Showing papers presented at "International Power Electronics and Motion Control Conference in 2020"

Design and Optimization of SiC MOSFET Wire Bondless Power Modules

Abstract: The electrical and thermal parameters of the package are key factors in achieving superior performance of silicon carbide (SiC) devices. To optimize the characteristics of a SiC power module, evaluating the electro-thermal design is an essential step before fabrication. However, due to the complex interactions of the semiconductor devices, package parameters, and system, it is a challenge to evaluate the output performance considering the electro-thermal characteristics of various components. In this paper, an integrated electro-thermal design and optimization method is proposed. The relationship between the package layout and the electro-thermal performance was evaluated with a 1200 V, 200 A half-bridge wire bondless SiC MOSFET power module. The effectiveness of the proposed method was verified at the system and circuit level. Thus, an advanced wire bondless power module with collaborative optimized electrical and thermal performance has been designed.

Radiated EMI Reduction by Layout Improvement in Power Converters in Automotive Applications

Abstract: Power converter layout is a critical factor for the radiated EMI. Because the radiation excitation is generated by the power converter and it is significantly influenced by the layout. The power converter layout includes the component location and the PCB trace layout. This paper develops noise modeling techniques to reveal the mechanisms of the layout’s influences. And based on the modeling researches, layout improvement guidelines for reducing the radiated EMI are produced, including the component location improvement, and the PCB layout improvement. Experimental verifications including the semi-anechoic chamber testing are conducted on a buck-boost power converter and on a buck power converter in automotive applications.

Advancement of SiC High-frequency Power Conversion Systems for Medium-Voltage High-Power Applications

Abstract: High voltage (HV) silicon-carbide (SiC) MOSFET has multiple advantages over its silicon (Si) counterpart including lower losses, higher blocking voltage, and improved thermal performance. SiC-based high-frequency power conversion solutions start to penetrate into medium voltage (MV) high-power areas due to high-density and high-efficiency. However, faster SiC switching transitions in MV lead to electromagnetic emissions, insulation degradation, and system-integration challenges. This paper provides several examples of using SiC high-frequency power conversion solutions in medium-voltage high power areas to illustrate the challenges and recent advancements. SiC device in series for MV two-level converters, HV PD-free PCB bus structure, SiC solid-state transformers, and MV insulated auxiliary power supply system are discussed.

Control of Hybrid Modular Multilevel Converter and its Capacitor Voltage Balancing

Abstract: Hybrid Modular Multilevel Converter (HMMC) is a hybrid converter combined by Modular Multilevel Converter (MMC) and classic three-level PWM voltage source converter (VSC). Using extra IGBT stacks, HMMC generates a midpoint manually, which can reduce maximum arm voltage stress. Compared to traditional MMC, only half number of sub-module is required for HMMC under same voltage rating. In this way, smaller system volume and weight and higher power density could be achieved. However, its capacitor voltage balance control strategy was not studied in detail. In this paper, the arm voltage balancing scheme based on optimal circulating current is investigated and illustrated. The control target varies according to various arm connection during a fundamental frequency. The simulation and experimental results are also provided to verify the feasibility proposed method.

Comparative Study of Temperature Sensitive Electrical Parameters for Junction Temperature Monitoring in SiC MOSFET and Si IGBT

Abstract: Online monitoring of power device junction temperature is a viable technique to ensure reliable operation of mission critical power electronic converters. This paper presents a comprehensive study of major temperature sensitive electrical parameters (TSEPs) of SiC MOSFETs and compares them to those of Si IGBTs. These static and dynamic parameters include on-state resistance R on , threshold voltage V TH , turn-off delay time t d−off , miller plateau voltage V GP , and turn-on di/dt. The experimental results conclude that R on and turn-on di/dt are more suitable TSEPs for SiC MOSFET while V TH , t d−off , and V GP are more suitable for Si IGBT.

