High-frequency link symmetrical active edge resonant snubbers-assisted ZCS-PWM DC?DC converter

A novel symmetrical zero current switching (ZCS)-pulse width modulation (PWM) cells-assisted high-frequency transformer link DC-DC converter using insulated gate bipolar transistor (IGBT) modules is presented. The proposed soft switching scheme is based on the switched-capacitor and inductive snubber in the high-voltage side inverter, assisted by active switching of MOSFET synchronous rectifier in the secondary-side low-voltage converter stage. By introducing the ZCS-PWM snubber cells, soft switching commutation which is less sensitive to the current level through the IGBTs can be achieved under the wide output power ranges. The converter circuit topology and the ZCS snubber cell operation are examined and evaluated with simulation results, and the feasibility of the converter topology is verified by experiments using a 1.0 kW-25 kHz prototype system.     

An active current-sensing constant-frequency HCC buck converter using phase-frequency-locked techniques

A hysteresis-current-controlled (HCC) buck converter with active current-sensing and phase-frequencylocked techniques is presented in this paper. The proposed active current-sensing technique can not only consume less power than previous techniques, but also fully sense the inductor current. Although the buck converter is HCC, the switching frequency can be constant due to the devised phase-frequency-locked technique. The proposed converter has been designed and implemented with TSMC 0.35 microm DPQM CMOS processes. It is shown in the experimental results that the HCC buck converter features the following characteristics: 1) up to 800 mA of load current, 2) wide input and output voltage range, 3) high power efficiency, and 4) constant-frequency operation.     

Design and implementation of FPGA-based phase modulation control for series resonant inverters

Owing to the tremendous advances in the digital technology, and improved reliability and performance of the digital control mechanisms, this paper focuses on design and implementation of digital controller using FPGA-based circuit design approach. The digital controller proposed is designed for series resonant inverter used in DC-DC converter applications. Phase modulation technique is proposed for the realization of digital controller on FPGA. The Series Resonant Converter (SRC) is considered in this paper as a preferred converter topology for high power, high voltage power supplies. This paper studies the implementation of phase shift modulation technique using FPGA. The inverter designed, is IGBT based, and Zero Voltage Switching (ZVS) technique is implemented due to reduced stresses on devices and increased efficiency. The phase modulated series resonant inverters (PM-SRC) promotes ZVS operation when its switching frequency is greater than resonant frequency. The designed PM controller is realized using FPGA on which control algorithm and other features of a controller are developed. The series resonant inverter is built and tested for full load under open loop and closed loop conditions at a switching frequency of 20 kHz. The results are presented under varying load conditions. The simulation and the experimental results were found to match closely.     

Design and analysis of a full bridge LLC DC-DC converter for auxiliary power supplies in traction

This paper focuses on an 8 kW LLC resonant full bridge DC-DC converter topology using a high frequency transformer for auxiliary power supply systems in traction. The full bridge DC-DC converter with the LLC resonant network has been tested under hard switching and zero current switching conditions with 100 kHz switching frequency. In addition to this, an observation made for the effect of dead time variation of the power switches to improve the overall system efficiency. This paper describes the efficiency of the ZCS full bridge converter by considering different input power levels and also compared with hard switched topology. This paper presents the operating principles, simulation analysis, and experimental verification for 3 kW to 8 kW LLC resonant full bridge converter with 1200 V/40 A IGBTs, and its efficiency comparison.     

Hybrid control approach for the output voltage regulation in buck type DC?DC converter

Buck converter is modelled as a hybrid automaton for the purpose of designing an appropriate control law to regulate its output voltage. The circuit when operated in continuous current mode is pulled into a limit cycle, specified by the regulation specifications, although the switching frequency varies with the load. On the other hand, under light-load conditions, the circuit is pulled into a fixed-frequency limit cycle in discontinuous current mode to satisfy the regulation criteria. Therefore, the controller design is generic in the sense that the required regulation is met throughout the operating range of the buck converter. The control problem is simplified as a guard selection problem and guards, denning the discrete states, are derived using a simple circuit theoretical approach, by imposing certain regulation and control constraints. Satisfactory operation of the buck converter under the proposed scheme is demonstrated using computer simulations and laboratory experiments. The suitability and simplicity of the proposed control scheme over a wide range of disturbances is highlighted.     

