Power Electronics

Power Electronics in Automobiles

 

In a conventional car, power electronics applications are a major area of future expansion. Look inside the audio system, for example; the amplifiers in today's car stereos are usually capable of delivering 40 W or more. But a 12 V supply applied to an 8 Ohm speaker produces 18 W output at best. To solve this power supply problem, designers use a power electronics boost converter to provide higher voltage power to the amplifier circuit. This allows car amplifiers to generate the same audio output power as home stereos.

 

Another nearly universal power electronics application is the automobile's ignition system. Thousands of volts are required to ignite the fuel-air mixture inside a cylinder so that internal combustion can occur. Today's cars employ all-electronic ignition systems, which have replaced the traditional spark plugs with boost converters coupled to transformers. A third example, now being used in some models, is an all-electronic power steering system. This system uses power electronics to control electric motors and assist in moving the steering rack. This system is replacing the traditional, belt-driven hydraulic pump. The results are improved steering response, lower energy consumption, and the elimination of noisy belt drives. Electric air conditioning systems are starting to appear as well. The high-intensity lamps now appearing in headlights, and the bright LEDs appearing in taillights all require power electronics to deliver electrical energy in the correct form.

 

Power electronics is a major growth area within the automotive industry. Electronic ignitions, power semiconductor voltage regulators, automatic motor controls, and audio systems are some of the most common applications. But in the future, electronic systems ranging from small motor controls for windows and seats up to high-power traction controls for electric drive systems will be present on cars. Perhaps most significant is the move to a higher-voltage electrical system. Cars of the near future will be designed around a 40 V to 50 V electrical supply in place of today's 10 V to 15 V systems.

 

Many people are curious about new electric and hybrid cars -- in which the primary electrical system is dominated by power electronics. Electric cars offer high performance, zero tailpipe emissions, and low costs, but are still limited in range by the need for batteries. Hybrid car designs use various strategies to combine both an engine and electrical elements to gain advantages of each. In both cases, inverters and dc-dc converters rated for many kilowatts serve as primary energy control blocks.

 

 

Shown here is a commercially-available hybrid-electric vehicle (produce by Toyota).

Some of the interesting power electronic components for electric and hybrid vehicles include:

1. Battery chargers that are now being designed to transfer higher levels of current at higher voltages than ever before. This has resulted in new ideas for power transfer and safety. One example is the Hughes inductive charger which uses a non-conductive paddle (similar to a ping-pong paddle) to connect an electric vehicle to a power outlet. This charger takes input 60 Hz ac power, and then converts it to high-frequency 80 kHz ac power for delivery through the magnetic paddle into the car. The paddle serves as the primary side of a transformer which electromagnetically couples the charger output to the electric vehicle's charging port. The input circuit mounted in the vehicle rectifies this ac voltage and regulates the dc current to charge the battery pack.



2. Electric vehicle drive trains use power electronic converters and electric motors in place of the traditional combustion engine. A variable speed drive supplies electric motors which are coupled to the axles either directly or through gearing. The drive is typically composed of a converter, a battery and control circuitry. Originally, electric vehicles used dc motors for the main propulsion, but all newer designs use ac induction motors or other types of ac machines. Compared to dc machines, ac motors are lighter, more efficient, require less maintenance, cost less, and have a broader torque and speed range. These ac motors require a power electronic inverter which uses power semiconductors and electronic controls to set the motor torque and speed.

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