Patent Publication Number: US-8115430-B2

Title: Methods, systems and apparatus for controlling operation of two alternating current (AC) machines

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The United States government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided by the terms of contract number DE-FC26-07NT43123 awarded by the United States Department of Energy. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to hybrid and electric vehicle power systems, and more particularly relates to controlling operation of two AC machines that are part of a hybrid and electric vehicle power system and that are controlled by a single five-phase PWM inverter module. 
     BACKGROUND OF THE INVENTION 
     Hybrid and electric vehicles (HEVs) typically include an alternating current (AC) electric motor which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Motor windings of the AC electric motor can be coupled to power inverter module(s) which perform a rapid switching function to convert the DC power to AC power which drives the AC electric motor, which in turn drives a shaft of HEV&#39;s drivetrain. Traditional HEVs implement two three-phase pulse width modulated (PWM) inverter modules and two three-phase AC machines (e.g., AC motors) each being driven by a corresponding one of the three-phase PWM inverter modules that it is coupled to. 
     Recently, researchers have investigated the possibility of replacing the two three-phase pulse width modulated inverter modules with a single five-phase PWM inverter module that simultaneously drives both of the three-phase AC machines. In addition, researchers have also investigated the possibility of using a single five-phase PWM inverter module that drives a first five-phase AC machine that is coupled to a second five-phase AC machine. One example of such research is described in a publication titled “Features of two Multi-Motor Drive Schemes Supplied from Five-Phase/Five-Leg Voltage Source Inverters,” by Dujić et al., May 27, 2008, which is incorporated by reference herein in its entirety. 
     While the possibility of using such inverter and motor configurations in HEVs is being explored, a lot of work remains to be done before these inverter and motor configurations can actually be implemented. One problem that has yet to be addressed is how to maintain the required output mechanical power of each machine while meeting voltage sharing constraints. 
     Accordingly, it is desirable to provide methods, systems and apparatus controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module that allow constant output power with voltage constraint i.e. in the field-weakening region. It would also be desirable to provide methods, systems and apparatus for increasing the voltage used to drive the two AC machines. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention relate to apparatus for it is controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module. 
     In accordance with one embodiment, a system is provided for controlling two alternating current (AC) machines. The system comprises a DC input voltage source that provides a DC input voltage, a voltage boost command control module (VBCCM), a five-phase PWM inverter module coupled to the two AC machines, and a boost converter coupled to the inverter module and the DC input voltage source. The boost converter is designed to supply a new DC input voltage to the inverter module having a value that is greater than or equal to a value of the DC input voltage. The VBCCM generates a boost command signal that controls the boost converter such that the boost converter generates the new DC input voltage in response to the boost command signal. When the two AC machines require additional voltage that exceeds the DC input voltage required to meet a combined target mechanical power required by the two AC machines, the boost command signal controls the boost converter to drive the new DC input voltage generated by the boost converter to a value greater than the DC input voltage. 
     For example, in one implementation, the voltage VBCCM can provide a boost command signal with a value equal to zero when the two AC machines require voltage that is less than or equal to the DC input voltage, and in this case the new DC input voltage will be equal to original DC input voltage. However, when the two AC machines require additional voltage to meet their target mechanical power that exceeds the DC input voltage, the voltage boost command signal has a value greater than zero and the new DC input voltage is regulated to a voltage higher than the original DC input voltage. 
     In one implementation, the system comprises a first control loop that generates a first modulation index, and a second control loop that generates a second modulation index. VBCCM receives a modulation index reference signal, the first modulation index from the first control loop and the second modulation index from the second control loop, and adds the first modulation index to the second modulation index to generate a modulation index feedback signal input, and then subtracts the modulation index feedback signal input from the modulation index reference signal input to generate a modulation index error signal. Based on the modulation index error signal, the boost command signal is calculated. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIGS. 1A-D  illustrate block diagrams of a torque control system  100  architecture implemented in motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention; 
         FIGS. 2A-C  illustrate block diagrams of a torque control system  200  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention; 
         FIGS. 3A-3D  illustrate block diagrams of a torque control system  300  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention; and 
         FIGS. 4A-4C  illustrate block diagrams of a torque control system  400  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention. 
