Abstract: A current suppression control unit calculates a correction amount of a reference voltage command value for operating a power converter as a voltage source, and sets an amplitude value of a voltage command value by reflecting the correction amount in an amplitude value of the reference voltage command value. The correction amount is set to make the amplitude value of the voltage command value smaller than the amplitude value of the reference voltage command value, in response to a decrease in an AC voltage at an interconnection point.

Abstract: A power conversion system including: a first self-commutated converter connected between a first AC power system, and a first DC main line and a DC return line for first high voltage DC transmission; a second self-commutated converter connected between the first AC power system, and the DC return line and a second DC main line for second high voltage DC transmission; and a control device, wherein when detecting a single or double line to ground fault inside the second self-commutated converter and detecting an occurrence of a missed zero crossing in a non-faulted phase of the first AC power system, the control device causes the first self-commutated converter to output a DC component for eliminating the missed zero crossing to the first AC power system, and then opens an AC circuit breaker in order to separate the second self-commutated converter from the first AC power system.

Abstract: A power conversion device includes a self-commutated power converter that performs power conversion between an AC circuit and a DC circuit, and a control device that controls switching operation of a switching element included in the self-commutated power converter. The control device performs first control to increase a switching frequency of the switching element when a control command value for the self-commutated power converter becomes equal to or greater than a first threshold value.

Abstract: A power conversion device includes a power converter and a control device. The power converter converts a DC power output from a power storage element into an AC power. The control device includes a phase synchronizing unit to estimate a reference phase of an output voltage of the power converter synchronized with a phase of an AC voltage at an interconnection point, a characteristics simulating unit to generate an active power command value based on a phase difference between a reference phase and the phase of the AC voltage at the interconnection point, a DC voltage command generating unit to generate a DC voltage command value, a voltage command generating unit to generate an AC voltage command value so that an output current of the power converter becomes less than a threshold, and a signal generating unit to generate a control signal based on the AC voltage command value.

Abstract: A power conversion device includes a power converter including an arm circuit having a plurality of converter cells connected in cascade. Each of the converter cells includes a bridge circuit including a plurality of semiconductor switching elements, and a power storage element connected to a first input/output terminal on a high potential side and a second input/output terminal on a low potential side through the bridge circuit. One or more of the converter cells are full-bridge converter cells. Among four arms that constitute the bridge circuit of the full-bridge converter cell, an arm between a high potential-side node of the power storage element and the second input/output terminal, or an arm between a low potential-side node of the power storage element and the first input/output terminal includes a resistor element connected in series with the semiconductor switching element.

Abstract: A control device includes a power generator simulation unit to generate a voltage command value, and a signal generation unit to generate a control signal for the power converter. The power generator simulation unit includes a first integrator to time-integrate a first difference between effective power and a target value of the effective power and output a first angular frequency, a second integrator to time-integrate the first angular frequency and output a phase of an AC voltage, and a voltage command generation unit to generate the voltage command value based on the AC voltage, a target value of the AC voltage, and the phase. When a voltage difference between the AC voltage and the target value of the AC voltage is greater than a threshold, the first integrator outputs a difference between an angular frequency of the AC voltage and a reference angle frequency as the first angular frequency.

Abstract: A power conversion system includes: a self-commutated converter connected between an AC power system, and a first DC main line and a DC return line; a line-commutated converter connected between the AC power system, and the DC return line and a second DC main line; and a control device. When activating the self-commutated converter and the line-commutated converter, the control device activates the self-commutated converter, and after completion of activation of the self-commutated converter, activates the self-commutated converter. The self-commutated converter can be activated first to take advantage of a function of the self-commutated converter that is not included in the separately-commutated converter.

Abstract: A power conversion device includes a power storage element, a power converter, and a control device. The control device includes: a power generator simulation unit to simulate characteristics of a synchronous power generator based on an active power command value and active power, to generate an angular frequency deviation; a constant setting unit to set at least one of an inertia constant and a damping constant of the synchronous power generator; a phase generation unit to generate a reference phase, based on the angular frequency deviation and a reference angular frequency; and a signal generation unit to generate a control signal, based on the reference phase and a reference voltage command value. When the AC voltage of the power system fluctuates, the constant setting unit sets at least one of the inertia constant and the damping constant such that active power to be inputted and outputted decreases.

Abstract: In an MMC-type power conversion device, a control device calculates an evaluation value representing the degree of variations in voltage of capacitors of individual converter cells. When this evaluation value exceeds a threshold value, the control device controls the converter cells as follows: (i) when current in a positive direction flows through a first converter cell with a voltage of the capacitor greater than a mean value, reducing an output time of positive voltage, (ii) when current in a negative direction flows through the first converter cell, increasing an output time of positive voltage, (iii) when current in the positive direction flows through a second converter cell with a voltage of the capacitor smaller than a mean value, increasing an output time of positive voltage, or (iv) when current in the negative direction flows through the second converter cell, reducing an output time of positive voltage.

