Patent Publication Number: US-11394278-B2

Title: Shunt wound DC motor driving device and electrical equipment

Description:
TECHNICAL FIELD 
     The present invention belongs to the field of DC motor driving devices, in particular to a shunt wound direct-current (DC) motor driving device and electrical equipment including the shunt wound DC motor driving device. 
     BACKGROUND 
     Exciting windings and armature windings of a shunt wound DC motor are connected in series and share the same power supply. The shunt wound DC motor has advantages of excellent speed control performance, large starting torque and high overload capacity, and is widely applied to rolling mills, electric locomotives, large machine tool spindle transmission systems and ships. 
     As shown in  FIG. 6 , throughout hundreds of years of history of motor development, a traditional shunt wound DC motor driving device  200  is composed of a shunt wound DC motor and a chopper. The shunt wound DC motor is only provided with one pair of external wiring terminals; and the pair of external wiring terminals are correspondingly electrically connected with one pair of power output terminals of the chopper. To ensure system reliability, maximum output current of the chopper is generally 2-3 times that of rated current of the motor. A high-power high-performance shunt wound DC motor, particularly a low-voltage large-current shunt wound DC motor, needs a chopper having extremely large continuous operating current. However, switching components in related choppers are expensive, and the maximum output current of the chopper used by the high-performance motor that can be purchased in the market is only less than one thousand amperes, thereby seriously restricting and affecting the development of the low-voltage large-current shunt wound DC motor. 
     The chopper controls switch-on and off of power switch tubes to change output voltage and output current by a pulse width modulation technology. The size of output current ripple is in direct proportion to sizes of output torque ripple and rotation speed ripple of the motor and is also inversely proportional to switching frequency of the power switch tubes, while switching loss (or temperature rise and a failure rate) of the power switch tubes is in direct proportion to the switching frequency of the power switch tubes. Therefore, to decrease the output current, torque and rotation speed ripple of the motor, the switching frequency must be increased. However, to decrease the switching loss of the power switch tubes, the switching frequency of the power switch tubes must be decreased. Such a contradictory relation affects the development of the shunt wound DC motor driving device, so that the shunt wound DC motor driving device is difficult to be applied to numerically-controlled machine tools and other devices having strict requirements on the rotation speed and the torque ripple. For example, due to invisible requirements, the shunt wound DC motor applied to national defense equipment shall greatly decrease the own vibration and noise, that is, requirements on the output torque ripple and the current ripple are particularly strict. At present, the traditional shunt wound DC motor applied to high-power national defense equipment difficultly deals with an increasingly advanced investigation technology. 
     Based on the above reasons, the development of the shunt wound DC motor driving device is restricted and affected, thereby further affecting development of electrical equipment including electric cars, electric ships and electric aircrafts, even electric war chariots, electric warships, electric aircrafts and electrically driven aircraft carriers in national defense, and affecting economic construction and national defense construction. 
     SUMMARY OF THE INVENTION 
     The present invention is provided for solving the above problems. A purpose of the present invention is to provide a shunt wound DC motor driving device and electrical equipment including the shunt wound DC motor driving device. 
     To achieve the above purpose, technical solutions of the present invention are adopted as follows: 
     &lt;Structure 1&gt; 
     The present invention provides a shunt wound DC motor driving device. The shunt wound DC motor driving device includes a shunt wound DC motor having a rated voltage; a DC power supply having a constant voltage that corresponds to the rated voltage; and a chopper that converts the constant voltage into a variable voltage based on a control signal and provides the variable voltage for the shunt wound DC motor. The chopper is provided with m chopping units; each of the chopping units is provided with a first power output end, a second power output end and w switching control ends; the control signal includes m unit control signals that respectively correspond to the m chopping units and are formed according to a preset phase stagger rule; each of the unit control signals includes w switching control signals that correspond to the w switching control ends in the corresponding chopping units; the w switching control ends are used for correspondingly receiving the w switching control signals; and m first power output ends of all the chopping units and m second power output ends of all the chopping units respectively correspondingly form m pairs of power output terminals. The shunt wound DC motor includes a casing; m pairs of electric brushes fixed in the casing; a stator, arranged in the casing and including m pairs of main poles corresponding to the m pairs of electric brushes and further including an exciting winding part; and a rotor that is arranged in the stator and includes a plurality of armature windings connected in a one-to-one correspondence manner in a preset connection manner. Each pair of the main poles includes an S-polarity main pole and an N-polarity main pole; two adjacent main poles have different polarities; two electric brushes in each pair of electric brushes have adjacent positions; and each pair of the electric brushes includes an S-pole corresponding electric brush that corresponds to the S-polarity main pole and an N-pole corresponding electric brush that corresponds to the N-polarity main pole. The exciting winding part includes m exciting winding units. Each of the exciting winding units is formed by respectively making exciting coils from insulated conductor strips composed of metal wires coated with insulating layers on at least one pair of main poles. The insulated conductor strip in each of the exciting winding units is provided with one end and the other end. The m ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form m first wiring terminals; meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form m second wiring terminals; or the m ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form m first wiring terminals. Meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form m second wiring terminals. The m first wiring terminals and the m second wiring terminals respectively correspondingly form m pairs of external wiring terminals; and the m pair of external wiring terminals are connected with the m pairs of power output terminals in a one-to-one correspondence manner, wherein m is a positive integer of being not less than 2; and w is 1, 2 or 4. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: w is equal to 1; each of the chopping units is further provided with an upper bridge arm and a lower bridge arm connected in series with each other; the upper bridge arm is connected with a positive pole of the DC power supply; the lower bridge arm is connected with a negative pole of the DC power supply; the upper bridge arm includes at least one power switch tube and a switching control end; each power switch tube is provided with a control pole; the switching control end is formed based on the control pole; the lower bridge arm includes at least one diode; the first power output end is arranged between the upper bridge arm and the lower bridge arm; and the second power output end is arranged at the connection end of the lower bridge arm and the DC power supply. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the preset phase stagger rule is that phases of the m switching control signals are respectively staggered by 1/m switching cycle in sequence; or, m is an even number, and the preset phase stagger rule is that the phases of the m switching control signals are respectively staggered by 2/m switching cycle in sequence. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: w is equal to 2; each of the chopping units is further provided with an upper bridge arm and a lower bridge arm connected in series with each other; the upper bridge arm is connected with a positive pole of the DC power supply; the lower bridge arm is connected with a negative pole of the DC power supply; the upper bridge arm and the lower bridge arm respectively include at least one power switch tube, at least one diode in reverse parallel connection with the power switch tube, and a switching control end; each power switch tube is provided with a control pole; the switching control end is formed based on the control pole; the switching control end in the upper bridge arm serves as an upper bridge arm switching control end, and the switching control end in the lower bridge arm serves as a lower bridge arm switching control end, used for correspondingly receiving two switching control signals; the first power output end is arranged between the upper bridge arm and the lower bridge arm; and the second power output end is arranged at the connection end of the lower bridge arm and the DC power supply. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the preset phase stagger rule is as follows: m phases that respectively correspond to the m unit control signals serving as m preset phases are staggered by 1/m switching cycle in sequence; in each of the chopping units, the switching control signal that corresponds to the upper bridge arm switching control end is set as a reference switching control signal; a phase of the reference switching control signal is set according to a preset phase corresponding to the control signal; a switching control signal that corresponds to the lower bridge arm switching control end is set reciprocal to the reference switching control signal; or, m is an even number, and the preset phase stagger rule is as follows: the m phases that respectively correspond to the m unit control signals serving as m preset phases are staggered by 2/m switching cycle in sequence; in each of the chopping units, the switching control signal that corresponds to the upper bridge arm switching control end is set as the reference switching control signal; the phase of the reference switching control signal is set according to the preset phase corresponding to the unit control signal; and a switching control signal that corresponds to the lower bridge arm switching control end is set reciprocal to the reference switching control signal. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: w is equal to 4; each of the chopping units is further provided with a first bridge arm and a second bridge arm connected in parallel with each other; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series with each other; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series with each other; the first upper bridge arm and the second upper bridge arm are connected with the positive pole of the DC power supply; the first lower bridge arm and the second lower bridge arm are connected with the negative pole of the DC power supply; the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm respectively include at least one power switch tube, at least one diode in reverse parallel connection with the power switch tube, and a switching control end; each power switch tube is provided with a control pole; the switching control end is formed based on the control pole; the switching control end in the first upper bridge arm serves as a first upper bridge arm switching control end, a switching control end in the first lower bridge arm serves as a first lower bridge arm switching control end, a switching control end in the second upper bridge arm serves as a second upper bridge arm switching control end, and a switching control end in the second lower bridge arm serves as a second lower bridge arm switching control end, used for correspondingly receiving four switching control signals; the first power output end is arranged between the first upper bridge arm and the first lower bridge arm; and the second power output end is arranged between the second upper bridge arm and the second lower bridge arm. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the preset phase stagger rule is as follows: m phases that respectively correspond to the m unit control signals serving as m preset phases are staggered by 1/m switching cycle in sequence; in each of the chopping units, two switching control signals that correspond to the first upper bridge arm switching control end and the second lower bridge arm switching control end are set as reference switching control signals. Phases of the reference switching control signals are set according to preset phases that correspond to the unit control signals. Two switching control signals that correspond to the first lower bridge arm switching control end and the second upper bridge arm switching control end are set reciprocal to the reference switching control signals; or, m is an even number, the preset phase stagger rule is as follows: m phases that respectively correspond to the m unit control signals serving as m preset phases are staggered by 2/m switching cycle in sequence; in each of the chopping units, the two switching control signals that correspond to the first upper bridge arm switching control end and the second lower bridge arm switching control end are set as the reference switching control signals; the phases of the reference switching control signals are set according to preset phases that correspond to the unit control signals; and two switching control signals that correspond to the first lower bridge arm switching control end and the second upper bridge arm switching control end are set reciprocal to the reference switching control signals. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the DC power supply is provided with m pairs of power supply output terminals that are respectively connected with the m chopping units. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the DC power supply is composed of m mutually independent DC power units; and each of the DC power units is provided with one pair of power supply output terminals. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the shunt wound DC motor driving device further includes a control part including a controller and an amplifier. The controller generates m unit control signals according to the preset phase stagger rule; and the amplifier amplifies w switching control signals in each of the unit control signals and provides the w amplified switching control signals for the w switching control ends in the corresponding chopping units. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: w is equal to 1; the amplifier is composed of m mutually independent amplifier units; the m amplifier units respectively correspond to the m chopping units; and each of the amplifier units is provided with an amplified signal output end in corresponding connection with the switching control end. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: w is equal to 2 or 4; the amplifier is composed of m mutually independent amplifier units; the m amplifier units respectively correspond to the m chopping units; each of the amplifier units is provided with an amplified signal output part; and the amplified signal output parts are composed of w amplified signal output ends. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the controller further generates m enable signals that respectively correspond to the m amplifier units; and each of the enable signals is used for controlling an operating state of a corresponding amplifier unit. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the m exciting winding units respectively correspond to the m pairs of main poles; and the insulated conductor strip in each of the exciting winding units is formed on one corresponding pair of main poles. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the exciting coils on the various main poles have the same number of turns; each pair of the main poles corresponds to spatial locations of one corresponding pair of electric brushes; and in each of the exciting winding units, a connection relationship of two exciting coils is any one of series connection and parallel connection, and the connection relationship of two exciting coils in each exciting winding unit is the same. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the insulated conductor strips in each of the exciting winding units are formed on the m pairs of main poles. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the m exciting coils on the various main poles have the same winding direction and the same number of turns; and in each of the exciting winding units, a connection relationship of 2m exciting coils is any one of series connection, parallel connection and series-parallel connection, and the connection relationship of the 2m exciting coils is the same in each of the exciting winding units. 
