Studies on DC System Interconnection by Means of Superconducting Magnetic Energy Storage

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1. Experimental Studies on DC System Interconnection Using Superconducting Coil ; Two sets of 3-phase thyristor AC-DC converter were composed, and a experimental DC transmission system was constructed with the superconducting coil ( L = 95 H, I_<max> = 20 A, Energy Storage Capacity = 1. kj ), which connects two distribution boards. Experiments of power absorption and release were done by means of personal computer control. The specified values of power were i) constant power, ii) switching of absorption and release with constant power, and iii) sinusoidal absorption and release. It was confirmed from the experiments that the power can be controlled from the two DC interconnected subsystems independently. It takes, however, as long as about 0.3 sec to complete one cycle of the input of measured values, the computation and the output of the control value, which puts the limit of about 0.6 Hz on the switching frequency of power absorption and rellease. It is the future problems to improve … More the control strategy and the computer programming for control.2. Improvement of Steady-State Stability by DC System Interconnection with Superconducting Coil ; The system stabilizing effect of DC system interconnection and superconducting coil was examined regarding the steady-state stability on a sample longitudinal power system by means of the eigenvalue analysis. It was made clear from the results of the analysis that DC system interconnection fairly improves the steady-state stability, and that the energy storage capability of superconducting coil can stabilize the system further if the both converters are controlled appropriately. When there is a power flow on the interconnection line, the system from which the power flows out ( rectifier side ) is remarkably stabilized.3. Improvement of Transient Stability ; The power swing damping effect was examined on the same sample power system as above by means of computer simulation. The disturbance assumed was a tripping of a generator. By dividing the system by DC interconnection, the disturbance on one subsystem does noto almost affect the other subsystem. The introduction of a superconducting coil can makes the power swing damping faster. Less