A Photovoltaic (PV) system uses a high step up converter for energy conversion
In the proposed system for PV energy conversion, a coupled inductor is used to provide high step up voltage conversion. The high stepup converter consists of a high voltage circuit, medium voltage circuit, clamped circuit and low voltage side circuit. The elements used in the first string are explained as follows. The low voltage side circuit consists of PV_{1}, capacitor C_{1}, primary inductor L_{P1 }and the main switch Q_{1}. The clamped circuit is formed by the elements C_{L1} and D_{LI}. The middle voltage circuit is constituted by the inductor N_{S1}, capacitor C_{H1} and the diode D_{C1}. The elements in the high voltage side are D_{H1} and V_{S1}.The input voltage and current in the low voltage side are represented as v_{in1}, v_{in2}, i_{in1 }and i_{in2}. In the high step up converter stage, the capacitors C_{1 }and C_{2} represents the filter capacitor in the low voltage side, C_{S1} and C_{S2} represent the filter capacitor in the high voltage side, C_{LI} and C_{L2} are the clamped circuit capacitors, C_{H1} and C_{H2 }are the middle voltage storage capacitors. The conventional multilevel inverter has power stages and a complex control circuit.
The dcdc converter control flow is depicted in
The extraction of maximum power using the solar panel is a fixed voltage and current for all the conditions. But the maximum power extracted from the solar panel varies with climatic conditions. The current obtained from the solar panel varies with the irradiation level and the voltage across the panel varies with the temperature of the solar panel. It has to be ensured that maximum power is extracted from the panel even during variable load conditions. By controlling the current and voltage using a suitable dcdc converter between the solar panel and the load, maximum power extraction from the panel can be obtained. It is possible to obtain maximum power transfer for all the operating conditions.
In this paper, a dcdc high step up converter with control algorithm between the solar panel and the inverter input terminals provides the maximum power transfer from the solar panel. There are many control algorithms developed for the extraction of maximum power from solar panel. This is done by measuring the initial voltage and current obtained from the solar panel. The purpose of the control algorithm in the converter circuit is to change the triggering angle so that maximum power is extracted from the solar panel with the available climatic conditions.
The logical sequence used for the maximum power tracking is shown in
In the case of conventional five level inverter circuits, there are bulky element connections and more complex control circuits. In order to simplify the fivelevel inverter structure, two capacitors are used and are connected across the dc bus.



S_{A1} 
S_{A2} 
S_{A3} 
S_{B1} 
S_{B2} 
S_{B3} 
V_{AB} 
L 
H 
L 
H 
L 
H 
2V_{s} 
L 
H 
H 
H 
L 
L 
V_{s} 
H 
H 
L 
L 
L 
H 
V_{s} 
H 
H 
H 
L 
L 
L 
0 
L 
L 
L 
H 
H 
H 
0 
H 
L 
L 
L 
H 
H 
V_{s} 
L 
L 
H 
H 
H 
L 
V_{s} 
H 
L 
H 
L 
H 
L 
2V_{s} 
The voltage level is controlled using the high step up converter. Thus, there are two voltage sources of 200V each. The CCHB inverter topology uses eight power switches for its operation. This topology uses phase shift pulse width modulation in the control circuit to generate pulses for the switches. When the switches S_{B1}, S_{A2} and S_{B3} are turned on to operate, the maximum voltage 2V_{s} appears across the output. Similarly in order to obtain maximum negative voltage in the output, the switches S_{A1}, S_{B2} and S_{A3 }are made ON. The medium level voltage Vs is obtained by operating the switches S_{B1}, S_{A2} and S_{A3 }or S_{A1}, S_{A2} and S_{B3}. Similarly, a negative value of medium level voltage is obtained by switching ON the switches S_{A1}, S_{B2} and S_{B3 }or S_{B1}, S_{B2} and S_{A3}. The zerovoltage level can be obtained by short circuiting one of the arms of the inverter across the load terminals. In the conventional method, the switching loss caused in circuit is proportional to 8V_{S}f_{S}. All the switches are operating at switching frequency. The proposed method uses phase shift of pulse width modulation control scheme to develop the control signal. This topology uses six switches for its operation in which two switches are operating at low frequency, 50Hz. But the proposed converter has switching losses which are proportional to 4V_{S}f_{S}. The switching loss expression clearly states that the switching loss of the developed inverter is half that of the CCHB inverter.
The circuit analysis is done on the assumption that all the elements used in the circuit are ideal in characteristics. The current through the primary side of the inductor increases linearly as the switching device is changed to ON state. Since the conduction is discontinuous, the increase in current is from zero and can be expressed as (1)
If the time interval during which the increase in inductor current occurs is taken as DTs, then the change in the inductor current is given below
The on time of the device can be expressed in terms of D and T_{s}. T_{s} is the time period of one highfrequency switching cycle. At the end of increase of current, the maximum value is obtained and is given by (3)
The increase in the current waveform and the maximum value of current are shown in
The primary inductor current is found out by integrating the current waveform over a cycle and is calculated as below.(5)
During the operation, the voltage across the primary inductor V_{L} is equal to the input voltage V_{PV}. Therefore, it can be written as (6)
The inductor voltage V_{I} can be expressed in terms of transformer turns ratio and V_{L }as below (7)
Now, the voltage V_{B} can be written as (8)
In order to have discontinuous conduction, using the voltage second balance equation, the inductor voltage V_{L} in the low voltage side to become zero is written as (9)
After simplification, the above equation becomes (10)
Since the voltage V_{CL} across capacitor C_{L} is equal to negative of the inductor voltage V_{L} in the low voltage side, voltage V_{CL} across capacitor C_{L }can be written as below (11)
Using Kirchhoff’s voltage law, the voltage V_{B} of the converter can be written as (12)
The inductor voltage V_{I} in the secondary to become zero is written as
From equations (11) – (13), the voltage gain of the converter is written as
Voltage gain (14)
In the inverter operation, the voltage variation has to be limited in the specified value. This is done by designing the capacitor. The power relation for the design is based on the assumption that the difference between the power obtained from the PV source and the power delivered to the load is stored in the capacitor. The capacitor power is given by
The net power difference is zero, the instantaneous power difference is stored in the capacitor. The difference voltage is taken as 10Volts. Based on this the capacitance calculated is around 2mF. The filter elements are calculated using the assumption that switching frequency is greater than
It is important to know the performance of the proposed converter, comparative simulations and experiments with the conventional method are carried out. The values of the various components used in the circuit are shown in





