Flexible power supply device for AC arc furnace, and control method thereof

A flexible power supply device for an AC arc furnace, comprising:

• a rectifier bridge, an inverter bridge, an arc furnace transformer, a rectifier bridge controller, an inverter bridge controller and an electrode position controller;
• the rectifier bridge is connected to an AC power grid, and the inverter bridge is connected to the AC arc furnace transformer, wherein,
• the rectifier bridge comprises three-phase rectifier bridge arms, and the inverter bridge comprises at least one-phase inverter bridge arm, and the three-phase rectifier bridge arms and at least one-phase inverter bridge arm are sequentially arranged and connected in parallel through positive and negative DC buses;
• the rectifier bridge arms of each phase have the same structure, including an upper rectifier bridge arm, a middle rectifier bridge arm, a lower rectifier bridge arm and two diode bridge arms, and the upper rectifier bridge arm, the middle rectifier bridge arm and the lower rectifier bridge arm are sequentially connected in series, and after the two diode bridge arms are connected in series in the same direction, they are parallel connected at both ends of the middle rectifier bridge arm, and the connection point of the two diode bridge arms is connected to each phase of the AC power supply grid;
• the at least one-phase inverter bridge arm has the same structure, including an upper inverter bridge arm and a lower inverter bridge arm, respectively, and the upper inverter bridge arm and the lower inverter bridge arm are connected in series, and the connection point is connected to the corresponding phase of the electric arc furnace transformer,
• the rectifier bridge controller is specifically used for:
• detecting a grid-side voltage of the rectifier bridge, and track the phase of the power grid through a phase lock loop;
• based on the relationship between a DC voltage udc of the rectifier bridge and a DC voltage command value udc* of the rectifier bridge, generating an active current command value id* of the rectifier bridge through a DC voltage controller;
• based on the active current command value id* of the rectifier bridge, calculating reactive power consumed on a grid-side impedance, and generating a reactive current command value ig* of the rectifier bridge to compensate the reactive power consumed on the grid-side impedance;
• generating dq voltage command values ud* and ug* of the rectifier bridge from the active current command value id* of the rectifier bridge and the reactive current command value ig* of the rectifier bridge through a current regulator, and generating AC modulation command values ua*, ub* and uc* of the rectifier bridge through ⅔ conversation;
• calculating a DC modulation command value ucom* of the rectifier bridge:
• u
• com
• *
• =
• the
• ⁢
• DC
• ⁢
• voltage
• ⁢
• command
• ⁢
• value
• ⁢
• u
• dc
• *
• ⁢
• of
• ⁢
• the
• ⁢
• rectifier
• ⁢
• bridge
• 2
• ⁢
• u
• N
• ,
• where uN is the capacitor voltage of the power modules;
• and
• adding or subtracting the AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge, and obtaining a trigger pulse of each rectifier bridge arm according to an AC current direction by nearest level modulation;
• the inverter bridge controller is specifically used for:
• controlling a current id and a current ig according to an active current command value id* of the inverter bridge and a reactive current command value ig* of the inverter bridge through a current regulator, and generating dq voltage command values ud* and ug* of the inverter bridge, and generating AC modulation command values ua*, ub* and uc* of the inverter bridge through ⅔ conversion, wherein the active current command value id* of the inverter bridge is a preset value, and the reactive current command value ig* of the inverter bridge is preset as 0;
• calculating a DC modulation command value ucom* of the inverter bridge:
• u
• com
• *
• =
• the
• ⁢
• DC
• ⁢
• voltage
• ⁢
• command
• ⁢
• value
• ⁢
• u
• dc
• *
• ⁢
• of
• ⁢
• the
• ⁢
• inverter
• ⁢
• bridge
• 2
• ⁢
• u
• N
• ,
• wherein uN is the capacitor voltage of the power modules;
• subtracting the DC modulation command value of the inverter bridge from the AC modulation command value of the inverter bridge to obtain a modulation signal for the upper inverter bridge arm, and adding the DC modulation command value of the inverter bridge and the AC modulation command value of the inverter bridge to obtain a modulation signal for the lower inverter bridge arm, and finally obtaining a trigger pulse of each bridge arm of the inverter bridge by nearest level modulation.