The present invention relates to a system for control of a hydraulic system primary for pitch control of at least one rotor blade for a windmill, which system comprises at least a pressure source, which pressure source through valves are connected to at least a first port in an actuator, which actuator comprises a first and a second volume, which first and second volume is separated by a piston, which piston is fastened to at least one shaft, which shaft is connected to at least one rotor blade, which pressure source is connected to at least a common inlet to first group of valves, where each valves in the first group is connected to the pressure source through flow reductio means, which flow reduction means has a different size, which first group of val ves are connected to a common outlet, which common outlet is connected to the first port of the actuator, which first port of the actuator is further connected through different flow reductions to a second group of valves, which second group of valves are connected to the tank.

Background of the Invention

EP 1835174 discloses an electro hydraulic control unit for rotor blade adjustment of a wind farm via a hydraulic cylinder. The hydraulic cylinder has one piston chamber and one piston rod chamber. Via an inflow valve assembly, a pressure fluid connection can be established between the pump and the piston chamber, while via an outflow valve assembly, a pressure fluid connection can be established between the piston rod chamber and the tank. Each valve assembly has at least tw ^r o parallel-connected switch valves, which open and can be closed in various combinations in order to establish a desired position of the hydraulic cylinder. This control unit makes precise regulation of the rotor blade possible.

Object of the Invention

The object o the invention is to achieve a reliable system for pitch control with extreme long meantime between failures. A further object is to achieve an emergency position of the valves for soft shut down of a wind mill.

Description of the Invention

The object can be fulfilled if the first group of valves comprises at least one Normal Open valve and at least one Normal Closed valve, which second group of valves are Normal Closed (NC) valves.

I Icrcby is achieved that normal pitch regulation can be performed by a number of on/off valves which probably can be Pulse With Modulated* PW\1). In that way can be formed normal operation of the pitch control up and down in pitch angle in the same way as traditional proportional valves can perform operation. Especially by designing the valves so that by an emergency situation, for example by total electric power failure which can occur if there is failure on a connected grid, an automatic adjustment towards feather pitch will be achieved by pressure hydraulic accumulators where the pressure is transmitted through valves, which by their design in Normal Open and Normal Closed, automatically defines the degree of flow towards the lowest pitch possible. In order to avoid oscillations in a windmill tower, it is very important also by emergency shutdown that the regulation towards feather pitch is performed in a rela- lively slow mode. A too fast regulation could in an emergency situation with extremely high wind lead to a collapse of the windmill tower. Therefore, a relatively slow regulation is necessary to avoid oscillations in the windmill. By a system where flow reductions are combined with the valves, the combination of Normal Open (NO) and Normal Closed (NC) can define the correct flow rate for emergency, simply by selecting the valves so in emergency there will be an open How path through the selected valve combinations. During normal operation can the valve combination by, for example, PWM or another modulation form adjust the flow through the valve combination in quite a normal manner. By more or less continuous operation of the valves with rapid switching on and off, it can be avoided that the valves are blocked with failure at the moment they have to be regulated. Because the valves are more or less continuous in movement, even if it is very slight movement of the valves and only very short periods for opening and closing, a continuous regulation can be formed where adjustment will take place, because the valves are so fast operating, but the flow is under control of the system so it is avoided that a valve is closed or maybe open for a longer period where there is a risk of blocking of the valve function. 1 Iereby is achieved an extremely reliable system.

