Study On Approaches To Synchronous Transmission Of Energy & Signal On Cascaded DC-DC Converters

Both energy and informational communication play a vital role in the course of industrialization and its strategic upgrade.As a segment for energy transmission,DCDC converters are widely used in renewables-based power generation and DC load power supply.Various converters are connected in different ways to form DC power supply system,the communication within which guarantees the flexible control of electrical power.Achievable via traditional dedicated cable communication,signal transmission between converters can also be carried out by channelization of converters and the DC bus,that is,synchronous transmission of energy and signal,which on some practical occasions combines resources and improves efficiency.Aimed at different control or performance objectives,this thesis proposes three approaches to synchronous transmission of energy and signal on cascaded converters,and analyzes the potential effect of signal modulation on system stability under each approach.First,seeing that DC-DC converters can exhibit bifurcation phenomena in certain circumstances,and that for their causing great increments of ripple amplitudes,common period-doubling bifurcations are usually regarded as circuit pathologies that should be avoided,the thesis discusses instances of bifurcations induced by main circuit parameters through rigorous analyses of nonlinear dynamics,and exemplifies with the input-voltage-induced bifurcation that using the subharmonic specific to bifurcation,we can signal according to FSK modulation,which means that keying the input voltage is equivalent to keying the frequency constituents of the ripple.With a particular scheme devised for modulation and demodulation and a principle demonstrated for parameter optimization,general small-signal port parameters and transfer functions are derived in accordance with the canonical circuit model,so as to facilitate stability analyses.The validity of this approach to synchronous transmission is substantiated by experiment.Second,the same circuit as is used for subharmonic modulation is taken as a contrast,on which OFDM communication method is implemented to improve the efficiency of signal transmission: multiple small signals are fed into the control circuit and made to transmit parallelly without cross-interference.Meanwhile,based on the fact that injecting certain small signals can enhance converters’ fast-scale stability,the thesis applies the Floquet theory to resolve the small-signal frequency set that satisfies the stability-enhancing trait,and selects the optimum small-signal amplitude and frequency according to bifurcation diagrams.It depends on the channel frequency response,however,to specify the corresponding parameters of ordinary small signals.The OFDM-based approach to synchronous transmission of energy and signal is tested by simulation and experiment.At the very beginning of this part is a thorough explanation of the principle of OFDM and the application of the Floquet theory to converters’ dynamics analyses,which contributes to settling the proper form of the integrated modulation of energy and signal as well as optimizing related parameters.Last,parallel to the OFDM-based approach,what succeeds an in-depth description of the features of spread-spectrum communications is the specific choice of the FHSS technology to perform the synchronous transmission of energy and signal,so that the ripple power spectral density is lowered.In addition,simplifying improvement is made to the traditional implementation of FHSS in order to accommodate converter control.Also,the specification of PI parameters and carrier frequencies is addressed in this part.As for stability analysis,except that the action of frequency hopping is to be equated with an instantaneous change of the duty ratio,which is needed to apply a linear model to analyze transfer functions,the small-signal model derived in the subharmonic modulation part is still applicable.Experiment shows that the FHSS-based approach to integrated modulation in this thesis can effectively decrease the ripple amplitude.This thesis contains 65 figures,7 tables,and 75 references.