Research Terms
This technique and apparatus can cancel the intrinsic Miller capacitance of MOSFETs, especially SiC MOSFETs, which results in significantly increased switching speed, significantly reduced crosstalk effect, significantly reduced switching power loss, and significantly reduced thermal stress. This can significantly improve SiC MOSFET performance, significantly reduce the failure rate, significantly improve reliability, and significantly increase power density. High-speed power semiconductors are important components of high-speed power modules in electric and hybrid vehicles aviation power electronics systems, renewable energy conversions, traction power electronics, and various mid- or high-power electronics applications, but are susceptible to damage and failure as a result of the crosstalk effect, higher thermal stress, and false triggering. Electric vehicle sales continue increasing and should account for 7 percent of the global vehicle fleet by 2030. Furthermore, renewable energy, traction power electronics, and other mid and high-power applications widely employ SiC MOSFETs in the next 5-10 years. As a result, SiC MOSFETs should have a $7.1 billion market share of power semiconductor devices and a CAGR of 16.1% by 2027.
By eliminating the crosstalk effect, increasing switching speed, and reducing switching power loss, for the mid- and high-power modules in electric vehicles and all other power electronics applications mentioned above, SiC MOSFETs can become more reliable and operate at higher frequencies for smaller size, lower cost, and lower weight. However, power module designers have attempted to eliminate the damaging factors with limited success in the past.
Researchers at the University of Florida have developed a method and apparatus to counteract the barriers by canceling Miller capacitance, eliminating the crosstalk effect, increasing switching speed, and reducing switching power loss of SiC MOSFETs. This allows for greater reliability, smaller thermal stress, and the ability to operate high-speed power modules at higher frequencies with smaller volumes.
Eliminates the crosstalk effect, increases the switching speed, and reduces the switching power loss in high-speed SiC power semiconductors important in electric and hybrid vehicles, more electric aircraft, renewable energy conversions, traction power electronics, and other mid- or high-power electronics applications
Counteracts the Miller effects by injecting a cancellation current, which has the same magnitude but inverse direction to the Miller current, to the gate of the SiC power modules. This negates the Miller effect and Miller plateau.
This grid tied cascaded H-bridge (CHB) multilevel AC/DC rectifier (converter) uses selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique to meet the harmonic standards for high power devices. Multilevel converters are used to give a high output power for medium voltage sources such as batteries or solar panels. In the industrial setting, CHB multilevel rectifiers are used in both motor and electric vehicle drives since they reduce stress and do not damage the motor, promoting longer life-times for motors. Currently, selective harmonic elimination-PWM (SHE-PWM) or selective harmonic mitigation-PWM (SHM-PWM) are the techniques used in CHB multilevel rectifiers to reduce harmonics, the frequent cause of power quality (e.g. overheating or misfiring) problems. The number of harmonics these techniques can eliminate is dependent on the switching frequency.
Researchers at the University of Florida have proposed the SHCM-PWM technique that can eliminate more orders of harmonics than SHE or SHM using the same number of switching frequencies. Doing this, the SHCM-PWM technique can meet the current harmonic requirements.
Selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique to optimize cascaded H-bridge multilevel rectifiers
Multilevel rectifiers are being increasingly used in electrical applications. This selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique optimizes their performance. It uses low switching frequencies for grid connected cascaded H-bridge multilevel rectifiers to meet harmonic requirements within an extended harmonic spectrum. Instead of using voltage references to calculate switching angles for rectifiers as in conventional SHE-PWM and SHM-PWM, current references can be used to compensate the current harmonics due to both grid voltage harmonics and rectifier input voltage harmonics. This technique can meet both harmonic and TDD limits with smaller coupling inductance compared to SHE-PWM and SHM-PWM, therefore reducing the cost and size of passive filters.
This common mode (CM) inductor design both reduces the near magnetic field couplings between components in electronic systems and attenuates differential-mode (DM) noise. Due to the demand for high power density in electronic systems, their components tend to sit close together increasing the chances of undesired near magnetic field couplings. These couplings can reduce the performance of a circuit or stop it from functioning altogether. To prevent this, smaller and denser electronic systems must be manufactured with internal shielding.
Researchers at the University of Florida have developed a two-cored inductor design with a lower near magnetic field radiation than conventional inductors, eliminating the need for shielding. This proposed inductor also has the added benefit of reducing more DM noise than conventional CM inductors with same size. When operating in high frequency range, the inductance of conventional CM inductors will decrease while the proposed CM inductor could maintain its high inductance and attenuate CM noise up to a higher frequency. It can be used in single-phase, three-phase, or multi-phase power electronics systems, as well as electromagnetic interference (EMI) filters and energy storage devices.
