| 摘要 |
A switching control arrangement for a multilevel convertor minimises the harmoni c content of the convertor voltage or current by an open-loop and/or a closed-loop control of the timing of the switching of the GTOs associated with the energy-storage component s (e.g. capacitors) in the convertor. In a first open-loop arrangement the convertor cur rent is quantized over its working range and different threshold values are provided in dependence on the quantization values of the current. In a second open-loop arrangement a c ontinuous, non-quantized control is provided based on at least a quadratic approximation to the desired current-dependent behaviour of the GTO switching angles. In a third, closed-loop arrangement, different GTO-switching threshold levels are provided as controlled by a Fourier integration process involving the nulling of those harmonics desired to be nulle d. The control arrangement is applicable to chain or stacked-capacitor multilevel convertors an d can be employed in SVC applications or applications in which the convertor draws real p ower as well as reactive power.
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