Research Terms
Engineering Electrical Engineering
Keywords
Famu-Fsu College Of Engineering
A power inverter which can provide sinusoidal voltage or current is the key apparatus in the field of electrical machine drive and utility interface, such as in renewable energy generation systems and energy storage power conditioning systems. In order to achieve a higher power rating, each phase of the inverter may be constructed of paralleled phase legs. If two paralleled legs are connected to an output terminal by a magnetic coupling device, such as an "inter-phase transformer", or a "multi-winding autotransformer", or an "inter phase inductor", the output terminal of each phase will have a multilevel staircase waveform, which is closer to the desired sinusoidal waveform. Therefore, the inverter will require smaller magnetic components while still providing the benefit of higher dynamic response.
The technology developed provides a finite state machine (FSM) based modulation method for parallel multi-level inverters. Within this invention, a modulation waveform is fed into a comparator to compare with carrier waveforms. Then, a digitized ideal waveform is generated, and the digitized ideal waveform is fed into a finite state machine (FSM) module to generate a switching pattern for each switch of the parallel multi-level inverter.
The cascaded multilevel inverter is considered to be a promising alternative for the low-cost and high-efficiency photovoltaic (PV) systems. However, the current leakage issue, resulting from the stray capacitances between the PV panels and the earth, needs to be solved for the cascaded inverter to be reliably applied in PV application.
The proposed technologies solve the leakage current issue in PV cascaded multilevel inverter by using passive filters. It can retain the simple structure of the inverter and does not complicate the associated control system. The system is a photovoltaic cascaded inverter, including inverter modules, which have both an AC and a DC side. In addition, the system includes a common DC-side choke coupled to the DC-side of each of the inverter modules and a common mode AC-side choke coupled to the AC-side of each of the inverter modules.
This invention provides a phase-shifted square wave modulation method for isolated modular multi-level DC/DC (IM2DC) converters. In the present invention, one square wave based modulation waveform with the same frequency and magnitude is applied to each cell of an isolated modular multi-level DC/DC converter and compared with a triangular carrier waveform to generate the gate signals. With the phase-shifted angle of the carrier waves, higher equivalent switching frequency can be achieved. Both full-bridge (FB) and half-bridge (HB) cells are allowed as the single cell.
This technology can be implemented to reduce the DC inductor size due to higher equivalent switching frequency. In addition, the required capacitor energy can be reduced, which decreases the capacitor size since they are dedicated to smooth the high switching frequency ripples only. Moreover, a high efficient power transfer capability can be achieved with the square wave compared to conventional sinusoidal waveforms.
In addition, this invention proposes a novel phase-shifted square wave modulation technique aiming at reducing passive components and devices sizes for single-phase and three-phase IM2DC applications in HVDC/MVDC systems. In various embodiments a square wave based modulation waveform is applied to each cell of IM2DC and compared to the phase-shifted carrier waveforms to generate device gate signals. Thus, higher equivalent switching frequency will be achieved and square wave based arm and AC link waveforms will be generated. The power flow of IM2DC is controlled by a phase shift angle of the square modulation waveforms between HVS and LVS. Compared to the conventional phase-shift sinusoidal method, the converter cell capacitors can be reduced significantly since they are required to smooth out the high switching frequency ripple components only. In addition, lower TDR can be achieved due to the higher power transferring capability of square waves. Both proposed method and quasi-two-level modulation can achieve low TDR and small cell capacitor size, however, the present invention can allow smaller DC inductors due to the multi-cell phase-shifted characteristics.
In this invention, a novel single-phase single-stage grid-interactive inverter based on a discrete Fourier Transform Phase Locked Loop technique is developed to separate the real and reactive power between different energy sources/storages. The hybrid modulation technique and sophisticated power allocation strategy are developed for the power generation system to achieve wide range reactive power compensation and enhance energy conversion efficiency. One distributed energy source and two energy storages are interfaced to the inverter with three cascaded H -bridge cells used to investigate the performance of the proposed system. Different energy source/storages with wide voltage change range can be directly connected in the invention and the single-stage energy conversion can be implemented. The present invention can integrate distributed energy sources/storages in one cascaded inverter. Due to the absence of DC-DC converter, single-stage energy conversion can be achieved. The hybrid modulation technique and power allocation strategy corresponding to the proposed system are developed to achieve the wide range reactive power compensation, voltage boost function, and the optimized power management.
