Traction Inverter Research Articles

High-Voltage Hybrid IGBT Power Modules for Miniaturization of Rolling Stock Traction Inverters

A type of 3.3-kV/450-A half-bridge insulated-gate bipolar transistor power module combining the silicon (Si) and silicon carbide (SiC) technologies has been developed and reported in this article, for the miniaturization of the Chinese high-speed railway rolling stock traction inverters. This module is developed by integrating the next-generation industrial standard high-voltage packaging topology and the state-of-the-art 3.3 kV wide bandgap semiconductor chip technology, to reduce the waste power dissipation during operation, which in turn can lead to effective downsizing of key components in the traction inverter design. The module layout characteristics and the SiC Schottky barrier diodes design for substitution of the conventional Si fast recovery diodes will be described in detail. The mechanical, thermal, and electrical performances of the hybrid module are compared comprehensively with the Si-based counterpart. Based on the experimental results, an inverter system level evaluation of both modules is also conducted by electro-thermal simulation. The hybrid module shows advantages in loss reduction leading to great potential of system miniaturization, which is a cost effective solution for massive upgrading of the existing high-speed train traction inverters.

Optimizing EV Power Electronics

Extending the Driving Range of EVs is one of the Key Challenges in the Automotive Industry, However Silver Sintering Technology is one Method to Increase the Efficiency of Traction Inverters

A Comparative Study of Over-Current Sensing for Traction Inverters

The over-current condition for a traction inverter can indicate flaws on control algorithms, interference on logic signals, hardware aging, or hardware misconduct. Thus, proper detection of over-current conditions during inverter operation is a critical item for inverter development and product validation. This paper reviews several widely used over-current detection methods and a few theoretically approved over-current detection methods. The main focus of this review includes the sensing bandwidth, sensing accuracy, and implementation complexity of the studied over-current detection methods. The advantages of those widely used methods and the application requirements for the theoretically and prototypingly approved methods are concluded by this review.

Implementation of the ACO algorithm in an electrical vehicle system powered by five-level NPC inverter

The ant colony optimization (ACO) algorithm is generally used to create an optimal PI regulator added to the pulse width modulation (PWM) strategy for a five-level neutral-point-clamped (NPC) inverter implemented in electric vehicle (EV). As heavy transportation is our main focus, the proposed system was formed by two induction motors (IMs); each of which was fed by one NPC inverter. The two IMs were fixed to the front axle and the rear axle, respectively. The PDC-PWM (Phases Disposition Carrier-PWM) strategies for the three-phase five-level NPC inverter was employed in the rotor-flux-oriented control (FOC) of the induction motor (IM). Special interest was given to the analysis of the total harmonic distortion (THD%). Considering the dynamic loading conditions of an EV driven by an IM, the proposed ACO algorithm effectively calculated the required PI parameter to find the best PI regulator gains values. These optimizations were applied to the PDC-PWM strategy in order to obtain the minimum THD% in both current and voltage outputs. The effectiveness of the introduced system for a wide range of torque/speed variations was proven through simulation by developing a model of an IM traction inverter drive with the FOC strategy for closed-loop control. As the experimental test realization of the designed system was not possible because it is very expensive, the ACO optimization performance was confirmed by means of MATLAB/SimPower Systems simulations.

A Review of Modulation and Control Techniques for Multilevel Inverters in Traction Applications

Traction inverter has been the subject of many studies due to its essential role in the proper performance of the drive system. With the recent trend in increasing the input voltage in battery-powered electric vehicles, multilevel inverters have been proposed in the literature as a promising substitute for conventional two-level traction inverters. A critical aspect of utilizing multilevel structures is employing proper control and modulation techniques. The control system structure must be capable of handling a number of key issues, like capacitor voltage balancing and equal power loss sharing, which arise in multilevel topologies. This paper presents a review of the present-day traction drive systems in the industry, control and modulation techniques for multilevel structures in the inverters, as well as the principal challenges that need to be addressed in the control stage of the multilevel traction inverter. A comparison has been made between different methods based on the most important criteria and requirements of the traction drive system. Finally, future trends in this application are presented and some suggestions have been made for the next generation of traction drives.