Abstract: A power conversion device includes: a power converter which includes a plurality of arms for each phase of an alternating-current system; and a control device. Each arm, among the plurality of arms, has a plurality of converter cells that are cascade-connected. The plurality of converter cells each have a plurality of switching elements, and a power storage element. The control device includes: a balance control unit to control a balance of voltages of power storage elements between predetermined groups, based on a balance command value; a circulating-current control unit to control a circulating current circulating through the power converter, based on a circulating-current command value; and an oscillation control unit to cause the balance command value to oscillate at a first frequency lower than a fundamental frequency of the alternating-current system, based on the voltages of the power storage elements included in the arm.

Abstract: In a power conversion system, a first power converter is connected between a first AC power system, and a first DC main line and a DC return line. A second power converter is connected between the first AC power system, and the DC return line and a second DC main line. A first control device controls the first power converter in accordance with a first active power command value. A second control device controls the second power converter in accordance with a second active power command value. A common control device sets the first active power command value and the second active power command value by distributing a command value of total active power output from the entire power conversion system to the first AC power system. The common control device makes the first active power command value and the second active power command value different from each other.

Abstract: A power conversion device includes a power converter connected between a multi-phase alternating-current circuit and a direct-current circuit, and a control device to control the power converter. The control device detects an unbalanced component indicating a voltage unbalanced component or a current unbalanced component of the alternating-current circuit and limits a magnitude of an alternating current flowing between the power converter and the alternating-current circuit based on the unbalanced component.

Abstract: A power conversion system includes a plurality of power conversion devices connected to a plurality of AC systems, respectively. The power conversion devices are further connected to a common DC circuit. The power conversion system further includes a start-up device to start up each power conversion device. The start-up device selects an AC system that satisfies a defined condition relating to power supply capability from among the plurality of AC systems based on system information of the plurality of AC systems and starts up a power conversion device connected to the selected AC system.

Abstract: A power conversion device includes: a power converter which includes a plurality of converter cells; and a control device.

Abstract: A power conversion device includes a power converter including a plurality of arms each having a plurality of converter cells connected to each other in cascade. Each converter cell includes a capacitor electrically connected to input/output terminals through a plurality of switching elements. A control device performs AC current control in accordance with a deviation between a detected AC current and an AC current command value and individual voltage control in accordance with a deviation between a voltage of each individual capacitor and an individual voltage command value. The control device calculates an evaluation value indicating the degree of variations in voltage of the individual capacitors. When the evaluation value is greater than a threshold value, the control device changes control of the power converter such that arm current flowing through each of the arms increases while the AC current control and the individual voltage control are being performed.

Abstract: A power conversion device includes a power conversion circuit unit including a plurality of leg circuits, and a control device. Each of the leg circuits includes a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having the capacitor and connected in series to each other. The plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current. The control device executes control processing for increasing a current flowing through the second converter cell when a voltage at the capacitor in the second converter cell is less than a first threshold value.

Abstract: A power conversion device includes a plurality of leg circuits and a control device. The control device controls an output voltage at a first converter cell, which is controlled not based on the circulating current, based on a first voltage instruction value. The control device controls an output voltage at a second converter cell using a first value based on a deviation between a circulating current and a circulating current instruction value and a second value based on a deviation between a capacitor voltage and a capacitor voltage instruction value in the second converter cell. When the capacitor voltage at the second converter cell is less than a first threshold, the control device linearly combines an auxiliary voltage instruction value including at least one of a DC component and a fundamental AC component of the AC circuit with the first value and the second value.

Abstract: A current suppression control unit calculates a correction amount of a reference voltage command value for operating a power converter as a voltage source, and sets an amplitude value of a voltage command value by reflecting the correction amount in an amplitude value of the reference voltage command value. The correction amount is set to make the amplitude value of the voltage command value smaller than the amplitude value of the reference voltage command value, in response to a decrease in an AC voltage at an interconnection point.

Abstract: A power conversion system includes: a self-excited converter connected between an AC power system, and a first DC main line and a DC return line; a separately-excited converter connected between the AC power system, and the DC return line and a second DC main line; and a control device. When activating the self-excited converter and the separately-excited converter, the control device activates the self-excited converter, and after completion of activation of the self-excited converter, activates the separately-excited converter. The self-excited converter can be activated first to take advantage of a function of the self-excited converter that is not included in the separately-excited converter.

Abstract: A current suppression control unit calculates correction terms of reference voltage command values for operating a power converter as a voltage source. The correction terms are calculated to compensate for respective current deviations of output currents transformed on two axes, with respect to current command values on a two-axis rotating coordinate system for suppressing an output current of the power converter to less than or equal to a control upper limit value. A proportional control unit has proportional elements to reflect the current deviations in the correction terms within the same axes of the two axes. A decoupling control unit has integral elements to reflect the current deviations in the correction terms between the different two axes.