Patent Publication Number: US-2021167652-A1

Title: Method for adjusting high efficiency region of permanent magnet motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to design of permanent magnet motor, in particular for regulating high efficiency region of permanent magnet motor, which belongs to field of motor manufacturing. 
     2. Description of Related Art 
     Nowadays, permanent magnet motor plays a very important role and has been widely used into variable applications, such as electric vehicle and ship propulsion. This is mainly due to several significant advantages of permanent magnet motors, including high torque density, high power density and small weight and volume. Meanwhile, peinianent magnet motor adopts magnetic material with high magnetic energy, instead of traditional excitation winding. It not only avoids the negative effects resulted from traditional excitation winding, but also simplifies the mechanical structure of motor, which improves the reliability of motor and reduces the mechanical loss. 
     Although the permanent magnet motor has a series of advantages, there are still some shortcomings in the application of electric vehicle drive system. Especially, the inconsistency between the driving cycles of the electric vehicle and high efficiency region of the permanent magnet motor, which causes the waste of energy and the decrease of efficiency. If the high efficiency region of permanent magnet motor should be adjusted to the area corresponding to the given driving cycle of the electric vehicle, the electric vehicle will operate in the high efficiency region, thus saving energy. Therefore, it is very valuable to study the method for adjusting the high efficiency region of permanent magnet motor. 
     At present, the regulation of high efficiency region has been studied deeply, such as optimizing the shape of permanent magnet, optimizing the ratio of axial length and winding turns, etc. One of common disadvantages of these methods is that they all expand the high efficiency region of the motor by reducing the loss, and then the high efficiency region is just improve, while the position of the high efficiency region is fixed. Therefore, it is necessary to study how to reveal the regulation method to move high efficiency region towards target area. 
     SUMMARY OF THE INVENTION 
     The aim of this invention is to propose a method to regulate high efficiency region. Base on accurate analysis of high efficiency region regulation method, the optimal loss combination among copper loss, iron loss and permanent magnet eddy-current loss will be obtained. Then, the high efficiency region will be regulated to the corresponding area of electric vehicle under given driving cycles, thus improving efficiency and saving energy. 
     Technical scheme of the invention is how to regulate high efficiency region of permanent magnet motor, including the following steps: 
     Step 1: Constant torque region of the target motor is firstly analyzed. In the constant torque region, point ‘ 1 ’ is set as the point with maximum efficiency, and points ‘2’, ‘3’, ‘4’ and ‘5’ are selected as four directions around point ‘1’. Then the relationship between the maximum efficiency point and other points is constructed. 
     Step 2: The relationships of speed and current between the maximum efficiency point ‘1’ and the top point ‘2’ in the constant torque region are n 2 =n 1  and I 2 =k 2 I 1 . Then, the copper loss relationship between two points is obtained as p copp2 =k 2   2 P copp1 . Furthermore, if the efficiency of point ‘1’ is greater than that of point ‘2’, the equation k 2 P copp1 ≥P iron1 +P PM1  will be deduced. 
     Step 3: The relationships of speed and current between the maximum efficiency point ‘1’ and the bottom point ‘3’ in the constant torque region are n 3 =n 1  and I 3 =k 3 I 1 . Then, the copper loss relationship between two points is obtained as P copp3 =k 3   2 P copp1 . Furthermore, if the efficiency of point ‘1’ is greater than that of point ‘3’, the equation k 3 P copp1 &lt;P iron1 +P PM1  will be deduced. 
     Step 4: The relationships of current, torque and speed between the maximum efficiency point ‘1’ and the right point ‘4’ in the constant torque region are I 4 =I 1 , T 4 =T 1  and n 4 =k 4 n 1 . Then, the relationships of copper loss, hysteresis iron loss, eddy-current iron loss, additional iron loss and permanent magnet eddy-current loss are obtained as P copp4 =P copp1 , P h4 =k 4 P h1 , P c4 k 4   2 P c1 , P E4 =k 4   1.5 P E1 , and P PM4 =k 4   2 P PM1 . Furthermore, if the efficiency of point ‘1’ is greater than that of point ‘4’, the equation P copp1 &lt;k 4 (P c1 +P E1 +P PM1 ) will be deduced. 
     Step 5: The relationships of current, torque and speed between the maximum efficiency point ‘1’ and the left point ‘5’ in the constant torque region are I 5 =I 1 , T 5 =T 1  and n 5 =k 5 n 1 . Then, the relationships of copper loss, hysteresis iron loss, eddy-current iron loss, additional iron loss and permanent magnet eddy-current loss are obtained as P copp5 =P copp1 , P h5 =k 5 P h1 , P c4 =k 4   2 P c1 , P E5 =k 5   1.5 P E1  and P PM5 =k 5   2 p PM1 . Furthermore, if the efficiency of point ‘1’ is greater than that of point ‘5’, the equation p copp1 ≥k 5 (P c1 +P E1 +P PM1 ) will be deduced. 
     Step 6: From Step 2 to Step 5, the maximum efficiency point needs to satisfy some equations, and then, the high efficiency point can be moved in horizontal and vertical direction according these equations. 
     Step 7: Since the equations from Step 2 to Step 5 is only deduced in constant torque region, the effectiveness of these equations should be verified in others region like the connective region between constant torque region and constant power region. 
     Step 8: The combination of copper loss, iron loss and permanent magnet eddy-current loss are analyzed to make point ‘1’ as the maximum efficiency point. Then, three methods for adjusting the ratio of loss in high efficiency region by changing the parameters of winding, permanent magnet and silicon steel sheet are put forward. 
     Step 9: The correctness of the proposed methods for adjusting high efficiency region is verified by a specific driving cycles. 
     Further, the detail process of Step 2 is realized as follow: 
     Firstly, the relationship of speed and current between point ‘1’ and point ‘2’ is established as: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         n 
                         2 
                       
