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In a power generator, three-phase armature windings and a switching unit are provided for each phase armature winding. The switching unit includes a pair of a high-side switching element with a first diode and a second low-side switching element with a second diode. The switching unit rectifies, thr

In a power generator, three-phase armature windings and a switching unit are provided for each phase armature winding. The switching unit includes a pair of a high-side switching element with a first diode and a second low-side switching element with a second diode. The switching unit rectifies, through at least one of the high-side switching element, the first diode, the second low-side switching element, and the second diode, a voltage induced in each phase armature winding. A zero-cross detector detects a point of time when a phase current based on the voltage induced in each phase armature winding is reversed in direction as a zero-cross point of the phase current. A determiner determines an off timing of the high-side switching element or the low-side switching element for each phase armature winding relative to the zero-cross point detected by the zero-cross detector.

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1. A power generator comprising: at least two-phase armature windings;a switching unit including, for each of the at least two-phase armature windings, a pair of a high-side switching element with a first diode parallely connected thereto and a second low-side switching element with a second diode p

1. A power generator comprising: at least two-phase armature windings;a switching unit including, for each of the at least two-phase armature windings, a pair of a high-side switching element with a first diode parallely connected thereto and a second low-side switching element with a second diode parallely connected thereto, the switching unit being configured to rectify, through at least one of the high-side switching element, the first diode, the second low-side switching element, and the second diode, a voltage induced in each of the at least two-phase armature windings;a zero-cross detector that detects a point of time when a phase current based on the voltage induced in each of the at least two-phase armature windings is reversed in direction as a zero-cross point of the phase current; anda determiner that determines an off timing of at least one of the high-side switching element and the low-side switching element for each of the at least two-phase armature windings relative to the zero-cross point detected by the zero-cross detector. 2. The power generator according to claim 1, wherein the determiner is configured to determine the off timing of the at least one of the high-side switching element and the low-side switching element for each of the at least two-phase armature windings relative to the zero-cross point of the phase current flowing through a corresponding one of the at least two-phase armature windings. 3. The power generator according to claim 2, wherein the zero-cross detector and the determiner are provided for each of the at least two-phase armature windings. 4. The power generator according to claim 2, wherein the zero-cross detector is configured to detect, in a plurality, the zero-cross point each time the phase current based on the voltage induced in each of the at least two-phase armature windings is reversed in direction, and the determiner is configured to determine the off timing of the at least one of the high-side switching element and the low-side switching element relative to one of the plurality of zero-cross points, the phase current being reduced so as to be reversed in direction at the one of the plurality of zero-cross points. 5. The power generator according to claim 1, further comprising a field rotor configured to rotate to generate a rotating magnetic field, the rotating magnetic field inducing the voltage in each of the at least two-phase armature windings, wherein the zero-cross detector is configured to detect, in a plurality, the zero-cross point each time the phase current based on the voltage induced in each of the at least two-phase armature windings is reversed in direction, and the determiner is configured to, when at least one of first and second conditions is met at a present time, determine the off timing of the at least one of the high-side switching element and the low-side switching element relative to at least one of the plurality of zero-cross points, the first condition being that an output current from the switching unit is equal to or lower than a preset value, the second condition being that a rotational speed of the rotor is equal to or hither than a preset value, the at least one of the plurality of zero-cross points being previously detected since the present time. 6. The power generator according to claim 1, wherein the determiner is configured to, for each of the at least two-phase armature windings, turn off one of the high-side switching element and the low-side switching element, and, after a lapse of a preset time since the off of the one of the high-side switching element and low-side switching element, turn on the other of the high-side switching element and low-side switching element. 7. The power generator according to claim 1, further comprising a field rotor configured to rotate to generate a rotating magnetic field, the rotating magnetic field inducing the voltage in each of the at least two-phase armature windings, wherein the determiner is configured to, when at least one of first and second conditions is met at a present time, determine the off timing of any one of the high-side switching element and the low-side switching element relative to the zero-cross point of the phase current flowing through the other of the high-side switching element and the low-side switching element, the first condition being that an output current from the switching unit is equal to or lower than a preset value, the second condition being that a rotational speed of the rotor is equal to or hither than a preset value. 