In a preferred embodiment for the invention can the pressure source be connected directly to the second port in the actuator to the second volume of the actuator. Hereby can be achieved, that the maximum pressure always exists in the second volume of the actuator. This second volume also comprises the shaft, therefore this actual pressure area inside the cylinder is reduced in relation to the first volume. Therefore, increasing pressure in the first volume up to a pressure equal to the pressure in the second chamber will automatically lead to a movement of the piston inside the cylinder and thereby also moving of the shaft. Full pressure in both chambers will in the system lead to feather pitch for the wing that is connected. Therefore, in a situation where pitch has to be regulated, a flow has to be performed from the first chamber down to the tank- where also pressurised hydraulic fluid has to flow into the second chamber, in order to fill up the chamber. When a new situation has been achieved, the pressure in the first chamber has to be regulated into a level a bit smaller than the maximum pressure operating in the second chamber. But by keeping high pressure both sides of the piston, the piston is so to say locked into the position. No forces at a wing of a windmill will be able to move the actuator from the actual position. Only if a regulation is allowed by opening the valves, it is possible to perform any regulation of the pitch. In a further preferred embodiment can the first flow reduction for the first valve of the first group of valves has a first opening, which second flow reduction for the second valve has a lager flow opening, which third flow reduction for the third valve has a lager flow opening than the second flow reduction which fourth flow reduction for the fourth valve is larger than the third flow reduction. Hereby is achieved that a digital regulation of the valves is possible where for example three valves will lead to eight combinations, four valves will lead to 16 combinations, five valves to 32 combinations and so on, just as known from digital systems. But in combination with, for example, PWM regulation it is possible to achieve a very precise regulation of the valves. Depending on the speed of which regulation has to formed, the correct valve combination can be selected. If a very fine regulation has to be formed, maybe valves with a very limited flow will be used, but if a rather fast regulation is required then valve combinations, maybe all the valves at the same time, will be opened. A good regulation can be performed if fast regulation is performed maybe up to 80 % of the result and the last 20 % is performed in a slower rate by modulating only the smaller valves. The numbers of combinations that are possible by for example PWM and digital valves are impossible to describe totally, but the number of flow combinations can be enormous.

In a further preferred embodiment can the first flow reduction for the first valve of the second group of valves have a first opening, which second flow reduction for the sec- ond valve has a lager flow opening, which third flow reduction for the third valve has a lager flow opening than the second flow reduction which fourth flow reduction for the fourth valve is larger than the third flow reduction. By using the same technology for the second valve group which performs regulation towards a tank, also the return flow can be controlled by the digital valve combinations combined with for example PWM regulation. It is possible to regulate both towards the pump and to the tank at the same time to achieve further possible pressure combinations, but because there in that situation will be a flow directly from pump to tank, there will an extremely high energy consumption of the hydraulic system, so in practical use one of the valve groups will operate and the other valve group is probably mostly closed.

In a further preferred embodiment can the valves the first group and the second group of valves be fast operating valves, which valves are controlled from the system. The faster the valves can operate, the more precisely can the PWM regulation be performed. The use of extremely fast operating valves makes it possible to use other modulation forms than PWM. Instead of modulating the width of the pulses, it is possible simply to adjust the number of pulses just as one example of another modulation form.

In a further preferred embodiment can a fall-back operation be performed in case of a single valve failure in one of the valves where the flow is PWM controlled in the other valves to achieve same flow as through the failed valve. In situations where the system detects that one of the valves has a failure, the system can be programmed so that this valve then is programmed not to be used and probably will end up in a closed sit- uation where the system automatically adjusts the regulation of the other valves so that normal operation of the pitch control is possible, but maybe extremely fast regulation is no longer possible. This is not the perfect way of operation of a system, but it is the possibility of operating system in a short period until maintenance is possible. In good weather situations, probably in summertime, a defect valve will in no way have any influence on the pitch regulation of a windmill. Therefore, even windmills at open sea can operate quite normally until the next planned maintenance, it is therefore important that the system is programmed in a way where a defect valve leads to a routine in the program that automatically takes care of the defect valve by further opening by the modulation of the parallel valves to achieve the same fluid flow through the valve block.

In a further preferred embodiment can the valves be incorporated into the housing of the actuator. It is possible that the housing of the actuator is constructed in such a way that the valve groups are integrated in the housing of the actuator. In that way, this invention can be used without any tubing from the valves into the actuator. This can be very important in windmills where the whole pitch control system is part of the rotating rotor of the windmill. In a further preferred embodiment can the flow reductions be formed as orifices, which orifices are integrated in the valves. Hereby can be achieved that no further components are to be used and if the flow reduction is well known for the valves, and the valves have to be used in a high number, it is highly effective to simply change the flow path through the valve, so that it is generating the correct orifices.

