Using Nyquist or Nyquist-Like Plot to Predict Three Typical Instabilities in DC-DC Converters

By transforming an exact stability condition, a new Nyquist-like plot is proposed to predict occurrences of three typical instabilities in DC-DC converters. The three instabilities are saddle-node bifurcation (coexistence of multiple solutions), period-doubling bifurcation (subharmonic oscillation), and Neimark bifurcation (quasi-periodic oscillation). In a single plot, it accurately predicts whether an instability occurs and what type the instability is. The plot is equivalent to the Nyquist plot, and it is a useful design tool to avoid these instabilities. Nine examples are used to illustrate the accuracy of this new plot to predict instabilities in the buck or boost converter with fixed or variable switching frequency.Comment: Submitted to an IEEE journal in 201

Digital Controlled Multi-phase Buck Converter with Accurate Voltage and Current Control

abstract: A 4-phase, quasi-current-mode hysteretic buck converter with digital frequency synchronization, online comparator offset-calibration and digital current sharing control is presented. The switching frequency of the hysteretic converter is digitally synchronized to the input clock reference with less than ±1.5% error in the switching frequency range of 3-9.5MHz. The online offset calibration cancels the input-referred offset of the hysteretic comparator and enables ±1.1% voltage regulation accuracy. Maximum current-sharing error of ±3.6% is achieved by a duty-cycle-calibrated delay line based PWM generator, without affecting the phase synchronization timing sequence. In light load conditions, individual converter phases can be disabled, and the final stage power converter output stage is segmented for high efficiency. The DC-DC converter achieves 93% peak efficiency for Vi = 2V and Vo = 1.6V.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

THE STUDY AND ANALYSIS OF MPPT CONTROLLER FOR SRBC

This work is about designing Maximum Power Point Tracker (MPPT) with Synchronous Rectifier Buck Converter (SRBC) circuit where the main purpose is to improve the performance and increase the output voltage and current. The MPPT controller controls the output current of the input (usually solar array) so that the output power converges on the maximum based on the linearity between the maximum output power and the optimal current. In this work, MPPT' s characteristics, performance, operation modes, advantages, and disadvantages are analyzed and observed. Then, combination ofMPPT and adaptive gate drive (AGD) will be applied to SRBC as the output circuit. PSPICE software is used in designing and simulating both circuits. The comparison is carried out based on the average output voltage and current, node voltage, output ripple voltage and current, gate-to-source voltage, and body diode conduction loss of the MPPT circuit and MPPT with AGD circuit. The details are discussed thoroughly that include limitations and advantages in the design of the controllers using I MHz switching frequency. It is found that by implementing MPPT controller with SRBC, the output voltage and output current have increased by approximately 12%- 13% for both CCM and DCM conditions. Besides that, it also reduces output voltage ripple and current around 70 % for CCM mode. However, in DCM condition, the output peak-to-peak ripple for both voltage and current have increased by 20 %

Digital Pulse Width Modulator Techniques For Dc - Dc Converters

Recent research activities focused on improving the steady-state as well as the dynamic behavior of DC-DC converters for proper system performance, by proposing different design methods and control approaches with growing tendency to using digital implementation over analog practices. Because of the rapid advancement in semiconductors and microprocessor industry, digital control grew in popularity among PWM converters and is taking over analog techniques due to availability of fast speed microprocessors, flexibility and immunity to noise and environmental variations. Furthermore, increased interest in Field Programmable Gate Arrays (FPGA) makes it a convenient design platform for digitally controlled converters. The objective of this research is to propose new digital control schemes, aiming to improve the steady-state and transient responses of a high switching frequency FPGA-based digitally controlled DC-DC converters. The target is to achieve enhanced performance in terms of tight regulation with minimum power consumption and high efficiency at steady-state, as well as shorter settling time with optimal over- and undershoots during transients. The main task is to develop new and innovative digital PWM techniques in order to achieve: 1. Tight regulation at steady-state: by proposing high resolution DPWM architecture, based on Digital Clock Management (DCM) resources available on FPGA boards. The proposed architecture Window-Masked Segmented Digital Clock Manager-FPGA based Digital Pulse Width Modulator Technique, is designed to achieve high resolution operating at high switching frequencies with minimum power consumption. 2. Enhanced dynamic response: by applying a shift to the basic saw-tooth DPWM signal, in order to benefit from the best linearity and simplest architecture offered by the conventional counter-comparator DPWM. This proposed control scheme will help the compensator reach the steady-state value faster. Dynamically Shifted Ramp Digital Control Technique for Improved Transient Response in DC-DC Converters, is projected to enhance the transient response by dynamically controlling the ramp signal of the DPWM unit

Design and Analysis of High Frequency Power Converters for Envelope Tracking Applications

In the field of power electronics, designers are constantly researching new methods to improve efficiency while optimizing dynamic performance. As communication technologies progress we are more often dealing with systems of increasing speed and complexity. For instance, from 1991 to 2013 we have observed the mobile broadband communication sector evolve from ~230 Kbits/s (2G) speeds to ~100 Mbits/s (4G LTE), a 430% increase in communication speed. In contrast, we have not observed the same evolutionary development in industrial power converters. Most switch-mode power supplies are still manufactured for 100 KHz to 800 KHz operating frequencies. The main reason for this is that most electrical devices only require steady-state DC power, so high speed conversion performance is largely unnecessary. But as size expectations for portable electronic devices continue to decrease, the only way to meet future demand is to realize power electronics that operate at much higher switching frequencies. Furthermore there is increasing demand to improve the transient response requirements in processor-based systems and achieve practical envelope tracking in RF communication systems. The most straightforward method of increasing the dynamic response for these systems is to increase the switching frequency of the power electronics in a sustainable and coherent manner

