11 kW sensorless AC servo drive

An elevator systems integrator replacing an ageing induction-motor traction package. Legacy units relied on discontinued drive electronics and required an encoder on every installation — a recurring field-service cost.

Sensorless startup under load. An elevator car is loaded at standstill. Open-loop ramping, the usual sensorless startup method, produces rollback — unacceptable in a passenger system.

Wide operating envelope. The same drive had to serve outrunner PM motors and legacy induction machines across 3.3, 5.5 and 7.5 kW installations without per-site retuning.

Ride quality. Torque ripple invisible in a pump application is felt directly by passengers.

• Implemented FOC with DTC fallback on a TMS320F28 series motor-control DSP, with a current loop above 1 kHz response bandwidth.
• For startup, used initial rotor position detection via high-frequency injection before torque release — eliminating the rollback window rather than ramping through it.
• Built a dynamic parameter-switching layer: motor characteristics held as profiles, selected and blended at runtime, so one firmware image serves all three power classes.
• Applied S-curve jerk limiting on the speed reference for ride comfort, and field weakening above base speed to hold torque across the full travel profile.
• Supported ABZ incremental, sinusoidal, and serial-protocol absolute encoders for installations that retain them.

• Startup rollback eliminated — no encoder required for standard installations
• One firmware image covering three power classes, removing per-site commissioning builds
• Verified operation to 11 kW, 380 V, 75 A, with parallel switching to four devices at the upper range
• Current-loop response sustained above 1 kHz