The document EP1965075A1 discloses a system comprising a doubly-fed inductor generator, a grid-side-converter, a grid-side-converter GSC, a machine-side-converter MSC, a DC link between both converters, a crowbar connected to rotor of the generator, a first control unit for controlling the crowbar depending on the DC link voltage, and a second control unit for controlling both converters GSC and MSC. The first and second controllers are independent of each other.
The document U.S. Pat. No. 8,373,293B2 discloses a system comprising a doubly-fed inductor generator, a grid-side-converter, a grid-side-converter GSC, a machine-side-converter MSC, a DC link between both converters, a chopper connected to the DC link, a crowbar connected to rotor of the generator, a converter controller for controlling both converters GSC and MSC, and a separate protection device for controlling both the chopper and the crowbar.
The protection system comprises a doubly-fed inductor generator comprising a rotor and a stator, which is part of a wind turbine; a grid-side-converter; a machine-side-converter; a DC link between both converters; a chopper connected to the DC link; a Final Hardware Protection System (FHPS) connected to the rotor of the generator; a first control unit for controlling the FHPS depending on the voltage in the DC link (it continuously reads the DC link voltage); a second control unit for controlling the chopper depending on the DC link voltage (it continuously reads the DC link voltage); and a third control unit for controlling both converters.
The chopper is responsible for absorbing the undesirable energy increase in the DC link, and the FHPS is responsible for disconnecting the generator if the DC link voltage increases to exceed a threshold value. When the FHPS is activated (it is a hardware controlled system that short circuits the rotor terminals without resistances) the wind turbine is disconnected from the grid and passes to an emergency state, unlike the crowbars described in prior art cited in the background field that include resistive elements and that are disconnected once the transient has passed.
The three control units are independent of each other, each control unit having its own processor, and with said independence at least the following advantages can be obtained:
These and other advantages and characteristics will be made evident in the light of the drawings and the detailed description thereof.
The proposed system comprises a doubly-fed inductor generator 100 comprising a rotor and a stator, which is part of a wind turbine; a grid-side-converter 101; a machine-side-converter 102; a DC link 103 between both converters; a chopper 104 connected to the DC link 103; a Final Hardware Protection System (FHPS) 105 connected to the rotor of the generator 100; a first control unit 1 for controlling the FHPS 105 depending on the voltage Vbus in the DC link 103 (it continuously reads the DC link voltage Vbus); a second control unit 2 for controlling the chopper 104 depending on the DC link voltage Vbus (it continuously reads the DC link voltage Vbus); and a third control unit 3 for controlling both converters 101 and 102.
The chopper 104 is responsible for absorbing the undesirable energy increase in the DC link 103, and the FHPS 105 is responsible for disconnecting the generator 100 if the DC link voltage Vbus increases to exceed a threshold value. When the FHPS 105 is activated (it is a hardware controlled system that short circuits the rotor terminals without resistances) the wind turbine is disconnected from the grid and passes to an emergency state, unlike the crowbars described in prior art cited in the background field that include resistive elements and that are disconnected once the transient has passed.
The three control units 1, 2 and 3 are independent of each other, each control unit 1, 2 and 3 having its own processor. Each processor can be a PLD (“Programmable Logic Device”), a CPLD (“Complex Programmable Logic Device”), a FPGA (“Field Programmable Gate Array”) or any other equivalent device. In
Alternatively, instead of a first communication link 13 between the first control unit 1 and the third control unit 3 and a second communication link 23 between the second control unit 2 and the third control unit 3 as shown in
With the independence between the three control units 1, 2 and 3 at least the following advantages are obtained:
Each control unit 1 and 2 can also comprise a specific power supply associated, so that both control units 1 and 2 can also be autonomous. The control units 1 and 2 are normally supplied by the grid (via DC-bus) or by an UPS (“Uninterruptible Power System”) comprised in the system, and if the voltage of the grid drops below a predetermined value and the UPS fails, thanks to the specific power supply, the control units 1 and 2 are operative during a predetermined time interval in order to control the FHPS 105 and the chopper 104 respectively during said time. Each specific power supply can comprise a bank or capacitors, a battery or other equivalent arrangement, designed for supplying power to the corresponding control unit 1 or 2 during said time interval.
The control over the chopper 104 works as follows:
The chopper 104 is formed by n-branches, each branch being formed by at least one semiconductor switch and a resistor (not shown in figures). Preferably, all the switches are operated simultaneously.
The second control unit 2 implements a conventional Pulse Width Modulation (PWM) control and a hysteresis control, as shown in
Each region is associated to the DC link voltage Vbus as shown in the following table:
The greater the DC link voltage Vbus the greater the energy that must be absorbed by the chopper 104, and thus the greater is the time that the switches of the chopper 104 must remain ON (closed) to absorb this energy.
If the value of the DC link voltage Vbus exceeds the Chopper Upper PWM Threshold CUPT (region 8=1285.50V) of the last modulation rate, it is assumed that the PWM control is not able to control the DC link voltage Vbus and the hysteresis control is activated. This hysteresis control is then activated when a Chopper Hysteresis Activation Threshold CHAT is reached, which can be equal to or, for safety purposes, lower than the Chopper Upper PWM Threshold CUPT. This means that the semiconductor switches of the chopper 104 remain closed (ON) along the period T, until the DC link voltage Vbus drops down to a Chopper Hysteresis Deactivation Threshold CHDT value (for example 997.6V, as shown in
If the hysteresis control is not able to reduce the DC link voltage Vbus, the first control unit 1 causes the FHPS 105 to be activated when the DC link voltage Vbus reaches or exceeds an FHPS Activation Threshold FAT (shown in
The second control unit 2 informs the third control unit 3 about its state continuously, in particular if it is operative or not, if the switches of the chopper 104 are ordered to be ON or OFF, and if there is an overload on any switch or any resistor of the chopper 104.
To detect an overload, the time that the switch is being fired is taken into account, taking also into account the time that it is going to be off (opened) during each period due to that the cooling during the off state is slower than the heating during ON state. Said time affects to the switch itself and also to the associated resistor, but due to the different characteristic of a switch and of a resistor, the switches and the resistors are preferably treated independently (one can be overloaded before the other one for example).
For example:
During an overload the firings over the switches are preferably ordered to be OFF, unless a higher-level priority reason occurs.
The control over the FHPS 105 works as follows:
As noted before, the system comprises a Final Hardware Protection System (FHPS) 105 comprising a thyristor, for the situations where the DC link voltage Vbus exceeds the FHPS Activation Threshold FAT value, controlled by a first control unit 1. The generator 100 is then stopped and decoupled from the grid. If said situation occurs, the first control unit 1 sends an appropriate signal to the thyristor of the FHPS 105 to short-circuit the rotor until said DC link voltage Vbus drops to the Chopper Hysteresis Deactivation Threshold CHDT (thus also defines as FHPS Deactivation Threshold FDT), as shown in
The first control unit 1 informs the third control unit 3 about its state continuously, in particular if it is operative or not, and if the FHPS 105 is ON or OFF.