Suppressing EMI Noise to CAN Communication by Using Active Gate Driver

Abstract: Electromagnetic compatibility has been always a big concern in a system where power electronics converters and communication systems operate together. With the advent of wide bandgap power semiconductor devices, converter switching-speed and -frequency get increasing and converter electromagnetic interference (EMI) noise is as well. Hence, communication networks, such as controller area network (CAN), could be a significant EMI victim in such the system. This paper presents experimental studies on an EMI reduction approach using an active gate driver (AGD) for a buck converter that causes an EMI on a nearby CAN system. The AGD enables to control switching speed of the converter MOSFET and also changes a converter switching noise waveform. Accordingly, the converter switching noise can be adjustable for suppressing the EMI. Experimental verification shows that the AGD is effective in suppressing communication failure due to the converter switching noise.

A Family of Hybrid Step-up DC-DC Converters based on Switched-capacitor Converters

Abstract: Five common step-up switched-capacitor converter (SCC) topologies - Ladder, Dickson, Fibonacci, Series-parallel, Voltage Doubler- have limited voltage regulation ranges, and the maximum voltage gains are predetermined by the circuit configurations. In this paper, one active switch in the five common SCCs is replaced by a filter inductor to form a family of hybrid step-up DC-DC converters. Compared with the traditional SCCs, the new hybrid converters feature wide voltage regulation range and high step-up gain, which is determined by both circuit configuration and duty cycle. A hybrid converter based on 3X Ladder SCC was built and tested to verify the analysis.

A Wide Input Voltage Range LLC Converter with Multi-mode Operations

Abstract: In this paper, a novel LLC resonant converter with multi-mode operation rectifiers is proposed to regulate the wide low voltage range photovoltaic panel and to connect the panel to the high voltage DC bus. The proposed converter can operate in three modes of operation: as a voltage-doubler rectifier (VDR), as a voltage-tripler rectifier (VTR), and as a voltage fifthfolder rectifier (VFR). Therefore, the proposed converter covers a wide voltage range by automatically changing the rectifier structure. The three operation modes keep the switching frequency range close to the resonant frequency resulting in increased performance efficiency. The benefits of this topology include improved efficiency and a narrow switching frequency range. Moreover, zero-voltage-switching (ZVS) and zero-current-switching (ZCS) are achieved in all power MOSFETs and power diodes. A 250 W LLC resonant converter for wide input voltage was designed and simulated to verify the theoretical analysis and the circuit functionality.

A High Efficiency Three-level Active Neutral Point Clamped Inverter Using Hybrid Si/SiC Switches

Abstract: This paper presents a high efficiency three-level Active Neutral-point Clamped (ANPC) inverter topology employing Silicon (Si) IGBTs for low frequency switches and hybrid Silicon (Si) and Silicon Carbide (SiC) switches for high frequency switches. The proposed semiconductor device configuration reduces both conduction and switching losses of the inverter so that a high efficiency, 99.5% peak, is achieved. The efficiency of the proposed ANPC inverter system is investigated and compared with other ANPC inverter configurations for different switching frequency and power factor values using PLECS. The investigation results show that the proposed ANPC inverter topology has higher efficiency than other ANPC inverter topologies for wide range of switching frequency and load power factor values. The cost of the semiconductor devices for the proposed inverter system is also estimated using off-the-shelf component prices obtained from Digi-key website. The cost estimation shows that the proposed ANPC inverter system has a cost at par with its silicon counterpart. Furthermore, since the proposed inverter system can be operated at much higher switching frequency compared to a silicon based inverter system, the cost of the passive components will be much lower.

Comprehensive Evaluation of Power Quality for Microgrid Based on CRITIC Method

Abstract: Due to the existence of power electronic equipment and uncertain load in the power generation side and the user side, power quality has gotten a great deal of attention. How to reasonably evaluate various power quality indicators is one of the problems in microgrid power management. A method based on CRITIC (Criteria Importance Though Intercriteria Correlation) is proposed which is applied to power quality assessment in this paper. By determining the weight of each index, the method effectively identifies the power quality problems and accurately evaluates the severity of various power quality problems.

Overview of Model Predictive Control of Converters for Islanded AC Microgrids

Abstract: This paper presents an overview of the recent advances in the application of model predictive control (MPC) to the control of the primary and secondary tiers of islanded AC microgrids (MGs). At the primary level of an islanded AC MG, MPC offers the advantages of faster dynamics, maximum utility of bandwidth and more stable inverter DC-link voltage. The superior dynamic features of MPC also enhance MG secondary control as well. The study shows that MPC has found effective applications in voltage source converters for power sharing, power quality regulation as well as frequency, voltage and current control in centralized, decentralized and distributed MG topologies. The challenges and future trends of MPC’s relevance to the MGs for the future smart grid are also discussed. We have presented real-time hardware-in-the-loop test results of the MPC-based control of AC inverters in an islanded AC microgrid.

