Research | Patent Applications on the Pitch System of Wind Turbines



Statistics and analysis show that Chinese firms are lagging behind their oversea counterparts in terms of the number of patents filed on technologies about the pitch system of wind turbines and the ability to follow up the top technologies. As the R&D of independent pitch system probably directs the prospect of the industry, joint efforts from companies and academic institutions are required to divert attentions back to basic disciplines.



The pitch control system of wind turbines automatically adjusts the blade pitch angle with the airflow based on the changing wind speed so that the generator rotates at a constant speed, or turns the blades 90 degrees to be parallel to the air flow in order to shut down the wind turbine. The basic principle is that the control system regulates the blade pitch to adjust the wind wheel rotation speed, manage the output power, and safely shut down the wind turbine using aerodynamic braking. For a normal operating wind turbine, if the wind speed goes faster than the rated value, the blade pitch will be regulated so that the wind wheel rotates at a constant rate, and in case of any power failures the blades will be moved to the feathering position. In a pitch control system, blades are attached to the hub using a shaft, a motor is geared to the pitch shaft, backup batteries must also be installed to supply power to ensure safe shutdown in case of emergencies, and a standby limit switch is required to guarantee safe braking if the main limit switch fails.  

 The paper studies the patents filed in China and other countries about pitch control systems and compares the statuses to learn the technological gap, after taking samples from World Patent Index (WPI) and China Patent Retrieve System (CPRS), respectively.


Study of global patents on pitch systems

This section focuses on the trend and the applicant ranking to study the global patent applications on pitch systems.

1 Application Trend

Figure 1 shows the changing numbers of global applications on the pitch control system of wind turbines. There are three stages for further discussions.

(1) Technology growing stage from 1970-2005

The first patent application on pitch systems was filed in the year 1970, though there had been a slow growing curve in the number of patents in this field since then. The applications peaked a little during 1978 to 1988, thanks to the wind power policies passed by the U.S. parliament in 1978 to set out the national wind power development plan in the following decade. American companies filed patents in flocks during this period, but quickly cooled down their passion during 1988 to 1999 when the number of applications experienced a small drop until the millennium. After 2000, pitch systems regained some attention and there was a tiny growth in the number of patent applications.


(2) Rapid development stage from 2006 to 2011

Pitch system technologies strode forward since 2006, and the number of applications was multiplied during 2006 and 2011. The Chinese government issued Renewable Energy Regulation on January 1, 2006 to encourage the development of renewable energy and allow integrating the generated power into the grid. The policy move stimulated a surge in patent applications from China.


(3) Steady stage from 2012 to now

After the rapid development, the wind turbine market saw a temporary saturation since 2012. A fall in the number of patent applications ensued, but there were still a considerable number of annual applications after that. It should also be noted that statistics after 2014 have not been released in time, so the real picture might differ slightly.


  1. Potent applicant ranking

Figure 2 lists the global applicants for pitch systems of wind turbines.

Only three Chinese companies made their way to the global top 10 name list for potent applications on pitch systems, and the total number of applicants from China is far less than that from foreign companies. We learn that Chinese companies have made some progresses in pitch system R&D and protection, though there is a substantial gap from our status quo to the global front runners. GE and Vestas are sitting on the top and second positions respectively. They have filed similar numbers of patents, and left others far behind them. Siemens and MHI follow as the third and forth. All top ten names on the list are companies or research institutions across the globe, and no individual applicant ever filed patent applications in this field. It is understandable since that the pitch system study requires high level technologies and industrialization.



Study of Chinese patents on pitch systems

This section studies the Chinese patent application on pitch systems in terms of the application trend, the technology focuses, and the comparison with oversea focuses.


  1. Application trend


Figure 3 shows the changing numbers of Chinese applications on the pitch control system of wind turbines.

The first patent application on pitch systems was filed in China in 1990, and the growth was slow until 2005 with a total of 26 cases during 15 years. Needless to say, this period had seen few development or progresses. The applications increased sharply since 2006, thanks to the Renewable Energy Regulation issued at the beginning of the year. Later the number peaked to over 200 cases from 2011 to 2012, and maintained a steady growth with about 100 annual cases in the following years. Since 2012, the growth in applications slowed down and there was a drop during 2013 and 2015.


  1. Technology focuses

Figure 4 shows the trend as well as the technology focuses of patent applications on pitch systems in China.

Based on the figure, we learn that among these Chinese patent applications, 29% is about pitch control equipment assembly, 25% is about pitch control methods, and others are about the electrical control system, safety, or reliability. Applications filed before 2004 were mostly about pitch equipment assembly and few of them were technologically focused. Since 2005, more patents about pitch equipment assembly and pitch control methods were filed. After the number of applications peaked in 2011, the share of patents on pitch equipment assembly dropped sharply, while the applications on pitch control methods kept growing steadily. More patents about electrical control structure and bearing gear since 2009 started to be filed. Patents about safety and reliability appeared early in the process, saw a surge in the patent number in 2007, and remain as a key technical topic since 2011.


3 Comparison with oversea focuses  

Figure 5 illustrates the comparison between Chinese patents and foreign patents. Note that the share of each technological focus is calculated based on the total applications (100) in the spider chart.

