COMPUTER OPTIMIZATION OF SWITCHING FREQUENCY OF TRANSISTOR PULSE-WIDTH CONVERTERS

Voltage source inverter (VSI) is one of the most common types of power converters, which is used in various industries. The energy efficiency indicators of the AVI depend not only on the IGBT or MOSFET-based transistors used in the AVI element, but also on the chosen modulation algorithm.The most commonly used in VSI is pulse width modulation (PWM) and single modulation. The advantage of PWM prior to single modulation is the ability to control the amplitude of the first harmonic of the output voltage and, accordingly, the current required both for scalar and vector control of an asynchronous electric drive.At the same time, the disadvantage of PWM is the need for a higher switching frequency of power switches, which results in higher dynamic losses. In addition, in the PWM mode, VSI at the same load parameters has a smaller amplitude of the first harmonic of the output voltage, and hence less output power.The article proposes the use the mode of overmodulation algorithm in the pulse-width modulation (PWM) mode for a three-level autonomous voltage inverter, which is relatively classical PWM with a modulation factor equal to one, justified and allows to increase the control range of the output power of the VSI, to reduce the dynamic losses in the power switches, to improve the sinusoidal output current, as well as reduce the ripple factor of the input current. Given the dependence of the energy indicators of the VSI on the modulation factor in the mode of overmodulation.In the specialized MelcoSim program from Mitsubishi, the calculation of static and dynamic losses in the power switches of an autonomous voltage inverter in the mode of overmodulation was performed. The dependences of the output power on the modulation coefficient, the dependence of the amplitude of the first harmonic of the output current on the modulation coefficient, the dependence of the coefficient of harmonic distortion of the output voltage on the modulation coefficient, the dependence of the harmonic distortion factor of the output current on the modulation coefficient, and the dependence of the losses in the power switches on the modulation coefficient.

Superconducting machine designs have historically focused on an isolated, cryogenic rotor and conventional (copper) stator due to unacceptable levels of AC loss in a superconducting stator. Thus, AC loss reduction in the armature windings is one of the key issues for achieving practical all-superconducting motors that could deliver an unprecedented power density and significantly reduce machine complexity. In this paper, a 100 kW, 1500 rpm, all - HTS motor operating at 65 K is designed and AC loss simulations in HTS armature windings wound with different types of (RE)BCO conductor arrangements are carried out by implementing the T-A formulation and a rotating mesh using commercial FEM software COMSOL Multiphysics. Either 4 mm-wide (RE)BCO conductors, 14/2 (14 strands, each strand is 2 mm wide) (RE)BCO Roebel cables, or striated (RE)BCO conductors with four 1 mm-wide filaments are considered in the armature windings. The simulation results show that armature windings wound with Roebel cables or striated conductors can significantly reduce the AC loss in the armature windings compared to windings wound with 4 mm-wide conductors. It is also shown that the AC loss in the armature winding wound with the 4 mm-wide (RE)BCO conductors decreases with decreasing operating temperature. The AC loss reduction can be attributed to the reduced magnetic field penetration associated with the increased $I_{\mathrm {c}}$ in the winding. Finally, a 2% AC loss reduction can be achieved in the armature winding wound with (RE)BCO conductors with asymmetric $I_{\mathrm {c}}(B$ , $\theta$ ) characteristics by simply flipping the direction of the conductors of the armature winding. The simulation results in this work have practical implications for designing all-HTS superconducting rotating machines. Such machines could be suitable for H2 powered electric vehicles like large interstate trucks, heavy machinery, or locomotives.

