Tomi Roinila

Online Grid Impedance Measurement Using Discrete-Interval Binary Sequence Injection

Grid impedance affects the stability and control performance of grid-connected power electronic devices, such as inverters used to integrate wind and solar energy. Adaptive control of such inverters, to guarantee stability under different grid conditions, requires online measurement of the grid impedance performed in real time. Such online measurement can be performed by injecting a current perturbation from the inverter into the grid and by reading the grid voltage responses. To minimize the impact on the inverter operation, the injection must be kept as small as possible while producing enough voltage perturbation that can be reliably measured and processed to extract its various frequency components. This paper proposes the use of a discrete-interval binary sequence (DIBS) for this application to minimize the injection. The DIBS is a computer-optimized binary sequence, where the energy is maximized at specified harmonic frequencies based on the expected grid-impedance characteristics. Experimental results based on a three-phase grid-connected inverter are presented to demonstrate the effectiveness of the proposed methods.

Circular correlation based identification of switching power converter with uncertainty analysis using fuzzy density approach

Abstract Switching power converters are extensively used in powering various electronics loads and processes. The proper functioning of those processes may be vital for the every day life of the society. Therefore, the reliable operation of the switched-mode converters is of prime importance and the functioning has to be verified reliably both during the design phase and in the production. It has been shown lately that the main deficiencies in the verification process are related to the dynamics of the converter which can be characterized with a certain set of transfer functions. This paper investigates the frequency response measurement methods by means of which the transfer functions can be identified fast and accurately being economically feasible to apply also in the production phase. Multi-period maximum length pseudo random binary sequence (m.l.b.s.) is used as the excitation signal and the transfer functions are identified from the measurement data with circular cross-correlation method. The measurement uncertainty is computed by means of fuzzy density approach yielding a certain confidence band around the measured nominal response. The proposed methods are verified both by simulations and experimental data from high-frequency switched-mode converters.

Fast Loop Gain Measurement of a Switched-Mode Converter Using a Binary Signal With a Specified Fourier Amplitude Spectrum

Switched-mode power converters are extensively used to power various electronic loads and processes. The use of low-cost components with high parameter variation together with the requirement of short time to market has set new challenges for the designers such as the necessity to characterize a large number of converters before production ramp-up. It has been shown that the frequency-domain characterization yields most useful information on the quality of a converter. The conventional frequency response analyzers can be used for measuring the responses, but the time required for one measurement is too long for characterizing hundreds or thousands of converters. Recent studies show that the time for single measurement can be drastically reduced by using broadband excitation signals such as the maximum length pseudorandom binary sequence (MLBS). The MLBS excitation signal is not well suited for measuring the voltage or current loop gains because of their sensitivity to the disturbance signals. This paper proposes a new method based on the use of MLBS but with a specified Fourier amplitude spectrum in order to avoid the said problem. The method is verified both with simulation and practical measurements, and the results are compared to the conventional MLBS technique.

Frequency-Response Measurement of Switched-Mode Power Supplies in the Presence of Nonlinear Distortions

Switched-mode converters have become extensively used in powering different consumer products. The increased mass production using low-cost components with high parameter variation has set new challenges to designers. Recent studies have shown that frequency-domain characterization yields most useful information about the dynamics and quality of a converter. This has been widely recognized and fast correlation-based techniques have been developed enabling the use of frequency-response measurements both in design and production phases. These techniques are based on a broad-band excitation signal that is injected into a converter and its response is analyzed. Most of the previous papers have used the pseudorandom binary sequence (PRBS) as the excitation. The conventional binary sequence do not, however, suit well for the processes suffering from strong nonlinear distortions. This paper proposes an excitation signal that can be used similarly to the conventional PRBS but provides much more accurate frequency-response estimates. Inverse-repeat binary sequence (IRS) is applied to cancel the effect of even-order nonlinearities and the frequency response is measured by means of spectrum method. The proposed technique is verified with practical measurements.

