Power supply apparatus for sub-module of MMC
Provided is a power supply apparatus for sub-modules of a Modular Multilevel Converter (MMC) which stably supplies power to the sub-modules of the MMC in connection with an HVDC system. The power supply apparatus for sub-modules of an MMC can include a charging unit in which an input voltage between P and N busses of the MMC is stored, a relay unit connected in parallel with the charging unit, a resistor connected in series with the relay unit, a TVS diode connected in series with the resistor, a Zener diode connected in series with the TVS diode, a transformer for delivering the input voltage (in a primary winding) to a secondary winding thereof, and a switch for switching the flow of current supplied to the transformer.
1. An apparatus for supplying power to a sub-module of a Modular Multilevel Converter (MMC), comprising:
a charging unit in which an input voltage between P and N buses of the MMC is stored;
a relay unit connected in parallel with the charging unit;
a resistor connected in series with the relay unit;
a TVS diode connected in series with the resistor;
a Zener diode connected in series with the TVS diode;
a transformer for delivering the input voltage received in a primary winding to a secondary winding thereof;
a switch connected to the primary winding of the transformer in series for switching a flow of current supplied to the transformer;
a control unit for enabling current to flow to the transformer by turning on the switch upon receiving a clamping voltage of the Zener diode; and
a relay switching unit for operating the relay unit upon receiving a voltage output from the secondary winding of the transformer,
wherein, when the input voltage reaches a rated voltage, the control unit turns on the switch so that a closed circuit is formed by the switch and the primary winding of the transformer, and thereby makes the current flow through the switch and the primary winding, and then the transformer outputs the voltage as a secondary voltage, and
wherein, the relay switching unit operates to open the relay unit by using the secondary voltage and opens so that no current is applied to the control unit through the relay unit.
2. The apparatus of claim 1 , wherein the input voltage increases from 0 V to a predetermined maximum voltage (Vmax).
3. The apparatus of claim 2 , wherein:
the relay unit includes a b-contact switch, and an initial state of which is set to a shorted state; and
before the increasing input voltage reaches the rated voltage for starting the power supply apparatus, the TVS diode does not conduct current, which is supplied through the b-contact switch, wherein no current flows to the control unit.
4. The apparatus of claim 3 , wherein:
when the input voltage increases and reaches the rated voltage, the TVS diode conducts the supplied current so as to be supplied to the control unit; and
the control unit turns on the switch when the supplied current is applied to the control unit.
5. The apparatus of claim 4 , wherein:
when the switch is turned on, a primary voltage is supplied to the transformer by the supplied current;
the transformer outputs the secondary voltage by delivering the primary voltage to the secondary winding; and
the relay switching unit receives the secondary voltage and opens the b-contact switch of the relay unit.
6. The apparatus of claim 5 , wherein:
after the b-contact switch of the relay unit is opened, the clamping voltage of the Zener diode is not input to the control unit; and
the control unit operates by receiving the secondary voltage of the transformer as operating power.