The proposed single-phase single-stage grid-interactive inverter is particularly suitable to meeting the increasing distributed power generation needs. It can facilitate to interface different distributed renewable energy sources or storages such as wind power, solar power, battery, fuel cell, Ultra-capacitor and so on. The switching loss will be decreased due to the cascaded structure and hybrid modulation technique.
In the present invention, different circuit-based implementations of stochastic anti-windup PI controllers are provided for a motor drive controller system. The designs can be implemented in a Field Programmable Gate Arrays (FPGA) device. The anti-windup PI controllers are implemented stochastically so as to enhance the computational capability of FPGA. The invention encompasses different circuit arrangements that implement distinct anti-windup algorithms for a digital PI speed controller. The anti-windup algorithms implemented by the circuit arrangements can significantly improve the control performance of variable-speed motor drives.
Compared with the existing technologies, the stochastic PI controller provides an efficient implementation approach that uses straightforward digital logic circuits but has the advantage of significantly reducing the circuit complexity. Therefore, the present invention notably improves the performance of the stochastic PI controller and saves digital resources in a motor drive control system. The immediate and/or future applications are motor drive controllers for induction motor systems, and more particularly, proportional-integral (PI) controllers. The use of the invention will increase the market of FPGA since the capability will be largely increased and the cost will be relatively reduced.
Two predictive-control based low-voltage ride-through methods for a grid-tied Inverter: a Finite-Control-Set Model-Predictive-Control or FCS-MPC based LVRT method, and a deadbeat control based LVRT method. Both methods can predict the grid voltage, so no voltage sensor is required. The control can operate with, or without, a phase-lock-loop. A significant cost and design complexity reduction on the grid-tied inverter is realized.
A voltage/current-sensing-less short-circuit (SC) protection for power devices that can identify which device has a SC fault within power modules or converters. It does NOT require sensing voltage or current magnitude of power device to detect and localize the SC fault, therefore it is low cost and enhances the noise immunity and reliability. This method can be applied to all switching power devices including muti-phase converters, modular converters, multilevel converters, and modular multilevel converters.
A charge pump gate driver circuit that provides an adjustable pump voltage level to achieve the active dv/dt control for wide bandgap devices. The driver circuit has two power supplies, which provides positive and negative reference voltages, two separate charge pump circuits with two capacitors, and a typical totem-pole drive with two decoupling capacitors. This achieves an online and active dv/dt regulation and eliminates extra power supplies to reduce cost and associated footprint.
A battery energy storage system (BESS) for medium voltage direct current (MVDC) or high voltage direct current (HVDC) grids or systems. The BESS comprises split-battery units and an isolated DC-DC converter interface connecting the battery units to the MVDC or HVDC system. The isolated BESS converter is a soft-switched modular multilevel dual-active-bridge (DAB) converter which has DC fault rid-through capability. The converters can be single-phase or poly-phase configurations and can be controlled to maintain a desired DC output under normal and DC grid fault conditions.
A gate driver for power semiconductors including metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs) that does not require isolated power supplies. The use of a circuit to transfer signal and power at the same time by a radio frequency (RF) transformer which works at several hundreds of a Megahertz and provides galvanic isolation. The frequency band is designed to be much larger than conducted electromagnetic interference (EM) frequency ranges, which are less than 30 Megahertz. The driver is free of standby power loss and has a built-in active gating function.
This invention presents a family of isolated battery energy storage system (BESS) topologies with multiple functions, which are suitable for high voltage and high-power DC grid application, including Medium Voltage Direct Current (MVDC) or High Voltage Direct Current (HVDC) applications. The modulation and control strategies of these topologies are also presented.
A device to solve over voltage issues caused by the reflected wave phenomenon (RWP). A motor drive connected to a motor through long cables can cause the reflection of the electromagnetic wave, resulting a voltage spikes at the motor side that is twice as high as the voltage at the drive side. This transient over voltage can damage the insulation of the motor or reduce its useful life. The canceler detects rising/following edge of the motor drive and generates a short pulse that breaks the voltage slope so that over voltage at motor side is suppressed.
A blanking-time-less desaturation protection method for power devices, by which the fault response time is shorter than the blanking time required by the existing protection methods.