Dynamical modelling of peak-current-mode-controlled converter in continuous conduction mode

Abstract Peak-current-mode (PCM) control has been a popular control method of switched-mode converters since its publication in late 1970s due to the inherent features it provides especially in buck derived converters such as high input-noise attenuation, first-order control dynamics as well as cycle-by-cycle current limiting. Its main disadvantages are considered to be the limited duty ratio, increased output impedance, and noise sensitivity due to the fast feedback-current loop. The observed peculiar dynamical behaviour associate to the PCM control has attracted the researchers for tens of years yielding multitude of dynamical modelling approaches. Application of sampling effect as the basis for the modelling has been considered to producing most accurate dynamical models as well as explanations for the observed phenomena. A consistent and easy-to-apply modelling approach is presented in this paper, which explains the observed dynamical phenomena, provides accurate dynamical power-stage models as well as comply with the other methods proposing the existence of an infinite small-signal duty-ratio gain leading to the observed behaviour. Experimental evidence is provided based on second and fourth-order buck converters.

CMOS MEMS-based thermoelectric generator with an efficient heat dissipation path

This paper presents a CMOS MEMS-based thermoelectric energy generator (TEG) device with an efficient heat dissipation path. For present CMOS MEMS-based thermoelectric generator devices, the output performance is greatly limited by the high thermal-contact resistance in the system. For the device proposed in the work, the silicon substrate is etched into two comb-shaped blocks thermally isolated from each other, which form the hot and cold sides. Thin-film-based thermal legs are densely located between the two blocks along the winding split line. Low internal thermal-contact resistance is achieved with the symmetrical thermal structure. When the TEG device is embedded between the heat source and heat sink, the heat loss can be well controlled with flat thermal-contact pads of the device. For a full device with 900 n/p-polysilicon thermocouples, the measured open-circuit voltage reaches as high as 146 mV K−1, and the power factor reaches almost five times higher value compared to the previously reported results. A test system integrated with a single device presents an open-circuit voltage of 110 mV K−1 when forcibly cooled by a Peltier cooler, or 26 mV K−1 when cooled by ambient air.

Corrected Mathematical Model of Quadruple Tank Process

A quadruple tank apparatus has been developed in many universities for use in undergraduate chemical engineering laboratories. The control experiment illustrates the performance limitations for multivariable systems posed by ill-conditioning, right half plane transmission zeros, and model uncertainties. The experiment is suitable for teaching how to select among multiloop, decoupling, and fully multivariable control structures. A number of these reports are, however, based on erroneous mathematical modeling and thus resulting incorrect results. Obviously all these reports refer originally to the one and same paper which includes this incorrect part of modeling. The error is significant if the pumps used in the experiment are not identical. If they are identical the error is, however, negligible. Mathematical derivation and simulation results are provided to give a corrected model and illustrate the effect of the widespread incorrect modeling.

On Frequency-Response Measurements of Power-Electronic Systems Applying MIMO Identification Techniques

Switched-mode converters are often the key to operating various electronic systems in everyday life. This means that the reliable operation of the converters is of prime importance and that the functioning must be verified during both the design phase and production. Recent studies have shown that the converters can be fully characterized by a set of frequency responses that can be efficiently used to validate the operation of the converters and analyze the related systems. Several methods have been proposed for quickly and accurately measuring the frequency responses, but surprisingly, the use of multiple-input multiple-output (MIMO) identification techniques has not been considered. Applying MIMO identification techniques, the operating conditions of a converter can be kept constant during the frequency-response measurements, and the overall measurement time can be further shortened. This paper reviews the techniques and proposes an implementation setup. The presented techniques provide efficient means to characterize the switched-mode converters during one measurement cycle. The methods can be used for example in field-programmable gate-array-based controller implementation and in fast online analysis. Experimental measurements are shown from a high-frequency switched-mode converter.

Dynamical profile of a switched-mode converter - reality or imagination

An electrical device such as a switched-mode converter has unique internal dynamical profile, which mainly dictates, how the device as a subsystem in an interconnected system would behave and how it will affect the other subsystems within the constellation. The paper defines the vital representative parameters by means of which the stability and dynamics of the individual electrical device as well as the overall interconnected system can be analyzed and predicted. The very existence of such a dynamical priflle is proved based on extensive experimental evidence.

Estimation of Electrical Cell–Capillary Admittance During Injection with Frequency Response Method

Abstract This paper describes electrical equivalent circuit models of cell–capillary admittance during injection of a living cell and presents a measurement system to estimate corresponding frequency responses during microinjection tests. Since the admittance estimate is calculated from data collected during injection, the amount of data is limited. To overcome this constraint, the approach proposed in this paper takes advantage of properties of periodic pseudo random binary sequence (PRBS) excitation signal and avoids end effect anomalies of correlation calculation. The fast and accurate estimation is used to detect the degree of contact during cell injection and to detect breakage and clogging of capillary during a sequence of multiple operations.