Introduction to Renesas RX MCU Solutions for Resolver Motors

The electromagnetic theory behind rotary transformer sensors is fundamentally similar to that of ordinary transformers. Please see the example below:

It mainly consists of excitation windings, sine windings, and cosine windings. The sine and cosine windings are designed according to the number of pole pairs and are wound alternately. The excitation winding is equivalent to the primary side of a transformer, generating an alternating magnetic field through the excitation voltage, while the sine and cosine windings are equivalent to the secondary side of the transformer, generating induced voltage. When the rotor rotates, the protruding part of the rotor causes periodic changes in the magnetic flux of the secondary side, and the secondary winding will produce voltage pulse signals related to the change in rotor position. By analyzing this group of pulse signals, the position information of the rotor can be obtained.

From the explanation of the above principles, it can be seen that during the rotation of the motor, the alternating electromagnetic signals of the rotary transformer sensor can synchronize and change rapidly according to the position information, providing high-precision position information for motor control. Its structure is mainly realized by winding and silicon steel, so compared to other sensors, it has advantages such as high reliability, resistance to high and low temperatures, waterproof and dustproof capabilities, vibration resistance, strong electromagnetic interference resistance, and low cost.

However, the voltage signals output by the rotary transformer sensor resemble fishbone patterns. If parsed directly by the MCU, it will impose a significant load on the MCU. Therefore, a common solution in the industry is to add a dedicated IDC to parse the resolver signals. After receiving the output signals from the sine and cosine windings, it parses the position signal and then outputs it to the MCU, improving system efficiency.

The RX MCU emits two square waves with a phase difference of 60 degrees, which are converted into sinusoidal excitation signals through a rectifier circuit and input into the IDC excitation pin CARRIER.

After processing in the RDC internal circuit, the excitation signal is generated and input into the resolver excitation winding.

When the rotor rotates, the sine and cosine windings will generate voltage pulse signals related to the change in rotor position. These two sets of signals can be input to the IDC’s XA (B) P (N) pins, respectively.

After inputting the two sets of voltage pulse signals into the IDC, the IDC will output square waves with position result information to the MCU after parsing. The MCU only needs to detect the phase shift of the new square wave signal to obtain the position result, greatly improving the system’s operational efficiency.

In particular, the Renesas IDC has internal amplification, filtering, and correction circuits that can compensate the signal in real-time, greatly improving the reliability of the signal. Internal tests have shown that using the Renesas IDC can reduce angle conversion errors to within ±0.2 degrees.

One is the resolver+stepping_motor sample project, which corresponds to a stepper motor application scenario using a rotary transformer sensor (You can copy the link below to your browser or scan the QR code to view).

Another is the resolver+BLDC sample project, which corresponds to a BLDC motor application scenario using a rotary transformer sensor. You can log onto the Renesas official website to obtain sample code and related support materials (You can copy the link below to your browser or scan the QR code to view).

The sample projects can run on the samples released by Renesas, allowing customers to familiarize themselves with chip performance, software engineering, and expand development based on this.

For different application scenarios, you can choose the model RTK0EMX270S01020BJ (RX Evaluation System for Stepping Motor with Resolver), corresponding to the resolver+stepping_motor development solution, or choose the model RTK0EMX270S00020BJ (RX evaluation system for BLDC motors), corresponding to the BLDC development solution.

Sample purchases can be made through the Renesas official website or by consulting local agents. (You can copy the link below to your browser or scan the QR code to view).

This article introduced the solutions from Renesas for rotary transformer sensors, including the general application principles of rotary transformer sensors, the system structure of the Renesas MCU solution, corresponding principles, and sample code locations. It facilitates customers to quickly integrate and apply them in system engineering.