Ye-Then Chang

Parameter Tuning Method for Digital Power Converter With Predictive Current-Mode Control

The objective of this paper is to present an online parameter tuning method for digital power converter with predictive current-mode control. The proposed method can effectively deal with the issues caused by variation of inductance, input voltage drift, and voltage drop caused by DCR. The proposed online parameter tuning method is based upon adding an additional current sampling between two pulsewidth-modulated outputs. Neither an additional sensor nor system parameter is required for the realization of the proposed method. Moreover, the effects of inductance variation, input voltage drift, and voltage drop caused by DCR are analyzed. It will be shown that inductance variation and DCR result in dc offset of the inductor current, and input voltage drift and DCR deteriorate the performance of both steady-state and transient responses. It will be confirmed by simulation and experimental results that these effects can be dealt with by using the presented online parameter tuning method. Experimental results will be presented to fully support the theoretical analysis.

Design and implementation of vector-controlled induction motor drives using random switching technique with constant sampling frequency

Recent results have shown that random switching techniques reduce electromagnetic interference, annoying acoustic noise, and other undesirable effects. However, to incorporate random switching techniques into digital-controlled induction motor drives, it requires dynamic adjustment of the gains of controllers. This paper presents details of the design and implementation of induction motor drives using a new random switching technique. It is shown, and confirmed by experimental results in this paper, that the sampling frequency of inverter control is constant, and therefore it is not required to adjust the gains of controllers dynamically. The details of controller design of the random switching inverter-controlled vector drives are fully explored, including the controller design in the discrete-time domain and the effect of the random technique on the speed response. Moreover, the advantages and disadvantages of inverter-controlled vector drives using random switching techniques are highlighted by experimental results.

Novel Random-Switching PWM Technique With Constant Sampling Frequency and Constant Inductor Average Current for Digitally Controlled Converter

A new 2-D random-switching pulsewidth modulation (PWM) technique is proposed to reduce the dominant harmonic clusters while retaining constant average inductor current and constant sampling frequency. The special feature of constant average inductor current can reduce the output voltage ripple. Moreover, the controller parameters of a digitally controlled power converter are not required to change, which is quite essential to digitally controlled systems. Current random PWM methods are discussed and compared with the proposed method in this paper. It will be shown that the merits of the presented method include random-switching frequency, constant sampling frequency, and constant average inductor current. An field-programmable-gate-array-based digitally controlled buck converter experimental system has been set up. The specifications of the converter include input voltage = 5 V, output voltage = 1.5 V, and switching frequency = 200 kHz. The proposed random-switching pattern is implemented by software. Experimental results demonstrate the effectiveness of the proposed random-switching pattern.

Online Parameter Tuning Technique for Predictive Current-Mode Control Operating in Boundary Conduction Mode

The objective of this paper is to present an online parameter tuning technique for digital power converters with predictive peak current-mode control operating in boundary conduction mode. The issues caused by both inductor variation and input voltage drift can be solved by the proposed online parameter tuning technique which is based upon the sampled currents between two pulsewidth modulation outputs. The proposed technique requires neither an additional sensor nor a system parameter. Furthermore, the effects of inductor variation and input voltage drift are analyzed. It will be demonstrated that the variation of the inductor and input voltage drift result in a dc offset of the inductor current and deteriorate the performance. It will be confirmed by experimental results that these effects can be coped with using the presented online parameter tuning technique. Experimental results derived from a field-programmable-gate-array-based digital controller will be presented to fully confirm the theoretical analysis.

Effect of sampling frequency of A/D converter on controller stability and bandwidth of digital-controlled power converter

Due to the merits of flexibility, reduction of analog components and no aging issue of external components, digital-controlled power converter becomes very promising. It is required to derive the discrete model of power converter for digital-power control. The effect of sampling frequency of A/D converter on the digital-controlled power converter is also very essential to the performance. The objective of this paper is to present a discrete-time model of power converter for digital-controlled applications and to investigate the effect of sampling frequency of A/D converter stability and bandwidth of digital controller. It will be shown as the sampling frequency increases, the controller bandwidth can be increased to speed up the transient while reducing the phase margin. The results shown in this paper will provide a quantitative reference for digital controller design. Experimental results will be presented for confirmation.

