Abstract
This paper proposes a power-synchronized control strategy for grid-following inverters (GFLIs) to regulate their power exchange with the grid without any need for sensing/regulating the point of connection voltage. Contrary to conventional GFLIs, which rely on phase-locked loops for grid synchronization and have difficulties in weak grid conditions, the proposed strategy is power synchronized and utilizes the inverter terminal voltage for power control leading to its seamless performance in ultra-weak grids. Additionally, since the proposed approach does not require any voltage regulation at the point of connection to the grid, contrary to grid-forming inverters, it can reliably operate in stiff and/or series-compensated grids as well. The proposed approach benefits from a decoupling control structure that is tuned using a loop-shaping method. Compared to conventional GFLIs, this approach does not need any extra hardware; hence, it can easily be retrofitted into the existing large fleet of GFLIs. The performance of the proposed controller is evaluated in Matlab/PLECS for both weak and stiff grids, and the findings are experimentally validated in a scaled-down setup.
Highlights
T HANKS to the increasing climate change concerns and accelerated decline in renewable energy costs, inverterbased resources (IBRs) are rapidly displacing synchronous generators in various power systems around the globe
Sensing/estimating the PoC voltage, its phase-angle and frequency are extracted by a phase-locked loop (PLLs), which are used by a vector current controller [5]–[7]
GFMIs regulate the PoC voltage while the frequency and magnitude of this voltage is provided by active and reactive power control loops, which mainly operate based on droop control
Summary
T HANKS to the increasing climate change concerns and accelerated decline in renewable energy costs, inverterbased resources (IBRs) are rapidly displacing synchronous generators in various power systems around the globe. IBRs need to get synchronized with the grid Their synchronization, is primarily based on control algorithms and differs from swing-equation-based synchronization of synchronous generators. GFLIs can seamlessly operate in strong grids and export their maximum power As they rely on PLLs, their performance in weak grids deteriorates, and operation in very weak grids can lead to their instability or side-band oscillations [13]–[16]. In [20], using a feed-forward loop from the PLL to the current control loop, symmetrical dynamics in the d- and q-axes are achieved All of these approaches, rely on a PLL and require the PoC voltage measurement.
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