Common-Mode Voltage Reduction of Modular Multilevel Converter Based on Six-Segment Carrier Level Shifted Sinusoidal Pulse Width Modulation

Abstract: High frequency fluctuation in common-mode (CM) voltage of the modular multilevel converter (MMC) causes serious CM electromagnetic interference (EMI), which could damage the load motor and shorten its life. In this paper, a six-segment carrier level shifted sinusoidal pulse width modulation (S2CLS-SPWM) method is firstly proposed for MMC, in order to keep the CM voltage constant and reduce CM EMI. The operation principle of the S2CLS-SPWM is firstly introduced, then a 5-level MMC simulation platform is established based on MATLAB/Simulink. Finally, the correctness and effectiveness of the proposed S2CLS-SPWM is verified by the simulation results. This paper provides a new way for solving the CM EMI problem in the MMC.

Modular Multilevel Converter Sub-modules for HVDC Applications

Abstract: The flexibility offered to the modular multilevel converter (MMC) by its sub-module (SM) based structure has led to the development of multiple SM circuit configurations that provide a diverse range of functionalities. This paper provides a comprehensive and up-to-date overview of MMC SM configurations, identifying suitable SMs for HVDC systems and classifying them based on various properties aimed at high-level characteristics of each SM. By developing multiple MMC models with different SMs and considering practical aspects of converter operation in HVDC systems, the paper also provides a preliminary comparison of MMC losses across 27 different SMs.

Fictitious Power Based MRAS Observer for Sensorless Control of Stand-Alone Brushless Doubly-Fed Induction Generators

Abstract: The aim of this paper is to design a sensorless voltage control strategy based on model reference adaptive system (MRAS) for brushless doubly-fed induction generators (BDFIGs) in the ship shaft stand-alone power generation applications. The proposed method is based on the power winding (PW) field-oriented control and the functional quantity of control winding (CW) fictitious power. The proposed sensorless control system ensures the efficacy and simplicity due to the absence of the flux computation process. Comprehensive simulation and experimental results based on a wound-rotor BDFIG are presented, which validates the good dynamic performance during various operations for BDFIGs in stand-alone systems.

Model Predictive Control Based on State-Space Averaging Model for Three-Level Flying Capacitor Boost Converter with Constant Switching Frequency and Improved Dynamic Performance

Abstract: In this paper, a simple model predictive control (MPC) based on state space averaging model for three-level flying capacitor boost converter (FCBC) is presented. The proposed MPC with constant switching frequency is used as the inner loop controller to control the inductor current and flying capacitor voltage. A new outer loop control strategy for the output voltage is proposed to provide a suitable inductor current reference to improve the dynamic response of the output voltage. Compared with the previous control method for three-level FCBC, the proposed control method shows better dynamic performance. The proposed control method is demonstrated through simulations and experimental results.

Investigation and Reduction of a Low-Frequency EMI Noise of AC/DC Power Adapters with Diode Bridge as Input Rectifier

Abstract: For AC/DC power adapters with a diode bridge as the input rectifier, when the differential mode EMI filter is placed at DC bus instead of AC line, a low-frequency component can be observed in the measured EMI noise spectrum, and it tends to violate the conducted EMI standard. The mechanism of such a phenomenon is introduced and quantified, the analysis model is built up in the paper. Besides, the methods to reduce the low-frequency noise component are investigated and validated by experiments, such as applying an X-capacitor on AC line or using fast recovery diodes, ultra-fast recovery diodes, and qspeed diodes. Both simulations and experiments verify the analysis.

