DEC Startup & Transients

Bringing the converters up in step with the plasma, and riding through upsets, is a coordinated sequence rather than a single switch.

No cold start into full beam

A direct converter cannot simply be switched into a full-power beam. Electrode voltages, RF phase, MHD loads, and suppressor biases must be brought up in a coordinated sequence as the plasma exhaust ramps, so that at every instant the converter is matched to the beam it is receiving. A mismatch during startup wastes energy as heat and can stress the high-voltage structures.

The startup sequence

• Establish vacuum and confirm high-voltage standoff before any beam.
• Bring up magnet fields and the expander geometry.
• Ramp plasma and exhaust while stepping converter voltages, RF phase, and biases to match.
• Close the grid interface once the DC bus is stable, in grid-following or grid-forming mode.

Riding through transients

Once running, the converter must tolerate upsets: a plasma fluctuation that changes the beam current, an arc in a high-voltage gap, or a grid fault seen through the inverter. The control system detects these and adjusts — backing off loads, re-phasing, or momentarily isolating a stage — so a local upset does not cascade. The DC-bus architecture helps by decoupling the fast converter physics from the grid.

Why this is central to firmness

MetroVolt's promise is firm, continuous power. Firmness is not only steady-state efficiency; it is the ability to start cleanly, hold through disturbances, and recover from faults without long outages. The startup and transient design is where that operational reliability is engineered, working closely with the control and tuning system described next.