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HomeMy WebLinkAboutEmerging Energy Technology Fund (EETF) Grant 731009 Genesis Machining and Fabrication Final Report - Dec 2016Page | 1 Final Report Grant #731009 Ultra-Efficient Generators & Diesel Electric Propulsion Genesis Machining & Fabrication Final Report December 2016 Page | 2 Table of Contents Acronymns and Abbreviations: ..................................................................................................................... 3 Introduction .................................................................................................................................................. 5 Project Scope ................................................................................................................................................ 5 Summary of Work Completed ...................................................................................................................... 5 Data Collection and Analysis ....................................................................................................................... 13 Deliverables Submitted ............................................................................................................................... 20 Technologies Developed ............................................................................................................................. 21 Patents ........................................................................................................................................................ 21 Lessons Learned .......................................................................................................................................... 22 Tasks Remaining for Commercial Development ......................................................................................... 22 Appendix A – Project Status Report 4/15-12/16 ........................................................................................ 23 Page | 3 Acronymns and Abbreviations: BMS: Battery Management System – An electronic system which protects batteries from various fault condicitons DFM: Design For Manufacturing – A design process which focuses on manufacturability PCB: Printed Circuit Board – A tecnology whereby electronic cirucits are printed onto a flat piece of material which is populated with electronic components CAN bus: Controller Area Network bus – a common automotive communications protocol TRL: Technology Readiness Level – A scale to indicate how close a product is to commercialization, 1 = a idea, 9 = a product on the market. CAD: Computer Aided Design – A computer system for designing mechanical systems VSG: Vaialble Speed Generator – A generator which varies RPM to match a given load SHG: Serial Hybrid Generator – A generator which employs batteries to store energy BSFC: Brake Specific Fuel Consumption – The amount of fuel consumed by an engine for a given load and RPM SVM: Space Vector Modulation – A method of controlling switches in an inverter to drive a motor UMIC: Universal Modular Inverter Controller – An inverter developed under this grant that can control a variety of loads and be setup in parallel IGBT: Insulated Gate Bipolar Transistor – A type of semi-conductor switch commonly used in inverters PWM: Pulse Width Modulation – Varying the duty cycle of a signal such that the average on time is somewhere between 0 and 100% GPIC: General Purpose Inverter Controller – A board made by National Instruments designed to control inverters FPGA: Field Programmable Gate Array – A type of computer chip that can be dynamically re- wired to perform a variety of functions EV: Electric Vehicle Page | 4 DC-DC: Direct Current to Direct Current converter – A power converter that converts DC at one voltage to DC at another voltage ACEP: Alaska Center for Energy and Power PDM: Power Dense Motor – A motor that optimizes the ratio of power to volume IP: Intellectual Property – Patents FEA: Finite Element Analysis – A numerical simulation that treats objects as composed of discrete blocks to evaluate thermal, fluid flow, or mechanical properties EPA: Environmental Protection Agency IC: Integrated Circuit – An electronic circuit formed on a small piece of semiconducting material, performing the same function as a larger circuit made from discrete components TIM: Thermal Interface Material – A material designed to transfer heat from a heat source to a heat sink FMEA: Fault Mode Effects Analysis – A systematic, proactive method for evaluating a process to identify where and how it might fail and to assess the relative impact of different failures, in order to identify the parts of the process that are most in need of change. Page | 5 Introduction The worldwide market for highly efficient diesel generators is quite large. However, there exists a fundamental mismatch between optimizing generator efficiency and the r equirement for a fixed 1800 rpm needed to maintain a 60 Hz output