基于快速傅里叶和小波变换的逆变数字锁相技术研究

Study on DPLL Technology for Invertors Based on Fast Fourier and Wavelet Transform

目前数字锁相环已广泛应用于逆变器并联、并网系统中。离散傅里叶变换(DFT)可解决传统过零点检测中谐波带来的多零点问题,提高了锁相可靠性及控制精度,但无法直接测量同步信号的周期。小波变换能有效分离混杂信号中基波信息,已广泛应用电力系统谐波分析。提出采用快速傅里叶和小波变换结合的一种改进逆变数字锁相方法:采用快速傅里叶变换(FFT)实现鉴相,通过小波变换得到基频同步信号的频率,修正鉴相过程,该方法有效改善了锁相环性能,并相比DFT提高了运算效率,仿真验证了该方法的可行性。

Digital phase locked loop is widely used in parallel invertor system and Grid- Connected Inverter system nowadays. The multi-zero- crossing problem resulting from harmonics in zero crossing detection DPLL can be solved by Discrete Fourier Transform(DFT),which improves reliability and control precision,but the fundamental frequency cannot be detected directly. Wavelet Transform can effectively extract the fundamental frequency from mixed signal and is extensive applied in power harmonic analysis. A improved DPLL method for inverters adopting Fast Fourier Transform and Wavelet Transform is proposed: Fast Fourier Transform is used for phase discrimination,while the fundamental frequency of Synchronous Signal is measured by Wavelet Transform to modify phase discrimination. The DPLL performance is promoted and the calculation efficiency is improved compared with DFT. Simulations validate its feasibility.