Three phase PWM converters are widely used in numerous
applications including adjustable speed motor drives, uninterruptible power
supplies and grid integration of renewable and distributed resources such as
solar photovoltaics. Some of the important metrics of performance for these
converters are related to the amount of total harmonic distortion (THD) in the
line current, switching losses in the power devices and dynamic performance.
Modular converters are also becoming increasingly popular for high power
applications due to the advantages of reduced voltage or current ratings for the
individual switching devices, reduced current or voltage ripple (hence smaller
filter size) by utilizing interleaving, unified design and increased reliability
through redundancy. Interleaving refers to appropriately phase shifting the PWM
signals to the different modular converters in such a way that the ripple
content in the individual converter currents tend to cancel each other in the
total line current.
Researchers at Arizona State University have developed
hybrid interleaved space-vector PWM schemes for parallel-connected modular
three-phase converters. The proposed schemes result in superior performance
especially in terms of reduced THD in the line current drawn by the interleaved
converters, compared to conventional schemes. These hybrid schemes make use of
certain new space vector PWM sequences that were originally developed at ASU for
single converter applications to reduce distortion and switching loss. The
invention disclosed here extends these concepts and sequences to interleaved,
modular converter applications. The process of developing the new hybrid schemes
involves selecting the optimal sequences as well as the optimal phase shift
among the modular converters in each switching cycle.
Potential Applications
- Uninterruptible Power Supplies (UPS)
- Grid Tie Renewable Resources (Photovoltaic Energy)
- Adjustable Speed Motor Drives
Benefits and Advantages
- Greatly reduced total harmonic distortion ? typical
reduction of about 40% with max reduction of 67%
- Significantly reduced filter size
- Reduced switching losses
- Reduced losses in the AC filter capacitor