517 research outputs found
Theory and Experimental Validation of Two Techniques for Compensating VT Nonlinearities
Inductive instrument transformers (ITs) are still the most used voltage and current sensors in power systems. Among the numerous applications that require their use, one of the most important is surely represented by harmonics measurement. In this case, the recent literature shows that, since they suffer from both a filtering behavior due to their dynamics and from nonlinear effects produced by their iron core, they can introduce errors up to some percent. This article wants to deeply investigate, in the very same experimental conditions, about the performance of two digital signal processing techniques, recently introduced for the improvement of harmonics measurements performed through ITs, namely, SINusoidal characterization for DIstortion COMPensation (SINDICOMP) and compensation of harmonic distortion through polynomial modeling in the frequency domain (PHD). These methods have been applied to two different voltage transformers, having different specifications, by using two measurement setups based on different architectures. The impact of the voltage generator employed during the identification on the achieved accuracy is theoretically and experimentally evaluated. Modified versions of SINDICOMP and PHD compensation, which are more robust against nonidealities of the measurement setup, are presented. The performances of the techniques are evaluated by adopting voltage waveforms similar to those that can be encountered during the normal operation in a real distribution grid
Adaptive Polynomial Harmonic Distortion Compensation in Current and Voltage Transformers Through Iteratively Updated QR Factorization
Measuring current and voltage harmonics has paramount importance for improving the power quality of distribution grids. However, the achieved accuracy strongly depends on the adopted instrument transformer (IT). This article proposes an adaptive technique that enables an effective compensation of both the filtering behavior and the harmonic distortion (HD) introduced by current and voltage transformers (VTs), namely the strongest nonlinear effect at low-order harmonics. The approach is based on a flexible, linear in the parameters polynomial modeling of HD in the frequency domain. Model complexity can be different from one harmonic to the other, and it is selected through an automatic iterative process to suit the nonlinear behavior at each specific harmonic order, while avoiding overfitting. In particular, the number of parameters is increased by progressively updating the QR factorization of the regressor matrix trough Householder reflections until a convergence condition is reached. Experimental tests performed on an inductive VT and current transformer (CT) highlight the effectiveness of the approach
Improving Harmonic Measurements with Instrument Transformers: a Comparison Among Two Techniques
The measurement of harmonics is essential in modern power systems in order to perform distortion level assessment, disturbances source detection and mitigation, etc. In this context, the role of Instrument Transformers (ITs) is crucial, as they are key elements in every power systems measuring instrument. However, inductive ITs, which are still the most widely used, suffer from both a filtering behavior due to their dynamics and from nonlinear effects due to their iron core. The target of this paper is to deeply analyze the performance of two digital signal processing techniques, recently proposed in literature, aimed at mitigating their nonlinear behavior: they are SINDICOMP and the compensation of harmonic distortion through polynomial modeling in the frequency domain. Their performance in improving the measurement of voltage harmonics are analyzed through numerical simulations, by adopting waveforms that can be typically encountered in power systems during normal operating conditions
Electrical stress monitoring of distribution transformers using smart grid techniques
Electrical stresses that distribution transformers rated 16 kVA up to 2 MVA are subjected to can often
cause premature transformer failures. In this study, research related to the development of cost
effective bushing embedded sensors that can measure the electrical stresses on the MV side of
distribution transformers has been conducted. An embedded screen in a specially designed 24 kV
bushing was used for both power frequency and transient voltage measurements. Observed results
showed that the screen-based bushing capacitive voltage divider offered results that are consistent
with those of a commercial capacitive voltage divider for power frequency voltages as low as 1 kV up
to 24 kV. Impulse voltage measurements were consistent with those of a wideband resistive divider
for voltages lower than 60 kV. Voltages higher than 60 kV revealed non-linear behaviour which
increases as the 150 kV BIL rating of a 22 kV transformer is reached. A nonlinear resistor added to
ATPdraw simulations was able to compensate for the observed nonlinearity. PD tests conducted on
the prototype bushing showed that the designed prototype had surface discharges which are affected
by the positioning of the bushing screen. A Rogowski coil embedded in the same bushing was used
for the measurement of both power frequency and transient currents. Measured coil parameters used
in ATPdraw simulations produced results that were consistent with the output of the Rogowski coils
when measuring 8/20 s current impulses. Numerical integration of the Rogowski coil output voltages
was successfully used in the recovery of both power frequency and measured impulse currents. The
Rogowski coil sensitivity is affected by both coil dimensions and terminating resistance. The designed
prototype bushing opens up opportunities for performing stress monitoring on the MV side of
distribution transformers
Nonlinear Load Compensation
Nonlinear loads pose significant problems to power engineers, and have proliferated in occurrence over the past few decades. This project seeks to design and simulate a process by which one might mitigate the harmful consequences that result from their usage, employing signals processing techniques, logical decision-making processes, and currently available power electronics hardware
Modeling and Observer Design of a Nonlinear LCL Filter for Three-Phase Grid-Connected Voltage Source Converter
This work presents an observer design for grid current and capacitor voltage of voltage source pulse-width modulation (PWM) converters with LCL filter. Theoretical aspects including the mathematical LCL filter system observability, observer placement strategy and practical discretization implementation. It gives insight to mathematical modelling of the line filters dynamics. By the limitations of how the components in the line filter operates, the Kalman filter is adjusted accordingly. The strategy for designing the Kalman filter is presented. A time-varying KF is developed, benchmarked and implemented in simulator. Through an explanation of the magnetic field fundamentals, a nonlinear model of the inductors is modeled and used. An observer scheduling development has been implemented on the nonlinear system. The effect of sampling frequency is studied for KF and for the observer as well. At last the results are presented and analyzed
Highly Linear Filtering TIA for 5G wireless standard and beyond
The demand for high data rates in emerging wireless standards is a result
of the growing number of wireless device subscribers. This demand is met
by increasing the channel bandwidth in accordance with historical trends. As
MIMO technology advances, more bands and antennas are expected to be used.
