Abstract
With the continuous penetration and development of renewable energy power generation, the distributed grid and the microgrid are becoming increasingly important in modern power systems. In distribution networks and the microgrid, the grid impedance is comparatively large and cannot be ignored. Usually, the parallel compensation is used to improve the grid quality. In the grid with parallel compensation, the large phase angle difference between the impedance of the grid-connected inverter and the impedance of the grid at amplitude intersection will result in high frequency resonance (HFR). Because the inverter shows filter characteristics due to limited bandwidth of the controller, the parallel compensation grid, respectively, performs as the capacitance characteristic and inductance characteristic in different high frequency range. Compared with the three-phase, three-wire system, an additional zero-sequence path exists in the three-phase four-wire split capacitor inverter (TFSCI) system, so that the existing high frequency resonance suppression methods will be not effective. Since the zero-sequence component is neglected, HFR will also occur, in addition to the positive-sequence component and the negative-sequence component. Therefore, in order to suppress the high frequency resonance caused by positive-sequence, negative-sequence and zero-sequence components, an impedance reshaping strategy based on current feedback is proposed in this paper. This proposed method can reshape the amplitude and phase of the inverter impedance in a high frequency range without affecting the performance of the fundamental frequency control and ensure that the inverter contains a sufficient phase margin. Additionally, the proposed method can reshape the impedance of TFSCI within a wide frequency range, which makes it able to cope with the challenge of the parallel compensation degree change. Theoretical analysis and experiments verify the availability of the proposed control strategy.
Highlights
With the continuous penetration and development of renewable energy power generation, distribution networks and micro-grids account for an increasing proportion of contemporary power grids [1,2,3]
It can be found that the high frequency resonance (HFR) issue of the grid-connected converter have been widely concerned, while it should be noted that these damping strategies mentioned above are only suitable for three-phase three-wire system
Zero-sequence impedance amplitude between three-phase four-wire split capacitor inverter (TFSCI) and grid based on a simplifying impedance of the TFSCI, when the TFSCI connects to the grid
Summary
With the continuous penetration and development of renewable energy power generation, distribution networks and micro-grids account for an increasing proportion of contemporary power grids [1,2,3]. [24] proposed a control strategy for the converter to suppress HFR based on voltage feedback, which can reshape the phase of the converter impedance without a resonant frequency identified process It may increase the harmonic currents caused by the background harmonic voltages of the grid because it significantly reduces the impedance magnitude of the inverter at high frequency region. It can be found that the HFR issue of the grid-connected converter have been widely concerned, while it should be noted that these damping strategies mentioned above are only suitable for three-phase three-wire system When it comes to three-phase four-wire systems, these methods are not completely applicable, because the zero-sequence component will cause high-frequency resonance in addition to the positive-sequence component and the negative-sequence component [26].
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