     The shunt wound DC motor driving device provided by the present invention may have characteristics as follows: the preset connection manner may be any one of single lap, multiplex lap and compound ripple. 
     &lt;Structure 2&gt; 
     The present invention further provides electrical equipment. The electrical equipment includes a shunt wound DC motor driving device, wherein the shunt wound DC motor driving device is the shunt wound DC motor driving device in the &lt;Structure 1&gt;. 
     The electrical equipment provided by the present invention may have characteristics as follows: the electrical equipment is any one of a rolling mill, an electric locomotive, a large machine tool spindle transmission system and a ship. 
     Actions and Effects of the Present Invention 
     According to the shunt wound DC motor driving device and the electrical equipment including the shunt wound DC motor driving device involved in the present invention, the chopper is provided with the m chopping units; each of the chopping units is provided with the first power output end, the second power output end and w switching control ends; the control signal includes m unit control signals that respectively correspond to the m chopping units and are formed according to a preset phase stagger rule; each of the unit control signals includes w switching control signals that correspond to the w switching control ends in the corresponding chopping units; the w switching control ends are used for correspondingly receiving the w switching control signals; and m first power output ends of all the chopping units and m second power output ends of all the chopping units respectively correspondingly form m pairs of power output terminals. The exciting winding part includes m exciting winding units. Each of the exciting winding units is formed by respectively making exciting coils from insulated conductor strips composed of metal wires coated with insulating layers on at least one pair of corresponding main poles. The insulated conductor strip in each of the exciting winding units is provided with one end and the other end. The m ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form m first wiring terminals; meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form m second wiring terminals; or, the m ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form m first wiring terminals; and meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form m second wiring terminals. The m first wiring terminals and the m second wiring terminals respectively correspondingly form m pairs of external wiring terminals; and the m pairs of external wiring terminals are connected with m pairs of power output terminals in a one-to-one correspondence manner. In other words, each pair of the external wiring terminals is connected with one exciting winding unit and a pair of electric brushes in mutual series-shunt connection. Therefore, a branch circuit composed of each exciting winding unit and the pair of electric brushes in corresponding connection is mutually independent; current of each branch circuit is also independent; each branch circuit can independently work, and power of each branch circuit is independently provided by one pair of corresponding power output terminals, i.e., each pair of the power output terminals only undertakes operating current of one branch circuit, wherein the operating current is only 1/m of rated input current of the motor. Therefore, even for the motor having extremely large rated input current, as long as the m is greater enough, the operating current of each branch circuit or output current of each pair of the power output terminals will be corresponding decreased, so that according to the low enough output current of the power output terminals, requirements on the high-power high-performance motor can be met without adopting a parallel current evenness technology but by using an ordinary power switch tube or a power module. Moreover, cost of the chopper is decreased; requirements of connecting wires and connectors between the external wiring terminals and the power output terminals on contact resistance and insulation are lowered; production and manufacture difficulty is lowered; and reliability and safety of the system are increased. 
     Moreover, since the control signal includes the m switching control signals that respectively correspond to the m chopping units and are formed according to the preset phase stagger rule, current ripple phases of each pair of the power output terminals are mutually different. Therefore, peak values of ripple peaks of the m superposed current ripples are decreased; peak values of ripple peaks of the output torque and the rotation speed are further decreased; the performance of the shunt wound DC motor is increased; and service life of the motor is prolonged. 
     To sum up, the shunt wound DC motor driving device in the present invention is simple in structure, short in connecting wire, simple in production process, easy to manufacture, convenient to maintain and low in production cost and maintenance cost, and has the advantages of reasonable structural design, simplicity and high reliability and safety. Therefore, the shunt wound DC motor driving device in the present invention can be applied to heavy-load electrical equipment such as electric cars, electric trucks, track cars, sightseeing tourist cars, trucks and ships, and can be further applied to high-performance electrical equipment such as numerically-controlled machine tools and submarines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 1 of the present invention; 
         FIG. 2  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 1 of the present invention when m is equal to 3; 
         FIG. 3  is a schematic diagram of a longitudinal section of a shunt wound DC motor in embodiments of the present invention; 
         FIG. 4  is a schematic diagram of circuit connection of a transverse section of a shunt wound DC motor in embodiments of the present invention; 
         FIG. 5  is an unfolded schematic diagram of single lap connection of an armature winding of a shunt wound DC motor in embodiments of the present invention; 
         FIG. 6  is a schematic diagram of circuit connection of a traditional shunt wound DC motor driving device; 
         FIG. 7  is an input current waveform graph of three pairs of electric brushes of a shunt wound DC motor in embodiments of the present invention; 
         FIG. 8  is an input current waveform graph of three exciting winding units of a shunt wound DC motor in embodiments of the present invention; 
         FIG. 9  is a comparison diagram of armature current of a shunt wound DC motor in embodiments of the present invention and armature current of a traditional shunt wound DC motor; 
         FIG. 10  is a comparison diagram of exciting current of a shunt wound DC motor in embodiments of the present invention and exciting current of a traditional shunt wound DC motor; 
         FIG. 11  is a comparison diagram of a torque of a shunt wound DC motor in embodiments of the present invention and a torque of a traditional shunt wound DC motor; 
         FIG. 12  is a comparison diagram of a rotation speed of a shunt wound DC motor in embodiments of the present invention and a rotation speed of a traditional shunt wound DC motor; 
         FIG. 13  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 1 of the present invention; 
         FIG. 14  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 2 of the present invention; 
         FIG. 15  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 2 of the present invention when m is equal to 3; 
         FIG. 16  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 2 of the present invention; 
         FIG. 17  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 3 of the present invention; 
         FIG. 18  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 3 of the present invention when m is equal to 3; 
         FIG. 19  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 3 of the present invention; 
         FIG. 20  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation examples of the present invention; 
         FIG. 21  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation examples of the present invention when m is equal to 3; and 
         FIG. 22  is a schematic diagram of circuit connection of a transverse section of a shunt wound DC motor in variation examples of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Specific embodiments of the present invention will be described below in combination with drawings. 
     Embodiment 1 
       FIG. 1  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 1 of the present invention; and  FIG. 2  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 1 of the present invention when m is equal to 3. 
     As shown in  FIGS. 1 and 2 , a shunt wound DC motor driving device  100  in the present embodiment 1 is arranged in electrical equipment such as a rolling mill, an electric locomotive, a large machine tool spindle transmission system and a ship, and is used for driving the electrical equipment. The shunt wound DC motor driving device  100  includes a shunt wound DC motor  10 , a chopper  20 , a DC power supply  30 , a sensing part  40  and a control part  50 . 
       FIG. 3  is a schematic diagram of a longitudinal section of a shunt wound DC motor in embodiments of the present invention; and  FIG. 4  is a schematic diagram of circuit connection of a transverse section of a shunt wound DC motor in embodiments of the present invention. 
     As shown in  FIGS. 1-4 , the shunt wound DC motor  10  has a rated voltage and rated current, and includes a casing  11 , a stator  12 , electric brushes  13 , a rotor  14  and a junction box (unshown in the drawing). As shown in  FIG. 1 , the number of pairs of the electric brushes  13  is set as m according to a value of the rated current, wherein m is an integer of being not less than 2. As shown in  FIGS. 2 and 4 , m is set as 3 in the present embodiment 1. 
     As shown in  FIGS. 1-4 , the stator  12  is arranged in the casing  11 , and includes 3 pairs of main poles  121 , totaling  6  main poles, and an exciting winding part  122 . Each of the main poles  121  includes 3 exciting coils  12211 . Each of the exciting coils  12211  is formed by respectively winding insulated conductor strips composed of conductors coated with insulating layers on the main poles  121 , wherein the insulated conductor strip is any one of enameled wire and insulated copper conducting bar. In the present embodiment, the insulated conductor strips are the enameled wires. In the present embodiment 1, the 3 exciting coils  12211  on each of the main poles  121  have the same winding direction and the same number of turns. 
     As shown in  FIGS. 2-4 , one exciting coil  12211  is respectively extracted from each of the main poles  121 ; and totally 6 exciting coils  12211  are connected into an exciting winding unit  1221 . An exciting winding part  122  includes 3 exciting winding units  1221 . The insulated conductor strip in each of the exciting winding units  1221  is provided with one end and the other end that are distinguished according to a preset current direction of the exciting coils  12211 . Each pair of the main poles includes an S-polarity main pole  1211  and an N-polarity main pole  1212  that correspond to the winding directions of the exciting coils  12211  and the preset current direction of the exciting coils  12211 . 
     In each of the exciting winding units  1221 , a connection relationship of the 6 exciting coils  12211  is any one of series connection, parallel connection and series-parallel connection; and the 6 exciting coils  12211  in each of the exciting winding units  1221  have the same connection relationship. In the present embodiment 1, the connection relationship of the 6 exciting coils  12211  is the series connection. 
     As shown in  FIGS. 3 and 4 , the 3 pairs of totally 6 electric brushes  13  are arranged in the casing  11 . Each pair of the electric brushes  13  includes an S-pole corresponding electric brush  131  that corresponds to the S-polarity main pole  1211  and an N-pole corresponding electric brush  132  that corresponds to the N-polarity main pole  1212 . 
     The electric brush  13  is any one of a narrow electric brush and a wide electric brush. The electric brush  13  in the present embodiment 1 is the narrow electric brush. Each of the electric brushes  13  includes an electric brush body or at least two electric brush bodies that are arranged along an axial direction of the motor and separately formed in electrical parallel connection. When each of the electric brushes  13  includes the at least two electric brush bodies, an actual contact area between each of the electric brushes and a commutator is increased, thereby improving commutation performance of the electric brushes. As shown in  FIGS. 2-4 , each of the electric brushes  13  in the present embodiment 1 includes one electric brush body. 
