Research And Implementation Of Servo-Driven SVPWM Overmodulation Algorithm Based On FPGA

With the development and progress of numerical control technology,higher requirements are put forward for the performance of servo drive system,such as high speed and high torque.The SVPWM over modulation algorithm can improve the output voltage of the servo drive inverter,so it can improve the maximum speed and output torque of the servo motor.Based on the characteristics of parallel operation and fast data processing,a SVPWM over modulation algorithm based on FPGA is studied and developed.The strategies of modifying amplitude and phase angle in I and II areas of SVPWM overmodulation are compared and analyzed.The realization scheme is to increase voltage amplitude without changing the phase angle in I area of overmodulation,while the amplitude and phase angle need to be modified in II area of overmodulation.In view of this scheme,the phase angle jump mode is adopted to avoid complex conversion of phase angle in II area of overmodulation,which is easy to be realized in engineering.The operation problems of modifying the voltage amplitude and calculating the reference voltage vector in the implementation flow of the over modulation algorithm are analyzed.To solve the problem of high load operation such as division and trigonometric function in over modulation algorithm,combining with the characteristics of FPGA programming and resource matching,a design scheme of over modulation algorithm is proposed.Based on the equal area method,the functional relationship between the over modulation coefficient and the control angle is derived.Combined with the functional relationship between the control angle and the modified voltage amplitude,the relationship curve between the over modulation coefficient and the modified voltage amplitude is drawn.By using the look-up table method,the modified voltage amplitude can be obtained by directly looking up the table according to the over modulation coefficient,and the calculation can be simplified.At the same time,the algorithm of CORDIC is used to realize the operation of trigonometric function.The feasibility of the over modulation algorithm is verified by simulation.The over modulation module is designed by FPGA programming,and the reference voltage vector is modified in advance.The off-line points of the relation curves in the over modulation module I and module II are designed and stored in 0.0001 step size.In the calculation process,the amplitude and phase angle are modified by looking up the offset address table.In order to cover the whole range of trigonometric function operation,the preprocessing and output processing are adopted on the basis of CORDIC iteration.So the calculation of reference voltage vector and voltage component is realized.The correctness and accuracy of the over modulation module are verified by simulation.The experimental platform is built to compare the over modulation algorithm based on FPGA.The results show that the maximum speed of servo motor can be increased by 7.4% by using the over modulation algorithm,which verifies the effectiveness of the over modulation algorithm based on FPGA.