Milijana Odavic

A Theoretical Analysis of the Harmonic Content of PWM Waveforms for Multiple-Frequency Modulators

This paper theoretically identifies the harmonic components of a carrier-based pulsewidth-modulated (PWM) voltage-source converter (VSC) output voltage when the modulating wave includes fundamental and baseband harmonic components. This occurs, for example, when a VSC is used as an active power filter. The general analytical solution provided can be applied with a minimum additional mathematical effort to any harmonic combination in the modulation signal. The analysis undertaken in this paper determines how the fundamental and low-order harmonics (in the modulation signal) interact with the carrier to produce the low (and high) order frequencies in the PWM VSC output voltage. The analysis is based on a double Fourier series expansion in two variables. This approach to harmonic identification is evaluated by a comparison with a fast Fourier transform analysis of simulated PWM waveforms.

Low Carrier–Fundamental Frequency Ratio PWM for Multilevel Active Shunt Power Filters for Aerospace Applications

Active power filters create sideband harmonics over a wide frequency range around the multiple carrier-frequency harmonics, and these can encroach into the low frequency range. This issue is particularly critical when low carrier-fundamental frequency ratios are used such as in aerospace applications, where high fundamental frequencies exist. A three-phase multilevel active shunt filter with a low switching frequency is proposed to mitigate the lowest order carrier-frequency terms. However, low carrier frequencies lead to reference voltage phase delay and attenuation and can introduce significant baseband harmonics. These effects cannot be hidden by employing multiple modulator converters. In addressing these problems, an improved modulation approach is proposed in this work that allows duty cycle updating (N - 1) times per switching period for each H-bridge of one phase of the N -level converter [rather than only once or twice as in the regularly sampled pulse width modulation (PWM)]. The proposed modulation approach is then combined with predictive current control in order to enhance the system performance. The control loop performance compared to regularly sampled PWM is verified through simulations and experimentally by employing a three-phase five-level active shunt power filters in a 400-Hz power network.

Control and Modulation of a Multilevel Active Filtering Solution for Variable-Speed Constant-Frequency More-Electric Aircraft Grids

The increase of power electronic subsystems in more-electrical aircrafts (MEA) brings severe challenges to aircraft power distribution in terms of power quality on board. Active filtering is a viable solution to this problem; however, given the high supply frequency in AC-MEA power networks, effective harmonic compensation using standard converter structures, traditional digital control and reasonable devices switching frequency is a demanding task. A five-level active shunt filter with an enhanced deadbeat current controller is proposed in this paper for a fixed frequency 400 Hz aircraft power grid. The controller shows higher immunity to measurement noise compared with the conventional deadbeat current controller. In order to enhance the system performance when the voltage reference has a high rate of change, a modified pulse width modulation algorithm is proposed. The effective reference tracking of the proposed modulation combined with the employed current control approach is experimentally verified. The proposed controller features a high bandwidth of the current control loop, capable of high frequency harmonic compensation, using a reduced devices switching frequency.

A Low Switching Frequency High Bandwidth Current Control for Active Shunt Power Filter in Aircrafts Power Networks

A five-level active shunt power filter (ASF) structure with a predictive current controller is proposed in this paper for application in aircraft power systems with variable fundamental frequency (ranging from 360 Hz to 800 Hz). The tested ASF is capable of a high bandwidth current control with a low switching frequency being able to effectively track harmonic current reference signals up to 5.6 kHz. Analysis of the proposed ASF structure for the aircraft applications includes current tracking performance and harmonic spectrum of the output ASF voltage. A comparison of the proposed five-level topology is made with the two-level one.

Improved dead beat control of a shunt active filter for aircraft power systems

This paper investigates the application of an improved dead beat digital control strategy to a 3-phase shunt active filter used for compensation of load harmonics in aircraft power systems. Due to the high rated frequency (400 Hz) such applications result particularly demanding for both power and control devices. To compensate the inherent delay of digital control systems, a simple method for predicting the values of relevant variables is proposed and analyzed. The converter topology, its analytical modeling and its control are described. Significant results obtained by experimental tests are finally reported and commented, referring to a prototype system purposely implemented.