We learn from the diagram that Chinese patents differ from foreign patents in their priorities. First, 26% of Chinese patents are about pitch equipment assembly, while 43% of foreign patents focus on pitch control method. A closer look tells us that Chinese patents pay attention to upgrading the pitch equipment structure, while foreign patents tend to offer more solutions to pitch control methods and the use of signals. Secondly, 21% of foreign patents are filed to improve reliability and safety, while only 6% of Chinese patents care about these topics. Then, Chinese patents show some interests in electrical control and hydraulic pitch systems, which are less common among foreign patents.


To sum up, there is an apparent gap for Chinese companies to catch up in patent applications on pitch systems. Based on studies of the application trends and technology focuses, we can conclude that the hot topics in this field should be pitch control methods, safety, and reliability. Obviously foreign applicants are on the right track and have made headway in these two directions. Chinese applicants pay far less attention in these areas, safety and reliability in particular, and are distracted more to pitch equipment structure upgrade. We lag behind our foreign counterparts in patent applications on these technical focuses.


Study on patent applications on independent pitch technology

The wind power technology has been steadily moving forward, bringing larger capacitance with increasing size of blades. The progresses present us with more challenges as well. There are more unpredictable factors which may change the load of blades, wind shear, turbulence, disturbance, effect of the tower, gravity and centrifugal force on blades, to name just a few. Since the fatigue loads of blades, hub, main shaft, and tower are becoming greater, the lifetime of these parts shortens and the wind turbine as a whole is less reliable. The good news is that the wind turbine load can be inspected constantly and reliably, thanks to the advanced development in load transducers. Independent pitch control system helps substantially to alleviate the fatigue load on the other main parts of wind turbines, offering us a more cost effective way to boost equipment reliability and lifetime other than seeking greater mechanical strength. Since 2005, there has been a remarkable increase in the number of patent applications on independent pitch technologies. The paper decides to discuss further about the top four companies who made the most patent applications in the field, GE, Vestas, Siemens, and MHI.

Figure 6 shows the number of patent applications on independent pitch technology filed by the four companies.

As a company dedicated exclusively to wind energy, Vestas has filed 32 patents on independent pitch technology, securing the top position on the list. The company delivers mostly large scale wind turbines with megawatt capacitance, and the independent pitch technology has been used for most of turbines.


Figure 7 describes the technology focuses of patent applications from the four companies. We learn from the diagram that these patents point to mostly the following three areas:

1. Load calculation. This technology aims to alleviate the fatigue load on each part during turbine operation when the output power is guaranteed. To properly calculate or analyze the load on each part is fundamental to the independent pitch technology. No wonder that GE, Vestas, and Siemens each filed nine cases about load calculation, trying to secure the dominance in this area.

2. Environment monitoring. A key factor causing the unbalanced load is that blades experience different wind velocities and directions, therefore real time, accurate, and reliable monitoring on wind speed and directions becomes crucial. Environment monitoring expands to cover as much as possible, including the ambient noise, blade vibration, tower stability, and ice on blades, all of which shall be taken into account for independent pitch technology so that their influence can be mitigated. We see eleven cases from Vestas and ten cases from GE on this topic, while Siemens and MHI show a lack of enthusiasm here.

3. Control strategy. After acquiring parameters of wind velocity, wind direction, load, etc., effective models and optimal control strategies must be used to make full use out of the data. Linear models and non-linear models are in common use. The former tends to neglect several wind turbine features, while the latter is complex and consumes too much efforts for analysis and calculation. Smart control strategies based on fuzzy control and control strategies based on fatigue load of blades are the key strategies. Vestas ranks first on this topic with twelve cases. MHI also files most of their patent applications in this area.

To sum up, GE pays more attention to load calculation and environment monitoring and clearly has a competitive edge in both. Vestas seems to be attaching equal importance to the three areas and wins in terms of the number of patents in each. Siemens chose to focus mainly on load calculation R&D, but also projects some influence in control strategies. MHI is a leader in control strategies and diverts little interests in load calculation and environment monitoring.



As wind turbines are using larger parts and equipment, hence the increasing load, global players including GE, Vestas, and Siemens are seeking a pitch system that alleviates the unbalanced load, and they are filing a great deal of relevant patents. These global leaders of the industry flocked into Chinese market, filed many patents on pitch systems, and raised the threshold. Chinese companies, on the other hand, remain on the peripheral area, studying on pitch equipment structure and parts upgrade and knowing barely anything about pitch control methods or boosting reliability and safety using pitch systems. Independent pitch control technology stands at the core of pitch system in the future. To have a bigger voice in this area, we need to work on load calculation for turbine parts, environment monitoring on wind velocity, direction, etc., and fuzzy control strategies based on linear and non-linear models. In retrospect, Chinese firms are lagging far behind. However, our foreign counterparts just started to make achievements only since recent years. Control strategies require more theoretical research and algorithm study than the other two areas, therefore we recommend that companies and academic institutions work jointly to strengthen research in fundamental disciplines and seek breakthroughs in control strategies for independent pitch systems.


Source: Wind Energy, 6th issue in 2017

Author: Ying Yiming, Wei Hong

Affiliation: Wind Power Machinery Branch of the Patent Department, State Intellectual Property Office of the P.R.C