Efficient LED back-light power supply for liquid-crystal-display

A highly efficient light-emitting-diode back-light power supply is proposed for liquid-crystal display. The proposed power supply consists of a bridgeless boost rectifier for power-factor correction and the asymmetrical half-bridge flyback converter with synchronous rectifier (SR) for DC-DC power conversion. In the proposed bridgeless boost rectifier, the diode reverse-recovery losses are reduced by achieving zero-current turn-off of the output diodes, as well as zero-current turn-on of the additional diodes. The reverse-recovery transients of the diodes are improved by a simple passive snubber circuit. For a DC-DC converter, the asymmetrical half-bridge flyback converter operates under zero-voltage switching for the power switches, and the SR switch operates under zero-current switching. The analysis of the proposed converter is presented and its design considerations are discussed in detail. Experimental results based on 28 V, 300 W back-light power are provided to demonstrate the performance of the proposed converter     

Analysis of thyristor DC chopper power converters including nonlinear commutating reactors

Dc chopper power converters are used to control the power supplied to a dc load from a dc source. In a battery-powered vehicle, for example, a dc chopper can control the dc series traction motor. Thyristors are favored for the switching element in high power applications. The particular circuit described here can be used as a voltage step-down converter or a voltage step-up converter and uses two auxiliary thyristors to turn off the main power thyristor. The behavior of the step-up circuit is described by exactly the same equations as the step-down circuit when the input voltage is replaced by the load voltage and the load current is replaced by the input current. The analysis treats the general case where saturating reactors are used to soften the commutation of current in the power semiconductors. The nonlinear characteristics of these reactors are approximated by two linear segments when molybdenum-Permalloy powder cores are used. Linear or square-loop cores are included by the theory as special cases. A design synthesis based on the analytical equations is best performed with the aid of a computer.     

High efficiency metal halide discharge lamp ballast with an internal igniter and low ripple lamp current

This is a proposal for a half-bridge type metal halide discharge (MHD) lamp ballast with a coupled inductor and a frequency-controlled synchronous rectifier. To avoid using an external igniter, the internal LC resonance of a buck converter is used to generate a high-voltage pulse for the ignition. A coupled inductor filter is used for steady state ripple cancellation. This filter allows the MHD lamp to avoid the acoustic resonance phenomenon. To improve the efficiency of the ballast, a synchronous buck converter is used for the DC/DC converter stage and a frequency control method is proposed. This scheme reduces the circulation current and turn-off loss of the metal-oxide semiconductor field effect transistor (MOSFET) switch in the constant power operation, which results in an increase of the efficiency of the ballast system compared to fixed frequency control. A front-end power factor correction circuit is included in the ballast. This proposal is verified with hardware experiments     

Analysis and design of a single-phase AC/DC step-down converter for universal input voltage

This work presents a single-phase AC/DC step-down converter, which is composed of two power stages, buck-boost converter and buck converter. The front stage is used for a power-factor-correction (PFC) circuit and is operated in discontinuous conduction mode (DCM) by using the pulse-width modulation (PWM) technique to achieve almost unity power factor and low total harmonic distortion of input current (THD_i). The rear stage is also operated in DCM to achieve voltage step-down and low DC-link voltage. The proposed converter can be applied for universal input voltage (85-265 V) and wide output power range. Also, the steady-state analysis of voltage gain and boundary operating condition are presented. Moreover, the selections of inductors, capacitors and input filter are depicted. Finally, a hardware circuit with simple control logic is implemented to illustrate the theoretical analysis.     