     As shown in  FIG. 1 , the m ends of the insulated conductor strips in all the exciting winding units  1221  are electrically connected with m N-pole corresponding electric brushes  132  in all the electric brushes  13  to form m first wiring terminals  1511 ; the m other ends of the insulated conductor strips in all the exciting winding units  1221  are electrically connected with m S-pole corresponding electric brushes  131  in all the electric brushes  13  to form m second wiring terminals  1512 ; and the m first wiring terminals  1511  and the m second wiring terminals  1512  respectively correspondingly form m pairs of external wiring terminals. Certainly, according to needs, the m ends of the insulated conductor strips in all the exciting winding units  1221  are electrically connected with m S-pole corresponding electric brushes  131  in all the electric brushes  13  to form the m first wiring terminals  1511 ; and meanwhile, the m other ends of the insulated conductor strips in all the exciting winding units  1221  are electrically connected with m N-pole corresponding electric brushes  132  in all the electric brushes  13  to form the m second wiring terminals  1512 . 
     In the present embodiment 1, as shown in  FIGS. 2 and 4 , the first wiring terminals  1511  and the second wiring terminals  1512  correspondingly form  1  pair of external wiring terminals  151 ; first wiring terminals  1521  and second wiring terminals  1522  correspondingly form  1  pair of external wiring terminals  152 ; and first wiring terminals  1531  and second wiring terminals  1532  correspondingly form  1  pair of external wiring terminals  153 . 
       FIG. 5  is an unfolded schematic diagram of single lap connection of an armature winding of a shunt wound DC motor in the embodiments of the present invention. 
     As shown in  FIGS. 1-4 , the rotor  14  is arranged in the stator  12  and includes a plurality of armature windings  141  connected in a one-to-one correspondence manner in a preset connection manner, wherein the number of the armature windings  141  is set as 2m×q; and the preset connection manner is any one of single lap, multiplex lap and compound ripple. In the present embodiment 1, as shown in  FIG. 5 , the connection manner of the plurality of armature windings  141  is the single lap; two adjacent electric brushes  13  are connected to form an armature winding branch; and each armature winding branch includes q armature windings  141 . 
     The junction box (unshown in the drawing) is fixed on the casing  11 . As shown in  FIGS. 2 and 4 , the 3 pairs of external wiring terminals  151 ,  152  and  153  are arranged in the junction box. 
     As shown in  FIG. 1 , the chopper  20  converts a constant voltage of the DC power supply  30  into an average voltage controllable variable voltage based on a control signal transmitted by the control part  50 , and provides the variable voltage for the shunt wound DC motor  10 . The chopper  20  includes m chopping units  21  that respectively correspond to the m pairs of electric brushes  13 . In the present embodiment 1, as shown in  FIG. 2 , the chopper  20  includes 3 chopping units  21 . 
     Each of the chopping units  21  includes an upper bridge arm  211  and a lower bridge arm  212  connected with each other in series, and a first power output end  2211  and a second power output end  2212 . 
     Each of the upper bridge arms  211  includes 1 power switch tube  2111  and a switching control end  2110 ; and each of the lower bridge arms  212  includes 1 fly-wheel diode  2121 . The power switch tube  2111  is provided with a control pole; and the control pole forms the switching control end  2110 . 
     When all the power switch tubes  2111  have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is I max , the m meets the following condition: m&gt;I max ÷I 1 . The maximum output current is an important parameter of the power switch tube. The power switch tube may stably operate only at such a current value; and if the operating current exceeds the current value, the power switch tube may be broken down and then damaged due to overcurrent. 
     In the present embodiment 1, all the power switch tubes are half-controlled or full-controlled devices. The half-controlled devices are ordinary thyristors; and the full-controlled devices are any one of power field effect transistors, gate-turn-off thyristors, integrated gate-commutated thyristors, insulated gate bipolar transistors and power bipolar transistors. 
     As shown in  FIG. 1 , the first power output end  2211  is arranged between the upper bridge arm  211  and the lower bridge arm  212 ; and the second power output end  2212  is arranged at the connection end of the lower bridge arm  212  and the DC power supply  30 . The m first power output ends  2211  of all the chopping units  21  and the m second power output ends  2212  of all the chopping units  21  respectively correspondingly form m pairs of power output terminals  221 ; and the m pairs of power output terminals  221  are connected with the m pairs of external wiring terminals  151  in a one-to-one correspondence manner. 
     In the present embodiment 1, as shown in  FIG. 2 , the first power output end  2211  and the second power output end  2212  correspondingly form  1  pair of power output terminals  221 ; the first power output end  2221  and the second power output end  2222  correspondingly form  1  pair of power output terminals  222 ; the first power output end  2231  and the second power output end  2232  correspondingly form  1  pair of power output terminals  223 ; and the 3 pairs of power output terminals  221 ,  222  and  223  are connected with the 3 pairs of external wiring terminals  151 ,  152  and  153  in a one-to-one correspondence manner. 
     As shown in  FIGS. 1 and 2 , the DC power supply  30  has a constant voltage corresponding to the rated voltage of the shunt wound DC motor  10 , and is provided with m pairs of power supply output terminals that are connected with the m chopping units  21  in a one-to-one correspondence manner. Each pair of the power supply output terminals includes a positive pole  311  and a negative pole  312 ; the positive pole  311  is connected with the upper bridge arm  211  in the corresponding chopping unit  21 ; and the negative pole  312  is connected with the lower bridge arm  212  in the corresponding chopping unit  21 . 
     As shown in  FIGS. 1 and 2 , the control part  50  receives an external instruction signal that corresponds to a displacement, a rotation speed or a torque output by the shunt wound DC motor  10 . 
     The sensing part  40  is used for detecting a physical quantity of the shunt wound DC motor  10  and outputting a feedback signal to the control part  50 . The sensing part  40  includes an output sensor  41  and a current sensor  42 . 
     The output sensor  41  detects the displacement, the rotation speed or the torque output by the shunt wound DC motor  10  and output a corresponding output feedback signal to the control part  50 . 
     The current sensor  42  detects line current values of electric brush outgoing lines in the shunt wound DC motor  10  and outputs a corresponding current feedback signal to the control part  50 . 
     The control part  50  includes a controller  51  and an amplifier  52 . 
     The controller  51  calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511  and an enable signal  512  to the amplifier  52 . The control signal  511  includes m switching control signals that respectively correspond to the m chopping units  21  and are formed according to a preset phase stagger rule; and the enable signal  512  is used for controlling an operating state of the amplifier  52 . 
     The amplifier  52  enters the operating state under control of the enable signal  512 , amplifies the m switching control signals and correspondingly provides the m switching control signals for the m switching control ends  2110 . The amplifier  52  is provided with m amplified signal output ends  521  that respectively correspond to the m chopping units  21 ; and the m amplified signal output ends  521  are connected with the m switching control ends  2110  in a one-to-one correspondence manner. 
     In the present embodiment 1, the preset stagger rule is as follows: phases of the m switching control signals are respectively staggered by 1/m switching cycle in sequence, so that peak values of ripple peaks of the superposed current ripples of the output current of the power output terminals of the m chopping units are decreased, thereby decreasing peak values of ripple peaks of the output torque and the rotation speed, further increasing the performance of the shunt wound DC motor and prolonging service life of the motor. Certainly, according to the needs, when the m is an even number, the preset stagger rule is as follows: the phases of the m switching control signals are respectively staggered by 2/m switching cycle in sequence. Thus, the output current of the power output terminals of every two chopping units corresponding to every two pairs of the electric brushes with opposite spatial positions has the same current ripples, thereby producing a couple moment in the motor, avoiding a friction moment between a shaft and a bearing caused by the reason that the torque ripple output by the motor cannot form the couple moment, decreasing wear between the shaft and the bearing, increasing the performance of the motor and prolonging the service life of the motor. 
       FIG. 7  is an input current waveform graph of three pairs of electric brushes of a shunt wound DC motor in the embodiments of the present invention;  FIG. 8  is an input current waveform graph of three exciting winding units of a shunt wound DC motor in the embodiments of the present invention;  FIG. 9  is a comparison diagram of armature current of a shunt wound DC motor in the embodiments of the present invention and armature current of a traditional shunt wound DC motor;  FIG. 10  is a comparison diagram of exciting current of a shunt wound DC motor in embodiments of the present invention and exciting current of a traditional shunt wound DC motor;  FIG. 11  is a comparison diagram of a torque of a shunt wound DC motor in the embodiments of the present invention and a torque of a traditional shunt wound DC motor; and  FIG. 12  is a comparison diagram of a rotation speed of a shunt wound DC motor in the embodiments of the present invention and a rotation speed of a traditional shunt wound DC motor. 
     In a stable state, the peak value of the current ripple peak is the difference of a maximum value and a minimum value; and a ripple factor is a percentage of the peak value to the mean. The peak value and the ripple factor are described below when the current ripple of the output current has the same frequency but the phases are staggered by ⅓ switching cycle in sequence and the switching frequency of the three electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  and the chopper is 1 KHz. 
     As shown in  FIG. 7 , the peak values of the input current ripples of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  in the shunt wound DC motor in the present embodiment 1 are all equal to 99.31−87.33=11.99 amperes; the mean of the input current is equal to 93.32 amperes; and the ripple factor is equal to 11.99/93.32×100%=12.84%. 
     As shown in  FIG. 8 , the peak values of input current ripples of the three exciting winding units  1221 ,  1222  and  1223  in the shunt wound DC motor in the present embodiment 1 is equal to 61.97−61.37=0.60 amperes; the mean of the current ripple is equal to 61.67 amperes; and the ripple factor is equal to 0.60/61.67×100%=0.97%. 
     As shown in  FIG. 9 , in the stable state, the armature current of the shunt wound DC motor in the present embodiment 1 is equal to the sum of the current of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3 ; the armature current ripple is equal to 281.95-277.98=3.97 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 3.97/279.97×100%=1.42%. The armature current ripple of the traditional shunt wound DC motor is equal to 297.94−261.98=35.96 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 35.96/279.97×100%=12.84%. Although the shunt wound DC motor in the present embodiment 1 and the traditional shunt wound DC motor have the same mean of the armature current, the armature current ripple and the ripple factor of the shunt wound DC motor in the present embodiment are only one ninth of the traditional shunt wound DC motor. 
     As shown in  FIG. 10 , in the stable state, exciting current of the shunt wound DC motor in the present embodiment 1 is equal to the sum of the current of the three exciting winding units  1221 ,  1222  and  1223 ; the peak value of the ripple peak of the exciting current is equal to 185.10−184.90=0.2 amperes; the mean of the ripple is equal to 185.0 amperes; and the ripple factor is equal to 0.2/185×100%=0.11%. The armature current ripple of the traditional shunt wound DC motor is equal to 185.9−184.1=1.8 amperes; the mean is equal to 185.0 amperes; and the ripple factor is equal to 1.8/185.0×100%=0.97%. Although the shunt wound DC motor in the present embodiment 1 and the traditional shunt wound DC motor have the same mean of the exciting current, the exciting current ripple and the ripple factor of the shunt wound DC motor in the present embodiment 1 are only one ninth of the traditional shunt wound DC motor. 