CM Inductor reduces risk of magnetic couplings and improves DM inductance in power electronic systems
This CM inductor design has two inductor cores, the smaller core positioned within the larger. Each core has two winding structures wrapped around each. These windings are symmetrical and in opposite directions to each other, allowing the coupling between them to outperform conventional inductor winding structures. The two cores, and small air gaps between them, provide reluctance paths for the DM magnetic flux. This means that the two-cored inductor has both small near magnetic field radiation and better DM inductance.
This circuit design based on four-quadrant modulation improves upon the main failing of both selective harmonic elimination/compensation (SHC/SHE), limited modulation index range. Conventional solutions that use SHC and SHE in power conversions to control undesired harmonics are restricted by this limited range. Because University of Florida researchers have found that the constraint of switching angle range is the most critical factor limiting the modulation index range, they have developed a design using four-quadrant modulation transforming transcendental equations to geometry-based diagrams, to significantly extend the modulation index range. This allows for broader industrial applications of SHC/SHE because it provides more efficient and controlled power conversion for systems that require high switching efficiency, control and current quality. Embodiments of this design can be applied to a wide range of devices and topologies.
A four-quadrant switching angle modulation technique for a larger modulation range in power conversion
A variety of electrical applications are increasingly using multilevel power. Selective harmonic elimination and compensation (SHC/SHE) can optimize performance of electronic devices by reducing unwanted harmonics. However, these techniques have a limited effective modulation index range, restricting their potential applications. By converting the transcendental equations into geometry-based diagrams, UF researchers have discovered that the crucial limiting factor is the constraint of the switching angle range. To remove this limitation, they have developed a design that uses four-quadrant modulation to extend the modulation index range. The four-quadrant design can determine switching angles without limitations, detect switching angles in undesired states, and transform them into desired states while leaving other angles alone. The improved control over the switching angles and lack of constraint increases the modulation index range, allowing SHC and SHE to be applied much more broadly.
These circuit designs use energy mitigation to improve the conventional sinusoidal pulse width modulation (SPWM). This technique can dampen both current harmonic and electromagnetic circuit noise. The need for shielding electromagnetic interference continues to grow as more electronic products are developed and the market projects it’s value to exceed $7 billion by year 2022. The generation of electromagnetic circuit noise, or electromagnetic interference (EMI) disturbs the components within electrical and mechanical devices, such as computer motor drives or power converters. Available technologies use a thin foil to coat components within the devices to prevent electromagnetic interference. However, this expensive tactic causes the device to overheat.
Researchers at the University of Florida have developed two complementary techniques that reduce harmonic and EMI noise as well as amplify voltage. Their simple designs allow either electrical or mechanical devices to achieve optimal performance.
Circuit designs use electromagnetic interference energy mitigation and sinusoidal pulse width modulation for harmonic and EMI noise suppression
These designs lessen electromagnetic circuit noise that interferes with the performance of devices. The mitigation technique limits the spread of electromagnetic interference in mechanical devices, including power converters, motor devices, and solar panels. Also, this technique amplifies the voltage of the transformers within devices, lowering current loss while powering them. The sinusoidal pulse with modulation (SPWM) technique suppresses the electromagnetic interference and harmonic noise in electrical devices such as a motor drive and an electric vehicle or train. This technique applies a DC offset to a sinusoidal modulation waveform to change the average duty cycle of a switching circuit, thereby reducing the total energy.
This multilevel, cascaded H-bridge (CHB) converter reduces DC current harmonic ripples, mitigating current variation in DC to AC power conversion, increasing battery lifetimes and stability of battery-powered circuits. Battery energy storage systems (BESSs) play an important role in power grids, renewable energies, smart grids, and electric vehicle charging stations. Accordingly, multilevel converters have widely been used in AC to DC current conversions for power grids. Multilevel converters can connect to battery energy storage systems to charge or discharge batteries or control the active or reactive power injected into the power grid. However, conventional multilevel converters have slightly inferior harmonic performances, causing significant drawbacks when used with power grids involving batteries. There is a need to develop a multilevel converter able to balance the DC harmonics with the AC side of a converter, meeting the requirements of the Institute of Electrical and Electronic Engineers (IEEE) 519 standard, and increasing converter efficiency.
Researchers at the University of Florida have developed a multilevel, cascaded H-bridge (CHB) converter to reduce harmonic discrepancies between the AC and DC cells. This results in increasing battery lifespans, eliminating the need for DC current sensors, reducing size requirements of passive filters, and stabilizing battery-powered circuits.
A cascaded H-bridge (CHB) converter balances and mitigates the current harmonic ripples in the DC to AC power conversion, increasing converter efficiency and battery lifespans
This multilevel, cascaded H-bridge (CHB) converter uses the AC current harmonics to control and reduce the current harmonic ripples on the DC side of the converter. This mitigates current variation in DC to AC power conversion. The model is a single-phase, grid-tied CHB converter, balancing and mitigating zero and even-order harmonics of the DC sides of the CHB. By doing this, the DC link voltage ripples are reduced without increasing the AC side filtering inductance of the converter. This capability confers additional flexibility in controlling the CHB converter and allows the converter to block fault currents, which arise from a short circuit between the positive and negative DC terminals.
