Passivity enhancement for LCL‐filtered grid‐connected inverters using the dominant‐admittance‐based controller

Abstract

LCL filters are widely used for power quality improvement. However, its resonance complicates the design process. Although the single‐loop filter‐based control reduces the cost, it is not reliable because of the grid impedance variation at the point of common coupling (PCC). This study proposes a dominant‐admittance‐based controller to improve the passivity of the inverter. Meanwhile, no extra hardware cost increases. It first offers a single‐loop damping method using a low‐pass filter, which frees inverter from the conventional limitation (fres>fs/6). A graphical procedure is applied to coordinate the current loop design to mitigate the low‐pass filter's negative effects on bandwidth. Then it introduces the dominant admittance concept for the inverter with PCC voltage feedforward control, which provides a new starting point for the admittance reshaping of the filter‐based damping inverter. Based on this concept, a PCC voltage feedforward control using a second‐order low‐pass filter is presented. The inverter output admittance is passive up to the Nyquist frequency with the feedforward control. Although the additional control loop is introduced, the controller requires no extra sensors because the PCC voltage measurement has already existed for the grid synchronisation. Experimental results validate the proposed scheme.

Designing Parameters to Reshape the Inverter Output Impedance Based on the D-Split Method under Weak Grid Conditions

“…Per the Equation (19), it is evident that the grid voltage feedforward occurs solely in the denominator of the inverter output impedance. The range of values for m is determined by initially setting n = 0 in G f (s) and focusing solely on the effect of m on the amplitude-frequency characteristic |H m | and phase-frequency characteristic ϕ m of the output impedance denominator.…”

“…However, this method is developed without accounting for control delay. Study [19] demonstrates the potential to expand the passive stability region of the inverter output impedance by integrating a phase angle lead compensator in series with the capacitor current feedback channel. However, this method introduces challenges in selecting system controller parameters.…”

Passivity Enhancement Strategy of Grid-Connected Inverter System Based on the Adaptive Active Damper

“…According to Chen et al (2020) and Cheng et al (2020), if the reshaped admittance Y sum shown in Figure 3 has a positive real part in the whole frequency range, the GCI system under the weak grid is passive and stable. With parameters of Tables 1, 2, the theoretical passivity improvement provided by an active damper is shown in Figure 5A.…”

Cascaded control for LCL filter based grid‐tied system with reduced sensors

“…Otherwise, the damping technique is mandatory to obtain a stable system. The critical frequency ($$\omega _{\text{c}}$$) for this region is given as $$\omega _{c} \approx \frac{\pi }{3T_{\text{s}}}$$ ($$f_{\text{c}} \approx \frac{f_{\text{s}}}{6}$$), where $$T_{\text{s}}$$ is the switching time which is reciprocal of switching frequency ($$f_{\text{s}}$$) [20]. On substituting the value of $$f_{\text{c}}$$ in $$f_{\text{c}} < f_{\text{r}}$$, the ratio obtained is $${f_{\text{s}}}/{f_{\text{r}}}<6$$.…”

“…), where T s is the switching time which is reciprocal of switching frequency ( f s ) [20]. On substituting the…”