Unbalanced Bridge Research Articles

A novel method for electric vehicle insulation detection based on the extended Kalman filter algorithm

Addressing the critical need for enhanced safety in the burgeoning electric vehicle market, this study presents a novel insulation detection method based on the Extended Kalman Filter (EKF) algorithm. To resolve the conflict between the response speed and detection accuracy of the insulation detection system caused by Y-capacitors, the Levenberg–Marquardt (L-M) algorithm is employed to effectively estimate the parameters of the feedback voltage model developed for an unbalanced electrical bridge. The state equation of the insulation testing system has been constructed, and the EKF algorithm is applied innovatively to monitor insulation resistance and Y-capacitance, demonstrating superior anti-interference capabilities. Simulation experiments have underscored the significant contributions of the L-M algorithm in expanding the detection scope of the system. Bench tests confirmed the ability of the approach to monitor changes in insulation resistance and Y-capacitance rapidly and accurately. Under normal conditions, the maximum relative error for insulation resistance measurement is 1.56%, with a response time of 1.5 s.

Ground fault detection in substation DC system based on improved differential current method

DC system is the main electrical equipment and control signal system in the substation, and its stability and reliability are directly related to whether the power system can operate safely. This paper firstly introduces the common methods of insulation detection of DC power system in substation and its advantages and disadvantages, and proposes the differential current method based on unbalanced bridge, i.e., using the combination of unbalanced bridge and leakage current sensor to detect the insulation condition of DC system, which makes up for the defects of the traditional differential current method that can only detect the faults of simple branch circuits, and realizes the detection of multi-branch grounding under complex situations. Finally, the feasibility of this method is verified by building a simulation model through simulink.

Resistance measurement using Whitson's unbalanced measuring bridge

The Wheatstone measuring bridge is one of the types of measuring bridge circuits and is used to measure resistance. The bridge was invented by Samuel Christie who created it in 1833 and was later improved by Charles Whitson in 1843. The purpose of the study is to check how the change in the supply voltage of the Whitson measuring bridge in the balanced state affects the value of the measured resistance, and to derive and verify the formula for calculating the resistance in the unbalanced bridge mode. To carry out research in a balanced mode, it is necessary to create a circuit of a Whitson bridge with a power source in the simulator of electronic circuits. When changing the supply voltage, check whether the readings of the voltmeter will change. To simplify the bridge balancing procedure, measurements are carried out in unbalanced mode. To do this, it is necessary to derive the formula for calculating the unknown resistance and check the calculated values with the resistance values obtained during modeling in the electronic simulator. The obtained results in the unbalanced mode will allow you to determine how the change in the voltage of the power source affects the value of the measured resistance. The calculation of the unknown resistance in the unbalanced mode will reduce the time for the measurement and will enable the use of microcontroller circuits to process the measurement result. A formula was derived by which the value of the resistance measured in the unbalanced mode can be calculated, and the obtained result was verified in the Falstad circuit simulator. The proposed method of resistance measurement using the Whitson bridge in unbalanced mode will increase the speed of measurement of unknown resistance and will enable the use of microcontroller processing of the measurement result.

A High-Precision Insulation Inspection Method Based on the Double-Arm Unbalanced Bridge for Electric Ships

In order to ensure the safe navigation of electric ships, it is especially important to detect the insulation status between the ship’s high-voltage system and the ship’s hull in real time. In this paper, a real-time insulation resistance (IR) detection method based on the double-arm unbalanced bridge method was proposed for the problem that the IR calculation results of electric ships have large errors. The detection principle was described, and an experimental test platform was built. The influence law of each branch resistance and voltage on the IR measurement error in this circuit was studied to provide a reference for the parameter selection of the double-arm unbalanced bridge and the effect of temperature on the measurement results was also considered. Besides, the Extended Kalman filtering (EKF) algorithm was used to reduce the influence of voltage fluctuation on the insulation detection error. The results show that the insulation testing method could accurately measure the IR, and the insulation testing error was less than 2.4%, and the error was about 0.18% after processing with the EKF algorithm. This proves that this paper improves the measurement accuracy of IR from three aspects: circuit design of insulation testing, bridge parameter selection and filtering algorithm.

