Abstract
All-pass-filter-based single-phase phase-locked loop (APF-PLL) is a widely used grid synchronization method in grid-connected power converters. However, the performance of APF-PLL degrades under distorted grid conditions and the estimated phase and frequency will contain low-frequency oscillation terms, which is not conducive to practical application. To deal with this problem, this paper proposes two advanced APF-PLLs, which have good ability to suppress harmonics and dc offset interference without sacrificing the dynamic response of the system. In the first one, a band-pass filter (BPF) is used as the prefilter of APF-PLL to process the input voltage signal, and in the second one, the APF-PLL input signal is processed by using a harmonic decoupling network (HDN) and multiple prefilters. In addition, their parameter design procedure is also described in detail and is easy to follow. The experimental results presented in this paper finally verify the superiority and effectiveness of the two proposed methods.
Highlights
In energy and power applications, such as pulse width modulation (PWM) rectifier, active power filters [1], distributed generation and uninterruptible power supplies (UPS) [2], it is extremely important to estimate grid voltage parameters
The single-phase phaselocked loops (PLL) consists of three parts: the phase detector (PD), the loop filter (LF), the voltage-controlled oscillator [3]
In [18], the SOGI-FLL with in-loop filter is proposed. Both methods improve the performance of SOGI-FLL and can effectively suppress dc offset and harmonic interference
Summary
In energy and power applications, such as pulse width modulation (PWM) rectifier, active power filters [1], distributed generation and uninterruptible power supplies (UPS) [2], it is extremely important to estimate grid voltage parameters (i.e., phase, frequency, and amplitude). In order to eliminate the influence of the dc offset on the PLL, [10] proposes the modified first-order filter-based PLL (MFOF-PLL) In this method, a degree of freedom (parameter k) is added to the APF-PLL structure. Both methods improve the performance of SOGI-FLL and can effectively suppress dc offset and harmonic interference Within this context, two advanced APF-PLLs, MFOFPLL with prefilter (MFOF-PLL-WPF) and MFOF-PLL with multi-prefilters (MFOF-PLL-WMPF), are proposed in this. To observe the effect of MFOF after adding a degree of freedom, Fig. 4 shows the M√FOF frequency res√ponse for three different values of k= 1/ 2, k = 1 and k = 2 From this plot and (2), we can obtain the following results: 1. The MFOF-PLL-WPF can effectively filter out the dc offset from the input signal, which can be proved by Fig. 6. We can obtain the optimal choice between overshoot and settling time when using the pre-filter to obtain the fundamental component of the input signal
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