초록 ▼

The excitation overcurrent detection unit for the doubly-fed electric machine is provided with a function to determine an excitation current magnitude relationship among three phases. The firing pulse is held to on-state or off-state to cause the largest-current phase and the second-largest-current

The excitation overcurrent detection unit for the doubly-fed electric machine is provided with a function to determine an excitation current magnitude relationship among three phases. The firing pulse is held to on-state or off-state to cause the largest-current phase and the second-largest-current phase to charge the DC capacitor by the operation of diodes. The conduction ratio of the third-largest-current phase or minimum current phase is controlled according to the detected current value to protect against a possible short-circuit across the DC capacitor. When the voltage of the DC capacitor exceeds a preset value, the voltage is suppressed by operating active or passive power devices.

대표청구항 ▼

1. A doubly-fed motor/generator comprising: a wound-rotor induction machine having its stator side armature winding connected to an electric power grid;a first power converter having three-phase bridge connected arms of an IGBT as a self-turn-off power device and a free-wheeling diode or a MOSFET as

1. A doubly-fed motor/generator comprising: a wound-rotor induction machine having its stator side armature winding connected to an electric power grid;a first power converter having three-phase bridge connected arms of an IGBT as a self-turn-off power device and a free-wheeling diode or a MOSFET as a self-turn-off power device, each of the arms having its AC side terminals connected to a rotor side excitation winding of the wound-rotor induction machine, wherein the first power converter pulse-width-modulation-controls the self-turn-off power devices;a DC capacitor connected between DC side terminals of the first power converter;a second power converter having its DC side terminals connected to both terminals of the DC capacitor and its AC side terminals connected to the power grid;an excitation current sensor to detect a current flowing in an excitation winding of the wound-rotor induction machine;an excitation current controller to calculate an excitation current command value for a slip frequency equal to a difference between a grid frequency and a rotor frequency of the wound-rotor induction machine and to output a first pulse command that causes the detected excitation current value from the excitation current sensor to match the excitation current command value, the first firing pulse command being fed to the self-turn-off power devices of the first power converter;a pulse command controller having a function to identify a phase with a minimum absolute current value sent from the excitation current sensor, the pulse command controller being adapted to give an on/off-fixed firing pulse to self-turn-off power devices between two phases excluding the minimum current phase and the positive and negative poles so as to charge the DC capacitor, give a pulse modulation factor firing pulse calculated from the detected current value of the minimum current phase to self-turn-off power devices between the minimum current phase and positive and negative poles, and output the pulse modulation factor firing pulse and the on/off-fixed firing pulse as a second pulse command; anda pulse switching controller to switch the firing pulse command between the first pulse command and the second pulse command bidirectionally for output to the first power converter, the pulse switching controller being adapted to switch the firing pulse command from the first pulse command to the second pulse command under conditions including one that any of the absolute values of the detected current values from the excitation current sensor exceeds an overcurrent preset level 1 and to switch from the second pulse command to the first pulse command under conditions including one that the absolute values of all the detected three-phase current values from the excitation current sensor fall to or below an overcurrent preset level 2. 2. The doubly-fed motor/generator according to claim 1, wherein, when the absolute value of any of the detected current values from the excitation current sensor exceeds the overcurrent preset level 1, a firing pulse constituting the second pulse command is issued to the self-turn-off power devices between the phase with the minimum absolute current value or the third-largest-current phase and the positive and negative poles; wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase is equal to or lower than the preset level, the pulse modulation factor is held to 50%;wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase exceeds the preset level, the firing pulse is held to on-state or off-state to charge the DC capacitor. 3. The doubly-fed motor/generator according to claim 1, wherein, when the absolute value of any of the detected current values from the excitation current sensor exceeds the overcurrent preset level 1, a firing pulse constituting the second pulse command is issued to the self-turn-off power devices between the phase with the minimum absolute current value or the third-largest-current phase and the positive and negative poles; wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase is equal to or lower than the preset level, the pulse modulation factor is held to 50%;wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase exceeds the preset level, the firing pulse is held to on-state or off-state to discharge the DC capacitor. 