This full bridge LLC resonant converter successfully reduces the common mode electromagnetic interference. Common mode electromagnetic interference is electrical noise that interferes with a circuit’s proper function. LLC resonant converters are used in a variety of applications, such as in TVs and computers. Electrical devices typically require passive filters to reduce electromagnetic interference, which makes them expensive and increases the device’s volume.
Researchers at the University of Florida have developed a full bridge LLC resonant converter that automatically dampens the amount of electromagnetic interference produced.
Full bridge LLC resonant converter diminishes random current signals innately to produce a quieter inductor within the circuit
Resonant converters are traditionally designed to receive input signals and then produce electric currents that are carried through the inductor. This process creates noise, which contributes to the noise interference already generated by the switch. Because noise is not isolated within the device, it interrupts functionality and can lead to fire or electrical shock. The arrangement of the capacitor and inductors in this full bridge LLC resonant converter produces a barrier containing the noise, preventing interference within the rest of the device. By lowering interference, the device is able to perform with a higher efficacy.
These compensation winding structures achieve balanced three-phase impedance on asymmetric E cores, widening the E core selection range for three-phase coupled inductors and transformers. Most U.S. commercial buildings use three-phase power applications of AC electric power generation, transmission and distribution because of its power density and flexibility. Three-phase power applications can supply more power without increasing the thickness of wires or provide the same power at a lower current, reducing costs for construction and energy. Voltage conversion is a fundamental component in proper electronic functionality. Likewise, inductors are essential in voltage conversion, being integral in the engineering of the voltage converter’s filter. Inductors have a wide range of applications and technological uses, and the inductor market is expected to reach $3.94 billion by 2022. Although inductors are fundamental to proper voltage conversion, certain challenges in inductor design remain. For example, a sudden increase in voltage can cause electronic noise in the voltage conversion process. This sudden voltage increase can ruin electronics and cause signal noise that interferes with the proper functioning of a device. Conventional inductor designs for three-phase power applications require EE or EI magnetic cores with the same cross section area on each limb. Sometimes three separated toroidal cores are adopted in three-phase inductor design that will largely increase the total volume of the three-phase inductor.
Researchers at the University of Florida have developed winding structures that when added to an asymmetric E core can achieve balance and quiet signal noise in the voltage conversion process by narrowing the range of incoming power to the inductor. This design broadens the types of E cores that can be used in three-phase power or three-phase transformer systems.
Winding design that increases range of E core selection for three-phase coupled inductors and transformers
This inductor design improves the voltage conversion process of electronic devices by providing a winding structure of the inducting coils. Inductors are widely used in design of voltage converter filters. Usually construction of these inductors involves separate magnetic cores; however, conventional three-phase coupled inductor design has a strict requirement on the shape of magnetic cores. The design is a winding structure that can apply to three-phase coupled inductors. By adding two additional compensation windings, the coupled inductor can achieve balanced three-phase impedance on an asymmetrical E core, providing protective measures against signal noise from voltage conversion. This structure also applies to three-phase transformer systems.
This quick-sampling test can easily detect an internal lithium-ion battery short circuit prior to operation, reducing the chance of damage to electronic devices. Lithium-ion batteries are high-energy, rechargeable batteries usable in several products, including electric vehicles, smartphones and laptops. However, these batteries occasionally suffer from internal short circuits (ISC), resulting in fires and presenting a critical safety issue. Additionally, current methods for detecting short circuits rely entirely on sensors which can report inaccurate readings if they are left operational for a long period of time.
Researchers at the University of Florida have developed a quick-sampling test which can quickly and accurately estimate the short-circuit resistance of lithium-ion batteries. Combining a resistor and inductor-based technique improves internal short-circuit detection, preventing complete battery failure.
Combined resistor and inductor-based detection circuits for internal short-circuit identification
Two detection circuits work to identify internal short circuits. In the resistor-based circuit, a test resistor and a switch connect in parallel with a battery load. A transient current travels through the first and second external battery terminals when the switch is turned on. This technique measures internal resistance and identifies short circuits. In the inductor-based circuit, a measurement resistor and an H-bridge comprised of an inductor and four switches lie adjacent to a battery. The top ends of the H-bridge connect to the battery's first terminal and the bottom ends connect to its second terminal. Once the two switches turn on, the measurement resistor records the transient current passing through and detects internal short circuits. The use of these two techniques can detect the internal short circuit in real-time operation of a battery.
