Search

This paper presents a concept of a power module with multiple series-connected power devices controlled by fully digital active gate drivers. The performance of series-connected power devices with lower voltage ratings is expected to be higher than the case of using only one device with higher voltage ratings. The required voltage balance of each power device to prevent an overvoltage issue can be achieved by a fine adjustment of the switching speed using the active gate control. As a first design example, a prototype module configured mainly by two series Si-MOSFETs, active gate drive circuits, and a fully digital controller was designed and developed. It was experimentally verified that suitable active gate control can realize the voltage balance in two series-connected MOSFETs under continuous operation.

This paper proposes a gate-oxide Time-Dependent Dielectric Breakdown (TDDB) evaluation system for SiC power devices under switching operation conditions. A constant voltage High-Temperature Gate Bias (HTGB) test is often used for long-term reliability test of the gate-oxide TDDB of power devices. However, the test condition is different from an actual operation condition. In this paper, a TDDB evaluation circuit that can perform the gate-oxide HTGB test under the operating conditions of the power conversion circuit is described. Using the proposed test circuit, the TDDB evaluation of 1.2 kV Silicon Carbide (SiC) Metal-Oxide-Semiconductor-Field-Effect Transistors (MOSFETs) under switching conditions were performed.

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.

This paper presents the reduction methods of conductive noise applied to Power Factor Correction (PFC) circuit. This is to generate a voltage of the opposite polarity simultaneously with the switching operations, and to inject a compensation current for the leakage current. This paper proposes two noise-canceling methods which are a fixed wave compensation method and a switching waveform tracking method. The fixed wave compensation method is effective for reducing the average (AV) value of the conductive noise. On the other hand, the switching waveform tracking method is effective for reducing both the AV value and the quasi-peak (QP) value. The switching waveform tracking is realized by injecting a compensation current proportional to dv/dt in the switching operation by a current mirror circuit. The results of experiments on each method are reported.

Recently, wireless power transfer(WPT) systems for electrical vehicles in 85 kHz band have gained lots of attention as the charging method. However, human exposure is concerned due to the leakage magnetic field because WPT systems are installed in proximity to the human body. Therefore, it is required to evaluate the biological effects induced by the magnetic field through the experimental verification for mice. A magnetic field generator which consists of a single-phase inverter and an LC resonant circuit has been already proposed for evaluating the biological effects, and a magnetic field generator, that comprises dual voltage source inverter and dual air-core coil, has been also proposed. This paper discusses expanding exposure area for the magnetic field generator, that comprises dual air-core inductor which two inductors are arranged in proximity, to perform the exposure experiment for multiple subjects simultaneously. Analysis of impedance frequency characteristic is discussed by focusing on the mutual inductance of dual air-core inductor in case the circuit parameters of the RLC resonant circuit for each inverter are asymmetry. The magnetic field distributions of two inductor structures are presented, and it is confirmed that the proposed magnetic field generator can expand the magnetic intensity range compared with the conventional magnetic field generator. Moreover, the validity of impedance and inverter operation analyses for proposed circuit is confirmed through the experimental verification rated at 150 V.

This paper proposes a new gate control method for the digital active gate drivers, which are installed in a three-phase PWM inverter. The proposed method changes the control parameters of the digital active gate driver according to the instantaneous value of an ac current. This control method enables to shape the gate voltage so as to reduce the surge voltage and switching loss with the consideration of their dependency on the output current. This paper also proposes a new optimization platform for automatically adjusting the control parameters of the digital active gate driver with a three-phase PWM inverter. This method applies the searching parameters for only any duration in an ac current cycle and fixed parameters for the other duration. Thus this method can search the optimal gate drive pattern according to the instantaneous value of the ac current. The validity of the proposed gate control method and the optimization platform were evaluated by using a 5-kW three-phase PWM inverter with digital gate drive ICs. As a result, it is confirmed that the combination of the proposed gate control method and optimization platform can reduce the surge voltage by 23% compared to conventional gate drivers under the condition of the same power loss.

Electromagnetic interference (EMI) on wired communication systems caused by a switched-mode power supply is often remarkable in practice. The EMI undermines the performance of the communication and robust operation of the system. In this paper, a test system where a buck converter and a controller area network (CAN) communication system are integrated enables to measure noise waveforms and analyze the EMI mechanism in the time-domain. The simulation model of the system also performs verification of the mechanism. In the system, the DC bus cables connected to the converter are closely adjacent to the communication cables and they have electromagnetic couplings. Hence, when the converter generates a switching noise in the DC bus, an induced noise happens in the communication cable, which results in communication failure. Based on the EMI mechanism, a noise elimination method is developed and implemented to the CAN of the test system to prevent communication failure. The proposed method is feasible in the converter controller and it does not require additional hardware components to reduce the communication failure. Through experimental verification, the proposed method enables to reduce communication failure.

