Hidden within the motor of the electric tricycle lies a precision sensor that is key to ensuring the vehicle's smooth operation.
As you navigate streets and alleys on an electric tricycle, you might never have considered what ensures its smooth starting and precise speed control. Inside the motor of the electric tricycle, a precision sensor called a "rotary transformer" is silently at work.
In recent years, with the continuous advancement of electric tricycle technology, the rotary transformer, a precision sensor originally used in aviation and military fields, has gradually become a core component enhancing the performance and reliability of electric tricycles.
01 What is a Rotary Transformer?
A rotary transformer is an electromagnetic sensor, also known as a resolver. It is a small AC motor used for measuring angles, specifically designed to measure the angular displacement and angular velocity of a rotating object's shaft.
The rotary transformer consists of two main parts: the stator and the rotor. The stator winding acts as the primary side of the transformer, receiving the excitation voltage, while the rotor winding acts as the secondary side, obtaining an induced voltage through electromagnetic coupling.
Its working principle is fundamentally similar to that of an ordinary transformer, but with one key difference: the primary and secondary windings of an ordinary transformer are relatively fixed, whereas those of the rotary transformer change their relative positions with the angular displacement of the rotor.
02 Why Do Electric Tricycles Need Rotary Transformers?
In the power system of an electric tricycle, the motor controller needs to know the precise position and speed of the motor in real time to achieve accurate control.
Traditional position sensing technologies, such as Hall sensors, have issues like poor interchangeability and significant impact of temperature changes on the output signal. The rotary transformer, with its high reliability and environmental adaptability, has become the ideal choice.
Especially since electric tricycles often operate in harsh environments, potentially facing challenges like oil stains, dust, humidity, and temperature variations. Thanks to their robust structure and stable performance, rotary transformers can operate stably under these conditions, ensuring reliable vehicle operation.
03 How Does a Rotary Transformer Work?
The working process of a rotary transformer is similar to a miniature power transmission system. In an electric tricycle, the MCU of the motor controller generates a PWM signal via the PWM module, which is then converted by the resolver excitation circuit into a sine wave signal.
This signal is input to the excitation winding of the rotary transformer, inducing two voltages in the output windings: one is a sine envelope signal, and the other is a cosine envelope signal.
When the rotor rotates, the relative position between the excitation winding and the secondary output winding changes, consequently altering the electromotive force induced in the secondary output winding. The amplitudes of these two output signals are proportional to the sine and cosine functions of the rotor's rotation angle, respectively.
The sine and cosine signals return to the resolver receiver circuit, are converted into single-ended signals, and sent to the MCU. The MCU uses these signals to obtain the real-time position of the motor rotor, thereby achieving precise control of the motor.
04 The Core Value of Rotary Transformers in Tricycles
For electric tricycles, the value of the rotary transformer is first reflected in its excellent environmental adaptability. Unlike optical encoders, rotary transformers are unaffected by oil, dust, and moisture, which is crucial for electric tricycles that often travel on rough roads.
Secondly, rotary transformers provide extremely high reliability and accuracy. Theoretically, they can provide analog output equivalent to infinite resolution, enabling precise position control and ensuring smooth starting and acceleration of the electric tricycle under various load conditions.
Furthermore, modern electric tricycle power systems often combine the rotary transformer with temperature sensors to monitor the motor winding temperature in real time, preventing damage from overheating to the motor windings or the encoder, thus significantly enhancing the reliability of the power system.
05 Challenges and Solutions
Applying rotary transformers to electric tricycles also faces some challenges. Both the rotary transformer and motor components are electromagnetic structures, and their simultaneous use can generate electromagnetic interference. Additionally, due to the compact structure and small size of electric tricycles themselves, it is often difficult to install rotary transformers in commonly used motors.
Solutions to these problems include using transition housings made of magnetic isolation materials, and optimizing electronic PCB design, such as implementing separate power and analog grounding, and using analog filters to eliminate common-mode noise on sensor signals, among others.
In terms of signal processing, using armored twisted-pair power and control cables to avoid interference, minimizing loops that act as EMI antennas, and striving for a near-perfect ground with the lowest possible impedance are key strategies.
06 Future Development Trends
With the continuous progress of electric tricycle technology, rotary transformer technology is also constantly innovating. More and more designs are adopting highly integrated decoding solutions, such as MCU-based soft decoding schemes, which helps reduce system costs.
System miniaturization is also an important development direction. Through optimized structural design, such as using transition housings and special fixing structures, rotary transformers can be installed within the limited space of electric tricycle motors.
Additionally, the introduction of intelligent diagnostic functions is noteworthy. Modern testing equipment can simultaneously monitor the output signals of the rotary transformer and other electrical parameters, such as motor voltage and current, enabling more comprehensive system status monitoring.
The rotary transformer, which has moved "from high-end fields to common use," may be inconspicuous, but it is an indispensable precision component in the power system of electric tricycles. It acts like the "nerve center" of the vehicle, providing real-time feedback on the motor's position and speed signals.
As the technology becomes more widespread, more electric tricycles will benefit from this high-reliability sensor in the future, making our travel safer and more reliable.