     It is known that electromagnetic torque and motion equations of the shunt wound DC motor are as follows: 
     
       
         
           
               
             
                 
             
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     In the equations, T em  is an electromagnetic torque; C T  is a torque constant; Φ is flux of a main magnetic field; L af  is mutual inductance of the exciting winding part and the armature winding and is a constant; I f  is the exciting current; I a  is the armature current; T load  is a load torque; J is a rotational inertia of the load and is a constant; and Ω is angular output velocity. 
     In the present embodiment 1, the input current of the shunt wound DC motor is equal to the sum of the armature current and the exciting current; and rated input current of the shunt wound DC motor is the maximum input current of the motor in a rated operating state. 
     In the equation (1), the electromagnetic torque T em  is in direct proportion to a product of the armature current I a  and the flux Φ of the main magnetic field; and the main magnetic field of the DC motor is excited by the exciting winding part powered by the chopper. It can be seen from the equation (1) that, the electromagnetic torque T em  is in direct proportion to the product of the armature current I a  and the exciting current I f  and according to the ripple factor of the exciting current I f  and the ripple factor of the armature current I a , the electromagnetic torque T em  produces a larger ripple factor; the angular output velocity Ω has larger pulsation or ripple; and the performances of the driving device and the electrical equipment are poorer. 
     In the present embodiment 1, L af  is equal to 1. In the stable state, as shown in  FIG. 11 , the peak value of torque ripple peaks of the shunt wound DC motor in the present embodiment 1 is equal to 52188.25-51398.38=789.87 N·m; the mean is equal to 51793.56 N·m; and the ripple factor is equal to 1.53%. The peak value of torque ripple peaks of the traditional shunt wound DC motor is equal to 55386.15-48229.93=7156.21 N·m; the mean is equal to 51798.89 N·m; and the ripple factor is equal to 13.82%. 
     As shown in  FIG. 12 , in the stable state, the peak value of the rotation speed ripple of the shunt wound DC motor  10  in the present embodiment 1 is equal to 1725.5157-1725.5142=0.0015 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.000087%. The peak value of the rotation speed ripple of the traditional shunt wound DC motor is equal to 1725.535-1725.4949=0.0401 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.002324%. Although the shunt wound DC motor  10  in the present embodiment 1 and the traditional shunt wound DC motor have the same mean of the rotation speed, a ratio of the peak value of the rotation speed ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 1 to those in the traditional shunt wound DC motor is 1/26.7. 
     In other words, although the shunt wound DC motor  10  in the present embodiment 1 has basically the same mean of the torque as the traditional shunt wound DC motor, the peak value of the torque ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 1 are only one ninth of the traditional shunt wound DC motor, thereby decreasing the peak value of the output torque ripple peak and the ripple factor of the motor and further decreasing the peak value of the output rotation speed ripple and the ripple factor of the motor. The rotation speed ripple factor of the shunt wound DC motor  10  in the present embodiment 1 is only 1/26 that of the traditional shunt wound DC motor. Finally, purposes of decreasing electromagnetic interference, vibration and noise of the motor and increasing the performances of the shunt wound DC motor and the driving device are achieved. 
     Variation Example 1 
     In the present variation example 1, with respect to the same structure as embodiment 1, the same symbol is given, and the same description is omitted. 
       FIG. 13  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 1 of the present invention. 
     As shown in  FIG. 13 , a shunt wound DC motor driving device  100 ′ in the present variation example 1 includes a shunt wound DC motor  10 , a chopper  20 ′, a DC power supply  30 ′, a sensing part  40  and a control part  50 ′. 
     As shown in  FIG. 13 , the chipper  20 ′ is composed of m chopping units  21 ′ that respectively correspond to m pairs of electric brushes  13 . 
     Each of the chopping units  21 ′ includes an upper bridge arm  211 ′ and a lower bridge arm  212 ′ connected with each other in series, and a first power output end  2211 ′ and a second power output end  2212 ′. 
     Each upper bridge arm  211 ′ includes p power switch tubes  2111 ′ connected in a one-to-one correspondence manner in parallel, and switching control ends  2110 ′, wherein p is a positive integer of being not greater than 2. Each lower bridge arm  212 ′ includes 1 fly-wheel diode  2121 ′. Each of the power switch tubes  2111 ′ is provided with a control pole; and all the control poles in each upper bridge arm  211 ′ form the switching control ends  2110 ′. 
     When all the power switch tubes  2111 ′ have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is I max , the m meets the following condition: m&gt;I max ÷(k×p×I 1 ), wherein k is a parallel connection coefficient, and 1/p&lt;k&lt;1. 
     In the present variation example 1, the p is equal to 2-4; the parallel connection technology is mature and reliable; the quantity of the m can be properly decreased; workloads and complexity in production and manufacture are decreased; and cost performance of the product is increased. 
     The first power output end  2211 ′ is arranged between the upper bridge arm  211 ′ and the lower bridge arm  212 ′; and the second power output end  2212 ′ is arranged at the connection end of the lower bridge arm  212 ′ and the DC power supply  30 ′. The m first power output ends  2211 ′ of all the chopping units  21 ′ and the m second power output ends  2212 ′ of all the chopping units  21 ′ respectively correspondingly form m pairs of power output terminals  221 ′. The m pairs of power output terminals  221 ′ are connected with the m pairs of external wiring terminals  151  in a one-to-one correspondence manner. 
     As shown in  FIG. 13 , the DC power supply  30 ′ is provided with m mutually independent DC power supply units  31 ′ and m pairs of power supply output terminals led out of each of the DC power supply units  31 ′. The m pairs of power supply output terminals are connected with the m chopping units  21 ′ in a one-to-one correspondence manner. Each pair of the power supply output terminals includes a positive pole  311 ′ and a negative pole  312 ′. The positive pole  311 ′ is connected with the upper bridge arm  211 ′ in the corresponding chopping unit  21 ′; and the negative pole  312 ′ is connected with the lower bridge arm  212 ′ in the corresponding chopping unit  21 ′. 
     As shown in  FIG. 13 , the control part  50 ′ includes a controller  51 ′ and an amplifier  52 ′. 
     The controller  51 ′ calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511 ′ and an enable signal  512 ′ to the amplifier  52 ′. The control signal  511 ′ includes m switching control signals that respectively correspond to the m chopping units  21 ′ and are formed according to a preset phase stagger rule; and the enable signal  512 ′ is used for controlling an operating state of the amplifier  52 ′. 
     The amplifier  52 ′ enters the operating state under control of the enable signal  512 ′, amplifies the m switching control signals and correspondingly provides the m switching control signals for the m switching control ends  2110 ′. The amplifier  52 ′ is provided with m mutually independent amplifier units  521 ′. The m amplifier units  521 ′ respectively correspond to the m chopping units  21 ′. Each of the amplifier units  521 ′ is provided with an amplified signal output end  5211 ′. The m amplified signal output ends  5211 ′ are connected with the m switching control ends  2110 ′ in a one-to-one correspondence manner. 
     Embodiment 2 
     In the present embodiment 2, with respect to the same structure as the embodiment 1, the same symbol is given, and the same description is omitted. 
       FIG. 14  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 2 of the present invention; and  FIG. 15  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 2 of the present invention when m is equal to 3. 
     As shown in  FIGS. 14 and 15 , a shunt wound DC motor driving device  100   a  in the present embodiment 2 includes a shunt wound DC motor  10 , a chopper  20   a , a DC power supply  30 , a sensing part  40  and a control part  50   a.    
     As shown in  FIG. 14 , the chopper  20   a  converts a constant voltage of the DC power supply  30  into an average voltage controllable variable voltage based on a control signal transmitted by the control part  50   a  and provides the variable voltage for the shunt wound DC motor  10 . The chopper  20   a  includes m chopping units  21   a  that respectively correspond to the m pairs of electric brushes  13 . In the present embodiment 2, as show in  FIG. 15 , the chopper  20   a  includes 3 chopping units  21   a.    
     Each of the chopping units  21   a  includes an upper bridge arm  211   a  and a lower bridge arm  212   a  connected with each other in series, and a first power output end  2211   a  and a second power output end  2212   a.    
     Each upper bridge arm  211   a  includes 1 power switch tube  2111   a , a diode  210   a  in reverse parallel connection with the power switch tube  2111   a , and an upper bridge arm switching control end  2110   a ; and each lower bridge arm  212   a  includes 1 power switch tube  2121   a , a diode  210   a  in reverse parallel connection with the power switch tube  2111   a , and a lower bridge arm switching control end  2120   a.    
     When the power switch tubes  2111   a  of all the upper bridge arms  211   a  and the power switch tubes  2121   a  of all the lower bridge arms  212   a  have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is I max , the m meets the following condition: m&gt;I max ÷I 1 . 
     In the present embodiment 2, all the power switch tubes are half-controlled or full-controlled devices. The half-controlled devices are ordinary thyristors; and the full-controlled devices are any one of power field effect transistors, gate-turn-off thyristors, integrated gate-commutated thyristors, insulated gate bipolar transistors and power bipolar transistors. 
     As shown in  FIG. 14 , the first power output end  2211   a  is arranged between the upper bridge arm  211   a  and the lower bridge arm  212   a ; and the second power output end  2212   a  is arranged at the connection end of the lower bridge arm  212   a  and the DC power supply  30 . The m first power output ends  2211   a  of all the chopping units  21   a  and the m second power output ends  2212   a  of all the chopping units  21   a  correspondingly form m pairs of power output terminals  221   a ; and the m pairs of power output terminals  221   a  are connected with the m pairs of external wiring terminal  151  in a one-to-one correspondence manner. 
     In the present embodiment 2, as shown in  FIG. 15 , the first power output end  2211   a  and the second power output end  2212   a  correspondingly form  1  pair of power output terminals  221   a ; the first power output end  2221   a  and the second power output end  2222   a  correspondingly form  1  pair of power output terminals  222   a ; the first power output end  2231   a  and the second power output end  2232   a  correspondingly form  1  pair of power output terminals  223   a ; and the 3 pairs of power output terminals  221   a ,  222   a  and  223   a  are connected with the 3 pairs of external wiring terminals  151 ,  152  and  153  in a one-to-one correspondence manner. 