                       = 
                       
                         n 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         I 
                         2 
                       
                       = 
                       
                         
                           k 
                           2 
                         
                          
                         
                           I 
                           1 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where n 2  is the speed of point ‘2’, n 1  is the speed of point ‘1’, I 2  is the winding current amplitude of point ‘2’, I 1  is the winding current amplitude of point ‘1’, and k 2  is a coefficient which is greater than 1. 
     Secondly, the corresponding torque, electromagnetic power and copper loss are obtained from the relationship of speed and current between point ‘1’ and point ‘2’: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         T 
                         2 
                       
                       = 
                       
                         
                           k 
                           2 
                         
                          
                         
                           T 
                           1 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           e 
                            
                           
                               
                           
                            
                           2 
                         
                       
                       = 
                       
                         
                           k 
                           2 
                         
                          
                         
                           P 
                           
                             e 
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           c 
                            
                           o 
                            
                           p 
                            
                           p 
                            
                           2 
                         
                       
                       = 
                       
                         
                           k 
                           2 
                           2 
                         
                          
                         
                           P 
                           
                             copp 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where T 2  is the torque of point ‘2’, T 1  is the torque of point ‘1’, P e2  is the power of point ‘2’, P e1  is the power of point ‘1’, P copp2  is the copper loss of point ‘2’, and P copp1  is the copper loss of point ‘1’. 
     Thirdly, ignoring motor mechanical loss and wind friction loss, the efficiency expressions of point ‘1’ and point ‘2’ are written out as follows: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         η 
                         1 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             1 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         η 
                         2 
                       
                       = 
                       
                         
                           P 
                           e2 
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where η 2  is the efficiency of point ‘2’, η 1  is the efficiency of point ‘1’, P 1ron2  is the iron loss of point ‘2’, P iron1  is the iron of point ‘1’, P PM2  is the permanent magnet eddy-current loss of point ‘2’, and P PM1  is the permanent magnet eddy-current loss of point ‘1’. 
     Finally, if the efficiency of point ‘1’ is greater than that of point ‘2’, the following equation will be obtained: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       y 
                       = 
                       
                         
                           
                             
                               
                                 k 
                                 2 
                               
                                
                               
                                 ( 
                                 
                                   
                                     k 
                                     2 
                                   
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                              
                             
                               P 
                               
                                 copp 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           &gt; 
                           
                             
                               ( 
                               
                                 
                                   
                                     k 
                                     2 
                                   
                                    
                                   
                                     P 
                                     
                                       iron 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                 - 
                                 
                                   P 
                                   
                                     iron 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                               
                               ) 
                             
                             + 
                             
                               ( 
                               
                                 
                                   
                                     k 
                                     2 
                                   
                                    
                                   
                                     P 
                                     
                                       PM 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                 - 
                                 
                                   P 
                                   
                                     PM 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                               
                               ) 
                             
                           
                         
                         = 
                         x 
                       
                     
                   
                 
                 
                   
                     
                       z 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   2 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 iron 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   2 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 PM 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         &gt; 
                         x 
                       
                     
                   
                 
               
             
           
         
       
     
     When point ‘1’ and point ‘2’ are very close to each other, P iron2  and P PM2  are slightly greater than P iron1  and P PM1 , respectively. Thus, z is slightly greater than x, while x is smaller than y. After simplification, the following equation can be obtained: 
     
