HF machine, also known as switched reluctance motor(SR), was born 160 years ago. But for a long period of time, it has always been considered a low-performance motor, so it is only used in a few low-power places.
Features of HF machine:
1. The starting current is small. The HF machine only needs 0.2~0.3 times of rated current to generate 1.5~2 times of rated starting torque. Whether it is brush or brushless DC motor, it needs 1.5~2 times of rated current to get 1.5~2 times of rated starting torque. In other words, if the same power of the motor of achieves the same starting torque, the starting current of the DC motor will be 5 to 10 times that of the HF machine.
2. It is high efficiency. HF machine guarantee high efficiency over a 1:50 speed range and a 1:5 torque range. The DC motor can only guarantee high efficiency under high speed and light load, and the high efficiency area is narrow. For variable speed and variable torque conditions such as electric bicycles, the average efficiency of HF machines will be 15% to 30% higher than that of brushed and brushless DC motors.
3. The system is safe and reliable and has a long life. The HF machine has neither a fragile commutator mechanical structure nor a permanent magnet with unstable performance. Whether it is life or operational stability, HF machines are much higher than brushed and brushless DC motors. The HF machine has four-quadrant operational symmetry, enabling energy regenerative braking of electric bicycles without adding any hardware. This not only increases the driving safety of the electric bicycle, but also increases the utilization efficiency of the battery.
4. It has strong overload capability. Since the working magnetic field of the HF machine is different from that of the brushless and brushless DC motors, it does not exhibit alternating heat, so the heat generation is small. It is called the "cold rotor", plus the permanent magnet without poor thermal performance. Therefore, HF machine have an unmatched overload capability with brushed and brushless DC motors. In a short period of time, the HF machine is allowed to overload 2 to 3 times, making its performance close to that of a gasoline engine. This is one of the main reasons why HF machine are used in electric vehicles in Europe and the United States.
5. The system is cost effective. The HF machine
system is a mechatronic product, and its control performance is mainly realized by computer software. Therefore, the price of its controller is only about 30% higher than that of the brushless DC motor controller. The HF machine eliminates the expensive rare earth permanent magnet, and the manufacturing process is simpler than the brushless DC motor. The price of HF machines should be about 15% lower than the price of brushless motors. Therefore, the price of the switched reluctance hub motor system (the price of the hub motor plus the controller) should be comparable to the price of the brushless DC hub motor system, that is, the HF machine system has a high cost performance.