In a further preferred embodiment can a single bank of 2/2 valves can be used to operate a pitch in regenerative operation by use of a pilot-to-open and pilot-to-close valve for selecting direction of movement. Hereby is achieved that only one group of digital valves is to be used, and because mostly only valve groups for positive or valve groups for negative flow are used independent of each other, it is possible by one switching valve to achieve change in the flow direction by the single 2/2 valve and perform flow regulation with the digital on/off valves. By only using one group of digital valves, it is possible maybe for smaller pitch regulation systems to integrate the valve group and the direction valve in an actuator.

The pending patent application further concerns a method for operating a pitch control system as previous described which method concerns at least the following sequence of steps. a: the system performs measurement of the pressure in the pressure source, b: the system performs measurement of the pressure in the first chamber of the actuator. c: the system performs measurement of the actual position of the piston of the actuator, d: the system performs measurement of the pressure in the second chamber of the actuator. e: the system performs analysis of the functionality of the valves of the first group and the second group are monitored by use of a number of states a-d.

Hereby can be achieved that the system based on input from a number of sensors can calculate the function of the valves and automatically get information about valve functions so that more functional valves will be indicated by the analysis of the input values. By the method is achieved a total regulation system for the pitch of a windmill wing. Of course there will be input to the system from the other controlled systems of a windmill so that a request from change of pitch also will take part of the regulation of the system. Therefore, an input or a request for a new pitch will automatically be accepted and regulation will be performed with the method as described.

By a preferred method the valves are to be used to achieve a controllable variable emergency stop speed-contribution. By selecting Normal Open and Normal Closed valves, it is possible to define a flow path in an emergency situation that will result in a controlled slow pitch regulation. Hereby is avoided that extremely strong forces are generated by a too fast pitch regulation. A too fast pitch regulation can generate forces at a windmill, tower that can lead to the collapse of the tower. Therefore, it is very important that in a situation where an emergency occurs, the pitch regulation is performed at a relatively slow regulation where the change of pitch angle per minute is controlled by the combination of Normal Open/Normal Closed valves.

1 he pending applications further concerns the use of a system as previously described where the valves of the first and the second group are used to achieve a controllable variable emergency stop function. By this valve combination, there is no need for an extra emergency flow path for achieving the correct flow in an emergency situation. The emergency flow path is generated through the normal regulation valves. Hereby is achieved that these valves are typically during continuous operation always operational and a controlled flow path can be generated through the valves.

In a preferred use of a system, the groups of valves are used to operate the pitch actuator in a closed loop position control. Based on feedback from pitch regulation in a windmill, it is possible by this system to perform a closed loop position control.

In a preferred use of a system the groups of valves are used to operate the pitch actuator in closed loop position and speed control.

Description of the Drawing

Fig. 1 shows a first possible embodiment of the system 2.

Fig. 2 shows an alternative embodiment of the system 102.

