The Effects of Humidity on Performance of Electric Vehicles - Report Example

The Effects of Humidity on Performance of Electric Vehicles Name: Lecturer: Course: Date: Table of Contents Table of Contents 2 Introduction 3 Comparison of Current EVs 4 Technical problems of EV electric motor assemblies 6 Batteries, fuel-cells and their technical problems in humidity 7 Suggestion 9 Conclusion 10 Introduction In applications such as electric vehicles, components such as inverters and electric motors are highly sensitive to environmental conditions such as humidity. Such uncontrolled environmental conditions may affect the reliability and performance of the vehicle as a result increasing maintenance cost and events of failures. This paper focuses on how electric vehicles are affected by humidity. The effect of humidity on batteries and electric motors and inverters is discussed. Further, the current EVs technologies in regards to humidity are compared. Also examined include a range of technical problems and to improve the performance of EV with regard to humidity (Ciprian & Lehman 2009). Electric vehicles (EV) provide a platform that allows for advanced energy management which give rise to advantages such as low running cost and simplicity of use (Khayyam et al 2008). In a typical electric car, the inverter and the electric motor are packed up as a single unit along with the heat sink that is set in the middle (Ciprian & Lehman 2009). The heat sink consists of a cold chamber developed with the view of absorbing maximal heat losses from the unit consisting of electric motor and inverter. A study by Lohse-Busch (2004) to examine the capability of thermal overload of the electric inverter and motor unit found that the unit experiences a range of challenges that aside from the packaging and design, has a host of concerns due to their temperature limits. The researcher demonstrated that the inverter and the motor temperatures rise during operation. Hence, they become susceptible to variations in humidity affecting their operation (Lohse-Busch 2004). Comparison of Current EVs Electric vehicle components are electric motor for vehicle propulsion, battery for storing energy, power control system, mechanical transmission and a generator. Currently, the main types of EVs exist include plug-in electric vehicles (PEV), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs) and Extended-range electric vehicles (TVA 2013). First, plug-in electric vehicles (PEV) included automobiles that are rechargeable from an external electric source. Energy is stored in rechargeable battery packs that drive the wheels. Two types of PEVs currently exist, namely plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs). BEVs contain no combustion engines. They are rechargeable from an electric grid. On the other hand, PHEVs have electric drive systems and a combustion engine that recharges the battery. BEVs are all electric vehicles, since they have no internal combustion engine. Therefore, they have to be plugged into an electric power sources to recharge the battery (Rahman, Zhang & Zhu 2008). Unlike PHEVs, they need large batteries of more than 35 kilowatt hours (TVA 2013). PHEVs therefore rely on electric battery that supplements the conventional internal engine combustion, which in turn increases the fuel-efficiency of the car. Additionally, the electric motor reduces the idling of the engine and increases the vehicle’s capability to accelerate or start. Unlike BEVs, they are dual-fuel cars where the internal combustion of the engine and electric motor are capable of driving the wheels (Yang & Roorda 2012). Both the plug-in hybrid cars and the hybrid cars use battery and internal combustion to drive electric motor. The difference between them however is that while plug-in hybrid vehicles can be recharged using an electric power source or outlet, the hybrids cannot (TVA 2013). Extended-range electric vehicles on the other hand utilize internal combustion engine that powers their electric generators, thus recharging the battery through a linear process. However, unlike the PHEVs, in these EVs, only the electric motor serves to power the wheels. On the other hand, the internal combustion engine serves to solely recharge the batteries (TVA 2013; Huang, Yin & Zhang, 2008). BEVs mostly utilize regenerative braking essential for recapturing energy likely to be lost through frictional losses or dissipation of heat, hence reducing efficiency or energy and reducing the wear and tear or the brake system. Like PHEVs, BEVs make use of high energy of torque located in electrical motors inside the motor assembly (SEI 2007). Some of the batteries used by the EVs include hydrogen-based fuel-cells (PEM), Lithium batteries and Ni-MH batteries. The fuel-cell converts hydrogen into electric energy through the process of oxidation. In EVs powered by fuel-cells, the electricity produced power the wheels as the PEM fuel-cell system and the battery pack supply power to the electric motor (Sun et al 2002). Lithium-ion batteries on the other hand use battery cells that are connected, with each cell having the three key elements, namely electrolyte, anode and cathode (Anderson & Carlson 