Optimized Cascaded Controller Design for a 10 kW / 100 kHz Large Signal Bandwidth AC Power Source

The control system of a phase-modular three-phase 10 kW / 230 V
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Ultra-High bandwidth series/parallel inter-leaved multi-level AC Power Source (UHPS) for P-HIL applications with 4.8 MHz effective switching frequency is optimized with respect to high bandwidth and low output impedance or output admittance (depending on whether output voltage or output current is controlled), by adding selected and effective enhancements to existing control structures. The theoretical findings are verified by means of a detailed simulation model, which also takes time-discretization effects arising from the FPGA-based digital control unit into account. The comparative evaluation of the investigated control structures reveals that the combination of capacitor current feedback, inductor voltage feed-forward, and reference prediction performs best for the control of both, output voltage and output current. In this regard, at 100 kHz and for operation with rated load resistance of 5.3 Ω, the phase-lag of the output voltage of the optimized voltage control system can be reduced from 19°, for the conventional two-loop control structure, to 7°; the small-signal bandwidth increases from 235 kHz to 427 kHz; and the output impedance at 100 kHz decreases from 0.6 Ω to 143 mΩ. In case of output current control, at an output frequency of 60 kHz, and for rated load resistance, the phase-lag of the output current can be reduced from 51° to 33°, for an optimized three-loop control structure, which is accompanied by an increase of the small-signal bandwidth from 63 kHz to 89 kHz and an increase of the output impedance from 11 Ω to 30 Ω at 60 kHz.