Primary Side Current Research Articles

Analysis and Research on A High-precision Remote Transformer Calibration Device Considering The Influence of Excitation Current

Abstract With the popularization of digital transformer substations, it is of great research significance to study the upgrade of electronic transformer calibration devices, especially in the scene of small signals and high precision. In this paper, a compensation correction method is proposed to obtain more accurate primary side current parameters of the tuning device. By establishing the J-A magnetic characteristic model of the CT, the relationship between the magnetic characteristics of the CT and the corresponding terminal voltage is analyzed, and the relationship model between the terminal voltage and the corresponding excitation current is established. The model is used as the correction value in the feedback loop of the current measurement of the integral inspection device, to obtain the accurate primary side current. This method is applied to an electronic transformer calibrator inspection device system based on the Beidou system, which improves the data measurement accuracy of the device sensor and ensures that the measurement data accuracy reaches 0.1S.

Investigating Harmonic Distortion in Power Transformers Due to Geomagnetically Induced Current Flows

Geomagnetically induced currents (GICs) flow through grounding circuits into power systems, when triggered by geomagnetic disturbances. Power transformers (with grounding connections) are the primary path for GIC flows into power systems. The flow of GICs through a power transformer can create adverse impacts on its operation, including large increases in its reactive power demands and significant harmonic distortions in the primary side currents. This paper presents case studies and analyses of the adverse impacts of GIC flows on power transformers. Presented case studies are conducted on two power transformers with different core types, power ratings, and voltage ratings. Each of these power transformers is tested for various levels of GIC flows with its loading being kept unchanged. Results of conducted case studies conclude that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic is the dominant in primary and side currents at all levels of GIC flows. Other harmonic components such as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3^{\text{rd}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4^{\text{th}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 5^{\text{th}},\ 6^{\text{th}},\ 7^{\text{th}}\ \text{and}\ 8^{\text{th}}$</tex-math></inline-formula> harmonic components, can be observed with lower magnitudes than the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic component.

Constant output voltage and non-communication-based maximum efficiency tracking for wireless power transfer systems: Single current control of primary-side

Wireless power transfer (WPT) technology is a novel power transmission technology using electromagnetic field as the transmission medium. It uses the advantages of electromagnetic coupling in the near field to realize contactless transmission of electric energy on the basis of resonance theory. This mode has the advantages of stability, flexibility, efficiency and safety. WPT is mainly used for non-contact charging of electrical equipment without electrical connection. It can safely, flexibly and quickly charge the electrical equipment, which makes up for the shortcomings of the traditional charging mode. Due to the change of the load or the transmission coil position in WPT system, the transmission efficiency will drop sharply. It is of great significance to maintain the maximum efficiency transmission. This paper proposes a novel maximum efficiency transmission method. This method can achieve the maximum efficiency transmission with constant voltage output by controlling the primary-side current without communication feedback between the primary-side and the-secondary side. The Buck-Boost converter with constant output voltage is introduced at the load-side to equivalent the actual load. By adjusting the duty ratio of the Buck converter on the primary side and detecting the minimum input current, the maximum transmission efficiency could be tracked. The theoretical conditions of the method are analyzed and experimental verification is performed. The experimental results of variable relative position load show that the transmission efficiency of the proposed method can still reach 83%.

Pulse Frequency Modulation for Parity-Time-Symmetric Wireless Power Transfer System

This article proposes and implements an advanced pulse frequency modulation (PFM) scheme to adjust the output power of the parity-time (PT) symmetric wireless power transfer (WPT) system. The key is to utilize PFM to adjust the duty ratio of the self-excited oscillating inverter for the PT-symmetric WPT system, hence transferring more power than that of the conventional forced oscillating inverter under the same input voltage and duty ratio. Besides, the transmission efficiency can maintain high when the coupling coefficient is larger than the critical value. With a proper signal processing circuit, the phase of the inverter output voltage can lead to that of the primary-side current, which can help reduce the switching loss. Therefore, the system efficiency of this self-excited oscillation scheme for WPT can keep high, while the output power can be larger than that of using the conventional forced oscillation scheme. Theoretical analysis and simulation results are given to verify the feasibility of the proposed scheme.

Wide Input Variable Mode ZVZCS Converter Design

With the emphasis on energy conservation and emission reduction in various countries, industries such as new energy power generation and electric vehicles have developed rapidly. In many applications, the converter needs to adapt to a wide input voltage range, for example, the input voltage range of electric car charger is 200 &#x007E; 450V. Based on this, this paper proposes a wide-input variable-mode ZVZCS converter for electric vehicles with two operating modes. Before the MOSFETs of the lagging-legs is opened, the primary side current is extinguished by the auxiliary circuit to realize ZCS. Due to the parasitic inductance and diode of MOSFETs, ZVS is realized by MOSFETs on leading-legs. It not only broadens the input voltage range of the traditional phase-shifted full-bridge ZVZCS converter, but also keeps the advantages of the traditional phase-shifted full-bridge ZVZCS converter, such as wide load range and small duty cycle loss. Experimental results with 60 &#x007E; 240 V input voltage are demonstrated to verify the advantages.

