Research On Synchronization Methods And Control Schemes For VIENNA Rectifiers Under Grid Disturbances

In modern grids, the total quantity as well as single unit power level of gird-connected power electronic devices has been increasing substantially. The properties such as non-linearity, impulsion and unbalancedness of these devices would cause distortion of voltage waveforms and current waveforms, and even gird faults. The research topic of improving the performance of the power electronic converters, which are the interfaces of power electronic devices to the modern grids, under normal or disturbed operation situations is now of most importance, in respect to grid power quality and grid-connected device operation environment improvements. VIENNA rectifier topology is well known for its simple structure of power and control circuit, low harmonics of the mains current, and low blocking voltage stress on the power semiconductors in comparison to the traditional rectifier topologies, which has been increasingly utilized in industrial motor drives, power supplies, active filters and charge station of hybrid vechile. Taking VIENNA rectifiers as the subject investigated, novel grid synchronization schemes, realization and performance improvements of VIENNA rectifiers control schemes with normal operation conditions, and novel control schemes for VIENNA rectifiers with voltage unbalances were proposed based on the conclusion of existing grid synchronization schemes and VIENNA topology control schemes.1. Single/three-phase grid synchronization schemes were studied in this paper. Firstly, based on the mathematical modeling of single/three-phase grid voltage signals and introduction of gradient descent signal approaching method, existing single/three-phase grid synchronization schemes were studied and evaluated from a brand-new perspective. Secondly, a Direct Decoupled Synchronization Method (DDSM) based on direct decoupling of fundamental symmetrical components was proposed in this paper. A decoupling scheme of positive and negative components of fundamental frequency form reference voltage ua,μβwas proposed, which exploits some existing advanced single phase PLL modules. Expanded DDSM (EDDSM) was also proposed after expansion of DDSM while dealing with severe low-order harmonics. DDSM was claimed to facilitate parameter acquisition and dealing with the situation while positive fundamental frequency differs from negative one. Finally, a novel In-phase/Quadrature-phase Waveforms Generator (IQWG) which generates the in-phase and quadrature-phase waveforms of input sinusoidal signal was proposed. After utilizing IQWG, block diagrams of EPLL based DEPLL and DDSM were simplified by sharing parameters sinφand cosqφyield by EPLL module. The simplified DEPLL-IQWG and DDSM-IQWG were verified to have preferable stationary and dynamic properties by experimental results.2. The control schemes for VIENNA rectifier topology with three-balanced grid voltages were studied in this paper. Firstly, the design and realization of the outer voltage loop, the inner current loop and neutral point balancing loop in abc natural frame control scheme for VIENNA rectifiers with three-balanced operation conditions were discussed, and additionally several novel PWM generators were proposed according to the current polarity restrictions. Secondly. a dq synchronous reference frame control scheme for VIENNA rectifiers with normal operation conditions was discussed. With simplicity, the dq frame scheme utilized a preferable space vector modulator and an efficient neutral point potential controller, in consideration of the particularity of VIENNA rectifier topology space vectors block diagram.3. The control schemes for VIENNA rectifier topology with three-unbalanced grid voltages were studied in this paper. With the control objective of DC-link voltage ripples and low frequency ripples of input active/reactive power elimination, a novel abc natural frame control scheme I of VIENNA topology with voltage unbalances was proposed. In comparison to the traditional dual frame hybrid vector control method, the proposed control schemeⅠhas the following merits:1) In efficient combination with DDSM, the reference current required can be directly calculated by the fundamental positive-/negative-sequence voltages and their parameters derived by DDSM; 2) By directly giving the main frequency sinusoidal current reference in abc frame, the proposed schemeⅠfacilitated current tracking and reduced total algorithm burdens. Then, at the first time, the stationary operation range of VIENNA rectifier topology was theoretically analyzed in this paper. The mathematical criterions were given and control schemeⅠwith severe voltage unbalance was claimed to break down because of unrealizable reference voltage vector out of the stationary operation range. Alternatively, with the control objective of ensuring appropriate operation of VIENNA rectifiers with all kinds of voltage unbalances, another novel abc natural frame three-unbalanced control schemeⅡwas proposed. The proposed control schemeⅡcould not eliminate DC-link ripples or low frequency active/reactive power ripples, but was suitable for all possible operation situations. In fact, control schemeⅠand schemeⅡcan be prefered according to the specific system design requirements. The current reference given methods by control schemeⅠand schemeⅡare also applicable in three-unbalanced control schemes for other kinds of grid-connected convertors.ADS 1103-VIENNA rectifier semi-physical simulation platform was developed in this paper. The properties and effectiveness of the proposed grid synchronization schemes, and the novel control schemes for VIENNA rectifier topology with three-balanced and three-unbalanced grid voltages, were demonstrated with experimental results by the DS1103-VIENNA platform.