4. The doubly-fed motor/generator according to claim 1, further comprising: a rectifier circuit connected to the power grid, the rectifier circuit having its negative side output terminal connected to the negative side terminal of the DC capacitor and its positive side output terminal connected to a collector of a second diode, the DC capacitor having its positive side terminal connected to a collector of a first diode;a high value selection diode circuit made up of the first and second diode with their emitters commonly connected; anda DC voltage regulator having its positive side input terminal connected with the emitter of the high value selection diode circuit and its negative side input terminal connected with the negative side terminal of the DC capacitor, the DC voltage regulator having its output connected as a power supply to the excitation current controller. 5. The doubly-fed motor/generator according to claim 1, further comprising: a DC voltage detector to detect a terminal voltage of the DC capacitor; andan active DC voltage suppressor circuit having a resistor and a self-turn-off power device PN serially connected;wherein the DC voltage detector and the active DC voltage suppressor circuit are connected parallelly between the terminals of the DC capacitor;wherein, when the detected DC voltage value exceeds a preset range, the self-turn-off power device PN of the active DC voltage suppressor circuit is on/off-controlled to suppress the DC voltage. 6. The doubly-fed motor/generator according to claim 1, further comprising: a passive voltage suppressor circuit made up of a non-linear resistor of zinc oxide or the like parallelly connected between the terminals of the DC capacitor;wherein, when the terminal voltage of the DC capacitor rises close to an upper limit, the passive voltage suppressor circuit is triggered to start conduction to suppress the DC voltage. 7. The doubly-fed generator according to claim 1, further comprising: a current bypass circuit provided between the rotor side excitation winding of the wound-rotor induction machine and the excitation current sensor;wherein an overcurrent preset level 3 is greater than the overcurrent preset level 1 and, when any of the detected absolute current values from the excitation current sensor exceeds the overcurrent preset level 3, the current bypass circuit is triggered to be turned on and all the firing commands to the self-turn-off power devices of the first power converter are made off. 8. The doubly-fed motor/generator according to claim 1, further comprising: a current bypass circuit and a DC voltage detector to detect a voltage of the DC capacitor, both provided between the rotor side excitation winding of the wound-rotor induction machine and the excitation current sensor;wherein, when the voltage from the DC voltage detector exceeds a preset range, the current bypass circuit is triggered to be turned on and all the firing commands to the self-turn-off power devices of the first power converter are made off. 9. The doubly-fed motor/generator according to claim 1, further comprising: a temperature estimation circuit to estimate heat generated by the power devices using the excitation currents from the excitation current sensor and the firing commands to the first power converter and to supply the estimated heat value to a phase delay circuit that simulates a thermal capacity;wherein, when a temperature estimated by the temperature estimation circuit exceeds a preset value, the current bypass circuit is triggered to be turned on and all the firing commands to the self-turn-off power devices of the first power converter are made off. 10. A doubly-fed variable-speed electric machine having functions of the doubly-fed generator of claim 1 and of a variable-speed electric machine. 11. A doubly-fed motor/generator comprising: a wound-rotor induction machine having its stator side armature winding connected to an electric power grid;a first power converter having three-phase bridge connected arms of an IGBT as a self-turn-off power device and a free-wheeling diode or a MOSFET as a self-turn-off power device, each of the arms having its AC side terminals connected to a rotor side excitation winding of the wound-rotor induction machine, wherein the first power converter pulse-width-modulation-controls the self-turn-off power devices;a DC capacitor connected between DC side terminals of the first power converter;a second power converter having its DC side terminals connected to both terminals of the DC capacitor and its AC side terminals connected to the power grid;an excitation current sensor to detect a current flowing in an excitation winding of the wound-rotor induction machine;an excitation current controller to calculate an excitation current command value for a slip frequency equal to a difference between a grid frequency and a rotor frequency of the wound-rotor induction machine and to output a first pulse command that causes the detected excitation current value from the excitation current sensor to match the excitation current command value, the first firing pulse command being fed to the self-turn-off power devices of the first power converter;a pulse command controller having a function to identify the three phases as