Improving the Accuracy of Digital Unbalanced Impedance Bridges

This article presents an automatic digital unbalanced impedance bridge for comparing two-port impedances: R-R, R-C and C-C. The bridge consists of a two-channel digital source of voltage sinusoidal waveforms supplying the bridge arms and a three-channel precise digitizer, by means of which the complex ratio of the source output voltages and the relative bridge unbalanced voltage are determined. The hardware implementation of the bridge is based on a relatively inexpensive universal data acquisition (DAQ) card by National Instruments, USB-6281, which contains, among others, a multi-channel 18-bit analog-to-digital converter (ADC) and two 16-bit digital-to-analog converters (DAC). Thanks to the new approach to the bridge operation algorithm, consisting in the use of the interpolation method in the comparison process, the influence of the accuracy of the measurement of the bridge unbalanced voltage and some bridge parasitic admittances on the uncertainty of the impedance comparison were minimized. This simplifies the measurement procedure and shortens its execution time. The obtained results confirmed that a relatively simple digital unbalanced bridge can compare impedance standards with an uncertainty of less than 10−5. By reducing the requirements regarding the uncertainty of the measurement, and thus its execution time, the presented bridge supplemented with impedance sensors can be used in many areas of industry.

A digitally assisted IVD calibration bridge using a programmable digital detector

This paper presents a development of a digitally assisted coaxial bridge suitable for Inductive Voltage Divider's (IVD) calibration. The bridge uses a programmable digital detector (PDD) based on difference voltage measurement. The PDD used in the presented bridge senses the difference voltage and computes the ratio corrections of the test IVD with unbalanced bridge equations. The measurement results of the digitally assisted IVD calibration bridge are compared with the manual bridge, which is based on null balancing. The uncertainties achieved with the digitally assisted IVD calibration bridge are 0.55 μV/V and 0.56 μV/V for in-phase and quadrature corrections. However, uncertainties achieved in a manual bridge are 0.63 μV/V and 1.50 μV/V for in-phase and quadrature corrections respectively. The digitally assisted IVD calibration bridge is better than the manual bridge. It is simple, precise, fast, and user-friendly, hence it can be used for day-to-day calibration requirements.

Electromagnetic Interference Filter Design for a 100 kW Silicon Carbide Photovoltaic Inverter Without Switching Harmonics Filter

The design of electromagnetic interference (EMI) filter with smaller size and lightweight for a high efficiency and high power density 100 kW SiC five-level T-type (5LT2) photovoltaic (PV) inverter becomes more challenging due to the increased EMI noise resulted by high switching frequency, fast switching transients, and the removal of LCL filter. This paper proposes an unbalanced Wheatstone bridge and a two-stage notch filter to attenuate the increased common mode (CM) and differential mode (DM) noise respectively. The conventional Wheatstone bridge will suffer size and weight penalty for 100 kW PV converter due to the high parasitic capacitance of the 100 kW PV panel. An unbalanced Wheatstone bridge with a one-stage LC filter is therefore developed to address this issue and reduce the total CM inductance. The proposed two-stage notch filter is designed to achieve high attenuation, solve its parameter variation issue and help reduce the size and weight of DM filter. The total weight of the designed EMI filter for this 100 kW PV inverter is 3.54 kg. The measured conducted EMI spectrum of the 100 kW SiC PV inverter with and without proposed EMI filter are provided to validate the effectiveness of the EMI filter design.

Improving the accuracy of insulation resistance measurements of a single arm unbalanced bridge using a parameter matching design and filtering algorithm for battery packs used in electric ships

In the DC system of electric ships, insulation drops and grounding will pose a threat to stable ship operation and personal safety. Therefore, it is necessary to monitor the insulation status of the battery pack between high voltage and ground in real time. However, traditional measurement methods have problems such as low accuracy, long measurement time, and poor reliability. In this paper, an insulation detection method based on an unbalanced bridge was proposed and the principle of insulation resistance detection was analyzed. The influence of different resistance values of insulation detection circuits on the measurement error of insulation resistance was studied by simulation analysis and experimental tests to obtain the optimal set of bridge resistance matching designs. Digital filter and Kalman filter were used to filter out noise in the voltage signal. The results show that measurement error of insulation resistance after optimization was less than 3% and drops to approximately 0.46% after processing by the Kalman filter algorithm, which proves that the insulation detection method designed in this paper has high measurement accuracy.