Adaptive High-Bandwidth Digitally Controlled Buck Converter with Improved Line and Load Transient Response

Digitally controlled switching converter suffers from bandwidth limitation because of the additional phase delay in the digital feedback control loop. In order to overcome the bandwidth limitation without using a high sampling rate, this paper presents an adaptive third-order digital controller for regulating a voltage-mode buck converter with a modest 2x oversampling ratio. The phase lag due to the ADC conversion time delay is virtually compensated by providing an early estimation of the error voltage for the next sampling time instant, enabling a higher unity-gain bandwidth without compromising stability. An additional pair of low-frequency pole and zero in the third-order controller increases the low-frequency gain, resulting in faster settling time and smaller output voltage deviation during line transient. Both simulation and experimental results demonstrate that the proposed adaptive third-order controller reduces the settling time by 50% in response to a 1 V line transient and 30% in response to a 600 mA load transient, compared to the baseline static second-order controller. The fastest settling time is measured to be around 11.70 s, surpassing the transient performance of conventional digital controllers and approaching that of the state-of-the-art analog-based controllers.postprin

COMPARATIVE ASSESSMENTS OF CONTINUOUS AND SELF-DRIVEN PWM FOR HIGH FREQUENCY CONVERTER DESIGN

In this project the comparison of the continuous gate drivers and self driven gate drivers' characteristics, performance, operation modes, advantages, and disadvantages are analyzed and observed. Both of the gate drivers will be applied at synchronous buck converter, SBC as the output circuit and also with switching frequency of 1 MHz. PSPICE software is used in designing and simulating the respective circuit. The comparison is carried out based on the output voltage, current, node voltage, output ripple voltage and current, gate-tosource voltage, and body diode conduction loss of the continuous and self-driven gate drivers. Type III compensator and AGD are applied to both switches in the SBC circuit. At the end of the simulation, adding AGD to the SBC reduces the dead time, body diode conduction and also cross-conduction losses in DCM. SBC shows an improvement up to 9.70% and 9.78 %on output voltage, current and also has virtually zero on the body diode conduction losses when both compensator and AGD are applied. For CCM and DCM, it is observed that SBC with COD, AGD and compensator-AGO produce high output current in CCM compared to DCM. COD with SBC, the output current in CCM improves 12.22 % compared to DCM. Besides, AGD with SBC is the least preferable circuit compared to compensator-AGO, MPPT-Vpulse, parallelism, and COD because of the lower output voltage and current produced, higher output ripple for voltage and current, and higher body diode conduction loss in the SBC. Here the output voltage and current is reduced to 15.30 % and 15.21 % respectively as it is compared to MPPT-Vpulse

SIMPLIS efficiency model for a synchronous multiphase buck converter

In this master’s thesis, an efficiency model was developed for the synchronous multiphase buck converters of the TPS6594x-Q1 integrated circuit using SIMPLIS simulator. The model includes internal losses occurring in power stage transistors, power stage drivers and bondwires. Modeled external losses include printed circuit board resistance and inductance, inductor direct and alternating current characteristics as well as capacitor nonidealities. Internal loss modeling was mostly based on Cadence simulations. Power stage transistors especially were thoroughly modeled. The capacitances of the power stage transistors were extracted by integrating gate and drain currents during the transistor on and off transitions. Charging of the parasitic capacitances followed the theory in turn-off and turn-on transitions and therefore the capacitance extraction was fairly simple. Nonlinearities of the parasitic capacitors were modeled in SIMPLIS with multiple linear approximations. Transistor gate drivers were very rough approximations of the real drivers but good enough for the simulation model. Drivers were modeled to match the gate currents simulated in Cadence, which were then combined the accurate switching transistor models in order to accurately model the switching characteristics. External loss models were based on measurements and simulations. Printed circuit board losses were based on Ansys simulations in which the printed circuit board inductances and resistances were solved from the geometry of the printed circuit board. Inductors were modeled to match the datasheet impedance and resistance graphs and the model was verified against the measurements done in the laboratory. An automated measurement testbench was done for the inductor measurements using LabVIEW and the results were parsed using Matlab. A ladder topology with resistances and inductances was used in the final inductor model to model the frequency characteristics of the inductor. The effect of direct current on inductance was also investigated but the inductance reduction did not have any significant impact on efficiency. Other external components such as capacitors also cause some external losses and they were modeled based on the capacitor datasheets. The simulation model was compared against single- and two-phase efficiency measurements with multiple different input and output voltages which were chosen to match the most common use cases. Efficiency curves were drawn for each configuration using the implemented simulation model and over 300 different comparison points were compared in total. A post processing script that was launched after a simulation completes had to be written with the programming language SIMPLIS supports to draw the efficiency graph from the simulated data. Using the script allowed to run the efficiency simulation without any additional licenses other than the SIMPLIS license. The final model achieved an average error of under 1 % between all the measured and simulated efficiency curves. The most accurate results were obtained with lower switching frequency and larger inductance. Apart from accuracy, the simulator had to be practical and therefore the simulation time had to be considered. Simulation time was attempted to be kept at minimum by simplifying the schematic in as many ways as possible without losing accuracy. For example, reducing the point of the linear approximations in the power stage transistors from 79 points to 17 points saved nearly 50 seconds in single-phase simulations without significant changes in simulation accuracy

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc