Keyue Smedley

One-cycle control of switching converters

A pulsed nonlinear control technique, one-cycle control, is introduced. This technique takes advantage of the pulsed and nonlinear nature of switching converters and achieves instantaneous control of the average value of the chopped voltage or current. This technique provides fast dynamic response and good input-perturbation rejection. It is suitable for the control of pulsewidth-modulated (PWM) converters and quasi-resonant converters. The one-cycle control theory is developed based on the analysis of the basic buck converter with conventional feedback control and current-mode control. Experiments were conducted to verify the feasibility of one-cycle control of the buck converter. The dynamic behavior of one-cycle controlled switching converters is studied. The Cuk converter is used as an example for the analysis and experiments. The one-cycle control theory is generalized to control all types of switching converters: constant frequency, constant turn-on time, constant turn-off time, and variable switches.<<ETX>>

Dynamics of one-cycle controlled Cuk converters

One-cycle control is a nonlinear control method. The flow-graph modeling technique is employed to study the large-signal and small-signal dynamic behavior of one-cycle controlled switching converters. Systematic design method for one-cycle control systems is provided with the Cuk converter as an example. Physical insight is given which explains how one-cycle control achieves instant control without infinite loop gain. Experimental results demonstrate that a Cuk converter with one-cycle control reflects the power source perturbation in one-cycle and the average of the diode voltage follows the control reference in one cycle. >

A cost-effective single-stage inverter with maximum power point tracking

Renewable energy, such as solar energy, is desirable for power generation due to their unlimited existence and environmental friendly nature. However, the high initial investment impedes its wide commercialization. This paper proposes a cost-effective single-stage inverter with maximum power point tracking (MPPT) in combination with one-cycle control (OCC) for photovoltaic power generation. This control scheme is based on the output current-adjusting feature of OCC. The output current of the inverter can be adjusted according to the voltage of the photovoltaic (PV) array so as to extract the maximum power from it. In the mean time, OCC guarantees that the output current is proportional and in phase with the grid voltage. All these are accomplished in one power stage and a simple control circuit. No detection and calculation of power are needed. Compared with previously proposed approaches, this method is much more efficient and cost-effective and yet exhibits excellent performance. The principle is explained qualitatively and extensive experiments have been carried out to verify the proposed method.

A family of continuous-conduction-mode power-factor-correction controllers based on the general pulse-width modulator

This paper presents a family of constant-switching-frequency pulse-width-modulated controllers for single-phase power-factor-correction (PFC) circuits that operate at continuous-conduction mode (CCM). Both trailing- and leading-edge pulse-width modulation (PWM) are used. These controllers do not require the multiplier and rectified-line-voltage sensor, which are needed by traditional control methods, and they can be implemented with a unified control circuit. Controller examples are analyzed and verified experimentally.

Unified constant-frequency integration control of active power filters-steady-state and dynamics

An active power filter (APF) is a device that is connected in parallel to and cancels the reactive and harmonic currents from a group of nonlinear loads so that the resulting total current drawn from the AC mains is sinusoidal. This paper presents a unified constant-frequency integration (UCI) APF control method based on one-cycle control. This method employs an integrator with reset as its core component to control the pulse width of an AC-DC converter so that its current draw is precisely opposite to the reactive and harmonic current draw of the nonlinear loads. In contrast to previously proposed methods, there is no need to generate a current reference for the control of the converter current, thus no need for a multiplier and no need to sense the AC line voltage, the APF current, or the nonlinear load current. Only one AC current sensor is used to sense the AC main current and one DC voltage sensor is used to sense the DC capacitor voltage. The control method features constant switching frequency operation, minimum reactive and harmonic current generation, and simple analog circuitry. It provides a low cost and high performance solution for power quality control. Steady-state and dynamic study is presented in this paper. Design example is given using a two-level AC-DC boost topology. A prototype was developed to demonstrate the performance of the proposed APF. This control method is generalized to control a family of converters that are suitable for APF applications. All findings are supported by experiments and simulation.