Detailed Description of the Invention

Fig. 1 shows a system 2 which indicates a pressure source 4 which could be a hydraulic pump and a hydraulic tank 6 where the pressure source could be connected to the tank 6 by pumping means. A flow line 8 connects pressure from the pressure source to a valve group 9 which valve group comprises a first flow reduction, 10 which is connected to a normally closed valve 12 from which valve 12 the hydraulic high-pressure liquid can flow to a line 26 towards the first chamber of the hydraulic actuator 29 through a port 28. Further, in the valve group 9 and in parallel to the already mentioned flow reduction 10 and valve 12 is further indicated flow reduction 14 connected to the normally closed valve 16. Further in parallel, further valves are indicated and flow reduction 18 which is cooperating with the normally open valve 20. Further there is flow reduction 22 connected to valve 24 which valve 24 is a normally closed valve. The output from all four valves of the valve group 9 are, as already mentioned, combined into the flow line 26 which is connected to the first port 28 of the hydraulic actuator 29 where liquid is flowing into the pressure chamber 13. The hydraulic actuator further comprises a piston 31 which is connected to a shaft 33. At the other end of the piston 3 1 a second pressure chamber 32 is indicated. Through a terminal 34 this pressure chamber is in flow connection with a line 36 which is connected directly to the pressure line 8. Further through a line 38 the first pressure chamber 13 is connected to a second valve group 39. This valve group also comprises four different valves with each having its own flow restriction. The first flow restriction 40 is connected to a normally closed valve 42. Through a line the valve 42 is connected directly to the tank. Further, and in parallel to the first valve and its flow reduction a flow reduction 44 and normally closed valve 44 are indicated. Further, and in parallel to the first two valves, a flow reduction mechanism 48 and normally closed valve 50 are indicated. Further flow reduction mechanism 52 is indicated which is connected to the normally closed valve 54. The line 56 is directly connected to the tank 6.

Further fig. 1 shows a flow regulation means 58 and a variable flow reduction 60. Further pressure sensors 62 arc indicated and there are indicated pressure accumulators 64 and 66.

In normal operation, the pressure in the chamber 30 will be regulated by pulse with modulation of the val ve in the valve groups. The valves in the valve groups are forming digital valves whereby each of the valve groups 9 and 39 can be adjusted into 15 different flow situations and a closest situation. Together with pulse modulation or other types of modulation of the valves, it is possible to perform a very precise regulation. By nearly continuous operation of the valves, it is possible always to know if the valves are operating correctly due the to the different flow sensors which already exist in the system, e.g. by measuring the pressure in the chamber 30 or the chamber 32. Small changes pressure can be performed with a very limited movement of the piston 31. But even very small changes in pressure are enough to indicate that the valves are operating as expected. In this way, continuous monitoring of the valves can be per- formed. Fast operating valves will have a very limited risk of being blocked in one of their positions. In an emergency situation where the power connection to a wind turbine is totally interrupted, the control system will relatively fast also lose the control over the valves. In this situation it is very important that the pressure accumulators can still deliver a pressure. In such a situation, the valve 62 is important because this valve closes for further flow in the direction of the pump. The pressure will automatically flow through the line 8 and through the flow reduction mechanism 18 and the normally open valve 20 into the line 26, and from here into the first actuator connection 28 and into the pressure chamber 30. 1 lere the pressure will automatically be increased so that the pressure is increasing to reach the same pressure as the pressure that exists in the chamber 32. Because the active area at the piston 31 in the chamber 30 is larger than the active area in the chamber 32, the piston 31 will be moved towards the right at fig. 1 into a position of feather pi tch.

Fig. 2 shows a system 102. This system comprises a pump 104 and a tank 106 with only one valve group 109. The valve group 109 comprises a flow restriction 1 10 which is connected to the normally closed valve 1 12 where, in parallel to the first valve and the first flow reduction mechanism, a further flow reduction mechanism 1 14 is indicated which is connected to the normally closed valve 1 16. The valve group 109 further comprises flow restriction 1 18 and normally open valve 120. Further flow re- duction 122 and normally closed valve 124 are indicated. A line 126 connects to the first terminal 128 of an actuator 129. Therefore pressure delivered from the valve group 109 is delivered into a pressure chamber 130. A piston 131 separates the actuator between a first pressure chamber and the pressure chamber 132. The second terminal 134 is connected by line 136 directly to the pressure source 104. Further in fig. 2 a pressure regulation mechanism 158 and a variable flow restriction mechanism 160 are indicated. Further a pressure indicator 162 and pressure accumulators 164 and 166 are indicated. Further a switching valve 163 is indicated which valve is able to control the opening of all valves 168 and 166. Hereby it is achieved that the valve group 109 can be changed from regulation from the pump to regulation towards the tank by means of the valve 163.

In operation, most of the functions previously described can be possible by the system 102 as indicated in fig. 2.