Maximum Power Point Tracking for Thermoelectric Generators with High Frequency Injection Romina Rodriguez, Matthias Preindl, Ali Emadi, and James Cotton McMaster Institute for Automotive Research and Technology (MacAUTO) McMaster University, Hamilton, Ontario, Canada Email: romina@mcmaster.ca, preindl@mcmaster.ca, emadi@mcmaster.ca, cottonjs@mcmaster.ca Abstract—Thermoelectric Generators (TEG) can harvest a part of the thermal energy otherwise lost in the exhaust gases of vehicles and are combined with Maximum Power Point Tracking (MPPT) schemes to maximize the power output. This paper proposes a novel TEG MPPT scheme named High Frequency Injection (HFI) method. The method injects a high frequency voltage to the TEG and yields a power with a high frequency component. This component is demodulated and yields a signal proportional to the distance from the optimal operation point. The duty cycle setpoint is adjusted with a proportional-integral (PI) controller. The method is compared to the Perturb & Observe method using a drive cycle. Both show good results in terms of dynamic tracking of the optimal operation point. However, the HFI method is shown to be significantly more robust against sensor noise. Index Terms—High Frequency Injection (HFI), Maximum Power Point Tracking (MPPT), Perturb & Observe, Thermo- electric Generator (TEG) Fig. 1. Left:TEG schematic Right: TEG equivalent circuit I. I NTRODUCTION A thermoelectric generator (TEG) is a solid state device that directly converts thermal energy to electrical energy when a temperature difference is applied across the TEG. Additional advantages of TEGs are their small size, reliability, low- maintenance cost and no moving parts (quiet operation). A schematic of a typical TEG is shown on the left in Figure 1 where heat flows through the hot-side and is dissipated in the cold-side while a portion of the thermal energy is converted to electricity. Due to the advantage of direct thermal to electrical energy conversion, TEGs are currently being investigated as a technology to recover waste heat from thermal processes to increase a system’s fuel efficiency. One application for TEGs is to recover thermal energy in the exhaust system of a vehicle. Currently, vehicles with a gasoline engine lose about 40% (varies with drive cycle and driving conditions) of their fuel energy as waste heat in the exhaust gases. The consumption of the fuel energy of a conventional internal combustion engine (ICE) vehicle is shown in Figure 2 [1]. As the fuel energy diagram shows, only about 15% of the fuel goes into driving the car while most of it is lost as thermal energy. The largest portion which is indicated as 40∼70% energy is lost as heat through the cylinder head and the exhaust system. If this energy could be recovered and converted to useful energy then the total amount of fuel used by a vehicle could be reduced, thus increasing the efficiency of the vehicle. Fig. 2. Typical ICE car fuel consumption [1] TEGs have only one Maximum Power Point (MPP) where a particular combination of voltage and current produces the highest output power for a given operating condition. As seen in the experimental work of [2], the voltage versus current curve is linear for a TEG and the power output is parabolic with only one maximum power point. The equivalent circuit for a TEG is shown on the right in Figure 1 and the voltage across the internal resistance and voltage across the load resistance is expressed as V OCV = V R TEG + V R Load . (1) Since waste heat can be considered as a “free” source of energy, focus is on maximizing the power output of the TEG instead of maximizing efficiency. During a vehicle’s drive cycle, the exhaust temperature of the gases and thus the operating condition of the TEGs is varying. To optimize power output, the TEG should not charge a battery with a constant load voltage. The goal is to maximize the power output at the terminal of the TEG. To find the maximum power, start with P = I 2 R Load . (2) The current is equal to the total voltage divided by the total resistance and since the TEG resistance and load resistance 004127 IECON2015-Yokohama November 9-12, 2015 978-1-4799-1762-4/15/$31.00 ©2015 IEEE