       
      
       k 
       2 
       P 
       copp1 
       ≥P 
       iron1 
       +P 
       PM1  
      
     
     Further, the detail process of Step 3 is realized as follow: 
     Firstly, the relationship of speed and current between point ‘1’ and point ‘3’ is established as follow: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         n 
                         3 
                       
                       = 
                       
                         n 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         I 
                         3 
                       
                       = 
                       
                         
                           k 
                           3 
                         
                          
                         
                           I 
                           1 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where n 3  is the speed of point ‘3’, I 3  is the winding current amplitude of point ‘3’, and k 3  is a coefficient which is smaller than 1. 
     Secondly, the corresponding torque, electromagnetic power and copper loss are obtained from the relationship of speed and current between point ‘1’ and point ‘3’: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         T 
                         3 
                       
                       = 
                       
                         
                           k 
                           3 
                         
                          
                         
                           T 
                           1 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         e3 
                       
                       = 
                       
                         
                           k 
                           3 
                         
                          
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           copp 
                            
                           
                               
                           
                            
                           3 
                         
                       
                       = 
                       
                         
                           k 
                           3 
                           2 
                         
                          
                         
                           P 
                           
                             copp 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Where T 3  is the torque of point ‘3’, P e3  is the power of point ‘3’, and P copp3  is the copper loss of point ‘3’. 
     Thirdly, ignoring motor mechanical loss and wind friction loss, the efficiency expressions of point ‘1’ and point ‘2’ are written out as follows: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         η 
                         1 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             1 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                               ] 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         η 
                         3 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where η 3  is the efficiency of point ‘3’, P iron3  is the iron loss of point ‘3’, and P PM3  is the permanent magnet eddy-current loss of point ‘3’. 
     Finally, if the efficiency of point ‘1’ is greater than that of point ‘3’, the following equation will be obtained: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       y 
                       = 
                       
                         
                           
                             
                               
                                 k 
                                 3 
                               
                                
                               
                                 ( 
                                 
                                   
                                     k 
                                     3 
                                   
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                              
                             
                               P 
                               
                                 copp 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           &gt; 
                           
                             
                               ( 
                               
                                 
                                   
                                     k 
                                     3 
                                   
                                    
                                   
                                     P 
                                     
                                       iron 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                 - 
                                 
                                   P 
                                   
                                     iron 
                                      
                                     
                                         
                                     
                                      
                                     3 
                                   
                                 
                               
                               ) 
                             
                             + 
                             
                               ( 
                               
                                 
                                   
                                     k 
                                     3 
                                   
                                    
                                   
                                     P 
                                     
                                       PM 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                   
                                 
                                 - 
                                 
                                   P 
                                   
                                     PM 
                                      
                                     
                                         
                                     
                                      
                                     3 
                                   
                                 
                               
                               ) 
                             
                           
                         
                         = 
                         x 
                       
                     
                   
                 
                 
                   
                     
                       z 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   3 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 iron 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   3 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 PM 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         &lt; 
                         x 
                       
                     
                   
                 
               
             
           
         
       
     
     When point ‘1’ and point ‘3’ are very close to each other, P iron3  and P PM3  are slightly smaller than P iron1  and P PM1 , respectively. Thus, z is slightly smaller than x, while x is smaller than y. After simplification, the following equation can be obtained: 
     
       
      
       k 
       3 
       P 
       copp1 
       &lt;P 
       iron1 
       +P 
       PM1  
      
     
     Further, the detail process of Step 4 is realized as follow: 
     Firstly, the relationship of current, torque and speed between point ‘1’ and point ‘4’ is established as follow: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         I 
                         4 
                       
                       = 
                       
                         I 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         T 
                         4 
                       
                       = 
                       
                         T 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         n 
                         4 
                       
                       = 
                       
                         
                           k 
                           4 
                         
                          
                         
                           n 
                           1 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     in where I 4  is the winding current amplitude of point ‘4’, T 4  is the torque of point ‘4’, n 4  is the speed of point ‘4’, and k 4  is a coefficient which is greater than 1. 
     Secondly, the corresponding electromagnetic power, copper loss, hysteresis iron loss, eddy-current iron loss, additional iron loss and permanent magnet eddy-current loss are obtained from the relationship of current, torque and speed between point ‘1’ and point ‘4’: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         P 
                         
                           e 
                            
                           
                               
                           
                            
                           4 
                         
                       
                       = 
                       
                         
                           k 
                           4 
                         
                          
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           copp 
                            
                           
                               
                           
                            