2012). However, the performance of these batteries and the electric motor assemblies that they power are affected by variations in humidity and extreme temperatures. Technical problems of EV electric motor assemblies Electric motor assemblies of EVs have a range of limiting factors caused by variations in humidity. The assembly consists of AC induction motors and DC/AC inverter (Lohse-Busch 2004). An induction motor is made of a stator and a rotor. The rotor consists of steel and aluminum. It is designed to respond to magnetic fields that drive it within the stator copper windings. Through circulation of AC current via the stator copper windings, fluctuation of magnetic fields is enabled. On the other hand, the rotor attempts to pursue the fields enabling the rotor to turn with some slip. This implies that the speed of the rotor is slower than that of the rotor that facilitates the torque. The current in the copper windings facilitates losses of ohms that translate into heating internally of the copper in the windings. This further implies that the copper windings are susceptible to thermal factors and humidity. In this case, high temperatures may melt the plastic insulation of the stator and that of the copper, hence representing a limiting factor to EVs (Lohse-Busch 2004). The DC/AC inverter on the other hand is designed to synthesize AC waveforms from the DC source of energy. It is controlled digitally. Additionally, the voltage is altered to maximum from zero in a fraction of time. However, the current in the windings does not alter instantly enabling the voltage to attain average value in a fraction of time. A high-powered switching device called “insulated gate bipolar transistor” (IGBT) alters the voltage. IGBT is susceptible to humidity and other thermal factors. IGBT has conduction and switching losses that heat them up, hence high temperatures causes a reduction in the power processing capacity and may also destroy the device (Lohse-Busch 2004). The two limiting factors of the inverter and the electric motor therefore require a heat sink that absorbs sufficient heat to keep the inverter and motor unit cool, hence preventing power loss and damage. However, forced air convection may cause humidity by failing to enable heat transfer with lower temperatures (Lohse-Busch 2004). Batteries, fuel-cells and their technical problems in humidity Materials of the battery membrane are applied in electric vehicles (EV) or hybrid electric vehicles (HEV). The battery membranes are of two categories, namely power-battery membrane and fuel-cell membrane (Yong, Jian & Jie 2012). Yong, Jian and Jie (2012) elaborated that in a fuel cell, energy is stored in hydrogen, where its chemical reaction with oxygen generates electricity. Such behaviour is exhibited by proton exchange membrane (PEM) fuel-cells. Low humidity and high temperature affect their operating state since they operate in moist state while one of its regions is exposed to air. PEM enables channel for proton which lowers internal energy resistance hence boosting power output. As a result, it directly influences the performance of fuel-cells. PEM is affected by humidity hence reducing power output. Humidity lowers the rate of degradation of catalyst. In addition, the humidity in the membrane of the electrode makes it easier for protons to channel into the electrolyte facilitating faster loss of catalyst (Yong, Jian & Jie 2012). Lohse-Busch (2004) explained that due to this susceptibility, an automotive type fuel-cell of electric vehicles requires a supporting systems such as air conditioning and supply system, fuel delivery and thermal management system. While the thermal system is designed to maintain suitable temperature for operation of the fuel cell, the fuel delivery system is designed to provide fuel cell stack with sufficient hydrogen at the required humidity. On the other hand, the air conditioning system provides the fuel cell with enough air at the required humidity (Lohse-Busch 2004). A study by Yong, Jian and Jie (2012) also found that Ni-MH batteries also used in electric vehicles are affected by humidity. The researchers found that thermal factors are a major cause of damage for separator materials of nickel-hydrogen. While increased temperatures degrade and break the separator material, variations in humidity cause the separator to expand and contract. The changes in pressure could cause rupture. For Lithium batteries, the separator materials serves to separate the negative and positive poles hence avoiding short circuits and enabling the flow of electrolyte ions. They therefore require high strength separators. However, thermal factors and humidity variations directly affect electrochemical performance (SEI 2007). The two may cause cracks, which further weaken electrode polarization contacts hence causing a loss of battery capacity. At this rate, the battery is affected by humidity and temperature. When the batteries are too hot or cold, they will behave unpredictably in a manner that is inconsistent with the way they are designed to operate. When exposed to conditions of extreme temperatures and relative humidity, they may contract, expand, bulge, or create sparks (SEI 2007). Suggestion The limiting factors of the inverter and the electric motor require a heat sink that absorbs sufficient heat to keep the inverter and motor unit cool, hence preventing power loss and damage. However, since forced air convection may cause humidity by failing to enable heat transfer with lower temperatures, the performance of heat sink is affected. The three-phase cables of the heat sink need to originate from the heat sink and passed to the windings in the motor. The equipment should further offer shielding from the electro-magnetic fields produced by flowing current through the windings within the stator (Zhang & Chow 2010). The effects of humidity on separator material of Ni-MH batteries can be solved using nanotechnology. Indeed, the emergence of nanotechnology into such batteries can minimize the resistance of the contact between the particles of Ni hence creating good conducting networks and improving their stability in EVs (Yong, Jian & Jie 2012). To control effects of humidity variations and thermal factors on lithium batteries, nanotechnology can be applied to increase the areas of contact between the electrolyte and electrode, hence improving the performance of batteries in EVs. For PEMs, this report proposes that batteries should be modeled in a way that increases their modeling accuracy and estimation of the battery state. The report further proposes a study on “online-model parameters identification methods” to enable the model to work optimally in various extreme environmental conditions of extreme temperatures and relative humidity (Zhang & Chow 2010). Conclusion In EVs, the key components such as inverters and electric motors are highly sensitive to environmental conditions such as humidity. Such uncontrolled environmental conditions may affect the reliability and performance of the vehicle. The main types of EVs exist include plug-in electric vehicles (PEV), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs) and Extended-range electric vehicles. Thermal overload of the electric inverter and motor unit makes the unit to experience a range of challenges due to their temperature limits. Hence, they become susceptible to variations in humidity affecting their operation. This implies that the copper windings electric motor assembly is susceptible to thermal factors and humidity. In this case, high temperatures may melt the plastic insulation of the stator and that of the copper, hence representing a limiting factor to EVs. The DC/AC inverter on the other hand has a high-powered switching device called IGBT that is susceptible to humidity and other thermal factors. Additionally, when the batteries are too hot or cold, they will behave unpredictably in a manner that is inconsistent with the way they are designed to operate. When exposed to conditions of extreme temperatures and relative humidity, they may contract, expand, bulge, or create sparks. References Anderson, D & Carlson, D 2012, Measurements of ABB's Prototype Fast Charging Station for Electric Vehicles: A contribution towards standardized models for voltage and transient stability analysis, Chalmers University Of Technology, Gothenburg Ciprian, R & Lehman, B 2009, Modeling Effects of Relative Humidity, Moisture, and Extreme Environmental Conditions on Power Electronic Performance, viewed 7 Jan 2014, http://www.ece.neu.edu/groups/power/lehman/Publications/Pub2009/2009_9_Ciprian.pdf Huang, Y, Yin, C & Zhang, J 2008, “Design Of An Energy Management Strategy For Parallel Hybrid Electric Vehicles Using a Logic Threshold and Instantaneous Optimization Method," International Journal of Automotive Technology, Vol. 10, No. 4, pp. 513−521 (2009) Khayyam, H, Kouzani, A, Nahavandi, S, Marano, V & Rizzoni, G 2008, Intelligent Energy Management in Hybrid Electric Vehicles, viewed 8 Jan 2014, http://www.intechopen.com/download/get/type/pdfs/id/10168 Lohse-Busch, H 2004, Thermal Overload Capabilities of an Electric Motor and Inverter Unit Through Modeling Validated by Testing , Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University Rahman, S, Zhang, N & Zhu, J 2008, Optimal Energy Management for Plug-In Hybrid Electric Vehicles, Proceedings of the 3rd International Conference on Mechatronics, ICOM’08 18 – 20 December 2008, Kuala Lumpur, Malaysia SEI 2007, A study on the costs and benefits of hybrid electric and battery electric vehicles in Ireland, AEA Energy & Environment, viewed 8 Jan 2014, http://www.seai.ie/News_Events/Press_Releases/Costs_and_benefits.pdf Sun, B, Parten, M, Turner, W & Maxwell, T 2002, Instrumentation of a PEM Fuel Cell Vehicle, Texas Tech University, viewed 8 Jan 2013, http://www.ni.com/pdf/academic/us/journals/lv02_35.pdf TVA 2013, Types of Electric vehicles, Tennessee valley Authority, viewed 8 Jan 2004, http://www.tva.gov/environment/technology/car_vehicles.htm Yang, H & Roorda, M 2012, Impact of Real-World Powertrain and Commute Patterns on Plug-in Hybrid Electric Vehicle Return-on-investment, University of Toronto, Toronto Zhang, H & Chow, M 2010, Comprehensive Dynamic Battery Modeling for PHEV Applications, viewed 8 Jan 2014, http://www.adac.ncsu.edu/projects/Battery%20Model/Docs/PESGM2010-000683.pdf Read More