doc. Ing. Miroslav Chomát, CSc.

Gyroid triply periodic minimal surfaces (TPMS) structures are vastly considered for thermal applications as they provide better surface to volume ratio and ensure mechanical properties. Its properties are significantly influenced by cell size, printing process, printing direction and volume fraction. To ensure the mechanical strength of the design, accurate stress measurements need to be done. TPMS structures do not behave the same as conventional structures or lattice structures due to their continuous curvature and nonlinearity. To evaluate accurate properties of TPMS structures, complex finite element approaches are needed. This study introduces complex finite element methods to evaluate accurate properties of the TPMS structures. Gyroid structures were also 3d-printed and tested to validate the simulation results. These structures were printed with varying printing direction and varying volume fractions using the selective laser melting (SLM) process. Surface roughness of the samples was recorded before and after post-processing. Tensile and compression tests were performed to investigate the impact of varying volume fraction and printing direction on mechanical behavior. Important finding of this paper is the precise and experimentally validated finite element method that could evaluate accurate mechanical properties of TPMS structures. Based on experimental data, predictive equations are designed which could predict the properties of the gyroid structure for any volume fraction.

This paper presents the implementation of a cyberattack detection system based on a watermarking strategy for a grid-connected power electronic converter equipped with an LCL filter. Mathematical models of the system are established to derive the detection equations. The proposed strategy was verified through both Matlab/Simulink simulations and laboratory experiments using a dSPACE-based control platform. The analysis focuses on voltage and current waveforms under both nominal operation and simulated scaling attacks on the sensors. The results demonstrate that the watermarking strategy is an effective tool for identifying compromised measurement data and ensuring the security of control systems in grid-connected converters.

BLDC motors are increasingly used in battery-powered and industrial applications due to their high efficiency and reliability. However, their performance is often degraded by current ripple and torque pulsations caused by higher-order harmonic components in the back electromotive force, which are not sufficiently addressed by conventional control strategies such as field-oriented control. This paper presents a feed-forward method for improving BLDC motor efficiency by injecting selected higher time-harmonic components into the inverter output voltages. The method aims to reduce current ripple and optimize torque generation without requiring additional hardware or significant modifications to standard FOC algorithms, making it suitable for existing motor control platforms. Simulation and experimental validation confirm that the proposed approach decreases phase current RMS values and minimizes torque pulsations. Experimental validation on a low-voltage BLDC motor shows that overall efficiency improvements are most significant at high speeds and low loads, with a maximum measured gain of 0.5%. Due to its simplicity and low computational requirements, the method is well-suited for embedded implementations in cost-sensitive applications.

With the advent of 3D printing, advancements in optimizing structures and innovations to 3D print new materials for electric machines are being developed. Conventional structures are being replaced by lattice structures which provide better properties. From plastics to metals, recent achievements have been made in the 3D printing of soft and hard magnetic materials. Hard magnetic materials are mostly printed by mixing them with ferrites or using a binder material. This paper focuses on all the different methods and compositions to 3D print metals and soft and hard magnetic materials. Although research is still undergoing to expand the use of different magnetic materials, we still have some limitations in their use in electric machines e.g., mixing hard magnetic materials with other materials for 3D printing weakens their electromagnetic properties. Some 3D printing processes provide a comparatively low mechanical strength. With research being undertaken to overcome these challenges, recent 3D-printed magnetic materials for the use in electric machines are discussed in this paper. Apart from materials, different optimization strategies are also introduced that increase the efficiency of the 3D-printed parts e.g., process optimization, topology optimization, and thermal optimization. Process optimization includes different multi-material strategies to reduce the time taken, print multiple parts in one process, and improve the properties of the part. Topology optimization revolves around optimized designs. The properties of electric machines are enhanced by using optimized shapes of rotor, stator, and coils. During the operation of electric machines, there is always some heat generation. The efficient removal of this heat from the system can increase the efficiency of the part. Thermal optimization to efficiently dissipate the heat to the atmosphere is achieved by using phase-changing materials (PCMs), by installing cooling systems, or by introducing optimized structures with better thermal properties. All these developments are discussed in this paper.

This paper analyzes the influence of input-voltage waveform on the performance of a three-phase brushless DC (BLDC) motor. The six-step control and the V/Hz control are used in the analysis with focus on time harmonics. The solution shows how to use higher time harmonics in the supply voltage to increase the current-torque ratio of BLDC motors. The simulation is made for both delta- and star-connected BLDC motors with high harmonic distortion of its back electromotive force (BEMF). The theoretical results are compared with experimental measurements.

The accuracy of induction motor (IM) drive with employed field-oriented control depends on precise identification of the IM equivalent circuit parameters. Those parameters can change significantly during the drive operation. Therefore, an adaptation of the IM model parameters is needed for a high-performance drive. Estimators based on model reference adaptive system (MRAS) are not computationally demanding, but they a priori exhibit sensitivity to the other, non-estimated parameters. This paper analyses the influence of the proper knowledge of the magnetizing inductance on the accuracy of the rotor resistance estimator based on the traditional reactive power MRAS. The paper also takes into account the load-dependent saturation of the IM, which is often omitted during the analysis and shows that the implemented load-dependent magnetization characteristic improves the MRAS and drive performance. Simulation and experimental results conducted on 12 kW IM are presented.

The sliding mode control technique applied to the drive control is analyzed in terms of dynamic response and energy saving in a stand-alone network. The drive is equipped with a surface-mounted permanent magnet synchronous motor fed by renewable power through a voltage-source inverter. The design of sliding mode control is presented, and it is shown that the developed control eliminates the influence of instability in the power flow of renewable energy sources on the drive behavior. The control also eliminates the reactive-power consumption. Simulations in MATLAB/Simulink verify the proposed sliding mode control.

Objective of this paper is induction machine simulation for various running conditions, after it check up of mechanical loading influence on the machine. Different capacitors were chosen for the simulation, loading torque was considered like the steady one. Mathematical model was compared with real machine.

The paper focuses on dependences of individual stator winding inductances on magnetic saturation in the induction machine. Magnetizing currents with a range of magnitudes and phase angles were considered to cause saturation of magnetic paths in the machine. Mutual inductances between stator phases for superimposed small signals that do not contribute to the saturation significantly were numerically computed and analysed. The finite element method was employed in the investigation.

The paper focuses on dependences of individual stator winding inductances on magnetic saturation in the induction machine. Magnetizing currents with a range of magnitudes and phase angles were considered to cause saturation of magnetic paths in the machine. Mutual inductances between stator phases for superimposed small signals that do not contribute to the saturation significantly were numerically computed and analysed. The finite element method was employed in the investigation.