Hello. My name is [inaudible] and I teach electrical engineering at the University of Michigan. My research includes power electronics and energy systems. In this video, I will talk to you about the journey energy takes from its generation through its distribution to an electrical vehicle's electrical and electromechanical systems, and ultimately powering locomotion. Let's talk about the pathway of energy transforming from one form to another. Electrical power can be generated by transforming different forms of energy to electricity. Electricity can be DC or direct current, where the electrons flow through conductors in a constant direction, or AC or alternating current, where the electrons move back and forth in a conductor analogous to ocean waves. Electric grids today are predominantly AC. Energy from the sun can be directly transformed to electricity using solar cells. The electricity from solar cells is DC. DC is converted to AC using power electronics. This particular type of power electronics is called an inverter. Aerodynamic forces from wind are transformed to kinetic energy in turbine blades, which in turn turn an electric generator to directly create AC. Energy from the fission of atoms is converted to heat, which converts water to steam. Steam is converted to electricity through turbine blades and an electric generator. Fossil fuels in the form of hydrocarbons are converted to heat by combustion or burning. Water is heated to steam, which through turbines and electric generators create AC power. Electrical power is measured in watts or megawatts. Electrical energy in megawatt-hours, joules, or the [inaudible]. One watt is one joule per second of energy transported, stored, or used. From generation, electric power is transported through the electric grid to homes, businesses, and electric vehicle chargers. These EV chargers can take grid AC and transform it to the DC current that batteries need. They can be outside a vehicle or under the hood. They charge quickly or slowly, depending on how much electric power is available. Energy can be transferred directly to a car through electric conductors and connectors or wirelessly through magnetic or electric fields. Within the vehicle, energy is stored electrochemically, predominantly through batteries. Although fuel cells have been used in some vehicles, it is not commonly used today. The terms ampere or C-rate refers to the amount of current flowing in or out of a battery. Amp-hours or ampere-hours refer to the amount of charge stored in the battery, which is proportional to the amount of energy stored. The amount of energy stored can be referred to as kilowatt hours or joules. Within an EV, electronic systems are used to transform electricity, regulate its use, and ensure safety. These include power electronics, which consist of active semiconductors, and passive devices that store energy in magnetic and electric fields. There are also digital electronic controllers, some of which are used to safely regulate the power to and from the battery. Batteries are arranged in hierarchical units. For example, cells are the smallest unit which are organized in modules. Modules are organized into battery packs. At each level of the hierarchy, electronics are used so that the batteries are operated evenly. The electronics are called battery management systems or BMS. Electromechanical systems transform electricity to useful mechanical motion. These systems consist of electrical machines that can operate both as motors and generators, and often include mechanical gears. Most electrical machines in vehicles operate with AC. However, batteries operate at DC. An inverter is used to transform into AC. Here is a simple tutorial of how electricity can be transformed into motion. AC current is transformed into an alternating magnetic field through a circular arrangement of electromagnets. The rotating magnet in this center is called the rotor. The alternating magnetic field is timed so that the magnetic field from the rotor is alternately attracted and repulsed by the adjacent magnetic fields. An example for an EV starts with low frequency 50 or 60 hertz from the grid. AC is converted to DC using an onboard charger. The goal of an onboard charger is to plug into any AC outlet and charge a vehicle. The predominant energy storage within a BEV or battery electric vehicle is a lithium-ion battery pack. These onboard chargers are often bidirectional, allowing power to flow in both directions, allowing not only charging, but also energy flow from the battery pack to the grid so that batteries can help with energy storage to support the grid when the EV is not being used for transportation. Even vehicle-to-vehicle charging is possible. Power electronic converters transform DC to high-frequency to AC, ranging from kilohertz down to hertz depending on the speed of the motor. Motors provide both rotational speed or RPMs and torque. The product of rotational speed and torque is mechanical power, which is transferred to the wheels. During breaking, some of this mechanical energy can be transferred back to the battery through regeneration. Mechanical power is transformed back to electrical power through the same electric motor, now behaving as a generator. Onboard chargers are built into an EV. They are lightweight and generally low power than chargers that are external. Level 1 charging is meant to be operated from single-phase AC, which is standard in your home electrical outlet. Three to five miles of range for every hour of charging is typical. Full battery charging typically takes overnight. Level 2 charging operates from higher power outlets. These are three-phase and operate at higher voltages and can charge often 10 times faster, offering 12-80 miles for every hour of charging. Level 3 charging, often known as DC fast charging or supercharging, offers 3-20 miles per minute. These types of chargers are significantly more expensive than Level 1 and Level 2 chargers, both in equipment and electrical installation. Two other types of charges are emerging. Ultra-fast charging, which requires installation on a portion of the electric grid that delivers very high power, has the potential to charge EVs to capacity within 8-12 minutes. Wireless charging transfers energy to EVs through magnetic or electric fields so that wires and connectors are not needed. This increases reliability and allows charging where human operators are not needed or not available. For example, with a large fleet or with autonomous vehicles. EV chargers can be external or internal to an EV. The typical demands on the electrical grid are illustrated in this duck curve. The curve shows how the energy demand from the grid varies throughout the day. If you squint, I suppose one sees a duck, the demand peaks in the early evening and is high in the morning, but it's relatively lower mid-day. As demand for electricity increases the prevalence of EVs, more will be needed from the electric grid. What does this mean for the grid? A combination of upgrades will be needed. More power lines will be needed to upgrade the distribution of electricity. New substations will be needed to distribute higher power electricity. Generation will have to shift from hydrocarbons to renewables. Or the environmental gains from vehicle electrification will be quickly lost to power plant carbon emissions. Intermittency of energy generation from renewable, such as solar and wind together with intermittency of electric vehicle charging, will require more energy storage to buffer the fluctuations in energy supply and demand. Solar generation, for example, peaks during the mid-day when energy demand is the lowest. Energy storage allows the shifting of this energy gap. I hope you enjoyed our exposition on the electrical vehicle energy voyage.