                           4 
                         
                       
                       = 
                       
                         P 
                         
                           copp 
                            
                           
                               
                           
                            
                           1 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           h 
                            
                           4 
                         
                       
                       = 
                       
                         
                           k 
                           4 
                         
                          
                         
                           P 
                           
                             h 
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           c 
                            
                           4 
                         
                       
                       = 
                       
                         
                           k 
                           4 
                           2 
                         
                          
                         
                           P 
                           
                             c 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           E 
                            
                           
                               
                           
                            
                           4 
                         
                       
                       = 
                       
                         
                           k 
                           4 
                           1.5 
                         
                          
                         
                           P 
                           
                             E 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           PM 
                            
                           
                               
                           
                            
                           4 
                         
                       
                       = 
                       
                         
                           k 
                           4 
                           2 
                         
                          
                         
                           P 
                           
                             P 
                              
                             M 
                              
                             1 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where P e4  is the power of point ‘4’, P copp4  is the copper loss of point ‘4’, P h4  is the hysteresis iron loss of point ‘4’, P e4  is the eddy-current iron loss of point ‘4’, P E4  is the additional iron loss of point ‘4’, P PM4  is the permanent magnet eddy-current loss of point ‘4’, P h1  is the hysteresis iron loss of point ‘1’, P c1  is the eddy-current iron loss of point ‘1’, and P E1  is the additional iron loss of point ‘1’. 
     Thirdly, ignoring motor mechanical loss and wind friction loss, the efficiency expressions of point ‘1’ and point ‘4’ are written out as follows: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         η 
                         1 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             1 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         η 
                         4 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             4 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               4 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               4 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               4 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               4 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where η 4  is the efficiency of point ‘4’. 
     Finally, if the efficiency of point ‘1’ is greater than that of point ‘4’, the following equation will be obtained: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       v 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   4 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 copp 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           &lt; 
                           
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     4 
                                     2 
                                   
                                   - 
                                   
                                     k 
                                     4 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   c 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                             + 
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     4 
                                     1.5 
                                   
                                   - 
                                   
                                     k 
                                     4 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   E 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                             + 
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     4 
                                     2 
                                   
                                   - 
                                   
                                     k 
                                     4 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   P 
                                    
                                   M 
                                    
                                   1 
                                 
                               
                             
                           
                         
                         = 
                         u 
                       
                     
                   
                 
                 
                   
                     
                       w 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   4 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   4 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 c 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   4 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   4 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 E 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   4 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   4 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 M 
                                  
                                 1 
                               
                             
                           
                         
                         &gt; 
                         u 
                       
                     
                   
                 
               
             
           
         
       
     
     When point ‘1’ and point ‘4’ are very close to each other, (k 4   2 −k 4 ) is slightly greater than (k 4   1.5 −k 4 ). Thus, w is slightly greater than u, while u is greater than v. After simplification, the following equation can be obtained: 
         P   copp1   &lt;k   4 ( P   c1   +P   E1   +P   PM1 ) 
     Further, the detail process of Step 5 is realized as follow: 
     Firstly, the relationship of current, torque and speed between point ‘1’ and point ‘5’ is established as follows: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         I 
                         5 
                       
                       = 
                       
                         I 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         T 
                         5 
                       
                       = 
                       
                         T 
                         1 
                       
                     
                   
                 
                 
                   
                     
                       
                         n 
                         5 
                       
                       = 
                       
                         
                           k 
                           5 
                         
                          
                         
                           n 
                           1 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where I 5  is the winding current amplitude of point ‘5’, T 5  is the torque of point ‘5’, n 5  is the speed of point ‘5’, and k 5  is a coefficient which is smaller than 1. 
     Secondly, the corresponding electromagnetic power, copper loss, hysteresis iron loss, eddy-current iron loss, additional iron loss and permanent magnet eddy-current loss are obtained from the relationship of current, torque and speed between point ‘1’ and point ‘5’: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         P 
                         
                           e 
                            
                           
                               
                           
                            
                           5 
                         
                       
                       = 
                       
                         
                           k 
                           5 
                         
                          
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           copp 
                            
                           
                               
                           
                            
                           5 
                         
                       
                       = 
                       
                         P 
                         
                           copp 
                            
                           
                               
                           
                            
                           1 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         h5 
                       
                       = 
                       
                         
                           k 
                           5 
                         
                          
                         
                           P 
                           
                             h 
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         c5 
                       
                       = 
                       
                         
                           k 
                           5 
                           2 
                         
                          
                         
                           P 
                           
                             c 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         E5 
                       
                       = 
                       
                         
                           k 
                           5 
                           1.5 
                         
                          
                         