A Review of Multilevel Inverter Topologies in Electric Vehicles: Current Status and Future Trends

Traction inverter, as a critical component in electrified transportation, has been the subject of many research projects in terms of topologies, modulation, and control schemes. Recently, some of the well-known electric vehicle manufacturers have utilized higher-voltage batteries to benefit from lower current, higher power density, and faster charging times. With the ongoing trend toward higher DC-link voltage in electric vehicles, some multilevel structures have been investigated as a feasible and efficient option for replacing the two-level inverters. Higher efficiency, higher power density, better waveform quality, and inherent fault-tolerance are the foremost advantages of multilevel inverters which make them an attractive solution for this application. This paper presents an investigation of the advantages and disadvantages of higher DC-link voltage in traction inverters, as well as a review of the recent research on multilevel inverter topologies for electrified transportation applications. A comparison of multilevel inverters with their two-level counterpart is conducted in terms of efficiency, cost, power density, power quality, reliability, and fault tolerance. Additionally, a comprehensive comparison of different topologies of multilevel inverters is conducted based on the most important criteria in transportation electrification. Future trends and possible research areas are also discussed.

Silicon Carbide Multi-Chip Power Module for Traction Inverter Applications: Thermal Characterization and Modeling

Semiconductor power modules are the key hardware components of a traction inverter. It drives motor speed and torque, managing the energy exchange from battery to motor and viceversa. The increasing demand for electric and hybrid vehicle requests high performance power modules. Power semiconductor devices based on wide band gap compound, like silicon carbide (SiC), have excellent electrical properties in terms of on-state resistance, stray inductance and performance at high commutation frequency. One of the most promising solution is silicon carbide MOSFET power module in which each switch is made by several different dies placed in parallel. Embedded direct cooling system and novel materials with high conductivity (e.g., active metal brazed substrates) can be considered to enhance thermal performance. A robust method is needed to characterize and to predict power module temperature behavior considering the importance of the thermal performance to improve reliability and to optimize module weight and dimensions. According to several parallel dies inside each switch, classic method based on temperature electric sensitive parameter (TSEP) shall be validated with direct measurement. In this framework, it has been reported the thermal characterization of a power module for a traction inverter based on eight silicon carbide MOSFETs for each switch. Both TSEP and infrared measurements have been employed. Thermal behavior has been numerically reproduced, creating a simplified equivalent network and developing a predictive model by finite element method (FEM).

The Potential Impact of Using Traction Inverters With SiC MOSFETs for Electric Buses

The efficiency improvements offered by adopting Silicon Carbide (SiC) devices in Electric Vehicle (EV) inverters has been widely reported in various studies. However, it has still not been established whether or when the efficiency benefits can counteract the high price of SiC devices, especially for the scenario of urban electric buses. In this paper, the potential impact of installing SiC devices on electric buses is analyzed from the perspective of economic benefits. The SiC inverter used in the drive system is based on a discrete MOSFET in parallel. For comparison, an Si inverter based on a sixth-generation IGBT produced by Infineon is also evaluated. A vehicle simulation platform is established in Simulink for an evaluation of energy consumption for different scenarios. It is shown that significant energy savings can be gained when the vehicle operates mostly in the partial load area. While in the nominal load area, energy savings are very limited. Based on the analysis, the conditions for offsetting the cost premium of SiC devices to realize system-level advantages are discussed using a multi-dimensional analysis considering the change in battery and device prices, driving range, vehicle mass, and driving cycles.

An 800-V High-Density Traction Inverter—Electro-Thermal Characterization and Low-Inductance PCB Bussing Design

The need to increase the power density of traction inverters for the electrified transportation systems offers an opportunity to adopt silicon carbide (SiC) devices. To ensure the system reliability, it is critical to select a SiC power module that can dissipate a sufficient amount of power to avoid operating beyond the maximum allowed junction temperature. In this work, a comprehensive electro-thermal characterization procedure based on the virtual junction temperature concept is proposed to characterize the module’s maximum power dissipation as a function of coolant temperature. Using the characterization results, it is feasible to determine the module’s safe operating area for a traction application in terms of the switching frequency and the coolant temperature. The proposed characterization method is demonstrated on a custom 1200-V SiC module to validate its feasibility for an 800-V, 150-kVA traction inverter system. In addition, the design approach for a low-inductance bussing structure using heavy copper printed circuit board (PCB) is presented in this work, which leads to a snubberless, compact and low-cost system design. Measurements and experimental studies have been performed to validate the effectiveness of PCB bussing design. The overall volume of the inverter system is around 1.75 L, which leads to a volumetric power density of 86 kVA/L.

