Development Of Three-phase Shunt Active Power Filter With Third Harmonic Injection And LCL Filter

With a large number of nonlinear loads accessed to power grid, the problem of harmonicpollution is increasingly more serious. Three-phase shunt active power filter (SAPF) isconsidered to be an effective means of harmonic pollution control based on the existingresearch results and practical applications. SAPF has been widely applied in Europe and theUS, and we have made good progress on topology design, harmonic detection and currentcontrol technology of SAPF in domestic. However, the theoretical study of key issues in theindustrialization (radiation, electromagnetic compatibility, insulation, cost and volume, safetyand stability) is not deep enough. As the power quality control part of the project of nationalhigh technology research and development program (863-plan)"Research on the keytechnology and integrated demonstration based on smart power grids of distributed energyresource" and based on the industry standard JB/T11067-2011(JB067) of low voltage activepower filter unit, this paper have made a systematic and in-depth theoretical research on thekey problem of industrialization of three-phase SAPF. It is committed to develop an activepower filters (APF) device which is stable, practical and cost-effective through innovation andimprovement of topological structure, current control technology, error correction method andprotection system. The main research contents and results are as follows:1) Topology design: Based on third harmonic passive injection technology, a kind ofapplied patent topology is proposed. The injection loops of third harmonic voltage and zerosequence current are constructed which utilizes the source of third harmonic voltage that isgenerated by SVPWM modulation and injected into power grid through capacitor. Comparedwith the traditional topology, DC voltage utilization is advanced, fever of power module isreduced, the shortage of device itself become a three-phase unbalanced load of power gridthat is caused by traditional topology which cannot provide zero sequence current dischargechannel is overcome, and the EMC and insulation performance are improved.2) Current control: By utilizing the character of harmonic periodic repetition, this paperdesigned a period repetitive control based on error prediction operator and realized thedeadbeat control of system, thereby avoiding the shortcoming of conventional deadbeatcontrol which is difficult to describe the harmonic current by a unified mathematical model.At the same time, the article proposes a half-period repetitive control (HPRC) based on sineoperator that reduced the delay of repeated control and improved dynamic performance.3) Measurement error correction: This paper proposes a steady-state correction (SSC)method for eliminating measurement errors, and the measurement errors are eliminated at no additional cost. The effect from the measurement error on the original control system isderived analytically, and the principle of lowering effect from measurement errors isexplained. Based on the SSC method analysis, an application of this method in SAPF isinvestigated and the effectiveness and viability of the scheme are demonstrated through thesimulation and experimental verifications.4) Protection system: This paper researched the noumenal protective measures of APFand the special status protective measures in running process and adopted the redundantdesign of hardware and software protection together for the key failures. The precharge circuitis improved, compared with the conventional precharge circuit which included three currentlimiting resistances, the improved precharge circuit is consist of a current limiting resistor. Soas to ensure the safe and stable operation of APF.Based on theoretical research and key technical breakthrough, a60KVA industrialprototype is developed under the cooperation between the research team and a large Ltd.company. Simulation and factory test result proved that the whole performance of theprototype meets the standard of JB067, the key technical indicators reached the level ofinternational well-known brand. The prototype can be run in863demonstration projects, andengineering foundation is established for the final industrialization of APF.