How does an Electric Vehicle works?
How does an Electric Vehicle work?
We know how gasoline-powered cars work as we have been around them every day (i.e., gasoline is burnt in an internal combustion engine, which provides the necessary power to drive the vehicle forward). But with the coming high demand for EV cars and having less mainstream, and so we will be looking for How does an Electric Vehicle works?
Generally, fuel cars use Gasoline engines whereas it has been replaced with Electric Motor in Electric cars. It is the motor that provides the "movement " in the vehicle. The motor is powered by rechargeable lithium-ion (electric) batteries. However, the motor can't be at the same power all the time.
Hence a controller (or compact inverter) is used and this ‘sits in the middle’ of the motor and the batteries. As its name would suggest, it controls the battery power that is fed to the electric motor, and it’s how your car will only slowly accelerate when your foot is only slightly touching down on the accelerator pedal:
So basically, this is an overview. Now let's talk about it in detail and know how it works!!
Accelerator pedal and controller/inverter interaction
In simple terms, whenever the driver puts their foot down on the accelerator pedal, this is detected by a pair of variable resistors known as potentiometers. These are used to measure electric potential and are also used in audio equipment, for example when adjusting the volume.
These potentiometers pass a signal to the controller/onboard inverter, essentially telling the controller how much power should be delivered. Naturally, no power should be delivered if the driver isn’t touching the pedal. And conversely, if the pedal is fully pressed down, full power should be delivered.
The power requirements to move a car at very high speeds mean that the battery and motor will be operating at high voltages, and the controller/inverter, therefore, has to deal witan h electric current of 15x that is found in a typical home air conditioning system. This high level of voltage/current means heat is a big potential problem, and thus cooling is very important in electric cars.
So, we know that the controller converts DC power to an AC motor (in most cases – sometimes there’s a non-AC motor, as we explore later on) via the signal from the potentiometers. However, this process is not as easy as turning on a tap and having water flow out, either slowly (if the tap is only slightly turned) or quickly (if the tap is fully turned). The very nature of taking digital power and applying it to a physical, analogue system (the motor) means that a process called pulse width modulation (PWM) is required. PWM is used by the controller/inverter to pulse the power, accordingly, ensuring that the motor turns at the required level (i.e., instead of operating too slowly or too quickly).
The controller/inverter also handles something known as ‘regenerative braking’, which is where the opposite of the above happens! When the driver brakes, this ‘extra’ power from the motor is collected and supplied back to the battery by the controller.
Finally, the controller/inverter doesn’t just ‘move’ power around. It also houses a range of control circuit technology. These manage other crucial features for EVs such as monitoring the torque and speed of the motor, energy regeneration (back to the battery), failure and anomaly diagnostics, and various safety measures (as set out in an international standard for road vehicle safety, known as ISO 26262).
Unlike mobile phone batteries which don’t need to supply much power (in relative terms), car batteries are comprised of multiple cells and modules to achieve the power needed. Think of these as multiple batteries being ‘stuck’ together, and the overall ‘battery’ (cells and modules) make up the pack.
Electric car batteries run at high voltages as well, for example, the i3’s battery runs at 360 volts and the Model S runs at 375 volts. Remember that most American homes have a 120V nominal voltage, and UK homes are supplied at 230V. So electric cars have a higher running voltage than the domestic supply to homes!
Each cell is connected to the module, and each module is connected to the pack, in a way that it broadly functions as a single battery. So when the controller decides that it needs power, the circuit will be closed and thus the (group of) battery cells will start discharging – supplying power to the controller.
In general, electric cars use one of two types of motors:
- DC Motor: this motor runs off DC power and it has 3 main components: the stator, motor, and brush system. The stator contains a permanent magnet system which ultimately provides the turning of the motor’s output shaft. The brushes are made out of electrically conductible material such as graphite, and (when charged) they supply the current through the motor’s commutator bars into the winding.
- AC Motor has just two main components: the outside stator (which has coils supplied with AC, triggering the rotational magnetic system) and the inside rotor (which produces a secondary magnetic field). The inside rotor attaches to the drive shaft.
Traditionally, DC motors have been more commonplace (in industry and thus in early EV cars), however, AC motors are now more popular – in large part due to being easier to produce, and install and they don’t have brushes that can wear out. DC motors tend to run at lower voltages (96-192 volts) than AC motors, which are usually 240 volts.
Both DC and AC motors are controlled via magnetic systems, and these magnetic effects are generated when electrical current is supplied to them So, following on from the earlier sections, the driver will put their foot down on the accelerator, meaning that the potentiometers will supply information to the controller about how much current is needed. This is ‘taken’ from the battery pack, and after converting from DC battery power to AC power (for an AC motor, that is) the controller supplies this to the motor. The motor’s magnetic field's function is such that the motor’s output shaft – aka the drive shaft of the vehicle – turns as expected, and so the wheels turn.
However, one future development to this process is the concept of an in-wheel motor – which Nissan’s technology page sums up well. The standard model of the motor taking the place of a combustion engine was mainly due to simplicity since the vast majority of parts (and designs) in the market were gasoline-vehicle-centric. But with an electrical-based system, there are fewer limitations and thus more scope for specific improvements. With an in-wheel motor, instead of having a single motor that drives the drive shaft, an EV would instead have two motors that are ‘attached’ to the wheel. This development will hopefully hit mainstream car tech in a few years, and it’ll lead to better handling and responsiveness when driving an EV.
EV diagram
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