Fast square root calculation for DTC magnetic flux estimator

Direct Torque Control (DTC) is a control strategy fully used with induction motors and permanent magnet synchronous motors due to a fast torque response, compared to other traditional control strategies. This paper presents a new technique for calculating the square root, which is the operation that presents the greatest difficulty when developing the DTC strategy on an FPGA. The architecture presented is in VHDL using a structural modeling style and a successive approximation register to calculate digit by digit, the square root of a binary unsigned 32-bit number, which can be easily expanded to a larger number of bits. With this architecture the flux estimator processing time was lowered to 1.12μs, when the lowest time reported was 5μs. This time reduction will allow a dramatic reduction in torque ripple, a common effect when using DTC.