Miro Milanovic

RC-RCD clamp circuit for ringing losses reduction in a flyback converter

An RCD clamp circuit is usually used in flyback converters, in order to limit the voltage spikes caused by leakage transformer inductance. Oscillation ringing appears due to the clamp diode, which deteriorates the converters power rate. This brief describes this ringing phenomenon and the use of an RC-RCD clamp circuit for damping the clamp diodes oscillation. This clamp circuit is capable for improving a flyback converters power ratio.

Fast Transitions Between Current Control Loops of the Coupled-Inductor Buck–Boost DC–DC Switching Converter

An already published current control strategy for the coupled-inductor buck-boost converter is able to change its aim from controlling the input current to controlling the output current, and vice versa, depending on the instantaneous operation point and the applied current references. The main drawback of the two PI-based control implementation is its slow response when the control aim is changed from one current to the other. Due to the magnetic coupling, the converters control-to-input and control-to-output current small signal transfer functions exhibit similar first-order characteristics. Therefore, it is possible to transform the previous control scheme to a PI-based one that exhibits faster and, in certain cases, much faster transitions between input and output current control operation. The presented experiments also show that the steady-state behavior of the converter is unaffected by the new control implementation.

Voltage and Current-Mode Control for a Buck-Converter based on Measured Integral Values of Voltage and Current Implemented in FPGA

This paper describes a complete digitally controlled dc-dc buck converter performed by field-programmable gate array (FPGA) circuitry. The voltage and current-mode control is based on a voltage control oscillator (VCO) performed measurements regarding output-voltage and inductor current, respectively. This measurement principle also uses digital-counters (digital-integrators) in order to obtain integral values for the output-voltage and inductor current. In analog current-mode control, the instantaneous inductor current-value-measurement is used for the switching action. When the VCO is used for the inductor current measurement, the integral is measured during the switching-on time set as an observation interval and the switching action occurs based on this measurement. Such a principle enables full digitalization of the voltage- and current-control loop and also the used measurement principle is capable of rejecting the switching disturbances during current and voltage measurements. All the tasks for current and voltage control were implemented within the FPGA. The algorithm was verified by simulation and experimentation at a switching-frequency of 25kHz.

IDF-Correction-Based PWM Algorithm for a Three-Phase AC–DC Buck Converter

This paper presents a pulsewidth modulation (PWM) algorithm for a three-phase ac-dc rectifier, where the third and fifth harmonics are indicated in the input phase voltages. A mathematical analysis, which includes this voltage harmonics components, shows that the unity input displacement factor (IDF) can be reached by appropriate evaluation of duty-cycle functions. A PWM algorithm is proposed based on this developed theoretical achievement. This approach enables current sensorless unity IDF rectification. The PWM algorithm is investigated theoretically and verified by simulations and experiment.

EMI reduction in randomized boost rectifier

Low frequency harmonics injection into AC power supply and small power factor are the main disadvantages of conventional rectifiers. By using the high power factor correction circuits (HPFCC) the input current has a sinusoidal form and is in phase with the power supply voltage. By solving the problem of power factor with high frequency switching current mode control, another problem arises-that of high frequency harmonics generated in radio-frequency (RF) range by the converter. Therefore the problem of electromagnetic interference (EMI) must be appropriately treated as well. This paper deals with randomized pulse width modulation (RPWM) strategy for the boost rectifier. The randomized modulation principle is introduced in an ordinary PWM control unit which is widely used in unity power factor correction circuits. Introduction of the RPWM results in smaller increases of the total harmonic distortion (THD) in the input current and consequently neglected decreasing of the power factor. On the other hand, this approach causes the high-order harmonics spectral components to be significantly reduced and dispersed around ordinary spectral lines, which means reduced conducted EMI as well.

DCM-Based Zero-Voltage Switching Control of a Bidirectional DC–DC Converter With Variable Switching Frequency

This paper investigates a control approach for achieving reliable zero-voltage switching transitions within the entire operating range of a conventional nonisolated bidirectional dc-dc converter that utilizes synchronous rectification. The approach is based on operation in the discontinuous conduction mode with a constant reversed current of sufficient amplitude, which is achieved by load-dependent variation of the switching frequency. This paper focuses on the obtained resonant voltage transitions and provides analytical models for determining the reversed current and timing parameters that would ensure safe, reliable, and highly efficient operation of the converter. In addition, the proposed approach solves the synchronous transistors spurious turn-on and body diode reverse recovery induced issues, does not require any additional components or circuitry for its realization, and can be entirely implemented within a digital signal controller. The effectiveness and performance of the presented control approach was confirmed in a 1-kW experimental bidirectional dc-dc converter that achieved 97% efficiency over a wide range of output powers at switching frequencies above 100 kHz.

Digital current mode and voltage control for the dc-dc step-up converter based on the FPGA technology

This paper introduces a digitally performed voltage and current control mode for dc-dc step up converter based on FPGA technology. The voltage and current measurement was realized by using A/D converters as peripheral units of the FPGA system. Special attention was performed with current measurement and its A/D conversion due to the used predictive current mode algorithm which enables the fully digitalization of the whole control processes.

Digitally controlled buck converter

Digitally controlled step down converter with different control law algorithms is studied in this paper. The state controller is designed to eliminate the start-up overshoot and reduce maximal dynamic error of load change response, but the state controller is not capable of eliminating the steady-state error under the load change condition. By using an additional discrete PID controller the steady state error could be eliminated. For the next consideration, the decomposed discrete fuzzy PID controller has been analyzed. All control algorithms are performed at a continuous current mode of operation. The experimental results are presented in the paper. The control algorithms were implemented on 16-bit microcomputer.

Voltage Ripple Cancellation in Buck Converter based on Hybrid Structured Connection

In applications where size and efficiency are critical switched mode power supply converters are used. A switched mode DC-DC buck converter or step-down converter use output filter capacitor to reduce output voltage ripple. To reduce size of buck converter, the elimination of the capacitor must be done. Instead of the capacitor the structure with additional linear amplifier is introduced for output voltage ripple reduction. The amplifier reduces ripple in output current and consequently ripple in output voltage. The structure operation is theoretically investigated and verified by simulations and experimental results

PWM spectrum evaluation and over-modulation phenomena in a three-phase inverters - analytical approach

This paper provides a comprehensive spectrum analysis of three-phase inverterspsila output voltages. The output voltages were generated by triangular Pulse Width Modulation algorithm (PWM). This approach is presented in order to improve engineering education based on the classic analytical approach where the advantages of Bessel function series and calculation of Fourier coefficients have been used. The over-modulation phenomena were also considered. This analysis offers a complete quantitative and qualitative knowledge of those PWM signals necessary for high harmonics influence study when different passive and active loads are connected to inverterspsila outputs.