This paper discusses a three-phase isolated rectifier with integrated buck functionality, derived from an unfolding three-phase inverter and a 7-level forward converter. Its operating principle is based on current shaping and unfolding methods. The circuit consists of 10 diodes, 3 low-frequency bidirectional switches and 8 high-frequency switches. It operates as a current source converter and requires only 3 filter capacitors at the ac input and a dc filter inductor at the dc output. Parasitic inductances from the ac grid enable direct connection to the utility. This paper discusses the basic operating principle and control method of the proposed inverter. It proposes a new unsymmetrical modulation method that can reduce switching frequency while maintaining the accuracy of current sampling. Also, an active damping method is used to overcome intrinsic oscillation due to unfolding operation. Finally, experimental verification is carried out to confirm stable operation of the proposed three-phase isolated rectifier.

This paper proposes control method for initial charge of grid connection converters using leg short-circuits with a dc capacitor voltage feedback. The proposed method makes short-circuits of a fixed time duration based on the dc capacitor voltage. In the experiments, the proposed method exhibits smaller energy consumption in each short-circuits than the control using an adjusted timing and duration. As a result, the proposed method can increase the number of short-circuits without complexity and extend the lifetime of power converters employing the initial charge method.

An active gate driving is effective to solve the trade-off between the switching loss and the current/voltage overshoot of power transistors. The test cost in the conventional digital gate drivers with four variables, however, is high, because more than 2000 measurements are required to find an optimum gate driving vector out of 644 (~1.7 x 107) combinations [1]. To minimize the test cost, a stop-and-go gate drive with only one variable is proposed. The switching loss and the current/voltage overshoot in turn-on/off state of IGBT of the conventional gate drive [1] and the proposed stop-and-go gate drive are measured by using a 6-bit programmable digital gate driver IC across nine conditions including different load currents (20 A, 50 A, and 80 A) and temperatures (25 °C, 75 °C, and 125 °C), and they are compared. The performance degradation of the switching loss and the current/voltage overshoot in the proposed stop-and-go gate drive over the conventional gate drive with four variables [1] is less than 8 % and 25 % across the nine conditions in turn-on/off state respectively.

This paper presents a design procedure of a low noise switching waveform considering AC resistance both the laminated bus bar and terminal geometry. It is hard to calculate the AC resistance which increases depending on the frequency because of skin and proximity effect. Hence the relationship between laminated bus bar geometry and its AC resistance is visualized to realize the design of AC resistance. Besides, it is shown that the terminal geometry, where the capacitor and power devices are connected, affects AC resistance components. The damped oscillation waveform, which is one of the causes of electromagnetic noise, under switching operations will occur under high-speed switching operation. In this case, the oscillation frequency depends on the parasitic parameters of the converter circuit geometry, and it is normally over 10 MHz. This paper presents that AC resistance considering the bus bar and terminal geometry, and it makes damping factor larger than that of only DC resistance to suppress the damped oscillation level. In this paper damped oscillation of drain-source voltage of SiC-MOSFET is simulated and experimented using buck converter circuit, rated at 500 V and 30 A.

A gate drive circuit for power devices requires a signal and power transmission function. The wires of the gate drive circuit tend to increase in circuits depending on a number of power devices. This paper proposes a gate drive circuit using SAW devices which can transmit signal and power for the power devices, simultaneously. The experimental result using a buck converter circuit was conducted by using the SAW device.

This paper proposes and evaluates an active gate control method of switching waveform design with digital gate drivers for a practical full-bridge inverter equipped with additional dc-link capacitors. The full-bridge inverter employs 1700-V, 150-A IGBT power modules and has a practical circuit layout with additional capacitors. The experimental system has a capability of optimizing driving patterns for shaping the designed switching waveform. In experimental verification, active gate control can suppress the surge voltage from 70% to 10% with 30% lower switching loss in three different circuit layout of the proposed practical 50-kVA full-bridge inverter. As a result, this paper reveals that active gate control achieves reduction in effect of stray inductance and increases a freedom of the circuit layout in power converters.

A digital gate driver is effective to solve the trade-off between the switching loss and the current/voltage overshoot of power transistors. A load current and temperature dependent optimization of the gate driving vectors for the digital gate drivers, however, is required [13], because an optimum vector at a particular load current and temperature does not often work at different conditions. When sensors for the load current and/or temperature are not available, the digital gate drivers are not useful under load current and temperature variations. To solve the problem, robust gate driving vectors to load current and temperature variations for the digital gate drivers are proposed. To compare a conventional single-step gate drive and the proposed robust gate driving vectors, the switching loss and the current/voltage overshoot in turn-on/off state of IGBT are measured by using a 6-bit programmable digital gate driver IC across nine conditions including different load currents (20 A, 50 A, and 80 A) and temperatures (25 °C, 75 °C, and 125 °C). The performance of the switching loss and the current/voltage overshoot of the proposed robust vectors is improved by 2% to 11 % and 16 % to 29 % across the nine conditions in turn-on/off state, respectively, which indicates that the proposed robust vectors requiring no current and temperature sensors are a useful method for the digital gate drivers.

Digital active gate drive enables the adjustable driving level in a switching transient for power devices. In this way, it is able to manage switching performance. However, to apply active gate drive in an inverter circuit, the sinusoidal output current turns out a critical problem for the design of driving profile because of its dependency on the load current. This paper aims to validate the feasibility of the digital active gate drive circuit using optimal patterns to adapt to sinusoidal output current of an inverter circuit. Firstly, a look-up table of optimal switching pattern under a certain load current condition was built in advance. It is noted that in the previous work, the online optimization system for finding the optimal pattern has been proposed and it is able to complete the searching of optimal switching pattern in an efficient time. Next, the output current of an inverter has been regulated to a sinusoidal waveform. Based on the output current, the corresponding optimal patterns are referred from the look-up table. Compared to conventional constant driving waveform, the power loss has been successfully reduced by 7% with the full optimal look-up table applied.

This paper proposes a high-efficiency boost integrated three-phase PV inverter. The proposed inverter can reduce total number of switching and increase its efficiency. The 1.2-kW experimental verifications confirm the validity of the proposed inverter and exhibit a great loss reduction of approximately 60% compared to the conventional boost-converter and three-phase-inverter approach.

This paper proposes a new current source three-phase AC to AC converter based on current unfolding and active damping principles. The proposed converter consists of two bidirectional three-phase AC/DC converters connecting in a Back-To-Back (BTB) configuration. Each of them is similar to a bidirectional SWISS rectifier but operating in current source mode with current unfolding and active damping techniques and thus does not need to employ passive ac filter and damping resistor. Comparing to a conventional BTB current source three-phase converter, this approach requires a total of 32 switches but only eight of them are operated at high frequency, thus resulting in a significant reduction in switching losses. The other 24 switches only operate at low frequency, and therefore have negligible switching losses, long life-time and can be parallel easily to reduce conduction losses. As a result, the proposed converter is expected to deliver high efficiency at small volume. This paper discusses the basic operating principle and control method for the converter. Simulation study confirms stable operation of the proposed inverter during both transient and steady states.

Active gate driving techniques using fully digital circuits and ICs have been actively investigated in the past half-decade. It has been reported that they contribute to improve loss and overshoot voltage and current, simultaneously during switching transients. However, a major concern of the digital active gate driver is an increase in the number of input signals for a practical implementation. This paper presents a verification of a digital gate driver IC with variable 63-level drivability controlled by serial four-bit input signals to decrease the implementation size and cost. Experimental results in a half-bridge converter using Si-IGBT module prove that the proposed gate driver IC realizes the active gate control effectively as the same with the conventional IC with parallel inputs despite the reduced number of the input signals. It is demonstrated that the developed digital gate driver circuit contributes to reduce the number of the input signals and digital isolators by one-thirds, and footprint of the PCB by 20% compared with the conventional gate driver IC with parallel 12-bit signal inputs.

In power converter circuits, it is well known that a bus-bar structure affects both surge voltage and switching loss. The stray inductance and capacitance depending on bus-bar structure also can be one of the causes such as the oscillation waveform that induces EMI issues. This paper proposes a design procedure of an optimized bus bar structure taking AC resistance into consideration. Those parameters that have frequency characteristics can be analyzed by finite element method, and it is shown that the AC resistance of the bus bar has an ability to suppress the oscillation. The validation of simulation results are shown by comparing the simulation and experimental results using a buck chopper circuit with input voltage of 300 V and output current of 30 A. The surge voltage and oscillation current are evaluated by using the bus bar modeled as S-parameters. In addition, the gate resistor is inserted to suppress them so that this paper includes among the surge voltage, oscillation and the switching loss. It is shown that the optimal parameters of busbar structure and gate resistor can reduce the surge voltage and oscillation current.