from a synchronous gener ator head. This is because the highest efficiency operating point (torque and RPM) varies with the load due to the fundamental physics of the engine. This is known as the load matching problem. One method to overcome this limitation is to generate power asynchronously so that the engine is always running at its peak efficiency point for a given load. This can be realized in a Variable Speed Generator (VSG) using an inverter fed induction machine as a generator and another inverter to output 60 Hz power. Generally speaking, the load matching problem most severely effects single generator implementations below 500 kW. Above this power level multiple smaller generators are often employed which can be dispatched individually to match efficiency to the load. A large market segment of interest for efficient diesel generators below 500kW is the industrial marine market. The core technologies required to implement a VSG system are an asynchronous generator head and a flexible, modular inverter platform. These techn ologies are also very well suited to solving the challenges related to Diesel Electric Propulsion. Significantly, an underserved market segment for diesel-electric propulsion is the commercial marine market for vessels 100’ and under, which typically require 1000kW of propulsion. This project has focused on developing a VSG and propulsion technology relevant for these marine power levels. Finally, we have also recognized the need for efficient energy storage to augment electric propulsion systems. To this end we have developed new Battery Management System (BMS) technologies as part of this project. Project Scope The scope of this project was to develop an ultra-high efficiency diesel generator technology along with a low cost method for diesel electric propulsion, and to bring these technologies to a pre-commercial level of development. While the intended market is commercial marine vessels, propulsion technology was tested in land based application first for ease of access. Likewise, the diesel generator technology was tested with controllable laboratory loads. Summary of Work Completed Work on this project began with initial proof-of-concept work to validate our inverter and motor concepts. A low power bread-board version was built first and then scaled up to a larger power. These were bench top systems and can be seen below in Figure 1. Page | 6 Figure 1 – Proof-of-concept inverters and motors used to validate core project concepts. These systems were 1.5 HP and 15 HP, from left to right. Next, we iterated to a TRL-6 inverter core design, which has proven to be very robust. Control for this inverter was then implemented with the Nation Instruments GPIC board, an OEM inverter control board with a real-time processor and FPGA (see Figure 2). These inverters are based on a unique topology with several advantages over traditional three-phase inverters. Details about this are given in our progress reports. Figure 2 - NI GPIC board controlling TRL-6 inverter core Figure 3 - TRL-6 inverter drive completed (left), inverter IGBT's and control boards (right) Page | 7 Along with the inverter build and firmware development, an electric vehicle test bed was built to validate the hardware in a real-world application. This test platform can be seen in Figure 4. It was equipped with a sophisticated data acquisition system that ran on software distributed between the inverter and an onboard PC. One core function of the inverter that was tested in this application was its implementation of generic outputs. An output was programmed as a DC-DC converter that supplied power to the car’s onboard 12 volt system. Considerable effort was also spent on tracking down the root cause of IGBT faults, RF noise, and optimizing the switching algorithm. This resulted in the development of a novel, high efficiency, IGBT switching algorithm. Thermal performance and data acquisition calibration was performed with an on- site visit from ACEP (see Figure 5). Finally, inverter efficiency, reliability, and load testing data was gathered using this platform. This testing is described in further detail below in the Data Collection and Analysis section. Figure 4 - Completed EV test-bed Figure 5 - Tom Johnson and Annie Goering of ACEP making FLIR picture of inverter (left), FLIR photo of inverter layer (right) Page | 8 Following the testing of our core inverter and motor technologies in our EV test-bed, our efforts were directed at building a 15 kW proof-of-concept Variable Speed Generator (VSG). The generator was equipped with fuel metering instrumentation and tested in VSG vs. Fixed Speed mode. After initial data collection, more sophisticated fuel metering was employed and automated test cycles were programmed to develop full BSFC maps for this generator. This genset shown in Figure 6. At this time we also kicked off the development of our TRL-7 inverter design. One of the main design challenges was the development of the TRL-7 PCB’s. This design