Untitled - ev-bg.com

Chapter 7: The Controller 161is common) and/or matched transistors to avoid imbalance. (Source: Zero ElectricVehicles Australia, www.zeva.com.au)Electronic ControllersElectronic switches can be switched on/off much faster, and don’t wear out. Thecontroller switches them on/off so fast (thousands of times per second) that the motorgets the average current rather than the peak or zero. This is called Pulse WidthModulation (PWM). PWM controllers are modestly priced, readily available in a widevariety of sizes, and provide smooth stepless motor control.AC ControllerThe AC motor with solid-state inverter is the most sophisticated type. They are used inhigh-end EVs where meeting performance objectives is more important than cost. AnAC induction motor or AC PM motor (often called a “brushless DC” motor) is drivenby an inverter that converts battery DC voltage into variable voltage variable frequency3-phase AC. New EV sports cars and the recent auto company produced EVs all usedAC drive systems. Like modern ICEs, these AC controllers are very complex andexpensive, but offer the most advanced features (like cruise control and regenerativebraking) and provide the best overall range.Controller ChoiceHigh reliability, high performance, and minimum cost are the key trade-offs that factorinto your EV controller choice.” You can pick one, or maybe two, but you can’t have allthree. Examples:• High reliability, high performance—means high cost(Cafe Electric Zilla controller, no know failures, 300v 2000a, $3500)• High performance, minimum cost—means low reliability(Logicsytems rebuilt Curtis controller, high failure rate, 156v 1000a, $1500)• High reliability, low cost—means low performance(used GE EV-1 SCR controller, 30 years old and still working, 72v 400a, $1000)If you’ve driven an EV, you’ll find that most electronic controllers do not imitate theaccelerator pedal response of a normal ICE vehicle! It is undesirable to do so!The throttle response of most ICEs is unpredictable and very “lumpy.” Some carsleap forward at the slightest touch; others gently creep ahead. As the pedal is pushedfarther, the amount of speed increase for a given amount of pedal movement variesconsiderably. On some cars, there is hardly any difference between half throttle and fullthrottle; on others it’s the difference between 30 mph and 120 mph. There is always anoticeable delay. It doesn’t coast, and letting up the pedal produces variable amounts ofengine braking. People just get used to these huge variations.The throttle response of EV controllers is completely different. It is entirelypredictable, repeatable, and instantaneous. Most people have to relearn it, but find itbetter than an ICE. The motor controller normally controls motor current and voltage,from 0 to maximum, as a direct function of throttle position, 0 to maximum (i.e. halfthrottle means half voltage and half current). Electric motors don’t need to idle, so