Embedded scientific Computing

Embedded scientific Computing - D e s i g n , S i m u l a t...

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Unformatted text preview: D e s i g n , S i m u l a t i o n a n d I m p l e m e n t a t i o n o f a Si n g l e P h a s e C o n t r o l l e d R e c t i f i e r K M P avan K uma r N ambur i Abdul l a B insa l em A bst r a c t A converter changes an ac input voltage to a dc output voltage or a dc input voltage to an ac output voltage of desired magnitude and frequency. The former is called the rectification and the latter is called the inversion. Converters are widely used in industrial applications such as variable speed ac drives, battery chargers and DC power supplies etc. Single phase uncontrolled rectifiers are extensively used in number of power electronic converters. The disadvantages of uncontrolled rectifiers are overcome by using controlled converters by replacing the diodes with thyristors. The project mainly deals with the simulation and implementation of both the control circuit and the power circuit of single phase fully controlled converter. This also includes the simulations results and the comparison of various performance parameters of single phase fully controlled converter for inductive filter, second order filter and with and without ac side inductance. A p p l i c a t ions Ac to dc converter is the most typical power electronic devices which are found in any electronic devices such as television sets, personal computers, battery chargers etc.The power is around tens of watts to several hundred watts. They are also used in industrial applications such as variable speed drives that is used to control an induction motor and power range of variable speed drives is from few hundred watts to tens of megawatts. Hence ac to dc converters are used every time an electronic device is co nnected to the mains. They are used as DC power supplies and power supply for a specific application like electroplating. . L i te r a t u r e r ev iew Muhammad H.Rashid second edition. It deals with the basics of converters, principle of a converter and its applications. [2] Ned Mohan, Tore M.Undeland, William P.Robbins, It deals with the converters applications and design and gave an idea about the implementation of control circuit. I . I n t r od u c t ion B a c k g r ou n d The control and conversion of electrical power by power semiconductor devices is known as power electronics. Single phase uncontrolled rectifiers are used to provide unregulated dc voltage which is to be further modified to a regulated dc by using a filter. They have few disadvantages such as inability to control the output dc voltage when input ac voltage is fixed. They are also unidirectional in nature. These two disadvantages can be overcome if the diodes are replaced by the thyristors and hence the resulting converters are fully controlled converters.Thyristors are semi controlled converters which can be turned on by applying a current pulse at its gate terminal. They cannot be turned off from the gate terminals. O v e r v i e w of t h e p r o j e c t The project mainly deals with the design, simulation and implementation of single phase full controlled rectifier. In this we explain the design of inductive filter, second order filter and the operation of basic converter circuit and the operation of control circuit used. We also explain the components used and block diagram and circuit implementation of the control circuit. We also simulate the control circuit and power circuit used for the single phase fully controlled rectifier and the result are shown. We also calculate the various performance parameters such as power factor and total harmonic distortion for various types of power circuits like with inductive filter, second order filter, circuit with and without ac side inductance and firing angle delay. Finally we show an experimental set up used to build our circuit. I I . C o n v e r t e r o p e r a t i o n a n d d es i g n B a si c c i r c u i t of the converter the load current may or may not remain zero over some interval of the input voltage cycle. If the load current is always greater than zero then the converter is said to be in continuous conduction mode. In this mode of operation the Q1Q3 and Q2Q4 conducts for each alternate half cycle of the input supply. But in discontinuous conduction mode none of the thyristors will conduct for some p ortion of the input half cycle. The load current remains zero for that period. D e s i g n of c om p o n e n t s a n d s e l e c t i o n The main components of the power circuit are the thyristors, Inductor, capacitor and a resistor. We are using the four thyristors which are specified as 2N6508, 600V, 25A. For the inductive filter the circuit voltage to be approximately 10% of average value of output voltage, we can calculate the inductor value to be 175mH.For the second order filter reducing the inductor value by 4 times i.e. choosing L=43.75mH, Figure1: Basic circuit of full controlled rectifier O p e r a t ion : Full bridge is the most popular configuration used with single phase fully controlled rectifiers. Operation, analysis and performance is studied here.Figure1 shows the circuit diagram of singe phase fully controlled bridge converter. The single phase fully controlled converter is obtained by replacing all the diodes in uncontrolled rectifier with the thyristors. Thyristors Q1 and Q3 are fired together while the thyristors Q2 and Q4 are triggered 180o after Q1 and Q3. From the circuit we can know that for any load current to flow atleast one thyristor from the top group (Q1,Q2) and one thyristor from the bottom group(Q3,Q4) must conduct. We can also say that neither Q1, Q2 nor Q3, Q4 can conduct at the same time. For example, when Q2 and Q4 are in forward blocking state and a gate pulse is applied to them, they turn on and at the same time a negative voltage is applied across Q1 and Q3 commutating them. This can be explained similarly in the case of Q1 and Q3.Therefore we can say that whenever Q1 and q3 conducts, the voltage across Q2 and Q4 becomes negative. Therefore Q2 and Q4 can be triggered only when input voltage is negative i.e during the negative half cycle of the input supply voltage. Similarly Q1 and Q3 can be triggered during the positive half cycle of