Stability

The transient response represents a system's initial reaction to input changes and diminishes to zero over time. The steady-state response is the behavior that persists after transient effects fade. Together, the transient and steady state response characterize how a linear time-invariant system behaves following a disturbance or input change.

System stability is determined by the roots of the characteristic equation, called poles. A system is stable when all poles lie in the left-half s-plane, producing bounded output for bounded input. If any pole lies in the right-half s-plane, the system becomes unstable and produces unbounded output.

Absolute stability indicates whether a system is stable or unstable based on pole locations. Relative stability measures the degree of stability, quantifying how stable a system is. Both concepts are essential for analyzing linear time-invariant systems and predicting their behavior under various input conditions.

A pendulum with damping experiences external or frictional forces that introduce energy dissipation. These forces cause the transient response to gradually decrease over time. Eventually, the pendulum achieves stable motion around its equilibrium position as damping eliminates oscillations and the system reaches steady state.

An inverted pendulum is unstable because its equilibrium position is inherently unstable. When disturbed by external forces, it does not return to its original position. Instead, it topples over, demonstrating exponential growth in motion and requiring active control to maintain stability.

Poles in the left-half s-plane produce decaying responses, ensuring system stability. Poles on the imaginary axis produce sustained oscillations. Poles in the right-half s-plane produce growing responses, causing instability. Engineers ensure all poles remain in the left-half s-plane to guarantee stable and reliable system performance.

Stability analysis ensures systems respond predictably to inputs and disturbances. By verifying that all poles lie in the left-half s-plane, engineers guarantee bounded outputs and robust performance. This understanding enables design of reliable systems that maintain control and prevent divergent behavior under operational conditions.