Description

ABSTRACT

The energy from the sun is known as solar energy, and the energy comes in form of heat and radiation. Natural energy sources that make use of a range of constantly evolving and better technology include solar thermal energy, solar architecture, solar heating, molten salt power plants, and artificial photosynthesis.

Due to numerous significance of electricity, researchers have made numerous invention or achievement in the quest to generate electricity in different forms. Cost of production, efficiency, reliability, control methods are some of the major issues to consider when generating electricity from any form.

Generating electricity from a dc source involves using dc – ac converters, and in the quest of achievable an uninterruptible power supply a  renewable energy source must be incorporated in the system which will serve as means of increasing efficiency of the system. However, different types of converter has been developed by different authors in different topologies. Therefore this study is on the review of dc – ac converter topologies for renewable energy applications.

INTRODUCTION

Presently, solar photovoltaic system as one of the green power source of energy is progressively replacing the traditional method of generating electricity this is due to some limitations seen in the modern method of electricity production.

Because of the inconsistent power supply seen in Nigeria from the national grid, the government of Nigeria is making an effort to provide a power system that will enable the country to have a steady power supply, and thereby ensuring a low power consumption cost [1]. Though, there is a discontinuous behavior of a solar photovoltaic system which makes it difficult to generate a consumer voltage input of 220vac. To overcome this challenge, power electronics is applied together with the energy storing system which are used to invert the produced energy of the solar PV to fulfill the requirement of demand.

Presently, power electronics based converter are widely used in different electronics gadgets such as in a smart mini and micro grid, home energy system, electric bike and vehicles and energy storage system either at the output DC or AC

In the past, different research groups have recommended different single stage dc to ac converter, but there is no review literature regarding recommendation that will help to compare their characteristics and at the same time know their applications.

However, this work is based on different review of dc to ac converter topology recommended by various recommended by different scientist in the past few years. This work reviews different DC – AC converter topology for renewable energy application:

Authors in [2] proposed non-isolated triple gate dc – ac converter which is a type of dc – ac inverter with inductors with limited gain, and their limited gain is due to the buck, boost, and buck converters it comprises. This system is as shown in the figure below:

Figure 1.Experimental setup [2]

Authors in [4][32] proposed the “isolated triple gate dc–ac converters”. This topology is a has multiple input source for the purpose of reducing energy protocol design and thereby decreasing the price of hybrid photovoltaic energy or any other renewable source [16][29]. The system is as shown below:

Figure 3.Triple gate simplified half-bridge configuration with the developing circuit [4]

 

Flyback mono-transistor inverter

Authors in [5] proposed a study flyback mono-transistor inverter which is a galvanically isolated topology using a high frequency (HF) transformer.  This a low power type of topology, which is achieved using a high frequency transformer. In this system, the output of the transformer are connected to the grid through two diodes, two transistors and a filter.

This configuration allows the Flyback converter to provide two currents of opposite signs. The two output transistors synchronously switch with the single transistor of the flyback converter in the high frequency regime. The Flyback converter operates in a discontinuous conduction mode (DCM) which implies that the current through the transformer reaches zero before the start of each switching cycle.

The major disadvantage of this topology lies in the fact that the decoupling of the power in parallel with the photovoltaic module is generally carried out using electrolytic capacitors of high values. Moreover, the two stages of this topology must be sized for a power equal to twice the nominal power. Finally, another drawback of this topology is the low power factor due to the existence of a zero-crossing distortion.

Figure 4. Flyback mono-transistor inverter

Authors in [6] proposed this topology flyback converter with high power decoupling. The topology is a modified version of the one presented in Figure 3 in order to avoid the use of high value electrolytic capacitors. Indeed, the decoupling capacitor is eliminated using a buck-boost converter. This is a topology where the transistor S_pv, the diode D_pv, the primary winding of the transformer, the freewheeling diode of the transistor S_DC and the capacitor C_DC form the buck-boost converter operating in the discontinuous conduction mode.

Each cycle begins with the conduction of the transistor S_PV which results in a linear increase of the magnetization current. When this current reaches a so-called reference value, the transistor S_PV is blocked and the energy stored in the magnetization inductance is transferred to the capacitor C_DC. The transistor S_DC must be active when the current is being discharged to the capacitor which implies the state of zero voltage switching.

In addition, one of the two output transistors is simultaneously activated with the transistor S_DC. Thus, the transistors on the secondary side of the inverter switch at high frequency regime unlike the topology of the Flyback inverter. The magnetization current continues to decrease until reaching a second reference. At this time, the transistor S_DC will turn OFF and the energy stored in the inductor is transferred to the secondary side of the transformer and then to the grid. The diode D_PV is used to eliminate the reverse voltage across the capacitor C_PV when the energy is being transferred to the secondary side.

This system consist of the flyback inverter with a buck boost converter, and the diagram is as shown below:

 

 

 

Figure 5. Flyback inverter with high power decoupling

The modified “SHIMIZU” inverter

Author [7] proposed a “modified SHIMIZU converter”. This topology was generated to overcome the voltage spiking challenge noticed in the previous topology. The voltage spike exist between the terminals of the circuit transistors. The system is as shown in Figure 6.

 

 

Figure 6. Modified “Shimizu” converter

 

Authors in [8] proposed a converter topology that is  made in the parallel-parallel configuration that is known as  “The isolated inverter with parallel-parallel configuration”. This type of topology is designed  that is designed to operate in the discontinuous conduction mode, DCM. This results in a discontinuous current in one of the inductances L_pv or L [21][22][27]. The system topology is as shown in the figure below:

Figure 7. Isolated inverter with parallel-parallel configuration

1.1.               The bi-transistor flyback inverter

Authors in [9] proposed a “bi-transistor flyback inverter”. Its output power is around 160W. At the beginning of a period of the grid current, the transistors S₁ and S₄ (S₂ and S₃ for the negative half-period) are activated. This will generate a current and the energy produced will be saved in the magnetization inductance. When these two transistors are deactivated, the energy will be transferred to the secondary side of the transformer and will subsequently be transmitted to the grid through the transistor S₅, the freewheeling diode of the transistor S₆ and the filter. This converter topology is shown in Figure 8

 

 

 

 

Figure 8. Inverter type flyback bi-transistor

Authors in [9] proposed a system with a fly-back converter which have a low frequency low frequency. This system was designed to generate 150W power, and transistor is used instead of power transistors as a switching device. This converter is as shown in the figure 9 below:

Figure 9. Low frequency inverter associated with a flyback converter

Authors in [10] proposed a topology of a converter (inverter with resonance converter) that is based on series resonance connected to a high frequency which is galvanically isolated. This topology was built to generate a minimium power of 110W and maximium of 250W [23][26]. The topology of the converter is as shown in the figure below:

 

 

H-bridge inverter

Authors in [11] proposed a topology that is that consist of multiple transistor units, without transforming unit. This topology can be used to control the speed of an AC motor  and also in uninterruptible power application system application. This system topology is shown in Figure 10 below.

 

 

Figure 11. H-Bridge inverter

Authors in [12] worked on the HERIC converter topology. This topology was first reviewed by Sunways which is as shown in Figure 22. This topology is a combination of unipolar and bipolar modulation as shown in Figure 12.

 

Figure 12. HERIC inverter topology

Conclusion

In this work, a review of dc-ac converter topologies for renewable energy application has been conducted. Different classification topologies discussed based on their major characteristics and functions which is based on the DC to AC converter. Their topology components were also discussed in this study.