     
    
    
     DESCRIPTION OF AN EXEMPLARY EMBODIMENT 
     As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in this Detailed Description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module. It will be appreciated that embodiments of the invention described herein can be implemented using hardware, software or a combination thereof. The control circuits described herein may comprise various components, modules, circuits and other logic which can be implemented using a combination of analog and/or digital circuits, discrete or integrated analog or digital electronic circuits or combinations thereof. As used herein the term “module” refers to a device, a circuit, an electrical component, and/or a software based component for performing a task. In some implementations, the control circuits described herein can be implemented using one or more application specific integrated circuits (ASICs), one or more microprocessors, and/or one or more digital signal processor (DSP) based circuits when implementing part or all of the control logic in such circuits. It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions for controlling operation of two AC machines, as described herein. As such, these functions may be interpreted as steps of a method for controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. 
     Overview 
     Embodiments of the present invention relate to methods and apparatus for controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module. The disclosed methods and apparatus can be implemented in operating environments where it is necessary to controlling operation of two AC machines that are controlled by a single five-phase PWM inverter module in a hybrid/electric vehicle (HEV). In the exemplary implementations which will now be described, the control techniques and technologies will be described as applied to a hybrid/electric vehicle (HEV). However, it will be appreciated by those skilled in the art that the same or similar techniques and technologies can be applied in the context of other systems which it is necessary to control operation of two AC machines. In this regard, any of the concepts disclosed here can be applied generally to “vehicles,” and as used herein, the term “vehicle” broadly refers to a non-living transport mechanism having an AC motor. Examples of such vehicles include automobiles such as buses, cars, trucks, sport utility vehicles, vans, vehicles that do not travel on land such as mechanical water vehicles including watercraft, hovercraft, sailcraft, boats and ships, mechanical under water vehicles including submarines, mechanical air vehicles including aircraft and spacecraft, mechanical rail vehicles such as trains, trams and trolleys, etc. In addition, the term “vehicle” is not limited by any specific propulsion technology such as gasoline or diesel fuel. Rather, vehicles also include hybrid vehicles, battery electric vehicles, hydrogen vehicles, and vehicles which operate using various other alternative fuels. 
     EXEMPLARY IMPLEMENTATIONS 
       FIGS. 1A-D  illustrate block diagrams of a torque control system  100  architecture implemented in motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention. In this embodiment, the system  100  can be used to control two three-phase AC machines  120  via a five-phase pulse width modulated (PWM) inverter module  110  connected to the two three-phase AC machines  120  so that the two three-phase AC machines  120  share a DC input voltage (Vdc)  139  available from the five-phase PWM inverter module  110  by adjusting current commands that control the two three-phase AC machines  120 . The AC machines are illustrated as being permanent magnet synchronous AC motors; however, it should be appreciated that the illustrated embodiment is only one non-limiting example of the types of AC machines that the disclosed embodiments can be applied to and that the disclosed embodiments can be applied to any type of AC machine. Here the term “AC machine” generally refers to “a device or apparatus that converts electrical energy to mechanical energy or vice versa.” AC machines can generally be classified into synchronous AC machines and asynchronous AC machines. Synchronous AC machines can include permanent magnet machines and reluctance machines. Permanent magnet machines include surface mount permanent magnet machines (SMPMMs) and interior permanent magnet machines (IPMMs). Asynchronous AC machines include induction machines. Although an AC machine can be an AC motor (i.e., apparatus used to convert AC electrical energy power at its input to produce to mechanical energy or power), an AC machine is not limited to being an AC motor, but can also encompass AC generators that are used to convert mechanical energy or power at its prime mover into electrical AC energy or power at its output. Any of the machines can be an AC motor or an AC generator. An AC motor is an electric motor that is driven by an alternating current (AC). An AC motor includes an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field. Depending on the type of rotor used, AC motors can be classified as synchronous or asynchronous. A synchronous AC motor rotates exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. In implementations where the AC machine is a permanent magnet synchronous AC motor this should be understood to encompass Interior Permanent Magnet motors. By contrast, an asynchronous (or induction) AC motor turns slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current. 
     As illustrated in  FIG. 1A , the system  100  comprises a first control loop  104 , a second control loop  105 , a Space Vector (SV) PWM module  108 , the five-phase PWM inverter module  110 , a first three-phase AC machine  120 -A coupled to the five-phase PWM inverter module  110 , a second three-phase AC machine  120 -B coupled to the five-phase PWM inverter module  110 , and a current command adjustment module  106  coupled to the first control loop  104  and the second control loop  105 . In one non-limiting implementation, the three-phase AC machines can be three-phase AC powered motors. 
