PT ferromagnetic resonance elimination method implemented by actively inputting resistance through electronic load

A PT ferromagnetic resonance elimination method implemented by actively inputting resistance through an electronic load, comprising the following steps:

• S1:
• setting up a PT comprising primary, secondary and open tertiary windings, and determining a mapping relationship between a secondary voltage and an open tertiary voltage;
• S2:
• based on a resistance matching algorithm and a PID control strategy, constructing a resonance elimination control system and presetting a resistance active-matching strategy;
• and
• S3:
• designing an engineering solution of using the electronic load to replace a DC motor and a circular rheostat for inputting resistance as an active resonance elimination device, the specific operating principle of the active resonance elimination device comprising the following steps:
• S3.1:
• accumulation of resonance energy:
• when in normal operation or when a three-phase load of the system is slightly unbalanced, not starting the active resonance elimination device;
• S3.2:
• slow energy consumption process:
• when the three-phase load of the system is unbalanced, the system has earth fault, starting the active resonance elimination device, inputting the resonance elimination resistance R0, and consuming electrostatic energy accumulated in a zero-sequence loop of the system;
• S3.3:
• resonance energy jump resonance excitation:
• if PT resonance excitation is caused by the disappearance of the earth fault of the system, lightning stroke, or operations such as a closing operation, allowing PT core characteristics to undergo an energy jump;
• S3.4:
• when a core tends to be saturated, converting the electrostatic energy stored in the zero-sequence loop capacitance of the system into electromagnetic energy in the PT core;
• S3.5:
• rapid energy consumption process I:
• inputting the minimum resonance elimination resistance Rmin into the open tertiary winding to consume the electromagnetic energy;
• and
• S3.6:
• rapid energy consumption process II:
• after the completion of Rmin input for 40 ms, entering the rapid energy consumption process II, inputting the initial resistance Ri0 at this time, monitoring the current Is of the open tertiary winding, and adjusting a duty cycle of the Is by means of a metal oxide semiconductor field effect transistor (MOSFET) to achieve the real-time dynamic adjustment of Ri, the Ri is a magnitude of resistance input in real time;
• wherein according to the engineering solution of using the electronic load to replace the DC motor and the circular rheostat for inputting the resistance in step S3, the implementation principle of the electronic load is as follows:
• the electronic load selects the initial resistance Ri0, the magnitude of which is the minimum when the resistance is put into operation;
• further, the electronic load performs full-wave rectification and transformation on the Us of the open tertiary winding by means of a rectifier bridge, thus becoming a pulsating signal with only positive polarity, Us is an effective value of a port voltage of the open tertiary winding that can be directly measured from an opening;
• and
• after being input, the initial resistance Ri0 is modulated by the MOSFET controlled by a PWM signal of 50000 Hz, so that an equivalent matching resistance for resonance elimination is obtained;
• and
• in step S3.1, under the condition of Us=3Uo<7V, the three-phase load of the system is slightly unbalanced, and the active resonance elimination device is not started, Uo is an effective value of a neutral point-to-ground voltage, i.e., a zero-sequence voltage.