Novel Phase-Shift Control Technique for Full-Bridge Converter to Reduce Thermal Imbalance Under Light-Load Condition

A new phase-shift control technique for the phase-shift full-bridge converter is proposed to reduce thermal imbalance of power devices. For the full-bridge converter with phase-shift control, zero-voltage switching (ZVS) can be realized. However, the power devices for the leading leg are with higher thermal temperature since the related current to achieve ZVS is much higher than that for the lagging leg. The proposed new phase-shift control technique is to swap the leading leg and the lagging leg with each other by either alternating control, temperature feedback, or pseudo random method. Experimental results derived from a digital signal processor-controlled full-bridge converter are presented for confirmation. It will be shown that thermal balance among power devices can be achieved, thereby confirming the effectiveness of the proposed control technique.

Practical considerations for the design and implementation of digital-controlled power converters

The main theme of this paper is to present practical considerations for the design and implementation of digital-controlled power converters and thereby providing archival reference for the development of digital power converter. First, the effects of A/D converter, software-based compensator and digital pulse-width modulator on digital power converter are introduced. Second, the selection of modulation methods considering the delay contributed by compensator calculation and DPWM is explored. Then modeling of digital controlled DC-DC converter taking the above-mentioned delay effects into account are analyzed and developed. Finally, compensator design based upon analogue-controlled converter model and fully digital-controlled system are presented. Illustration using a digital-controlled buck converter as an example is designed and implemented. Several compensators which are popular for analog-controlled converter are discussed. It will be shown that for the same design specifications, two-pole two-zero compensator has the least phase lag and the highest phase margin. Experimental results derived from an FPGA-based system are presented for confirmation.

New Self-Commissioning Digital Power Converter with Peak Current Mode Control and Leading Edge Modulation Using Low Sampling Frequency A/D Converter

This paper present a novel self-commissioning digital power converter control technique which will significantly reduce the sampling frequency of A/D converter while not requiring slope compensation nor resulting in performance deterioration. The technique includes self-commission of controller and power converter control. In the self-commissioning process, the circuit parameter is identified before start up and then the controller parameters of digital control are calculated automatically according to the identification results and assigned design specifications. Peak current mode control is realized based upon the estimated current using low sampling frequency A/D converter to significantly reducing the cost. Experimental results of an FPGA-based digital power converter are presented. The results show that the voltage ripple is within 3% under both steady and transient conditions.

Novel random switching PWM technique with constant sampling frequency and constant inductor average current for digital-controlled converter

A new two-dimensional random switching PWM technique is proposed to reduce the dominant harmonic clusters while retaining constant average inductor current and constant sampling frequency. The special feature of constant average inductor current can reduce the output voltage ripple. And the controller parameters of digital-controlled power converter are not required to change which is quite essential to digital-controlled system. Current random PWM methods are discussed and compared with the proposed method in this paper. It will be shown that the presented method is with the merits of randomly changes switching frequency while keeping constant sampling frequency and average inductor current. An FPGA-based digital-controlled buck converter experimental system has been set up. The specifications of the converter includes: input voltage = 5 V, output voltage = 1.5 V and switching frequency = 200 kHz. The proposed random switching pattern is implemented by software. Experimental results demonstrate the effectiveness of the proposed random switching pattern.

Robust control of digital-controlled buck converter based upon two-degree-of-freedom controller

The main theme of this paper is to present a robust controller for digital-controlled power converters. The controller design and digital implementation to robust control to achieve robustness to load disturbance while retaining steady state performance of digital-controlled buck converter are presented. The robust controller is designed based upon two-degree-of-freedom control law. The specifications of the designed and implemented buck converter include: input voltage of 12 V, output voltage of 3.3 V and output current of 20 A. Experimental results derived from the DSP-based system demonstrate that the buck converter based upon the designed two-degree-of-freedom digital controller provides superior tracking and load regulation performance as compared to conventional controller.