                           P 
                           
                             E 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         
                           PM 
                            
                           
                               
                           
                            
                           5 
                         
                       
                       = 
                       
                         
                           k 
                           5 
                           2 
                         
                          
                         
                           P 
                           
                             P 
                              
                             M 
                              
                             1 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where P e5  is the power of point ‘5’, P copp5  is the copper loss of point ‘5’, P h5  is the hysteresis iron loss of point ‘5’, P c5  is the eddy-current iron loss of point ‘5’, P E5  is the additional iron loss of point ‘5’, and P PM5  is the permanent magnet eddy-current loss of point ‘5’. 
     Thirdly, ignoring motor mechanical loss and wind friction loss, the efficiency expressions of point ‘1’ and point ‘5’ are written out as follows: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         η 
                         1 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             1 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         η 
                         5 
                       
                       = 
                       
                         
                           P 
                           
                             e 
                              
                             
                                 
                             
                              
                             5 
                           
                         
                         
                           
                             P 
                             
                               e 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                           + 
                           
                             P 
                             
                               copp 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                           + 
                           
                             P 
                             
                               iron 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                           + 
                           
                             P 
                             
                               PM 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Where η 5  is the efficiency of point ‘5’. 
     Finally, if the efficiency of point ‘1’ is greater than that of point ‘5’, the following equation will be obtained: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       v 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   5 
                                 
                                 - 
                                 1 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 copp 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           &lt; 
                           
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     5 
                                     2 
                                   
                                   - 
                                   
                                     k 
                                     5 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   c 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                             + 
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     5 
                                     1.5 
                                   
                                   - 
                                   
                                     k 
                                     5 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   E 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                             + 
                             
                               
                                 ( 
                                 
                                   
                                     k 
                                     5 
                                     2 
                                   
                                   - 
                                   
                                     k 
                                     5 
                                   
                                 
                                 ) 
                               
                                
                               
                                 P 
                                 
                                   P 
                                    
                                   M 
                                    
                                   1 
                                 
                               
                             
                           
                         
                         = 
                         u 
                       
                     
                   
                 
                 
                   
                     
                       w 
                       = 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   k 
                                   5 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   5 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 c 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   5 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   5 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 E 
                                  
                                 1 
                               
                             
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   k 
                                   5 
                                   2 
                                 
                                 - 
                                 
                                   k 
                                   5 
                                 
                               
                               ) 
                             
                              
                             
                               P 
                               
                                 M 
                                  
                                 1 
                               
                             
                           
                         
                         &lt; 
                         u 
                       
                     
                   
                 
               
             
           
         
       
     
     When point ‘1’ and point ‘5’ are very close to each other, (k 5   2 −k 5 )P E1  is slightly smaller than (k 5   1.5 −k 5 )P E1 . Thus, w is slightly smaller than u, while u is greater than v. After simplification, the following relationship can be obtained: 
         P   copp1   ≥k   5 ( P   c1   +P   E1   +P   PM1 ) 
     Further, in Step 6, the high efficiency point can be moved in horizontal and vertical direction, when the loss in the motor satisfies following equation: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         P 
                         Vertical 
                       
                       = 
                       
                         
                           
                             P 
                             copp 
                           
                            
                           
                               
                           
                           - 
                           
                             ( 
                             
                               
                                 P 
                                 iron 
                               
                               + 
                               
                                 P 
                                 
                                   P 
                                    
                                   M 
                                 
                               
                             
                             ) 
                           
                         
                         ≈ 
                         0 
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         Horizontal 
                       
                       = 
                       
                         
                           
                             P 
                             copp 
                           
                           - 
                           
                             ( 
                             
                               
                                 P 
                                 c 
                               
                               + 
                               
                                 P 
                                 E 
                               
                               + 
                               
                                 P 
                                 PM 
                               
                             
                             ) 
                           
                         
                         ≈ 
                         0 
                       
                     
                   
                 
               
             
           
         
       
     
     Where P copp  represents copper loss, P iron  represents iron loss, P PM  represents permanent magnet eddy-current loss, P c  represents eddy-current iron loss, and P E  represents additional iron loss. When P vertical  is greater than 0, the efficiency of the point is greater than that of top point; When P vertical  is smaller than 0, the efficiency of the point is greater than that of bottom point; When P Horizontal  is greater than 0, the efficiency of the point is greater than that of left point; When P Horizontal  is smaller than 0, the efficiency of the point is greater than that of right point. If high efficiency region is desired to be adjusted to the target area, P vertical  and P Horizontal  of the points of the target area should be optimized to approach 0. 
     Further, since the current will be smaller and the speed will be lower under the junction region of the constant torque region and the constant power region in Step 7, the current angle does not change and this region still meets the equation of high efficiency regulation in the constant torque region. 
     Further, in Step 8, the copper loss, iron loss and permanent magnet eddy-current loss can be represented by expressions as: 
     
