Minimum On-time Research Articles

A valley-sensed emulated peak current controlled buck converter for automotive applications

This paper presents an emulated peak current-mode control topology targeted for a high voltage buck converter for automotive applications, where one of the key challenges is to protect the devices from the high voltage stress. The proposed controller scheme eliminates the issue of the voltage stress and at the same time reduces the design complexity of the current sensing block. In addition to that, the inherent issue of sub-harmonic oscillations in the current-mode controller has been resolved by the proposed adaptive slope compensation. The input operating voltage of the converter ranges from 5 V to 36 V with output of 3.3 V. The proposed controller, designed in TSMC 180-nm Bipolar-CMOS-DMOS (BCD) process achieves a minimum on-time of 28 ns and a minimum off-time of 120 ns. It can drive a maximum load of 3.3 A while operating at a switching frequency of 2.1 MHz. The peak power efficiency, achieved at 2 A load, is 93.63%.

A 51-ns Response-Time, Fully Integrated, High-Side Current Sensor for a 40-V 6-A dc–dc Converter

A 130-nm CMOS high-side current sensor for peak-current DC-DC converters, operating with an input voltage up to 40 V is presented. A loop pre-biasing technique is used to prevent the proposed sense-FET-based current sensor from losing its linear behavior, thus achieving fast response time and, hence, allowing operation of the DC-DC converter with short minimum on-time. The proposed circuit also exploits a feedback resistance emulation technique for preventing the feedback loop to open during the blanking time. The current sensor has been integrated within a complete 40-V peak-current DC-DC buck converter that achieves 1-mV/A load regulation and 0.1-mV/V line regulation performances, even with a minimum on-time of 51 ns, with a peak efficiency of 92.5%.

Fully integrated high‐efficiency high step‐down ratio DC–DC buck converter with predictive over‐current protection scheme

A high-efficiency fully integrated 36 V–3 A stepping down DC–DC converter with high step-down ratio and predictive over-current protection scheme is introduced. To achieve high-voltage conversion ratio, emulated current mode and dedicated current sensing circuits were involved. A novel predictive over-current scheme is proposed to overcome inherent lack of emulated current-mode control and provide fast response to over-current events. In addition, due to N-type field effect transistor (NFET) was adopted to improve efficiency, a floating rail regulator is presented to generate bootstrapped voltage for driver stage. The proposed converter was simulated and fabricated in 0.18 μm bipolar-complementary metal–oxide–semiconductor (MOS)-double-diffused MOS process. Experimental results show the features work well, and with 35 ns minimum on-time, this converter can convert up to 36 V input voltage to 1.8 V at 1 MHz switching frequency with single stage and compact solution. Measured peak efficiency is 89.5% and over 80% efficiency for 3 A output current is realised as well.

Unit commitment problem: A new formulation and solution method

In this paper, we present a new formulation and solution method for the well known unit commitment problem (UCP) for scheduling the thermal generators in a day-ahead electricity market. Compared to the traditional approach, our approach has several advantages such as: (a) reducing the combinatorial complexity (i.e., the size of the binary state space) significantly, (b) eliminating the need for linearizing the constraints associated with the minimum ON time and minimum OFF time for any thermal generator, (c) eliminating the need for defining new binary decision variables to represent the startup and shutdown decisions for any thermal generator in each hour and (d) eliminating the need to linearize the non-linear cost functions associated with any thermal generator (e.g., time dependent exponential startup cost function). According to our formulation, the UCP can be stated as finding a feasible path of ON–OFF states for each generator (i.e., a sequence of unit commitment states that satisfy the corresponding minimum ON time and minimum OFF time constraints over the scheduling horizon) such that the total generation cost is minimized while meeting the demand and reserve requirement in each hour for the next day. We show how a near optimal solution for the UCP can be constructed using our solution method which is based on the Lagrangian relaxation (LR) method. Although only a near optimal solution is found, we show that our solution is comparable to that obtained when the UCP is modeled as a mixed integer linear program (MILP).

Generation, Analysis of Switched Mode Dc to Dc Converters by the Use of Converters Cells

The conventional PWM converter topologies limit the operation to lower switching frequencies because of the minimum ON-time of the transistor switch. The quadratic feature is interesting for application where a wide voltage range is necessary, a quadratic buck-boost converter is presented. The converter cell is showed, the quadratic buck converter with the converter cell can convert to the quadratic buck-boost converter without increasing elements.