     As shown in  FIGS. 14 and 15 , the DC power supply  30  is provided with m pairs of power supply output terminals that are connected with the m chopping units  21   a  in a one-to-one correspondence manner. The positive pole  311  in each pair of the power supply output terminals is connected with the upper bridge arm  211   a  in the corresponding chopping unit  21   a ; and the negative pole  312  is connected with the lower bridge arm  212   a  in the corresponding chopping unit  21   a.    
     As shown in  FIGS. 14 and 15 , the control part  50   a  includes a controller  51   a  and an amplifier  52   a.    
     The controller  51   a  calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511   a  and an enable signal  512   a  to the amplifier  52   a . The control signal  511   a  includes m unit control signals that respectively correspond to the m chopping units  21   a  and are formed according to a preset phase stagger rule; each of the unit control signals includes two switching control signals  512   a  and  522   a  that correspond to the two switching control ends  2110   a  and  2120   a  in the corresponding chopping units  21   a ; and the enable signal  512   a  is used for controlling an operating state of the amplifier  52   a.    
     The amplifier  52   a  enters the operating state under control of the enable signal  512   a , amplifies the two switching control signals in each of the unit control signals and provides the two switching control signals for the two switching control ends  2110   a  and  2120   a . The amplifier  52   a  is provided with m amplified signal output parts that correspond to the m chopping units  21   a . Each of the amplified signal output parts is composed of two amplified signal output ends  521   a  and  522   a . The two amplified signal output ends  521   a  and  522   a  of each of the amplified signal output parts are respectively correspondingly connected with the two switching control ends  2110   a  and  2120   a  in the corresponding chopping units  21   a , i.e., the amplified signal output end  521   a  is connected with the upper bridge arm switching control end  2110   a ; and the amplified signal output end  522   a  is connected with the lower bridge arm switching control end  2120   a.    
     In the present embodiment 2, the preset phase stagger rule is as follows: the m phases that respectively correspond to the m unit control signals serve as m preset phases and are staggered by 1/m switching cycle in sequence. In each of the chopping units, the switching control signal that corresponds to the upper bridge arm switching control end is set as a reference switching control signal; and a phase of the reference switching control signal is set according to the preset phase that corresponds to the unit control signal. The switching control signal that corresponds to the lower bridge arm switching control end is set reciprocal to the reference switching control signal, so that peak values of ripple peaks of the superposed current ripples of the output current of the power output terminals of the m chopping units are decreased, thereby decreasing peak values of ripple peaks of the output torque and the rotation speed, further increasing the performance of the shunt wound DC motor and prolonging service life of the motor. Certainly, according to the needs, when the m is the even number, the preset stagger rule is as follows: the m phases that respectively correspond to the m unit control signals serve as the m preset phases and are staggered by 2/m switching cycle in sequence. Thus, the output current of the power output terminals of every two chopping units corresponding to every two pairs of the electric brushes with opposite spatial positions has the same current ripples, thereby producing a couple moment in the motor, avoiding a friction moment between a shaft and a bearing caused by the reason that the torque ripple output by the motor cannot form the couple moment, decreasing wear between the shaft and the bearing, increasing the performance of the motor and prolonging the service life of the motor. 
     The peak value and the ripple factor are described below when the current ripple of the output current has the same frequency but the phases are staggered by ⅓ switching cycle in sequence and the switching frequency of the three electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  and the chopper is 1 KHz. 
     As shown in  FIG. 7 , the peak values of the input current ripples of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  in the shunt wound DC motor in the present embodiment 2 are all equal to 99.31−87.33=11.99 amperes; the mean of the input current is equal to 93.32 amperes; and the ripple factor is equal to 11.99/93.32×100%=12.84%. 
     As shown in  FIG. 8 , the peak values of input current ripples of the three exciting winding units  1221 ,  1222  and  1223  in the shunt wound DC motor in the present embodiment 2 is equal to 61.97−61.37=0.60 amperes; the mean of the current ripple is equal to 61.67 amperes; and the ripple factor is equal to 0.60/61.67×100%=0.97%. 
     As shown in  FIG. 9 , in the stable state, the armature current of the shunt wound DC motor in the present embodiment 2 is equal to the sum of the current of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3 ; the armature current ripple is equal to 281.95−277.98=3.97 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 3.97/279.97×100%=1.42%. The armature current ripple of the traditional shunt wound DC motor is equal to 297.94−261.98=35.96 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 35.96/279.97×100%=12.84%. Although the shunt wound DC motor in the present embodiment 2 and the traditional shunt wound DC motor have the same mean of the armature current, the armature current ripple and the ripple factor of the shunt wound DC motor in the present embodiment 2 are only one ninth of the traditional shunt wound DC motor. 
     As shown in  FIG. 10 , in the stable state, exciting current of the shunt wound DC motor in the present embodiment 2 is equal to the sum of the current of the three exciting winding units  1221 ,  1222  and  1223 ; the peak value of the ripple peak of the exciting current is equal to 185.10−184.90=0.2 ampere; the mean of the ripple is equal to 185.0 amperes; and the ripple factor is equal to 0.2/185×100%=0.11%. The armature current ripple of the traditional shunt wound DC motor is equal to 185.9−184.1=1.8 amperes; the mean is equal to 185.0 amperes; and the ripple factor is equal to 1.8/185.0×100%=0.97%. Although the shunt wound DC motor in the present embodiment 2 and the traditional shunt wound DC motor have the same mean of the exciting current, the exciting current ripple and the ripple factor of the shunt wound DC motor in the present embodiment 2 are only one ninth of the traditional shunt wound DC motor. 
     In the present embodiment 2, L af  is equal to 1. In the stable state, as shown in  FIG. 11 , the peak value of torque ripple peaks of the shunt wound DC motor in the present embodiment 2 is equal to 52188.25−51398.38=789.87 N·m; the mean is equal to 51793.56 N·m; and the ripple factor is equal to 1.53%. The peak value of torque ripple peaks of the traditional shunt wound DC motor is equal to 55386.15−48229.93=7156.21 N·m; the mean is equal to 51798.89 N·m; and the ripple factor is equal to 13.82%. 
     As shown in  FIG. 12 , in the stable state, the peak value of the rotation speed ripple of the shunt wound DC motor  10  in the present embodiment 2 is equal to 1725.5157−1725.5142=0.0015 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.000087%. The peak value of the rotation speed ripple of the traditional shunt wound DC motor is equal to 1725.535−1725.4949=0.0401 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.002324%. Although the shunt wound DC motor  10  in the present embodiment 2 and the traditional shunt wound DC motor have the same mean of the rotation speed, a ratio of the peak value of the rotation speed ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 2 to those in the traditional shunt wound DC motor is 1/26.7. 
     In other words, although the shunt wound DC motor  10  in the present embodiment 2 has basically the same mean of the torque as the traditional shunt wound DC motor, the peak value of the torque ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 2 are only one ninth of the traditional shunt wound DC motor, thereby decreasing the peak value of the output torque ripple peak and the ripple factor of the motor and further decreasing the peak value of the output rotation speed ripple and the ripple factor of the motor. The rotation speed ripple factor of the shunt wound DC motor in the present embodiment 2 is only 1/26 that of the traditional shunt wound DC motor. Finally, purposes of decreasing electromagnetic interference, vibration and noise of the motor and increasing the performances of the shunt wound DC motor and the driving device are achieved. 
     Variation Example 2 
     In the present variation example 2, with respect to the same structure as embodiment 2, the same symbol is given, and the same description is omitted. 
       FIG. 16  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 2 of the present invention. 
     As shown in  FIG. 16 , a shunt wound DC motor driving device  100   a ′ in the present variation example includes a shunt wound DC motor  10 , a chopper  20   a ′, a DC power supply  30 ′, a sensing part  40  and a control part  50   a′.    
     As shown in  FIG. 16 , the chopper  20   a ′ is composed of m chopping units  21   a ′ that respectively correspond to m pairs of electric brushes  13 . 
     Each of the chopping units  21   a ′ includes an upper bridge arm  211   a ′ and a lower bridge arm  212   a ′ connected with each other in series, and a first power output end  2211   a ′ and a second power output end  2212   a′.    
     Each upper bridge arm  211   a ′ includes p power switch tubes  2111   a ′ connected in a one-to-one correspondence manner in parallel, diodes  210   a ′ in reverse parallel connection with the power switch tube  2111   a ′, and upper bridge arm switching control ends  2110   a ′; and each lower bridge arm  212   a ′ includes p power switch tubes  2121   a ′ connected in a one-to-one correspondence manner in parallel, diodes  210   a ′ in reverse parallel connection with the power switch tube  2121   a ′, and lower bridge arm switching control ends  2120   a ′, wherein p is a positive integer of being not greater than 2. Each of the power switch tubes is provided with a control pole; all the control poles in each upper bridge arm  211   a ′ form the upper bridge arm switching control ends  2110   a ′; and all the control poles in each lower bridge arm  212   a ′ form the lower bridge arm switching control ends  2120   a′.    
     When all the power switch tubes  2111   a ′ of the upper bridge arms  211   a ′ and all the power switch tubes  2121   a ′ of the lower bridge arms  212   a ′ have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is Liu, the m meets the following condition: m&gt;I max ±(k×p×I 1 ), wherein k is a parallel connection coefficient, and 1/p&lt;k&lt;1. 
     In the present variation example 2, the p is equal to 2-4; the parallel connection technology is mature and reliable; the quantity of the m can be properly decreased; workloads and complexity in production and manufacture are decreased; and cost performance of the product is increased. 
     The first power output end  2211   a ′ is arranged between the upper bridge arm  211   a ′ and the lower bridge arm  212   a ′; and the second power output end  2212   a ′ is arranged at the connection end of the lower bridge arm  212   a ′ and the DC power supply  30 ′. The m first power output ends  2211   a ′ of all the chopping units  21   a ′ and the m second power output ends  2212   a ′ of all the chopping units  21   a ′ respectively correspondingly form m pairs of power output terminals  221   a ′. The m pairs of power output terminals  221   a ′ are connected with the m pairs of external wiring terminals  151  in a one-to-one correspondence manner. 
     As shown in  FIG. 16 , the DC power supply  30 ′ is provided with m mutually independent DC power supply units  31 ′ and m pairs of power supply output terminals led out of each of the DC power supply units  31 ′. The m pairs of power supply output terminals are connected with the m chopping units  21   a ′ in a one-to-one correspondence manner Each pair of the power supply output terminals includes a positive pole  311 ′ and a negative pole  312 ′. The positive pole  311 ′ is connected with the upper bridge arm  211   a ′ in the corresponding chopping unit  21   a ′; and the negative pole  312 ′ is connected with the lower bridge arm  212   a ′ in the corresponding chopping unit  21   a′.    
     As shown in  FIG. 16 , the control part  50   a ′ includes a controller  51   a ′ and an amplifier  52   a′.    
