1. Technical Field
This invention relates to the technical field of a turbo charger generator configured to supply compressed intake air to an internal combustion engine by driving a gas turbine and a compressor with exhaust gas discharged from the internal combustion engine, and to supply AC power generated by driving a generator connected to an end of a shaft of the compressor to an electric power system via a power conversion unit.
2. Description of the Related Art
There are known turbo charger generators, for example, which are devised to improve the output of an internal combustion engine by supplying compressed intake air to the internal combustion engine by driving a gas turbine and a compressor with exhaust gas discharged from the internal combustion engine, and to generate power by means of a generator using excess energy left from the driving of the compressor. The power output from the generator varies according to an operating condition (e.g. energy of the exhaust gas) of the internal combustion engine. Therefore, the power generated by the generator is converted into an appropriate frequency and voltage with a power conversion unit that is an inverter or the like before being supplied to the electric power system.
In a turbo charger generator disclosed in Japanese Patent Application Publication No. 2008-286016, a rotating speed of the generator is maintained at an appropriate value by feedback controlling the rotating speed of the generator based on a detection value. This patent document claims that the generator is able to perform efficient power generation by utilizing excess energy while improving the intake pressure generated by the turbo charger.
Patent Document 1: Japanese Patent Application Publication No. 2008-286016
JP 2008-286016 intends to control the output power by maintaining the rotating speed of the generator at a predetermined value. However, in an internal combustion engine, the engine speed at which the internal combustion engine can operate efficiently (optimum engine speed) varies as the load varies. Therefore, when the engine speed is controlled so as to be maintained at a predetermined value like in JP 2008-286016, the engine speed will differ from the optimum engine speed, leading to degradation in use efficiency of energy. Consequently, the technique of JP 2008-286016, which controls the output power based on engine speed, has the drawback that good load followability cannot be obtained when the load varies.
Further, when as in the case of a vessel, a plurality of generators are provided, and one or some of those generators is/are turbo charger generator(s), the power supplied to an electric power system must be adjusted by establishing coordination between the turbo charger generator(s) and the other generator(s) (by controlling the power generated by the turbo charger generator(s) and the power generated by the other generator(s) so that the total generation of power does not become excessively large). However, no consideration is given in JP 2008-286016 to control of power generation under such coordination control. In particular, since good followability cannot be obtained when the load varies, as described above, a protection circuit must be provided so that it is activated when excessive power is supplied to the electric power system. Thus, the technique of Patent Document 1 has a problem that the general configuration becomes complicated.
Furthermore, according to JP 2008-286016, the rotating speed is detected based on an output voltage waveform of an electric motor. However, the voltage amplitude is very small when the generator is rotating at a low speed, and the detection is difficult. This causes a problem that it is difficult to ensure a high control accuracy during low-speed operation of the generator particularly when the electric power system is synchronously operated.
Still further, in JP 2008-286016, a speed detector or a frequency detection unit must be provided in order to detect a rotating speed of the generator. This complicates the detection equipment and the control circuit, and makes it difficult to embody the technique.