Abstract
This paper analyzes the presence of undesired quantization-induced perturbations (QIP) in a dc-dc buck-boost converter using a two-loop digital current control. This work introduces design conditions regarding control laws gains and signal quantization to avoid the quantization effects due to the addition of the outer voltage loop in a digital current controlled converter. The two-loop controller is composed of a multisampled average current control (MACC) in the inner current-programmed loop and a proportional-integrator compensator at the external loop. QIP conditions have been evaluated through simulations and experiments using a digitally controlled pulse width modulation (DPWM) buck-boost converter. A 400 V 1.6 kW proof-of-concept converter has been used to illustrate the presence of QIP and verify the design conditions. The controller is programmed in a digital signal controller (DSC) TMS320F28377S with a DPWM with 8.96-bit equivalent resolution, a 12-bit ADC for current sampling, and a 12-bit ADC for voltage sampling or a 16-bit ADC for voltage error sampling.
Highlights
Digital control in dc-dc converters is of interest because its many potential advantages such as low power consumption and flexibility to program and design advanced control strategies to improve the system performance [1,2,3]
Many works report disadvantageous quantization effects related to the existence of limit cycles in digitally controlled pulse width modulation (DPWM) converters
Static and dynamic models taking into account the quantization effects are derived and used to explain the origins of limit-cycle oscillations (LCO) for voltage single-loop digital control in [10,11]
Summary
Digital control in dc-dc converters is of interest because its many potential advantages such as low power consumption and flexibility to program and design advanced control strategies to improve the system performance [1,2,3]. DPWM with resolution higher than the ADC is usually implemented in order to reduce the effect of limit-cycle oscillations in voltage single-loop digital. Analysis of LCO are given in [22,23,24] for digital current mode control In these works, the resolution of the DPWM is greater than the ADC resolution in the outer voltage loop. In [22], an estimation algorithm has been applied to the average current control of a buck converter in order to reduce quantization effects in the inductor current loop and, the presence of limit cycle oscillations. In order to improve the resolution of the DPWM in single-loop digital voltage controllers, some authors use sigma-delta modulation to eliminate the quantization noise and the LCO.
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