DC Bus Current Research Articles

Model-Free Bidirectional Synchronous Rectification Control Scheme for LLC-Based Energy Storage System in Electric-Vehicle Energy Router

LLC resonant converters have been widely used in electric-vehicle energy router (EVER) as part of energy storage (ES) system, resulting in the increased demand for bidirectional synchronous rectification (SR) control. However, conventional bidirectional SR schemes are respectively limited by high cost of current sensing, difficulty of high voltage sensing, narrow operating range or high computational burden, especially for EVER. To deal with this problem, this paper proposes a model-free bidirectional SR control scheme for LLC-based ES system in EVER. Firstly, a novel SR tuning principle based on Kirchhoff’s law and phase relationship between inverter control signal and rectifier-side current is proposed. It no longer needs to calculate complicated models. Based on this principle, SR control signals in both forward and reverse modes are tuned by known signals available from main controller in ES system. To this end, no additional sensing component is required and the cost of SR is reduced. Meanwhile, an adaptive DC bus current compensation strategy is designed. It can guarantee high SR accuracy in reverse mode without sensing DC bus current. Moreover, an analog-digital mixed implementation is provided in which signal computation is performed by analog circuit. With these effects, the proposed scheme can achieve bidirectional SR control effectively over a wide operating range with low computational burden on controller. A 400-V/36-V 1-kW bidirectional LLC prototype is built to verify the proposed scheme.

Topologies and Operations of Hybrid-Type DC–DC Converters Interfacing DC-Current Bus and DC-Voltage Bus

Along with the application of current source converter (CSC), there will be more and more dc-current bus (DCB) for supporting power conversion. The DCB usually provides a common current, and the bidirectional voltage is employed to realize the bidirectional power transmission. In current power system, the dc-voltage bus (DVB) is most widely used DC terminal. Then, it will be foreseeable that topologies which can connect the DCB and the DVB will be urgently needed in the future grid system, such as the dc grid and electric vehicle. However, to connect these two dc terminals, the middle ac power stage is usually required since the power transfer characteristics of these two dc terminals are incompatible. So, the hybrid-type dc-dc converter concept interfacing the DCB and the DVB will be discussed, and the potential hybrid dc-dc converters without or with electric isolation are presented in this paper. Moreover, for these hybrid dc-dc converters, the basic principle for the modulation operation is proposed and analyzed. In addition, by using a non-isolated two-level bidirectional hybrid dc-dc converter and an isolated full-bridge hybrid dc-dc converter as examples, the modulation methods for bidirectional transferred power are illustrated in detail. Finally, simulation and experiment results of the isolated full-bridge hybrid dc-dc converter are used to verify the effectiveness of the proposed hybrid dc-dc converter idea and the corresponding modulation methods.

NOC-Based Multiple Low-Order Harmonic Currents Suppression Method

In a microgrid system, the dc bus contains a significant amount of undesired low-order harmonic currents (LHC) when multiple converters of various types and with nonlinear behavior are connected. To address the issue, this article proposes an iterative control strategy based on a negative-order capacitor (NOC) branch on dc bus. In the proposed method, the reference voltage of decoupling capacitors in the NOC circuit is obtained based on the dc bus current. The voltage difference between the two decoupling capacitors is taken as the control objective, leaving little dc difference between the two capacitors and resulting in maximum LHC suppression ability. To refactor the reference voltage, a singularity points hunting strategy is proposed, helping to reduce the current spike. More importantly, the iterative control strategy is employed in the virtual current loop, decreasing steady-state error from device deviation or control deviation. Finally, an 800 W prototype is built to validate the effectiveness of the proposed method.

A Novel Methodology to Enhance the Smooth Running of the PM BLDC Motor Drive Using PWM-PWM Logic and Advance Angle Method

This paper addresses the active torque ripple compensation of a permanent magnet brushless direct-current motor (PMBLDC) drive with a new pulse width modulation (PWM) technique and advance angle method. Torque ripple is a well-known problem in BLDC motors which is produced by a discrepancy between the stator current and the back electromotive force (back-emf) waveforms. The advanced angle method proposed in this paper generates a maximum torque in the PM BLDC motor by decreasing the displacement between the phase voltage and phase current in proportion to the load. Further, a simple and comprehensive PWM-PWM logic is proposed in this paper to reduce the torque ripples. The test results show that the BLDC motor drive achieves good steady-state performance while maintaining a quick dynamic response. The performance of the PWM-PWM logic and advance angle method, have been tested and compared with the practical results for the characteristics of DC bus voltage, DC bus current, electromagnetic torque, shaft torque, mechanical torque, phase voltage, phase current and PWM signal.

