Self‐capacitor voltage balancing method for optimally hybrid modulated cascaded H‐bridge D‐STATCOM

Abstract

A hybrid modulation (HM) for cascaded H-bridge converters is suggested which is a fusion of selective harmonic elimination (SHE) and carrier based bipolar pulse width modulation. It differs from its counterparts in the sense that only one triangular carrier for all H-bridges is used as opposed to multi-triangle waveform set and only one level of capacitor voltage and single type of semiconductor are considered. HM eliminates calculating and storing offline delay angles for each modulation index as in case of SHE. A novel self-voltage balancing mechanism is also proposed for HM which is based on strategically swapping redundant switching states. This mechanism is free from voltage sorting, current measurement, extra circuitry, or additional controllers. The comparison with phase and level shift pulse width modulation schemes reveal that the HM has 15% more DC voltage utilisation, and lower harmonic content for wide interval of modulation index. Moreover, HM has low semiconductor losses, as low as 0.55%. The tests on 1500 kVAR distribution static synchronous compensator shows that HM generates only 4% voltage ripple at the cost of few increase in average switching frequency. Voltage and reactive power balancing in each phase are also established with high power efficiency.

Direct current control strategy of SVG based on dual sequence dq coordinates under asymmetric load condition

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“…Recently, more loads with fluctuating and impacting characters are being widely used in industries. Thus, the power grid has become vulnerable to harmonics and reactive power and become unstable [1][2][3] . To stabilize the power grid, many types of handling equipment must be installed to clean the power grid at the customer's end.…”

Harmonic reduction under unbalanced operating conditions of PV‐connected cascaded H‐bridge multilevel inverters using fault tolerant adaptive phase‐shifted pulse width modulation

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A DC-DC converter-based infinite level inverter as DSTATCOM

“…Traditionally, shunt passive filters consisting of tuned LC filters 6 and/or high-pass filters are used to terminate the harmonics, 7 and power capacitors are employed to improve the PF of the utility/mains. 8,9 But they have the limitations of fixed compensation and large size and could also excite resonance conditions. Active power filter is a viable alternative to the classical passive filters for harmonics and reactive power compensation.…”

“…Hence, it is very essential to conquer these undesirable features. Traditionally, shunt passive filters consisting of tuned LC filters and/or high‐pass filters are used to terminate the harmonics, and power capacitors are employed to improve the PF of the utility/mains . But they have the limitations of fixed compensation and large size and could also excite resonance conditions.…”