초록 ▼

A method is disclosed to protect a power converter arrangement with a power converter that has a DC side that is connected to a DC intermediate circuit, an AC side, and controllable switches that can be controllably switched at a high frequency to invert the DC voltage of the DC intermediate circuit

A method is disclosed to protect a power converter arrangement with a power converter that has a DC side that is connected to a DC intermediate circuit, an AC side, and controllable switches that can be controllably switched at a high frequency to invert the DC voltage of the DC intermediate circuit into an AC voltage. A protective device that can be activated and deactivated is provided to protect the power converter from overload by connecting an external thyristor rectifier bridge with a brake resistor (Rb ext) to the AC side of the power converter. If a predetermined error situation is detected, the external thyristors are triggered to turn on, to activate the protective device. If it is detected that the predetermined error situation has disappeared, the external thyristors are turned off. A power converter arrangement with a device to protect against overload is also disclosed.

대표청구항 ▼

1. A method to protect a power converter arrangement with a power converter device that has a direct current side that is connected with a DC intermediate circuit, an alternating current side, and controllable switching elements that can be controllably switched at a high frequency to convert the DC

1. A method to protect a power converter arrangement with a power converter device that has a direct current side that is connected with a DC intermediate circuit, an alternating current side, and controllable switching elements that can be controllably switched at a high frequency to convert the DC voltage of the DC intermediate circuit into a multi-phase AC voltage, the method comprising: providing a protective device, that can be activated and deactivated, to protect the power converter device from overload by connecting a rectifier circuit with rectifier elements, at least some of which are thyristors, to the AC side of the power converter device, and connecting a bypass branch to a DC side of the rectifier circuit, the bypass branch having a brake resistor for transforming energy dissipated from the AC side of the power converter device into thermal energy, when necessary; andif a predetermined error situation is detected, triggering the thyristors of the rectifier circuit to turn them on, to activate the protective device; andif it is detected that the predetermined error situation disappears, turning off the thyristors of the rectifier circuit by ending the triggering of the thyristors and actively controlling the power converter switching elements to produce a sequence of voltage pulses of suitable polarity and amplitude to serve as a thyristor turn-off sequence which is applied to the protective device to force commutation of the current from the protective device to the power converter to deactivate the protective device;wherein to limit a current commutation speed (di/dt) when the thyristors of the protective device are turned off, the switching elements of the power converter device apply voltage pulses with a reduced amplitude Vconv, to the protective device, according to the following equation: Vconv=V⁢d⁢⁢cm-1,where Vdc is the positive voltage of the DC intermediate circuit and m corresponds to the number of levels of the multi-level power converter. 2. The method of claim 1, wherein if the predetermined error situation is detected, the switching elements are controlled to open, and all switching elements are kept open until it is detected that the predetermined error situation has disappeared. 3. The method of claim 1, wherein to produce the thyristor turn-off sequence, the polarity and amplitudes of the currents in the protective device are monitored to determine the suitable sequence and polarity of voltage pulses. 4. The method of claim 1, further comprising providing an internal brake chopper device , which monitors and protects the intermediate circuit voltage, the brake chopper device having at least one internal brake resistor that transforms excess energy in the intermediate circuit into thermal energy, and at least one switch controllable by pulse-width modulation to allow or prevent a current flow through the at least one internal brake resistor, the protective device being activated if the duty ratio of the at least one switch reaches 100%. 5. The method of claim 1, wherein inductors are further arranged between the power converter device and the protective device to limit the rate of change of the commutation current. 6. The method of claim 1, wherein before the triggering of the switching elements of the power converter device to turn off the thyristors, the current through the bypass branch comprising the external brake resistor Rb ext is limited to a value Iclamp by applying a voltage pulse with reduced amplitude Vconv, such that: Iclamp=VconvRb⁢⁢ex⁢⁢t. 7. The method of claim 1, wherein the thyristor turn-off sequence comprises the following steps: applying a first voltage pulse having a certain voltage amplitude and polarity between a first phase line and a second phase line, to which the rectifier circuit is connected;applying another voltage pulse having the reverse polarity between these phase lines;subsequently applying yet another voltage pulse having a certain voltage amplitude and polarity between the first and second phase lines, which are connected in parallel with one another, and a third phase line, to which the rectifier circuit is connected; andapplying a voltage pulse of reverse polarity between the phase lines. 8. The method of claim 1, wherein once the error situation is past and the current has commutated from the protective device to the power converter device, a normal operating mode is resumed in which the controllable switching elements of the power converter device are controlled at the high frequency by pulse-width modulation to invert the DC voltage of the DC intermediate circuit. 9. A power converter arrangement comprising: a power converter device that has a direct current side that is connected with a DC intermediate circuit, an alternating current voltage side, and controllable switching elements that can be controllably switched at a high frequency to convert the DC voltage of the DC intermediate circuit into a multi-phase AC voltage to feed the AC side;a protective device, that can be activated and deactivated, to protect the power converter device from overload, the protective device having a rectifier circuit that is connected to the AC side of the power converter device and having rectifier elements, at least some of which are thyristors, and a bypass branch that is connected to a DC side of the rectifier circuit, the bypass branch having a brake resistor for transforming energy dissipated from the AC side of the power converter device into thermal energy, when necessary; anda control device for controlling the thyristors of the rectifier circuit, to selectively turn on and off the thyristors, to activate or deactivate, respectively, the protective device;the control device being configured to selectively turn off the thyristors of the rectifier circuit to deactivate the protective device by actively controlling the switching elements of the power converter device to produce a sequence of voltage pulses of suitable polarity and amplitude to serve as a thyristor turn-off sequence which is applied to the protective device to force commutation of the current from the protective device to the power converter device;wherein to limit a current commutation speed (di/dt) when the thyristors of the protective device are turned off, the switching elements of the power converter device apply voltage pulses with a reduced amplitude Vconv, to the protective device, according to the following equation: Vconv=Vd⁢⁢cm-1,where Vdc is the positive voltage of the DC intermediate circuit and m corresponds to the number of levels of the multi-level power converter. 10. The power converter arrangement of claim 9, wherein the control device is part of a controller for the power converter device which in normal operating mode controls the switching elements at the high frequency by pulse-width modulation, to invert the DC voltage of the DC intermediate circuit. 11. The power converter arrangement of claim 9, wherein the control device is configured to recognize predetermined error situations, and thereupon to control the switching elements to open them, and keep all switching elements open until it detects that the error situation has disappeared. 12. The power converter arrangement of claim 9, wherein the control device is configured to monitor the polarities and amplitudes of the currents in the protective device. 13. The power converter arrangement of claim 9, wherein the power converter device further comprises means for rectifying the AC voltage of the AC side and feeding it into the DC intermediate circuit. 14. The power converter arrangement of claim 9, wherein the power converter device has an m-level n-phase power converter, where m >=2 and n >=3. 15. The power converter arrangement of claim 9, wherein the power converter device has an internal brake chopper device that monitors and protects the intermediate circuit voltage, the brake chopper device comprising at least one internal brake resistor that transforms excess energy in the DC intermediate circuit into thermal energy, and at least one controllable switch that selectively allows or prevents a current flow through the at least one internal brake resistor. 16. The power converter arrangement of claim 9, wherein inductors are arranged between the power converter device and the protective device to limit the rate of change of the commutation current. 17. The power converter arrangement of claim 9, wherein the rectifier circuit is formed by a multi-phase thyristor bridge. 18. The power converter arrangement of claim 9, wherein the power converter arrangement is configured to control a rotor current in a rotor circuit of a doubly fed induction machine.