       
         
           
               
             
               { 
               
                 
                   
                     
                       
                         P 
                         copp 
                       
                        
                       
                           
                       
                       = 
                       
                         
                           m 
                            
                           
                               
                           
                            
                           
                             I 
                             2 
                           
                            
                           R 
                         
                         2 
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         iron 
                       
                       = 
                       
                         
                           P 
                           h 
                         
                         + 
                         
                           P 
                           c 
                         
                         + 
                         
                           P 
                           E 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                         P 
                         PM 
                       
                       = 
                       
                         
                           
                             K 
                             2 
                           
                            
                           
                             f 
                             2 
                           
                            
                           
                             L 
                             a 
                           
                            
                           
                             B 
                             m 
                             2 
                           
                            
                           
                             L 
                             m 
                             2 
                           
                            
                           V 
                         
                         
                           1 
                            
                           2 
                            
                           
                             ρ 
                              
                             
                               ( 
                               
                                 
                                   L 
                                   a 
                                 
                                 + 
                                 
                                   L 
                                   m 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where m represents phase number of the motor, I represents winding current amplitude, represents winding resistance per phase, P h  represents hysteresis iron loss, K represents a electromotive force constant, f represents frequency, L a  represents axial length of the motor, B m  represents maximum flux density, L m  represents width of the permanent magnet, V represents volume, and ρ represents resistivity. Copper loss can be adjusted by changing the winding current amplitude or winding resistance, and winding resistance is mainly determined by the winding length after the determination of the line diameter. Iron loss can be adjusted by changing the magnitude of the armature magnetic field or the permanent magnetic field. Permanent magnet eddy current loss can be adjusted by rotor opening, radial or axial segmentation, changing the pole-arc coefficient of permanent magnet, changing the opening size of stator slot, and changing the permanent magnet material. 
     Further, in Step 8, the methods of adjusting the loss ratio of high efficiency region by changing the parameters of winding, permanent magnet and silicon steel sheet are put forward. To make high efficiency region move towards the top or left, the following measures can be adopted: reducing the current amplitude and increasing the number of winding turns, increasing the pole-arc coefficient of the permanent magnet, and increasing the opening size of the stator slot; Relatively, to make high efficiency region move towards the bottom or right, the following measures can be adopted: increasing the current amplitude and reducing the number of winding turns, reducing the pole-arc coefficient of the permanent magnet, reducing the opening size of the stator slot, and radial or axial segmentation of permanent magnet. 
     Finally, the proposed efficiency regulation method is suitable for any type of permanent magnet motor. 
     The beneficial effect of the invention:
         a) In the invention, the area under the junction region of the constant torque region and the constant power region in efficiency map is deeply analyzed and the conditional relation of the efficiency between points and points in this region is revealed. Thus, the distribution of efficiency in the efficiency map is easier to be understood.   b) In the invention, the method to regulate high efficiency region reveals the equations that high efficiency region needs to satisfy. It provides theoretical guidance for adjusting high efficiency region to target area, and thus saving a lot of design time.   c) In the invention, the method to regulate high efficiency region is suitable for any type of permanent magnet motor. Firstly, it is suitable for radial, axial and transverse flux permanent magnet motors from the angle of the direction of the magnetic field. Also, it is suitable for integer slot distributed winding and fractional slot concentrated winding permanent magnet motor from the view of winding structures. Moreover, it is suitable for surface-mounted, embed and inset permanent magnet motors from the angle of permanent magnet installation.   d) In the invention, the method to regulate high efficiency region is suitable for a lot of driving cycles such as UDDS, NEDC and so on.   e) In the invention, the method can combine the high efficiency region with electric vehicle driving cycles. Thus, it can enhance the motor efficiency, reduce the energy consumption and increase the range of electric vehicles.       

