4,620 research outputs found
Exploitation of Digital Filters to Advance the Single-Phase T/4 Delay PLL System
With the development of digital signal processing technologies, control and monitoring of power electronics conversion systems have been evolving to become fully digital. As the basic element in the design and analysis phases of digital controllers or filters, a number of unit delays (z-1) have been employed, e.g., in a cascaded structure. Practically, the number of unit delays is designed as an integer, which is related to the sampling frequency as well as the ac signal fundamental frequency (e.g., 50 Hz). More common, the sampling frequency is fixed during operation for simplicity and design. Hence, any disturbance in the ac signal will violate this design rule and it can become a major challenge for digital controllers. To deal with the above issue, this paper first exploits a virtual unit delay (zv-1) to emulate the variable sampling behavior in practical digital signal processors with a fixed sampling rate. This exploitation is demonstrated on a T/4 Delay Phase Locked Loop (PLL) system for a single-phase grid-connected inverter. The T/4 Delay PLL requires to cascade 50 unit delays when implemented (for a 50-Hz system with 10 kHz sampling frequency). Furthermore, digital frequency adaptive comb filters are adopted to enhance the performance of the T/4 Delay PLL when the grid suffers from harmonics. Experimental results have confirmed the effectiveness of the digital filters for advanced control systems
Power Talk in DC Micro Grids: Constellation Design and Error Probability Performance
Power talk is a novel concept for communication among units in a Micro Grid
(MG), where information is sent by using power electronics as modems and the
common bus of the MG as a communication medium. The technique is implemented by
modifying the droop control parameters from the primary control level. In this
paper, we consider power talk in a DC MG and introduce a channel model based on
Thevenin equivalent. The result is a channel whose state that can be estimated
by both the transmitter and the receiver. Using this model, we present design
of symbol constellations of arbitrary order and analyze the error probability
performance. Finally, we also show how to design adaptive modulation in the
proposed communication framework, which leads to significant performance
benefits.Comment: IEEE SmartGridComm 201
Analysis and mitigation of dead time harmonics in the single-phase full-bridge PWM converters with repetitive controllers
In order to prevent the power switching devices (e.g., the Insulated-Gate-Bipolar-Transistor, IGBT) from shoot through in voltage source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in Pulse-Width Modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as "dead time harmonics" hereafter) have to be compensated in order to achieve a satisfactory current quality as required by standards. In this paper, the emission mechanism of dead time harmonics in single-phase PWM inverters is thus presented considering the modulation schemes in details. More importantly, a repetitive controller has been adopted to eliminate the dead time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional resonant-based
fundamental current controller so as to mitigate the dead time harmonics and also maintain the control of the fundamental frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead time harmonics and other low-order distortions, and also it is a simple method without hardware modifications
Fast Adaptive Robust Differentiator Based Robust-Adaptive Control of Grid-Tied Inverters with a New L Filter Design Method
In this research, a new nonlinear and adaptive state feedback controller with a fast-adaptive robust differentiator is presented for grid-tied inverters. All parameters and external disturbances are taken as uncertain in the design of the proposed controller without the disadvantages of singularity and over-parameterization. A robust differentiator based on the second order sliding mode is also developed with a fast-adaptive structure to be able to consider the time derivative of the virtual control input. Unlike the conventional backstepping, the proposed differentiator overcomes the problem of explosion of complexity. In the closed-loop control system, the three phase source currents and direct current (DC) bus voltage are assumed to be available for feedback. Using the Lyapunov stability theory, it is proven that the overall control system has the global asymptotic stability. In addition, a new simple L filter design method based on the total harmonic distortion approach is also proposed. Simulations and experimental results show that the proposed controller assurances drive the tracking errors to zero with better performance, and it is robust against all uncertainties. Moreover, the proposed L filter design method matches the total harmonic distortion (THD) aim in the design with the experimental result
Multiuser Communication through Power Talk in DC MicroGrids
Power talk is a novel concept for communication among control units in
MicroGrids (MGs), carried out without a dedicated modem, but by using power
electronics that interface the common bus. The information is transmitted by
modulating the parameters of the primary control, incurring subtle power
deviations that can be detected by other units. In this paper, we develop power
talk communication strategies for DC MG systems with arbitrary number of
control units that carry out all-to-all communication. We investigate two
multiple access strategies: 1) TDMA, where only one unit transmits at a time,
and 2) full duplex, where all units transmit and receive simultaneously. We
introduce the notions of signaling space, where the power talk symbol
constellations are constructed, and detection space, where the demodulation of
the symbols is performed. The proposed communication technique is challenged by
the random changes of the bus parameters due to load variations in the system.
To this end, we employ a solution based on training sequences, which
re-establishes the signaling and detection spaces and thus enables reliable
information exchange. The presented results show that power talk is an
effective solution for reliable communication among units in DC MG systems.Comment: Multiuser extension of the power talk concept. Submitted to IEEE JSA
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