Pre-charging of module capacitors of MMC when the module switches are driven by a source derived from the module capacitor

A modular multilevel converter (MMC) is one of the latest multilevel converters used for high and medium-voltage power conversion. It is based on cascade connection of multiple identical modules using IGBTs as switching devices. Module switches of MMC are preferably driven by a source derived from the module capacitor. In each MMC module, the control circuit, consisting of gate drivers, is powered from a dc supply derived from the local capacitor. The module capacitors need to be pre-charged, to power the control circuit. The problem faced while doing so experimentally for MMC with two modules per arm and a solution have been reported earlier. If a fly-back converter is used to generate the power supply for driving the control circuit, the module capacitor voltages become unstable during uncontrolled pre-charging. It has been reported earlier that the reason for this is approximately constant power load on the module capacitor. This work provides theoretical understanding of the problem and shows by analysis that the power supply can be made stable if the load on the module capacitor is made a positive resistance load. As the complexity of MMC with more than two modules per arm is higher, the phenomenon is studied by simulation for MMC with four modules per arm. It shows that when a fly-back converter is used for generating the power supply, similar instability occurs in MMC with four modules per arm. It shows that when the module capacitor is made to have a load with positive resistance characteristics, the module capacitor voltages and consequently the power supplies stabilize even for MMC with four modules per arm. It further shows that even if the load on the module capacitor is negative resistance type, when fly-back converter is used to generate the module power supply, by switching devices in those modules where power supply becomes available first, followed by sorting algorithm, stable power supplies can be developed on all the modules and the capacitors can be fully charged to the desired voltage.     

Feedforward simple control technique for on-chip all-digital three-phase AC/DC power-MOSFET converter with least components

A novel simple control technique for on-chip all-digital three-phase alternating current to direct current (AC/DC) power-metal oxide semiconductor field-effect transistors (MOSFET) converter with least components, which is employed to obtain small current and DC output voltage ripples as well as excellent performance, and using a feedforward simple control method for DC output voltage regulation is proposed. The proposed all-digital feedforward controller has the features of low cost, simple control, fast response, independence of load parameters and the switching frequency, it has no need for compensation, and high stability characteristics; moreover, the proposed controller consists of three operation amplifiers and few digital logic gates that are directly applied to the three-phase converter. The power-MOSFETs are also known as power switches, whose control signals are derived from the proposed all-digital feedforward controller. Instead of thyristors or diodes, the application of power-MOSFETs can reduce the loss of AC/DC converter that is proper to the power supply system. The input stage of an AC/DC converter functions as a rectifier and the output stage is a low pass inductor capacitor (LC) filter. The input AC sources may originate from miniature three-phase AC generator or low-power three-phase DC/AC inverter. The maximum output loading current is 0.8 A and the maximum DC output ripple is less than 200 mV. The prototype of the proposed AC/DC converter has been fabricated with Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 2P4M complementary MOS (CMOS) processes. The total chip area is 2.333 1.960 mm². The proposed AC/DC converter is suitable for the following three power systems with the low power, DC/DC converter, low-dropout linear regulator and switch capacitor. Finally, the theoretical analysis is verified to be correct by simulations and experiments.     

High power factor operation of resonant converters on the utility line

Operation and characteristics of resonant converters on the utility line are presented. Series-parallel (LCC-type) resonant converter operating with discontinuous current mode and continuous current mode (variable frequency control as well as fixed-frequency) are considered. Design examples are presented. SPICE simulation and experimental results obtained for the designed converters (rated at 150 W) are presented to verify the theory. It is shown that high line power factor (>0.95) and line current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter for a wide load range (from full load to 10% rated load) without any active control, and the switch peak current decreases with the load current. With active line current control, low distortion and zero voltage switching for the entire cycle are realized.     

Design,analysis and application of high set-up ZVT DC–DC converter with direct power transfer

In this paper, a new snubber cell for soft switched high set-up DC–DC converters is introduced. The main switch is turned on by zero-voltage transition and turned off by zero-voltage switching (ZVS). The main diode is turned on by ZVS and turned off by zero-current switching. Besides, all auxiliary semiconductor devices are soft switched. Any semiconductor device does not expose the additional current or voltage stress. The new snubber transfers some of the circulation energy to the output side when it ensures soft switching for main semiconductor devices. Thus, the current stress of auxiliary switch is significantly reduced. Besides, the total efficiency of converter is high due to the direct power transfer feature of new converter. A theoretical and mathematical analysis of the new converter is presented, and also verified with experimental set-up at 500 W and 100 kHz. Finally, the overall efficiency of new converter is 97.4% at nominal output power.     

