A Universal Formulation for Multilevel Selective Harmonic Elimination - PWM with Half-Wave Symmetry

Selective harmonic elimination - pulse width modulation (SHE-PWM) can be utilized to improve the efficiency of multilevel voltage source converters due to its ability to provide low switching frequency and tight control of low-order harmonics. In addition, SHE-PWM with half-wave (HW) symmetry provides a higher number of solutions than quarter-wave (QW) symmetry and therefore, the waveform design can be improved. This work proposes a universal formulation, which can be utilized with HW symmetry, that provides a unique system of equations valid for any possible multilevel waveform. Thereby, without using predefined waveforms, this formulation provides the ability to search simultaneously both the firing angles and the switching patterns, simplifying significantly the search process and providing a high number of solutions. With the aim of selecting the optimum sets of firing angles, the solutions provided by HW and QW symmetries are compared, based on several metrics of harmonic performance, for particular test cases. Experimental results also validate the universal formulation with HW symmetry.Eusko Jaurlaritza; Secretaria de Estado de Investigacion Desarrollo e Innovacio

Comparison of the heat transfer capabilities of conventional single-phase and two-phase cooling systems for electric vehicle IGBT power module

This paper presents a comparison of conventional single-phase water/glycol liquid and innovative two-phase cooling technology for thermal management of high power electronics automotive IGBT modules during full drive cycle. The proposed two-phase cooling system is built using conventional automotive air conditioning components (condenser, expansion valve, compressor, and vapor and liquid lines) and conventional cold plate as used for single-phase cooling, thus the design does not require the development of new technology for its implementation. 3-D numerical simulation in COMSOL and experimental results of two-phase cooling have been obtained on a prototype and compared to conventional water/glycol cooling high power electronics modules, with considerable improvement on working temperature, power transfer capacity and equalization of die temperatures during a full driving cycle. These results suggest that two-phase cooling using the same cold plates as in single-phase cooling can be used to substantially improve the performance and reliability, of EV power converters without major changes

Interleaving Modulation Schemes in Asymmetrical Dual Three-Phase Machines for the DC-Link Stress Reduction

The DC-Link capacitor plays a crucial role as far as power density and reliability are concerned: it occupies approximately 40% of the inverter, and causes approximately 30% of its failures. Asymmetrical dual three-phase (ADTP) multiphase arrangements are gaining relevance in the automotive sector for powertrain applications. This work focuses on reducing the impact that the widely used double zero sequence injection (DZSI) family of PWM techniques have on such a bulky and failure-prone component in an ADTP arrangement by means of interleaving techniques. By using the double Fourier integral formalism, the input current spectra and the overall performance of these PWM techniques have been derived, in terms of current rms value and voltage ripple in the DC-Link capacitor. Simulations have shown that choosing an adequate interleaving scheme and angle considerably relieves both current and voltage stresses on the DC-Link capacitor compared to noninterleaved operation. Reductions of 84% current rms and 86% voltage ripple have been achieved at static operating points. Finally, by averaging the rms current over WLTP standard driving cycle, reductions up to 26% have been obtained under more realistic conditions. All this would enhance the reliability and reduce the size of the onboard capacitors in future electric vehicles

Digital control of multiphase Series Capacitor Buck converter prototype for the powering of HL-LHC Inner Triplet magnets

A major upgrade will be conducted in the Large Hardon Collider (LHC) at CERN. This high luminosity (HL) version of the LHC will increase the nominal luminosity by a factor of five. One of the key technologies of the HL-LHC are the new superconducting Inner Triplet (IT) magnets, responsible of producing high magnetic fields to focus particle beams. To power the IT magnets from the grid, a multi-stage power supply with an intermediate 24 V battery pack is being considered. In such topology, a lowvoltage high-current DC/DC converter operating with a very high step down-ratio is required for the final conversion stage. In this work, an interleaved multiphase Series Capacitor Buck converter is proposed to feed the IT magnets from the battery pack. A novel voltage regulation approach that ensures the current balance between the paralleled Series Capacitor cells is also proposed, where one cell is responsible for the output voltage regulation, while the remaining cells are current regulated. A balanced current sharing between the Series Capacitor cells is achieved, when the current controlled cells are referenced by the actual current of the 1st one. The proposal is theoretically analysed and experimentally validated in a six cell 1000 A prototype unit

Circulating current control for modular multilevel converter based on selective harmonic elimination with ultra-low switching frequency

Multilevel converters (MCs) are utilized in medium voltage (MV) high power applications due to its higher efficiency than two level converters. On the other hand, modular multilevel converters (MMCs) provide several advantages with regard to other MCs, such as higher scalability, reliability and no requirement of a common DC capacitor. Particularly, low switching frequency modulations, such as (2N+1) selective harmonic elimination (SHE) - pulse width modulation (PWM), may improve the efficiency of MMCs when they are utilized in MV and high power applications, where the number of sub-modules is not high. This work presents a new circulating current control for MMC when (2N+1) SHE-PWM is utilized. Therefore, it is possible to operate the converter simultaneously with low switching frequency and low capacitor voltage ripple at every sub-module besides a correct energy balance between arms. In addition, a new method to implement (2N+1) SHE-PWM for MMCs, which is also valid to implement standard SHE-PWM for any MC, is provided. Using this method, different equation systems are not required for every switching pattern. In this way, this technique provides simultaneously both the switching patterns and the firing angles which solve the SHE problem, simplifying the searching task. Simulation results which have been obtained from a MMC with 5 sub-modules at every arm, have validated the novel proposed circulating current control. Furthermore, the spectrum of the simulated line to line voltage waveform has proved the correct performance of the proposed (2N+1) SHE-PWM implementation method. Several sets of angles have been provided throughout the ma range, where 17 harmonics have been controlled

Circulating Current Control for Modular Multilevel Converters with (N+1) Selective Harmonic Elimination - PWM

Modular multilevel converters (MMCs) require control of the circulating current, i_circ, to improve their operation and efficiency. This is particularly important when low switching frequency modulation techniques, such as selective harmonic elimination (SHE-PWM) are applied. This work provides a novel method to control the circulating current along with (N+1) SHE-PWM. Unlike the case of (2N+1) SHE-PWM, explicit redundant levels are not available and, therefore, different modulation indexes, m_1 and m_2, are employed in the upper and lower arms to obtain the desired modulation index m_a. Unlike previous (N+1) circulating current methods, the distances between m_a, m_1 and m_2 remain constant to not disturb the phase output voltage, with an interchange of m_1 and m_2 between the arms used to follow the desired i_circ. The control adjusts the dc component of the circulating current and the energy stored in the SMs to their references, while maintaining the energy balance between the upper and lower arms. Simulation tests and experimental results, obtained from a single-phase laboratory prototype MMC, validate the proposed control technique