions for Stabilization of DC Microgrids With Instantaneous Constant-Power Loads

Constant-power loads on dc microgrids create a destabilizing effect on the circuit that can lead to severe voltage and frequency oscillations. Amplitude death is a coupling induced stabilization of the fixed point of a dynamical system. This paper applies amplitude death methods to the stabilization problem in this constant-power setting. The amplitude death methods provide an open-loop control solution to stabilize the system. Two methods, one using delay, the other using circuit heterogeneity, are examined. Each method is demonstrated through numerical simulations.

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

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.

Analysis of Boundary Control for Buck Converters With Instantaneous Constant-Power Loads

This paper examines a boundary control for dc-dc buck converters subject to instantaneous constant-power loads. These loads introduce a destabilizing nonlinear effect on the converter through an inverse voltage term that leads to significant oscillations in the main bus voltage or its collapse. Converter dynamics are analyzed in both switching states and the various operating regions of switch interaction with a first-order switching surface (boundary) are identified. Furthermore, sufficient conditions for large-signal stability of the closed-loop system are established. The analysis indicates that a linear switching surface with a negative slope passing through the desired operation point yields a stable operation. It is also shown that instability as well as system-stalling, which we term the invariant-set problem, may still occur in reflective mode. However, a hysteresis band that contains the designed boundary may be used to prevent system-stalling. This hysteresis band also allows for a practical implementation of the controller by avoiding chattering. Design considerations are included and recommendations are given. The theoretical analysis is verified by simulations and experimental results.