Lawrence J. Borle

Current Sensing Techniques: A Review

This paper provides a thorough review of state-of-the-art current sensing techniques. It catalogues the current sensors according to the underlying physical principle in order to point out their strengths and weaknesses.

Zero average current error controlled power flow for AC-DC power converters

Unity and controlled power factor AC-DC power converters require a current control technique with zero average current error (ZACE) in each switching period. Acting on the current error signal alone, a ZACE controlled converter offers complete real and reactive power flow control with negligible low order current harmonics, a narrow switching frequency band, and relative immunity to DC link or AC line voltage harmonics. Slope-generated hysteresis, a new ZACE current control method is introduced. Simulation and experimental results in a three phase converter are presented. >

A grid current-controlling shunt active power filter

In this paper, the implementation of a three-phase shunt active power filter is presented. The filter is essentially three independent single-phase current-controlled voltage source inverters (CC-VSI) with a common DC bus. The CC- VSI is operated to directly control the AC grid current to be sinusoidal and in phase with the grid voltage. The APF consists of a current control loop, which uses polarized ramptime current control and a voltage control loop, which employs a simple Proportional Integral control. The experimental results indicate that the active filter is able to handle predominantly the harmonics, as well as the unbalance and reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical.

Design and Development of Digital Ramptime Current Control Technique

A new all-digital current control technique, called Digital Ramptime current control, is presented in this paper. The control technique, based on Ramptime current control technique, uses multisampling as the sampling strategy that results in a high accuracy of control. In an active power filter experiment, compared with the original Ramptime current control, the performance of the Digital Ramptime current control is found to be satisfactory.

Lossless Inductor Current Sensing Method With Improved Frequency Response

The lossless inductor current sensing method is well-known and is frequently applied in the measurement of output current in DC-DC converters due to its low cost and simplicity. This technique uses a low-pass filter that is matched to the inductance (L) and winding resistance to compensate for induced voltages due to the inductor. However, the waveform fidelity above the corner frequency of the inductor is generally poor due to large production tolerances and thermal drift. In this letter, we propose the use of a coupled sense winding, which increases the corner frequency of the sensing circuit by more than two orders of magnitude. We show, as an example, that for a 3.85 muH inductor the corner frequency of the measurement circuit can be increased from 36 Hz using the conventional approach to 5.8 kHz using the coupled sense winding method. Above the new corner frequency, a low-pass filter is still required but may now be constructed using a smaller capacitor and with improved high-frequency response.

Investigation Into Static and Dynamic Performance of the Copper Trace Current Sense Method

This paper investigates the static and dynamic performance of current sense methods, which exploit the resistive voltage drop across the current carrying copper trace. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. A microcontroller can be used to calibrate the copper trace resistance and implement a temperature drift compensation by means of a temperature sensor. Given that today almost every electronic device has at least one microcontroller that can provide the small computation power required for this current sensing technique, the additional cost of such a technique is small.While the proposed technique appears straightforward, theoretical modeling and hardware experiments revealed two unexpected obstacles. First, the thermal resistance between the busbar and the temperature sensor notably alters correction for the temperature drift. We found that it is possible to rectify this behavior by implementing a more sophisticated temperature compensation method inside the microcontroller. Second, it is demonstrated that the self-inductance of the busbar arrangement is not important for the dynamic behavior (frequency response) of this measurement method, and the response is determined by the mutual inductance between main loop and sense loop. Based on simulation and measurements, we demonstrated that a simple RC-compensation network can significantly improve the frequency response.

Analysis of a Series Inductance Implementation on a Three-phase Shunt Active Power Filter for Various Types of Non-linear Loads

Abstract In this paper, the implementation of a shunt active power filter with a small series inductor for a three-phase system is presented. The filter consists of a three-phase current-controlled voltage source inverter (CC-VSI) with a filter inductance at the ac output and a dc-bus capacitor. The series inductor is primarily used to handle the harmonic voltage source. The main concern is the size of the series inductance so that it is as small as possible but effective in compensating the harmonics. In order to select the proper value of the series inductance, the simulation is conducted to evaluate the value for different types of loads.

Design and implementation of a low cost sine wave inverter

This paper proposes a systematic procedure for designing a single-phase H-bridge inverter. It includes mathematical calculations, computer simulations and experimental verification on a scaled down prototype inverter.

Current or Time Sharing Switches for High Efficiency Photovoltaic Power Systems

This paper presents a comparative analysis of the parallel operation of different switches in a switch mode power converter. In high power applications, multi-switch PWM power conditioners may be preferred despite a higher component count, due to the absence of low frequency filters, reduced switching losses and fault tolerance. The paper demonstrates how current sharing (CSH) and time sharing (TSH) lead to the reduction of switching stress in the parallel operation of switches in any converter. The solutions proposed in this study can be applied on different scales to other power conditioners for renewable energy applications. Discussions of the concepts, hypotheses and computer simulations are verified by 1 kW experimental results

Transformer based DC current sensor for digitally controlled power supplies

Twenty years ago, R. Severns presented a transformer based circuit which is able to measure DC currents. However, this circuit did not experience a break-through in the industry or even academic world because it requires too many components and is unable to measure small currents. This paper enhances this circuit so that it becomes feasible to measure currents down to zero. The circuit complexity is no longer an obstacle because in digital controlled power supplies the DSP provides the required auxiliary functionalities. The feasibility of the proposed circuit has been proven by hardware experiment.