There are two ways to change the rotation direction of the DC motor.
One is the armature reverse connection method, that is to keep the polarity of the end voltage of the excitation winding constant, and reverse the motor by changing the polarity of the end voltage of the armature winding.
The two is the inverse connection method of the excitation winding, that is, the polarity of the end voltage of the armature winding is kept constant, and the motor is adjusted by changing the polarity of the end voltage of the excitation winding. When the voltage polarity changes at the same time, the rotation direction of the motor is constant.
The excitation and Shunt DC motor generally adopts the armature reverse connection method to achieve positive and reverse. The reason that the excitation winding and Shunt DC motor should not adopt the inverse connection method of excitation winding is the reason that the number of excitation windings is more and the inductance is larger. When the excitation winding back, the excitation winding will produce large electromotive force. The insulation which will damage the knife and excitation winding.
Series induction DC motor should adopt excitation winding reverse connection to achieve positive inversion because the voltage at both ends of series DC motor is higher, and the voltage at both ends of excitation winding is very low, so it is easy to reverse connection. Motor vehicle often uses this method.