BESS-PV Integrated Islanded Operation of ST-based Meshed Hybrid Microgrid

Abstract: Smart transformer (ST) has emerged as a promising solution for interfacing energy sources into the electric grid. Due to increase in DC sources and loads in the distribution grid, hybrid grids have gained popularity where there is parallel existence of AC and DC subgrids. This paper proposes a battery energy storage system (BESS) and photovoltaic (PV) integrated three stage ST-based meshed hybrid microgrid. The proposed system operates low voltage (LV) side of microgrid in islanded mode. When islanding is necessary, whether due to faults or maintenance, the mode of operation of the BESS is changed from current controlled mode (CCM) to voltage controlled mode (VCM) to maintain the voltage at the ST LVDC link. This ensures that the LV grid along with all the distributed generation (DG) converters operate undisturbed. A power management strategy for an LV side islanded operation of the distribution grid is proposed. With the control of LVAC voltage, the BESS critical state of charge (SOC) information is communicated to the LVAC side loads for connection or disconnection. Moreover, in the proposed scheme, as the islanding is done at the MVAC grid, the issues of synchronization during re-closure do not arise for all DG converters.

A Decentralized Control Strategy with Output Voltage Deviation-Correction for Input-Series-Output-Parallel DC Transformer Based on Dual-Active-Bridge

Abstract: DC transformers with dual-active-bridge (DAB) as units are widely used in DC distribution network. Usually it adopts input-series-output-parallel (ISOP) structure. This paper presents a decentralized control strategy with output voltage deviation-correction for this configuration. Under decentralized control, each DAB unit is self-contained and no central controller is needed. It improves the system stability, flexibility and reduces the cost. However, the existing decentralized control strategy will cause a deviation between the output voltage and the reference. With the proposed control strategy, decentralized control is achieved and the deviation of the output voltage is almost eliminated. Even if the transmission power of the system changes, the output voltage will not deviate from the reference value. And the operation principle of decentralized control is also introduced. The design method of output voltage deviation-correction is included. Finally, the simulation results verify the effectiveness of the proposed control strategy.

Performance Evaluation of Different Freewheeling Device Implementations for SiC MOSFETs with Kelvin Source Connections

Abstract: This paper discusses the optimization of freewheeling device implementation for SiC MOSFET’s with kelvin source connections. Kelvin contacts permit improved switching speed by reducing error voltages resulting from unwanted current effects. However, Kelvin contacts can also permit the switching transient reverse recovery (RR) phenomenon to be more easily observed. The behavior of the body diode of SiC MOSFETs with Kelvin source connections will be different to that of traditional packages without Kelvin source connections. This paper aims to test whether the body diode of a SiC MOSFET is a limiting factor for high speed switching of MOSFET’s with Kelvin source connections. Two characterization platforms were developed to measure the pulse switching energy and continuous switching efficiency of a ‘phase leg’ SiC MOSFET’s stage with different freewheeling device implementation including SiC MOSFET body diode with and without anti-parallel Schottky Barrier Diodes (SBD). The switching energy and converter efficiency results are presented to quantify the benefits of adding antiparallel SBD on loss reduction and EMI noise mitigation for SiC MOSFETs with Kelvin source.

Torque Ripple Reduction of Consequent-pole Permanent Magnet Machine by Shaped Rotor

Abstract: In this paper, the sinusoidal + third (Sin+3rd) harmonic shaped PM is used to suppress the high torque ripple of consequent-pole machine (CPM). This paper will introduce the general development status of CPM machine and the research actuality of torque ripple of CPM machine. The parameters of conventional CPM machine and Sin+3rd shaped CPM machine will be optimized by 2D finite element analysis. Moreover, the optimal results of air-gap magnetic flux density, cogging torque, torque waveform of different machines will be compared and analyzed in this paper. The results show that the PMs adopting Sin+3rd shaping can reduce the torque ripple of CPM machine and further improve the utilization ratio of rare earth PM material.

Compensation of Nonlinearity of Inverter through Estimation of Dead Time Effect

Abstract: This paper proposes a method to compensate for the nonlinearity of an inverter through the estimation of the dead time effect of the inverter. The dead time effect varies with manufacturing tolerance of the inverter circuit itself and operating conditions such as conducting current, voltage, and temperature. And, for the accurate compensation of the nonlinearity, the effect of the dead time should be estimated in real-time. The effect to the control of the inverter has a strong dependency on PWM scheme because the dead time occurs only at the switching instant of the inverter, and the switching is solely decided by PWM scheme. The proposed method exploits the difference of dead time effect according to different PWM scheme. By comparing the effects with two different PWM schemes, namely Continuous PWM and Discontinuous PWM, the voltage error to a specific inverter caused by the dead time can be identified. Several experimental tests are carried out to verify the validity of the proposed method. The results reveal that the voltage error due to dead time can be identified in the range of 100 mV at 300 V DC link. It is equivalent to 30 ns resolution in dead time.

