An improved model of hybrid multi converter used for grid connected applications

ABSTRACT

The applications of chopper fed inverter [9,10] and grid applications for a single output voltage. Multiple inputs are used to obtain a single DC-DC output which are limited for fewer applications [11][12][13]. Literature study on conversion stages of DC-DC converter like single stage, three stage conversions have been regarded [14][15]. The boost Converter [16] with modified switching pattern and reduced number of components with improved input power factor is presented. The proposed method is also adopted with bridgeless construction to reduce forward voltage drops of the switches. More over the efficiency and the power factor of converter are improved by the proposed switching pattern which is adopted in PFC chips with the slight modifications. Mainly the thermal stability of the converter circuit is improved with reduced components. In addition, the noise inference and losses associated with switches are the decreased with the proposed switching pattern.
A new integrated three level AC to DC converter [17] fed DC motor with cascaded filter is presented. This converter integrates the operation of the boost power factor correction and the three-level DC-DC converter. This converter is made to operate with two independent controllers-input controllers that performs power factor correction (PFC) and regulates the dc bus and an output controller that regulates the output voltage. The circuit is analyzed for different criterion and the results are presented.
To get a nearer unity power factor, Vienna rectifier [18] is employing the two current control methods. They are (i) Hysteresis current control. (ii) Fuzzy logic control. The combined arrangement of the fixed pitch wind turbine driving a permanent magnet synchronous generator is interfaced with this Vienna rectifier. The rectifier arrangements are used to compare the performance of the proposed converter without any current control methods. The wind speed variations and the constant wind speed conditions are used to study the performance of this converter for the stand alone loads. A simple buck converter [19][20] at the output stage of three phase diode rectifier with bidirectional switches. The buck converter regulates the voltage at the output stage for speed control applications. The fuzzy logic based control method is developed to improving the conduction period of the bi directional switches. The new technique is simulated with DC drive application by PI controller as well as Fuzzy controller and the results are compared.
A Hybrid Multi Converter Topology (HMCT) has been designed exclusively for DC applications with better advantages to overcome the voltage conversion process, stability and to increase the range of applications. Figure 1 shows the Hybrid multi converter topology which consists of a multi Cuk converter and a buck converter. Source to the circuit is fed from the renewable energy source using solar panels. The proposed hybrid multi converter topology can simultaneously produce DC output of various step output voltages. Two Different type converters have been implied. Multi Cuk converter produces different outputs higher than the supply voltage. Input voltage produced can be stepped up and high magnitude output voltages can be obtained using Cuk converter. Simultaneously, from converter 3 using buck converter lower voltage can be obtained. Complexity of the proposed system is reduced commendably with simple operation and control technique. One of the advantages is, with a separate switch for each converter synchronization issue can be avoided with a suitable control mechanism. To increases the stability of the system, PI control technique is implemented distinctly each for Cuk & buck converters. Concurrently manifold output voltages are acquired. Diverse applications based on DC source can be served; industrial applications can be realized with the proposed converter topology where DC motors of dissimilar voltages can be used. Multistep output from mono input RES by means of DC-DC converter has been obtained by modifying the converter topology. The system is explained through locked loop control using MATLAB. The paper is prearranged as

PROPOSED TOPOLOGY DESCRIPTION
The traditional Cuk converter from Figure 2(a) is designed by two inductors L 1 and L 2 , capacitor C 1 , semiconductor switch S1 and diode D. Similarly Buck converter in Figure 2(b) is designed using an inductor L 1 , switchS 1 , diode D. The Cuk is designed as a high output converter, while the buck is designed to be a low output converter. Continuous conduction mode has been used since it produces better efficiency and effective use of active elements and passive elements.
V= Input Voltage; |V|= Output Voltage; the ratio of duty cycle (D) is given by on time (T ON ) to the total time period (T S ). Cuk and Buck converters, though they have a similar working for varying voltages, they differ with their operation and principle. Cuk converter can invert the polarity and change the magnitude whereas buck converter can modify the output magnitude to a lower level. With a significant combination of Cuk-Buck converters, simultaneous high output voltage and low output voltage with dissimilar values can be accomplished.
From Figure 3, the operation of hybrid multi converter topology, supply from the photo voltaic panels is fed to the circuit. Switch S 1 & S 2 are closed at the same time, the supplied energy will be stored in the inductors L 1 , L 01 and L 2 , L 02 . Alternate to the input and output capacitor C and C 0 are connected; C 1 and C 01 are also connected in the similar fashion. During the ON period L 01 and L 02 store the energy while capacitor C and C 01 discharges. At this time interval, freewheeling diodes, D1 and D 2 are turned off; supplied energy to the loads is delivered by the output capacitors given with C 0 and C 01 . After a while, S1and S 2 are switched off, capacitors C and C 01 get recharged through inductors by means of freewheeling diodes, D 1 and D 2 . Cuk converter distributes two simultaneous outputs of different voltages. Further, the output from Cuk converter is fed to buck converter.