Characterization of a 3.3-kV Si-SiC Hybrid Power Module in Half-Bridge Topology for Traction Inverter Application

A state-of-the-art 3.3-kV/450-A hybrid power module for the next generation traction inverter of rolling stock is reported in this paper, combining the silicon (Si) insulated-gate bipolar transistor (IGBT) and silicon carbide Schottky barrier diodes (SBDs) chips. Compared with the existing hybrid technology at the same voltage level, this module is characterized by a half-bridge topology, in which 6 IGBT and 12 SBD chips are integrated in each switch. The outnumbering of the diodes represents a promising mitigation to the low availability of SBDs at this voltage level. Both static and dynamic test of this module and an equivalent Si-based module are carried out comparatively. Apart from describing the features of compactness, low-inductance, and good current distribution among chips, this module is characterized by low turn-ON current overshooting and turn-ON loss of IGBTs, negligible diode reverse recovery time and loss, as well as flexible allowance of IGBT turnON current rising rate dI/dt. A parameterized study is carried out to benchmark the advantage of this new topology. Based on the experimental results, the performance of the hybrid module in a three-phase traction inverter circuit is also evaluated by means of electro-thermal simulation. The hybrid module distinguishes itself by describing much lower power loss and junction temperature than its Si-based counterpart.

On-Board Single-Phase Integrated Electric Vehicle Charger With V2G Functionality

Mass adoption of electric vehicles (EVs) is contingent on the availability of charging infrastructure. One solution to this issue is the introduction of on-board fast chargers, but such solutions typically require the installation of additional magnetic components that increase EV mass. An alternative approach is the dynamic redeployment of drivetrain components for charging when the vehicle is stationary. This article proposes an on-board single-phase charger that reuses the traction inverter and motor. The system consists of a dual-inverter drivetrain, which affords higher voltage charging compared to conventional systems. In addition, the system is able to operate bidirectionally and operate at any power factor for grid support services with real and reactive power exchange without subjecting the motor to low frequency harmonic currents. Experimental tests demonstrated operation at 19.2 kW using a 110-kW EV motor and a full-scale, state-of-the-art, dual-inverter drive prototype. Measured peak efficiencies of over 97% demonstrate the viability of integrated charging in a real-world scenario.

Reconfigurable Line-Side Converter for DC Voltage Matching and Ripple Suppression in Multisystem Locomotives

The multisystem locomotive traction drive system is fed by different kinds of railway traction power supply systems (TPSSs). The direct connection of the dc TPSSs and the traction inverter are broadly adopted. However, the dc-link voltage is influenced by the variable and fluctuant catenary voltage, therefore wasting the capacity of the devices, complicating the wiring of motor as well as reducing the reliability of system. In this article, the line-side converter, which is used as an ac/dc four-quadrant converter in ac supply system, is reconfigured as a dc/dc chopper for dc voltage matching in dc supply systems. The quadruple interleaved structure is adopted to eliminate the current ripple caused by the chopper. First, structures and corresponding switching method of the reconfigurable line-side converter are introduced. With the help of modal analysis, the principle of chopper operation, the mechanism, and the influencing factors of current ripple suppression are revealed. The system control method and configuration switching algorithm for voltage matching and stabilizing are then presented. Finally, the proposed conceives are validated by hardware-in-the-loop-based system.