Analysis of a Series‑Parallel Resonant Converter for DC Microgrid Applications

An input-series output-parallel soft switching resonant circuit with balance input voltage and primary-side current is studied and implemented for direct current (DC) microgrid system applications. Two resonant circuits are connected with input-series and output-parallel structure to have the advantages of low voltage stresses on active devices and low current stresses on power diodes. A balance capacitor is adopted on high voltage side to balance two input capacitor voltages. The LLC (inductor–inductor–capacitor) resonant circuit cells are employed in the converter to have soft switching operation for power semiconductors. The magnetic coupling component is adopted on the primary-side to automatically realize current balance of the two resonant circuits. In the end, a laboratory hardware circuit is built and tested. Experiments demonstrate and prove the validity of the resonant converter.

Seamless Mode-Switch Control Scheme for Primary Side Regulation Flyback With Capacitorless Self-Adaptive Startup

A seamless mode-switch control scheme for primary side regulation flyback with capacitorless self-adaptive startup is presented in this article to increase the system stability for full-load range and reduce the area cost. Instead of traditional soft-startup, a peak current of primary side (PCPS) control scheme without off-chip capacitor is adapted during the startup process and a homologous startup modeling is built. Including the traditional pulsewidth modulation (PWM), the pulse frequency modulation (PFM), and deep pulsewidth modulation (DPWM) are adapted to reduce the standby power at utralight load. Meanwhile, a seamless control scheme is proposed to assure the continuity among the PCPS, PWM, PFM, and DPWM mode switch. The controller chip is fabricated in 0.18 μm BCD process. The experiment results show that the startup time and overshoot voltage are, respectively, 35 ms and 4 V at 0.8 A load current, 48 ms, and 0.2 V at 0.008 A load current. The accuracy of output voltage is within ±0.98% under different input voltages and loads while the peak power efficiency of 88.52% is achieved.

Cost-Effective High-Performance Digital Control Method in Series-Series Compensated Wireless Power Transfer System

This paper proposes a control method for a digital signal processor based series-series (SS) compensated wireless power transfer system. In the control method, load resistance and mutual inductance are identified simultaneously, and output voltage can be estimated by using only the primary side voltage and current without direct feedback from the secondary side circuit. Since this estimation method requires a complex mathematical calculation procedure, a digital signal processor is used in this system. One of the major disadvantages of using a digital controller in this system is a limitation of sampling rates. Therefore, in this paper, several current reconstruction methods with limited sampling rates are investigated and applied. As a result, this controller not only reduces the cost of the system but also shows good estimation performance within the limited digital controller unit resource. The proposed control concept is verified by experimental results with a 48W laboratory prototype.

Flyback CC/CV AC–DC converter with high precision and reliability based on two-winding topology

Due to the rapid development of consumer electronics, the demand for power adapters is increasing. Therefore, a high-precision, high-reliability, low-cost flyback AC–DC converter without auxiliary winding was proposed in this paper. The converter adopted a primary-side regulation (PSR) topology to sample the output voltage and current from the primary inductor, and adjusted the switching frequency to achieve a constant output voltage. By alternately switching the main power BJT and the auxiliary MOSFET, with the advantage of the base charge storage effect, the chip was powered by the primary-side current. A primary-side sampling resistor was placed at the negative terminal of the ground potential of the chip, which approached real-time monitoring of the primary-side current. This improved the reliability and output accuracy of the system. To verify the feasibility and performance of the proposed circuit, an IC controller was designed and fabricated under the NEC 1 μm BCD process. Experimental result showed that deviations of the output voltage and current do not exceed ± 1.4% and ± 2.3%, respectively. These results also showed that the maximum conversion efficiency can reach a level of 78.7%, which satisfies the consumer market very well.

Peak Current Control-Based Power Ripple Decoupling of AC–DC Multichannel LED Driver

AC–DC light-emitting diode (LED) drivers suffer from short lifetime because of the low-lifetime electrolytic capacitors used for dc bus decoupling. In this paper, a primary-side peak current control method applied for driving a two-stage multichannel LED driver is proposed. The LED driver consists of an ac–dc boost power factor correction stage and an isolated dc–dc nonresonant stage. A long-lifetime and small film capacitor is used for implementing the intermediate dc bus. The proposed method, which controls the peak value of the primary-side current of the transformers, is applied to the dc–dc stage to ensure constant dc current output of LEDs in spite of the widely varying dc bus voltage due to low bus capacitance. The proposed method compensates the effect of the large dc bus voltage ripple by varying the switching frequency of the primary-side switches. Detailed design procedure, theoretical analysis, and experimental results of the LED driver operating at 180 W with the proposed method are provided. The LED driver with the proposed control method is proved to have high overall efficiency.