process was started in conjunction with senior EE students at Worcester Polytechnic Institute, which was partnering with us. We also began working with our patent attorney on securing IP for our inverter, genset, and BMS concepts. Figure 6 - 15 kW proof-of-concept Variable Speed Generator Using our 15 kW test generator we were able to develop a BSFC map for the operating space of the engine (Figure 7 - Brake Specific Fuel Consumption (BSFC) map for experimental 15 kW VSG) and demonstrate a fuel efficiency gain when operated in VSG mode. This deliverable is described in further detail below in the Data Collection and Analysis section. Page | 9 Figure 7 - Brake Specific Fuel Consumption (BSFC) map for experimental 15 kW VSG One of the most challenging design aspects of our TRL-7 inverters was the heat sink. We leveraged both Finite Element Analysis modelling (FEA) as well as experimental tests to come up with an optimized design. Heatsink modelling led us to a square pin -fin geometry. To this end we developed specialized tooling (Figure 8) to build these heat -sinks for our prototype inverters. We also focused on identifying an optimal Thermal Interface Material (TIM) and developed a test rig to evaluate different candidates. Figure 8 - Pin-fin heatsink cutting arbor cuttting aluminum test block Representatives from ACEP visited our facility and provided thermal imaging of our heatsink design, see Figures 9 and 10. This provided us with a visual conf irmation of our heatsink performance. Page | 10 Figure 9 - AEA / ACEP site visit - Tom Johnson, Alan Baldivieso, and Jason Myer Figure 10 - FLIR image of heatsink test (left), heatsink test setup (right) Page | 11 Figure 11 - Panelized and assembled TRL-7 BMS boards (Left), Seraphim McGann programming boards (Right) Other development efforts included the TRL-7 BMS and inverter printed circuit boards. The assembled BMS boards are shown in Figure 11. A 3D model of this TRL-7 inverter PCB assembly is shown in Figure 12. On a side note, our BMS system took 2nd place in the Arctic Innovation Competition and we contributed the winnings to help fund the grant work. Figure 12 - Rendering of TRL-7 PCB Assembly Many components for the inverters were prototyped including the 3D printed coolant plenums and the machined heatsink assemblies. Figure 13 shows the TRL-7 PCB’s and the coolant plenums. Page | 12 Figure 13 - TRL-7 PCB's (left), TRL-7 coolant plenums 3D printed (right) Unfortunately we had to put things mostly on-hold from 4/15 to 11/16 due to the loss of our shop space and need to relocate. During this time we continued work on a few tasks that did not require our shop facility. We continued developing our BMS PCB’s and firmware, perfor med more integration of TRL-7 inverter components (see Figure 14), and researched how to implement Space Vector Modulation (SVM) on our novel H-Bridge inverter design. The appendix includes our 4/15 to 11/16 progress report. Figure 14 - TRL-7 Inverter PCB's integrated with other components To date we have brought our inverter, motor, and BMS technologies from a conceptual level to a TRL-6 level, and are almost ready to begin testing our TRL-7 level components. We have integrated these technologies as a working proof-of-concept Variable Speed Generator, and an Electric Vehicle propulsion test-bed. Using these engineering resources we have acquired efficiency and performance data. Page | 13 Data Collection and Analysis 1) TRL-6 Inverter Calibration During the 4/13-6/13 reporting period, Tom Johnson from ACEP worked with us to calibrate the UMIC’s voltage and current sensors and determined their degree of linearity and calibration coefficiencts. This voltage data is shown below and has been submitted separately. Current sensing was again calibrated by a professional from Alaris, LLC. The UMIC was calibrated by comparing values recorded by the UMIC voltage and current sensing hardware with a Fluke multi-meter. The UMIC showed very a very high degree of linearity for voltage and current sensing (R^2 = 1 and R^2 = .9999, respectively). From these calibration lines, measurement coefficients were calculated and used in all subsequent measurements. Figure 15 - TRL-6 Input side voltage calibration (performed under ACEP supervision) Page | 14 Figure 16 – TRL-6 Output side sensor calibration (performed under ACEP supervision) 2) 15 kW Variable Speed Generator (VSG) Brake Specific Fuel Consumption (BSFC) map A BSFC map was developed from the 15 kW experimental VSG. Calibration of voltage and current measurement was provided by ACEP and Alaris LLC (see Figure 18). The latter also provided torque sensor calibration and instrumentation (see figure 19). Fuel flow rate sensor calibration was provided by the sensor manufacturer. The test setup shown in Figure – 17 was used. This allowed a BSFC map of the generator to be developed (Figure 20). Page | 15 Figure 17 - Diagram of 15 kW VSG test setup Figure 18 - The system was calibrated using a Hoiki 3197 Power Quality Analyzer. Current