     Space Vector (SV) modulation is coupled to first control loop  104  and the second control loop  105  and is used for the control of pulse width modulation (PWM). In general, the SVPWM module  108  receives voltage command signals  103  and generates switching vector signals  109  which it provides to the five-phase PWM inverter module  110 . In particular, the SVPWM module  108  receives a first sinusoidal voltage command (Va_ 1 )  103 -A 1 , a second sinusoidal voltage command (Vb_ 1 )  103 -A 2 , a third sinusoidal voltage command (Vc_ 1 )  103 -A 3 , a fourth sinusoidal voltage command (Va_ 2 )  103 -A 4 , a fifth sinusoidal voltage command (Vb_ 2 )  103 -A 5 , a sixth sinusoidal voltage command (Vc_ 2 )  103 -A 6 , and uses these inputs to generate a first switching vector signal (Sa)  109 -A, a second switching vector signal (Sb)  109 -B, a third switching vector signal (Sc)  109 -C, a fourth switching vector signal (Sd)  109 -D, and a fifth switching vector signal (Se)  109 -E. The particular SV modulation algorithm implemented in the first SV PWM module  108 -A can be any known SV modulation algorithm. The switching vectors can be generated using modulation signals from Equation (4) from Dujic&#39;s paper (referenced above) and comparing it with a carrier signal. 
     The five-phase PWM inverter module  110  is coupled to the Space Vector (SV) PWM module  108  and uses the switching vector signals  109  to generate sinusoidal voltage signals at inverter poles  111 - 115 . In the particular embodiment, the five-phase PWM inverter module  110  receives the first switching vector signal (Sa)  109 -A, the second switching vector signal (Sb)  109 -B, the third switching vector signal (Sc)  109 -C, the fourth switching vector signal (Sd)  109 -D, and the fifth switching vector signal (Se)  109 -E. The five-phase PWM inverter module  110  includes a plurality of inverter poles including a first inverter pole  111  that generates a first sinusoidal voltage (Va_*), a second inverter pole  112  that generates a second sinusoidal voltage (Vb_*), a third inverter pole  113  that generates a third sinusoidal voltage (Vc_*), a fourth inverter pole  114  that generates a fourth sinusoidal voltage (Vd_*), and a fifth inverter pole  115  that generates a fifth sinusoidal voltage (Ve_*). 
     The first three-phase AC machine  120 -A is coupled to the five-phase PWM inverter module  110  via the first inverter pole  111 , the second inverter pole  112  and the third inverter pole  113 . The first three-phase AC machine  120 -A generates mechanical power (Torque×Speed) and a first shaft position output (θ_r 1 ) based on the first sinusoidal voltage (Va_*), the second sinusoidal voltage (Vb_*) and the third sinusoidal voltage (Vc_*). In one implementation, the first shaft position output (θ_r 1 ) can be measured via a position sensor (not illustrated) that measures that angular position of the rotor of the first three-phase AC machine  120 -A. 
     The second three-phase AC machine  120 -B is coupled to the five-phase PWM inverter module  110  via the third inverter pole  113 , the fourth inverter pole  114  and the fifth inverter pole  115 . In other words, the second three-phase AC machine  120 -B and the first three-phase AC machine  120 -A share the third inverter pole  113 . The second three-phase AC machine  120 -B generates mechanical power (Torque×Speed) and a second shaft position output (θ_r 2 ) based on the third sinusoidal voltage (Vc_*), the fourth sinusoidal voltage (Vd_*) and the fifth sinusoidal voltage (Ve_*). 
     As will be explained in greater detail below, the current command adjustment module  106  receives d-axis current command signals  156 , and modulation index signals  177 -A,  177 -B, from the first control loop  104  and the second control loop  105 , respectively, and torque command signals  136 A, B and modulation index reference signal  101  and generates adjusted d-axis and adjusted q-axis current command signals  194 ,  196 - 198  based on these signals. Prior to describing the operation of the current command adjustment module  106 , operation of the first control loop  104  and the second control loop  105  will be described. 
     As illustrated in  FIG. 1B , the first control loop  104  includes a first stationary-to-synchronous conversion module  130 -A, a first torque-to-current mapping module  140 -A, a second summing junction  152 -A, a third summing junction  162 -A, a fourth summing junction  154 -A, a fifth summing junction  164 -A, a first current controller module  170 -A, a first modulation index computation module  175 -A, and a first synchronous-to-stationary conversion module  102 -A. Operation of the first control loop  104  will now be described. 
