Freewheeling Current Research Articles

Analysis, Design, and Experimental Results for a High-Frequency ZVZCS Galvanically Isolated PSFB DC-DC Converter over a Wide Operating Range Using GaN-HEMT

This paper investigates the potential of the emerging gallium nitride (GaN) high-electron mobility transistors (HEMT) power devices to meet certain power conversion challenges. The advantages of utilizing GaN HEMT transistors in a high-frequency, high-power isolated DC-DC topology are explored experimentally. Using the GaN HEMT’s parasitic elements, e.g., output capacitance, and the leakage inductance of the transformer, a soft switching zero-voltage zero-current switching (ZVZCS) phase shift converter is proposed. Accordingly, the freewheeling current is terminated, and soft switching is realized for most of the primary and secondary active devices. Furthermore, without using any additional circuitry, the overshoot voltage across the bridges of active rectifier diodes is clamped at their voltage level. In addition, a high-frequency power transformer is optimized to minimize the overall transformer losses (e.g., winding and core losses). Combined the conductor types, e.g., litz wire and copper foil, shows good electrical and thermal performance by reducing the AC and DC resistance. Finally, a 5 kW, 100–250 kHz prototype is built and tested. The experimental results show a conversion efficiency of up to 98.18% for the whole converter.

Commutation Auto-Correction Method for Position Sensorless BLDCM With the Anti-Interference Ability Against Current Variation

Precise commutation is crucial to improve the sensorless brushless dc motor efficiency. In order to achieve the high-precision commutation, this article develops a commutation auto-correction method. Three challenges of the conventional correction method based on signal integral have been addressed. First, the line voltage difference of adjacent phases is integrated to construct the feedback quantity, which avoids the interference from the phase current variation. Second, the integration interval compression strategy is proposed, which avoids the impact of commutation freewheeling current. Third, a novel averaging circuit is designed, which realizes the high-precision acquisition of the integral. At last, by using the integral as the feedback quantity, a proportional integral controller is introduced to implement the commutation auto-correction. In contrast to the conventional method, the above three approaches ensure the accurate commutation in cases of the phase current variation and high motor speed. The effectiveness of the auto-correction method is verified by the experimental results on a magnetically suspended turbo molecular pump.

Suppressing Voltage Spikes of MOSFET in H-Bridge Inverter Circuit

Power electronics devices are made from semiconductor switches such as thyristors, MOSFETs, and diodes, along with passive elements of inductors, capacitors, and resistors, and integrated circuits. They are heavily used in power processing for applications in computing, communication, medical electronics, appliance control, and as converters in high power DC and AC transmission in what is now called harmonized AC/DC networks. A converter’s operation is described as a periodic sequencing of different modes of operation corresponding to different topologies interfaced to filters made of passive elements. The performance of converters has improved considerably using high switching frequency, which leads to a significant improvement in a power converter’s performance. However, the high dv/dt through a fast-switching transient of the MOSFET is associated with parasitic components generating oscillations and voltage spikes having adverse effects on the operation of complementary switches, thereby affecting the safe operation of the power devices. In this paper, the MOSFET gate-driver circuit performance is improved to suppress the H-Bridge inverter’s voltage spikes. The proposed technique is a simple improvement to the gate driver based on the IR2112 driver (IC) by adding a capacitor to attenuate the effect of parasitic components and the freewheeling current, suppressing the negative voltage spikes. This paper’s main contribution is to improve the gate driver circuit’s capability for suppressing the voltage spikes in the H-Bridge inverter. The improved gate driver circuit is validated experimentally and is compared with the conventional gate driver. The experimental results show that the proposed technique can effectively suppress the MOSFET’s voltage spikes and oscillations.

Freewheeling Current-Based Sensorless Field-Oriented Control of Five-Phase Permanent Magnet Synchronous Motors Under Insulated Gate Bipolar Transistor Failures of a Single Phase

Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor. On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive. Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information. Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability. The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC. By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates. Experimental results are provided to validate the proposed sensorless FOC philosophy.