     The controller  51   a ′ calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511   a ′ and an enable signal  512   a ′ to the amplifier  52   a ′. The control signal  511   a ′ includes m unit control signals that respectively correspond to the m chopping units  21   a ′ and are formed according to a preset phase stagger rule; each of the unit control signals includes two switching control ends  2110   a ′ and  2120   a ′ in the corresponding chopping unit  21   a ′; and the enable signal  512   a ′ is used for controlling an operating state of the amplifier  52   a′.    
     The amplifier  52   a ′ enters the operating state under control of the enable signal  512   a ′, amplifies the two switching control signals in each of the unit control signals and correspondingly provides the two switching control signals for the two switching control ends  2110   a ′ and  2120   a ′. The amplifier  52   a ′ is provided with m mutually independent amplifier units  521   a ′. The m amplifier units  521   a ′ respectively correspond to the m chopping units  21   a ′. Each of the amplifier units  521   a ′ is provided with an amplified signal output end. Each amplified signal output part is composed of two amplified signal output ends  5211   a ′ and  5212   a ′. The two amplified signal output ends  5211   a ′ and  5212   a ′ of each amplified signal output part are respectively correspondingly connected with the two switching control ends  2110   a ′ and  2120   a ′ in the corresponding chopping unit  21   a ′, i.e., the amplified signal output end  5211   a ′ is connected with the upper bridge arm switching control end  2110   a ′, and the amplified signal output end  5212   a ′ is connected with the lower bridge arm switching control end  2120   a′.    
     Embodiment 3 
     In the present embodiment 3, with respect to the same structure as the embodiment 1, the same symbol is given, and the same description is omitted. 
       FIG. 17  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in embodiment 3 of the present invention. 
     As shown in  FIGS. 17 and 18 , a shunt wound DC motor driving device  100   b  in the present embodiment 3 includes a shunt wound DC motor  10 , a chopper  20   b , a DC power supply  30 , a sensing part  40  and a control part  50   b.    
     As shown in  FIG. 17 , the chopper  20   b  converts a constant voltage of the DC power supply  30  into an average voltage controllable variable voltage based on a control signal transmitted by the control part  50   b  and provides the variable voltage for the shunt wound DC motor  10 . The chopper  20   b  includes m chopping units  21   b  that respectively correspond to the m pairs of electric brushes  13 . In the present embodiment, as show in  FIG. 18 , the chopper  20   b  includes 3 chopping units  21   b.    
     Each of the chopping units  21   b  includes a first bridge arm  211   b  and a second bridge arm  212   b , and a first power output end  2211   b  and a second power output end  2212   b . The first bridge arm  211   b  includes a first upper bridge arm  2111   b  and a first lower bridge arm  2112   b  connected in series with each other; the second bridge arm  212   b  includes a second upper bridge arm  2121   b  and a second lower bridge arm  2122   b  connected in series with each other; and the first bridge arm  211   b  and the second bridge arm  212   b  are connected in parallel with each other. The first upper bridge arm  2111   b  includes a power switch tube  21111   b , a diode  210   b  in reverse parallel connection with the power switch tube, and a switching control end  21110   b ; the first lower bridge arm  2112   b  includes a power switch tube  21121   b , a diode  210   b  in reverse parallel connection with the power switch tube, and a switching control end  21120   b ; the second upper bridge arm  2121   b  includes a power switch tube  21211   b , a diode  210   b  in reverse parallel connection with the power switch tube, and a switching control end  21210   b ; and the second lower bridge arm  2122   b  includes a power switch tube  21221   b , a diode  210   b  in reverse parallel connection with the power switch tube, and a switching control end  21220   b.    
     When the power switch tubes  21111   b  of all the first upper bridge arms  2111   b , the power switch tubes  21121   b  of all the first lower bridge arms  2112   b , the power switch tubes  21211   b  of all the second upper bridge arms  2121   b  and the power switch tubes  21221   b  of all the second lower bridge arms  2122   b  have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is I max , the m meets the following condition: m&gt;I max ÷I 1 . 
     In the present embodiment 3, all the power switch tubes are half-controlled or full-controlled devices. The half-controlled devices are ordinary thyristors; and the full-controlled devices are any one of power field effect transistors, gate-turn-off thyristors, integrated gate-commutated thyristors, insulated gate bipolar transistors and power bipolar transistors. 
     As shown in  FIG. 17 , the first power output end  2211   b  is arranged between the first upper bridge arm  2111   b  and the first lower bridge arm  2112   b ; and the second power output end  2212   b  is arranged between the second upper bridge arm  2121   b  and the second lower bridge arm  2122   b . The m first power output ends  2211   b  of all the chopping units  21   b  and the m second power output ends  2212   b  of all the chopping units  21   b  correspondingly form m pairs of power output terminals  221   b ; and the m pairs of power output terminals  221   b  are connected with the m pairs of external wiring terminal  151  in a one-to-one correspondence manner. 
     In the present embodiment, as shown in  FIG. 18 , the first power output end  2211   b  and the second power output end  2212   b  correspondingly form  1  pair of power output terminals  221   b ; the first power output end  2221   b  and the second power output end  2222   b  correspondingly form  1  pair of power output terminals  222   b ; the first power output end  2231   b  and the second power output end  2232   b  correspondingly form  1  pair of power output terminals  223   b ; and the 3 pairs of power output terminals  221   b ,  222   b  and  223   b  are connected with the 3 pairs of external wiring terminals  151 ,  152  and  153  in a one-to-one correspondence manner. 
     As shown in  FIGS. 17 and 18 , the DC power supply  30  has a constant voltage corresponding to a rated voltage of the shunt wound DC motor  10 , and is provided with m pairs of power supply output terminals that are connected with the m chopping units  21   b  in a one-to-one correspondence manner. Each pair of the power supply output terminals includes a positive pole  311  and a negative pole  312 ; the positive poles  311  are connected with the first upper bridge arms  2111   b  and the second upper bridge arms  2121   b  in the corresponding chopping units  21   b ; and the negative poles  312  are connected with the first lower bridge arms  2112   b  and the second lower bridge arms  2122   b  in the corresponding chopping units  21   b.    
     As shown in  FIGS. 17 and 18 , the control part  50   b  includes a controller  51   b  and an amplifier  52   b.    
     The controller  51   b  calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511   b  and an enable signal  512   b  to the amplifier  52   b . The control signal  511   b  includes m unit control signals that respectively correspond to the m chopping units  21   b  and are formed according to a preset phase stagger rule; each of the unit control signals includes four switching control signals  5211   b ,  5212   b ,  5221   b  and  5222   b  that correspond to four switching control ends  21110   b ,  21120   b ,  21210   b  and  21220   b  in the corresponding chopping units  21   b ; and the enable signal  512   b  is used for controlling an operating state of the amplifier  52   b.    
     The amplifier  52   b  enters the operating state under control of the enable signal  512   b , amplifies the four switching control signals in each of the unit control signals and provides the four switching control signals for the four switching control ends  21110   b ,  21120   b ,  21210   b  and  21220   b . The amplifier  52   b  is provided with m amplified signal output parts that correspond to the m chopping units  21   b . Each of the amplified signal output parts is composed of four amplified signal output ends. The four amplified signal output ends  5211   b ,  5212   b ,  5221   b  and  5222   b  of each of the amplified signal output parts are respectively correspondingly connected with the four switching control ends  21110   b ,  21120   b ,  21210   b  and  21220   b  in the corresponding chopping units  21   b , i.e., the amplified signal output end  5211   b  is connected with the first upper bridge arm switching control end  21110   b ; the amplified signal output end  5212   b  is connected with the first lower bridge arm switching control end  21120   b ; the amplified signal output end  5221   b  is connected with the second upper bridge arm switching control end  21210   b ; and the amplified signal output end  5222   b  is connected with the second lower bridge arm switching control end  21220   b.    
     In the present embodiment 3, the preset phase stagger rule is as follows: the m phases that respectively correspond to the m unit control signals serve as m preset phases and are staggered by 1/m switching cycle in sequence. In each of the chopping units, the two switching control signals that correspond to the first upper bridge arm switching control end and the second lower bridge arm switching control end are set as reference switching control signals; and phases of the reference switching control signals are set according to the preset phases that correspond to the unit control signals. Two switching control signals that correspond to the first lower bridge arm switching control end and the second upper bridge arm switching control end are set reciprocal to the reference switching control signals, so that peak values of ripple peaks of the superposed current ripples of the output current of the power output terminals of the m chopping units are decreased, thereby decreasing peak values of ripple peaks of the output torque and the rotation speed, further increasing the performance of the shunt wound DC motor and prolonging service life of the motor. Certainly, according to the needs, when the m is the even number, the preset stagger rule is as follows: the m phases that respectively correspond to the m unit control signals serve as the m preset phases and are staggered by 2/m switching cycle in sequence. Thus, the output current of the power output terminals of every two chopping units corresponding to every two pairs of the electric brushes with opposite spatial positions has the same current ripples, thereby producing a couple moment in the motor, avoiding a friction moment between a shaft and a bearing caused by the reason that the torque ripple output by the motor cannot form the couple moment, decreasing wear between the shaft and the bearing, increasing the performance of the motor and prolonging the service life of the motor. 
     The peak value and the ripple factor are described below when the current ripple of the output current has the same frequency but the phases are staggered by ⅓ switching cycle in sequence and the switching frequency of the three electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  and the chopper is 1 KHz. 
     As shown in  FIG. 7 , the peak values of the input current ripples of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3  in the shunt wound DC motor in the present embodiment 3 are all equal to 99.31−87.33=11.99 amperes; the mean of the input current is equal to 93.32 amperes; and the ripple factor is equal to 11.99/93.32×11.99/93.32×100%=12.84%. 
     As shown in  FIG. 8 , the peak values of input current ripples of the three exciting winding units  1221 ,  1222  and  1223  in the shunt wound DC motor in the present embodiment 2 is equal to 61.97−61.37=0.60 amperes; the mean of the current ripple is equal to 61.67 amperes; and the ripple factor is equal to 0.60/61.67×100%=0.97%. 
     As shown in  FIG. 9 , in the stable state, the armature current of the shunt wound DC motor in the present embodiment 3 is equal to the sum of the current of the three pairs of electric brushes A 1 B 1 , A 2 B 2  and A 3 B 3 ; the armature current ripple is equal to 281.95-277.98=3.97 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 3.97/279.97×100%=1.42%. The armature current ripple of the traditional shunt wound DC motor is equal to 297.94−261.98=35.96 amperes; the mean of the ripple is equal to 279.97 amperes; and the ripple factor is equal to 35.96/279.97×100%=12.84%. Although the shunt wound DC motor in the present embodiment 3 and the traditional shunt wound DC motor have the same mean of the armature current, the armature current ripple and the ripple factor of the shunt wound DC motor in the present embodiment 3 are only one ninth of the traditional shunt wound DC motor. 