IGBTs need to be immediately turned off when a short circuit occurs [1]. This paper discusses the optimized gate control in this emergency turn-off process. The optimized gate waveform minimizes the energy loss, hence the heat generation, while keeping the maximum collector-emitter voltage overshoot within a certain allowable value. The optimized waveform is found by theoretical analysis and is verified by measurements for the first time. Analytical expressions are derived for the optimized control, which explains well the experimental results. The optimized gate waveform is realized only by a digital gate driver (DGD)whose output drivability is programmable over 64 strength levels. The DGD decreases the energy loss by 22 % compared with the conventional resistor gate driver [2]–[4].

This paper proposes an improved initial-charge method for the de-capacitor in voltage source power converters. The proposed method makes multiple short-circuits in each leg by using power devices in the converter, which discharges the dc capacitor and suppresses its overvoltage due to the initial charge. Short time periods of short-circuit occur several times in each leg for reducing the power consumption in and peak junction temperature of power devices. The experimental verification using a 200-V, 5-kVA three-phase converter shows that the proposed method can reduce the power consumption by 6% and suppress the estimated peak temperature by 200 ° C. The experimental results exhibit a good overvoltage suppression capability of the proposed method without SiC-MOSFET degradation. As a result, the proposed method makes it possible to remove the initial charge circuit resulting in reduction in the size and cost of power converters.

Conventional power converter circuits include two types of current sensors, one for current control and the other for overcurrent protection. Recently, research has been conducted on current sensors intended to be integrated inside power modules. These sensors are supposed to protect a power device from overcurrent. In addition, power converter circuits must implement current sensors for ac-side current control. Normally, these current sensors are used independently; thus, two types of sensors are required. However, if the sensors for protection could also undertake current control, then the sensor for current control can be eliminated. The current waveform of power devices is in the form of pulsed waveforms. Thus, a sampling technique considering sensor position and synchronous sampling is necessary. This paper proposes a control procedure for output current using current sensors integrated inside the power modules. It is clear that the relationship between the sensor position and the sampling point for unipolar-modulated single-phase inverters. The validity of the proposed method is proved through an experiment with common current sensors installed in series with the power device. In addition, it should be considered that a practical current has the frequency characteristics, so the simulation including sensor characteristics was performed. Finally, the validity of a current control method is experimentally confirmed.

Aim: Development of a wireless power transfer (WPT) systems that uses an intermediate frequency (IF) range is currently under development for practical use. Among various WPT systems. the system for electric vehicles is expected to produce a particularly large output. Under these conditions, the exposure level to human bodies supposed to be increased. Thus, in this study, in order to investigate the nonthermal effect of the intermediate frequency band magnetic field in the 85 kHz band on health, after developing an exposure apparatus for the mouse, we carried out exposure to the mouse

Power converter circuits are becoming widespread, and higher-voltage and larger-current converter circuits are increasingly used in automotive and utility applications. In particular, research and development on silicon carbide(SiC) power devices are being actively pursued for achieving larger current ratings by connecting SiC power modules in parallel. However, a current imbalance phenomenon may occur in the parallel-connected power modules because of the difference in device characteristics and parasitic impedances. This paper proposes a practical current balancing method for parallel-connected power modules based on only circuit implementations. In addition, a laminated bus bar integrated magnetic material for current balancing in parallel-connected MOSFET modules is proposed based on the analysis results. The validity of the proposed method is clarified through experiments using SiC-MOSFET.

Due to significant issue of energy consumption and sharp power demand of information and computing systems in worldwide, the applications of DC micro-grid that can utilize renewable energy sources such as photovoltaic power and wind energy have been advanced. Consequently, a DC micro-grid should be upgraded to achieve high reliability in power distribution systems. For DC power distribution in a data center, power managements including power flow control and demand analysis are highly recommended. In this paper, a prototype of DC power distribution system is proposed using the triple active bridge (TAB) converter for data centers. Furthermore, the power management for distributed system uses the TAB converter for power flow control is introduced. Eventually, performance test of power management in high reliable system is verified by simulation, and the reliability analysis proofed the reliability of proposed system superior than the conventional power distribution systems.

A gate driving for power devices is the key technology to further improve switching characteristics of power converter circuit. With the help of digital gate driver IC, the enhancement on switching behavior of power devices can be achieved even under high-speed switching. In this paper, an optimization system to find the switching pattern of active gate drive control is proposed for an inverter circuit. A high-speed optimization system is built up to search the advantageous switching pattern which is able to reduce total switching loss of two power devices in the inverter circuit and constrain overshoot voltage in the meanwhile. The proposed online optimization is carried out and demonstrates its feasibility for the investigated inverter circuit, rated at 500 V with digital active gate drive.