These integrated inductor coils produce low overall magnetic field emissions, reducing the effects of electromagnetic interference in electronics. Power circuit designers consistently face the challenges of reducing electromagnetic interference and other sources of electronic noise. Electromagnetic interference caused by near-magnetic field coupling can potentially hinder the transfer of electrical energy, weaken the performance of electrical components, and generate unwanted current in sections of a circuit. Available methods to counteract electromagnetic interference include arranging passive filters formed by inductors and capacitors so that a reduced electromagnetic interference noise flows through the system. However, the performance of such practices is limited by unintended near-magnetic field couplings between the inductors and nearby circuits, counteracting the initial aim of the inductors.
Researchers at the University of Florida have developed an integrated inductor design that generates a weaker near-magnetic field while providing both the common mode and differential mode inductances, reducing electromagnetic interference and maintaining optimal conditions for proper circuit performance.
Integrated inductor coils that limit the magnetic noise in power converters for electronic devices such as cell phones, tablets or laptops
Inductance is the instance when an electrical conductor induces a potential difference with itself and nearby components. In an effort to reduce electromagnetic interference caused by near-magnetic field coupling, electrical engineers use shielding metals to limit the magnetic field within the circuit. This configuration of integrated inductors generate small leakage magnetic field without using any shielding materials. The configuration consists of a series of inductor coils wrapped around suture legs that results in a dampened near-magnetic field. By limiting the extent of magnetic noise among smaller distances, these integrated inductors allow developers to construct smaller and stronger electronic circuits for more powerful and compact devices.
This common mode electromagnetic interference (EMI) filter reduces the electromagnetic resonance interfering in DC/AC power converters. In modern power electronics, Gallium-Nitride (GaN) devices can operate at higher switching frequencies than conventional Si MOSFET devices. However, with the ever-increasing development of high-switching frequency and the high-power density of power electronics, electromagnetic interference (EMI) is a significant problem. In power-electronic applications such as power adapters and electric vehicles, a common-mode current is a dominant source of EMI radiation. Additionally, the high-power density layout of the GaN devices degrades the EMI filter performance. At high frequencies, DC/AC power conversions produce electromagnetic resonance, causing power conversion inefficiency or failure. While reducing the common mode currents flowing between transformer primary and secondary windings can suppress the EMI radiation, the high-frequency performance of the devices leaves much to desire. It is vital to investigate the couplings within converters in high power-density designs.
Researchers at the University of Florida have developed a common-mode electromagnetic interference (EMI) filter for reducing EMI radiation in power converters. This filter will enable DC/AC power conversions at higher frequencies, improving conversion efficiency and reliability.
Common mode filter reduces electromagnetic interference (EMI) in DC/AC power converts to enable performance at higher frequencies with improved reliability
This common mode electromagnetic filter completes DC/AC power conversions at higher frequencies with reduced electromagnetic resonance and, in turn, greater efficiency. When DC/AC power conversions occur at higher frequencies, they produce electromagnetic resonance and can cause conversion inefficiency or even failure. The filter has multiple sets of Y-capacitors, as opposed to one, and shielding for connecting to the primary ground and secondary ground nodes. The converter can be one or more of an isolated converter, LLC resonant power converter, flyback converter, forward converter, or push-pull converter.
This selective harmonic current mitigation pulse width modulation (SHCM-PWM) and phase-shifted pulse width modulation (PSPWM) hybrid increases the efficiency of converters during steady-state and transient conditions. This hybrid modulation is advantageous when using DC to DC power converters, which are used in many electronic devices, such as cell phones, laptops, or charging stations, and it can also maximize the energy harvest for photovoltaic systems and wind turbines. Both SHCM-PWM and PSPWM are used separately now, but each exhibits individual problems with modulation. SHCM-PWM has poor dynamic performance, due to a low number of switching transitions, and often has an inadequate power range. PSPWM has low efficiency because it requires high switching frequencies and requires passive filters to meet the power quality requirements.
Researchers at the University of Florida have developed a SHCM-PWM and PSPWM hybrid that alternates between the two modulations depending on whether the system is in steady-state or transient conditions.
Hybrid current modulation system that increases the efficiency of four-quadrant, grid-tied converters for use in electronics such as electrical vehicle charging stations, renewable energy harvesting, or HVDC and PET applications
This hybrid modulation technique combines SHCM-PWM and PSPWM to achieve high dynamic performance for four-quadrant grid-tied converters. This hybrid uses SHCM-PWM under steady-state and PSPWM under transient conditions. During steady state conditions SHCM-PWM increases the efficiency of the system, while PSPWM updates switching transitions several times in each fundamental cycle to achieve high dynamic response performance under transient conditions. A specifically designed controller switches between these two modulations. In order to process four-quadrant active and reactive power, the modulation index range of SHCM-PWM greatly extends by modifying the constraints of switching angles. The lowest number of switching transitions for PSPWM prevents a reduction in efficiency and performance of the indirect controller.