     As shown in  FIG. 10 , in the stable state, exciting current of the shunt wound DC motor in the present embodiment 3 is equal to the sum of the current of the three exciting winding units  1221 ,  1222  and  1223 ; the peak value of the ripple peak of the exciting current is equal to 185.10−184.90=0.2 amperes; the mean of the ripple is equal to 185.0 amperes; and the ripple factor is equal to 0.2/185×100%=0.11%. The armature current ripple of the traditional shunt wound DC motor is equal to 185.9−184.1=1.8 amperes; the mean is equal to 185.0 amperes; and the ripple factor is equal to 1.8/185.0×100%=0.97%. Although the shunt wound DC motor in the present embodiment 3 and the traditional shunt wound DC motor have the same mean of the exciting current, the exciting current ripple and the ripple factor of the shunt wound DC motor in the present embodiment 3 are only one ninth of the traditional shunt wound DC motor. 
     In the present embodiment 3, L af  is equal to 1. In the stable state, as shown in  FIG. 11 , the peak value of torque ripple peaks of the shunt wound DC motor in the present embodiment 2 is equal to 52188.25−51398.38=789.87 N·m; the mean is equal to 51793.56 N·m; and the ripple factor is equal to 1.53%. The peak value of torque ripple peaks of the traditional shunt wound DC motor is equal to 55386.15−48229.93=7156.21 N·m; the mean is equal to 51798.89 N·m; and the ripple factor is equal to 13.82%. 
     As shown in  FIG. 12 , in the stable state, the peak value of the rotation speed ripple of the shunt wound DC motor  10  in the present embodiment 3 is equal to 1725.5157-1725.5142=0.0015 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.000087%. The peak value of the rotation speed ripple of the traditional shunt wound DC motor is equal to 1725.535-1725.4949=0.0401 revolutions per minute; the mean is equal to 1725.515 revolutions per minute; and the ripple factor is equal to 0.002324%. Although the shunt wound DC motor  10  in the present embodiment 3 and the traditional shunt wound DC motor have the same mean of the rotation speed, a ratio of the peak value of the rotation speed ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 3 to those in the traditional shunt wound DC motor is 1/26.7. 
     In other words, although the shunt wound DC motor  10  in the present embodiment 3 has basically the same mean of the torque as the traditional shunt wound DC motor, the peak value of the torque ripple peak and the ripple factor of the shunt wound DC motor  10  in the present embodiment 3 are only one ninth of the traditional shunt wound DC motor, thereby decreasing the peak value of the output torque ripple peak and the ripple factor of the motor and further decreasing the peak value of the output rotation speed ripple and the ripple factor of the motor. The rotation speed ripple factor of the shunt wound DC motor in the present embodiment 2 is only 1/26 that of the traditional shunt wound DC motor. Finally, purposes of decreasing electromagnetic interference, vibration and noise of the motor and increasing the performances of the shunt wound DC motor and the driving device are achieved. 
     Variation Example 3 
     In the present variation example 3, with respect to the same structure as embodiment 1, the same symbol is given, and the same description is omitted. 
       FIG. 19  is a schematic diagram of circuit connection of a shunt wound DC motor driving device in variation example 3 of the present invention. 
     As shown in  FIG. 19 , a shunt wound DC motor driving device  100   b ′ in the present variation example 3 includes a shunt wound DC motor  10 , a chopper  20   b ′, a DC power supply  30 ′, a sensing part  40  and a control part  50   b′.    
     As shown in  FIG. 19 , the chopper  20   b ′ is composed of m chopping units  21   b ′ that respectively correspond to m pairs of electric brushes  13 . 
     Each of the chopping units  21   b ′ includes a first bridge arm  211   b ′ and a second bridge arm  212   b ′, and a first power output end  2211   b ′ and a second power output end  2212   b′.    
     Each first upper bridge arm  2111   b ′ includes p power switch tubes  21111   b ′ connected in a one-to-one correspondence manner in parallel, diodes  210   b ′ in reverse parallel connection with the power switch tubes, and switching control ends  21110   b ′; each first lower bridge arm  2112   b ′ includes p power switch tubes  21121 ′ connected in a one-to-one correspondence manner in parallel, diodes  210   b ′ in reverse parallel connection with the power switch tubes, and switching control ends  21120   b ′; each second upper bridge arm  2121   b ′ includes p power switch tubes  21211   b ′ connected in a one-to-one correspondence manner in parallel, diodes  210   b ′ in reverse parallel connection with the power switch tubes, and switching control ends  21210   b ′; and each second lower bridge arm  2122   b ′ includes p power switch tubes  21221   b ′ connected in a one-to-one correspondence manner in parallel, diodes  210   b ′ in reverse parallel connection with the power switch tubes, and switching control ends  21220   b ′, wherein p is a positive integer of being not greater than 2. Each of the power switch tubes is provided with a control pole; all the control poles in each first upper bridge arm  2111   b ′ form the first upper bridge arm switching control ends  21110   b ′; all the control poles in each first lower bridge arm  2112   b ′ form the first lower bridge arm switching control ends  21120   b ′; all the control poles in each second upper bridge arm  2121   b ′ form the second upper bridge arm switching control ends  21210   b ′; and all the control poles in each second lower bridge arm  2122   b ′ form the second lower bridge arm switching control ends  21220   b′.    
     When the power switch tubes  21111   b ′ of all the first upper bridge arms  2111   b ′, the power switch tubes  21121   b ′ of all the first lower bridge arms  2112   b ′, the power switch tubes  21211   b ′ of all the second upper bridge arms  2111   b ′ and the power switch tubes  21221   b ′ of all the second lower bridge arms  2122   b ′ have the same maximum output current I 1 , and the maximum current of the shunt wound DC motor  10  is I max , the m meets the following condition: m&gt;I max ÷(k×p×I 1 ), wherein k is a parallel connection coefficient, and 1/p&lt;k&lt;1. 
     In the present variation example 3, the p is equal to 2-4; the parallel connection technology is mature and reliable; the quantity of the m can be properly decreased; workloads and complexity in production and manufacture are decreased; and cost performance of the product is increased. 
     The first power output end  2211   b ′ is arranged between the first upper bridge arm  2111   b ′ and the first lower bridge arm  2112   b ′; and the second power output end  2212   b ′ is arranged between the second upper bridge arm  2121   b ′ and the second lower bridge arm  2122   b ′. The m first power output ends  2211   b ′ of all the chopping units  21   b ′ and the m second power output ends  2212   b ′ of all the chopping units  21   b ′ respectively correspondingly form m pairs of power output terminals  221   b ′. The m pairs of power output terminals  221   b ′ are connected with the m pairs of external wiring terminals  151  in a one-to-one correspondence manner. 
     As shown in  FIG. 19 , the DC power supply  30 ′ is provided with m mutually independent DC power supply units  31 ′ and m pairs of power supply output terminals led out of each of the DC power supply units  31 ′. The m pairs of power supply output terminals are connected with the m chopping units  21   b ′ in a one-to-one correspondence manner Each pair of the power supply output terminals includes a positive pole  311 ′ and a negative pole  312 ′. The positive pole  311 ′ is connected with the first upper bridge arm  2111   b ′ and the second upper bridge arm  2121   b ′ in the corresponding chopping unit  21 ′; and the negative pole  312 ′ is connected with the first lower bridge arm  2112   b ′ and the second lower bridge arm  2122   b ′ in the corresponding chopping unit  21 ′. 
     As shown in  FIG. 19 , the control part  50   b ′ includes a controller  51   b ′ and an amplifier  52   b′.    
     The controller  51   b ′ calculates generation according to the external instruction signal and the output feedback signal and the current feedback signal of the sensing part  40  and outputs a control signal  511   b ′ and an enable signal  512   b ′ to the amplifier  52   b ′. The control signal  511   b ′ includes m unit control signals that respectively correspond to the m chopping units  21   b ′ and are formed according to a preset phase stagger rule; each of the unit control signals includes four switching control signals  5211   b ′,  5212   b ′,  5221   b ′ and  5222   b ′ that correspond to four switching control ends  21110   b ′,  21120   b ′,  21210   b ′ and  21220   b ′ in the corresponding chopping units  21   b ′; and the enable signal  512   b ′ is used for controlling an operating state of the amplifier  52   b′.    
     The amplifier  52   b ′ enters the operating state under control of the enable signal  512   b ′, amplifies the four switching control signals in each of the unit control signals and correspondingly provides the four switching control signals for the four switching control ends  21110   b ′,  21120   b ′,  21210   b ′ and  21220   b ′. The amplifier  52   b ′ is provided with m amplified signal output parts that correspond to the m chopping units  21   b ′. Each of the amplified signal output parts is composed of four amplified signal output ends  5211   b ′,  5212   b ′,  5221   b ′ and  5222   b ′. The four amplified signal output ends  5211   b ′,  5212   b ′,  5221   b ′ and  5222   b ′ of each of the amplified signal output parts are correspondingly connected with the four switching control ends  21110   b ′,  21120   b ′,  21210   b ′ and  21220   b ′ in the corresponding chopping units  21   b ′, i.e., the amplified signal output end  5211   b ′ is connected with the first upper bridge arm switching control end  21110   b ′; the amplified signal output end  5212   b ′ is connected with the first lower bridge arm switching control end  21120   b ′; the amplified signal output end  5221   b ′ is connected with the second upper bridge arm switching control end  21210   b ′; and the amplified signal output end  5222   b ′ is connected with the second lower bridge arm switching control end  21220   b′.    
