Abstract
ABSTRACTThis paper presents a complete solution for constrained control of a permanent magnet synchronous machine. It utilizes field-oriented control with proportional-integral current controllers tuned to obtain a fast transient response and zero steady-state error. To ensure constraint satisfaction in the steady state, a novel field-weakening algorithm which is robust to flux linkage uncertainty is introduced. Field weakening problem is formulated as an optimization problem which is solved online using projected fast gradient method. To ensure constraint satisfaction during current transients, an additional device called current reference governor is added to the existing control loops. The constraint satisfaction is achieved by altering the reference signal. The reference governor is formulated as a simple optimization problem whose objective is to minimize the difference between the true reference and a modified one. The proposed method is implemented on Texas instruments F28343 200 MHz microcontroller and experimentally verified on a surface mounted permanent magnet synchronous machine.
Highlights
Permanent magnet synchronous machine (PMSM), due to its inherently high torque density and premium efficiency stands out as a motor of choice in a wide array of applications and especially proves as a perfect fit in electric traction applications
With addition of loss minimization requirement, the control strategy of a PMSM can be divided into three segments: an algorithm for finding the optimal current vector which minimizes the copper losses or total copper and iron losses in a steady state, field-weakening algorithm which ensures that voltage constraints are not violated in steady state, and a control algorithm responsible for tracking of reference current trajectory
The verification of the presented field-weakening algorithm and current reference governor was performed in two steps, namely through simulation and through experiment on the real PMSM drive
Summary
Permanent magnet synchronous machine (PMSM), due to its inherently high torque density and premium efficiency stands out as a motor of choice in a wide array of applications and especially proves as a perfect fit in electric traction applications. The main objective is to ensure reaching the reference torque with a good dynamic performance while achieving loss minimization in the steady state This can be achieved by a proper current control algorithm which must respect PMSM drive voltage and current limits. The drawback of the feedback method is a slow field-weakening dynamics which creates problems during transitional states due to possible premature activation of field-weakening operation during current transients, when rapid change of current reference (i.e. desired torque reference) results in the voltage constraint violation and saturation of current controllers. With the use of feed-forward component, good dynamic response of field-weakening operation is achieved, while the feedback is added to compensate the influence of mathematical model or machine parameter uncertainty The flaws of this method are related to problems considering acquiring the feed-forward 2D look-up tables and memory required to save them, along with computing requirements in real-time implementation. The paper is organized as follows: In Section 2 the standard FOC of PMSM is presented, Section 3 presents a reference governor as a solution for constraint satisfaction during transients, Section 4 presents a novel field-weakening solution which ensures constraint satisfaction in the steady state, Section 5 presents simulation and experimental results and Section 6 concludes the paper
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