An Active Interphase Transformer for 12-Pulse …

1 978-1-4799-5141-3/14/$ 2014 IEEE An Active Interphase Transformer for 12-Pulse rectifier system to Get the Performance Like 24- pulse rectifier system Milan Anandpara Tejas Panchal Vinod Patel Deaprtment of Electrical Engineering Deaprtment of Electrical Engineering AGM, R&D Department Institute of Technology Institute of Technology Amtech Electronics (I) Ltd. Nirma University Nirma University Gandhinagar, India 382 028 Ahmedabad, India 382 481 Ahmedabad, India 382 481 Email: Email: Email: Abstract- in this paper, an Active Interphase Transformer is implemented in 12-Pulse diode bridge rectifier system . This system draws near sinusoidal supply from the utility.

2 In this paper, simulation results are provided for two schemes. Scheme I consists of an autotransformer ( P0 (PU)), two Active Interphase Transformer , two diode bridge rectifiers & PWM VSI. A PWM VSI injects triangular shaped current into the auxiliary winding of Active Interphase Transformer connected between two diode bridge rectifiers. This modification result in reduction of harmonics in utility line current. In scheme II boost converter is incorporated across the auxiliary winding of Active Interphase Transformer . Both schemes draws clean power from the utility & is suitable for powering high power ac motor drive system , power supplies, UPS system to meet IEEE-519 harmonic current limit. A PWM VSI & boost converter connected across auxiliary winding of Active IPT is of low kVA & it is not directly exposed to line transients. Simulation results are provided for 415 V, 50 kVA 12-Pulse rectifier system for both schemes.

3 Index Terms- autotransformer, actie Interphase Transformer , PWM VSI, harmonic reduction, boost PFC circuit. I. INTRODUCTION In most power electronics applications, diode rectifiers are commonly used in the front end of power converter as an interface with the electrical utility. The nonlinear operation of the diode bridge rectifiers causes highly distorted input current. The non-sinusoidal shape of the input current drawn by the rectifiers causes a number of problems in the sensitive electronic equipment. The distorted input current flowing through the system produces distorted voltages at the point of common coupling (PCC). Due to nonlinear nature of the diode bridge rectifier input line current have significant harmonics. For ac motor drive systems with no dc link smoothing inductor, the discontinuous conduction of the diode bridge rectifier result in a high THD in utility line current.

4 [5] A number of methods have been proposed for harmonics reduction in utility line current. A conventional 12-Pulse diode bridge rectifier results in 5th& 7th harmonics cancellation in utility line current. Many multipulse converters have been introduced to achieve clean power such as 12-Pulse & 24- pulse systems. These multipulse converters are formed by combination of 6- pulse converter & isolation Transformer (Y-Y & Y- ), which increase cost & complexity. In this scheme an Active Interphase Transformer is incorporated in 12- pulse diode bridge rectifier system with autotransformer arrangement. An Interphase Transformer is required to ensure the independent operation of two parallel connected diode bridge rectifiers.[5] In this paper two possible ways for implementation are shown and are named scheme I & II. In both schemes an autotransformer of low kVA ( P0) is employed to generate 30 phase shift between two diode bridge rectifier which drastically reduces the cost, weight & volume over the conventional system (Y-Y & Y- connected 12-Pulse rectifier system ).

5 Primary winding of Active IPT works as ZSBT. This winding will offer high impedance to cross conduction paths between two diode bridge rectifiers & offer low impedance and give independent operation of rectifier bridges in 12-Pulse rectifier system . In scheme I low kVA PWM VSI (Full Bridge) is connected across the auxiliary winding of Active IPT. It will inject triangular shaped current Ix into auxiliary winding of Active IPT, near sinusoidal line current flow from the utility. In scheme II boost converter is connected across the auxiliary winding of Active Interphase Transformer . It will draw triangular shaped current Ix, this will reduce harmonics in the utility line current to near sinusoidal current shape. Both the schemes I & II are rugged & give good performance with reduced kVA components. II. SCHEMEI Active IPT WITH PWM VSI (FULL BRIDGE) shows the circuit diagram of this system .

6 This system employs a polyphase autotransformer to provide 15 phase shift between two rectifier Bridges I & II & Active Interphase Transformer . In this scheme inductance of Interphase reactor (primary winding) & line impedances Ls1& Ls2 are designed properly to get 12-Pulse operation. A PWM VSI (full bridge inverter) injects triangular shape current (Ix) into the auxiliary winding (Nx) of Active Interphase Transformer , by doing this near sinusoidal currents flow from the utility with less than 5% THD. This 12-Pulse rectifier system has lower kVA magnetic & fewer component counts. If the PWM VSI were to fail, this circuit will give 12-Pulse operation with 5th& 7th harmonics cancellation in utility line current. Circuit diagram of 12-Pulse rectifier system with actransformer& PWM VSI. (a) (b) Delta connected autotransformer (a) vector configuration on a three limb core.

7 Ctive Interphase diagram (b) winding A. Implelentation of PWM gatbridge inverter Block diagram of PWM gating sig Fig. 3 shows the block diafor PWM inverter. The referesynchronized with the input vstandard digital logic circuits & The reference current acompared and the current etriangular carrier wave to geninverter. The close loop operatfollow for clean power requB. Analysis of scheme I In this section, analysis of sFig. 2(a) & 2(b) show the wdiagram of the autotransformer , sin , sin , , 1 tan15 , Where is the rms of the linekVA rating of delta connected a 6| This 12-Pulse rectifier requ20% of the system kVA. Thus80% as compared to convenscheme. C. kVA rating of Active InterphThe Voltage (Vm) across prima tingsignal generator for full gnal generator for PWM VSI.

8 Gram of gating signal generator ence for the injected current is voltages & is configured with & phase locked loop electronics. and the feedback current are error is then compared to a nerate PWM gating signals for tion of this scheme ensures to uirement. scheme I is presented in detail. winding configuration & vector . (1) n 15 (2) 1 , (3) (4) (5) e to line voltage. autotransformer is found out by, || | 3| || | (6) (7) uires a Transformer kVA of only s Transformer size is reduced by ntional (Y-Y & Y- ) 12-Pulse hase Transformer & PWM VSI ary winding is found out by, (8) The voltage (Vx)

9 Across the auxiliary windinterphase Transformer is given by, The rms value of injected current Ix is given The kVA rating of Active Interphase transform The kVA rating of PWM VSI is given by, Magnetizing inductance L1 for primary winterphase Transformer is given by, . , Where K1 is the desired percentage ripple of The Active Interphase Transformer employed designed for turn ratio NP: Nx = 1: 2. III. SCHEME II Active IPT WITH Circuit diagram of 12-Pulse rectifier system wtransformer& Boost PFC Circuit. In this scheme boost converter is connectewinding of Active Interphase Transformer .

10 Thoutput is fed back to the dc link. The bcontrolled by ON SEMICONDUCTORS MCin the auxiliary winding of Active IPT reducutility line current to a near-sinusoidal curcurrent Ix become zero, this circuit widing in the Active (9) by, (10) mer is, (11) (12) (13) (14) winding of Active (15) load current I0. in simulation was ST PFC CIRCUIT with Active Interphase d across auxiliary he boost converter boost converter is C34262. Current Ix e harmonics in the rrent shape. When ill give 12-Pulse operation with 5th& 7th harmocurrent.