A comparison of voltage-mode soft-switching methods for PWM converters

A comparison study was conducted to characterize the loss mechanisms, component stresses, and overall efficiencies of a group of voltage-mode soft-switching pulse width modulation (PWM) methods, including two methods developed by the authors. All soft-switching methods in the selected group allow zero voltage turn-on and turn-off of the main switch and utilize a single auxiliary switch with some resonant components. Advantages and disadvantages are identified for each method. Experimental verification for each soft-switching method is provided. It was found that only those methods that softly switch the auxiliary switch, minimize redirection current, and recover the auxiliary circuit energy improve efficiency over most of the load range.

A topology survey of single-stage power factor corrector with a boost type input-current-shaper

A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most of reported single-stage PFC rectifiers cascade a boost type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of a single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on this group. It is found that many of these topologies can be implemented by combining a 2-terminal or 3-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a 3-terminal ICS cell to a 2-terminal ICS cell using an additional winding from the transformer and vice versa. According to the translation rule, many of reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule.

Three-Phase Boost-Type Grid-Connected Inverter

Alternative energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free property. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected DC-to-AC inverters are required for alternative energy source power generation. For many of these applications, the input dc voltage is usually below peak voltage of the output and may vary in a wide range. Thus single-stage buck-type inverters may not be adequate, since they have very limited input voltage range and require the input DC voltage to be higher than the peak of the output voltage. For this reason, two-power-stage topologies, cascaded topologies and multilevel topologies are reported for applications where the input voltage is lower than the peak of the output voltage. Typically, one DC-DC power stage is required to boost the DC voltage in addition to an inverter for DC-AC conversion, which yields increased circuitry complexity. One-stage inverters for low DC voltage to high AC voltage conversion have been reported for non-grid-connected inverters based on the topology of a current source inverter. In this paper, the one-cycle control (OCC) method and the pulse width modulation (PWM) method have been proposed for a three-phase boost-type grid-connected inverter. The inverter features a single power stage that converts dc power to grid-connected ac power by injecting three in phase sinusoidal currents into grids, which may reduce power losses and circuit complexity. The input dc voltage is lower than the peak grid voltage and can vary in a wide range, which greatly suits the power conversion from photovoltaic or fuel cells to grid lines. The DC inductance may be kept low because the average DC current is maintained constant in a switching cycle. With the OCC method, the inverter preserves the advantages of simple circuitry, good stability and fast dynamic response and maximum power point tracking (MPPT) function can be conveniently integrated into the control core. Experiments have been performed with a 1.5-kW laboratory prototype that demonstrated the good performance of the inverter and MPPT function.

Properties and synthesis of passive lossless soft-switching PWM converters

This paper derives general topological and electrical properties common to all lossless passive soft-switching power converters with defined characteristics, and proposes a synthesis procedure for the creation of new power converters. The synthesis procedure uses the properties to determine all possible locations for the resonant inductors and capacitors added to achieve soft switching. A set of circuit cells is then used to recover the energy stored in these resonant elements. This paper also explains the operation of the circuit cells and the many new passive lossless soft-switching power converters. A family of soft-switching boost converters is given as an example of the synthesis procedure. Experimental waveforms are also shown for a new soft-switching Cuk converter.

A general three-phase PFC controller for rectifiers with a parallel-connected dual boost topology

A general constant-frequency power-factor-correction (PFC) controller is proposed for three-phase rectifiers with parallel-connected dual-boost topologies. This paper shows that unity power factor and low current distortion in all three phases can be realized by one-cycle control using one integrator with reset along with a few near and logic components. This new extension of one-cycle control provides the core PFC function to the dual-boost topologies. It does not require multipliers, as used in most other control approaches to scale the current reference according to the output power level. In each 60/spl deg/ of AC line cycle, only two switches are switched at high frequency; therefore the switching losses are significantly reduced. All switches are switched at low current, which results in reduced current ratings. This control method is simple and general. It is applicable to three-phase rectifiers that can be decoupled into parallel-connected dual-boost topologies by slight modification of the logic circuit. This control method is verified by experimental results. The proposed controller is suitable to be integrated into a three-phase PFC control chip.