In many high-temperature superconducting (HTS) applications, HTS-coated conductors carry a DC current under an external AC magnetic field. In such operating conditions, dynamic resistance will occur when the traversing magnetic flux across the HTS conductors. Consequently, AC loss within the superconductors is composed of the dynamic loss component arising from dynamic resistance and the magnetization loss component due to the AC external magnetic field. This AC loss is one of the critical issues for HTS applications, such as persistent current switches, flux pumps, and rotating machines. In this work, the dynamic resistance and the total loss in a three-tape HTS coated conductor stack were measured at 77 K under perpendicular AC magnetic fields up to 80 mT and DC currents (I dc) up to the critical current (I c). The stack was assembled from three serial-connected 4 mm wide Superpower wires. The measured dynamic resistance results for the stack were well supported by the results from 2D H-formulation finite element modelling (FEM) and broadly agree with the analytical values for stacks. The FEM analysis shows asymmetric transport DC current profiles in the central region of the superconductor. We attribute the result to the superposition of DC currents and the induced subcritical currents which explains why the measured magnetization loss values increase with DC current levels at low magnetic field. The onset of dynamic loss for the stack for low i (I dc/I c) values is much slower when compared to that of the single tape and hence the contribution of the dynamic loss component to the total loss in the stack is much smaller than that of the single tape. Dynamic loss in the stack becomes comparable to the magnetization loss at i = 0.5 and becomes greater than the magnetization loss at i = 0.7. Both magnetization loss and dynamic loss in the stack are smaller than those of the single tape due to shielding effects. The difference between the Q total behaviours in the stack and single tape is due to the variation of the penetration depths of the stack and single tape at the different magnetic field amplitudes.

This paper first presents an adaptive switching frequency modulation that optimizes the efficiency of the cascaded buck-boost (CBB) converter. Such bidirectional dc–dc CBB topology is typically deployed in PV-battery-device systems. A precise loss-model that accounts for component nonlinearities is developed to determine power-loss distribution. According to the loss model, optimal switching frequencies are selected that correspond to the lowest total loss in both the buck and the boost modes of the operation. Then, a small volume low-profile planar-nanocrystalline inductor is designed to further increase efficiency and power density. Finite element analysis method is used to evaluate the inductor design. A digital control system is designed to periodically adjust the optimal switching frequencies to modulate the pulsewidth modulation duty cycle and to take into account any load and line regulations. The objective of this paper is to achieve ultra-high efficiency (over 99%) for a well-known CBB converter. A 100 W CBB converter prototype was built to verify the proposed algorithm and designed nanocrystalline inductor. A California Energy Commission weighted efficiency of 98.87% with a peak efficiency of 99.31% was achieved for the buck mode and 98.58% with a peak efficiency of 99.25% was achieved for the boost mode, both at nominal voltage. Also, a power density of 3.67 kW/L was reported.

This paper presents an analytical model for prediction of open circuit eddy current loss in armature windings and permanent magnets of series double excitation synchronous machines. The developed model can either be used in the case of internal or external rotor radial-field machines topologies. First, a 2D exact analytical solution of open circuit magnetic field distribution in an actual geometry of a series double excitation synchronous machine is established. It involves solution of Maxwell's equations in stator slots, airgap, PM's region and rotor slots. Results from this analytical model are compared to corresponding finite element analyses. Then, magnetic vector potential solutions in the stator slots and PM's region are respectively used for prediction of resistance limited eddy current in armature windings and permanent magnets. This analytical model is then used to estimate eddy current loss in armature windings and permanent magnets.

Physics-based modeling aids in designing efficient data center power and cooling systems. These systems have traditionally been modeled independently under the assumption that the inherent coupling of effects between the systems has negligible impact. This study tests the assumption through uncertainty quantification of models for a typical 300 kW data center supplied through either an alternating current (AC)-based or direct current (DC)-based power distribution system. A novel calculation scheme is introduced that couples the calculations of these two systems to estimate the resultant impact on predicted power usage effectiveness (PUE), computer room air conditioning (CRAC) return temperature, total system power requirement, and system power loss values. A two-sample z-test for comparing means is used to test for statistical significance with 95% confidence. The power distribution component efficiencies are calibrated to available published and experimental data. The predictions for a typical data center with an AC-based system suggest that the coupling of system calculations results in statistically significant differences for the cooling system PUE, the overall PUE, the CRAC return air temperature, and total electrical losses. However, none of the tested metrics are statistically significant for a DC-based system. The predictions also suggest that a DC-based system provides statistically significant lower overall PUE and electrical losses compared to the AC-based system, but only when coupled calculations are used. These results indicate that the coupled calculations impact predicted general energy efficiency metrics and enable statistically significant conclusions when comparing different data center cooling and power distribution strategies.