     The first stationary-to-synchronous conversion module  130 -A receives a first resultant stator current (Ias_ 1 )  122 , a second resultant stator current (Ibs_ 1 )  123 , and a third resultant stator current (Ics_ 1 )  124  that are measured phase currents from motor  120 -A, as well as the first shaft position output (θ_r 1 )  121 -A. The first stationary-to-synchronous conversion module  130 -A can process or convert these stator currents  122 - 124  along with the first shaft position output (θ_r 1 )  121 -A to generate a first feedback d-axis current signal (Ids_e_ 1 )  132 -A and a first feedback q-axis current signal (Iqs_e_ 1 )  134 -A. The process of stationary-to-synchronous conversion can be performed using Clarke and Park Transformations that are well-known in the art and for sake of brevity will not be described in detail. One implementation of the Clarke and Park Transformations is described in “Clarke &amp; Park Transforms on the TMS320C2xx,” Application Report Literature Number: BPRA048, Texas Instruments, 2007, which is incorporated by reference herein in its entirety. 
     The first torque-to-current mapping module  140 -A receives a first torque command signal (Te*_ 1 )  136 -A that is input from a user of the system  100 , a first speed (ω 1 )  138 -A of the shaft that is calculated based on the derivative of the first shaft position output (θ_r 1 ), and the DC input voltage (Vdc)  139  as inputs. The first torque-to-current mapping module  140 -A uses the inputs to map the first torque command signal (Te*_ 1 )  136 -A to a first d-axis current command signal (Ids_e*_ 1 )  142 -A and a first q-axis current command signal (Iqs_e*_ 1 )  144 -A. The mapping can be calculated using motor parameters and the following equation. 
             T   =       3   2     ·     P   2     ·     [         k   e     ·     I   qs       -       (       L   q     -     L   d       )     ·     I   qs     ·     I   ds         ]             
for I ph ≦I max  and V ds =r s ·I ds −ω e ·L q ·I qs , V qs =r s ·I qs +ω e ·(L d ·I ds +k e ) for V ph ≦K·V max , where I ph =√{square root over (I ds   2 +I qs   2 )}, and  V   ph =√{square root over (V ds   2 +V qs   2 )} the Ids and Iqs currents are calculated such that torque per ampere is maximized.
 
     Upon receiving the first d-axis current command signal (Ids_e*_ 1 )  142 -A and an adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196  (from the current command adjustment module  106 ), the second summing junction  152 -A adds the first d-axis current command signal (Ids_e*_ 1 )  142 -A to an adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196  to generate a first new d-axis current command signal (IdsNew_e*_ 1 )  156 -A. Upon receiving the first new d-axis current command signal (IdsNew_e*_ 1 )  156 -A and a first feedback d-axis current signal (Ids_e_ 1 )  132 -A from the first stationary-to-synchronous conversion module  130 -A, the third summing junction  162 -A subtracts the first feedback d-axis current signal (Ids_e_ 1 )  132 -A from the first new d-axis current command signal (IdsNew_e*_ 1 )  156 -A to generate a first error d-axis current signal (Idserror_e_ 1 )  166 -A. 
     Similarly, upon receiving the first q-axis current command signal (Iqs_e*_ 1 )  144 -A and a first adjusted q-axis current command signal (Iqs_e*_Adj_ 1 )  197  (from the current command adjustment module  106 ), the fourth summing junction  154 -A adds the first q-axis current command signal (Iqs_e*_ 1 )  144 -A to the first adjusted q-axis current command signal (Iqs_e*_Adj_ 1 )  197  to generate a first new q-axis current command signal (IqsNew_e*_ 1 )  158 -A. The fifth summing junction  164 -A then receives the first new q-axis current command signal (IqsNew_e*_ 1 )  158 -A and a first feedback q-axis current signal (Iqs_e_ 1 )  134 -A from the first stationary-to-synchronous conversion module  130 -A, and subtracts the first feedback q-axis current signal (Iqs_e_ 1 )  134 -A from the first new q-axis current command signal (IqsNew_e*_ 1 )  158 -A to generate a first error q-axis current signal (Iqserror_e_ 1 )  168 -A. 
     The first current controller module  170 -A receives the first error d-axis current signal (Idserror_e_ 1 )  166 -A and the first error q-axis current signal (Iqserror_e_ 1 )  168 -A and uses these signals to generate a first d-axis voltage command signal (Vds_e*_ 1 )  172 -A and a first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A that are used to control or regulate current. The process of current to voltage conversion can be implemented as a Proportional-Integral (PI) controller, which is well-known in the art and for sake of brevity will not be described in detail. 
