High-Frequency Current Ripple Sample Anti-Aliasing Strategy of Digitally Controlled Converter Based on Notch Filter

Abstract

The digital controller of the grid-connected converter achieves closed-loop control by sampling key voltage and current signals. High-frequency commutation of power electronic switches introduces high-frequency ripples into the signals, which may cause sampling aliasing. Severe distortion may happen in the output current of the converter because of the sampling aliasing. This paper explains how the aliasing problem arises by analyzing the spectrum of signals for sampling control. The explanation shows the severity of the aliasing problem and the necessity of adopting anti-aliasing methods. Next, this paper analyzes the impact of commonly used anti-aliasing low-pass filters on current control stability. From the conclusions, adopting a low-pass anti-aliasing filter reduces the stability margin of the current loop, which needs improvement. So this paper proposes a novel hybrid anti-aliasing filter based on the combination of the notch and low pass analog filters. An experiment on a 6kVA prototype verifies the proposed anti-aliasing method. This paper shows distortion and step-response oscillation of the output current when proposed and traditional anti-aliasing methods adopted. The comparison shows the advantages of the proposed anti-aliasing method.KEYWORDS grid-connected converter, high-frequency ripples, anti-aliasing strategy, stability margin.

Aliasing Suppression Method for a Three-Phase Grid-Connected Photovoltaic Inverter Based on Multi-Sampling and Mean Filtering

“…The total harmonic distortion (THD), 5th harmonic, and 7th harmonic can be reduced by less than 0.1% by the harmonic and aliasing suppression method in [18], while the method has not been further experimentally verified. Both the proposed method in this paper and the method in [26] are able to reduce the 5th and 7th harmonics to less than 0.1%, and the proposed method in this paper has a lower THD. Therefore, the proposed method in this paper has better harmonic suppression capability.…”

“…Method in [7] 0.481% 0.844% 1.690% Method in [8] <0.100% <0.100% 0.940% Method in [9] ≈0.250% ≈0.190% 2.840% Method in [10] <0.100% <0.100% 0.510% Method in [11] ≈0.200% ≈0.160% 0.730% Method in [18] <0.100% <0.100% 0.090% Method in [25] ≈0.200% ≈0.400% 1.100% Method in [26] <0.100% <0.100% 2.230% Method in [27] ≈1.700% ≈0.400% 2.460% Method in this paper 0.041% 0.046% 1.124%…”

“…However, repetitive filtering reduces the advantage of multiple sampling and only removes integer switching harmonics, resulting in the presence of low-frequency harmonics in the control loop. A novel hybrid anti-aliasing filter based on a combination of notch and low-pass analog filters was proposed in [26]. However, the effect of anti-aliasing filters in the control loop to eliminate switching harmonics is in contradiction with the phase lag, so the introduction of anti-aliasing filters in the control loop as mentioned above will reduce the stability margin and affect the transient response [27,28].…”

Research summary of high frequency ripple of lithium battery

“…In the research process of high-frequency ripple, the commonly used processing methods include using filters, changing sampling rates, smoothing techniques, nonlinear processing, wavelet transform, etc. Ma [9] designed an anti-aliasing filter to reduce the high-frequency ripple in the grid-connected inverter by mixing the low-pass filter and the notch filter. Ren [10] used Matlab software to simulate the circuit, limiting the high frequency ripple in the lithium battery power system; Zhang [11] theoretically analyzed and discussed the high frequency ripple generated during the operation of the high frequency Buck converter, and proposed that the parasitic parameters of the output capacitor path determine the output voltage ripple value in the high frequency state.…”