Self-Commissioning of Inverter Nonlinear Effects in AC Drives

The paper presents a novel technique for an accurate identification of the inverter nonlinear effects, such as the dead-time and on-state voltage drops. The proposed technique is very simple and it is based only on a current control scheme. If the inverter load is an AC motor, the inverter effects can be identified at drive startup using as measured quantities the motor currents and the inverter DC link voltage. The identified inverter error is stored in a Look-Up Table (LUT) that can be subsequently used by the vector control algorithm. The proposed method has been tested on a 1 kVA inverter prototype and the obtained results demonstrate the feasibility of the proposed solutio

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

A Novel Control Method For Grid Side Inverters Under Generalized Unbalanced Operating Conditions

This thesis provides a summary on renewable energy sources integration into the grid, using an inverter, along with a comprehensive literature research on variety of available control methods. A new generalized method for grid side inverter control under unbalanced operating conditions is also proposed. The presented control method provides complete harmonic elimination in line currents and DC link voltage with adjustable power factor. The method is general, and can be used for all levels of imbalance in grid voltages and line impedances. The control algorithm proposed in this work has been implemented by using MATLAB Simulink and dSPACE RT1104 control system. Simulation and experimental results presented in this thesis are in excellent agreement

A Comprehensive AC Current Ripple Analysis and Performance Enhancement via Discontinuous PWM in Three-Phase Four-Leg Grid-Connected Inverters

open5siA complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections.openMandrioli, Riccardo; Viatkin, Aleksandr, Hammami, Manel; Ricco, Mattia; Grandi, GabrieleMandrioli, Riccardo; Viatkin, Aleksandr, Hammami, Manel; Ricco, Mattia; Grandi, Gabriel

Induction motor parameter identification in elevator drive modernization

Tässä työssä tutkitaan, miten oikosulkumoottorin sähköiset parametrit voidaan identifioida askel- ja taajuusvastemenetelmien avulla pyörittämättä roottoria. Oikosulkumoottoria voimanlähteenä käyttävien hissien ohjaustarkkuus riippuu pitkälti siitä, miten tarkasti taajuusmuuttajan momentti- ja nopeussäätäjän parametrit vastaavat todellisia varsinkin, jos hissin paikkaa tai nopeutta ei mitata. Vanhojen hissien modernisoinnin yhteydessä ongelmaksi muodostuu se, että olemassa olevaa moottoria ei voi identifioida perinteisillä oikosulku- ja tyhjäkäyntikokeilla, koska moottoria ei voi pyörittää kuormattomana. Sen sijaan identifiointi voidaan tehdä analysoimalla vaihejännitteitä ja -virtoja, joita esiintyy, kun staattorikäämityksiin syötetään sellainen heräte, joka ei aiheuta pyörivää sähkömagneettista kenttää eikä siten vääntömomenttia. Esitettävässä askelvastemenetelmässä moottoria syötetään tasavirtapulsseilla, jolloin halutut parametrit saadaan, kun vaihejänniteen ja -virran mittaukset prosessoidaan tilamuuttujien suodatuksella ja saatu lineaarinen yhtälöryhmä ratkaistaan rekursiivisella pienimmän neliösumman algoritmilla. Toisessa, taajuusvasteeseen perustuvassa, menetelmässä moottoria syötetään yhtä aikaa sekä tasa- että vaihtovirralla. Tällöin moottorin parametrit voidaan ratkaista vaihejännitteen ja -virran välisen amplitudisuhteen ja vaihe-eron perusteella lasketun moottorin liittimistä näkyvän induktanssin taajuusriippuvuuden avulla. Molempia menetelmiä on tutkittu sekä tietokonesimuloinneilla että kokeellisilla menetelmillä. Tulosten perusteella havaittiin valitun menetelmän olevan kompromissi parametrien tarkkuuden ja testin suoritusajan välillä.A study is presented where an induction motor, whose rotor is not allowed to rotate, is identified using system identification methods based on transient and frequency response tests. Precise control of elevators powered with frequency converter fed induction motors depends on the accuracy of the parameters used in the motor controller, particularly when no external position or speed sensors are used. When an elevator is modernized with a new control system, the old motor cannot be identified with a regular locked rotor and no-load tests as the motor is not allowed to rotate. However, the identification can be performed in such conditions by analyzing the voltages and currents when the motor windings are excited with such an AC or DC that does not produce torque. A step response method is introduced for the DC excitation where the desired motor parameters are obtained as a result when the measured data is processed with state variable filters, and the produced linear system of equations is solved with a recursive least-squares algorithm. The frequency response method presented uses both DC and AC excitation. The method is based on finding the amplitude ratio and the phase difference between the voltage and current phasors using the properties of the Fourier series. This information is then used to calculate the inductance between the motor terminals, from which the other motor parameters can be solved. Both methods are tested with simulations and experiments. The final choice of the proper identification method is found to be a compromise between the parameter accuracy and measurement time