    
    
     
       BRIEF DESCRIPTION OF APPENDED DRAWINGS 
       The invention can be better understood on reading the following detailed description of non-restrictive illustrative embodiments of the invention and on examining the appended drawing, wherein: 
         FIG. 1  illustrates the relationship diagram between point ‘1’ and points ‘2’, ‘3’, ‘4’, ‘5’ in the constant torque region of the permanent magnet motor. 
         FIG. 2  illustrates the relationship diagram between point ‘1’ and point ‘2’ in the constant torque region of the permanent magnet motor. 
         FIG. 3  illustrates the relationship diagram between point ‘1’ and point ‘3’ in the constant torque region of the permanent magnet motor. 
         FIG. 4  illustrates the relationship diagram between point ‘1’ and point ‘4’ in the constant torque region of the permanent magnet motor. 
         FIG. 5  illustrates the relationship diagram between point ‘1’ and point ‘5’ in the constant torque region of the permanent magnet motor. 
         FIG. 6  shows UDDS driving cycle. 
         FIG. 7  shows corresponding torque and speed distribution diagram based on UDDS driving cycle and motor parameter. 
         FIG. 8  shows an embodied permanent magnet motor with three phases. 
         FIG. 9  shows motor efficiency map of the permanent magnet motor when pole-arc coefficient equals to 1. 
         FIG. 10  shows motor efficiency map data of the permanent magnet motor when pole-arc coefficient equals to 1. 
         FIG. 11  shows motor efficiency map of the permanent magnet motor when pole-arc coefficient equals to 0.3. 
         FIG. 12  shows motor efficiency map data of the peinianent magnet motor when pole-arc coefficient equals to 0.3. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the appended drawings in the embodiment of the invention, the detailed embodiment of the invention is clearly and completely described as following. 
     The following embodiments are exemplary, only to explain the invention, but not as a limitation to the invention. 
       FIG. 2  illustrates the relationship diagram between point ‘1’ and point ‘2’ in the constant torque region of the permanent magnet motor. According to the position relation of two points in constant torque region, the relation between two points is listed as: n 2 =n 1 , I 2 =k 2 I 1 ; According to the relationship of speed and current, the torque, electromagnetic power and copper loss of two points are calculated as T 2 =k 2 T 1 , P e2 =k 2 P e1 , P copp2 =k 2   2 P copp1 . If the efficiency of point ‘1’ is greater than that of point ‘2’, equation k 2 P copp1 ≥p iron1 +P PM1  will be deduced. 
       FIG. 3  illustrates the relationship diagram between point ‘1’ and point ‘3’ in the constant torque region of the permanent magnet motor. According to the position relation of two points in constant torque region, the relationship between two points is listed as n 3 =n 1 , I 3 =k 3 I 1 ; According to the relationship of speed and current, the torque, electromagnetic power and copper loss are calculated as T 3 =k 3 T 1 , P e3 =k 3 P e3 , P copp3 =k 3   2 P copp1 , If the efficiency of point ‘1’ is greater than that of point ‘3’, equation k 3 P copp1 ≥P iron1 +P PM1  will be deduced. 
       FIG. 4  illustrates the relationship diagram between point ‘1’ and point ‘4’ in the constant torque region of the permanent magnet motor. According to the position relationship of two points in constant torque region, the relationship between two points is listed as I 4 =I 1 , T 4 =T 1 , n 4 =k 4 n 1 ; According to the relationship of current, torque and speed, the electromagnetic power, copper loss, hysteresis iron loss, eddy-current iron loss and additional iron loss are calculated as P e4 =k 4 P e1 , P copp4 =P copp1 , P h4 =k 4 P h1 , P c4 =k 4   2 P c1 , P E4 =k 4   1.5 =k 4   1.5 P E1 . If the efficiency of point ‘1’ is greater than that of point ‘4’, equation P copp1 &lt;k 4 (P c1 +P E1 +P PM1 ) will be deduced. 
       FIG. 5  illustrates the relationship diagram between point ‘1’ and point ‘5’ in the constant torque region of the permanent magnet motor. According to the position relationship of two points in constant torque region, the relationship between two points is listed as I 5 =I 1 , T 5 =T 1 , n 5 =k 5 n 1 ; According to the relationship of current, torque and speed, the electromagnetic power, copper loss, hysteresis iron loss, eddy-current iron loss and additional iron loss are calculated: P e5 =k 5 P e1 , P copp5 =P copp1 , P h5 =k 5 P h1 , P c5 =k 5   2 P c1 , P E5 =k 5   1.5 P E1 . If the efficiency of point ‘1’ is greater than that of point ‘4’, equation P copp1 ≥k 5 (P c1 +P E1 +P PM1 ) will be deduced. 