     The first modulation index computation module  175 -A receives the first d-axis voltage command signal (Vds_e*_ 1 )  172 -A and the first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A, and uses these signals to generate a first modulation index (Mod. Index  1 )  177 -A. As used herein, “modulation index (MI)” can be defined via the equation 
                 M   ⁢           ⁢   I     =         V   ph       V   dc       ·     π   2         ,         
where V ph =√{square root over (V ds   2 +V qs   2 )}, and Vds and Vqs are the first d-axis voltage command signal (Vds_e*_ 1 )  172 -A and the first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A output by current controller  170 . The range of modulation index is from 0 to 1.
 
     The first synchronous-to-stationary conversion module  102 -A receives the first d-axis voltage command signal (Vds_e*_ 1 )  172 -A and the first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A, and based on these signals, generates a first sinusoidal voltage command (Va_ 1 )  103 -A 1 , a second sinusoidal voltage command (Vb_ 1 )  103 -A 2 , and a third sinusoidal voltage command (Vc_ 1 )  103 -A 3 . The process of synchronous-to-stationary conversion is done using inverse Clarke and Park Transformations that are well-known in the art and for sake of brevity will not be described in detail. One implementation of the inverse Clarke and Park Transformations is described in the above referenced document “Clarke &amp; Park Transforms on the TMS320C2xx.” 
     As illustrated in  FIG. 1C , the second control loop  105  includes similar blocks or modules as the first control loop  104 . The second control loop  105  includes a second stationary-to-synchronous conversion module  130 -B, a second torque-to-current mapping module  140 -B, a sixth summing junction  152 -B, a seventh summing junction  162 -B, an eighth summing junction  154 -B, a ninth summing junction  164 -B, a second current controller module  170 -B, a second modulation index computation module  175 -B, and a second synchronous-to-stationary conversion module  102 -B. As will now be described, the second control loop  105  operates in a similar manner as the first control loop  104 . 
     The second stationary-to-synchronous conversion module  130 -B receives the third resultant stator current (Ias_ 2 )  125 , a fourth resultant stator current (Ibs_ 2 )  126 , a fifth resultant stator current (Ics_ 2 )  127  and the second shaft position output (θ_r 2 )  121 -B, and generates, based on these stator currents  125 ,  126 ,  127  and the second shaft position output (θ_r 2 )  121 -B, a second feedback d-axis current signal (Ids_e_ 2 )  132 -B and a second feedback q-axis current signal (Iqs_e_ 2 )  134 -B. 
     The second torque-to-current mapping module  140 -B receives a second torque command signal (Te*_ 2 )  136 -B that is input from a user of the system  100 , a second speed (ω 2 )  138 -B of the shaft, and the DC input voltage (Vdc)  139 . The second torque-to-current mapping module  140 -B maps the second torque command signal (Te*_ 2 )  136 -B, the second speed (ω 2 )  138 -B of the shaft, and the DC input voltage (Vdc)  139  to a second d-axis current command signal (Ids_e*_ 2 )  142 -B and a second q-axis current command signal (Iqs_e*_ 2 )  144 -B as explained above. 
     The sixth summing junction  152 -B receives the second d-axis current command signal (Ids_e*_ 2 )  142 -B and the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194  (from the current command adjustment module  106 ), and adds the second d-axis current command signal (Ids_e*_ 2 )  142 -B to the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194  to generate a second new d-axis current command signal (Ids New_e*_ 2 )  156 -B. 
     The seventh summing junction  162 -B receives the second new d-axis current command signal (Ids New_e*_ 2 )  156 -B and the second feedback d-axis current signal (Ids_e_ 2 )  132 -B, and subtracts the second feedback d-axis current signal (Ids_e_ 2 )  132 -B from the second new d-axis current command signal (Ids New_e*_ 2 )  156 -B to generate a second error d-axis current signal (Idserror_e_ 1 )  166 -B. 
     The eighth summing junction  154 -B receives the second q-axis current command signal (Iqs_e*_ 2 )  144 -B and the second adjusted q-axis current command signal (Iqs_e*_Adj_ 2 )  198  (from the current command adjustment module  106 ), and adds the second q-axis current command signal (Iqs_e*_ 2 )  144 -B to the second adjusted q-axis current command signal (Iqs_e*_Adj_ 2 )  198  to generate a second new q-axis current command signal (IqsNew_e*_ 2 )  158 -B. 
     The ninth summing junction  164 -B receives the second new q-axis current command signal (IqsNew_e*_ 2 )  158 -B and the second feedback q-axis current signal (Iqs_e_ 2 )  134 -B, and subtracts the second feedback q-axis current signal (Iqs_e_ 2 )  134 -B from the second new q-axis current command signal (IqsNew_e*_ 2 )  158 -B to generate a second error q-axis current signal (Iqserror_e_ 2 )  168 -B. 
