Multi-Level Converters

The future smart grid will be full of multi-level converters, simulating them poses unique challenges

Modular and Multi-level converters are increasingly more important as the grid becomes smarter and renewables make up a greater share of generation. Simple multi-level and MMC converters can be a few switches with more complex systems comprising of hundreds of switches. Accurate and fast simulations are the crux of their development.

The configurations, topologies, and options for these types of converters requires you to be able to consider the trade-offs and optimizations of:

Losses and efficiency of topology
“Controllability” and interactions with other local converters
Total Harmonic Distortion, Electromagnetic spectrum, and other harmonics related issues

Topology Losses and Efficiency

An efficient converter, needs less heatsinking and uses less energy.
Critical design consideration made even more important if your power source is a battery.

"Controllability" and Interactions with Other Local Converters

Power converters do not play nice with each other, it is much better to do thorough testing in simulation than face failure in the field.

Total Harmony

Total Harmonic Distortion, Electromagnetic spectrum and other harmonics related issues.

With so many aspects to consider you cannot spend lots of time waiting around for each simulation to finish. Also, actually implementing a large converter with several dozen PWMs with different carriers can be a major challenge, which will likely require you to pursue an FPGA-based solution.

Topology Losses and Efficiency

Going to multiple levels in a converter allows the voltage rating to be split across multiple switches, this, in turn, drives down switching losses but can come at an increase in conduction losses as more switches are required to handle the current. Another important consideration is that an increase in levels will decrease the base harmonic distortion of the output waveform, especially if a pure sine wave is required, this will reduce your output filtering requirements. PSIM will allow for switching and conduction losses of particular devices to be simulated and the impact of the heatsink and thermal interface can be considered. DSIM will allow for very fast and accurate simulations of the losses at particular junction temperatures and the impact of switching speed and levels on the losses of the output filters.

Learn More:

Webinar: Compare Device Switch and Conduction Losses w/ Heatsink and Different Operating Conditions (37:49)
Tutorial: Thermal Module Improvements (5:57)
Product Page: Thermal module

“Controllability” and Interactions with Other Local Converters

Multi-level converters are unlikely to be standalone converters and are destined to form the backbone of the smart grid. You need to be able to simulate how your converter responds to other converters working together over time periods of a few seconds. Without real-time simulation this task is daunting for traditional simulation tools, that is until you unlock the power of DSIM.

Learn More:

Webinar: Microgrid Design and Simulation (1:34:28)
Webinar: Multi-Level and MMC Design Comparison (1:15:29)
Webinar: Get Started with PE Expert 4 – Easy Implementation of a Modular Multi-Level Converter (MMC) (53:43)

Total Harmonic Distortion, Electromagnetic Spectrum, and Other Harmonics Related Issues

The world of multi-level and MMC converters contains many different topologies and gating strategies. A designer needs to care about the spectrum of electromagnetic interference/noise that the converter will introduce into the system. Further, if a pure sinusoidal or low total harmonic distortion (THD) output voltage is required for an inverter then inductor and capacitor elements are required. The size of these L and C elements can be a function of the topology used.

Adding more “levels” to any form of an inverter will reduce the output THD and it will be close to a pure sinusoidal waveform. A reduction in THD from the inverter output is useful as it decreases the size of the filter L and C values, which has two main benefits. Reduced cost and losses of these elements, and the possibility for more aggressive control with a higher cross frequency. However, running a few cycles of a 50 or 60 Hz fundamental with a large number of switches requires a simulation tool specifically designed for this task.

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