Fault Tolerant Control of Large LED Systems

Abstract

This chapter describes a system-level design method of automatically diagnosing and compensating LED degradations in large LED systems, also known as solid-state lighting (SSL) systems. A failed LED may significantly reduce the overall illumination level, and destroy the uniform illumination distribution achieved by a nominal system. The main challenge in diagnosing LED degradations lies in the usually unsatisfactory observability in a large LED system, because the LED light output is usually not individually measured. In this chapter, we review a solution which we have recently developed in ref. (Dong et al. Optics Express 19:5772-5784, 2011). This solution tackles the observability problem by assigning pulse width modulated (PWM) drive currents with unique fundamental frequencies to all the individual LEDs. Signal processing methods are applied therein to estimate the individual illumination flux of each LED. Statistical tests are described to diagnose the degradation of LEDs. Duty cycle of the drive current signal to each LED is reoptimized once a fault is detected, in order to compensate the destruction of the uniform illumination pattern by the failed LED. The combined diagnosis and control reconfiguration is known as fault tolerant control (FTC) in control theory literature. In this chapter, we first review the essential technical details of the solution in ref. (Dong et al. Optics Express 19:5772-5784, 2011), and then focus on detailed simulation case studies, which clearly verify the effectiveness of this FTC solution for multiple LED degradations at the same time.