Primary Control Method of Wireless Charging System Based on Load Characteristics

Aiming at the output control issues of a lithium ion battery wireless charging system, a primary side control method based on load characteristic identification is proposed. The primary side impedance is calculated by detecting the effective value of the primary side voltage and current, and the mapping relationship between the equivalent load and the primary side impedance is established based on the AC impedance model. Using this mapping relation, the output of the secondary side can be regulated indirectly by controlling the input voltage of the inverter. Compared with the traditional control methods, the proposed control method not only eliminates the communication requirement between the primary side and secondary side, but also simplifies the hardware circuit design, reduces the complexity of the control circuit and also reduces the volume and cost of the system. In the paper, the impedance characteristics of the lithium ion battery at constant current and constant voltage stage are analyzed. The principle of the primary side control method is expounded and the realization method is given. The feasibility of the proposed control method is verified by simulation and experiment.

Laboratory Test of Current Transformer Operates under Harmonic Conditions

This research focused on the effect of harmonic to the performance of current transformer (CT) operates under harmonic conditions. Due to the increasing of harmonic in power system, the CT did not perform well. The CT may saturates due to the presence of voltage and current harmonics. In this project, a laboratory test was conducted to investigate and analyze the influence of harmonics to the CT performance. This CT has been test with different Total Harmonic Distortion Current (THDi) at primary side and constant primary current. The experiment result shows the secondary current CT errors will increases when THDi increases.

Half-Bridge Zero Voltage Switching Converter with Three Resonant Tanks

This paper presents a zero voltage switching (ZVS) converter with three resonant tanks. The main advantages of the proposed converter are its ability to reduce the switching losses on the power semiconductors, decrease the current stress of the passive components at the primary side, and reduce the transformer secondary windings. Three resonant converters with the same power switches are adopted at the low voltage side to reduce the current rating on the transformer windings. Using a series-connection of the transformer secondary windings, the primary side currents of the three resonant circuits are balanced to share the load power. As a result, the size of both the transformer core and the bobbin are reduced. Based on the circuit characteristics of the resonant converter, the power switches are turned on at ZVS. The rectifier diodes can be turned off at zero current switching (ZCS) if the switching frequency is less than the series resonant frequency. Therefore, the reverse recovery losses on the rectifier diodes are overcome. Experiments with a 1.6kW prototype are presented to verify the effectiveness of the proposed converter.

Design of Novel Integrated Heating and Riveting Control System for TB2 Titanium Alloy Rivet

A novel integrated heating and riveting control system for TB2 titanium alloy rivet based on the precise heating temperature and the heating time control is designed in this paper. The novel heating and riveting control system is implemented by using a linear current sensor to measure primary side current of output transformer of the control system so as to determine heating temperature, and using a microcontroller to precisely control heating time. Comparing to the difficult heating temperature control of the traditional rivet heating system of which heating time is controlled by time relay, our novel control system has implemented precise heating temperature control by precise heating time control and heating current control. The experimental results show the heating time error of rivet heater of this research is less than 0.1 second, and the novel control system is more reliable, convenient and accuracy than that traditional one controlled by time relay. The actual production results show required riveting temperature can be attained accurately under the condition of working voltage even with ±10% fluctuation, and the novel control system brings to increase the rate of finished products of riveted TB2 titanium alloy rivet about 15%.

Fault detection in the secondary side of electric arc furnace transformer using the primary side data

SUMMARY This paper presents a novel methodology for detecting fault conditions in the secondary side of electric arc furnace (EAF) transformer. The major focus of this study is to design a digital algorithm which uses solely the primary side current. Therefore, in this new methodology, only the primary side current is measured, and the fault presence in the secondary side is investigated. Here, there are two main objectives. The first objective is minimizing the fail-to-trip functioning probability, and the second one is minimizing the Mal-Trip operation probability. The fault characteristics are extracted using accurate simulation of EAFs installed in the Mobarakeh Steel Company (MSC) in Isfahan, Iran to fulfill the first objective. Three-phase field data of instantaneous current from the primary side of eight EAF transformers of MSC is also provided to evaluate performance of the proposed algorithm in the normal conditions and to achieve the second objective. The proposed algorithm is based on the sudden reduction of current harmonics in the fault conditions which is evaluated by a proposed special index which is called “the difference function” in this paper. Overall reliability assessment (dependability and security) of the proposed protective scheme demonstrates that even in this highly varying and unpredictable environment, the proposed algorithm is so precise and fast in fault detection. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of an Interleaved Three-Level ZVS Converter With Series-Connected Transformers

