Detailed Explanation of Electric Vehicle Inverters

An inverter is a device that converts direct current (DC) supplied by a battery into alternating current (AC). The motor of an electric vehicle (EV) is driven by this AC power. To improve the overall energy efficiency of an EV, it is crucial to minimize the energy loss of the inverter.

What is an Inverter?

Overview of Inverters

An inverter in an electric vehicle is responsible for converting the direct current (DC) supplied by the battery into alternating current (AC). This is necessary because most traction motors installed in EVs operate on AC power. The output power of the inverter is set according to the output power of the motor (ranging from 30 kW to 400 kW, etc.).

Typically, an EV is equipped with one or two inverters. However, in the case of in-wheel motor systems (where each wheel is driven by an individual motor), each motor requires its own inverter.

Types of Motors

Motors are mainly categorized into two types: brushed motors and brushless motors.

• Brushed motors are commonly used in small devices and are easy to control because they are powered by direct current (DC voltage).
• Brushless motors, on the other hand, focus on energy efficiency and are suitable for applications that require precise speed control, such as traction motors in electric vehicles. Since brushless motors operate on AC power, an inverter is essential to convert DC into AC.

Market Trends and Device Development

As the number of electric vehicles increases, the demand for inverters will also grow. Additionally, with the trend of improving vehicle performance, motors are being designed for higher power output, necessitating inverters with higher power capacity.

The electronic components that make up inverters are expected to meet certain requirements in the future, including:

• Higher power capacity
• Better heat resistance
• Smaller size and lighter weight

Key Requirements for Future Inverters

1. Higher Power Capacity
   To support high-output motors, inverters must also increase their power capacity. This includes operating at higher voltages (e.g., increasing from the current 400V to future 800V) and handling higher currents. Consequently, the semiconductors and other components used in inverters must be designed to support high-power applications.
2. Better Heat Resistance
   As electronic components become smaller, the amount of heat per unit area increases. Enhancing heat resistance is crucial to prevent aging and deterioration caused by self-generated heat and heat absorbed from surrounding components.
3. Smaller Size and Lighter Weight
   The increase in power output often leads to larger and heavier equipment, which negatively affects vehicle range. Therefore, inverters must be designed to be compact and lightweight while still supporting high power output.

Circuit Configuration of an Inverter

Overall Structure

An inverter consists of the following circuits:

• Noise filter: Suppresses noise from external sources or within the circuit itself.
• Voltage measurement: Measures voltage to control the conversion circuit.
• Voltage conversion circuit: Converts voltage through switching operations using FETs (Field-Effect Transistors) or similar components.
• Current measurement: Measures current to control the conversion circuit.
• Control circuit: Controls the conversion circuit and other components.
• DC/DC converter: Supplies power to the control circuit.
• Communication interface: Facilitates communication with external circuits.

The role of an inverter is to convert the DC power supplied by the battery into AC power. As the production of electric vehicles increases, the number of inverters installed is also expected to rise. There is a growing demand for high-output inverters, while miniaturization remains a key challenge. The electronic components used in inverters must support "higher power capacity," "better heat resistance," and "smaller size and lighter weight."