小幅低频调制PWM波脉宽提高稳频控制精度

Improving the control performance of frequency stabilized system for transverse Zeeman laser tube

建立了以８０９８单片机为控制核心的横向塞曼热稳频系统，由模型预测控制算法计算控制量，通过输出ＰＷＭ波经低通滤波及功率放大后热补偿激光器腔长实现稳频。由于这由ＰＷＭ波实现Ｄ／Ａ变换的精度较低，控制量量化误差将严重地影响控制系统的性能。为此，提出一种通过将ＰＷＭ脉宽作小幅低频调制实现高精度Ｄ／Ａ变换的方法，显著地改善了控制系统的性能，并在此基础上增大了系统的控制裕度，实现了长达１０ｈ的稳频，通过Ｓ曲线估算得频率稳定度为８．７×１０－１０。这种方法简单、实用，可适用于其它智能控制系统。

A real industry scale frequency stabilized system for transverse Zeeman laser tube is composed.It is based on 8098 single chip computer system,which calculates control voltage with MPC algorithm and outputs PWM wave to realize thermal compensation.Because the control voltage calculated from MPC algorithm is always real number,it must be rounded to integer.This round error can influence the control performance seriously.A method of improving D/A converting precision by modulating pulse width of PWM wave with low frequency and little amplitude is introduced.The experiment show that it is effctive.By adopting this method,control range is enlarged,so that the system can be stabilized over longer period than 10h.The laser tube reached frequency stability of 8.7×10 -10 with sample time period of 10s.