LCC resonant converter with power factor correction for power supply units

This article presents a power supply using an LCC resonant converter having power factor correction with burst mode operation. In order to improve the performance from no load to full load, a microcontroller with an active control has been introduced. The light load efficiency is increased using burst mode operation. The proposed controller provides zero voltage switching. Mathematical analysis is done, and steady state characteristics are drawn. A simple design example is given based on the equations. The proposed converter has good efficiency with good power factor at all loading conditions. This is shown by the simulation and experimental results obtained through testing the prototype.     

EMC of power converters: the self-compatibility approach

Analysis of the internal electromagnetic compatibility of digitally controlled power converters is discussed. In particular, the optimum layout of the circuit configuration is designed on the basis of the actual electromagnetic interference between the power and the control section of a power converter. Besides, further improvements can be achieved by means of an auto- tuning additional board, which scans all the possible converter switching frequencies and analyses the distortion on the control signals corresponding to each frequency. Its main task is to select only the ones which produce low disturbances on the control signals as operating frequencies for the converter.     

Sliding mode direct control of matrix converters

The direct control problem of matrix converters with input inductive capacitive (LC) filter using a new approach based on the sliding mode control technique is solved. This approach allows the design of the controller considering the converter and the dynamics of its associated LC filter. Together with the space vector representation technique, sliding mode allows the precise determination of switching times between the bi-directional switches, thus being appropriate to the nonlinear ON/OFF behaviour of the matrix converter power semiconductors. As the switching occurs just in time, this technique guarantees fast response times and precise control actions, ensuring that the output voltages and the input currents track their references and making input power factor regulation independent of the input filter parameters. This feature has special interest in applications requiring unity input power factor, when feeding AC drives, or applications needing variable and accurate input power factor regulation, usually related to power quality enhancement. The designed sliding mode controllers are tested and the obtained simulation and experimental results show that they ensure the direct control of matrix converters over a wide range of output frequencies, guaranteeing a leading or lagging input power factor regulation     

Averaged modelling of switched-inductor cells considering conduction losses in discontinuous mode

Many PWM DC-DC converters contain a switched-inductor cell for which an average-value model is required. However, the presence of parasitics associated with the cell's components complicates the development of accurate averaged models, especially for the discontinuous conduction mode. Here is described an improved full-order, large-signal averaged switching cell. The proposed averaged cell takes into account conduction losses as required by the energy conservation principle and provides a more accurate duty-ratio constraint. The final model shows improvement over several previously established averaged cells in predicting large-signal, time-domain transients as well as small-signal, frequency-domain characteristics     

ZVT interleaved boost converters for high-efficiency, high step-up DC-DC conversion

The narrow turn-off period of the conventional boost converters limits their applications in high step-up DC-DC conversion. The voltage gain is extended without an extreme duty-cycle by the winding-coupled inductor structure. However, the leakage inductance induces large voltage spikes when the switch turns off. An active-clamp circuit is introduced here to clamp the switch turn-off voltage spikes effectively and to recycle the leakage energy. Both the main switches and the auxiliary switches are ZVT during the whole switching transition. Meanwhile, the output diode reverse-recovery problem is alleviated because the leakage inductance of the coupled inductors is in series with the output diode. Furthermore, a family of ZVT interleaved boost converters for high efficiency and high step-up DC-DC conversion is deduced. The experimental results based on 40-380 V front-end applications verify the significant improvements in efficiency     

Apparatus and method for heat-run test on high-power PWM converters with low energy expenditure

Before installation, a voltage source converter is usually subjected to heat-run test to verify its thermal design and performance under load. For heat-run test, the converter needs to be operated at rated voltage and rated current for a substantial length of time. Hence, such tests consume huge amount of energy in case of high-power converters. Also, the capacities of the source and loads available in the research and development (R&D) centre or the production facility could be inadequate to conduct such tests. This paper proposes a method to conduct heat-run tests on high-power, pulse width modulated (PWM) converters with low energy consumption. The experimental set-up consists of the converter under test and another converter (of similar or higher rating), both connected in parallel on the ac side and open on the dc side. Vector-control or synchronous reference frame control is employed to control the converters such that one draws certain amount of reactive power and the other supplies the same; only the system losses are drawn from the mains. The performance of the controller is validated through simulation and experiments. Experimental results, pertaining to heat-run tests on a high-power PWM converter, are presented at power levels of 25 kVA to 150 kVA.