clamps and voltage probes are shown on the left, the analyzer is shown on the right. Linearity was shown for the entire power range tested Figure 19 – Wheatstone Bridge Strain gauge (left), gauge wired to RF transmitter (right) Page | 16 Figure 20 - BSFC map of 15 kW VSG 3) VSG efficiency improvement vs. fixed speed generator Samples of BSFC were taken along the 2.5kW, 3kW, and 5kW lines respectively to show the increase in efficiency when the engine is throttled down. The results (shown in Figure 21) were 44%, 34%, and 20%, respectively for an engine throttled back from 1800 RPM to the most efficient RPM available.1 The red circles in Figure 21 show a normal fixed-speed generator’s fuel consumption at 1800 RPM, while the green circles show the VSG performance. It is impossible to quantify the exact efficiency improvement as a single number for VSG vs. Fixed-Speed performance. This is because the load profile must be taken into consideration. The performance of the two modes can be compared for a given load profile. As a rule of thumb, however, improvement can be quantified as the efficiency gain at 50% of the continuous operating point. In the case of our test generator the continuous operating power is 10 kW (typical for a 15 kW peak output machine). At 5 kW, there is a 20% gain in efficiency in VSG mode vs. Fixed speed mode. 1 The scatter plots reveal the noise from the displacement fuel sensor. This is attributed to the operation of the mechanical lift pump of the engine, small amounts of static air in the fuel line, and fuel hose flexing. Cleaner data is possible by using hard fuel lines and longer data acquisition periods. Each sample in this BSFC chart was only 10 seconds long. We also recommend updating the fuel meter to have a quadrature encoder rather than the simple frequency encoder. This will allow it to detect any reverse flow caused by lift pump operation. Page | 17 If being half loaded is the average operating condition for a given load profile, then we are seeing about a 20% gain in fuel efficiency. Figure 21 - BSFC along 2.5 kW, 3kW, and 5 kW iso-power lines showing 44%, 34%, and 20% improvement in efficiency, respectfully. The red circles show a normal fixed-speed generator’s fuel consumption at 1800 RPM, while the green circles show the VSG performance. 4) Measured inverter efficiency The TRL-6 Universal Modular Inverter Controller (UMIC) efficiency was measured up to 30 kW during actual driving in the EV test-bed. At the time of the test the system output was limited due to faulty IGBT’s. Only the upper envelope of the scatter plot rep resent the actual efficiencies. This is because transients during driving skew the power measurements. Data points generated during steady state conditions show the actual efficiency values. Figure 22 shows that the TRL-6 inverter efficiency settles at around 98% above 20 kW. This data has been submitted separately. It should be noted that the peak inverter power is much higher than 30 kW (~500kW / inverter layer). After the faulty IGBT’s were replaced, we did not attempt to re -measure efficiency over the full operating band because 1) the EV test bed could not provid e continuous loads that high, and 2) we had planned on testing the TRL -7 inverters which Page | 18 will have greater ability to dissipate heat. However, we have not yet completed the TRL - 7 inverters and have therefore not measured the efficiency over the full operat ing band. Figure 22 - TRL-6 Inverter efficiency vs. output 5) TRL-7 heatsink performance measurement A major design consideration for the TRL-7 inverter were the IGBT heatsinks. We went through several heatsink and Thermal Interface Material (TIM) iterations before reaching our current design. The top two choices were a metal foil called Tin Plus with an aluminum heatsink or directly soldering the IGBT’s to a copper heatsink. The two choices were evaluated experimentally using the setup shown in Figure 23. Page | 19 Figure 23 - Test setup for Thermal Interface Material (TIM) comparison The results of these trials, shown in Figures 24 and 25, show a much lower thermal resistance for the soldered copper solution, .0074 K/W compared to .023 k/W. Figure 24 – Evaluation of the thermal resistance (Rjc) of Tin-Plus Thermal Interface Material with Aluminum Pin Fin heatsink Page | 20 Figure 25 - Evaluation of thermal resistance (Rjc) using a soldered copper pin-fin solution Deliverables Submitted 6/13 – UMIC efficiency data This deliverable is a data set of electrical conversion efficiency measurements of the Universal Modular Inverter Controller under a real-world propulsion situation. 12/13 – 15 kW genset test results and initial motor efficiency results This deliverable is a data set of fuel efficiency measurements of the experimental 15kW Variable Speed Generator under a controlled laboratory situation, as well as initial motor efficiency results. Page | 21 Technologies Developed Three technologies were developed under this grant for use in diesel-electric propulsion systems and Variable Speed Generators (VSG’s). 