Development of an Electronic Instrument for Eddy Current Testing

This article presents the development of a portable electronic variable frequency instrument for eddy current testing. Variations in the conductivity, permeability, or physical characteristics of non-ferromagnetic and ferromagnetic materials cause the impedance of the probe (or coil) connected to a Wheatstone bridge circuit to change. Impedance change causes bridge unbalance, which is indicated by analog and digital indicators on the front panel. The main applications of the equipment are: detection of cracks and surface faults in conductive materials, evaluation of the depths of detected discontinuities, classification of these materials through the variation of conductivity, and evaluation of the thickness of non-conductive layers on a conductive basis. Eddy current testing instruments are superior to equipment that does not use electromagnetic principles for the applications described above. The reason is due to the accuracy and ease of carrying out the inspection. The device developed in this work also has the advantage of the circuits simplicity, the low cost of the electronic components, and the ease of finding them in the market for eventual maintenance. Some test results performed are presented. The instrument performed well for the intended applications.

Gas temperature meter

Purpose: of the article is to develop a digital portable gas temperature meter in the range of -50…+600°C. To measure the temperature of dusty gas flows in the air pollution sources with the least significant digit of the digital device 1°C. Design/methodology/approach: The microprocessor measuring unit, probe and software is proposed. It leads to build a high-precision temperature meter based on a thin film sensor HM220 type "pt100". Findings: The calculation of the electrical schematic diagram parameters for signal conditioning of the sensor relative to the input range of the analog-to-digital converter. The experimental measuring unit and the probe of the gas temperature meter are assembled. The principle of the gas temperature meter calibration with the help of a precision resistance box MSR-60M is considered. The experimental gas temperature meter has a total standard uncertainty determined by type B for a maximum value of the measurement range of 1.94°C. The error of the sensor "pt100" makes the largest contribution to the total standard uncertainty, so the error increases in proportion to the value of the measured temperature. Research limitations/implications: On the basis of the proposed design of gas temperature meter it is possible to construct devices with various lengths of probes. Practical implications: The proposed meter is designed for environmental laboratories that measure the velocity, flow and sampling of dust and gas emissions from sources of air pollution. Originality/value: The device design differs due to the use of thermostable wire made of constantan as extending conductors of the temperature sensor, which is included in the unbalanced Wheatstone bridge. This solution allows the use of unipolar power supply 3.3 V for both analog and digital part of the meter. Temperature meter based on a thin film resistance thermometer is characterized by relative ease of manufacture, low material consumption, cost and high reliability.

Diagnostics of Electric Arc versus the Development of Universal Mathematical Models

The article presents universal mathematical static current-voltage characteristics- based models of electric arc and indicates primary issues concerned with arc diagnostics related to the determination of the above-named models. Particular attention was paid to the experimental determination of AC-powered arc voltage. Diagnostics-related purposes involved the use of bridge systems with one or two sources of current. Computer-aided simulations involving sinusoidal and trapezoidal current-based excitations made it possible to demonstrate the possibility of obtaining minimum values of bridge unbalance voltage. Such a condition indicated the proper determination of AC-powered arc ignition voltage.

Calculation of the components of the temperature measurement error by a resistance thermocouple of an installed unbalanced bridge

The article has devoted to solving an urgent problem related to the determination and calculation of the components of the temperature measurement error. A grain drying machine had selected as the object of research, in which the temperature of the grain at the exit from the machine is measured with the help of a Cu50 resistance thermocouple installed in an unbalanced bridge. It had found that the scale of the measuring device, calibrated in degrees Celsius, will have a nonlinearity error, which increases towards the end of the measurement range. For the Cu50 resistance thermocouple installed in the grain drying machine, when measuring the temperature in the range of 0 … 100 °C in absolute terms, the nonlinearity error was 0.3 mA, in relative terms - 4.4 %, which is quite large. The measurement error has calculated with a tolerance for the nominal resistance of the thermistor ± 0.1 Ohm, which in the given form was 0.5%. The resulting value indicates that this component will have an insignificant effect on the total measurement error. The measurement error due to the supply voltage drop by 0.2 V in relative form was 4.2 %. Thus, the voltage drops when using an unbalanced bridge will have a significant effect on the measurement result.

