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Islanded mixed-source CERTS microgrids that include photovoltaic (PV) microsources and natural gas gensets are vulnerable to the collapse of the dc bus voltage in the CERTS-compatible PV microsources designed with voltage-source characteristics during dynamic overload conditions. Control techniques tailored to prevent the bus voltage collapse are explored. Simulation and experimental verification...
There is an increasing need to model large networks of inverter-based distributed generation due to the limits of existing simulation tools. A deliberate enforcement of intra-feeder coherency between adjacent droop-controlled inverters is a worthwhile objective, as phase angle coherency will allow for a deliberate partitioning of fast and slow dynamics within the network. This partitioning, in turn,...
This paper presents the results of experimental tests designed to verify analytical predictions of the rotor demagnetization characteristics of a 0.6 kW (cont.) 9-slot/6-pole fractional-slot concentrated winding (FSCW) interior permanent magnet (IPM) synchronous machine. The demagnetization characteristics of the rotor magnets in this commercially produced FSCW-IPM machine are measured using a test...
A design approach is presented to mitigate demagnetization vulnerability in permanent magnet synchronous machines (PMSMs) by proper selection and design of stator windings and rotor configurations. First, a comparative analysis of the stator demagnetizing MMFs and leakage inductances for surface PM machines equipped with integral-slot distributed windings (ISDW) and fractional-slot concentrated windings...
For battery and ultracapacitor hybrid energy storage systems, the design and control of the DC-DC converter is an important stage of the system design process. The design approach for a model-based controller for a half-bridge DC-DC converter is presented with experimental results from a scaled test configuration. The contribution of this paper lies in presenting a well-behaved discrete-time system...
A promising approach is proposed for extending the appealing features of the CERTS microgrid concept beyond its robust plug-and-play and autonomous control characteristics to include the integration of photovoltaic (PV) microsources with reduced volatility at the grid interface. The steady-state and transient characteristics of a proposed CERTS PV microgrid that incorporates a droop-controlled PV...
Several high-performance control algorithms for ac machine drives and other applications require accurate knowledge of the instantaneous converter output voltages. The use of a simple low-pass filter to remove the PWM switching frequency harmonics from the AC voltage measurements introduces undesirable amplitude and phase lag errors into the voltage measurements. This work presents compensation functions...
This paper presents the results of experimental tests designed to verify analytical predictions of the rotor demagnetization characteristics of a 0.6 kW (cont.) 9-slot/6-pole fractional-slot concentrated winding (FSCW) interior PM (IPM) synchronous machine. The demagnetization characteristics of the rotor magnets in this commercially-produced FSCW-IPM machine are measured using a test configuration...
This paper proposes a new Coulomb counting state-of-charge (SOC) algorithm for a lithium iron phosphate battery that achieves accurate results (3.8% standard deviation) for several drive cycles and temperatures between −10°C and 20°C. The basis for this method is a physics-based battery model that compensates for the influences of drive dynamics and temperature on the SOC estimates, instead of the...
This work investigates post-demagnetization characteristics of permanent magnet synchronous machines (PMSMs). A combination of closed-form analysis using a magnetic equivalent circuit model and finite element (FE) analysis is used to provide physical insights into the flux paths associated with demagnetizing electromotive force (MMF). Post-demagnetization behavior in several types of PMSMs is studied...
The task of applying numerical design optimization techniques to traction motors increases in complexity when there are complicated combinations of demanding performance specifications and physical dimension constraints that must be satisfied. This paper presents a constrained optimization routine that can be used to efficiently optimize electric machine designs to meet demanding U.S. DRIVE traction...
This paper investigates the uncontrolled generator (UCG) operating characteristics of permanent magnet (PM) synchronous machine drives using current-source inverters with normally-on switches. This special mode occurs when a PM machine is spinning at a high speed and gating signals are simultaneously removed from all of the inverter switches. This investigation shows that the UCG operating characteristics...
This paper investigates fault-tolerant PM machine drive converter topologies that seek to minimize the number of switches while retaining as much of their original pre-fault performance capabilities as possible. Four six-phase drive topologies have been selected and compared with conventional half-bridge and full-bridge converters. All four topologies use fewer half-bridge phase-legs than the baseline...
In order to ensure resilient and high power quality microgrid operation, P-f and Q-V microgrid droop control algorithms rely on the calculation of active and reactive power outputs based on locally-measured voltage and current. A low-pass filter (LPF) on the calculated power signal is often incorporated by design into the droop controller, but the complete effect of the LPF on microgrid dynamics has...
This paper investigates the single-switch short-circuit fault response of a permanent magnet (PM) machine drive using a current source inverter (CSI). The CSI offers some appealing advantages over conventional voltage-source inverters (VSIs) during short-circuit fault conditions originating inside the inverter. Two post-fault strategies are investigated in this paper, consisting of either: 1) turning...
This paper presents an improved analytical model for predicting the ac losses in form-wound windings used in high-performance ac machines attributable to the stator currents. The complete model comprises two sub-models that separately calculate the ac losses contributed by the in-slot and end-winding portions. 3D finite element analysis and experimental tests are conducted to demonstrate the usefulness...
Distributed controls have promising applications that include both highly fault-tolerant motor drives and modular drivesfor large machines. Communications speed limitations of these drive systems require each modular sub-drive to operate nearly independently over short timescales. As a result, sensor errors and system unbalances that cause only minor performance degradation in conventional drive systems...
This paper presents the calculated demagnetization characteristics of different types of permanent magnet synchronous machines (PMSMs) under the influence of demagnetizing MMF contributed by the stator currents (i.e., armature reaction). The demagnetization of NdFeB magnets is quantified in terms of demagnetized magnet volume and loss of magnet remanence using finite element (FE) analysis. The impact...
This paper investigates the principles underlying torque production in a flux-switching permanent magnet (FSPM) machine. Because the phase windings and permanent magnets in FSPM machines are both located on the stator, the torque production mechanism is not the same as for a conventional PM synchronous machine. Spatial harmonic analysis is applied to examine the frequency components present in the...
This paper deploys electrochemical impedance spectroscopy (EIS) to investigate the impact of temperature and dc bias current on battery impedance characteristics. Measured test results are used to demonstrate that, under conditions where the nonlinear Butler-Volmer equation is necessary to model the electrode charge transfer characteristics, the semicircular trajectory that typically appears in the...
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