Single-Phase to Three-Phase AC-AC Converter Fed Low Speed Induction Motor Drive With Encoderless Control

This paper proposes the control of a three-phase (3ϕ) induction motor drive (IMD) from a single-phase (1ϕ) grid using bi-directional AC-AC matrix converter without a DC link. The exclusion of DC link electrolytic capacitor enables high power density and enhanced reliability. However, it inevitably introduces an inconsistency in the instantaneous active power between the 3ϕ load and the 1ϕ grid. In the absence of energy storage, power quality performance of the converter is observed to deteriorate, as it attempts to instantly match the active power between its 3ϕ and 1ϕ sides. To tackle this challenge, a low output frequency application such as a low speed motor drive is targeted and the existing energy storage elements in the motor and input filter are mathematically modeled to deliver improved power quality on either side. In order to ensure precise encoderless operation in the low speed region, an improved variant of the discretized adaptive full order observer is used with certain refinements to enhance estimation accuracy in the presence of a double-frequency component of the 1ϕ grid on the motor side. Performance of the 1ϕ-3ϕ AC-AC converter fed drive, as well as the low speed estimation algorithm is well illustrated through simulation results.