The advantages and disadvantages of dc motor controller to share

Compared to ac motor controller, dc motor controller what has strengths and weaknesses? The below small make up to introduce. Dc motor controller advantage: 1. Good start and speed control characteristic; 2. A torque is larger; 3. On the maintenance is cheaper; 4. Compared to ac motor controller of ac, dc motor controller of dc more energy conservation and environmental protection. But there are also disadvantages: 1. Dc motor controller manufacturing cost comparison of the ac motor controller; 2. A carbon brush.