An improved droop controller for parallel operation of single-phase inverters using R-C output impedance

Power Calculation Algorithm for Single-Phase Droop-Operated Inverters Considering Nonlinear Loads and unsing n-Order SOGI Filtering

“…for small values of ξ <<1 has a strong harmonic attenuation, but at an expense of a very long settling time. Taking profit of these BPF characteristics for only linear loads and considering the drawbacks of the described conventional P-Q calculation, an attempt to cancel the double frequency pulsations in (7)-(8) was proposed in [18]. This method was intended to accelerate the calculation of the active and reactive powers, as shown in the .…”

“…In this operation, vo(t) can be obtained by different approaches such as a transport delay (TD) in [13] and [14], an extended three-phase dq SRF approach applied to single-phase systems in [15]- [16], and a method using the quadrature output of a SOGI filter in [17]. In [18] another method based on the calculation of powers and later cancellation of the double frequency component extracted by means of a SOGI, similarly to [6], was proposed. This method used a LPF and showed to reduce the time needed for calculating the powers in one order of magnitude, but using only linear loads did not consider nonlinear loads.…”

“…However, the validity of these approaches is only partial when sharing nonlinear loads or under harmonic voltage pollution. This paper proposes a modification in the power evaluation schemes shown in [6] and [18], using a n-order SOGI (nSOGI) approach for obtaining the fundamental components of the inverter output voltage and current when sharing a nonlinear load and under a 3 rd harmonic and 5% amplitude voltage pollution. The method uses the amplitude of the voltage and current fundamental components and the measured phase angle between the voltage and current for the calculation of P and Q.…”

“…The nSOGI proposal leads to faster P and Q calculations, since overcomes the speed limitations that other approaches have due to the LPF used in their structure. Comparisons with the classical droop method and with the methods proposed in [6] and [18] are made under the assumption of causing the same amplitude ripple at the final derived averaged powers when using a R-C rectified type nonlinear load. This paper is organized as follows, in Section II the power calculation block used in a classical droop method for a singlephase inverter is described.…”

“…This paper is organized as follows, in Section II the power calculation block used in a classical droop method for a singlephase inverter is described. In Section III an advanced method for calculating P-Q based on [18] is shown exposing the problems when using nonlinear loads and harmonic voltage distortion. Section IV proposes the novel power calculation algorithm using the fundamental components using the nSOGI approach and showing simulation results for validating the proposal.…”