a largest-current phase, a second-largest-current phase and a third-largest-current phase in order of decreasing magnitude of absolute current value sent from the excitation current sensor, the pulse command controller being adapted to check a polarity of the detected current value of the largest-current phase, fix to a turn-on side the firing pulse to either a self-turn-off power device P1 between the largest-current phase and a positive pole or a self-turn-off power device N1 between the largest-current phase and a negative pole so as to charge the DC capacitor, fix to a turn-off side the firing pulse to the other self-turn-off power device, fix the firing pulse to a self-turn-off power device P2 between the second-largest-current phase and the positive pole to the same side as the firing pulse to the self-turn-off power device N1 and fix the firing pulse to the a self-turn-off power device N2 between the second-largest-current phase and the negative pole to the same side as the firing pulse to the self-turn-off power device P1, and output a firing pulse of a pulse modulation factor calculated from the detected current value for the third-largest-current phase as a second firing pulse command to a self-turn-off power device P3 between the third-largest-current phase and the positive pole and to a self-turn-off power device N3 between the third-largest-current phase and the negative pole; anda pulse switching controller to switch the firing pulse command between the first pulse command and the second pulse command bidirectionally for output to the first power converter, the pulse switching controller being adapted to switch the firing pulse command from the first pulse command to the second pulse command under conditions including one that any of the absolute values of the detected current values from the excitation current sensor exceeds an overcurrent preset level 1 and to switch from the second pulse command to the first pulse command under conditions including one that the absolute values of all the detected three-phase current values from the excitation current sensor fall to or below an overcurrent preset level 2. 12. A doubly-fed motor/generator comprising: a wound-rotor induction machine having its three-phase stator side windings connected to an electric power grid;a first power converter having semiconductor power devices connected at their AC side terminals to the three-phase rotor side windings of the wound-rotor induction machine;a DC capacitor connected between DC side terminals of the first power converter;a second power converter having its DC side terminals connected to both terminals of the DC capacitor and its AC side terminals connected to the power grid;an excitation current sensor to detect an excitation current of each phase supplied from the first power converter; andan excitation current controller to output a first firing pulse command to the semiconductor power devices of the first power converter to control the excitation current produced by the first power converter according to an operation condition of the wound-rotor induction machine;wherein the three phases are identified as a largest-current phase, a second-largest-current phase and a third-largest-current phase in order of decreasing magnitude of absolute current value sent from the excitation current sensor, the largest-current phase having an absolute current value of the excitation current that is a maximum among the excitation currents of the three phases, a polarity of a detected current value of the largest-current phase is checked, andwherein, when a detected absolute current value of a minimum current phase or the third-largest-current phase exceeds an overcurrent preset level, the firing pulse to the semiconductor power devices of each phase in the first power converter is held to an on-state or an off-state to charge the DC capacitor. 13. The doubly-fed motor/generator according to claim 12, wherein a circuit between the positive and negative side terminals of the DC capacitor is used as a power supply for the excitation current controller. 14. The doubly-fed motor/generator according to claim 13, further comprising: a DC voltage regulator connected between the positive and negative side terminals of the DC capacitor;wherein an output of the DC voltage regulator is used as a power supply for the excitation current controller. 15. A doubly-fed variable-speed electric machine configured to operate as a doubly-fed generator and a variable-speed electric machine, the doubly-fed variable-speed electric machine comprising: a wound-rotor induction machine having its stator side armature winding connected to an electric power grid;a first power converter having three-phase bridge connected arms of an IGBT as a self-turn-off power device and a free-wheeling diode or a MOSFET as a self-turn-off power device, each of the arms having its AC side terminals connected to a rotor side excitation winding of the wound-rotor induction machine, wherein the first power converter pulse-width-modulation-controls the self-turn-off power devices;a DC capacitor connected between DC side terminals of the first power converter;a second power converter having its DC side terminals connected to both terminals of the DC capacitor and its AC side terminals connected to the power grid;an excitation current sensor to detect a current flowing in an excitation winding of the wound-rotor induction machine;an