Abstract
Finite control set model predictive control (FCS-MPC) has been widely studied and applied to the power converters and motor drives. It provides the power electronics system with fast dynamic response, nonlinear system formulation, and flexible objectives and constraints integration. However, its variable switching frequency feature also induces severe concerns on the power loss, the thermal profile, and the filter design. Stemming from these concerns, this article investigates the variable switching frequency characteristics of FCS-MPC on the grid-connected inverters. An intuitive relationship between the switching frequency and the magnitude of the converter output voltage is proposed through the geometry analysis, where the switching frequency is maximized when the converter output voltage is around one-third of the DC bus voltage and decreasing when the output voltage moves away from this value. The impacts of this variable switching frequency property on the power loss and current harmonics are also analyzed. Simulation and experimental results both verify the proposed property. With this intrinsic property, FCS-MPC can autonomously achieve a less-varying temperature profile of power modules and an improved reliability compared with the conventional control strategy.
Highlights
Power converters are playing a significant role in the distributed energy resource (DER) systems to transmit and synchronize the power from the front-end renewable energy mechanisms to the main utility grid
The most common layout in these DER systems is designed with a grid side converter unit which is interconnected between the DC bus and the main utility grid [1]
In finite control set model predictive control (MPC) (FCS-MPC), it is the problem formulation, which consists of the objective functions, the input variables and the constraints, that determines the steady state of the power converter, including the specific switching frequency
Summary
Power converters are playing a significant role in the distributed energy resource (DER) systems to transmit and synchronize the power from the front-end renewable energy mechanisms to the main utility grid. Thereby, a stricter filter design has to be considered to cover a wider frequency spectrum for the converter controlled by FCS-MPC Suffering from these impacts of the variable switching frequency property, several researchers manipulate the problem formulation or add a switching penalty objective function to either fix or limit the switching frequency [34][41]. In FCS-MPC, it is the problem formulation, which consists of the objective functions, the input variables and the constraints, that determines the steady state of the power converter, including the specific switching frequency. At this point, the basic problem formulation with the current vector objective function, which is widely used in power electronics systems, is focused in this paper. The experimental validations and one application to reduce the thermal stress are given in Section V, and conclusions come to the last
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