Abstract: According to one aspect, embodiments of the invention provide a power meter comprising a voltage sensor, at least one current and phase sensor circuit, and a central metering unit, wherein the voltage sensor is further configured to measure a voltage on an input line and transmit a signal related to the voltage to the central metering unit, wherein the at least one current and phase sensor circuit is further configured to measure a current and a voltage phase shift of a feeder line, and to transmit a signal related to at least one of the current of the feeder line and the voltage phase shift of the feeder line to the central metering unit, and wherein the central metering unit is configured to calculate power provided to a load via the feeder line based on the signal transmitted from the at least one current and phase sensor circuit.

Abstract: According to one aspect, embodiments of the invention provide a power meter comprising a voltage sensor, at least one current and phase sensor circuit, and a central metering unit, wherein the voltage sensor is further configured to measure a voltage on an input line and transmit a signal related to the voltage to the central metering unit, wherein the at least one current and phase sensor circuit is further configured to measure a current and a voltage phase shift of a feeder line, and to transmit a signal related to at least one of the current of the feeder line and the voltage phase shift of the feeder line to the central metering unit, and wherein the central metering unit is configured to calculate power provided to a load via the feeder line based on the signal transmitted from the at least one current and phase sensor circuit.

Abstract: Devices and methods of commodity usage monitoring determine the amount of commodity used by individual elements of multi-element systems having a common source. An amount of commodity drawn from the source by all the users is determined. A user-state that indicates use of the commodity by each user is determined. Individual user consumption of the commodity for each of the users is determined using repeated determinations of the amount of the commodity and the user-state, for a number of repetitions greater than or equal to the number of users. Determining individual consumption can be performed using minimum least square estimation, singular value decomposition, discriminant function analysis, or other computational or analytical solution method. Duration and consumption information can be used to calculate the total amount of the commodity consumed by the particular user. Useful commodities include, but are not limited to, gas, electricity, mechanical, pneumatic, hydraulic, and water.

Abstract: An induction motor having a rotor and a stator is protected during running overloads by connecting the motor to an overload protection relay that can be tripped to interrupt power to the motor in the event of an overload, tracking the stator winding temperature of the motor during running overloads with a hybrid thermal model by online adjustment in the hybrid thermal model, and tripping the overload protection relay in response to a predetermined running overload condition represented by the tracked stator winding temperature. In one embodiment of the invention, the stator winding temperature is tracked by use of an online hybrid thermal model that uses the resistance of the rotor as an indicator of rotor temperature and thus of the thermal operating conditions of the motor. The hybrid thermal model incorporates rotor losses and heat transfer between the rotor and the stator, and approximates the thermal characteristics of the rotor and stator.

Abstract: A phase locked loop (PLL) circuit provides ac devices, such as power inverters and power measurement devices, with a reliable means for synchronizing to ac electrical systems. In an exemplary embodiment, the PLL circuit is configured for operation with single-phase electrical systems and offers substantial noise immunity by basing its locking operations on measured fundamental components, i.e., measured x-y phasors, of the electrical system voltage. Further, with its phasor-based locking operations and with its timer/counter-based operation, the PLL circuit can be implemented partly or wholly in digital processing logic.

Abstract: A control circuit synchronizes an ac power inverter to the mains voltage of an electrical grid by matching the fundamental phasor components of the inverter's output voltage to the fundamental phasor components of the mains voltage. Once such matching meets an acceptable voltage error threshold, the control circuit initiates contactor closure, verifies contactor closure, and then initiates a changeover from voltage-mode control used in synchronization operations to a current-mode control of the inverter's output. The control circuit provides corresponding disconnection control when disconnection from the grid is desired, wherein the regulated power of the inverter is ramped down in controlled fashion until it reaches a lower threshold whereupon contactor opening is initiated. Once contactor opening is verified, regulation control reverts to stand-alone voltage mode control or to shut down, as needed or desired.

Abstract: A power inverter includes a regulator circuit that controls real and reactive power output by the inverter. The regulator measures real and reactive output power by calculating x-phasor components of the inverter's voltage and current output waveforms. Phasor calculation can be adapted for one or more pairs of single-phase voltages and currents. Determining the fundamental in-phase and quadrature components of output voltage and current reduces computational complexity by permitting the regulator to perform its power control processing largely in a dc signal domain, and enables separate real and reactive power control. The power inverter can include islanding detection logic, which exploits the ability to separately control reactive power. Exemplary islanding detection logic is based on determining whether changing the amount of reactive power output by the inverter induces an output frequency shift.