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control_loops [2016/05/18 13:51]
coolstage [Current Closed Loop (loop_function 1)]
control_loops [2018/05/22 10:33] (current)
Line 1: Line 1:
 +====== Control Loops ======
  
 +
 +
 +The QuimDC has four control modes, one is an open loop and the others are closed loops. Default mode is PWM Open Loop control mode.
 +
 +===== PWM Open Loop (loop_function 0) =====
 +
 +In open loop, ref_speed is used to control the motors, here is an example :
 +
 +
 +With ref_speed set to 0, the pwm value is 128.
 +
 +With ref_speed set to 62, the pwm value is 190.
 +
 +With ref_speed set to -18, the pwm value is 110.
 +
 +----
 +===== Current Closed Loop (loop_function 1) =====
 +
 +The current control period is 1 ms.
 +
 +
 +This loop needs the current amount that passes through the motor. The QuimDC has a 12 bits ADC but has no clue about the current sign. We need to estimate the current sign using this formula :
 +
 +<​code>​
 +Vbemf = ((60 * speed) / (ticks_per_turn_motor * 0.001)) / kv_motor
 +Voltage = nominal_power_voltage * ( pwmDuty - 128 ) / 128      with pwmDuty [0;255]
 +itemp = (Voltage - Vbemf) / resistance_motor
 +</​code>​
 +
 +We use the itemp sign to estimate the current sign. By default we have the following value :
 +
 +<​code>​
 +resistance_motor = 1.0
 +kv_motor = Inf
 +ticks_per_turn_motor = 1
 +nominal_power_voltage = 1.0
 +</​code>​
 +
 +With this value, the current sign is estimated with the pwm sign. Resistance_motor,​ kv_motor, ticks_per_turn_motor and nominal_power_voltage are only used in this formula.
 +
 +{{pidquimdccurrent.png}}
 +
 +
 +----
 +===== Speed Current Closed Loop (loop_function 2) =====
 +
 +In this loop, we have two PID in cascade. The output of the speed PID is used as a reference for the second current PID. To ensure that the current doesn'​t exceed the ref_current,​ the first PID output is saturated by ref_current.
 +
 +
 +The speed is obtained by doing the difference between the encoder value at period n and period n-1 and then convert it into tick per second. We can change the period of the speed loop by setting the position_speed_period parameter.
 +
 +If the quadrature encoder channel are swap, you can use the polarity to make them work (the polarity must be set to 1 or -1, any other value will not send error but will lead to unexpected results).
 +
 +{{pidquimdcspeed.png}}
 +
 +
 +----
 +===== Position Speed Current Closed Loop (loop_function 3) =====
 +
 +
 +There are three PID in cascade, position, speed and current.
 +
 +{{pidquimdcposition.png}}
 +
 +
 +
 +----
control_loops.txt ยท Last modified: 2018/05/22 10:33 (external edit)