This paper presents a new interleaved three-level soft-switching converter with series-connected transformers to achieve zero-voltage switching for all MOSFETs, less transformer secondary windings, and partial ripple current cancellation. Two circuit modules are adopted in the proposed circuit to share the load current and reduce the ripple currents at the input and output capacitors with the interleaved pulse-width modulation (PWM). In each circuit module, two three-level PWM circuits with the same MOSFETs are operated with the phase-shift by one-half of switching period to reduce the input ripple current. The voltage stress of all switches is clamped at Vin/2. The secondary windings of two transformers are connected in series to balance the primary side currents. The current doubler rectifiers are adopted on the secondary side to partially cancel output inductor ripple current. Experiments with a 1-kW prototype, verifying the effectiveness of the proposed converter, are described.

Analysis and implementation of a new soft switching DC/DC PWM converter

This study presents a new DC/DC converter with series-connected transformers to achieve zero voltage switching (ZVS) for power switches, less transformer secondary winding and partial ripple current cancellation. Two three-level circuits using the same active switches are operated with interleaved half switching cycle. The voltage stress of all switches is clamped at Vin/2. The transformers secondary windings are connected in series to balance the primary side currents. The current-doubler rectifier is adopted on the output side. Thus, the output inductor ripple currents can be partially cancelled each other and the resultant ripple current at the output capacitor is reduced compared with the output ripple current of the centre-tapped rectifier topology. Based on the resonant behaviour by the output capacitance of active switches and the leakage inductance (or external inductance), all power switches are turned on at ZVS. Laboratory experiments with a 1 kW prototype, verifying the effectiveness of the proposed converter, are described.

Implementation of an interleaved pulse‐width modulation converter for renewable energy conversion

SUMMARYThis paper presents an interleaved soft switching converter to achieve the features of zero voltage switching (ZVS) turn‐on for power switches, zero current switching turn‐off for rectifier diodes at full load, less transformer secondary winding with full‐wave diode rectifier topology, and balance primary currents with series connection of the transformer secondary windings. Two circuit modules are adopted in the proposed circuit, and they are operated with an interleaved pulse‐width modulation. Thus, ripple currents at the input and output sides are reduced. In each module, two ZVS converters using the same switches are operated with interleaved half switching cycle. The secondary windings of transformers are connected in series in order to ensure that the primary side currents are balanced. The full‐wave diode rectifier topology is used on the output side such that the voltage stress of rectifier diodes equals output voltage, rather than being two times the output voltage as in a conventional center‐tapped rectifier topology. Laboratory experiments with a 1000‐W prototype are provided to describe the effectiveness of the proposed converter. Copyright © 2011 John Wiley &amp; Sons, Ltd.

ZVS Resonant Converter With Series-Connected Transformers

This paper presents a new series-resonant converter with series-connected transformers in order to realize zero voltage switching (ZVS) for power switches, zero current switching (ZCS) for rectifier diodes at full load, less transformer secondary winding with a full-wave rectifier, and load current sharing. Two series-resonant converters using the same switches are operated with interleaved half switching cycle. The secondary windings of transformers are connected in series in order to ensure that the primary side currents are balanced to share load current. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is adopted on the output side such that the voltage stress of the rectifier diodes is equal to the output voltage, rather than being two times the output voltage as in a conventional center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at ZVS, and rectifier diodes are turned off at ZCS if the switching frequency is less than the series resonant frequency. The proposed converter can be applied for the power supply unit of all-in-one PCs, liquid crystal display (LCD) TVs and servers, and dc-dc converters for fuel-cell power system. Laboratory experiments with a 1000-W prototype, verifying the effectiveness of the proposed converter, are described.

ZVS Resonant Converter With Parallel–Series Transformer Connection

A new series resonant converter with a parallel-series transformer connection is proposed in order to achieve zero voltage switching (ZVS) for all power switching, zero current switching (ZCS) for rectifier diodes at a full load, and less transformer secondary winding with a full-wave rectifier. For high-output-voltage applications, the primary windings of two transformers are connected in parallel in order to share the input current and reduce the root-mean-square rms current on the primary windings such that the copper losses on the transformers are reduced. The secondary windings of the two transformers are connected in series in order to ensure that the primary side currents are balanced and the secondary winding turns are also reduced. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is used on the output side. Thus, the voltage stress of the rectifier diode is equal to the output voltage rather than being two times the output voltage as that in a center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at the ZVS, and the rectifier diodes are turned off at the ZCS if the operating switching frequency is less than the series resonant frequency. The laboratory experiments with a 660-W prototype, verifying the effectiveness of the proposed converter, are described.