The advantages of resonant power converters, such as high efficiency and high power density, make them a suitable solution for domestic applications such as induction heating (IH) cookers. The control systems of these appliances require performing accurate and smooth power control while assuring the safety of the power devices. In order to accomplish these tasks, it is necessary to have information about the target output power, which is selected by the user, and the specific parameters of the output current. In this paper, a single-bit second-order sigma-delta ( Σ-Δ) analog-to-digital converter (ADC) is proposed to measure the magnitude of interest in resonant power converters. An optimized digital low-pass filter architecture is proposed to extract the output current from the digitized bit stream. This filter improves the accuracy while having low logic-resource consumption. The proposed ADC has been verified using a resonant inverter applied to the IH cooktop application. The inverter switching frequency is in the range of 40-80 kHz. A statistical analysis of the final measurement system has been performed to assess the system accuracy. The proposed system achieves good accuracy in the inverter operating range.

Design and Evaluation of a Low-Cost High-Performance $ \Sigma$ – $\Delta$ ADC for Embedded Control Systems in Induction Heating Appliances

Low-cost switching converter systems are provided which combine analog generation of a current signal with digital generation of a loop error signal that is realized with a control loop that includes a high-resolution, low-bandwidth sigma-delta modulator and a low-resolution digital-to-analog converter. The current signal and error signal are differenced to provide a control signal to the switching converter. This economical system structure facilitates quick and easy digital alteration of system parameters (e.g., loop compensation and voltage reference). System embodiments add a high-frequency analog feedback path in parallel with the control loop to supplement and enhance its control performance.

Switching converters controlled via sigma delta modulation

In this paper, the proposed multi-channel sampling technique is applied to the one-comparator counter-based sampling so as to make the system more robust than ever. Without changing any circuit structure, this is experimentally demonstrated by some gain margins of Bode plots.

Applying multi-channel sampling to one-comparator counter-based sampling to enhance system robustness

In this paper, the proposed sampling structure based on one-comparator sampling is presented, which can improve the transient response. This method is verified by a synchronously-rectified buck converter with switching frequency of 240kHz, and the digital controller takes as a control kernel the EP1C3T100 FPGA created by Altera Co., along with the VHDL language to program this controller.

One-comparator sampling based on positive-slope and negative-slope saw-toothed waves

One-comparator sampling design for the digital power converter is presented herein. The one-comparator sampling method is quite simple without any actual analog-to-digital converter. However, how to design it has not been studied. Consequently, in this paper, in order to design the digital power converter based on one-comparator sampling, the associated mathematical deductions are provided firstly, and a design example is given secondly.

One-comparator sampling design for digital power converters

Sigma-delta (SigmaDelta) modulators offer cost advantages in digitally controlled power supplies. Due to its noise shaping, high resolution, high speed ADCs and DACs are not necessary for digital control. This paper presents a low cost current-mode controller. The outer voltage loop is digital with SigmaDelta modulator and low resolution DAC. The inner current loop is kept analog with analog comparator and SR latch. An experimental circuit includes a SigmaDelta modulator test chip, a controller implemented on an FPGA, and a 30 V-to 3.3 V 10 W fly-back converter operating at 100 kHz. Experimental results demonstrate this mixed structure is a suitable solution for digital power supplies.

Botao Miao

Papers

Δ ADC based current mode power supply controller with digital voltage loop