1) Low cost Power Dense Motor (PDM) The PDM technology developed under this grant has applications as both a low cost motor for diesel electric propulsion systems and as a generator head for VSG applications. The technique is based on modifying inverter-ready industrial induction motors for higher power density. Primarily, this is done by modifying the cooling strategy from air-cooled to direct oil cooling. Modifications include machining and balancing of the rotor, modifying the housing, installing high-speed bearings, and removing the Y-winding center-tap to support three independent phase coils. These low-cost changes allow the motor to operate at high RPM’s and torque while staying in their rated temperature range. The winding modification, when operated with our unique inverter topology, allows the motor to run at higher RPM’s with full torque without exceeding the voltage limits dictated by the winding insulation. 2) Universal Modular Inverter Controller (UMIC) The UMIC system was developed under this grant as a ground -up, parallel-ready, multi- purpose inverter platform. The UMIC is unique from other inverter systems in that it has generic outputs which can be programmed for arbitrary functions. It is also unique in its parallel output capability. This is accomplished by a high speed bus with nanosecond timing resolution shared by all inverter module layers. Finally, the UMIC is unique in its very high power density. The UMIC was developed to be scalable and to support our diesel electric propulsion and VSG applications. 3) Arctic BMS for prismatic lithium battery cells The Arctic BMS system was specifically developed to control prismatic lithium cells in cold climates. The unique feature of this BMS system is the ability to maintain pack temperatures by directly heating the battery terminals of prismatic cells. Heat then transfers through the terminals to the whole volume of the cell. The technology allows lithium storage to be used in cold climates and maintain isothermal conditions across the pack. The target applications for this technology are battery banks for diesel electric propulsion systems and batteries used in conjunction with VSG’s as serial hybrid type generators (see below). Patents A patent application was filed for the Arctic BMS system under application # US20160181845 A1. The patents for the VSG and inverter architecture need some modification before filing. Page | 22 Lessons Learned Many lessons were learned under this grant. Among the most important is that the Variable Speed Generator is a viable method for optimizing the efficiency of diesel generator. This was demonstrated clearly by our 15 kW which showed efficiency gains over two-thirds of its operating band. These gains will need to be quantified in relation to typical load profiles so that customers can clearly understand the fuel savings that these generators will provide. Another important lesson we have learned during this grant is that the initial scope of work was too broad. While all of the technologies developed are useful to our company portfolio, more focus on the generator application would have gotten us further faster. However, the inverter and PDM technologies which are core to any generator system have been developed well beyond the proof-of-concept phase. We have also learned the value of simulation during this grant. Our initial focus was hardware intensive, but it is clear that we could have gained significant learning from more simulation of the generator systems up-front. Simulation tools developed in parallel to hardware would have significant value allowing for faster iteration and system design. This capacity can still be built, but it would have been good to leverage it from the start. Finally, we have learned how critical energy storage is for our product portfolio. Initially, this fact was not realized as we were focused on generation and conversion. However, many mo re options are available to customers when proprietary storage systems are available. Tasks Remaining for Commercial Development The work done under this grant has allowed us to develop a clear development plan for commercialization. First of all, the TRL-7 hardware which has been developed requires final integration and testing. This will allow for evaluation of the VSG concept at ful l scale. Additionally, a simulation comparing the VSG and SHG concepts needs to be evaluated to determined which type of system will be most economical. Additionally, a Failure Modes and Effects Analysis (FMEA) study should be completed prior to any field deployment. Following this study, we are recommending a pilot program to test a full-scale TRL-7 generator in a market representative application. This could include a marine, remote-industrial, or rural power setting. During this process the system will be evaluated and debugged so that iteration to TRL- 8 can occur. The transition to TRL-8 should focus on