Resolvers provide accurate and high-reliable position feedback in industrial drives like servo drives, especially in harsh industrial environments with dust and temperatures above 150°C. A resolver is an absolute mechanical angle sensor and operates as a variable coupling transformer. This means that the amount of magnetic coupling between the primary winding and two secondary windings varies according to the angle position of the rotating element (rotor), which is typically mounted on the motor shaft. Resolvers can withstand severe conditions for a very long time, making them the perfect choice for industrial motor controls, servos, robotics (including service robots and manufacturing robots), power-train units in hybrid- and full-electric vehicles, and many other applications that require precise shaft rotation.
Industrial drive manufacturers using resolvers in their designs tend to care about robustness, the reliability of the absolute angle measurement and the overall system cost. Because a resolver involves differential signals for input as well as output, this greatly improves their ability to reject common-mode noise. Electromagnetic compatibility (EMC) plays a major role in defining drive robustness. EMC compliance to specific standards is a must. Most industrial servo drives typically use shielded cables to connect to the motor and position-feedback sensor like the resolver. Cable lengths can be 100m and even more. At longer cable lengths, impulse noise currents on the cable’s shield induced by the inverter’s pulse-width modulation (PWM) switching can couple into the resolver’s differential signal pairs. Very fast transient bursts – like crosstalk from the switching inverter power cable with high dV/dt in the range of ~10kV/µs – can impact the performance of resolver-to-digital converters (RDCs).
The recently released EMC-Compliant Single-Chip Resolver-to-Digital Converter (RDC) Reference Design provides a solution for EMC-compliant RDC through a single-chip PGA411-Q1 with 12-bit angle resolution. See Figure 1.
Figure 1: Simplified system block diagram of the TIDA-00363 reference design with Piccolo™ F28069M MCU LaunchPad™ development kit
What benefits does this design provide?
Table 1: TIDA-00363 EMC immunity test results according to IEC618000-3
Figure 2: Step response for 1-degree angle change
Figure 3: Angle error with 7Vrms and 4Vrms excitation modes
Figure 4: Important faults related to the resolver and RDC
Solving many of the challenges for RDC application, this reference design provides highly integrated EMC-compliant solution with easy real-time evaluation.
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