Dynamic magnetic losses in powders consisting of metallized dielectric particles at microwaves

In this paper, a low frequency hybrid cascaded phase shift-PWM (PSPWM) and asymmetric selective harmonic mitigation-PWM (ASHM-PWM) modulation technique is proposed to meet limits of power quality standard with the low number of switching frequency. For this aim, the low order harmonics of PSPWM technique are reduced by the ASHM-PWM technique. The equations of both modulation techniques are included in the optimization process to meet standard for all of the low order current harmonics of grid-tied cascaded h-bridge (CHB) converter. The proposed technique has advantages of both PSPWM and ASHM-PWM modulation techniques. Furthermore, the critical parameters of grid-tied CHB converter such as inductance and switching frequency of converter are derived based on the equations of proposed hybrid PSPWM and ASHM-PWM technique. The simulation and experimental results were conducted on 7-level CHB converter to validate the proposed modulation technique.

In some high temperature superconducting (HTS) applications, HTS coated conductors carry DC current under external AC magnetic fields. Dynamic resistance occurs when the amplitude of the magnetic field is greater than the threshold magnetic field of the coated conductors. The resulting AC loss, termed as total loss, consists of dynamic loss due to dynamic resistance and magnetization loss due to the shielding currents caused by the AC magnetic field. Conductor on round core (CORC) cables wound with HTS coated conductors have attracted broad attention due to their large current-carrying capability and mechanical flexibility for coil applications. However, there has been no report on dynamic resistance and total loss in CORC cables. In this work, we present 3D FEM simulation results on the dynamic resistance and total loss of a spiral tape and three CORC cables, based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\boldsymbol{T-A}}$ </tex-math></inline-formula> formulation. The number of layers of the CORC cables, the amplitude of the AC magnetic field and transport DC current levels have been varied to study the impact of those parameters on dynamic resistance and total loss of the three CORC cables. The simulation results show that magnetization loss without current in a spiral tape can be analytically estimated by Brandt and Indenbom’s theoretical equation for a superconducting strip under perpendicular AC magnetic field with a geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . Furthermore, dynamic resistance of the spiral tape and each tape in a single-layer cable can be predicted by the analytical equation for a strip carrying DC current under perpendicular AC magnetic field, also taking into account the geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . The simulation results also show that the difference of total loss values in the three CORC cables depends on the shielding effect: the more layers of CORC cables, the lower each loss component. The two-layer Cable with each tape in the outer layer sitting on top of the tape in the inner layer has the lowest loss and the highest threshold magnetic field.

In this article, we investigate the loss reduction of permanent magnet machines, whose armature windings consist of parallel wires. First, the impact of the loss caused by the circulating currents in the parallel armature wires is estimated by finite-element analysis. The calculated total electrical loss is compared with the experimental result of a prototype motor. The measured and calculated results are found to be in good agreement. In addition, it is revealed that the circulating armature current loss is larger than the usual copper loss, which is estimated only by the total armature current and the armature winding resistance. Next, the loss reduction by reducing the number of parallel wires is discussed. The optimal number of parallel wires is found by considering the tradeoff between the reduction of circulating current loss and increases in the other losses, such as usual copper loss and core loss.

This paper investigates the torque production and the torque ripple reduction of a six-stator/seven-rotor-pole (6/7) variable flux reluctance machine (VFRM). As a main advantage, the 6/7 VFRM produces higher torque density, but less torque ripple compared with the 6/4 VFRM. The instantaneous torque equation of the 6/7 VFRM is derived by considering the spectra of the winding inductance and current. Based on the derived equation, the average torque is found to be mainly produced by the mutual inductance between the field and armature windings. The even-order harmonics of self-inductance and odd-order harmonics in mutual inductance between the field and armature windings are eliminated due to the opposite polarity connection of the armature coils in each phase. This results in the elimination of the third harmonic torque ripple, while a multiple of the sixth harmonic torque ripple exists. In order to mitigate the sixth harmonic torque ripple, the harmonic current injection method is implemented into the field winding. The field harmonic current is calculated from the analytical torque ripple equation. The performance of the proposed methods is verified by both finite element analysis (FEA) and experiment.

This paper presents an improved analytical model for predicting the ac losses in form-wound windings used in high-performance ac machines attributable to the stator currents. The complete model comprises two sub-models that separately calculate the ac losses contributed by the in-slot and end-winding portions. 3D finite element analysis and experimental tests are conducted to demonstrate the usefulness of the model. The results also confirm the vulnerability of form-wound windings to steep increases in the winding ac resistance as the excitation frequency increases. The model is subsequently used to investigate the impact of key machine parameters on the winding ac losses, including the excitation frequency, phase arrangement, conductor thickness, and PWM switching frequency.

