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The Research On Power Supply Method Transforming Between Three-Phase And Single-Phase Based On Balance Transformer

Posted on:2009-09-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y F OuFull Text:PDF
GTID:1102360242490316Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Along with the rapidly increasing requirement of electrical power supply and higher criterion towards power quality, problems of negative, harmonic, and reactive power are caught to people's attention. The main causes of the drop of power quality are all kinds of asymmetry and non-linear loads in power system, which includes the AC single-phase electric railway traction supply system and petrochemical industry single-phase power supply system, etc. Those asymmetry loads bring disadvantage to the power system's operation. In this paper, the research's topic that the balance transform between three-phase and single-phase, and the aim is to compositively deal with the negative sequence, harmonic currents, and the reactive power. The research on which is significant to be continued in theory and in applying.Firstly, the three-phase and single-phase transforming supply method based on balance transformer and phase-shifted method has been researched. According to structures of general kinds of balance transformers, the commonness has been picked up, and the balance principle transforming between three-phase system and two-phase system of balance transformers is analyzed. Three-phase and single-phase transform power supply methods using phase-shift are developed. Their calculations of matching components are rendered in simpler forms, owning to the orthogonality of two-phase voltages in balance transformer. The topologies of three-phase and single-phase transform are discussed, and three different combined modes along with their calculations are given, which work respectively for resistance, inductive and capacitive loads. The asymmetry factor affected by the non-ideal matching components and the fluctuating load is analyzed, and a resolution of suppressing the correspondingly produced negative currents is given. The simulated data and experimental results are verified on a 2kVA balance transformer prototype shows that the proposed calculation formulas are valid and feasible.Aiming to the defect of asymmetry system while loads of balance transformer are unequal betweenα-phase andβ-phase sides, a new current balance compensation method utilizing inverter is proposed, which is mainly used to compensate negative sequence current. The system structure of this method is constituted by balance transformer and an AC-DC-AC single-phase inverter connected in parallel. Active power energy can flexibly flow from one arm-side with light load to the other arm-side with heavy load to suppress harmonic current and compensate reactive current, under control of the system. The result isαandβphases equivalent loads of the transformer reach to balance state, and eliminates the precondition to bring negative sequence current to insure the current symmetry of three-phase side of the transformer.Considering of certain occasion that three-phase electric equipments are need, but single-phase power system is supplied only, such as the single-phase electric power distribution among remote villages, a novel single-phase to three-phase power supply method based on balance transformer is discussed. It is the method that single-phase power source is separated into two branch circuits in parallel. One branch connects directly with primary side of balance transformer asα-phase, and the other branch connects asβ-phase via a phase-shift converter. Theα-phase andβ-phase are orthogonal in angel and equal in amplitude each other, and match the two-phase to three-phase symmetry transformation condition of balance transformer. So that a high quality symmetrical three-phase voltage system is produced in the secondary side of balance transformer. Comparing with traditional single-phase to three-phase converter, the phase-shift converter needs less power-electronic devices and bears only half capacity of three-phase loads. Besides, the phase-shift converter can detect and compensate theα-phase harmonic current while supplyingβ-phase equivalent load. It makes the input single-phase current sinusoid and high power factor.According to the circuit structure of three-phase to single-phase balance compensation method, a twin single-phase instantaneous harmonic current detect method is proposed. This detect method detects the active current ofαandβ-phase load, works out the mean of them. Also, it detects the harmonic currents and reactive power. The balance inverter compensates two phases load currents, and makes the two side output currents are orthogonal in angle and equal in amplitude. That meets the compositive demand on active power transfer, reactive power compensation and harmonic suppression of the balance compensation method. Besides, a single phase instantaneous current detect method is proposed also, special for the structure of single-phase to three-phase power supply method.It is proposed that a hysteresis current control method using single phase voltage vector. And it is utilized that an optimized double PWM hystereses control strategy on the base of the control method, which can make frequency of each switcher lower and less loss. It is proposed a double close-loop control method towards the inverter part of the single-phase to three-phase power supply, which keeps the output voltage along with the reference signal. That insures that the orthogonality of two-phase voltages in balance transformer.In this paper, it is discussed that the main system components of power electronic three-phase and single-phase transform power supply methods. The selecting method of AC side filtering inductance value, DC bus voltage value and DC bus capacitance are given, using the method of theoretical analysis.Finally, a simulation system of power electronic supply methods which are mentioned is built with Matlab/Simulink tool. The situations include active power flow, harmonic suppression, reactive power compensation, response of the load changing, and the power distributing on components are analyzed in detail. The results prove that the methods, including structures, detecting systems and control strategies, which are mentioned, are correct and available in realization.
Keywords/Search Tags:Three-phase and single-phase transform, Current balance compensation, Balance transformer, Negative sequence current, Harmonics detect, Hysteresis control
PDF Full Text Request
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