cost, reliability, and Design for Manufacturing (DFM). An additional TRL-8 pilot study should follow with multiple units in a variety of intended applications. At the same time, several lab units should undergo rigorous accelerated life-cycle testing to discover failure points. During the above steps several other pre-commercial activities need to be undertaken. The most important of which is the raising of capital to fund the final development efforts and build the required infrastructure to begin commercialization. Part of this effort will be more in- depth market research to quantify the value proposition, EPA certification, and research Page | 23 identifying any other legal or homologation concerns. Another large part of this effort will be the building a corporate structure capable of growth along the lines of the calculated value proposition for the company. As capital is raised, successful pilot programs are demonstrated, and engineering is iterated to TRL-8, several logistical steps must be taken to ensure a successful product launch. First, based on the amount of capital raised, the initial level of vertical integration must be identified. Then we can identify vendors for outsourced components and manufacturing processes and develop strategic partnerships where needed. This will be especially important when selecting a diesel engine manufacturer. A sales team must also be built and vendors be in place at the time of product launch. Additionally, a service team must be in place to install and maintain units in the field. Appendix A – Project Status Report 4/15-12/16 Following is the progress report for 4/15-11/16, it has also been submitted separately: Progress Report Grant #731009 Ultra-Efficient Generators & Diesel Electric Propulsion Genesis Machining & Fabrication Reporting Dates: 4/2015-11/2016 Page | 24 Deliverables Submitted: None at this time. Budget: We are invoicing for $21,175.00 in labor and $12,980.00 in match for the period from 4/2015 to 11/2016. Work Progress 4/15 – 11/16: Since April, 2015 this project has been mostly on-hold due to the loss of our facilities in Kodiak and the need to relocate. However, the following work has been done during this period: 1. Contiunued development of the Battery Management System (BMS) PCB The BMS prototype system was outfitted with new communication bus adapters to be prepared for deployment into our test battery system. We found the original daisy-chain cable connectionn between BMS boards to be cumbersome. An adapter board was designed and installed on the BMS boards to accommodate a new arrangement. Figure 26 - Adapter boards (left), modified BMS boards (right) Page | 25 Figure 27 - Modified batch of BMS boards Future revisions of the BMS system will include this feature on a single PCB. Also, we will likely be moving to a CAN bus architecture rather than our original custom communication bus. 2. BMS firmware coding, BMS master control programming and testing The BMS master control was expanded to handle a full battery bank and tested with the BMS firmware. Below is a screenshot of this control software: Figure 28 - One of the screens of the BMS Master control software Addititionally, the following tasks were completed:  Built test routine to test all BMS functions on a chain of BMS’s  Front end development to communicate with multiple BMS boards  Deep sleep algorithm, to avoid draining battery  Reading / controlling data from a chain of cells  Updating firmware via bootloader to a chain of cells Page | 26 We also developed a list of future changes to improve the BMS system:  Hardware reset  Board layout changes  Communication bus changes, possibly different architecture  Thermal cycle testing on BMS Figure 29 - BMS board regulating single test-cell Figure 30 - BMS boards regulating test-cell bank 3. Additional integration of inverter components Integration work was done to begin bring-up of the TRL-7 inverters. The PCB’s were partially populated and the fitment and clearance of the PCB’s with the other Page | 27 mechanical components was checked against the CAD model. No major problems were noted. Figure 31 - Initial build of TRL-7 inverter components 4. VSG vs. Serial Hybrid During our research into Variable Speed Generators (VSG) we have noted that developing a Serial Hybrid Generator (SHG) may have certain advantages while solving the same fundamental problem. In the case of a VSG, throttle is varied according to load so that the generator operates at its peak efficiency point for a given load. In the SHG model, the generator is always operated at its absolute peak efficiency point and the power is used to charge a battery bank. The VSG and SHG concepts are shown below in Figure 6. We were able to analyze a BSFC map (see Figure 7) to compare fixed speed, VSG, and SHG using the same engine as the power source. The results show that the SHG offers only marginally better performance (around 1%) over VSG for most of the operating range of the generator. This gain would almost certainly