     Actions and Effects of the Embodiments 
     According to the shunt wound DC motor driving device and the electrical equipment including the shunt wound DC motor driving device involved in the present embodiments 1-3, the chopper is provided with the m chopping units; each of the chopping units is provided with the first power output end, the second power output end and the w switching control ends; the control signal includes m unit control signals that respectively correspond to the m chopping units and are formed according to a preset phase stagger rule; each of the unit control signals includes w switching control signals that correspond to the w switching control ends in the corresponding chopping units; the w switching control ends are used for correspondingly receiving the w switching control signals; and m first power output ends of all the chopping units and m second power output ends of all the chopping units respectively correspondingly form m pairs of power output terminals. The exciting winding part includes m exciting winding units. Each of the exciting winding units is formed by respectively making exciting coils from insulated conductor strips composed of metal wires coated with insulating layers on at least one pair of corresponding main poles. The insulated conductor strip in each of the exciting winding units is provided with one end and the other end. The m ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form the m first wiring terminals; meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form the m second wiring terminals; or, the m ends of all the insulated conductor strips are electrically connected with m N-pole corresponding electric brushes in all the electric brushes to form the m first wiring terminals; and meanwhile, the m other ends of all the insulated conductor strips are electrically connected with m S-pole corresponding electric brushes in all the electric brushes to form the m second wiring terminals. The m first wiring terminals and the m second wiring terminals respectively correspondingly form m pairs of external wiring terminals; and the m pairs of external wiring terminals are connected with m pairs of power output terminals in a one-to-one correspondence manner. In other words, each pair of the external wiring terminals is connected with one exciting winding unit and a pair of electric brushes in mutual series-shunt connection. Therefore, a branch circuit composed of each exciting winding unit and the pair of electric brushes in corresponding connection is mutually independent; current of each branch circuit is also independent; each branch circuit can independently work, and power of each branch circuit is independently provided by one pair of corresponding power output terminals, i.e., each pair of the power output terminals only undertakes operating current of one branch circuit, wherein the operating current is only 1/m of rated input current of the motor. Therefore, even for the motor having extremely large rated input current, as long as the m is greater enough, the operating current of each branch circuit or output current of each pair of the power output terminals will be corresponding decreased, so that according to the low enough output current of the power output terminals, requirements on the high-power high-performance motor can be met without adopting a parallel current evenness technology but by using an ordinary power switch tube or a power module. Moreover, cost of the chopper is decreased; requirements of connecting wires and connectors between the external wiring terminals and the power output terminals on contact resistance and insulation are lowered; production and manufacture difficulty is lowered; and reliability and safety of the system are increased. 
     Moreover, since the control signal includes the m switching control signals that respectively correspond to the m chopping units and are formed according to the preset phase stagger rule, current ripple phases of each pair of the power output terminals are mutually different. Therefore, the peak values of ripple peaks of the m superposed current ripples are decreased; peak values of ripple peaks of the output torque and the rotation speed are further decreased; the performance of the shunt wound DC motor is increased; and service life of the motor is prolonged. 
     To sum up, the shunt wound DC motor driving device in the present invention is simple in structure, short in connecting wire, simple in production process, easy to manufacture, convenient to maintain and low in production cost and maintenance cost, and has the advantages of reasonable structural design, simplicity and high reliability and safety. Therefore, the shunt wound DC motor driving device in the present invention can be applied to heavy-load electrical equipment such as electric cars, electric trucks, track cars, sightseeing tourist cars, trucks and ships, and can be further applied to high-performance electrical equipment such as numerically-controlled machine tools and submarines. 
     In addition, since the insulated conductors in each of the exciting winding units are formed on the m pairs of main poles, when the electric brushes, the exciting winding units and the connecting wires in the motor fail, only the parts at which failures are located shall be masked, and the other normal parts may still work. Thus, a phenomenon that the traditional shunt wound DC motor is suddenly out of control can be avoided; and the reliability and safety of the system are increased. 
     Moreover, since the upper bridge arm includes one power switch tube and the lower bridge arm includes one diode in the embodiment 1, the upper bridge arm and the lower bridge arm only include one power switch tube and the diode in reverse parallel connection with the power switch tube in the embodiment 2, and each of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm only includes one power switch tube and the diode in reverse parallel connection with the power switch tube in the embodiment 3, the chopper in the Embodiments 1-3 is simple in structure, reliable, high in safety, easy to control and low in cost. 
     In addition, since the upper bridge arm in the variation example 1 includes the p power switch tubes connected in parallel in a one-to-one correspondence manner, the upper bridge arm and the lower bridge arm in the variation example 2 includes the p power switch tubes connected in parallel in a one-to-one correspondence manner, each of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm in the variation example 3 includes the p power switch tubes connected in parallel in a one-to-one correspondence manner, wherein p is a positive integer of being not less than 2, the output current of each of the chopping units can be increased to a certain degree due to a relatively reliable and stable technology under a condition that the rated current of the motor is constant, relative to a condition that p is equal to 1, particularly a condition that the p is equal to 2-4. Thus, the numerical value of the m can be correspondingly decreased. The number of the electric brushes can be decreased; the number of power lines of the motor and the number of output lines of the chopping units are decreased; repair and maintenance difficulty is lowered; and production cost is properly decreased. Moreover, a heat radiating area can be enlarged; temperature rise is decreased; the reliability is increased; and the service life is prolonged. 
     Moreover, since the DC power supply in the variation examples 1-3 is provided with the m mutually independent DC power supply units, and one pair of power supply output terminals is led out of each of the DC power supply units, when the power supply output terminals or connecting wires of a certain DC power supply unit fail, only the parts at which failures are located shall be masked, and the other normal parts may still work. Thus, the phenomenon that the traditional shunt wound DC motor is suddenly out of control in case of failure can be avoided; and the reliability and safety of the system are increased. Moreover, the shunt wound DC motor can output a larger effective torque so as to be maintained in the operating state. Further, in the power supply aspect, a single high-capacity DC power supply is replaced with a plurality of independent DC power supply units with relatively low capacities. Compared with a traditional banked battery, the independent DC power supply units decrease overall performance attenuation of the power supply caused by parallel connection under a condition that the number of the power supply units is the same, increase the energy density, power, performance, durability and safety, and may well ensure endurance and performance of the electrical equipment. 
     In addition, since the amplifier in the variation examples 1-3 is composed of the m mutually independent amplifier units, and each of the amplifier units is correspondingly connected with one chopping unit, one exciting winding unit and one pair of electric brushes, when any one of the amplifier units, chopping units, electric brushes and exciting windings fails, after the shunt wound DC motor driving device in the present invention calculates the current value detected by a current sensor and judges the failed amplifier units, chopping units, electric brushes and exciting windings, the control part outputs the enable signal to enable the corresponding amplifier unit to stopping working, so that the damaged amplifier units, chopping units, electric brushes and exciting windings are masked and isolated, thereby avoiding further expansion of the failure, ensuring that the electrical driving device and the electrical equipment can continuously normally work or operate under a light load, and greatly decreasing the safety incident probability of the electrical equipment, particularly electrical equipment operating at a high speed. 
     The above embodiments are preferred cases of the present invention, rather than limiting the protection scope of the present invention. 
     For example, in the above embodiments, the exciting winding units in the shunt wound DC motor are formed by respectively making the exciting coils from the insulated conductor strips on the m pairs of main poles. However, the exciting winding units may also be formed by respectively making the exciting coils from the insulated conductor strips on one pair of main poles. The device is described below by taking variation of the exciting winding part in the embodiment 1 as an example. 
       FIG. 20  is a schematic diagram of circuit connection of the shunt wound DC motor driving device in the variation examples of the present invention;  FIG. 21  is a schematic diagram of circuit connection of the shunt wound DC motor driving device in variation examples of the present invention when m is equal to 3; and  FIG. 22  is a schematic diagram of circuit connection of a transverse section of the shunt wound DC motor in variation examples of the present invention. 
     As shown in  FIGS. 20-22 , a stator  12   c  in a shunt wound DC motor driving device  100   c  includes m pairs of main poles  121  and further includes an exciting winding part  122   c.    
     Each of the main poles  121  includes an S-polarity main pole  1211  and an N-polarity main pole  1212 . Two adjacent main poles  121  have the opposite polarity in all the main poles  121 . 
     The exciting winding part  122   c  includes m exciting winding units  1221   c . The m exciting winding units  1221   c  respectively correspond to the m pairs of main poles  121 . Each of the exciting winding units  1221   c  is formed by respectively making exciting coils  12211   c  from the insulated conductor strips composed of metal wires coated with insulating layers on one corresponding pair of main poles  121 . The insulated conductor strip is any one of enameled wire and insulated copper conducting bar. In the present invention, the insulated conductor strips are the enameled wires. The exciting coils  12211   c  on each of the main poles  121  have the same number of turns, so that the motor is uniform in magnetic field during normal operation and has a constant moment. 
     The insulated conductor strip in each of the exciting winding units  1221   c  is provided with one end and the other end that are distinguished along a preset current direction of the exciting coils  12211   c . The S-polarity main pole  1211  and the N-polarity main pole  1212  in each pair of the main poles  121  correspond to the winding directions of the exciting coils  12211   c  and the preset current direction of the exciting coils  12211   c . The exciting coils  12211   c  of two adjacent main poles  121  have opposite current surrounding directions. 
     In each of the exciting winding units  1221   c , the connection relationship of the two exciting coils  12211   c  is any one of the series connection and parallel connection; and the two exciting coils  12211   c  in each of the exciting winding units  1221   c  have the same connection relationship. In the present embodiment 4, a connection relationship of the two exciting coils  12211   c  is series connection. 
     Each pair of the electric brushes  13  corresponds to the spatial positions of each corresponding pair of main poles  121 , so that the maximum magnetic field intensity in the armature windings can be maintained when other non-corresponding exciting winding units fail. Therefore, the maximum moment can be produced. 
     Since the m exciting winding units respectively correspond to the m pairs of magnetic poles, and the insulated conductor strips in each of the exciting winding units are formed on one corresponding pair of main poles, when the electric brushes, exciting winding units and connecting wires in the motor fail, only the parts at which failures are located shall be masked, and the other normal parts may still work. Moreover, the magnetic field excited by the exciting winding units at the non-failed part mainly acts on an armature winding branch circuit connected with the corresponding electric brushes, so that a phenomenon that the traditional shunt wound DC motor is suddenly out of control in case of failure can be avoided; and the reliability and safety of the system are increased. Further, the shunt wound DC motor can output a larger effective torque in failure so as to be maintained in the operating state. 
     Further, the lower bridge arm in the embodiment 1 and the variation example 1 includes 1 fly-wheel diode; each of the upper bridge arm and the lower bridge arm in the embodiment 2 and the variation example 2 includes a diode in reverse parallel connection with the power switch tube; and each of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm in the embodiment 3 and the variation example 3 includes a diode in reverse parallel connection with the power switch tube. However, in the present invention, the corresponding upper bridge arms, lower bridge arms, first upper bridge arms, first lower bridge arms, second upper bridge arms and second lower bridge arms may also include a plurality of fly-wheel diodes connected in parallel in a one-to-one correspondence manner Under the circumstances, when any one of the fly-wheel diodes fails, the other diodes may also normally work, thereby increasing the reliability and safety of the system. 
     Moreover, in the Embodiments 1-3, if the shunt wound DC motor driving system in the present invention needs to normally work, the amplifier must be in an operating mode. Therefore, the enable signal may not be applied to the amplifier. 
     Moreover, on an occasion that the requirements on the armature current, the rotation speed and the torque are high during steady-state operation of the shunt wound DC motor, the m may be set according to the peak values of the corresponding armature current, the rotation speed and torque ripple peaks and the ripple factor. 
     Further, the upper bridge arm and the lower bridge arm in the embodiment 2 and the variation example 2 and the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm in the embodiment 3 and the variation example 3 may also be power switching devices; and the power switching devices are equivalent to the power switch tubes and the diodes in reverse parallel connection with the power switch tubes.