A review on multilevel H-Bridge cascaded inductor less hybrid inverter for Electric vehicles with PWM control

This article explains a cascaded H-bridge without inductor for Electric operated and Hybrid Electric operated Vehicles applications. Power inverter systems, DC-DC converter [8] is now available for hybrid electric operated vehicles to improve conventional battery stored voltages. The existing inverters for HEV traction drives have High density of power, costly and poor performance, they need a bulky inductor. This paper proposes An H-bridge cascaded without inductor MLI for Electric operated and Hybrid Electric operated Vehicles applications. Any H-bridge historically requires a DC Electricity. In the proposed cascaded inductor less H-bridge, a regular 3-leg (one leg per phase) is used and a series H-Bridge using a DC power source condenser with each inverter leg. The PWM switching scheme is used to control [18] the modulation and create a five-stage phase voltage. Results indicate that the proposed circuit generates an improved AC voltage which can be the performance of a multilevel inductor less DC - AC H-Bridge cascaded inverter.

Accelerated Life Testing Method of Metallized Film Capacitors for Inverter Applications

DC-link capacitors are one kind of reliability-critical component in traction inverters. As such, it is essential to evaluate the degradation characteristics of dc-link capacitors. Accelerated life testing is an effective and standard method to evaluate the capacitors’ lifetime and degradation mechanisms. Therefore, an accelerated life testing method for dc-link capacitors in three-phase inverter applications is proposed in this article. In order to reproduce the same encountered stress, exactly reflecting the real condition for the capacitor under test, a three-phase inverter with the capacitor under test and a three-phase balanced inductor load are used as the evaluation circuit. Due to the employment of the inductor load, the power consumption of the inverter can be reduced, while the full-scale current rating can be maintained so that the capacitor under test is subjected to the practical ripple current stress. In order to estimate a capacitor’s capacitance with high accuracy, an effective and direct condition monitoring method, which is based on the proposed evaluation circuit, is also proposed in this article. By injecting an ac voltage into the dc link, the ac current and voltage components in the dc-link capacitor are generated. Then, the capacitance mathematical model can be developed by analyzing the injected voltage component and the resultant current component. As the proposed method only requires estimating the parameters from the input voltage and current, there is no need to install additional capacitor current sensors, which are usually difficult to install. Moreover, the amount of monitored and processed data can be reduced. Thus, the proposed method is easy to implement for accelerated life testing in practice. In addition, experiments are carried out to verify the analysis and effectiveness of the proposed solution.

Open-circuit fault diagnosis of traction inverter based on improved convolutional neural network

In the traction system of high-speed EMUs, the inverter’s Insulated Gate Bipolar Transistor (IGBT) often occurs open-circuit (OC) faults. However, traditional fault diagnosis relies mainly on signal processing to extract fault features, which is susceptible to environmental interference, resulting in poor generalization ability of the model. Aiming at this problem, a fault diagnosis method based on an improved convolutional neural network is proposed. Firstly, the three-phase stator current signal is preprocessed by wavelet domain denoising. Secondly, fault features are independently learned through a convolutional network. Finally, a fully-connected layer is used for fault diagnosis. The experimental results show that this method could resolve the OC fault diagnosis problem of the inverter’s IGBT effectively, and also achieve higher accuracy under the interference of noise, and the diagnosis can be made at 0.01s after the fault occurs.

Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel-Three-Dimensional Manifold Coolers—Part 2: Parametric Study of EMMCs for High Heat Flux (∼1 kW/cm2) Power Electronics Cooling

Abstract Thermal management of power electronics modules is one of the limiting factors in the peak power capability of the traction inverter system and overall efficiency of the e-drive. Liquid cooling using embedded microchannels with a three-dimensional (3D)-manifold cooler (EMMC) is a promising technology capable of removing heat fluxes of >1 kW/cm2 at tens of kPa pressure drop. In this work, we utilize computational fluid dynamics (CFD) simulations to conduct a parametric study of selected EMMC designs to improve the thermofluidic performance for a 5 mm × 5 mm heated area with the applied heat flux of 800 W/cm2 using single-phase water as working fluid at inlet temperature of 25 °C. We implemented strategies such as: (i) symmetric distribution of manifold inlet/outlet conduits, (ii) reducing the thickness of cold-plate (CP) substrate, and (iii) increasing fluid–solid interfacial area in CP microchannels, which resulted in a reduction in thermal resistance from 0.1 for baseline design to 0.04 cm2 K/W, while the pressure drop increased from 8 to 37 kPa.

