Cooling Techniques in Direct-Drive Generators for Wind Power Application

Abstract

Direct-drive generators are an attractive candidate for wind power application since they do not need a gearbox, thus increasing operational reliability and reducing power losses. However, this is achieved at the cost of an increased generator size, larger inverter and decreased thermal performance. The associated cooling system is therefore crucial to keep the generator and inverter sizes down and to operate within the safe thermal limits. Various cooling techniques suitable for generators are therefore reviewed and analyzed in this paper. The performance and maintenance requirements are unavoidable compromises that need to be investigated together, especially for large generators. The location of the wind turbine is also important and dictates critical issues such as accessibility and maximum size. The key novelty in this paper is the assessment of the cooling methods based on generator size, reliability and maintenance requirements.

Perspective of Thermal Analysis and Management for Permanent Magnet Machines, with Particular Reference to Hotspot Temperatures

“…Generally, the electrical parameters, i.e., stator resistance R s and PM flux linkage ψ pm , are temperature-dependent (19), and thus, can be used as indicators to reflect average temperatures of winding and PM for online condition monitoring. Since the 2000s, the techniques of online parameter estimation for PM machines have been extensively investigated.…”

“…Firstly, the temperature coefficients (absolute values) of the copper and the PM are considerably small at 0.39 %/ • C and <0.2 %/ • C, respectively. When the variations of stator resistance and the PM flux linkage are used to reflect their temperatures (19), the conversion coefficients equal the inverse of the small temperature coefficients. Therefore, the estimated temperatures are very sensitive to measurement errors, VSI nonlinearity, and parameter variations.…”

“…In high power applications, e.g., automotive traction machines, the forced liquid cooling technique is more popular due to its effectiveness [18,19]. Generally, compared to the forced air cooling method, the forced liquid cooling system requires additional apparatuses, e.g., high-pressure and scavenge pumps, liquid temperature control units, pressure and flow rate sensors, etc.…”

“…LPTMs that were initially modelled for IMs have also been widely applied to PM machines [38,[46][47][48][49]. In addition, the LPTM based commercial thermal analysis software Motor-CAD [54] was also developed in 1999 and then further widely employed [13][14][15][16][17][18][19].…”

“…However, as aforementioned, numerous new techniques in thermal analysis techniques have been developed over the last 10 years or so which are also worth reviewing and evaluating. More recently, many survey papers have reviewed various cooling techniques specific to different applications, such as wind power generation [19], aerospace [20,21], automotive [22][23][24], advanced manufacturing techniques [28,29], etc., which are summarized in Table 2. Obviously, common cooling techniques have been extensively reviewed so far, while the accurate estimation of machine temperatures, particularly hotspot temperatures of winding and PM, are equally or even more important.…”