Reverse Conduction Loss Minimization in GaN‑Based PMSM Drive

Gallium nitride (GaN) devices are becoming more popular in power semiconductor converters. Due to the absence of the freewheeling substrate diode, the reverse conduction region is used in GaN transistors to conduct the freewheeling current. However, the voltage drop across the device in the reverse conduction mode is relatively high, causing additional power losses. These losses can be optimized by adequately adjusting the dead-time issued by the microcontroller. The dead-time loss minimization strategies presented in the literature have the common disadvantage that either additional hardware or specific converter data are needed for their proper operation. Therefore, this paper’s motivation is to present a novel dead-time loss minimization method for GaN-based high-frequency switching converters for electric drives that does not impose additional requirements on the hardware design phase and converter data acquisition. The method is based on optimizing the current controllers’ output with a simple perturb-and-observe tracker. The experimental results show that the proposed approach can minimize the dead-time losses over the whole drive’s operating range at the cost of only a moderate increase in software complexity.

A Voltage Balancing Method for Series-Connected Power Devices in an LLC Resonant Converter

This letter proposes a voltage balancing method for series-connected power devices in an LLC resonant converter. Series connection of power devices can allow an LLC resonant converter to operate in high-voltage applications. One key problem of series-connected power devices is the voltage imbalance due to device parameter deviations and gate drive delays. To achieve voltage balancing, an auxiliary module (AM) is connected in parallel with each power device. Each AM consists of a capacitor and an auxiliary switch with an antiparallel diode. The AM operates as a clamping circuit and voltage among the series-connected power devices can be shared evenly if the AM capacitor voltages are well-balanced. The AM capacitors are charged during the asynchronous period of the series-connected power devices. The excess energy of AM capacitors can be released by the freewheeling current during dead time in an LLC converter. By assigning a pulsing gate signal to AMs with higher voltages in every switching cycle, the AM capacitor voltages can be balanced. The proposed method will not induce additional power loss and does not affect the normal operation of power devices. Experimental results are provided to verify the effectiveness and feasibility of the proposed method.

High-Efficiency Phase-Shifted Full-Bridge Converter With a New Coupled Inductor Rectifier (CIR)

A conventional phase-shifted full-bridge (PSFB) converter is one of the most promising topologies in high-efficiency and high-power applications because of its small RMS current, inherent zero-voltage switching capability, and clamped voltage stress of the primary switches. However, when the PSFB converter operates with a small duty ratio, a large freewheeling current of an output inductor flows in the primary side, and it causes a large circulating current. In addition, it has a large voltage stress in the rectifier diodes due to a voltage ringing between parasitic components. To solve these problems, a new PSFB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the PSFB converter instead of the full-bridge rectifier, the proposed converter eliminates the freewheeling current in the primary side, which significantly reduces the primary circulating current. In addition, the two rectifier diodes of the CIR do not have voltage ringing. As a result, the proposed converter not only reduces the conduction loss in the primary side, but can also use two diodes in the rectifier with a low voltage rating. The effectiveness and feasibility were verified with a 320-400 V input and 56-V/12.8-A output prototype.

A Novel Sensorless Control Strategy for Brushless Direct Current Motor Based on the Estimation of Line Back Electro-Motive Force

In this paper, a novel sensorless control strategy based on the estimation of line back electro-motive force (BEMF) is proposed. According to the phase relationship between the ideal commutation points of the brushless direct current motor (BLDCM) and the zero-crossing points (ZCPs) of the line BEMF, the calculation formula of line BEMF is simplified properly and the commutation rule for different positions of the rotor is presented. The estimation error of line BEMF caused by the freewheeling current of silent phase is analyzed, and the solution is given. With the phase shift of the low-pass filter considered, a compensation method using “60°-α” and “120°-α” is studied in this paper to eliminate the error. Finally, the simulation and experimental results show that the rotor-position-detection error is reduced effectively and the motor driven by the accurate commutation signal can work well at low and high speed.

Measuring structure functions of power devices in inverters

This paper proposes the measuring of structure function from power devices on-board induction motor drives and multilevel converters. It puts forward the issues and methodology related to on-board measurement of the cooling curve and derivation of the structure function during idle times in induction motor drives for maintenance purposes. The structure function uses the thermal resistances and capacitances in the Cauer form to identify changes in the device structure. The advantage of the structure function is that it does not only reveal the value but also the location of the thermal resistance and capacitance in the heat flow path. The novelty in this work is the methodology used to achieve the measurement of the cooling curve and obtaining the structure function despite issues related to freewheeling current due to energy stored as a result of motor inductance. A detailed description of the measurement circuit is presented. The possibility of applying this technique to multilevel converters in different application is also elaborated.

