EV Special Topic 1: How can permanent magnet motors make electric vehicles more energy efficient?

In recent years, the global electric vehicle industry has experienced explosive growth, which is largely due to major breakthroughs in battery and permanent magnet motor technology. Permanent magnet motors are based on the principle of electromagnetic induction, which can efficiently convert electrical energy into mechanical energy, thereby replacing traditional internal combustion engines. These motors embed high-performance neodymium magnets on the rotor, using permanent magnets to generate magnetic fields, which in turn replaces traditional excitation motors.

As the electric vehicle market continues to expand, the application prospects of permanent magnet motors are becoming increasingly broad, and it is expected to be more widely used and further improved in the future.

Energy consumption comparison

1. Electric motor and internal combustion engine

Electric motors typically have high energy conversion efficiency. The motor efficiency of electric vehicles is usually between 70% and over 90%, sometimes even reaching over 97%. This means that most of the electrical energy input to the motor is effectively converted into mechanical energy to propel the vehicle forward.

The efficiency of automotive internal combustion engines (ICEs) is typically low because they generate a large amount of useless waste heat during combustion. The efficiency of internal combustion engines is generally between 20% and 40%, which means that only a small portion of the chemical energy of the fuel is converted into mechanical energy to propel the vehicle forward. In some modern high-efficiency internal combustion engines, the efficiency may be close to 50%, but these are usually measured under ideal conditions.

Obviously, electric motors have higher energy conversion efficiency, which means that electric vehicles can travel farther distances with the same amount of energy consumption. In addition, permanent magnet motors have smaller volume and weight, which enables electric vehicles to achieve lower weight distribution and improve vehicle stability and handling performance under the same endurance capacity. However, limited by current battery energy storage technology, the endurance capacity of electric vehicles in winter below zero is still inferior to that of fuel vehicles, generally only reaching 40%-60% of the standard endurance level.

2. Permanent magnet motor and excitation motor

Permanent magnet synchronous motor: Compared with excitation motor, permanent magnet synchronous motor has obvious advantages in energy saving. Permanent magnet synchronous motor uses permanent magnets to provide excitation, eliminating excitation current, thereby reducing energy loss. This type of motor is simpler in structure, removing the excitation coil and carbon brush, further reducing the weight of electric vehicles and improving battery life.

During normal operation, the rotor and stator magnetic fields of permanent magnet synchronous motor operate synchronously, without induced current in the rotor, and there is no rotor resistance loss, which can improve the efficiency of the motor by 4% to 50%. Due to the absence of induced current excitation in the rotor of permanent magnet motor, the stator winding may be a pure resistive load, making the motor power factor almost 1.

Asynchronous motor: During operation, the rotor winding of an asynchronous motor requires electrical energy for excitation, and some of this energy is ultimately consumed by heating in the rotor winding, accounting for approximately 20-30% of the total motor loss, resulting in increased energy consumption. According to the international energy efficiency standard IEC60034-30-1, asynchronous motors can achieve up to level 2 energy efficiency. Permanent magnet synchronous motors are now even superior to level 1 energy efficiency (IE5, or ultra-premium efficiency).

Permanent magnet motors: Brake regeneration

Permanent magnet motors

Energy recovery is one of the core technologies for energy conservation in electric vehicles. Research shows that in urban traffic environments, electric vehicles consume about 40% to 50% of the total driving energy during braking due to frequent acceleration and deceleration operations. In some large cities with more complex road conditions, the energy consumed by braking can even reach 80%. Even in suburban road conditions, at least 20% of the driving energy is wasted during braking.

Permanent magnet motors can efficiently convert this energy from kinetic energy back into electrical energy and store it back into the battery, with a conversion efficiency of up to 68%.

When the electric vehicle needs to brake, the electric motor can reverse its role and become a generator. At this time, the rotor of the motor remains rotating under the inertia of the vehicle, cutting the magnetic induction lines of the stator to generate current. After being processed by accessories such as inverters and high-voltage distribution units, the alternating current is converted into direct current with suitable voltage to charge the battery.

The generation of current will produce electromagnetic resistance, namely Lorentz force. This force will resist the motion of the rotor, thus playing a role of deceleration, replacing some traditional mechanical brakes.

According to test data, energy recovery typically increases the NEDC (New European Driving Cycle) mileage by around 15%, while better-performing permanent magnet motors can achieve 20%. This is decisive for improving the overall energy efficiency of electric vehicles.

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