     According to the relationship between point ‘1’ and points ‘2’, ‘3’, ‘4’, ‘5’ in four directions, the equations that high efficiency region satisfies are summarized: P Vertical =P copp −(P iron +P PM )≈0, P Honzontal =P copp −(P c +P E +P PM )≈0·P copp  represents copper loss, P iron  represents iron loss, P PM  represents permanent magnet eddy-current loss, P c  represents eddy-current iron loss, and P E  represents additional iron loss. When P vertical  is greater than 0, the efficiency of the point is greater than that of top point; When P vertical  is smaller than 0, the efficiency of the point is greater than that of bottom point; When P Horizontal  is greater than 0, the efficiency of the point is greater than that of left point; When P Horizontal  is smaller than 0, the efficiency of the point is greater than that of right point. Finally, the method to regulate high efficiency region is revealed: if high efficiency region is desired to be adjusted to the target area, P vertical  and P Horfronfal  of the points of the target area should be optimized to approach 0. 
     Since the current will be smaller and the speed will be lower under the junction region of the constant torque region and the constant power region, the current angle does not change and this region still meets the equation of high efficiency regulation in the constant torque region. 
       FIG. 6  shows a diagram of the UDDS driving cycle, which represents a 31 minutes-18 km city travel with  23  stops. The average speed is 32 km/h and the maximum speed is 90 km/h. 
       FIG. 7  shows corresponding torque and speed distribution diagram based on UDDS driving cycle and motor parameter. As shown in  FIG. 7 , the motor operate mainly in low-torque medium-speed region under this driving cycle. If high efficiency region of the motor locates at this region, energy can be greatly saved. Otherwise, the energy will be wasted. 
     As shown in  FIG. 8 , the three-phase surface-mounted permanent magnet motor includes an outer rotor ( 1 ) and an inner stator ( 2 ). Meanwhile, the outer rotor ( 1 ) comprises rotor core ( 3 ) and  10  permanent magnetic poles ( 4 ). Besides, the inner stator ( 2 ) comprises 12 stator slots ( 5 ) and armature windings ( 6 ). 
     As shown in  FIG. 9 , the high efficiency region locates at a high torque region where the torque ranges from 6.14 Nm to 9.45 Nm and the speed ranges from 1000 rpm to 1500 rpm. The high efficiency region does not match with the driving cycle as shown in  FIG. 7 , which results in waste of energy. 
     The data from the efficiency map in  FIG. 9  are extracted and remarked in  FIG. 10 , aiming at analyze the reasons for the location of the high efficient area in  FIG. 9 . As shown in  FIG. 10 , every point includes three parts, and they represent P vertical , P Horizontal  and efficiency of corresponding points. Taking the point in the second row and second column (15.6/21.2/92.5%) as an example, its efficiency (92.5%) is higher than the upper point (92.0%) and lower than the point below (92.8%) because P Vertical  (15.6) is greater than 0. Also, the efficiency of the point (92.5%) is higher than the left point (88.1%) and lower than the right point (93.8%) because P Horizontal  (21.2) is greater than 0. Moreover, only a few points in  FIG. 10  dissatisfy the aforesaid description and this is because the P Vertical  or P Horizontal  of these points is very close to 0, which leads to errors. 
     According to the method to regulate high efficiency region, the reason why high efficiency region locates at the high torque region is that P Vertical  of points in this region are close to 0, while P Vertical  of points in low torque region is less than 0. Thus, the efficiency of low torque region is less than that of the upper high torque region. It can be seen that iron loss and permanent magnet eddy-current loss should be reduced or copper loss should be increased if high efficiency region is desired to move towards low torque region. 
     As shown in  FIG. 11 , the efficiency map is obtained by optimizing the pole-arc coefficient of the permanent magnet to 0.3. After the decrease of the pole-arc coefficient, the permanent magnetic field is weakened which leads to reduction of iron loss and permanent magnet eddy-current loss. In order to keep the peak torque constant, the current value increases, resulting in the increase of copper loss. It can be seen from  FIG. 11  that the high efficiency region locates at a low torque area where the torque ranges from 2 Nm to 4.6 Nm and the speed ranges from 1350 rpm to 3500 rpm. It means that high efficiency region moves from high torque region to low torque region. 
     The data from the efficiency map in  FIG. 11  are extracted and remarked in  FIG. 12 . It can be seen that every point in the constant torque region accords with the method to regulate high efficiency region. 
     In summary, the invention discloses a method to regulate high efficiency region of permanent magnet motor. By establishing the relationship between points in the constant torque region of efficiency map, the conditions that high efficiency region meets are derived. 
     Thus, high efficiency region can be regulated by optimizing loss. Based on given driving cycles of electric vehicles, high efficiency region is regulated by adopting regulating methods so as to improve efficiency and save energy. 
     Although the method herein described, and the forms of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and forms of apparatus, and that changes may be made in either without departing form the scope of the invention, which is defined in the appended Claims.