Grounding fault detection and type determination of substation DC system

The DC system is used as the power supply for all kinds of protection, measurement and control, safety automation and other devices in the substation. It is the fundamental guarantee of power system control and protection. If the substation DC system fails, it will have a destructive impact on the entire substation system and function. Based on this, in order to solve the problems of maloperation and refusal of protection device caused by grounding fault of DC system, a method combining unbalanced bridge method with leakage current sensor is proposed to detect the grounding resistance of bus and branch. On this basis, the neural network optimized by quantum particle swarm optimization is used to determine the fault type. Finally, the effectiveness of the proposed method is verified by MATLAB/Simulink simulation.

Phase transition in triglycine sulphate investigated using two-phase bridge measurements

The heterogeneity of the phase transition in triglycine sulfate (TGS) samples is investigated in this study, using a two-phase bridge and four-electrode sample setup. It is the practical continuation of our previous – theoretical works. Four-electrode samples and two-phase bridge measurements demonstrate interesting opportunities for observation of the dynamics of the blurred phase transition in two areas of the samples. In order to design and produce infrared sensors with desired properties it is crucial to understand the physical mechanisms and phenomena present in the investigated material. In model calculations, a characteristic peak of the bridge unbalance voltage is observed in the case of the phase transition temperature shift of less than 0.05 °C. Four-electrode samples were fabricated and bridge measurements were conducted for four frequencies and at a temperature range of 29–65 °C. Experimental results were compared with model calculations.

Insulation Monitoring Method for DC Systems with Ground Capacitance in Electric Vehicles

Owing to the influence of ground capacitance in electric vehicles, in the traditional unbalanced electric bridge DC insulation monitoring (DC-IM) method, the voltage of positive and negative electric bridges changes slowly. To calculate the insulation resistances, sampling should be conducted once the voltage of the bridge becomes stable, that will inevitably extend the monitoring cycle. To reduce the monitoring cycle, this study proposes a three-point climbing algorithm, namely, three-bridge voltage sampling with equal sampling intervals, to predict the evolution of the bridge voltage curve. However, due to the existence of sampling errors, the insulation resistances calculated by sampling values will deviate from the actual values. Then, this article also proposes the filter and correction methods of three sampled voltages to improve monitoring accuracy. Through experimental data, the influences of different parameters on the results are verified, and comparisons with the traditional method are shown in the back. The conclusion is that compared with the traditional method, the proposed method can monitor insulation resistance more quickly and ensure fixed monitoring cycles under different ground capacitance values and keep the similar monitoring accuracy.

AC insulation monitoring technology for EAST fast control power supply

To ensure the stable operation of Experimental Advanced Superconducting Tokamak (EAST) fast control power supply, a new alternating current insulation monitoring technique is presented in this Letter which is suitable for the high-frequency and high-voltage working environment of EAST fast control power supply. The method uses alternately switching resistance in an unbalanced bridge to change the voltage, and detects the voltage in real time, then calculates the insulation resistance. The simulation platform based on Simulink was built to carry out real-time insulation monitoring analysis of EAST fast control power supply as voltage input, the waveforms of which were consistent with the expected. Through experimental verification, the new method can work well for EAST fast control power supply.

Maxwell-Wien bridge with vector voltmeter system for measurement small and rapid changes in inductive-loop sensor impedance components

The paper presents a low-cost electronics system for impedance measurement of an inductive-loop sensor as well as small, rapid changes in impedance components. The idea of the system is based on the adaptation of a vector voltmeter instead of the Maxwell-Wien bridge balance indicator and supporting the system with a microcontroller. The proposed procedures, based on the complex voltage of bridge unbalance, allow to calculate the resistance that can balance the bridge in a short time. This, in turn, allows to measure the sensor impedance components, identically, as in the case of a well-known balanced bridge method. However, what is original in this work, is that measurements can be taken in a state of bridge imbalance and with high relative accuracy to small changes in sensor impedance.

