基于DSP在线实现特定谐波消除技术的2种方法

Two DSP-based methods of online specific harmonic elimination

在数字信号处理器中分别用线性插值法和牛顿迭代法实现了特定谐波消除脉宽调制(SHEPWM)技术开关角度的在线计算。首先,利用三角函数倍角关系将级联七电平逆变器SHEPWM消谐方程组转换为代数多项式方程组的形式;然后,利用数学软件MATLAB中的Solve函数对其进行求解得到了调制比区间[0.485,1.07]内的所有解,并绘制了开关角度随调制比变化的轨迹,分析了开关角度变化的特点。选取其中一组开关角度,分别用数据查表结合线性插值的方法和对开关角度进行一元线性拟合并用拟合方程求解的开关角度作为牛顿迭代的初值而后用牛顿迭代法计算开关角度的方法,实现了级联七电平逆变器SHEPWM开关角度的在线计算,对2种方法的特点进行了分析和比较。仿真和实验证明了利用Solve函数求解多项式方程组得到的开关角度解是正确的,所述2种方法是可行的。

The online calculation of switching angles for SHEPWM（Specific Harmonic Elimination Pulse Width Modulation） is implemented in DSP（Digital Signal Processor） by applying the linear interpolation method and Newton iteration method. The SHEPWM equations of cascaded seven-level inverters are converted in form to the algebraic polynomial equations and the Solve function of mathematical software MATLAB is applied to obtain all the solutions of switching angle within the modulation ratio range [0.485,1.07]. The curves of switching angle vs. modulation ratio are drawn and the features of switching angle variation are analyzed.One group of switching angle is selected and two methods are applied to online calculate the switching angles for the SHEPWM of cascaded seven-level inverters. One method is the table look-up plus linear interpolation and the other is the Newton iteration,for which,the initial switching angle is the solution of fitted linear equation. The characteristics of two methods are compared and analyzed. Simulation and experiment validate that,the switching angles solved by the polynomial equations with Solve function are correct and the proposed methods are feasible.