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Two-dimensional stability analyses for open-cycle supersonic disk MHD generators are carried out which take into account electrical boundary conditions. A method of r-θ two-dimensional linear stability analysis for supersonic disk MHD generators is proposed which examines the time growth rate of perturbations. The growth rate is determined by the characteristic equation which is derived from the electrical boundary conditions. Whether the perturbations grow or decay is judged diagrammatically in a way similar to the Nyquist method. A coal-fired outflow supersonic disk MHD generator of commercial scale is analyzed under several types of boundary conditions. The stability is much affected by the electrical boundary conditions and also by the azimuthal wavenumber of disturbances. Two-dimensional analysis has revealed an azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the one-dimensional analysis. The analysis also shows that the instability can be suppressed by subdividing the load section with control electrodes. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 23–30, 1997 [ABSTRACT FROM AUTHOR]

A new power control method is proposed which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line-commutated inverter. The thermal input of the generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method can realize both high performance for part load operation and fast output power control of which the time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance. [ABSTRACT FROM AUTHOR]

Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analysis, and (2) time-dependent 1-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u - a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u - a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current. Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u - a and u waves are unstable. [ABSTRACT FROM AUTHOR]

Performance characteristics of self-excited pulsed MHD power systems are investigated with one-dimensional time-dependent calculations using a gas–liquid two-fluid model. First, the Russian pulsed MHD power system “Pamir-3U” is analyzed. The result of numerical simulations of hot-fire tests shows good agreement with the experimental data, confirming the validity of the mathematical model. Performance analysis of Pamir-3U reveals that the power output is approximately constant with the variation of load resistance, while the ballast resistor consumes a large amount of electric power. It is also shown that the system has been optimally designed to supply a large load current. Next, a new system yielding larger power output is proposed and analyzed. The obtained characteristics show that the new system can provide the maximum power output of 25 MW, which is 10 MW larger than that of Pamir-3U. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 30–37, 2000 [ABSTRACT FROM AUTHOR]

The authors propose a new power consolidation-inversion-control system for the Faraday MHD generator using the voltage source PWM inverters. The dc output power for each electrodes pair of the MHD generator is at first inverted into three-phase ac power by a voltage source PWM inverter, and then the ac powers are consolidated by transformers. The proposed system does not need such expensive equipment as an ac filter or phase modifier and can independently and simultaneously control the active and reactive powers provided to the electric power system. Numerical simulations of the whole system, including the Faraday MHD generator, the proposed system can stably and steadily transit and control the electric power from the MHD generator to the electric power system. It is also confirmed that the proposed system can be independently and simultaneously control the active and reactive powers and can be used as a fast power controller. [ABSTRACT FROM AUTHOR]