Controlled Rectifiers with Inductive Loads, Inverters and Frequency Converters (KPI course text, 2010)
A 24-page course treatment of phase-controlled rectifiers, current continuity, grid and forced commutation, autonomous inverters, and AC-drive frequency-converter structures. It supplies historical derivations that must be reframed around present-day switch and drive practice.
This is the most substantial of the five KPI converter texts. It derives why an inductive load changes rectifier behaviour: current cannot jump to zero when a source voltage changes sign, so stored magnetic energy determines conduction interval, freewheeling, overlap, commutation, and possible inversion. It then distinguishes converters whose switching is imposed by the AC network from autonomous inverters whose power switches and commutation network establish output timing.
Concepts graduated into GTK #
- Firing angle controls average bridge voltage only under stated current-continuity and commutation assumptions.
- Source inductance causes overlap, reduces average output voltage, and couples converter current into the supply waveform.
- A freewheel path changes load-current continuity, output-voltage intervals, reactive-power demand, and device stress.
- Line-commutated inversion requires the source to accept power and sufficient extinction margin; “negative average DC voltage” alone is not a safe inverter design.
- Modern voltage-source and current-source inverters differ in the stored-energy element they regulate, their natural fault modes, and the switching states available to the load.
- A frequency converter is an energy and control architecture: direct AC–AC conversion or a rectifier/DC-link/inverter chain, with braking and regeneration determined by the front end and DC link.
Visual audit #
The 24-page text contains 24 circuit and waveform figures. They were audited as technical claims rather than copied wholesale. Many use historical thyristor arrangements or dense scanned notation; GTK redraws the load-bearing conduction paths and switching states as theme-aware diagrams after checking them against current device/application documentation. The original scans are not clearer than those redraws and are not retained as runtime assets.
Limits #
The thyristor derivations remain valuable for line-commutated equipment and history, but they do not describe the dominant control and fault behaviour of modern PWM voltage-source drives. Gate technology, dead time, common-mode voltage, semiconductor protection, active front ends, harmonic mitigation, and motor-insulation stress require current sources.