Parallel full-bridge converter with wide ZVS and low freewheeling current

ABSTRACTThe main objective of this paper is to present a direct current to direct current topology with high circuit efficiency. In this studied circuit, two full-bridge circuits and a half-bridge circuit connected in parallel are introduced to achieve the advantages of low switching loss, less primary current, low conduction loss and low filter size compared to the traditional parallel full-bridge converters. The circuit diagram, operation principles, steady-state analysis and experiments are provided to demonstrate the effectiveness of the studied topology. Finally, a 1.44-kW laboratory prototype is constructed to verify the validity of the theoretical analysis. Experimental results show that highest efficiency of 95.3% can be achieved.

Comparison Analysis of Demagnetization and Torque Ripple in Accordance With Freewheeling Current in PM BLDC Motor

Demagnetization and commutation torque ripple are affected by freewheeling current (FC) when inverter switch turns on or off. Recently, many studies on commutation torque ripple considering the FM are actively conducted for high efficiency [1]. However, the studies on the demagnetization considering the FM are not actively conducted. So, we conducted demagnetization analysis depending on the variation of (FC) for improving the reliability of brushless dc (BLDC) motor. If fault of BLDC motor is occurred such as inter-turn fault owing to broken coil insulation, the input current increases and is destroyed by the electrical and magnetic imbalance [2]. For this reason, the inter-turn fault generates demagnetization. If demagnetization phenomenon is occurred, magnetic flux is reduced by decrease of back electromotive force, and then electric loading is beyond magnetic loading by increase of input-current. So, we need to analyze the demagnetization phenomenon.

Switching Overvoltage Characteristics of <formula formulatype="inline"><tex Notation="TeX">$\pm $</tex></formula>1100-kV UHVDC Converter Station

The present study analyzed the characteristics of switching overvoltage, and discussed in detail the main influencing factors and worst-case conditions of switching overvoltage in the ±1100-kV ultra-high-voltage direct-current (UHVDC) converter station. The results showed that ac bus overvoltage was produced by oscillation, and would not be a threat to the equipment in the converter station. The results also showed there were two cases for overvoltage on related valves. In the first case, the valve overvoltage was on converter valves in the upper three-pulse group of the 12-pulse converter, and was caused by the voltage difference between the dc line and ac bus at the valve side under a specific fault. In the second case, the overvoltage was on other valves, and was caused by a phase-to-phase switching surge that penetrated into the valve hall. Other results were that overvoltage on the dc bus was mainly caused by the full reflection of the wave, and overvoltage on the neutral bus was caused by high-voltage sources, such as the dc source creating stress on the neutral bus under specific faults, or the freewheeling current of the metal return line and the smoothing reactors.

Current Zero Crossing Detection Circuit for Synchronous Rectification Model Buck Converter

In order to reduce the power consumption of the synchronous rectification model buck converter, a current zero crossing detection circuit is designed in this paper. The detection circuit determines the freewheeling current of the synchronous rectification power switch is zero or not by detecting the drain voltage of synchronous rectification power switch. Due to use transistors instead of resistors in the voltage conversion, the accuracy of the detection circuit is less affected by temperature and process corner. From the experimental results, the detection circuit can make accurate current zero crossing detection in different temperatures and process corners, and the detection circuit has strong robustness.

A Sensorless Starting Control Strategy for Switched Reluctance Motor Drives with Current Threshold

A new sensorless starting scheme for a three-phase switched reluctance motor is proposed in this article. To implement this scheme, the following was done. First, at standstill, the phase inductance subregion logic is developed for estimating the initial exciting phase. Next, at low-speed operation, by injecting high-frequency pulses in the non-excited phases, the current slope differences are estimated and compared for estimating commutation signals. Finally, in order to avoid the large negative torque generated by the freewheeling current, a modified sensorless control logic is developed by using a preset current threshold. The experimental results are presented and compared for verification. The results show that this scheme can start the switched reluctance motor without hesitation, and it is quite easy for implementation without adding any additional hardware and complex calculation.