Development of Ultra-Short Pulse Power Supply Applicable to Micro-ECM

A nanosecond pulse power supply for micro-ECM (Electrochemical Machining) has been developed, and the minimum pulse on-time is 50 ns. After the influence of ultra-short pulse on micro-ECM was analyzed, complementary chopper circuit was presented to avoid waveform distortion, which can achieve higher pulse frequency. A fast protect circuit was designed, and its response time is less than 5μs, which can avoid damaging workpiece and electrical components by switching off machining voltage and step motor as soon as a short circuit was detected. A series of ECM experiments using the power supply have been carried out, and results of test have proved that high frequency, short pulse width power supply helps to achieve better quality surface, higher machining accuracy.

Improved PWM control for GTO inverters with pulse number modulation

A pulse width modulated (PWM) inverter using GTOs is one of the promising power converters for AC motor drives. There are, however, still some unsolved problems with GTO inverters: (1) the modulation factor of conventional GTO inverters is limited to about 0.8 in order to maintain the minimum on-time of every GTO. If a modulation factor of 1.0 is possible in the bridge-type inverter, the output capacity would be larger in proportion to the modulation factor. The pulse number modulation (PNM) is proposed as an effective measure for this modulation factor improvement; and (2) the minimum on-time of a GTO brings about uncontrollability for a low voltage reference in the neutral point clamped (NPC) inverter. The authors propose a new procedure using the PNM technique to solve this voltage uncontrollability. The PNM method contributes to make an equivalent unity modulation factor in PWM inverters and to linearize voltage control characteristics in NPC inverters. >

Consideration on PWM Control for Neutral Point Clamped Inverter.

Pulse width modulated inverters using GTOs are aptly used high quality AC motor drives. A nuetral point clamped (NPC) inverter with three level output voltage is of great advantages to large capacity AC motor drives: lower ripple currents and higher output voltages.GTOs in inverters call for the minimum on-time to discharge the capacitive energy of snubber circuits. The NPC inverter cannot control the pulse-wise voltage for a small reference on account of the minimum on-time.This paper describes the details of control characteristics of the NPC inverter and proposes a new PWM control to cover the whole operating ranges. The digital simulations and the experimental results are described to clear the effects of new control methods.Finally, the NPC inverter is compared with the conventional bridge inverter at the point of applying to AC moter drives.

Switching converters with wide DC conversion range

Compared to basic converter topologies (buck, boost, buck-boost, Cuk, etc.), pulse-width modulation (PWM) converters with quadratic DC conversion ratios, M(D)=D/sup 2/, M(D)=D/sup 2//(1-D) or M(D)=D/sup 2//(1-D)/sup 2/, offer a significantly wider conversion range. For a given minimum ON-time and, consequently, for a given minimum duty ratio D/sub min/, D/sup 2/ in the numerator of M(D) yields a much lower limit on the minimum attainable conversion ratio. By applying a systematic synthesis procedure, six novel single-transistor converter configurations with quadratic DC conversion ratios are found. The simpler, single-transistor realization is the most important advantage over the straightforward cascade of two basic converters. As far as conversion efficiency is concerned, it is clear that a single-stage converter is usually a better choice than a two-stage converter. The quadratic converters proposed are intended for applications where conventional single-stage converters are inadequate-for high-frequency applications where the specified range of input voltages and the specified range of output voltages call for an extremely large range of conversion ratios.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A nondissipative snubber circuit for high-power GTO inverters

A novel snubber circuit for high-power GTO inverters is composed of only passive components which, idealized, produce no losses. The stored energy in the turn-on and turn-off snubbers is completely recovered during a switching cycle. In the absence of a permanent circulating current in the recovery transformer, the minimum on-time duration of one half-bridge is very low. The nondissipative operation of the snubber circuit permits a liberal design of the snubber components by which the switching losses in the power semiconductors are greatly reduced. >

A Two-Quadrant Transistor Chopper for an Electric Vehicle Drive

A two-quadrant dc-dc transistor converter capable of delivering 400 A motoring current and of generating 200 A braking current is described. The chopper operates from a 108-V dc source (54 lead-acid cells) and supplies the armature current of a separately excited dc machine in an electric vehicle application (3000-lb commuter-type vehicle). The chopper employs high-current transistors specifically developed for the application and power diodes packaged together in power module form. Snubber networks which reduce both turn-on and turn-off device stresses are employed. The interaction of the snubber networks for the motoring and braking transistors is described and design considerations presented. It was found that for these snubbers a minimum on-time and a minimum off-time for the transistors must be maintained to ensure that the transistors' dynamic load lines never enter into the region of forward bias or reversed bias second breakdown. A technique is described which instantaneously detects a transistor failure and initiates the appropriate action in order to prevent machine overcurrent and overtorque. Factors are discussed which are crucial to ensure proper transitions from motoring to braking and to inhibit device power dissipation due to parasitic currents. The selection of a variable-frequency/variable-pulsewidth switching strategy and protection and control techniques unique to high-current transistor choppers are discussed.