Fuji Electric Co., Ltd.

Hokuriku Electric Power Company

Kansuke Fujii

Toshiya Yamada

Masaki Katoh

Motohiro Katayama

Hiromu Takubo

Kazuyoshi Umezawa

Norikazu Kanao

A momentary-voltage-drop compensation apparatus interconnecting a power system and a DC power supply to a load. The apparatus includes a system interconnection switch connected between the power system and the load, a first power converter that performs DC-AC conversion to DC power of the DC power supply, a second power converter that includes a first terminal connected to the first power converter and the DC power supply, and a second terminal connected between the system interconnection switch and the power system, for performing AC-DC conversion to the AC power supplied from the power system, and a control unit that is connected to the first power converter, and is configured to control, in response to a voltage drop in the power system, the first power converter to output a zero-phase current, a current value of which is no larger than that of a current flowing through the system interconnection switch.

Momentary-voltage-drop compensation apparatus and momentary-voltage-drop compensation system

A 3-level power conversion circuit, including a high potential terminal configured to receive a high potential from a direct current (DC) power source, a low potential terminal configured to receive a low potential from the DC power source, an intermediate potential terminal configured to receive an intermediate potential from the DC power source, and an alternating current (AC) terminal configured to output an AC, the 3-level power conversion circuit being configured to perform power conversion between the high, low and intermediate potential terminals and the AC terminal. The 3-level power conversion circuit further includes a switching element and a diode connected in series between the intermediate potential terminal and the AC terminal, where the diode, but not the semiconductor switching element, includes a wideband gap semiconductor, and an ampacity of the switching element is greater than an ampacity of the diode.

3-level power conversion circuit including serially-connected switching element and diode

The present disclosure provides a controller for a power converter that converts input power to a prescribed form and outputs the power by switching a semiconductor switching device ON and OFF and that has an output circuit including a filtering reactor on an output side, the controller including: a carrier calculating unit that generates a carrier having prescribed frequencies for generating a control signal that switches the semiconductor switching device ON and OFF, wherein the carrier calculating unit generates the carrier such that a carrier frequency at phase angles where ripple components in a current flowing through the reactor are relatively high in magnitude, which is defined as a high ripple carrier frequency, is higher than a carrier frequency at phase angles where the ripple components are relatively low in magnitude, which is defined as a low ripple carrier frequency.

Controller for power converter with frequency modulated carrier

The disclosed distributed power supply system does not become disconnected from a grid simultaneously with others when the grid voltage falls instantaneously. In a distributed power supply device which controls an inverter circuitbased on a control signal obtained by comparing a predetermined carrier signal and voltage command signals of three phases and which converts DC power to AC power and supplies the AC power to a power grid of a three-phase AC power supply, fundamental wave signals of three phases are generated from a grid voltage of the three-phase AC power supply. A reference cosine wave signal is generated from the fundamental wave signals of three phases. A third harmonic signal is generated from the reference cosine wave signal and the fundamental wave signals of three phases. The three-phase fundamental wave signals and the third harmonic signal are added to generate voltage command signals of three phases.

Distributed power supply system

With a method whereby reactive power is changed from a fluctuating output to a constant output by a frequency rise or fall monitor circuit stage level being exceeded, and an isolated operation is detected, a problem occurs with a small scale grid in that, as the frequency is liable to fluctuate due to a load fluctuation, there is liable to be a false detection of an isolated operation. In contrast, an abnormal frequency stage detection can be performed such that the frequency at a point when the rising edge of a reactive power fluctuation is detected, and the frequency at a point when the falling edge is detected, are detected sequentially, and an abnormal frequency stage detection is recognized when the order of the difference between the current detection value and the previous detection value is 'increase', 'decrease', &#x201c;increase&#x201d;.

Isolated operation detection device

Aspects of the invention can include capacitors which series-divide the voltage of a DC power source, an inverter circuit formed by bridge-connecting semiconductor switching elements to which diodes are antiparallel-connected, and bidirectional switches connected between a connection point of the capacitors and the AC output terminals of the inverter circuit. When the voltage of the DC power source is lower than a prescribed value, the inverter circuit can be caused to operate as an ordinary three-phase inverter, and when the voltage of the DC power source is higher than a prescribed value the inverter circuit can be caused to operate as a V-connected inverter, and when caused to operate as a V-connected inverter, a halted phase can be switched in sequence according to line voltages or output currents.

Three level inverter device

A distributed power supply system in which no simultaneous disconnection from the system occurs when a system voltage momentarily drops is provided. It includes an inverter circuit that converts a direct current power generated by a direct current power supply and that supplies the alternating current power to an alternating current power supply power system, and an inverter control circuit for carrying out PWM control of the inverter circuit, wherein the inverter control circuit includes a three-phase voltage command signal generation unit, that is configured of a three-phase fundamental wave signal generation unit that generates three-phase fundamental wave signals from two phase components of voltage detected by a voltage detector, and a third harmonic signal generation unit that adds together third harmonic components of respective phases, having a predetermined amplitude, generated based on the three-phase fundamental wave signals.

Distributed power supply system with harmonic signal generation for stabilization

A grid-connected inverter includes first and second power conversion circuits, a contactor and a control circuit. The first conversion circuit converts a first DC voltage to a second DC voltage. The second conversion circuit converts the second DC voltage to an AC voltage. The contactor connects an output side of the second conversion circuit to a power system. The control circuit includes a decision circuit and controls start and stop operations of the conversion circuits, and opening and closing of the contactor. The decision circuit decides whether a condition of the contactor is abnormal by detecting, after the control circuit controls the contactor to be open, whether or not a value of the second DC voltage is less than a threshold value, and if the value of the second DC voltage is detected to be not less than the threshold value, decides that the condition of the contactor is abnormal.

Grid-connected inverter

A DC power supply system delivers a DC output that has a neutral point and is higher than the input voltage of a single DC power supply, by a circuit with series-connected switching elements. The DC power supply system addresses the problem of imbalance between the voltage between a positive terminal and the neutral point and the voltage between a negative terminal and the neutral point. In operational control of the DC power supply system, a capacitor voltage between the neutral point and the positive terminal and a capacitor voltage between the neutral point and the negative terminal are compared, and four switching elements are operated to equalize the two capacitor voltages.

Output side capacitor voltage balancing DC power supply system

In a unit inverter system where multiple unit inverters are connected in parallel, the quantity of operating unit inverters is determined in accordance with an amount of power to be converted. A gate signal of a semiconductor switching element of a unit inverter is turned off after an output current of the inverter is reduced when reducing the quantity of inverter units, thereby improving the partial load efficiency of the system without an adverse effect on the system. A regulator connected to the inverter determines dead time of the inverter according to the output current value and an average output current value of the unit inverters, waits for the determined dead time so as to reduce the output current of the unit inverter, and then turns off the gate signal.

Unit inverter system

During single operation of a distributed power supply system that has been disconnected from a commercial electric power system, a frequency increase monitoring circuit is operated and an instruction to output a larger amount of a constant reactive current is given to a reactive current controlling unit. After the output frequency of the distributed power supply exceeds a frequency increase level, the level of an active current is limited in accordance with the level of the outputted reactive current.

Growing community of inventors

Machida, Japan

Kansuke Fujii