Current-mode Converter Research Articles

Development of a Low Cost Fuel Cell Inverter System With DSP Control

In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull dc-dc converter to boost the fuel cell voltage (48V) to /spl plusmn/200 VDC. A four switch [insulated gate bipolar transistor (IGBT)] inverter is employed to produce 120-V/240-V, 60-Hz ac outputs. High performance, easy manufacturability, lower component count, safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage dc bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end dc-dc converter in current mode. The paper details extensive experimental results of the proposed design on Department of Energy (DoE) National Energy Technology Laboratory (NETL) fuel cell.

Quantitative characterization of higher-order mode converters in weakly multimoded fibers

We present a rigorous analysis methodology of fundamental to higher order mode converters in step index few mode optical fibers. We demonstrate experimental conversion from a fundamental LP01 mode to the higher order LP11 mode utilizing a multiple mechanical bend mode converter. We perform a quantitative analysis of the measured light intensity, and demonstrate a modal decomposition algorithm to characterize the modal content excited in the fiber. Theoretical modelling of the current mode converter is then performed and compared with experimental findings.

Study of system instability in solar-array-based power systems

A study of power system stability, based on analytical modeling, is presented for application to a current-mode dc-dc converter power system with a solar array input and a line-filter interface. A fundamental analytical background is provided for use in analyses of systems of similar architecture. With this architecture, there is a potential for two sources of instability: (1) the relatively high-Q resonant tank formed by the input filter inductance (L) and the array capacitance (C) combined with excessive array voltage regulation loop-gain; and (2) positive feedback due to in-phase response produced by the current-mode converter at low frequencies. Such a low-frequency instability is dependent upon the magnitude of the array current, the array impedance, and the array voltage regulation loop-gain.

CMOS Design of a Current-Mode Multiplier/Divider Circuit with Applications to Fuzzy Controllers

Multiplier and divider circuits are usually required in the fields of analog signal processing and parallel-computing neural or fuzzy systems. In particular, this paper focuses on the hardware implementation of fuzzy controllers, where the divider circuit is usually the bottleneck. Multiplier/divider circuits can be implemented with a combination of A/D-D/A converters. An efficient design based on current-mode data converters is presented herein. Continuous-time algorithmic converters are chosen to reduce the control circuitry and to obtain a modular design based on a cascade of bit cells. Several circuit structures to implement these cells are presented and discussed. The one that is selected enables a better trade-off speed/power than others previously reported in the literature while maintaining a low area occupation. The resulting multiplier/divider circuit offers a low voltage operation, provides the division result in both analog and digital formats, and it is suitable for applications of low or middle resolution (up to 9 bits) like applications to fuzzy controllers. The analysis is illustrated with Hspice simulations and experimental results from a CMOS multiplier/divider prototype with 5-bit resolution. Experimental results from a CMOS current-mode fuzzy controller chip that contains the proposed design are also included.

A new power conditioning strategy

In this paper, a new power conditioning strategy is proposed. It can solve the problemsof harmonic pollution, power factor improvement, and backup power simultaneously. The proposed conditioning strategy is implemented by the voltage-mode voltage-source converter and the current-mode voltage-source converter. The test results show that both of the developed prototypes have the performance of an active power line conditioner and provide backup power.

Robust control of multimodule current-mode controlled converters

A robust controller for multimodule current-mode push-pull converters is presented. First, the small-signal equivalent circuit and the transfer function model of the multimodule converter system are obtained. Then, the selection of slope compensation and the model reduction are performed using the concept of dominant energy mode. Based on the reduced converter model, a PI (proportional plus integral) controller is quantitatively designed according to the prescribed regulating specifications using a systematic design procedure. A robust controller is proposed and augmented to improve the control performance when the parameter variations caused by system configuration change and operating point shift have occurred. The performance of the converter and the effectiveness of the proposed controller are demonstrated by simulation and experimental results. >

COMPUTER-AIDED ANALYSIS OF CYCLICALLY SWITCHING CIRCUITS WITH IMPLICIT CONTROLLED TRANSITION TIMES

The power electronics circuits can be seen as a subset of periodically switched networks. Their distinctive feature is the variable duration of the switching stages, dependent on implicit, threshold conditions. The paper presents a new computer-oriented approach for transient and steady-state analysis of this class of electronic circuits. The switching elements are extracted in a linear time-variable two-port, which is defined by its nodal equations. A set of modified nodal equations is obtained for describing the overall transient of the circuit. No small-signal approximations are required. The analytical expressions of the network waveforms are found accurately for each switching stage. The transient computation is based on the cyclical use of these expressions together with the threshold conditions. The general method is then applied to simulation of current-mode quasi-resonant converters. Transients due to large-signal changes in the line voltage and load are studied. The influence of the load value on transient peaks is pointed out. The voltage conversion ratio versus switching frequency is studied for both the half- and full-wave mode operation. A computer program for time-domain simulation of power quasi-resonant converters is developed based on this approach.

A new current mode control process and applications

A refined stability analysis of constant-frequency current-mode power converters is presented. The authors introduce a new current-mode control method that overcomes the limited duty cycle range of stability. They apply the method to half-bridge and full-bridge converters. A description is given of an improved-performance uninterruptible power supply based on the new control method. The authors have used a two-level modulation in the full-bridge circuit, with high-frequency switching in the four branches of the power circuit. Large protection times are required, with consequent duty-cycle and frequency limitations. The use of a three-level modulation will overcome these problems and permit a reduction of the output filter. >