Operation of hybrid multi converter topology
Converter 1 produces the output voltage V 01, where V 01 > V S i.e., obtained output (V 01 ) will be boosted above the supply voltage (V S ). Switch S3 will be closed in Converter 3, the output, V 01 from Cuk converter will be fed to the buck converter. Buck converter produces extremely a low output. i.e V 03 < V 01 In a similar working pattern, the output voltage obtained across converter 2 will be, V 02 > V S. . Cuk converter with output voltage V 02 is left for a future protraction of inverter. Analysis for Cuk converter,  Figure 4 explains the operation and working characteristics of the proposed hybrid multi converter topology. Mode I: One of the Cuk converter and buck converter are operated, switch S 1 is turned on, the converter produces output voltage V 01 further the output V 01 is fed to the buck converter, switch S 3 is turned on which produces output V 03 . Here, both the converters are operated simultaneously. Mode II: Both the Cuk converters are operated simultaneously, switch S 1 and S 2 are turned on which produces output V 01 and V 02 . Both the Cuk converters are fed with same input voltage whereas they produce a different output. Cuk converter is operated which produces the output V 02 . In future the output from Cuk converter two which produces comparatively high output voltage then other converter can be used for the inverter protraction. The complete operation of the proposed hybrid multi converter topology operates in the closed loop mechanism. The control over the circuits is obtained from PI controller for Cuk converter and PI controller for buck converter. Improved efficiency has been observed, S 1 , S 2 , S 3 , switches are triggered using the control mechanism of analog controllers. The output voltage is fed to the controller and a constant reference voltage set through battery is fed and both are compared. Stable output is produced exactly around the set voltage.  Average performance values of inductor and capacitor are illustrated in the Table 1. Instead of all switches, an average value is taken for switch and diode crosswise the link capacitor and inductors. A link capacitor and inductor connected crosswise to buck and Cuk converters will have high values to avoid the flow of negative current and to reduce the reverse effect on the converters.

RESULTS & DISCUSSIONS
A design of the proposed hybrid multi converter topology has been developed using the software tool. Various results have been simulated. The design of the converter topology has been simulated using MATLAB. Input voltage of 14V is given through the Renewable energy source using photo voltaic panel. The input is fed to the circuit is boosted using Cuk converter. Figure 5, shows the different waveforms for boosted voltage obtained from Cuk converter. Waveform portrays three outputs with different voltage. Converter 1 produces V 01 Similarly other converter 2 and 3 produces V 02 and V 03 . Overall output (V out ) obtained from Multi converter stays around 180 V. (i.e. V 02 + V 03 = V out ). Duty Cycle value D was found to be 0.9. When output voltage value calculated with respect to duty cycle, the theoretical value is 198.8V. The difference with the practical value is 18.8V. V 01 voltage obtained from Cuk converter output is fed to the buck converter which ladders down the voltage to lower magnitude value around 10 V.

CONCLUSION
Hybrid multi converter topology has been proposed, simulation results have been presented. In the proposed design the multi converters have the identical ratio of voltage conversion. They produce alike output with dissimilar values. Diverse level of voltages has been produced with the design of Hybrid multi converter topology. The prime advantage of the proposed design is accomplished through a mono input multi output system. The dissimilar voltages permit the extensive range of application to get realized. The design produces an enhanced and more cost-effective system with the intake of mono-squat input from renewable energy source. Switching system mechanism works in the same sync which makes the driver system to work more efficiently and effective control system produces controlled output through single control system. Isolation performances have been avoided since the system is maintained stable for both balanced and unbalanced condition which reduces the complexity of the design and economically effective. A protraction port for inverter which can be used for AC applications as future augmentations.