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A power generation apparatus and method includes an AC energization synchronous generator, a switching device which connects to a network disposed on a stator side of the AC energization synchronous generator, an energizing device which applies a variable frequency AC to a secondary winding of the A

A power generation apparatus and method includes an AC energization synchronous generator, a switching device which connects to a network disposed on a stator side of the AC energization synchronous generator, an energizing device which applies a variable frequency AC to a secondary winding of the AC energization synchronous generator, and a first voltage detection unit which detects a voltage of the switching device on the stator side. A rotational frequency of the AC energization synchronous generator is estimated or calculated based on a frequency of a stator side voltage of the switching device, while the switching device is open.

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The invention claimed is: 1. A power generation apparatus comprising: an AC energization synchronous generator; a switching device which connects to a network disposed on a stator side of the AC energization synchronous generator; an energizing device which applies a variable frequency AC to a seco

The invention claimed is: 1. A power generation apparatus comprising: an AC energization synchronous generator; a switching device which connects to a network disposed on a stator side of the AC energization synchronous generator; an energizing device which applies a variable frequency AC to a secondary winding of the AC energization synchronous generator; a controller which controls the switching device and the energizing device; a first detector which detects a network side of the switching device; a second detector which detects a voltage of the switching device on a stator side; and a calculator which calculates a slip frequency of the AC energization synchronous generator from a frequency of a stator side voltage generated by energizing a secondary side of the AC energization synchronous generator at a predetermined frequency and makes the secondary side excitation frequency to be coincident with the calculated slip frequency, while the switching device is open; wherein the controller enables changing of an energization current so as to make an amplitude of a stator voltage generated by exciting the secondary side at the slip frequency to be coincident with an amplitude of the network voltage, and enables changing of an excitation frequency so as to make a phase of a stator voltage generated by exciting the secondary side at the slip frequency to be coincident with a phase of a network phase; wherein when the amplitude of the stator voltage is not larger than a predetermined value, the controller controls the secondary side excitation frequency to be fixed in the calculated slip frequency; and wherein when the amplitude of the stator voltage is larger than the predetermined value, the controller controls both of the amplitude of the stator voltage and the slip frequency to be fixed, so that the slip frequency, the phase and the amplitude of the stator voltage and the network voltage take values within predetermined ranges. 2. A power generation apparatus according to claim 1, wherein the controller adjusts the frequency of AC from the energizing device to control the frequency of a stator side voltage of the switching device. 3. A power generation apparatus according to claim 1, wherein the controller enables closing of the switching device and connecting of the AC energization synchronous generator to the network at a rotation speed of the AC energization synchronous generator which is different from a synchronization speed synchronizing the network. 4. A power generation apparatus according to claim 1, wherein the energizing device includes a first power converter which converts AC power to DC power, a second power converter which converts DC power to AC power, and a capacitor disposed between a DC side of the first power converter and a DC side of the second power converter. 5. A power generation apparatus according to claim 1, wherein a rotor of the AC energization synchronous generator is driven by a wind turbine. 6. A method of generating electric power for a power generation apparatus, wherein the power generation apparatus includes; an AC energization synchronous generator; a switching device which connects to a network disposed on a stator side of the AC energization synchronous generator; an energizing device which applies a variable frequency AC to a secondary winding of the AC energization synchronous generator; a controller which controls the switching device and the energizing device; a first detector which detects a network side of the switching device; a second detector which detects a voltage of the switching device on a stator side; a calculator which calculates a slip frequency of the AC energization synchronous generator from a frequency of a stator side voltage generated by energizing a secondary side of the AC energization synchronous generator at a predetermined frequency and makes the secondary side excitation frequency to be coincident with the calculated slip frequency, while the switching device is open; the method comprising the steps of: utilizing the controller to enable changing of an energization current so as to make an amplitude of a stator voltage generated by exciting the secondary side at the slip frequency to be coincident with an amplitude of the network voltage, and to enable changing of an excitation frequency so as to make a phase of a stator voltage generated by exciting the secondary side at the slip frequency to be coincident with a phase of a network phase; wherein when the amplitude of the stator voltage is not larger than a predetermined value, utilizing the controller to control the secondary side excitation frequency to be fixed in the calculated slip frequency; and wherein when the amplitude of the stator voltage is larger than the predetermined value, utilizing the controller to control both of the amplitude of the stator voltage and the slip frequency to be fixed, so that the slip frequency, the phase and the amplitude of the stator voltage and the network voltage take values within predetermined ranges. 7. A method according to claim 6, further comprising the step of utilizing the controller to adjust the frequency of AC from the energizing device so as to control the frequency of a stator side voltage of the switching device. 8. A method according to claim 6, further comprising the step of utilizing the controller to enable closing of the switching device and connecting of the AC energization synchronous generator to the network at a rotation speed of the AC energization synchronous generator which is different from a synchronization speed synchronizing the network. 9. A method according to claim 6, wherein the energizing device includes a first power converter which converts AC power to DC power, a second power converter which converts DC power to AC power, and a capacitor disposed between a DC side of the first power converter and a DC side of the second power converter. 10. A method according to claim 6, further comprising the step of utilizing a wind turbine to drive a rotor of the AC energization synchronous generator.