A Pulse-Frequency-Modulated Full-Bridge DC/DC Converter With Series Boost Capacitor

The conventional zero-voltage switching phase-shift full-bridge (ZVS PSFB) converter has a large circulating energy during the freewheeling interval caused by the small duty cycle, which could increase the primary-side conduction losses, the turn-off switching losses of lagging-leg switches, and the current ripple through the output inductor. To overcome these problems, this paper proposes a new pulse-frequency-modulated full-bridge direct-current (dc)/dc converter with a series boost capacitor (SBC). The proposed converter controls the output voltage by varying the voltage across the SBC according to the switching frequency and has no freewheeling interval due to a 50% fixed duty operation. As a result, since its freewheeling current is eliminated, the conduction losses can be considerably reduced, as compared with those of the conventional ZVS PSFB converter. Moreover, the ZVS of all power switches cannot only be ensured along wide load ranges, but the current ripple through the output inductor can be also significantly reduced. Therefore, it has very desirable merits such as high efficiency, small output inductor, and improved heat generation. Operational principles, theoretical analysis, and design considerations are presented. To confirm the operation, the validity, and the features of the proposed converter, experimental results from a prototype that is 400-12 V/100 A are presented.

0 ~ 100 % 시비율을 갖는 새로운 모드 가변형 비대칭 풀 브리지 DC/DC 컨버터

In this paper, a new mode changeable asymmetric full bridge dc/dc converter is proposed to solve the freewheeling current problem of the conventional zero voltage switching(ZVS) phase shift full bridge(PSFB) dc/dc converter of low output voltage and high output current applications. The proposed converter is operated as an asymmetric full bridge converter when the duty cycle is less than 50% and active clamp full bridge converter when the duty cycle is greater than 50%. As a result, since its freewheeling current is eliminated, the conduction loss is lower than that of the conventional ZVS PSFB dc/dc converter. Moreover, ZVS of all power switches can be ensured along a wide load ranges and output current ripple is very small. Therefore, high efficiency of the proposed converter can be achieved. Especially since its operation mode is changed to the active clamp full bridge converter during hold up time and can be operated with 50~100% duty ratio, it can produce the stable output voltage along wide input voltage range. The operational principles, theoretical analysis and design considerations are presented. To confirm the operation, validity and features of the proposed converter, experimental results from a 1.2kW() prototype are presented.

A Current-Controlled Tristate Boost Converter With Improved Performance Through RHP Zero Elimination

A novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP), and improves the dynamic performance. The tristate boost converter contains an additional switch across the inductor. Within a clock cycle, the inductor current first rises during the on interval of the main switch, then falls during the off or capacitor charging interval, and finally, remains almost constant during the freewheeling interval when the additional switch is turned on. In the proposed controller, the peak value of the inductor current is controlled by peak current mode control using an outer voltage feedback loop, whereas the freewheeling current is controlled by the input voltage and the reference voltage feedforward path. Applying both feedback as well as feedforward control on the inductor current significantly improves the output voltage regulation, audio susceptibility, and transient responses. We show that the RHP zero is completely eliminated from the closed-loop control-to-output transfer function. This results in a very large bandwidth, and hence a superior dynamic performance. The latter is established by comparison with the voltage-mode- and current-mode-controlled classical boost converters that suffer from the RHP zero problem, as well as with other tristate boost converter control techniques like the constant charging interval and dual mode control, recently proposed in the literature. Significant superiority of the proposed scheme is established both through simulation and experimentation.

Load-Independent Control of Switching DC-DC Converters With Freewheeling Current Feedback

A new control scheme of freewheeling current control is proposed for switching DC-DC converters. The output voltage is regulated by a comparator operation, and in the main current loop, the freewheeling current is feedback-controlled to a reference level in average. The converter control loop is no longer dependent on the values of the inductor, output capacitor, or the load equivalent resistance. The design of a loop compensator is therefore greatly simplified and the loop response can be very fast approaching that of a hysteresis converter. As an example, a single-inductor bipolar-output DC-DC converter with the proposed freewheeling current control is implemented in a 0.5 mum BiCMOS process. The converter has one positive output of 4 V and one negative output of -4.8 V. A maximum efficiency of 81% is achieved at a total output power of 250 mW with a switching frequency of 800 kHz.

A Simple and Highly Efficient Energy Recovery Circuit for a Plasma Display Panel (PDP)

A simple and highly efficient energy recovery circuit (ERC) for a plasma display panel (PDP) is proposed. The main concept of the proposed circuit is the use of the current source type to charge and discharge the panel. As a result, all H-bridge switches can achieve zero voltage switching and every auxiliary switch can also do zero current switching. Moreover, since the inductor current can compensate for the large gas-discharge current, current stress in the main H-bridge switches can be reduced. Although the current source type is used to recover energy in the PDP, there is also very low freewheeling current. This means that the proposed ERC has higher efficiency, a simpler structure, less mass, less cost, and lower electromagnetic interference than those of many prior circuits.