Abstract
This paper proposes a digital adaptive hysteresis current control method for multi-functional inverters in a power-flow control device called digital grid router. Each inverter can be controlled in master, grid-connected, or stand-alone modes, which can be specified by the controller. While the popular linear sine-triangle pulse width modulation (SPWM) control technique requires complicated proportional-integral (PI) regulators with an unavoidable time delay, hysteresis current control has a simple structure, fast responses, and robustness due to its independent system of parameters. Since the hysteresis current control method controls the output current stay around the reference current directly, in the multi-functional inverter, the reference output is not given by a current directly. Thus, the reference current used to implement the hysteresis current control in this study is calculated from the given reference voltage or power in each control mode. The controller uses high-speed sampled data at MHz level and is implemented by using a field-programmable gate array (FPGA). Experimental results show good performances of the proposed controller in controlling power exchanges in the digital grid router.
Highlights
Nowadays, distributed energy resources have become a solution to address energy security concerns, quality of power grids, and greenhouse gas emission standards in most countries [1,2].The power grid has been developed with various distributed small sources, such as fuel turbines, gas, diesel, and renewable energy generations including photovoltaic, wind turbine, etc
The inverter can supply a given power with the output current is in phase with the grid voltage by using hysteresis current control, where the reference current given by Equation (10), without the complicated PI regulator and phase lock loop (PLL) tool [23]
A digital adaptive hysteresis current control has been proposed for the multi-functional inverter in the digital grid router (DGR), which plays an important role in the digital grid concept
Summary
Since a digital controller usually requires an efficient high sampling frequency at MHz level to control the hysteresis current with an accurate switching time, it is difficult to implement the hysteresis current control on a conventional microcomputer or digital signal processor (DSP), which have the sampling frequency at kHz level [12,13] Calculations for such the high sampling frequency can be implemented on a high-speed field programmable gate array (FPGA), which is being used in more and more applications of the inverter control. We propose a control method for the multi-functional inverter in the DGR using FPGA-based digital adaptive hysteresis current control.
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