Marco Degano

Control Design and Implementation for High Performance Shunt Active Filters in Aircraft Power Grids

This paper presents the design and implementation of a Shunt Active Filter (SAF) for aircraft power networks using an accurate wide-band current control method based on Iterative Learning Control (ILC). The SAF control system is designed to compensate harmonic currents, with a 400 Hz supply voltage. This work introduces useful design strategies to increase the error-decay speed and improve the robustness of the SAF control system by using a hybrid P-type ILC controller. Detailed design of the hybrid P-type ILC controller and simulation results are presented. The overall system implementation is demonstrated through experimental results on a laboratory prototype.

Modulated Model Predictive Control for a Three-Phase Active Rectifier

Model predictive control (MPC) has a number of desirable attributes which are difficult to achieve with classical converter control techniques. Unfortunately, the nature of power electronics imposes restriction to the method, as a result of the limited number of available converter states. This, combined with the spread spectrum nature of harmonics inherent with the strategy, complicates further design. This paper presents a method for removing this characteristic without compromising the desirable functionality of predictive control. The method, named modulated MPC, is applied to a two-level three-phase converter and compared with a number of similar approaches. Experimental results are used to support theoretical analysis and simulation studies.

Iterative Learning Control With Variable Sampling Frequency for Current Control of Grid-Connected Converters in Aircraft Power Systems

This paper investigates the feasibility of an iterative learning control (ILC) with variable sampling frequency for current control of power converters in frequency-wild power systems. The proposed solution is explained and demonstrated for the case of a shunt active filter in new-generation aircraft, where a variable-speed variable-frequency power system, typically between 360 and 900 Hz, is nowadays used. Due to the high supply frequency, such application is particularly demanding for both power and control devices, requiring control capabilities even for frequencies up to several kilohertz. Furthermore, variable supply frequency leads to variable frequency harmonics in the aircraft grid that are challenging to track and compensate. An original and effective solution based on an ILC approach, where both the number of samples per period and the sampling frequency are changed, is studied and implemented. Experimental results confirm the validity of the proposed strategy.

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.

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.

HF induction motor modeling using automated experimental impedance measurement matching

High-frequency (HF) models of electrical motors and power converters are greatly important for electromagnetic compatibility characterization of electrical drives and for electromagnetic interference (EMI) filter design. In this paper, an accurate and effective method for the characterization and tuning of HF models (150 kHz-30 MHz) for induction motors has been proposed based on experimental measurements of the motor impedance. Impedance measurements have been taken in three different configurations: between all the six winding terminals which are shorted and grounded; between the three input terminals which are shorted and grounded (common mode); and between one input terminal and the other two which are shorted (differential mode). Once an HF motor model structure has been chosen and modeled using a state-space representation, its parameters have been tuned using genetic algorithm to match the real impedance in each corresponding configuration. Comparison between the experimental impedance measurements and the model impedance estimate are shown for all the tested configurations, in order to validate the model within the frequency range of interest for EMI.

Model Predictive Control for Shunt Active Filters With Fixed Switching Frequency

This paper presents a modification to the classical Model Predictive Control (MPC) algorithm and its application to active power filters. The proposed control is able to retain all the advantages of a finite control set MPC while improving the generated waveforms harmonic spectrum. In fact, a modulation algorithm, based on the cost function ratio for different output vectors, is inherently included in the MPC. The cost function-based modulator is introduced and its effectiveness on reducing the current ripple is demonstrated. The presented solution provides an effective and straightforward single loop controller, maintaining an excellent dynamic performance despite the modulated output and it is self-synchronizing with the grid. This promising method is applied to the control of a shunt active filter for harmonic content reduction through a reactive power compensation methodology. Significant results obtained by experimental testing are reported and commented, showing that MPC is a viable control solution for active filtering systems.

Modulated model predictve control (M 2 PC) for a 3-phase active front-end

One of the main issues with Model Predictive Control (MPC) applied to Power Electronics Converters is the ability to select only one output voltage vector which is applied during the whole sampling period. Such mode of operation requires, in order to improve the harmonic content, an increasing of the converter switching frequency which is variable depending on the operating conditions. In order to overcome these issues, whilst preserving all the advantages of MPC, this paper presents a novel Modulated Model Predictive Control, with the aim of obtaining a modulated waveform at the output of the converter without implementing an explicit modulation scheme. The proposed control technique is applied to the current control of a 2-Level, 3-Phase Active Rectifier, validated through simulation and experimental testing and compared to a traditional Model Predictive Control.

Grid Parameter Estimation Using Model Predictive Direct Power Control

This paper presents a novel finite-control-set model predictive control (FS-MPC) approach for grid-connected converters. The control performance of such converters may get largely affected by variations in the supply impedance, especially for systems with low short-circuit ratio values. A novel idea for estimating the supply impedance variation, and hence the grid voltage, using an algorithm embedded in the MPC is presented in this paper. The estimation approach is based on the difference in grid voltage magnitudes at two consecutive sampling instants, calculated on the basis of supply currents and converter voltages directly within the MPC algorithm, achieving a fast estimation and integration between the controller and the impedance estimator. The proposed method has been verified, using simulation and experiments, on a three-phase two-level converter.