This paper introduces a novel single-phase asymmetrical multilevel inverter suitable for hybrid renewable energy sources. The proposed inverter consists of two isolated DC sources and six power semiconductor controlled switches. The suggested inverter is capable of generating seven-level output when the input DC voltage is taken in the ratio of 1:2. The higher magnitude DC source is fed from Photo Voltaic (PV) panels, whereas the lower magnitude DC source is fed from Wind Turbine (WT) driven Permanent Magnet DC (PMDC) generator. Both the renewable energy sources are connected to the inverter via two DC-DC boost converters connected in cascade ( i.e. one for maximum power point tracking and another for DC-link voltage control). The proposed hybrid renewable energy source inverter is connected to single-phase grid via proper control systems. The complete system is simulated using MATLAB/SIMULINK and the results are presented in detail.
In recent years, Renewable Energy Sources (RES) are gaining more importance over the globe because of the exhausting nature of the conventional energy sources, rise in earth’s temperature due to carbon dioxide emissions, ever increasing oil price, non availability of power supply in the rural areas, etc. [
In order to connect RES to the grid, two stages of power conversion are used. First stage is to boost up the low voltage output of RES and to track its Maximum Power Point (MPP), whereas the second stage is used to convert DC into AC signal as required by the grid [
To improve the harmonic profile of the output voltage of the inverter Multilevel Inverters (MLIs) are suggested in [
The remaining part of this paper is structured as follows. The operation and description of the modified ASMLI topology along with switching logic are detailed in Section 2, the suggested ASMLI fed from RES along with proper control system is described in Section 3, Section 4 details the simulation results obtained from MATLAB/SIMULINK and the performance of the system is recapitulated at the conclusion.
The proposed topology consists of a two bidirectional switches added to the conventional H bridge inverter. The proposed topology has been derived from the topology proposed in [
The proposed topology of ASMLI consists of two isolated DC sources with the ratio of 1:2, six power semiconductor devices in which two devices are bidirectional (i.e.
In order to generate gating signals for the proposed inverter, six level shifted carrier waves are used as shown in
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OFF | OFF | OFF | OFF | ON | ON | 0 | - |
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The proposed inverter is a best fit for grid connected renewable energy applications.
The PV and VI Characteristics of TATA BP 180 W panel is shown in
PV Module | Wind Turbine | PMDC | |||
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Power Output | 180 W | Rated Power | 1.8 kW | Rated Power | 1.1 kW |
Voltage at | 35.8 V | Rated Wind Speed | 10 m/s | Armature Voltage | 37.2 V |
Current at | 5.03 A | Radius | 1.525 m | Rated RPM | 1000 |
Open Circuit Voltage | 43.6 V | Gear Ratio | 5 | Armature Resistance | 0.3 |
Short Circuit Current | 5.48 A | Air density | 1.08 m3/kg | Armature Inductance | 0.06 mH |
small, it gives poor dynamic performance and the algorithm becomes very slow. On the other hand when large value of chosen, the steady state error becomes very high [
In sliding mode control sliding surface is determined by finding the MPP for various environmental conditions (i.e. irradiation, module temperature and wind velocity) through simulation. Once the MPP is determined for various environmental conditions, sliding surface equation is determined by using curve fitting toolbox in MATLAB/SIMULINK. The sliding surface equation for PV module and WT are shown in
The sliding surface of PV module is given by
where Y is the PV module current and X is the PV module Voltage. Since the sliding surface equation is passing through the maximum power points, the result of the above equation should be zero to ensure MPP. Hence PV module current and voltage are sensed and Equation (1) is calculated instantaneously. When the result of the
above equation is greater than zero, the switch
In order to evaluate the proposed sliding mode algorithm, step change in the irradiance is given and the corres-
ponding power output is measured and compared with actual MPP power as shown in
Similarly the sliding surface of WT is given by
where Y is the power output of PMDC generator and X is the WT rotor speed. When the result of the above equation is greater than zero, the switch
order to evaluate the proposed sliding mode algorithm, step change in the wind speed is given and the corresponding power output is measured and compared with actual MPP power as shown in
By comparing
Two boost converters are connected in cascade between the RES and the inverter DC sources as shown in
Similarly the output voltage of MPPT boost converter of WT also varies when there is a variation in the wind speed. Hence the Voltage control boost converter is connected in cascaded to have stiff voltage at the DC link of the inverter.
The proposed inverter fed from renewable energy sources is connected to grid through control components as shown in
The upper DC link of the proposed inverter (
modulation index of 0.95. When the modulation index is reduced to 0.6, the inverter is capable of generating only five levels which is shown in
In this paper a novel asymmetrical multilevel inverter is proposed. The operation of the proposed inverter is discussed and simulated in MATLAB/SIMULINK environment and the results are presented. The proposed inverter is fed from renewable energy sources through two boost converters connected in cascade: one for
tracking the MPP and another for voltage control. Further the proposed inverter is connected to the single phase grid through proper control structure. The complete system is simulated and the results are presented.
C. P. Boopathy,M. Kaliamoorthy, (2016) A Novel Asymmetrical Single-Phase Multilevel Inverter Suitable for Hybrid Renewable Energy Sources. Circuits and Systems,07,932-945. doi: 10.4236/cs.2016.76079