Design of the ROV Dedicated Seafloor Heat Flow Probe

As the exploration of the natural gas hydrate is developed towards the target drilling phase, the traditional EWING-type and LISTER-type heat flow probe is unable to meet the needs of fine detection of the seafloor heat flow in the target area of the nature gas hydrate. The ROV (Remotely Operated Vehicle) dedicated seafloor heat flow probe is designed based on the status and operating characteristics of ROV which has been already adopted in China, which is suitable for measuring the large-scale and high-density seafloor in-situ heat flow, analyzing and understanding the fine thermal structure and thermal state of the special geological structure, and focusing on solving seafloor heat flow measurements in local structure. In the ROV dedicated seafloor heat flow probe, a high-precision NTC thermistor is adopted as the sensor, and ADUC845 chip with an internal integration of 24-bit high-resolution A/D converter is selected as the main processor. Furthermore, the ROV (Remotely Operated Vehicle) dedicated seafloor heat flow probe can measure the resistance values of the thermistors in five channels through the measurement mode of DC unbalanced bridge in a way of time sharing, and use STEINHART & HART equation to conduct R-T conversion, thus obtaining a more accurate geothermal gradient curve of the seafloor sediments after correction by the seven-point three-phase data conversion method, of which the measurement accuracy is 0.005℃ and the resolution ratio reaches 0.001℃. And it can also obtain the valuable raw data of the heat flow with the sea trial of the “SeaLion ROV” of Chinese scientific investigation vessel “Ocean VI” and the “Jiaolong HOV (Human-Occupied Vehicles)” of “Xiangyanghong XVI” vessel.

Differential measurements of light power variations through Si photodiodes in a bridge configuration for high-sensitivity chemical/biological optical sensing

This paper reports on a new optoelectronic technique based on the differential measurement of currents for the detection of small variations of the molar concentrations of chemical and biological substances by measuring changes of light power through two Si-photodiodes used in a bridge configuration. The solution exhibits high sensitivity, linear response and allows for the compensation of the initial bridge unbalance without changing its elements so optimising the output signal amplification and detection resolution. The proposed optoelectronic approach allows obtaining unique performances with respect to those ones achievable by using the standard synchronous demodulation technique for amplitude and phase measurements implemented by lock-in amplifiers. Moreover, the overall optoelectronic apparatus is simple and suitable for portable integrated sensor systems. Its main performances have been experimentally evaluated through a prototype PCB employing off-the-shelf components demonstrating the capability to detect light power variations with a settable maximum sensitivity of 300mV/nW with a resolution of about 3pW. Furthermore, a comparison with amplitude measurements based on the standard synchronous demodulation technique performed by lock-in amplifiers has demonstrated that the proposed optoelectronic system allows for a sensitivity enhancement of 2.9×104. As a case example, the optoelectronic system has been employed to determine variations of the molar concentration of a Rhodamine B solution diluted in ethanol with a resolution of about 5pM by performing optical absorption measurements.

Current-Based High-Sensitivity Differential Detection of Light Power Using Si Photodiodes in Bridge Configuration for Chemical/Biological Optical Sensing

We present a new optoelectronic technique based on the differential measurement of currents for the detection of the variations of low concentrations of chemical and biological substances by measuring light power absorption through two Si-photodiodes (SiPD) in a bridge configuration. The solution exhibits high sensitivity, linear response and allows the compensation of the initial bridge unbalance without changing its elements so optimising signal amplification gain and detection resolution. The technique shows unique performances with respect to voltage amplitude measurements performed by lock-in amplifiers. Moreover, the experimental apparatus is simple and suitable for portable integrated sensor systems. Its main performances have been evaluated through a prototype PCB demonstrating the capability to detect light power variations with a settable maximum sensitivity of 30mV/nW and a resolution of 33pW.