Multi-objective Optimization Control for Input-Series Output-Parallel Dual-Active-Bridge DC-DC Converter in EER Application

Abstract: For reducing backflow power and improving dynamic performance of the input-series output-parallel dual-active-bridge (ISOP-DAB) converter in the electric energy router application, a hybrid control strategy based on the extended-phase-shift (EPS) output voltage model predictive control and gradient descent algorithm (MPC-GDA) is proposed. Firstly, the backflow power models under single-phase-shift (SPS) and EPS control are established, and the output voltage state space averaging equation under EPS control is also derived. Then the output voltage model predictive control is obtained, and the gradient descent algorithm for backflow power optimization is proposed. Finally, the overall control block diagram of the ISOP-DAB based on MPC-GDA control is derived. The simulation models of ISOP-DAB under MPC-GDA and SPS control are built and compared. It is verified that the MPC-GDA control shows better dynamic response and backflow power optimization compared with the traditional SPS control.

High Performance Speed Sensorless Finite-Set Predictive Thrust Control of a Linear Induction Motor based on MRAS and Fuzzy Logic Controller

Abstract: An improved finite-set predictive thrust control (FSPTC) is proposed in this paper, in which the fuzzy logic control (FLC) is applied instead of PI control in both speed control loop and adaptation mechanism of the model reference adaptive system (MRAS) with a lower number of membership functions to reduce the computation time. The MRAS observer based on primary flux linkage is implemented to estimate the linear speed. The output of the FLC serves as the reference thrust of the FSPTC while as speed in the MRAS observer. The developed control targets are to improve the characteristics of the drive system, where a significant ripple reduction in thrust and primary flux linkage, fast dynamic response, and lower cost can be guaranteed. Comprehensive simulation results have demonstrated the effectiveness of the proposed method based on one arc induction machine with 3kW rated power.

Modular Three-phase Single-stage Isolated AC-DC Converter for Electrolytic Capacitor-less EV DC Charging

Abstract: This paper presents a three-phase AC-DC converter formed by three single-stage electrolytic capacitor-less isolated AC-DC modules. The parallel output connection of the three modules provides DC battery current despite the pulsating current of each module at twice the mains frequency. The two interleaved totem-pole circuits are switched at fixed 50% duty, resulting in a ripple-free sinusoidal grid current with very small filter inductors. The control is simple and easy to implement since the phase-shift angle is the only control variable. The proposed control is able to provide DC current under unbalanced conditions. ZVS turn-on of all switches is achieved in both directions of power flow. A 11kW prototype of the proposed converter achieved a volumetric power density of 5.5 kW/L (90.4 W/in3). The prototype demonstrates 96.3% peak efficiency and maintains relatively high efficiency over wide ranges of power and battery voltage.

Synergetic Control of a 3-Φ Buck-Boost Current DC-Link EV Charger Considering Wide Output Range and Irregular Mains Conditions

Abstract: A wide output voltage range EV charger employing a three-phase (3-Φ) buck-type current source rectifier (CSR)-stage and a series-connected boost-type DC/DC-stage is introduced. The system employs a novel control structure, enabling robust operation even under heavily unbalanced 3-Φ mains conditions. It is verified how the proposed concept achieves PFC operation while regulating the output voltage in a wide range, which requires both buck and boost functionality. This includes a synergetically combined control of the 3-Φ CSR input stage and of the subsequent DC/DC output stage. In this context, a variable DC-link current control strategy referred to as 2/3-PWM is implemented, which allows to switch only two out of the three phases of the CSR-stage. Moreover, seamless transitions between the different operating modes and modulation schemes are demonstrated for different output voltage regions. Finally, the performance of the proposed synergetic control structure is comprehensively validated with closed-loop circuit simulations, focusing on buck-boost operation and on irregular 3-Φ mains conditions, including harmonics distortion, phase loss (phase open-circuit or phase zero-voltage faults), and voltage spikes.