8. The power generator according to claim 1, wherein the determiner is configured to: determine each of the off timing and an on timing of each of the high-side switching element and the low-side switching element for each of the at least two-phase armature windings to a timing after a lapse of a preset time since the zero-cross point of the phase current flowing through a corresponding one of the at least two-phase armature windings, the preset time being determined based on the zero-cross point of the phase current flowing through the other of the at least two-phase armature windings. 9. The power generator according to claim 1, wherein the determiner is configured to simultaneously turn on any one of: the high-side switching element for one of the at least two-phase armature windings, and the high-side switching element for the other of the at least two-phase armature windings; andthe low-side switching element for one of the at least two-phase armature windings, and the low-side switching element for the other of the at least two-phase armature windings. 10. A power generator comprising: at least two-phase armature windings;a switching unit including, for each of the at least two-phase armature windings, a pair of a high-side switching element with a first diode parallely connected thereto and a second low-side switching element with a second diode parallely connected thereto, the switching unit being configured to rectify, through at least one of the high-side switching element, the first diode, the second low-side switching element, and the second diode, a voltage induced in each of the at least two-phase armature windings;a phase detector that directly detects a phase of a phase current, the phase current being generated based on the voltage induced in each of the at least two-phase armature windings; anda controller configured to operate, in a phase control mode, to turn on each of the high-side switching element and the low-side switching element within an on period, the on period being delayed since a start of a conductive period of a corresponding one of the first and second diodes, the on period of each of the high-side switching element and the low-side switching element being determined based on the detected phase of the phase current. 11. A power generator according to claim 10, wherein the phase detector includes a zero-cross detector that detects, as a zero-cross point of the phase current, a point of time when the phase current generated based on the voltage induced in each of the at least two-phase armature windings is reversed in direction, the zero-cross point of the phase current being information indicative of the phase of the phase current. 12. The power generator according to claim 11, wherein the controller is configured to operate, in a synchronous control mode, to turn on and off each of the high-side switching element and the low-side switching element such that the on period of each of the high-side switching element and the low-side switching element is within the conductive period of a corresponding one of the first and second diodes, the controller being configured to selectively operate in one of the phase control mode and the synchronous control mode, an on timing and an off timing of each of the high-side switching element and the low-side switching element being determined relative to the zero-cross point detected by the zero-cross detector. 13. The power generator according to claim 12, further comprising a field rotor configured to rotate to generate a rotating magnetic field, the rotating magnetic field inducing the voltage in each of the at least two-phase armature windings, wherein the controller being configured to selectively operate in the phase control mode when power requirement for the power generator is higher than a preset value and a rotational speed of the rotor is lower than a preset value. 14. A power generator comprising: a rotor including a field winding;at least two-phase armature windings, when the field winding is energized with the rotor being rotated to generate a rotating magnetic field, each of the at least two-phase armature winding being configured to induce a voltage therein based on the generated rotating magnetic field;a switching unit including, for each of the at least two-phase armature windings, a pair of a high-side switching element with a first diode parallely connected thereto and a second low-side switching element with a second diode parallely connected thereto, the switching unit being configured to rectify, through at least one of the high-side switching element, the first diode, the second low-side switching element, and the second diode, a voltage induced in each of the at least two-phase armature windings;a voltage regulator having a switching element connected with the field winding, the voltage regulator being configured to control a duty cycle of the switching element to thereby regulate an output of the switching unit; anda controller configured to:operate, if a rotational speed of the rotor is higher than a first preset value and lower than a second preset value higher than the first preset value, and a value of the duty cycle of the switching element is equal to or higher than a preset value, in a phase control mode to turn on each of the high-side switching element and the low-side switching element within an on period, the on period being delayed since a start of a conductive period of a corresponding one of the first and second diodes; andoperate, if at least one of the rotational speed of the rotor is equal to or lower than the first preset value, the rotational speed of the rotor is equal to or higher than the second preset value, and the value of the duty cycle of the switching element is lower than the preset value, in a synchronous control mode to turn on and off each of the high-side switching element and the low-side switching element such that the on period of each of the high-side switching element and the low-side switching element is within the conductive period of a corresponding one of the first and second diodes.