Added the Active Disturbance Rejection Control (ADRC) Algorithm

Author: Divyansh Agrawal

Diff for: control_algorithms/adrc.py

@@ -0,0 +1,64 @@
+"""
+Active Disturbance Rejection Control (ADRC) is a robust control strategy
+that estimates and compensates for disturbances in real-time without needing
+an explicit mathematical model of the system.
+
+It consists of:
+1. Tracking Differentiator (TD) - Smooths the reference signal
+2. Extended State Observer (ESO) - Estimates system states and disturbances
+3. Nonlinear State Error Feedback (NLSEF) - Generates the control signal
+
+Refer - https://en.wikipedia.org/wiki/Active_disturbance_rejection_control
+"""
+
+
+class ADRC:
+    def __init__(self, beta1: float, beta2: float, beta3: float, setpoint: float = 0.0):
+        """
+        Initialize the ADRC controller.
+
+        :param beta1: Gain for error correction in ESO
+        :param beta2: Gain for disturbance estimation in ESO
+        :param beta3: Gain for acceleration estimation in ESO
+        :param setpoint: Desired target value
+        """
+        self.beta1 = beta1
+        self.beta2 = beta2
+        self.beta3 = beta3
+        self.setpoint = setpoint
+
+        self.z1 = 0.0  # Estimated system output
+        self.z2 = 0.0  # Estimated system velocity
+        self.z3 = 0.0  # Estimated total disturbance
+
+    def compute(self, measured_value: float, dt: float) -> float:
+        """
+        Compute the control signal based on error estimation and disturbance rejection.
+
+        :param measured_value: The current process variable
+        :param dt: Time difference since the last update
+        :return: Control output
+        """
+        error = self.setpoint - measured_value
+
+        # Extended State Observer (ESO) Update
+        self.z1 += dt * (self.z2 - self.beta1 * (self.z1 - measured_value))
+        self.z2 += dt * (self.z3 - self.beta2 * (self.z1 - measured_value))
+        self.z3 -= self.beta3 * (self.z1 - measured_value)
+
+        # Control Law (Nonlinear State Error Feedback - NLSEF)
+        control_output = self.z2 - self.z3
+        return control_output
+
+    def reset(self):
+        """Reset the estimated states."""
+        self.z1 = 0.0
+        self.z2 = 0.0
+        self.z3 = 0.0
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()
+
+