EVALUATION OF ELECTROMAGNETIC FIELDS IN HUMAN BODY EXPOSED TO INVERTER OF PURE ELECTRIC VEHICLE.

On the basis of the basic principle of electromagnetic dosimetry, the paper studies the electromagnetic exposure of a passenger's body to a compound electromagnetic field caused by the combined action of DC and AC bus currents of a pure electric vehicle inverter. By building an electromagnetic model of a pure electric vehicle body, adult human body and inverter, the finite element method is used to calculate the magnetic induction intensity(|B|), induced electric field intensity(|E|) and induced current density(|J|) of the compound electromagnetic field to the human trunk and central nervous system in the driver and front seat passenger. The numerical results are compared with the exposure limits defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The fields are well below the safe exposure limits defined by ICNIRP.

Minimum DC Voltage Ripple Switching Sequence Elicitation for Dual Inverter Through AC Load Error Volt-Sec Computation

In voltage source inverters (VSI), the output voltage is synthesized in an average sense using pulsewidth modulation (PWM) techniques. In space vector PWM techniques, the average realization of the space vector using volt-sec balance results in an instantaneous error that influences the dc bus current. The instantaneous ac load error voltage maps onto the dc bus derive the dc bus current ripple signatures that would be useful to size the dc capacitor. Exploiting concept of instantaneous mapping of ac error voltage onto the dc bus through power factor axis coordinates, in this work, the unprecedented dc ripple voltage computational method is presented. The established synchronous power factor reference frame ensures accurate mapping of ac error voltage onto the dc bus and makes the computational method independent of sensing actual ac load current unlike conventional methods. With the eliminated actual load current dependence, the proposed model can predict the minimum dc voltage ripple yield switching sequence for VSIs at different loading conditions. The efficacy of the proposed model in terms of optimum switching sequence elicitation is demonstrated on the dual inverter configuration experimentally considering the inflated switching stress due to two inverter's switching.

Series Arc Fault Detection of Grid-Connected PV System via SVD Denoising and IEWT-TWSVM

Series arc fault (SAF) is one of the most harmful faults during the operation of photovoltaic (PV) systems. It is a challenging task to find SAFs promptly for avoiding the PV fire. Aiming at the SAFs under different operating conditions, a novel detection algorithm by combining the Hankel singular value decomposition (Hankel-SVD) denoising method and the improved empirical wavelet transform–twin support vector machine (IEWT-TWSVM) is proposed. The Hankel-SVD algorithm is used to denoise the dc-bus current, which alleviates the influence of switching frequency and irrelevant background noise effectively. Then, the denoised current is decomposed by the IEWT, and the composite multiscale permutation entropy of each frequency band is input into the TWSVM classifier of the salp swarm optimization for completing the fault detection. The proposed algorithm not only can detect SAFs at various fault locations, but also resist dynamic shading, inverter startup, strong wind, and other interference phenomena. Moreover, the detection performance due to the arc transient process, a long-line fault, a single string array fault, a multiply string array fault, and different sampling rates of this model is verified in this study, and the corresponding results are relatively ideal. Experimental results show that the detection accuracy of the proposed method is as high as 98.10% for the measured data, which is more superior than other methods, such as wavelet decomposition, empirical mode decomposition, statistics methods including mean, standard deviation, and entropy.

X-Type Current Source Converters

In this article, a novel topology generalization of a current source converter (CSC) that allows controlling of multiple single-phase ac converters independently sharing the same dc-bus, with the advantage of having a reduced number of conducting switches and a lower dc-bus current, is presented. A conventional n-output/port single-phase CSC that uses the same dc-bus needs to have n H-bridge converters connected in series, which means that it always has 2 n conducting switches. The new topology allows generating any n ac output currents always having only (n+1) conducting switches in a switching period. This represents (1-1/n)·50% less conduction losses when compared with the equivalent conventional multiport single-phase CSC. A scalar pulsewidth modulation to control the converters with switching optimization and its generalization is also presented. Details of topology, control strategy, and modulation are presented. Simulation and experimental results are provided to validate the theoretical approach.

