Abstract
The high-power Asymmetric half-bridge Converter (AHBC) LED constant current driver controlled by digital current mode is a fourth-order system. Static operating point, parasitic resistance, load characteristics, sampling effect, modulation mode and loop delay will have great influence on its dynamic performance. In this paper, the small-signal pulse transfer function of the driver is established by the discrete-time modeling method for two operating points with three modulation modes of trailing-edge, leading-edge and double-edge. And, the effects of parasitic parameters, delay, sampling and load etc. are fully considered in modeling. For a large number of complex exponential matrix operations, the first order Taylor formula is used for approximate calculation after the coefficient matrix is obtained by substituting the data. Then, the designed average current mode compensators based on state-space averaging small-signal model(SSA) are used for analog and digital control, and the loop characteristics and control performance are analyzed. Simulation and experimental comparison results show that the proposed discrete-time model(DTM) can more accurately describe the characteristics of resonant peak, high-frequency dynamic and loop delay, and is very suitable for the design of high frequency digital controller.
Highlights
LED light source has many advantages such as high efficiency, energy saving, long life, high reliability and environmental friendliness, so it has been widely used in indoor and outdoor lighting
The high-power Asymmetric half-bridge Converter (AHBC) LED constant current driver controlled by digital current mode is a fourth-order system
Simulation and experimental comparison results show that the proposed discrete-time model(DTM) can more accurately describe the characteristics of resonant peak, highfrequency dynamic and loop delay, and is very suitable for the design of high frequency digital controller
Summary
LED light source has many advantages such as high efficiency, energy saving, long life, high reliability and environmental friendliness, so it has been widely used in indoor and outdoor lighting. The establishment of a more accurate small-signal discrete model will be beneficial to the improvement of digital control performance when parasitic parameters, modulation effects, quantization effects and loop delay are taken into account comprehensively[16]. Abedinpour established the AHBC state-space averaging small-signal model(SSA) for voltage mode control considering parasitic resistance[18]. The SSA has been widely used in the design of analog controllers and has obtained better closed-loop control performance Based on this model, the discrete-average model(DAM) of the converter can be obtained by using the mapping theory and considering the effects of sampling, modulation and delay[20]. The discrete-time modeling is used to model the AHBC LED constant-current driver controlled by digital current mode. After adding the small-signal disturbance, removing the DC component and taking Laplace transform, the open-loop transfer function of state-space average small-signal from duty ratio to inductance current and LED current can be derived, as shown in Equation (3)
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