一种定周期控制下实现特定消谐调制的方法

Method for Implementing Specific Harmonic Elimination PWM using Fixed Sampling Period

提出了一种在矢量闭环控制系统当中实现特定谐波消除调制(specific harmonic elimination PWM,SHEPWM)的方法,并将其应用于三电平有源前端(active front-end,AFE)装置的控制。推导了系统在电网电压定向dq旋转坐标系下的数学模型,采用电压、电流双闭环结构实现矢量解耦控制,得到电压给定矢量的幅值、角度和频率。以角度为初值对频率进行数值积分得到相对连续的角度,经单调处理后查表实现特定消谐脉冲输出。所述方法在一台10 kW试验样机上做了验证,控制器采用DSP+FPGA构成主、从结构,矢量控制算法在DSP中实现,采样及运算周期为700μs;角度积分及SHEPWM输出在FPGA中实现。试验结果表明,配合适当的输入滤波器,所述方法在稳态时能够显著抑制网侧电流的低次谐波,同时在突加负载动态过程中能够快速、准确的响应。

A method for implementing specific harmonic elimination PWM(SHEPWM) in closed loop control system using fixed sampling period is proposed and used for three-level active front-end(AFE) control. Grid voltage oriented mathematical model of the system in rotating dq references is derived. Voltage and current double loop control structure is used to implement decoupled vector control,and reference voltage vector is obtained. Then,a relatively continuous angle can be computed by integrating frequency of the reference voltage with its phase angle used as initial value. By looking up a table calculated offline according to the refined angle and magnitude of reference voltage vector,output voltage of the corresponding phase can be determined to be 1,0 or-1. The proposed method is verified in a 10 kW prototype. Controller of the prototype is combined with a DSP and FPGA,which is configured as master and slave controller respectively. Vector control algorithm is implemented in DSP with sampling and control period of 700 μs. Angle integration and SHEPWM lookup table are implemented in FPGA. Experimental results show that,with properly designed input filter,the proposed method can effectively reduce low order harmonics of input current in steady state and behave fast and accurately in transient states such as sudden load.