Analysis and design of a multi‐channel constant current LED driver based on DC current bus distributed power system structure

The colourful light emitting diode (LED) strings require the corresponding driver to achieve independent control of each output current in the applications of RGB mixed colour LED lighting, LED projection etc. For this purpose, a multi-channel constant current LED driver based on DC current bus distributed power system structure is proposed and analysed here, which is composed of a source converter and several load converters as needed. The source converter adopts the flyback converter to realise power factor correction, electrical isolation, and the load converter adopts the current-type buck converter to realise independent control of the corresponding output current. A 60 W experimental prototype for 42.8 V/0.35 A, 40 V/0.5 A, 35.7 V/0.7 A three outputs with the universal input voltages 90–264 V is designed and implemented, and the experimental results are presented to verify the correctness of the theory analysis.

Estimation of multiphase currents using DC bus current and switching state

AbstractThe voltage of solar cell strings can be controlled in residential photovoltaic systems using a multiphase convertor. However, multiphase convertors require a few current sensors. The authors examined how to reduce the current sensor for each phase of a multiphase convertor. This paper presents the analysis of a multiphase convertor based on DC bus current, phase currents, and switching state, and it proposes an estimation method for multiphase currents. The estimation method can be implemented with constant sampling frequency. Experimental results demonstrate the validity of the estimation method of multiphase currents for current‐controlled three‐phase convertor.

Synchronized Switching Modulation to Reduce the DC-Link Current in SRM Drives

Switched Reluctance Machines (SRM) are emerging as a possible alternative in terms of cost and supply stability to rare earth based electric vehicle traction systems. However, because of the huge amounts of energy stored and transferred back and forth between the DC source and the SRM, large DC-link capacitors must be used as buffers, which increases overall costs and size. This paper proposes a novel modulation technique which forces the exchange of energy between phases while decreasing the energy transfer between the DC bus and the SRM. This means lower DC bus currents (capacitor size and cost reduction) and lower Joule-effect conduction losses (better efficiency). The proposed modulation has been validated experimentally in a test bench and compared with the conventional torque-sharing function.

Estimation of Multi-Phase Currents Using DC Bus Current and Switching State

The voltage of solar cell strings can be controlled in residential photovoltaic systems using a multi-phase convertor. How-ever, multi-phase convertors require a few current sensors. The authors examined how to reduce the current sensor for each phase of a multi-phase convertor. This paper presents the analysis of a multi-phase convertor based on DC bus current, phase currents, and switching state, and it proposes an estimation method for multi-phase currents. The estimation method can be implemented with constant sampling frequency. Experimental results demonstrate the validity of the estimation method of multi-phase currents for current-controlled three-phase convertor.

Phase Current Digital Analysis of Power Converter for Freewheeling Diode Fault Diagnosis on Switched Reluctance Motor Drive

Power converter is critical but prone to be failure in switched reluctance motor (SRM) drives. The open- and short-circuit fault characteristics of freewheeling diode in asymmetric bridge power converter are analyzed in details. Based on logic judgment, four online fault diagnostic methods with digital phase current analysis of power converter are proposed in this paper. The fault features are extracted by analyzing the relationship between chopping signal and the current information from some special positions. The four fault diagnostic methods are carried out according to the current obtained by detecting dc bus current and the lower freewheeling bus current, the chopped bus current, the upper excitation bus current and lower freewheeling bus current, the lower excitation bus current, and dc bus current, respectively. Comparisons between the four diagnostic methods are conducted. Simulations and experiments on a 12/8 SRM validate the effectiveness of the proposed methods.

DC current bus distributed power system and its stability analysis

DC distributed power systems (DPSs) have attained much attention because of its characteristics of high efficiency, high power density and flexible configuration. However, when converters are interconnected in a system, adverse interactions may occur due to the converter sensitivity to the external impedance, these interactions may degrade converters transient performance or cause stability issues. Currently, research mainly focuses on DPS with a DC voltage bus, including stability analysis and approaches to improve system stability. This study is to establish stability criteria for DPS with a DC current bus. Firstly, basic current type DC/DC converters and their small signal models are introduced. Then, the current bus DPS is derived, discussed, and the stability criteria are obtained by using two-port small signal model. The proposed criteria are verified by comparing the results of theoretical calculations and simulations. Finally, an experimental prototype is built to validate the theoretical analysis and simulation.