Multi-sampled carrier-based PWM for multilevel active shunt power filters for aerospace applications

Active power filters create sideband harmonics over a wide frequency range around the multiple carrier-frequency harmonics and these can encroach into the low frequency range. This issue is particularly critical when low carrier-fundamental frequency ratios are used such as in aerospace applications, where high fundamental frequencies exist. A multilevel Active Shunt Filter with a low switching frequency is proposed to mitigate the lowest order carrier frequency terms. However low carrier frequencies lead to reference voltage phase delay and attenuation and can introduce significant baseband harmonics. These effects cannot be hidden by employing multiple modulator converters. In order to overcome these problems, a multi-sampled modulation approach is proposed, which allows duty cycle updating (n−1) times per switching period for each H-bridge of one phase of the n-level converter (rather than only once or twice as in the regularly sampled PWM). The proposed modulation approach was combined with predictive current control in order to enhance the system performance. The control loop performance compared to regularly sampled PWM is experimentally verified by employing a five-level ASF in a 400Hz power network.

A comparative study of two high performance current control techniques for three-phase shunt active power filters

In recent years, the increase of non-linear loads in electrical power system has sparked the research in power quality issue. The shunt active power filter (SAPF) is a power electronic device which has been developed to improve power quality. The current control of shunt power filters is critical since poor control can reinforce existing harmonic problems. Various control strategies have been proposed by many researchers. In this paper, a comparative evaluation of the performance of two current control techniques, resonant and predictive controller, is presented with identical system specification. The design procedure and principle of both current control methods are also presented in detail. Simulation results show the comparison of transient response, steady state control and performance in the presence of variation of supply impedance between two control techniques.

A Novel Zero-Sequence Model-Based Sensorless Method for Open-Winding PMSM With Common DC Bus

This paper proposes a zero-sequence model-based sensorless control strategy for open-winding permanent-magnet synchronous machine (OW-PMSM) with common dc bus. The third harmonic back electromotive force (EMF) in zero-sequence is utilized to estimate the rotor position information. The novelty is that the third harmonic back EMF is reconstructed based on the zero-sequence model together with zero-sequence current, instead of using voltage transducer and three phase resistance network which can be eliminated from the control system. Due to the essence of back EMF, the developed method is appropriate for the applications including wind power generation and motor drives operating above certain speed. Meanwhile, the phase shift-based space vector pulse width modulation method for OW-PMSM is also presented for easier implementation to form zero voltage disturbance in zero-sequence from the inverter side and hence the corresponding influence can be consequently minimized. The torque ripple, loss, and parameter sensitivity analysis are also carried out, as confirmed by predictions of two-dimensional finite element analysis. Due to the essence of decouple, the estimation can be more robust than the conventional fundamental model-based sensorless methods. Finally, the effectiveness of the proposed method is validated experimentally on a 3-kW OW-PMSM drive system with 2.5 kg·m2 total inertia.

A Modeling Methodology for Robust Stability Analysis of Nonlinear Electrical Power Systems Under Parameter Uncertainties

This paper develops a modeling method for robust stability analysis of nonlinear electrical power systems over a range of operating points and under parameter uncertainties. Standard methods can guarantee stability under nominal conditions, but do not take into account any uncertainties of the model. In this study, stability is assessed by using structured singular value (SSV) analysis, also known as μ analysis. This method provides a measure of stability robustness of linear systems against all considered sources of structured uncertainties. The aim of this study is to apply the SSV method for robust small-signal analysis of nonlinear systems over a range of operating points and parameter variations. To that end, a modeling methodology is developed to represent any such system with an equivalent linear model that contains all system variability, in addition to being suitable for μ analysis. The method employs symbolic linearization around an arbitrary operating point. Furthermore, in order to reduce conservativeness in the stability assessment of the nonlinear system, the approach takes into account dependences of operating points on parameter variations. The methodology is verified through μ analysis of the equivalent linear model of a 4-kW permanent magnet machine drive, which successfully predicts the destabilizing torque over a range of different operating points and under parameter variations. Further, the predictions from μ analysis are validated against experimental results.

Real-time fault diagnostics for a permanent magnet synchronous motor drive for aerospace applications

This paper describes the development and implementation of a permanent magnet synchronous machine controller for safety critical applications which embeds independent real-time mechanical-fault diagnostics into the drive controller. The drive is intended for aerospace applications and therefore must employ an ASIC or FPGA as the main control “processor” to provide a more suitable route to flight-product certification. Motor Current Signature Analysis (MCSA) is employed to indicate the development or existence of faults within the drive system and this is achieved by embedding a real-time frequency analysis of the motor current within the FPGA, operating independently of the motor control. Experimental results are provided to validate the proposed control and condition monitoring.