Basic structure of DC motor test bench
Magnet fixation+coil rotation+electric brush
The output torque of a DC motor can be achieved through the electromagnetic force between the magnetic flux of the permanent magnet and the armature current. There is a magnet on the stator and a coil (armature) on the rotor. Electric brushes can pass current through coils, while commutators can ensure continuous output of torque.
EV permanent magnet DC motors use magnets to generate a magnetic field and are typically used in small devices. This type of motor cannot adjust the magnetic flux, but can achieve torque output by adjusting the current of the coil.
The structure of a 12 slot 8-pole motor consists of stacked armatures and armature coils made of thin silicon steel plates. Adopting a skewed groove structure to reduce the tooth slot torque caused by the magnetic resistance difference in the tooth slot segment. The armature coil is connected to the rectifier and is supplied with DC current by electric brushes. In addition, permanent magnets are arranged and fixed inside the yoke. DC motor type DC motor is driven by DC, which is generated by replacing permanent magnets with excitation coils (DC). This type of electric motor can be roughly divided into three categories:
A separately excited electric motor: The armature and excitation coil are independent.
Parallel excitation motor: The armature coil is connected in parallel with the excitation coil and powered by the same power source.
C-series excited motor: The armature and excitation coil are connected in series, and the current is the same. "F" is an excitation coil
Basic calculation method for performance of DC motor test bench
Terminal voltage of electric motor V:
Where E is the reverse electromotive force and Ia is the armature current; Ra is the sum of the reactance of the armature coil and the contact resistance of the brush. In addition, use the following formula to calculate the inverse EME and torque τ.
K1 and K2 are proportional constants, and n is the rotational speed; Φ is the magnetic flux (Wb) of each electrode. The rotation speed n can be obtained from the formula:
Mechanical properties of motors
In the formula, the angular velocity ω=2 π n (rad/s).
Basic performance of He excited DC motor
The relationship between torque and speed
It includes a permanent magnet separately excited DC motor, with the longitudinal axis representing the motor torque and the transverse axis representing the speed, and controlling the armature current to be constant. The basic speed mentioned here refers to the rate at which the speed increases, the voltage remains constant, and the power reaches its maximum at the rated torque. Before reaching the basic speed, a large torque can be obtained. In addition, when the speed of the electric motor is higher than the base speed, the torque will also decrease accordingly.
The Influence of Torque on Basic Speed
When the speed is higher than the base speed, the voltage at the terminal will significantly decrease, and subsequently, under a weak magnetic field, the rotational speed will increase. Permanent magnet motors are not prone to generating weak magnetic fields and are only driven by constant torque. In the equation, the proportional relationship between torque and armature current is the same when the magnetic flux is constant. By controlling the armature current, torque control can be achieved. Reduce magnetic flux by half and torque by half. From formula 4, it can be seen that when the terminal voltage and armature current are constant, and the rotational speed doubles, the power of the motor remains unchanged.
Basic performance of parallel excited DC motor
Just like he drives the motor
The parallel excitation motor and the separately excited motor are basically the same. In the design of control circuits, attention should be paid to preventing interference between excitation and armature coils.
Basic performance of series excited DC motor
Iron armature current=winding current
The current of the excitation coil and armature coil of a series excited motor is the same, so the current of the coil cannot be controlled separately like that of a separately excited and parallel excited motor. The relationship between the rotational speed and torque of a series excited motor. As mentioned earlier, a series excited motor can only control one voltage at different voltages.