Design, analysis, and testing of PP‐IGBT‐based submodule stack for the MMC VSC HVDC with 3000 A DC bus current

Design, analysis, and testing of PP‐IGBT‐based submodule stack for the MMC VSC HVDC with 3000 A DC bus current

Minimization of DC-Bus Current Ripple in Modular Multilevel Converter Under Unbalanced Conditions

In a modular multilevel converter (MMC), the zero-sequence currents at twice the fundamental frequency and its multiples flow through the dc bus and cause dc-bus power fluctuations during unbalanced conditions. These fluctuations appear in dc-bus current, considering that the dc-bus voltage is stiff. In this paper, a model-predictive control is proposed to minimize the ripple in dc-bus current. The proposed approach takes the advantage of internally generated zero-sequence voltage to mitigate the zero-sequence current during unbalanced conditions. To implement the proposed approach, a generalized mathematical model of the MMC, which includes the zero-sequence voltage, is presented. The performance of the proposed approach is verified through MATLAB/Simulink simulations on a 4.16-kV/5-MW system and dSPACE/DS1103-based experiments on a 208-V/3-kW laboratory prototype.

Improving the Dynamic Stiffness in a Self-Sensing BLDC Machine Drive Using Estimated Load Torque Feedforward

This paper presents a load torque estimation method for self-sensing brushless dc drives. Torque ripples in brushless dc machines can be reduced using load torque information. This method uses the terminal voltage, the virtual neutral point voltage, and the dc bus current of the machine. The algorithm uses the variation of successive back electromotive force (back EMF) samples to estimate the rotor speed. The rotor position is estimated by defining an intermediate function of estimated speed and back EMF samples. An estimate of acceleration is used to estimate load torque. The load torque information is used for increasing the dynamic stiffness of the drive. The mathematical background is given and discussed, and the simulations and the experimental results prove the performance of the proposed method.

Combinational-Logic-Based Traction Inverter Fault Diagnosis

This paper presents a combinational-logic-based approach for identifying faults that could occur in the drivetrain of an electric vehicle (EV). A real-time simulation model of an EV is used to study the behavior of available sensor signals and control commands, with specific measured quantities, during vehicle operation. Those quantities could be, but are not limited to, mean values of the phase currents, DC bus current, traction motor speed (if available), in addition to control command quantities. Focus is given to these quantities which are abundant in vehicle inverters and controllers for no added sensing costs. Those quantities carry information of offsets and disturbances that could occur under faulty operating conditions compared to nominal operation, and are thus observed and studied under these conditions. Using such information, a method is developed using simple combinational logic and thresholds to diagnose a fault occurring at any time during a vehicle drive cycle. By combining features of measured quantities that behave similarly irrespective of when the fault occurs during a driving cycle, the proposed method is fault-time-insensitive. The proposed method is presented and validated by real-time simulations to capture over 20 different faults injected at different drive cycle times and in different drivetrain components-electric machine, inverter, transmission, and sensors. Results show that the proposed method is able to robustly and successfully diagnose different faults irrespective of when would they occur.

Firing thyristors with negative firing angle using multilevel current reinjection concept: an experimental evaluation

Thyristor based multilevel current reinjection (MLCR) current source converter (CSC) provides self-commutation capability to thyristors. It also has high quality line current waveform by accurately shaping the DC bus current using an auxiliary reinjection bridge. However the theoretical and PSCAD/ETDC simulation analysis do not take into account the inevitable stray capacitances and inductances which may influence the thyristor turn-on/off and the simulation switching model may not represent the switching characteristics of the main bridge thyristors fully or accurately. Questions have been raised about the ability to achieve self-commutation with thyristors and the possibility of operating thyristors with negative firing angles. Therefore, it is necessary to experimentally verify whether neglecting the real-world artefacts actually impedes the performance of thyristor based MLCR CSC. The experimental results presented in this paper prove that the auxiliary reinjection circuit can force the thyristor to commutate independently from their respective line-to-line voltages and thyristor converter can operate with a negative firing angle.

Regenerative Braking System of Electric Vehicle Driven by Brushless DC Motor

Regenerative braking can improve energy usage efficiency and can prolong the driving distance of electric vehicles (EVs). A creative regenerative braking system (RBS) is presented in this paper. The RBS is adapted to brushless dc (BLDC) motor, and it emphasizes on the distribution of the braking force, as well as BLDC motor control. In this paper, BLDC motor control utilizes the traditional proportional-integral-derivative (PID) control, and the distribution of braking force adopts fuzzy logic control. Because the fuzzy reasoning is slower than PID control, the braking torque can be real-time controlled by PID control. In comparison to other solutions, the new solution has better performance in regard to realization, robustness, and efficiency. Then, this paper presents the simulation results by analyzing the battery state of charge, braking force, and dc bus current under the environment of MATLAB and Simulink. The simulation results show that the fuzzy logic and PID control can realize the regenerative braking and can prolong the driving distance of EVs under the condition of ensuring braking quality. At last, it is verified that the proposed method is realizable for practical implementation.