the input supply. Under normal operating conditions 400µF. Theoretically, the output voltage is found to be 108.04V and the output current is found to be 10.8A. We use another inductor which is 10% of the inductance obtained from inductive filter calculation i.e. 10 %( 175mH) which is 17.5mH. I I I . C o n t r o l C i r c u i t D es i g n C i r c u i t I m p l e m e n t a t i o n of C o n t r ol C i r c u i t Figure2: Circuit implementation of control circuit D e s c r i p t i o n of c o n t r o l c i r c u i t First we are stepping down the input voltage which is in the range of comparator circuit. The other input for the comparator is DC voltage. A trigger pulse is generated when supply input is greater than dc input. Variation of the DC supply gives the firing angle range. Pulse transformers are used at the end to generate the pulses and are supplied to the corresponding gate and cathode terminals. Vs Ig1 C o m p o n e n t V a l u es f o r t h e c o n t r o l c i r c u i t Table 1: Component values Description Specifications OP-AMP LM741 Power Mosfets IRF450,500V,13A Resistors Transformer 120V/20V,2A Quantity 3 2 2 1 Ig2 Figure4: Simulation of control circuit fo S i m u l a t i o n R es u l t s f o r co n t r o l c i r c u i t I V . S i m u l a t i o n a n d r es u l t s Vs Ig1 Ig2 Figure3: Simulation Here Vs is the stepped down supply voltage so that the Voltage is in the range of comparator circuit. Ig1 and Ig2 are the currents which trigger the thyristors. Figure5: Converter circuit for inductive filter with L=175mH, R , C=0 Vs Vd Vo IL Is Figure8: Converter circuit for second order filter with L=43.75mH, C=400µF, R Figure6 Here Vs is source voltage, Vd is rectified voltage, Vo is output voltage, IL is inductor current and Is is source current. The output voltage ripple is 10.75V. The ripple is 10.1 % of the average output. The power factor is 0.886,Vol tage THD is nearly 0 and it is seen that average voltage across the inductor and average current through the cap acitor is zero provided firing angle is zero. Vs Vd Vo Vs IL Is Figure9: Simulation circuit for second order filter From the simulation the output voltage ripple is 15V and it is 14% of the average output voltage. Here the power factor is 0.8801 and the voltage THD is 0.081 provided firing angle is zero. Vd Vo IL Is Figure7:Simulation of inductivefilter circuit From the simulation the output voltage ripple is15V an d the ripple is 16.6% of the average output. Here the po wer factor is found to be 0.7748 and the current THD i Vs Vs Vd Vd Vo Vo IL IL Is Is Figure10: Simulation circuit for second order filter From the simulation the output voltage ripple is 20V and is 21.7% of the average output. Here the power factor is found to be 0.7521 and the current THD is Figure12: Simulation of inductive filter circuit with ac side inductance 17.5mH and firing angle From the simulation the output voltage ripple is 15V and is 20.7% of the average output. Here the power factor is 0.5552 and average inductor current is 6.769A and the current THD is found to be 0.1478.The average Voltage across the inductor is found to be zero. Vs Vd Vo IL Is Figure11: Converter circuit of second order circuit for an ac side inductance of 17.5mH Figure13: Simulation of inductive filter with an ac side From the simulation the output voltage ripple is 15V and is 26.3% of the average output. Here the power factor is found to be 0.578 and the Voltage THD is 0.0007, Current THD is 0.2595 and the average inductor current is found to be 6.635A average voltage across the inductor and the average current through the capacitor is found to be zero. Vs D i sc ussi on of si m u l a t i on r es u l ts Vd Vo average IL average Voltage THD Current THD Ic average VL average Power factor 106.4V 10.6A 0 0.473 0.03V 0.886 93.02V 9.326A 6.4e-005 0.4331 0 0.7748 Vo IL Is Figure14: Simulation of second order filter circuit with ac side inductance and From the simulation the output voltage ripple is 16V and is 22.2% of the average output. Here the power factor is found to be 0.6028 and the average inductor current is 7.167A. The voltage THD is almost zero and the current THD is 0.1506.Here the average current through the capacitor is found to be zero. Table3: For second order filter with L=43.75mH, Vo average IL average Voltage THD Current THD Ic average VL average Power factor 106.8V 10.63A 0 0.4474 0 0.081 0.8801 92.9V 9.32A 0.000187 0.2859 0 0.2 0.7521 Vs Table4 and with an ac side inductance of 17.5mH Vo average IL average Voltage THD Current THD Ic average VL average Power factor 67.97V 6.768A 0.00979 0.1478 0.3206 0.5552 65.73V 6.635A 0.000705 0.2595 -0.8389 0.578 Vd Vo IL Table5: For second order filter with L=43.75mH, C=400µF, 17.5mH Vo average IL average Voltage THD Current THD Ic average VL average Power factor 71.99V 7.167A 8.3e-005 0.1506 0 -0.7507 0.6028 67.97V 6.768A 0.00979 0.1478 0 0.3206 0.5552 Is Figure15: Simulation of second order filter circuit with From the simulation the output voltage ripple is 16V and is 23.5% of the average output. Here the power factor is found to be 0.552 and the current THD is 0.1478 and the voltage THD is 0.009 almost zero. The We can conclude that the simulation results are nearly equal to the theoretical results. V . E x p e r i m e n t a l se t u p a n d R es u l t s We build the control circuit and we are able to get the pulses from the pulse transformer but when we tried to build the power circuit the thyristor was not triggered properly. We tried to work it out but we V I . C on c l usions Single Phase fully controlled converters are obtained by replacing the diodes of uncontrolled rectifiers by thyristors. In a fully controlled rectifier the output voltage can be controlled by varying the firing angle delay of the thyristors. Single phase fully controlled rectifiers are extensively used for small dc motor drives. The fully controlled bridge converter can circuits shown above the average voltage across the inductor is zero and the average current across the capacitor is zero. V I I . R e f e r e n c es [1] Ned Mohan, Tore M.Undeland, William P.Robbins, Power electronics: converters, applications, and design . [3] www.nationalsemiconductor.com [4] www.nationals.com [5] www.datasheetcatalogue.com [6] www.nptel.iitm.ac.in ...
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