excitation current controller to calculate an excitation current command value for a slip frequency equal to a difference between a grid frequency and a rotor frequency of the wound-rotor induction machine and to output a first pulse command that causes the detected excitation current value from the excitation current sensor to match the excitation current command value, the first firing pulse command being fed to the self-turn-off power devices of the first power converter;a pulse command controller having a function to identify a phase with a minimum absolute current value sent from the excitation current sensor, the pulse command controller being adapted to give an on/off-fixed firing pulse to self-turn-off power devices between two phases excluding the minimum current phase and the positive and negative poles so as to charge the DC capacitor, give a pulse modulation factor firing pulse calculated from the detected current value of the minimum current phase to self-turn-off power devices between the minimum current phase and positive and negative poles, and output the pulse modulation factor firing pulse and the on/off-fixed firing pulse as a second pulse command;a pulse switching controller to switch the firing pulse command between the first pulse command and the second pulse command bidirectionally for output to the first power converter, the pulse switching controller being adapted to switch the firing pulse command from the first pulse command to the second pulse command under conditions including one that any of the absolute values of the detected current values from the excitation current sensor exceeds an overcurrent preset level 1 and to switch from the second pulse command to the first pulse command under conditions including one that the absolute values of all the detected three-phase current values from the excitation current sensor fall to or below an overcurrent preset level 2. 16. The doubly-fed variable-speed electric machine according to claim 15, wherein, when the absolute value of any of the detected current values from the excitation current sensor exceeds the overcurrent preset level 1, a firing pulse constituting the second pulse command is issued to the self-turn-off power devices between the phase with the minimum absolute current value or the third-largest-current phase and the positive and negative poles;wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase is equal to or lower than the preset level, the pulse modulation factor is held to 50%; andwherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase exceeds the preset level, the firing pulse is held to on-state or off-state to charge the DC capacitor. 17. The doubly-fed variable-speed electric machine according to claim 15, wherein, when the absolute value of any of the detected current values from the excitation current sensor exceeds the overcurrent preset level 1, a firing pulse constituting the second pulse command is issued to the self-turn-off power devices between the phase with the minimum absolute current value or the third-largest-current phase and the positive and negative poles;wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase is equal to or lower than the preset level, the pulse modulation factor is held to 50%;wherein, when the detected absolute current value of the minimum current phase or the third-largest-current phase exceeds the preset level, the firing pulse is held to on-state or off-state to discharge the DC capacitor. 18. The doubly-fed variable-speed electric machine according to claim 15, further comprising: a rectifier circuit connected to the power grid, the rectifier circuit having its negative side output terminal connected to the negative side terminal of the DC capacitor and its positive side output terminal connected to a collector of a second diode, the DC capacitor having its positive side terminal connected to a collector of a first diode;a high value selection diode circuit made up of the first and second diode with their emitters commonly connected; anda DC voltage regulator having its positive side input terminal connected with the emitter of the high value selection diode circuit and its negative side input terminal connected with the negative side terminal of the DC capacitor, the DC voltage regulator having its output connected as a power supply to the excitation current controller. 19. The doubly-fed variable-speed electric machine according to claim 15, further comprising: a DC voltage detector to detect a terminal voltage of the DC capacitor; andan active DC voltage suppressor circuit having a resistor and a self-turn-off power device PN serially connected;wherein the DC voltage detector and the active DC voltage suppressor circuit are connected parallelly between the terminals of the DC capacitor;wherein, when the detected DC voltage value exceeds a preset range, the self-turn-off power device PN of the active DC voltage suppressor circuit is on/off-controlled to suppress the DC voltage. 20. The doubly-fed variable-speed electric machine according to claim 15, further comprising: a passive voltage suppressor circuit made up of a non-linear resistor of zinc oxide or the like parallelly connected between the terminals of the DC capacitor;wherein, when the terminal voltage of the DC capacitor rises close to an upper limit, the passive voltage suppressor circuit is triggered to start conduction to suppress the DC voltage.