This voltage imbalance assessment method is for a power conversion device comprising a forward converter for rectifying the voltage of a three-phase AC power supply, a smoothing capacitor for smoothing the rectified voltage, a detection unit for detecting the smoothed voltage, and a control unit. The control unit: uses the detected voltage to generate data indicating frequency components; compares, in the data indicating frequency components, the magnitude of the component that is four times the power supply frequency with the magnitude of the component that is six times the power supply frequency; and assesses the voltage imbalance of the three-phase AC power supply on the basis of the comparison.

An induction machine with localized voltage unbalance compensation is disclosed. The use of an induction machine with a voltage unbalance correction compensator (VUC) may be used to maintain proper working conditions of the machine during intervals of voltage unbalance.

A voltage detecting circuit includes a rectifying circuit, a voltage dividing circuit, and a comparing circuit. The rectifying circuit is configured to rectify a plurality of AC phase voltages to output a plurality of rectified voltages respectively. The voltage dividing circuit is configured to divide the plurality of rectified voltages respectively to output a plurality of sampling voltages. The comparing circuit is configured to compare the plurality of sampling voltages with a reference voltage respectively to provide a plurality of corresponding phase failure detecting voltages. On the condition that the AC phase voltages are unbalanced, the phase failure detecting voltage switches between a high level and a low level.

Various embodiments relate to detecting theft of electrical energy. A method of detecting theft of electrical energy may include measuring, for each time sample of a number of time samples, a neutral current of an electrical energy metering system. The method may further include summing, for each time sample of the number of time samples, a number of measured phase current values of the electrical energy metering system to determine an imputed neutral current. Further, the method may include determining, for each time sample of the number of time samples, a squared difference between the measured neutral current and the imputed neutral current. Moreover, the method may include integrating, for each time sample of the number of time samples, the squared difference to determine an accumulator value. In addition, the method may include detecting, based on the accumulator value, theft of electrical energy from the electrical energy metering system.

In accordance with an example embodiment of the invention, a three-phase power control device is configured to synchronize firing thyristor or SCR sets in consecutive combinations of two of the three phases, to supply current to consecutive combinations of two of the three loads in a three-phase load configuration, to determine real branch impedance of each load from three combinations of two supplied loads, without need of any electrical neutral reference.

A method of assessing a condition of a multi-phase power system comprises the steps of: acquiring a voltage signal and a current signal for each phase of the multi-phase power system; calculating a product of the voltage signal for each phase of the multi-phase power system with one of the current signals such that the product is between a voltage signal for one phase and a current signal for a different phase for at least two of the products; summing the calculated products; and identifying the possible existence of a fault in the multi-phase power system based on a frequency analysis of the summed calculated products.

SOGI based apparatus and methods for providing balanced three phase output signals free of harmonics, DC components and imbalance present in the input signals, are disclosed. In addition, such apparatus and methods for providing corresponding output signals which are drift-free integrals of the input signals and which signals may enable the control of a power electronics inverter for improved and robust grid power injection and for motor control are disclosed.

A fault detection circuit according to the present disclosure includes a rectangular pulse comparison circuit configured to generate, for each combination of the pulse width modulated signals, detection signals each indicating a difference component between pulse widths of two pulse width modulated signals having phases adjacent to each other, and a fault diagnosis unit configured to detect a fault in an inverter based on a shift in a combination of logic levels of a plurality of the detection signals output by the rectangular pulse comparison circuit from a preset determination value. The fault diagnosis unit uses the determination value that is different for each motor rotation angle assuming in advance that two alternating-current signals having phases adjacent to each other among the three-phase alternating-current signals have the same voltage.

A fault detection circuit according to the present disclosure includes a rectangular pulse comparison circuit configured to generate, for each combination of the pulse width modulated signals, detection signals each indicating a difference component between pulse widths of two pulse width modulated signals having phases adjacent to each other, and a fault diagnosis unit configured to detect a fault in an inverter based on a shift in a combination of logic levels of a plurality of the detection signals output by the rectangular pulse comparison circuit from a preset determination value. The fault diagnosis unit uses the determination value that is different for each motor rotation angle assuming in advance that two alternating-current signals having phases adjacent to each other among the three-phase alternating-current signals have the same voltage.

A voltage detecting circuit includes a rectifying circuit, a voltage dividing circuit, and a comparing circuit. The rectifying circuit is configured to rectify a plurality of AC phase voltages to output a plurality of rectified voltages respectively. The voltage dividing circuit is configured to divide the plurality of rectified voltages respectively to output a plurality of sampling voltages. The comparing circuit is configured to compare the plurality of sampling voltages with a reference voltage respectively to provide a plurality of corresponding phase failure detecting voltages. On the condition that the AC phase voltages are unbalanced, the phase failure detecting voltage switches between a high level and a low level.