A DC power transmission system interconnects a plurality of AC systems via a DC line. A plurality of power conversion devices are connected between the plurality of AC systems and the DC line. One of the plurality of power conversion devices controls the voltage on the DC line, while the remaining power conversion device controls a current input and output to and from the DC line. In a restart which resumes power conversion from a stopped state for controlling a DC current on the DC line, the power conversion device performing current control monitors the voltage on the DC line and starts a restart operation without transmitting or receiving information to or from the other power conversion device.

Embodiments of the present disclosure relates to a method and device for balancing a supply current. In one embodiment, a current supply current for a load is detected. A first signal representing the current supply current is transmitted to a digital logic module. A second signal representing a maximum supply current and a third signal representing a minimum supply current are received from the digital logic module. A subsequent supply current for the load is determined based on the current supply current, the maximum supply current and the minimum supply current. By using the method and device according to the embodiments of the present disclosure, the supply currents of a plurality of power supply units for the load can be balanced a simple way with a low hardware cost.

A switching power supply device includes: a plurality of power supply circuits which include a first power supply circuit and a second power supply circuit and respectively correspond to a plurality of phases of a multiphase AC power supply; a switching circuit; an inrush current prevention (ICP) circuit; and a control circuit. The control circuit causes the switching circuit to switch a phase to be connected to the second power supply circuit to a phase corresponding to the first power supply circuit, and causes the ICP circuit to function so that initial charge of electrolyte capacitors included in the respective power supply circuits is performed. After the initial charge is completed, the control circuit causes the switching circuit to switch the phase to be connected to the second power supply circuit to the phase corresponding to the second power supply circuit, and causes the ICP circuit to turn off.

The switching power supply device is provided with: a plurality of power supply circuits corresponding to phases of a multi-phase AC power supply; a switching circuit that is capable of switching a phase connected to a power supply circuit not corresponding to one discretionary phase of the multi-phase AC power supply between the one discretionary phase and a phase to which the power supply circuit corresponds; an inrush current prevention circuit for preventing inrush current that is provided on a negative-electrode-side power supply line of the multi-phase AC power supply and at a position further toward the multi-phase AC power supply than is a connection point to which each of the plurality of power supply circuits are connected; and a filter circuit that is provided between the multi-phase AC power supply and the inrush current prevention circuit and has all lines of the plurality of phases magnetically coupled thereto.

The power supply apparatus includes a switching element connected to a primary winding of a transformer to which an input voltage is applied; a feedback unit configured to output a first feedback voltage according to an output voltage, the output voltage induced in a secondary winding of the transformer and output to a load; a current detection unit for detecting a current flowing to the switching element and output a second feedback voltage according to the current detected; a limiting unit for limiting the first feedback voltage so that the current flowing to the switching element is below a predetermined current value; an output unit for outputting a driving signal for the switching element based on the first feedback voltage limited by the limiting unit and on the second feedback voltage; and a control unit for controlling the switching element according to the driving signal output from the output unit.

A DC power transmission system interconnects a plurality of AC systems via a DC line. A plurality of power conversion devices are connected between the plurality of AC systems and the DC line. One of the plurality of power conversion devices controls the voltage on the DC line, while the remaining power conversion device controls a current input and output to and from the DC line. In a restart which resumes power conversion from a stopped state for controlling a DC current on the DC line, the power conversion device performing current control monitors the voltage on the DC line and starts a restart operation without transmitting or receiving information to or from the other power conversion device.

An AC capacitor is coupled to a totem-pole type PFC circuit. In response to detection of a power input disconnection, the PFC circuit is controlled to discharge the AC capacitor. The PFC circuit includes a resistor and a first MOSFET and a second MOSFET coupled in series between DC output nodes with a common node coupled to the AC capacitor. When the disconnection event is detected, one of the first and second MOSFETs is turned on to discharge the AC capacitor with a current flowing through the resistor and the turned on MOSFET. Furthermore, a thyristor may be simultaneously turned on, with the discharge current flowing through a series coupling of the MOSFET, resistor and thyristor. Disconnection is detected by detecting a zero-crossing failure of an AC power input voltage or lack of input voltage decrease or input current increase in response to MOSFET turn on for a DC input.

A resistor ladder comprising identical resistors is disposed electrically in parallel with a multicell battery to calibrate voltage-controlled oscillators or analog-to-digital convertors for voltage balancing the battery cells in the multicell battery. Switches in a first state provide the voltage across each resistor as inputs to the VCOs or ADCs. The number of oscillations of the output signal of each VCO or ADC over a predetermined time period are compared to determine an offset error. Switches in a second state provide the voltage across each battery cell as inputs to the VCOs or ADCs. The battery cells with a higher relative voltage can be discharged until they are balanced. Some aspects describe temperature-adjusted and interpolated determinations of electrical quantities in the cells such as voltage and/or current.

Since a power converter including a modular multilevel converter uses a large number of cells each combining a plurality of switching elements and a DC capacitor, there is a problem of conduction loss due to the switching elements. The conduction loss is reduced by connecting a bypass circuit between terminals of each of the cells, controlling to open and close the switching element, and controlling to short-circuit the bypass circuit connected to the cell controlled to output zero voltage.

A first voltage control circuitry controls a first representative value, i.e., an average-value corresponding value of DC capacitor voltages of all converter cells to follow an overall voltage command value. A phase balance control circuitry controls second representative values, i.e., average-value corresponding values of DC capacitor voltages of the converter cells in leg circuits for respective phases to follow the first representative value. A positive-negative balance control circuitry controls deviations of third representative values, i.e., average-value corresponding values of the DC capacitor voltages of the converter cells in the positive and negative arms of the leg circuits for respective phases to become zero between the positive and negative arms. An individual balance control circuitry controls DC capacitor voltages of all the converter cells to follow the third representative values.