A hybrid converter for medium voltage using a low-voltage current source active filter connected via a series capacitor

Investigations in the Modeling and Control of a Medium-Voltage Hybrid Inverter System That Uses a Low-Voltage/Low-Power Rated Auxiliary Current Source Inverter

“…This paper expands on previous work relating to the Hybrid concept in [13] by investigating the challenges of applying the same technique to connect the auxiliary CSI via series capacitors to the MV grid/main inverter via their split inductance that typically will form an LCL filter and lead to the known associated stability problems reported already in literature [20]. The resulting topology is shown in Fig.…”

“…The reference waveform to the CSI is therefore the switching current ripple of the main bridge which can be sensed and the calculated reactive fundamental current component to achieve the desired voltage drop. The detailed hybrid converter model including the phasor diagrams used to derive the control and the design equations are detailed in [13]. In Table I, the specifications for the hybrid converter used in this simulation study are summarised.…”

“…In [13] the authors of this paper have proposed a hybrid solution aimed at improving the harmonic performance of a slow switching medium/high voltage inverter by means of employing an auxiliary current source inverter with very low installed power to cancel the switching harmonics caused by the main converter. The CSI is used because it is very good at synthesizing an AC current reference, in this case the switching current ripple which is in the hundreds Hz range of the main MV inverter, with the lowest switching frequency.…”

“…The Modular Multilevel Converter (MMC) proposed few years ago [6,7] has gained increased popularity in a short period of time due to its reliance on a large number of identical building blocks that would enable cost effective mass production and allow flexibility in implementing any custom design system solutions. Hybrid converter implementations have been proposed in the past to enhance the behaviour of passive filters [8,9] or to improve the waveform quality of slow converters by adding low current rated auxiliary converters [10][11][12][13][14][15][16][17].…”

“…The maximum capacitance value is usually restricted based on the allowed reactive power generated therefore a similar range of capacitances for C s can be considered as the previous design i.e. 55-110μF with respective resonant frequencies between 500-360HzFor the following design, a value of 100μF has been chosen to enable lowest consumption of CSI installed power devices, as detailed in [13] where it was shown that the result of the Cs versus CSI installed power optimisation is convergent even when a large range of CSI losses are considered as seen in Fig. 7a and 7b under the assumption that the CSI efficiency typically ranges from 85%-95% of the apparent power processed, depending on switching frequency.…”