Drone Control System Design

Overview:

Designed and tuned a cascaded control system for drone pitch stabilization and longitudinal position tracking using Simulink. While the inner pitch rate and angle loops were provided, I was responsible for achieving strict performance targets through tuning, and independently developed a 2-DOF PID controller for the outer position loop. This enabled smooth, accurate tracking with robust performance under nonlinear dynamics.

Loop	Requirement
Pitch Rate	T_r < 0.25s %OS < 10% e_ss < 0.01 rad/s
Pitch Angle	T_r < 0.5s %OS < 2% e_ss < 0 rad
Position	T_s(2%) < 5s e_ss < 0 m

Controller design:

Cascaded control loop diagram showing the three control loops

Provided (Pre-built in Simulink)

Pitch Rate Loop: Inner most loop with PI control (untuned)
Pitch Angle Loop: Middle loop with a P controller (untuned)

I tuned these controllers through theoretical derivation of control gains, assuming linearized dynamics. The obtained values were used as a starting point. Full derivation is withheld to maintain academic integrity.

Designed (Independent work)

Position Loop: Outermost loop, designed from scratch using a 2-DOF PID controller block

Tuning Strategy:

To meet the system's dynamic constraints under nonlinear conditions, a 2-DOF PID controller was selected for the outer position loop. This structure allowed separate weighting of the reference input in the proportional and derivative paths, improving setpoint tracking and reducing derivative kick.

Due to the system’s nonlinearity, linear tuning methods like Ziegler-Nichols were avoided. Instead, a linearized approximation was used to obtain initial gains, followed by iterative tuning based on simulated step responses.

A small initial K_P led to oscillations, so integral action was avoided to prevent amplification
Derivative control was added gradually to dampen oscillations and reduce overshoot
Setpoint derivative weighting (γ) was lowered to minimize spikes in control effort from step changes

Controller Performance:

Loop	Controller	Parameters	Performance
Pitch Rate	PI-Control	K_p = 0.215 K_i = 0.15	T_r = 0.243s %OS = 8.77% e_ss < 8x10^-3 rad/s
Pitch Angle	PI-Control	K_p = 3.25	T_r = 0.39s %OS = 1.45% e_ss = ~0 rad
Position	PI-Control	K_p = 0.1 K_i = 0.01	T_s(2%) = 3.1s e_ss = ~0 m