**8. Power conditioning and maximum power point tracking**

In AETEG, the output voltage changes dynamically in a nonlinear way over a wide range with the fluctuation of flow rate and temperature of exhaust gas. Therefore, a proper power conditioning circuit similar to the ones used in photovoltaic power system with a maximum power point tracking (MPPT) control is essential between the TEG and the load. A number of different power conditioning circuits for AETEG to step-up or step-down the voltage have been proposed. Some of the prominent circuits are DC-DC converters such as Ćuk converter, SEPIC converter, and Boost-buck cascade converter. MPPT is an algorithm used to operate a power system at its maximum power capability under various operating conditions. Different MPPT techniques such as load matching method, incremental conductance technique, ripple correlation, perturbation and observation (PAO) method has been developed. The PAO method is the most commonly used one due to its simplicity and system independence.

In automotive exhaust waste heat conversion, MPPT can be used, for example, between the TEG system and a battery pack so that power flow is regulated to obtain the maximum power transfer. Eakburanawat et al. proposed an MPPT technique based on feedback from battery current alone assuming constant battery voltage [40]. However, all practical batteries have a significant change

up to 40% by using low-cost materials with higher zT [44]. In an analysis carried out in conventional vehicles operated in Korea, Bang et al. reported that the application of TEG in mid-size sedan and the medium-duty truck can save 0.15 and 1.04 kL fuel, respectively, at a driving speed of 80 km/h. Such fuel savings show that the economically acceptable costs of the TEG system for these two vehicles are 744 \$/kW (mid-size sedan) and 2905 \$/kW (medium duty truck) [45]. A comprehensive cost analysis of the real application scenario of automotive TEG using skutterudites module by Hendricks et al. suggests that the heat exchangers cost most often dominate the overall AETEG cost, and it is necessary to bring down from the current 10\$/W to l \$/W or lesser [46]. They observed that the minimum system cost is coinciding with the maximum power point which is governed by factors such as exhaust temperature, ΔT between the hot and cold side of the module, zT of the materials, thermal conductance between the hot and cold sides, heat exchanger cost factor and the parasitic losses. The rolling resistance arising due to the weight of the TEG alone would attract the penalty of a significant fraction of the power produced. In a 1.5 L engine family car tested under new European drive cycle incorporating an AETEG showed a power loss of 12 W/kg [47]. The additional load for the coolant pump for circulating the coolant to the cold side heat exchanger would further add up to the power loss. Employing low-density materials in both the heat exchanger/s and TE modules would considerably reduce

Automotive Waste Heat Recovery by Thermoelectric Generator Technology

http://dx.doi.org/10.5772/intechopen.75443

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the AETEG cost by decreasing its weight and parasitic losses associated with it.

Duraisamy Sivaprahasam\*, Subramaniam Harish, Raghavan Gopalan and

Centre for Automotive Energy Materials (CAEM), ARC-International, IIT Madras Research

\*Address all correspondence to: sprakash@arci.res.in

Hydrocarbon-based fuels will continue to be a primary source of energy for transportation for the next few decades. Improving the efficiency of the vehicles by even few percentages will have a tremendous effect on the fuel savings and controlling the emissions. Automotive TEG is one potential technology which can increase the vehicle fuel efficiency. Though the technique is known for several decades, significant progress has been made in materials, modules, and systems over the past 20 years only and as of today it is far from commercialization. The high cost and low efficiency of the currently available modules make the overall cost of the TEG much higher than \$1/W barrier apt for implementation this technology in vehicles. The high zT observed in several low-cost materials in recent years need to be translated into reliable high-power output modules. An innovative design which reduces the overall weight of the AETEG with improved efficiency is a key necessity to make this

**10. Summary**

**Author details**

Govindhan Sundararajan

Park, Chennai, India

technology commercially successful.

**Figure 7.** Schematic of power conditioning system based on battery voltage and current [40].

of terminal voltages, especially during charging, which should not be neglected. Later, Yu et al. proposed the MPPT technique based on the measurement of TEG power which is derived from its terminal voltage and current [41]. However, such maximization has not taken into account the power converter loss, which should not be a constant value. Subsequently, the same group has proposed a DC-DC Ćuk converter-based power regulation system with the MPPT technique which considers both the terminal voltage and current of the battery to maximize the TEG output power instead of using terminal voltage and current [42]. **Figure 7** shows the schematic of power conditioning scheme proposed based on battery voltage and current. The variation of battery voltage and power converter loss is also taken into account in this system.

Fang et al. proposed a novel MPPT scheme which involves the aggregated dichotomy and gradient (ADG) method for rapid tracking the maximum power in an automotive TEG [43]. They carried out the steady state and transient tracking experiments under various load conditions of dynamometer and compared the ADG method with traditional methods like single gradient method (SGM), single dichotomy method (SDM) and perturbation and observation method (PAO). The results showed that the ADG had better tracking accuracy and speed compared to the traditional methods.