Thermal and Electrical Performance in High-Voltage Power Modules With Nonmetallic Additively Manufactured Impingement Coolers

As high voltage, wide-band-gap power modules increase in power density with high switching frequency, they create localized hot spots and harmful electromagnetic interference (EMI). If not treated properly, these issues can drastically reduce the reliability of the devices. In this article, we propose a solution to address both of these challenges created by power module building blocks which are designed for use in a hybrid-electric aircraft traction inverter. Additive manufacturing is used to fabricate a nonmetallic jet impingement device to decrease power module temperatures. Moreover, the nonmetallic structure limits the accentuation of EMI created by the module operating at high switching frequencies. Conjugate heat transfer simulations are used to predict the thermal performance of the cooler. In this article, a reduction of maximum die temperatures is observed, along with an increase in temperature uniformity throughout the base plate. Experimental results show a minimum thermal resistance of 0.1 K/W and an average heat transfer coefficient up to 3600 W/m2.K at peak operation. Finally, EMI tests are performed to show a two orders of magnitude reduction of parasitic capacitance using the nonmetallic cooler compared with a metallic heat sink. This directly leads to a 25 dB decrease in the common mode noise.

Traction Inverter Highly Accelerated Life Testing With High-Temperature Stress

Highly accelerated life testing (HALT) is one of the most popular step-stress testing methodologies for identifying the weaknesses and increasing product reliability in a fast and cost-efficient way. The traction inverter plays a critical role in EV/HEV power train systems, and the requirements on its reliability at the harsh environment operation are becoming more demanding. In this article, to evaluate the weak links and various components performance and ascertain the effect of high temperature on the traction inverter, the traction inverter HALT was carried out with high-temperature stress between 190 °C–220 °C taking the IGBT on-die temperature as the benchmark. Nine traction inverters were tested, which were divided into four groups with respect to the designed step-stress test profile. The changes in electrical and thermal indicators were observed online using the proposed monitoring system. At the end of each test, the effects of different conditions on the overall testing time, failure modes, and damage were examined, and the damages were listed systematically and discussed. Furthermore, the characteristics of the dc-link capacitor at different temperatures and the related degradation were observed online. The results show that the inverter can operate hundreds of hours with the IGBT on-die temperature of 200 °C, and the gate driver board chip of 127 °C. The findings in this study could help to the improvement design of the traction inverter, as well as to keep the design life prediction never be overestimated.

Comparative Study on Power Module Architectures for Modularity and Scalability

Abstract Silicon carbide (SiC) wide bandgap power electronics are being applied in hybrid electric vehicle (HEV) and electrical vehicles (EV). The Department of Energy (DOE) has set target performance goals for 2025 to promote EV and HEV as a means of carbon emission reduction and long-term sustainability. Challenges include higher expectations on power density, performance, efficiency, thermal management, compactness, cost, and reliability. This study will benchmark state of the art silicon and SiC technologies. Power modules used in commercial traction inverters are analyzed for their within-package first-level interconnect methods, module architecture, and integration with cooling structure. A few power module package architectures from both industry-adopted standards and proposed patented technologies are compared in modularity and scalability for integration into inverters. The current trends of power module architectures and their integration into inverter are also discussed. The development of an eco-system to support the wide bandgap semiconductors-based power electronics is highlighted as an ongoing challenge.

An Approach for Estimating the Reliability of IGBT Power Modules in Electrified Vehicle Traction Inverters

The reliability analysis of traction inverters is of great interest due to the use of new semi-conductor devices and inverter topologies in electric vehicles (EVs). Switching devices in the inverter are the most vulnerable component due to the electrical, thermal and mechanical stresses based on various driving conditions. Accurate stress analysis of power module is imperative for development of compact high-performance inverter designs with enhanced reliability. Therefore, this paper presents an inverter reliability estimation approach using an enhanced power loss model developed considering dynamic and transient influence of power semi-conductors. The temperature variation tracking has been improved by incorporating power module component parameters in an LPTN model of the inverter. A 100 kW EV grade traction inverter is used to validate the developed mathematical models towards estimating the inverter performance and subsequently, predicting the remaining useful lifetime of the inverter against two commonly used drive cycles.