Instantaneous Average Current-Sharing Scheme

For proper load-sharing control, the RMS values of the output currents are shared among the modules [26] and the average active and reactive loads shared [52]. These methods have good performances, but their current-sharing responses are very slow [53]. To overcome this issue, an instantaneous average current-sharing scheme based on sharing the instantaneous average current values among the inverters was designed [53-56]. In this method, a current-sharing bus measures deviations of the individual output currents and generates a current reference value for all DGs, as shown in Fig. 9.11. The voltage reference of each generator is different, but synchronisation is required to make the voltage phase angles of all inverters the same to ensure equal load-sharing. Each inverter has three control loops, inner current, outer current and inner voltage. The inner voltage and current loops control the inverter to provide good sharing in both steady-state and transient conditions for each single inverter. The outer current loop ensures equal sharing of the load by each inverter. This method is improved by introducing an adaptive gain-scheduling approach that modifies the current error signal [54]. The advan­tage and limitations of this method are [35]:

• It performs well for both current-sharing and voltage regulation, even if the output currents contain many harmonics, but

• The necessary interconnections between the inverters limit the flexibility of the system and degrade redundancy,

• The highest current control deteriorates the current distribution and output voltage regulation,

• The non-identical component characteristics and input voltage variations of the paralleled inverters might also deteriorate system performance, and

• This method is designed for equal power-sharing only.

Updated: October 23, 2015 — 12:41 pm