Development of Robust Control Schemes with New Estimation Algorithms for Shunt Active Power Filter

The widespread use of power electronics in industrial, commercial and even residential electrical equipments causes deterioration of the quality of the electric power supply with distortion of the supply voltage. This has led to the development of more stringent requirements regarding harmonic current generation, as are found in standards such as IEEE-519. Power Quality is generally meant to measure of an ideal power supply system. Shunt active power filter (SAPF) is a viable solution for Power Quality enhancement, in order to comply with the standard recommendations. The dynamic performance of SAPF is mainly dependent on how quickly and how accurately the harmonic components are extracted from the load current. Therefore, a fast and accurate estimation algorithm for the detection of reference current signal along with an effective current control technique is needed in order for a SAPF to perform the harmonic elimination successfully. Several control strategies of SAPF have been proposed and implemented. But, still there is a lot of scope on designing new estimation algorithms to achieve fast and accurate generation of reference current signal in SAPF. Further, there is a need of development of efficient robust control algorithms that can be robust in face parametric uncertainties in the power system yielding improvement in power quality more effectively in terms of tracking error reduction and efficient current harmonics mitigation. The work described in the thesis involves development of a number of new current control techniques along with new reference current generation schemes in SAPF. Two current control techniques namely a hysteresis current control (HCC) and sliding mode control (SMC) implemented with a new reference current generation scheme are proposed. This reference generation approach involves a Proportional Integral (PI) controller loop and exploits the estimation of the in phase fundamental components of distorted point of common coupling (PCC) voltages by using Kalman Filter (KF) algorithm. The KF-HCC based SAPF is found to be very simple in realization and performs well even under grid perturbations. But the slow convergence rate of KF leads towards an ineffective reference generation and hence harmonics cancellation is not perfect. Therefore, a SMC based SAPF is implemented with a faster reference scheme based on the proposed Robust Extended Complex Kalman Filter (RECKF) algorithm and the efficacy of this RECKF-SMC is compared with other variants of Kalman Filter such as KF, Extended Kalman Filter (EKF) and Extended Complex Kalman Filter (ECKF) employing simulations as well as real-time simulations using an Opal-RT Real-Time digital Simulator. The RECKF-SMC based SAPF is found to be more effective as compared to the KF-HCC, KF-SMC, EKF-SMC and ECKF-SMC. Subsequently, predictive control techniques namely Dead Beat Control (DBC) and Model Predictive Control (MPC) are proposed in SAPF along with an improved reference current generation scheme based on the proposed RECKF. This reference scheme is devoid of PI controller loop and can self-regulate the dc-link voltage. Both RECKF-DBC and RECKF-MPC approaches use a model of the SAPF system to predict its future behavior and select the most appropriate control action based on an optimality criterion. However, RECKF-DBC is more sensitive to load uncertainties. Also, a better compensation performance of RECKF-MPC is observed from the simulation as well as real-time simulation results. Moreover, to study the efficacy of this RECKF-MPC over PI-MPC, a comparative assessment has been performed using both steady state as well as transient state conditions. From the simulation and real-time simulation results, it is observed that the proposed RECKF-MPC outperforms PI-MPC. The thesis also proposed an optimal Linear Quadratic Regulator (LQR) with an advanced reference current generation strategy based on RECKF. This RECKF-LQR based SAPF has better tracking and disturbance rejection capability and hence RECKF-LQR is found to be more efficient as compared to RECKF-SMC, RECKF-DBC and RECKF-MPC approaches. Subsequently, two robust control approaches namely Linear Quadratic Gaussian (LQG) servo control and H∞ control are proposed in SAPF with highly improved reference generation schemes based on RECKF. These control strategies are designed with the purpose of achieving stability, high disturbance rejection and high level of harmonics cancellation. From simulation results, they are not only found to be robust against different load parameters, but also satisfactory THD results have been achieved in SAPF. A prototype experimental set up has been developed in the Laboratory with a dSPACE-1104 computing platform to verify their robustness. From both the simulation and experimentation, it is observed that the proposed RECKF-H∞ control approach to design a SAPF is found to be more robust as compared to the RECKF-LQG servo control approach in face parametric uncertainties due to load perturbations yielding improvement in power quality in terms of tracking error reduction and efficient current harmonics mitigation. Further, there is no involvement of any voltage sensor in this realization of RECKF-H∞ based SAPF resulting a more reliable and inexpensive SAPF system. Therefore, superiority of proposed RECKF-H∞ is proved amongst all the proposed control strategies of SAPF