be outweighed by the round trip losses associated with the batteries. There are side benefits associated with SHG such as quiet times when the generator is not running and being able to scale back the generator size for a given load. Only careful simulation will help uncover which configuration is optimal for a given load profile. In any case, the core technologies developed under this grant can be applied to either configuration. Page | 28 Figure 32 - Variable Speed Generator (VSG) vs. Serial Hybrid Generator (SHG) concepts Figure 33 - Brake Specific Fuel Consumption (BSFC) map for 275 HP Cummins Engine with iso-power lines superimposed Page | 29 Figure 34 - Fixed Speed / VSG / SHG normalized fuel consumption vs. power for 275 HP Cummins engine 5. H-Bridge Topology Inverter Research Additional work was done in this reporting period to understand implementing Space Vector Modulation (SVM) on our inverter platform. This is an important task as it will further increase the efficiency of our inverter. The fruit of this research is the recognition that our unique inverter/motor topology can support a new converter law with potential efficiency benefits, lower switching harmonics, as well as other potentially useful (though unexplored) motor states. This will be important as we bring our TRL-7 inverter online. Future research will include developing this converter law and applying it to a Space Vector Modulation (SVM) algorithm. The following is a brief summary of the research performed: Figure-10 shows the difference between a standard 3-phase inverter compared to our H-bridge topology: 0 5 10 15 20 25 30 35 40 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250Normalized Fuel Consumption (%)Generator Output (kW) Fixed Speed / VSG / SHG Normalized Consumption vs Power Fixed Speed VSG Serial Hybrid Page | 30 Figure 35 - Standard 3-phase inverter configuration (left), UMIC independent H-Bridge configuration (right) In a standard inverter, all switches are modulating all the time, as seen below in Figure -11. Thus H-Bridge efficiency is higher because the current only passes through one modulated switch per motor coil, hence the switching losses (Psw) is half a standard inverter. Conduction losse s are still present. The design requires twice as many IGBT’s, but the burden per IGBT is less because it switches only 1/4 of the time. The economics of this inverter would undoubtedly vary by application. Figure 36 - H-Bridge vs. standard inverter modulation One counter-intuitive result of this operating mode is that the efficiency gain of the H-Bridge inverter over its standard three-phase counterpart actually increases with switching frequency. This is particular beneficial because the core losses of an induction motor will also decrease with increasing switching frequency. There will be a limit at which rising losses per IGBT will outweigh the efficiency gains. More simulation/physical testing will be needed to identify this limit and choose the optimal H-bridge switching frequency. Page | 31 Figure 37 - Efficiency gain increases with switching frequency for H-Bridge vs. typical three-phase bridge Working toward a SVM converter law based on H-bridge topology, we need to consider the standard SVM pi plane diagram: Figure 38 - SVM pi plane, the γ component is seen in the Z dimension of the graph In standard SVM the γ component is non-zero, and this leads to the voltage gain of SVM over standard PWM modulation. This will no longer apply in the full H-Bridge mode as the following relationship will always apply: 0 5 10 15 20 25 30 35 40 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 19 20 21 22 23 24 25 26 27 28 30 31 32 33 34 35 36 37 38 39 41Efficiency gain (%)Switching Frequency (kHz) H-Bridge Topology Efficiency Gain vs. Switching Frequency Page | 32 Equation 1 - Inverse Clarke's transformation In this case the γ component, or the common mode component, of will always be equal to zero. So all space vector modulation can now be entirely understood as superposition on the π plane: Figure 39 - SVM modulation superposition on pi plane The next step is to expand superposition from a standard 3-phase SVM bridge to the 3-phase H- bridge. This yields a SVM plane now with 8 rather than 2 null vectors. This means 4X the degrees of freedom than standard bridge SVM and therefore additional efficien cy gains. Also, the new plane contains two mysterious “anti-null” vectors which are unique to this topology. These states would both tend to expel field from the rotor and could have unknown useful value, but at least represent additional degrees of freedo m. Figure 40 - Standard SVM plane (left), 3-phase H-bridge plane (right) More research is needed to complete the development of SVM control for our H -bridge topology. One issue is identifying any converter states which include circulating currents and Page | 33 eliminating them. Once the SVM control algorithm is implemented, it will yiel d high inverter efficiencies for our TRL-7 inverter system.