An electronic inverter — also known as a power inverter or simply an inverter — is a device that converts direct current (DC) to a form of alternating current (AC). Inverters are used in a variety of household and industrial applications, including:
- Electric vehicles, which we’ll focus on throughout this article.
- Solar power systems, whether they’re on your roof or part of a solar farm.
- Uninterruptible power supplies that can provide emergency power for a short time.
To better understand how inverters work, let’s review the difference between DC and AC power.
What Are Direct Current and Alternating Current?
Direct current is a type of electric current where the flow of charge is always in one direction. DC circuits are used in electronics and in any system that involves a battery, including electric vehicles. DC voltage and current are constant over time.
Alternating current, on the other hand, periodically reverses the direction of charge. AC power is used in power transmission to homes, businesses, and industrial sites around the world. AC voltage and current vary periodically to appear as a waveform.
Inverter AC Waveform Output
An inverter is designed to output one of several possible AC waveforms, including:
- Sine waves
- Square waves
- Modified square waves, such as step waves
- Triangle waves
- Trapezoidal waves
When Do You Need an Inverter?
In many cases, DC systems are designed to accept DC power sources (such as from a battery), while AC systems are designed to accept AC power sources (such as from the power grid). But what happens when you have AC equipment and access only to a DC power source? Such a system is possible, but not without an inverter. While this sort of set-up might sound unusual or uncommon, it’s actually used all the time. In fact, electric vehicles are great examples of inverters at work.
How Are Inverters Used in Electric Vehicles?
Inverters are part of what make electric vehicles (EVs) possible. All EVs are powered by a battery, which can only output DC current. At the same time, EVs run on motors that require some form of AC current to operate. This is because of how the motors are designed.
Every motor has a moving part (the rotor) and a fixed part (the stator). Think of the rotor of an electric motor as a spinning magnet. And if you remember making an electromagnet in science class using a battery, a nail, and some wire, then you have a good idea of what a motor stator looks like. Imagine several of these electromagnets installed on the stator and around the rotor. Finally, picture each of these individual electromagnets pushing and pulling on the magnetic rotor to make it spin. Each electromagnet on the stator needs to change polarity — in other words, current — at the right time so that it’s always working in sync with the rest of the stator. Depending on the type of motor, an inverter can provide a specific form of AC current that allows the motor to work properly by changing the flow and direction of current to each part of the stator.
Do All EV Motors Need an Inverter?
Some motors can run purely on DC current. These motors, called brushed DC motors, are inexpensive to build but have severe limitations on maximum speed and torque. Therefore, brushed motors are used in low-power applications such as windshield wipers and side window control.
But while all EV powertrain motors do need an inverter, they don’t all need the same kind of inverter. Each motor type works using a distinct AC waveform and, therefore, using a distinct inverter.
Summary
- Inverters are used to convert DC power to AC power.
- Electric vehicle systems incorporate batteries, which output DC power, as well as motors that need a form of AC power to function.
- Inverters can output different types of AC waveforms, including sine waves, square waves, and modified square waves. Different types of motors require different types of wave inputs to operate properly.