Input low voltage source 
v_{IN1}, v_{IN2} 
12V 
Input high voltage source 
V_{S1}, V_{S2} 
200V 
Switching frequency 
f_{s} 
50KHz 
Primary Inductance 
N_{P1}, N_{P2} 
2μH 
Secondary Inductance 
N_{S1}, N_{S2} 
50μH 
Filter Capacitor in low voltage side 
C_{L1}, C_{L2} 
50μF/50V 
Filter Capacitor in high voltage side 
C_{H1}, C_{H2} 
20μF/500V 
Capacitor in clamped circuit 
C_{C1}, C_{C2} 
90μF/250V 
Middle voltage Capacitor 
C_{M1}, C_{M2} 
10μF/500V 
Bus Capacitor 
C_{S1}, C_{S2} 
2000μF/400V 


Output inductor 
L_{0} 
2mH 
Output Capacitor 
C_{0} 
47μF/500V 
The harmonic content of the output voltage V_{AB} can be calculated from the magnitude of the fundamental and harmonic components using MATLAB software for both the CCHB inverter and the proposed inverter. Both the CCHB inverter and the proposed inverter are made to operate at the similar conditions by selecting the switching frequency of operation is 50 kHz



1 
248.5V 
267.8V 
3 
14.9V 
13.6V 
5 
7.457V 
6.1V 
9 
3.6V 
2.3V 
11 
0.7V 
0.6V 
%THD of v_{0} 
18.09 
15.56 
The modulation index values considered are M=0.6 and M=0.7. The low voltage side input voltage is v_{IN1}= v_{IN2}=20V. The input voltage to the inverter is V_{S1}=V_{S2}=200V.



1 
268.9V 
292.4V 
3 
8.3V 
7.1V 
5 
6.9V 
5.8V 
9 
1.5V 
1.2V 
11 
0.24V 
0.19V 
%THD of v_{0} 
2.99 
2.84 
It can be concluded from
The inverter is designed for 200watts with an output voltage of 200 volts having the switching frequency of 50KHz and the operating line frequency of 50Hz. The experimental results of the developed microcontroller based five level inverter for the PV system are taken. The control of the pulse width is done using the PIC microcontroller of PIC16F877. The voltage developed across the switches is obtained from the test results. The switches are undergoing lower stress than the CCHB inverter.
The experimental results of the PV panel output are measured and it shows a steady value of voltage for the irradiation level as shown in fig.14. The diode current for the medium voltage and low voltage from the prototype are shown in fig. 15. The drain to source voltage of the inverter switches S_{A1}, S_{A2} are shown in fig. 16and fig.17. Fig. 18 shows steady state waveforms of output voltage v_{0} and output current i_{0} for the inverter with a resistive load of 40 Ω. The conversion efficiency of the implemented inverter in this case is approximately 94%.
The temperature of the surrounding environment is 36.2 and the solar radiation was 1000W/m2. The solar panel temperature was 55. The power obtained from the solar panel was 200W. The output voltage from the solar panel is steady and stable. The implementation of the MPPT algorithm has produced a control signal based on the panel voltage and inductor current. Maximum power tracking is done effectively. The output current and voltage of the inverter after filtering the harmonics was sinusoidal waveform. From the %THD of the output voltage, it can be concluded that harmonic balance is obtained with the proposed system. The capacitors are performing the operation of energy balancing. The ripple voltage is controlled within the limits. The comparison of the proposed converter configuration with other types of inverter topology is given in






Capacitor 
4 
4 
3 
2 
2 
Sources 
1 
1 
1 
2 
6 
Voltage Balancing 
hard 
hard 
hard 
hard 
easy 
High Frequency switches 
8 
8 
6 
8 
6 
The stress produced in the switches of the proposed converter is less. The performance parameters of some of the converters are discussed in





26 
93.7 
665 

1638 
97.0 
40 

35 
96.6 
256 

3090 
96.6 
100 

48 
92.5 
24 

10 
95.9 
60 
proposed 
12 
94.0 
200 
The paper presents a new type of inverter developed for a PV system. The stepup voltage conversion of the generated dc voltage has been obtained using simple coupled inductor elements. The developed highly efficient high step up DCDC converter is connected in the front end. This topology uses a single switch to attain the stepup operation. The proposed fivelevel inverter topology uses less number of switches required to implement multilevel output for PVs. The proposed inverter provides some advantages like better output waveforms with small size filter elements and lowers THD.
The main drawback of the proposed configuration using coupled inductors is the leakage inductance, which may resonate with the parasitic capacitance of the switches. This may lead to high voltage peaks. Control circuit of the inverter is complex to find out the voltage level of the capacitors. These limitations are to be eliminated in the future work by implementing new techniques..