The most recent 5G standard makes use of mm-wave bands above 24GHz to
expand the channel bandwidth. Channel bandwidth can exceed 2GHz when
carrier aggregation is used. From the receiver’s point of view, this makes the
baseband filter’s design, which is often a TIA, more difficult. This is due to
the fact that as the bandwidth approaches the GHz range, the TIA’s UGBW
should be more than 5GHz and it should have a high loop gain up to high
frequencies. A closed-loop TIA with configurable bandwidth up to 1.5GHz
is described in this scenario. Operational Transconductance Amplifier (OTA)
closed in shunt-feedback is the foundation of the TIA. The proposed OTA is
based on FeedForward topology (FF) together with inductive peaking technique
to ensure stability rather than using the traditional Miller compensation
technique. The TIA is able to produce GLoop unity gain bandwidth of
7.5GHz and high loop gain (i.e. 27dB @ 1GHz) using this method. The mixer
and LNA’s linearity will benefit from this. Utilizing TSMC 28nm CMOS technology,
a prototype has been created using this methodology. The output
integrated noise from 20MHz to 1.5GHz is lower than 300ÎĽVrms with a power
consumption of 17mW, and the TIA achieves In-band OIP3 of 33dBm.
Additionally, a direct-conversion receiver for 5G applications is described. The
7GHz RF signal is down-converted to baseband by the receiver. Two cascaded
LNTAs based on a common-gate transformer-based design make up the frontend.
With an RF gain of 80mS and a gain variability of 31dB, it provides
wideband matching from 6GHz to 8GHz. A double-balanced passive mixer is
driven by the LNTA. The channel bandwidth from 50MHz to 2GHz is covered by two baseband paths. The first path, called as the low frequency path (LF),
covers the channel bandwidth ranging from 50MHz to 400 MHz. In contrast,
the second path, called as the high frequency path (HF), covers the channel
bandwidth between 800MHz and 2GHz. Two baseband provide gain variability
of 14dB, making the overall receiver able to have a gain configurability
from 45dB to 0dB. Out-of-band (OOB) selectivity at 4 times the band-edge
is greater than 33dB for each configurability. When the gain is at its maximum,
the noise figure is less than 5.8dB, and the slope of the noise rise as
the gain falls is less than 0.7dB/dB. The receiver guarantee an IB-OIP3 larger
than 21dBm for any gain configuration. The receiver has been implemented
in TSMC 28nm CMOS technology, consuming 51mW for LF path and 68mW
for HF path. The measurement results are in perfect accordance with the
requirements of the design
Modulation and Control Techniques for Performance Improvement of Micro Grid Tie Inverters
The concept of microgrids is a new building block of smart grid that acts as a single controllable entity which allows reliable interconnection of distributed energy resources and loads and provides alternative way of their integration into power system. Due to its specifics, microgrids require different control strategies and dynamics of regulation as compared to ones used in conventional utility grids. All types of power converters used in microgrid share commonalities which potentially affect high frequency modes of microgrid in same manner. There are numerous unique design requirements imposed on microgrid tie inverters, which are dictated by the nature of the microgrid system and bring major challenges that are reviewed and further analyzed in this work. This work introduces, performs a detailed study on, and implements nonconventional control and modulation techniques leading to performance improvement of microgrid tie inverters in respect to aforementioned challenges
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