Talking about PWM control motor

Let's talk about these patterns in a nutshell.
(1) Bipolar mode, that is, the armature voltage polarity is positive or negative alternating,
Advantages: Can forward and reverse operation, start fast, high speed precision, dynamic performance, speed adjustment, small, speed range, can accelerate, deceleration, braking, reversing, in the load over the set speed, to provide reverse torque, can overcome the static friction motor bearings, resulting in very low speed.
Disadvantage: The control circuit is complex.
(2) unipolar mode, that is, the motor armature driving voltage polarity is a single
Advantages: Fast start, can accelerate, braking, energy consumption braking, energy feedback, speed performance is not as good as bipolar mode, but the difference is not much, the motor characteristics are better. Inversion can also be achieved if the H-bridge mode is connected.
Reverse torques can also be provided during load overspeed.
Disadvantage: When braking, can not slow down to 0, speed near 0 speed without braking force. Can't suddenly reverse. The dynamic performance is not good, the speed of static difference slightly larger.
(3) Limited unipolar mode, in addition to the unipolar modulation, the energy-saving braking path is limited.
Advantages: The control circuit is simple, if connected to the H-bridge mode, can also turn positive and negative.
Disadvantages: Can not brake, not energy braking, the load exceeds the set speed can not provide reverse torque.

Speed adjustment static difference is big, the speed performance is very poor, the stability also is not good.

First of all, the PWM and PWM are already processed, can directly drive the power of the signal, rather than the microcontroller output PWM signal, as for the MoS Tube drive method, not discussed here.
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The PWM signal is complementary to the PWM signal and is logically complementary rather than complementary to the level.
and the default. These two signals have been controlled by the dead zone, and do not return to the problem of simultaneous conduction.
In addition to the first diagram, the Power tube must be in parallel with the freewheeling diode, either in the MoS tube itself, or the BJT in parallel, or MOS parallel Schottky.

In fact, we all usually control the motor with the same look as shown in Figure 1,
This mode is called limited unipolar modulation, only the acceleration and speed control function, there is no braking function, the motor speed decreased by the load friction, there is no negative torque.
For example, the set speed is 50%, but the motor because of the external force speed reached 60%, the motor will not slow down, only the motor speed of more than 100%, the motor generated by the reverse electromotive force over the supply voltage, will produce reverse torque, that another matter.
Like the previous brush electric bicycle used is this control method, can only accelerate, can not slow down, speed control is not accurate, but enough to meet the requirements.

Second, we want the motor to achieve positive and negative rotation, but also the use of Figure 2 and Figure 4 Look,
Although this is connected to the appearance of H-bridge, but in fact, is limited to the single-pole modulation, the figure 2 of the Q4 took off, Q1 into a diode, the circuit has become a figure 1 look. The other graphs are the same.

single-pole and bipolar modulation

If you want to have a brake function, ___ A PWM signal that is complementary to the PWM signal must be used. This signal provides a continuous flow path for the motor during the PWM shutdown, Equivalent to the synchronous continuation of switching power supply, also known as synchronous rectification. According to reason, the diode can also provide a continuation of the flow path as shown in Figure 6, Q1, However, there are 2 advantages to using MOS tube as a continuous circulation channel, First, the on-off pressure is reduced, less heat than the diode, more efficient, Second, the diode cannot produce a reverse current, and the MoS tube can pass the reverse current In fact, the reverse current of the diode is a positive current for the MoS tube, Motor back EMF in the PWM shutdown time of the volt seconds is greater than the supply voltage in the PWM opening time plus the volt seconds on the motor, less than, then the motor will produce reverse current, so that the motor produces reverse torque, Because the torque of the DC permanent magnet motor is proportional to the current, the reverse current will produce a reverse torque. Depending on the size of the current, the motor can slow down or brake. And the reverse current on the motor will also be in the PWM opening time back to the power supply, to achieve the energy feedback. If the power supply is two times the battery, then this is beneficial, if not the battery, will make the bus voltage rise, to do some energy consumption measures. Plainly, is your PWM duty ratio can control the speed of the motor, the speed of the motor will follow your PWM duty ratio changes, your duty ratio increases, the motor will accelerate, your duty ratio decreases, the motor will slow down, you reduce the speed, the equivalent of braking, if the control is good, you can do very fast but very soft braking effect. But if your duty ratio suddenly reduced to 0, it is equivalent to the motor short-circuit, which is the brakes, will be damaged to see the resistance of the motor, power, inertia, but also to see the power of the overload capacity of the tube. Of course also test the mechanical strength of the motor, because this brake from the surface, as if directly with the hard object to the motor stuck the effect of the same, the sound is also very large metal sound. Of course, there are more urgent braking method, is to switch the motor to the reverse state of operation, but this method is a great hidden danger, often cause damage to the device. But then again, the kind of limited unipolar pwm modulation method, can only use these 1 kinds of braking or deceleration mode, neither good effect, and easy to damage the device. So if you need a motor with a brake, try using unipolar or bipolar modulation, and do not use restricted unipolar modulation mode. General Electric wheelchair motors are used in this mode control. Say Bipolar mode, Bipolar mode, only the H-bridge is a method of connection, and 4 tubes work simultaneously. As shown in Figure 11 Diagonal two tubes pass the same phase signals, such as Q1 and Q4, while the other two tubes are driven by complementary signals. On the PWM conduction device, the drive voltage on both ends of the motor is positive, and the drive voltage at both ends of the motor is negative at the PWM shutdown device. When the PWM duty ratio is 50%, the motor remains stationary, and when the PWM duty ratio is greater than 50%, the motor is turned and the motor reverses when the PWM duty ratio is less than 50%. In fact, when the duty ratio is 50%, the motor is not static, but in situ jitter, because the electric current on the motor is also a communication, the jitter can effectively overcome the static friction of the motor, so that the motor can be quickly started, rapid response, applicable to the need for dynamic performance of the occasion, for example, the CD-ROM drive inside the control of DC Servo motor, there is now the craftsman is doing the two-wheel car drive wheel motor is also suitable for this method to drive. Of course, unipolar and bipolar modulation can also turn off all 4 tubes, allowing the motor to decelerate freely, rather than relying on the direction torque to decelerate.