Recently, with research and development of SiC power devices, 1.2-V SiC MOSFETs have become commercially available. Over 3.3-kV SiC-MOSFETs have also been developed; however, it is difficult to use those devices without any special applications. When the medium-voltage converter circuit is designed using commercial SiC-MOSFETs, the 1.2-kV SiC-MOSFETs have to be connected in series. However, the voltage sharing under turn-off operations may not be balanced because each characteristic of the MOSFET is different, and the propagation time delay of the gate drive circuit is also different. This paper proposes a voltage balancing control strategy for series-connected SiC MOSFETs under steady state and start-up conditions using digital control circuits. To compensate for voltage unbalance conditions, feedback control of each drain-source voltage of the MOSFET under the OFF-state is proposed. The control circuit is based on a digital circuit, where controlling the voltage balancing under any conditions can be achieved. Experimental results using a buck chopper circuit utilizing SiC MOSFETs rated at 1.2 kV are also presented.

This paper proposes a three-phase solar inverter with integrated boost function. The circuit operating principle is based on current unfolding and injection method. This approach requires only two high frequency switches for the boost function as well as shaping its output currents, thus leading to a significant reduction in switching losses. Other switches only operate at line frequency to unfold the output currents to sinusoidal three-phase currents, and thus can be optimized to reduce conduction losses. The proposed inverter therefore could deliver high efficiency. This paper discusses the basic operating principle and control method for the inverter. The paper proposes an active damping method to overcome intrinsic oscillation due to overlapping time in switching operation. It also shows that the inverter is capable of supplying reactive power up to a limit of 0.866 power factor. Stable operation of the proposed inverter is confirmed by both simulation and experiment.

In recent decade, the demand for power distribution system in data centers are significantly climbed, while the requirements for advanced power flow control for DC power distribution systems are in urge needed. This paper presents higher-reliability DC power distribution systems using a triple active bridge (TAB) converter that can be applied in a data center, and it will be shown a power flow control among the three DC power distribution systems. The TAB converter is composed of three DC/AC converters connected via a transformer, and has ability to transmit the power to arbitrary directions. This paper proposes DC power distribution systems for data center using the TAB converter for balancing the power from the voltage sources. The feature of this system has no batteries. Then, the power flow control with closed-loop feedback control and the load balancing control are explained for adjusting the unbalanced load condition in data centers. The simulation designed the operation of DC power distribution system using 380V TAB converter in data center, and the power flow control for the power distribution system. From these results, the performance of the power flow control is confirmed, while the functional behavior of proposed three DC power distribution systems using the TAB converter is proved.

Recently, high-speed switching circuits using SiC power modules have been developed for using the next-generation power converter circuits. The stray inductances inside the converter circuit caused by among DC capacitors, bus bars, and power module package are one of the most critical parameters, which influence not only the over-voltage but also the switching loss. This paper proposes a quantitative design procedure for the switching losses depending the stray inductances. This paper focuses on the effects of stray inductance on both the turn-on and turn-off losses, and the quantitative analyses are explained using a stray inductance scaling method. To verify the design procedure, experimental results rated at 500 V and 160 A are demonstrated using an all-SiC power module.

This paper proposes a bi-directional current detection circuit using current-transformers for bi-directional DC-DC converters. This current detection circuit consists of CT(Current transformer) and electric components. The features of the current sensor based on CT can detect a pulse current contain DC component without any magnetic saturation. This paper shows a circuit configuration of the bi-directional current sensor and the principle of detection error of this circuit is analyzed. The validity of this analysis is verified through experiment under the DC-DC converter rated at 1.4 kW.

This paper proposes a control method of initial charging of the dc-capacitor in voltage source power converters. The proposed method is suitable for the power converter equipped with a small dc capacitor and is capable of removing the initial charge circuit. The proposed method makes a leg short-circuit by using power devices in the power converter, which discharges the dc capacitor and suppresses its overvoltage due to the initial charge. The short-circuit operation is a short time period and is used one time in each leg for distributing the loss to each power devices. The experimental verification using a 200-V, 5-kVA three-phase converter shows that the proposed method can reduce the peak voltage of the dc capacitor from 520 V to 420 V. The experimental results exhibit a good capability of the proposed method of suppressing the overvoltage due to the initial charge without fatal damage to the power devices. As a result, the proposed method makes it possible to remove the initial charge circuit resulting in a reduction in the size and cost of power converters.