Battery Loss and Stress Mitigation in a Cascaded H-Bridge Multilevel Inverter for Vehicle Traction Applications by Filter Capacitors

Abstract

In this paper, two types of filter capacitors of varying capacity, were connected to the battery packs of a cascaded H-Bridge single-star multilevel vehicle traction inverter, and their influence on the battery losses has been analyzed. The battery and capacitor simulation models used are experimentally verified in a down-scaled system. Different capacitor configurations were simulated for four drive cycle scenarios to determine the potentials for the mitigation of current pulse stresses and battery loss reduction with respect to the added weight. By adding capacitors corresponding to a weight of 4% of the initial battery storage, the peak current is reduced by 5%-20%, depending on the operating point from DC to a few kHz, and the battery losses are reduced by 10%. In comparison, it is demonstrated that adding supercapacitors is more beneficial for lower output frequencies, while adding electrolytic capacitors is better for higher output frequencies. Furthermore, the low-order voltage harmonics of the DC-rails between the converter and battery were reduced by 10%-30% for frequencies above 9 kHz, which decreases the potential of electromagnetic disturbances. In addition, during cold battery temperatures, when it is very important to avoid heavy cyclings, the loss reduction using the capacitors was 2.5 times larger than for nominal temperature.

Battery Modeling and Parameter Extraction for Drive Cycle Loss Evaluation of a Modular Battery System for Vehicles Based on a Cascaded H-Bridge Multilevel Inverter

“…for Vehicles Based on a Cascaded H-Bridge Multilevel Inverter multilevel inverters (MLI) are gaining interest in the field of vehicle propulsion applications [5]- [7], such as the neutral point clamped (NPC) and the cascaded H-bridge (CHB) inverter, referred to as modular battery systems [8]. These inverter topologies have several advantages compared to the classical two-level inverter, for example, possible fault tolerant operation [9]- [11], efficiency enhancement [11]- [14], and especially, low output voltage harmonic and electromagnetic emissions [15], [16]. In [6], [11], and [14], the CHB topology utilizing low voltage MOSFETs is considered.…”

“…On the other hand, the battery packs in a CHB inverter are subjected to a low-frequency (LF) current ripple, containing a substantial amount of low-order harmonics, especially a second-order harmonic component. Thus, the LF current ripple varies in frequency depending on the operating point (OP) of the vehicle [16], [24]. This, in turn makes accurate energy calculations and efficiency comparisons between two-level and various MLIs difficult.…”

“…with k as the number of the chosen RC-pairs [16]. Since the RC-pairs do not have a physical representation, the joule losses can be calculated using the measured battery current and cell voltage, as well as the estimation of the open circuit voltage, as…”

“…Therefore, six typical OPs of the speed-torque characteristic, as can be seen in Table III, are initially chosen to assess the dynamic behavior of the battery models in relation to characteristic vehicle loads [6]. To obtain the equivalent OPs for the small-scale system, the OPs in Table III are down-scaled according to (16) and (18), shown in Table IV. Fig.…”

A Single-Carrier-Based Pulse-Width Modulation Template for Cascaded H-Bridge Multilevel Inverters

“…This trend is a direct response to the global quest and search for sustainable and more environmental-friendly electrical power sources and utilizations. In this scenario, inverters/dc-ac converters are among the cardinal power electronics devices deployed in various key areas such as high-voltage direct-current (HVDC) transmission, [1,2], Flexible AC Transmission Systems (FACTS), [3,4], renewable energy grid integration, [5][6][7][8], railway and vehicle traction, [9][10][11], energy storage systems, [12], marine propulsion, [13], solar water pumping system, [14], grinding and rolling mills, [15], compressors and extruders, [16], to mention. Such deployment requires certain criteria to be met by the power electronics inverters of which high output voltage and a range of operational output power quality indices are crucial.…”