A MILP program for integrated global optimization of electrical cables systems in Offshore Wind Farms (OWFs) is presented. Electrical cables encompass the cable layout in collection systems to interconnect Wind Turbines (WTs), and transmission systems to couple Offshore Substations (OSSs) to the Onshore Connection Point (OCP). The program is solved through a modern branch-and-cut solver, demonstrating the ability to tackle large-scale instances with hundreds of WTs and several OSSs. The model supports as objective function the initial investment plus economic losses due to total electrical power losses. The importance and functionality of incorporating electrical losses is demonstrated, along with the need to simultaneously optimize the cable layout, OSSs location, and transmission cables. The method is tested for three case studies. The results show that (i) points near the global optimum, with an imposed maximum tolerance, are calculable within reasonable computational time and effort, and (ii) the integrated model can be much more efficient than a benchmark approach based on enumeration, i.e., exhaustive evaluation of all possible optimization problems derived from unique OSSs locations.

Nowadays transducers are ubiquitous as interfaces between the increasingly digital world and the real physical world. The same holds for the power amplifiers driving them. This thesis focuses on the design and optimization of high-voltage class-D amplifiers, which are used for driving capacitive piezoelectric actuator loads in active vibration/noise control applications. The main objective is to further enhance class-D power efficiency compared to existing class-D designs. To gain insight in class D power efficiency, a detailed analysis of high-voltage class-D dissipation sources is performed and a dissipation model including all the major dissipation sources is developed. The analysis shows that switching loss is a potential dominating dissipation source in high-voltage applications, while its contribution can be minimized by fast switching to eliminate V-I overlap losses. Moreover, it is shown that when varying the class-D switching frequency, a minimum total dissipation exists, with the optimal switching frequency depending on the output power. Furthermore, idle loss reduction by increasing the switching frequency and inserting a dead time to the power stage is backed by the analysis. Following the analysis, a fast-switching power stage is designed to aim for switching loss minimization. This output stage design features immunity to the on-chip supply bounce, realized by internally regulated floating supplies, variable driving strength for the gate driver, and an efficient 2-step level shifter design. Fast switching transitions and low switching loss are achieved with 94% peak efficiency for the complete class-D power stage in the realized chip. In addition, gate driver sizing procedures for the class-D output stage are discussed, showing that the variable gate driving strength can greatly improve efficiency when on-chip supply bounce is the limiting factor. Also based on the dissipation analysis, this thesis describes the design of an efficiency-improved high-voltage class-D power amplifier. The amplifier adaptively regulates its switching frequency for optimal power efficiency across the full output power range. This is based on detecting the switching output node voltage level at the turn-on transition of the power switches. For the final chip prototype, the amplifier achieves 93% efficiency at 45W output power, &gt;80% power efficiency down to 4.5W output power and &gt;49% efficiency down to 0.45W output power. Finally, for the aim of idle loss reduction, the linearity degradation of dead time insertion and switching frequency increase is discussed in this thesis. To cope with this linearity degradation, both open-loop and closed-loop error correction techniques are explored and it is further shown that a higher-order loop filter combined with uniform sampling once per switching cycle is potentially a suitable choice for closed-loop fixed-carrier class-D implementations.

This paper compares two converter configurations for a multi-10 MVA gate-turn-off (GTO) reactive power compensator (STATCOM) from the viewpoints of converter connection and switching frequency. One is a single-bridge system consisting of a three-phase bridge converter unit and a transformer. Its pulsewidth modulation (PWM) frequency varies from 450 to 1800 Hz, and its line frequency is 50 Hz. The other is a multiconnected converter system consisting of plural, single-, or three-phase converter units and transformers. Its switching frequencies are chosen to be the lowest possible. The evaluated items are harmonic distortion, power loss, GTO utilization factor, and control response. Our simulation study shows that the multiconnected converter system with the lowest switching frequency is superior to the single-bridge system with the higher switching frequency in every case, even when there are severe line faults requiring very quick response. A new control strategy is adopted for obtaining quick response.