A Four-Phase Current-Fed DC-DC Converter for Wide Voltage Range Applications

Abstract: High power isolated bidirectional dc-dc converters with wide voltage range are attracting increasing attention in many applications. The bidirectional current-fed DC-DC converters are known to be suitable for wide voltage range application, compared to DAB based converters, due to reduced circulating current and current ripple. However, for wider voltage range application where the duty cycle becomes lower than 0.33 or higher than 0.66, power transfer capability of the existed three-phase current-fed converters is limited due to increased circulating current. In this paper, a four-phase current-fed push-pull DC-DC converter is proposed for wide voltage range applications, the duty cycle range can widely varies from 0.25 to 0.75 without increasing the circulating current. Also, the proposed converter reduces the current ripple and size of filter inductor, and current stress of the switch. Further, the concept of combined four-phase transformer is proposed for eliminating the DC-flux offset caused by DC current through each phase. Experimental results from a 15kW prototype of four-phase push-pull are provided to validate the proposed converter.

A Voltage-Droop-free Reactive Power Sharing Solution in Microgrids

Abstract: The proper active and reactive power sharing is one of the fundamental control targets for distributed generators in microgrids. Currently, the most common solution is to use the active power-frequency (P-f) and reactive power-voltage (Q-V) droop control. In this paper, a virtual impedance based reactive power sharing solution is proposed as an alternative to voltage droop for reactive power sharing among paralleled units in a microgrid. By adopting the new proposal, the active and reactive power sharing will be naturally less sensitive to the R/X ratio, while the reactive power sharing performance is as good as conventional voltage droop control. In addition to that, the two methods are compared to unveil the inner connection. In order to validate the effectiveness of the proposed method, comparative experiments are carried out and the experimental results are consistent with the analytical results.

Decoupled Average Current Balancing Method for Interleaved Buck Converters with Dual Closed-Loop Control

Abstract: Dual closed-loop feedback control is commonly used to regulate the output voltage of interleaved buck converters. Meanwhile, current balancing control is used to balance inductor currents between the sub-modules. However, the coupling of dual closed-loop and balancing loop will cause interaction between control loops and complicate the design of controller parameters. In this paper, a decoupled average current balancing method with parallel dual closed-loop control is proposed. Based on the small signal model of interleaved buck converters, the decoupling conditions of dual closed-loop and balancing loops are derived. Then, the decoupled average current balancing control is designed. The small-signal transfer functions show that proposed current balancing loops and dual closed-loop are decoupled. Therefore, the controller parameters of each control loop can be designed independently. Finally, the experimental results are presented to validate the effectiveness of the proposed control method.

Model Predictive Control of a Phase-Shifted Full-Bridge DC-DC Converter

Abstract: A DC-DC converter with current control is widely used in the charging system of electric vehicles and electrochemical processing, and the response speed is an important index to evaluate the converter performance. In this paper, a model predictive control method based on a current mode control (MPC-CMC) is proposed for a phase-shifted full-bridge (PSFB) DC-DC converter to improve the dynamic performance of the converter. Delay compensation and integral compensation are introduced to improve the control accuracy and response speed of the model predictive control. The simulation and experimental results verify that the proposed method can effectively improve the dynamic response speed of the converter and obtain good dynamic performance when the desired output current of the load steps up or down.

Power Profile Measurement and System Design Analysis for a Wearable Photovoltaic Application

Abstract: As wearable devices are gaining popularity for applications, like fitness trackers and health monitoring devices, an important aspect is how to most effectively power them. Solar photovoltaic (PV) power has great potential for powering wearable devices, but faces some challenges. The PV panels used in wearable applications will face different angles and capture different amounts of sunlight, which is challenging to model. To determine a realistic power profile for PV wearables, the power generated from each PV panel is measured for a variety of usage scenarios. A measurement device was developed that can simultaneously measure and log data of four identical PV panels used in a wearable bag application under realistic conditions. After data was collected, a modeling and fitting procedure was used to calculate the irradiance level on each PV panel. The resulting model was used to determine the PV profiles over time for the maximum power point (MPP) voltage, current, and power. These realistic profiles were then used to properly design, simulate, and compare three different converter architectures that transfer power from the wearable PV panels to the load.