     The second current controller module  170 -B receives the second error d-axis current signal (Idserror_e_ 2 )  166 -B and the second error q-axis current signal (Iqserror_e_ 2 )  168 -B, and generates a second d-axis voltage command signal (Vds_e*_ 2 )  172 -B and a second q-axis voltage command signal (Vqs_e*_ 2 )  174 -B. The second modulation index computation module  175 -B receives the second d-axis voltage command signal (Vds_e*_ 2 )  172 -B and the second q-axis voltage command signal (Vqs_e*_ 2 )  174 -B, and generates a second modulation index (Mod. Index  2 )  177 -B as described above. 
     The second synchronous-to-stationary conversion module  102 -B receives the second d-axis voltage command signal (Vds_e*_ 2 )  172 -B and the second q-axis voltage command signal (Vqs_e*_ 2 )  174 -B, and generates a fourth sinusoidal voltage command (Va_ 2 )  103 -A 4 , a fifth sinusoidal voltage command (Vb_ 2 )  103 -A 5  and a sixth sinusoidal voltage command (Vc_ 2 )  103 -A 6 . 
     The first and the second control loop  104  and  105  respectively share the SVPWM module  108 . As described above, the SVPWM module  108  receives the sinusoidal voltage commands (Va_ 1 )  103 -A 1 , (Vb_ 1 )  103 -A 2 , (Vc_ 1 )  103 -A 3  from the first synchronous-to-stationary conversion module  102 -A, and also receives the sinusoidal voltage command (Va_ 2 )  103 -A 4 , (Vb_ 2 )  103 -A 5 , (Vc_ 2 )  103 -A 6  from the second synchronous-to-stationary conversion module  102 -B, and uses these signals to generate switching vector signals (Sa)  109 -A, (Sb)  109 -B, (Sc)  109 -C, (Sd)  109 -D, and (Se)  109 -E. 
     The five-phase PWM inverter module  110  receives the DC input voltage (Vdc)  139  and switching vector signals  109 , and uses them to generate alternating current (AC) waveforms  111 - 115  that drive the first three-phase AC machine  120 -A at varying speeds based on the DC input voltage (Vdc)  139 . Although not illustrated in  FIG. 1 , the system  100  may also include a gear coupled to and driven by the first three-phase AC machine  120 -A shaft and the second three-phase AC machine  120 -B shaft. 
     Operation of the current command adjustment module  106  will now be described with reference to  FIG. 1D . As illustrated in  FIG. 1D , the current command adjustment module  106  includes a first summing junction  180 , a voltage controller  185 , a negative limiter module  190  and a current adjustment computation module  195 . The current command adjustment module  106  operates as follows. The first summing junction  180  receives a modulation index reference signal input  101  and a modulation index feedback signal input  179 , and subtracts the modulation index feedback signal input  179  from the modulation index reference signal input  101  to generate a modulation index error signal  181 . The voltage controller  185  receives the modulation index error signal  181 , and generates a first output command signal  186  based on the modulation index error signal  181 . In one implementation, the voltage controller  185  that processes the modulation index error signal  181  can be a Proportional-Integral Controller (PI). The negative limiter module  190  receives the first output command signal  186  and limits the first output command signal  186  between a negative value and zero. The resulting limited value of the first output command signal  186  becomes the adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196 . 
     The current adjustment computation module  195  receives a first torque command signal (Te*_ 1 )  136 -A, a second torque command signal (Te*_ 2 )  136 -B, a first new d-axis current command signal (IdsNew_e*_ 1 )  166 -A, and a second new d-axis current command signal (Ids New_e*_ 2 )  166 -B. When the current adjustment computation module  195  receives the adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196  (i.e., when its output by the negative limiter module  190 ), the current adjustment computation module  195  generates a second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194  based on the first adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196 , a first adjusted q-axis current command signal (Iqs_e*_Adj_ 1 )  197  and a second adjusted q-axis current command signal (Iqs_e*_Adj_ 2 )  198 , based on the first adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196 , the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194 , the first torque command signal (Te*_ 1 )  136 -A, the second torque command signal (Te*_ 2 )  136 -B, the first new d-axis current command signal (IdsNew_e*_ 1 )  166 -A, and the second new d-axis current command signal (Ids New_e*_ 2 )  166 -B. 
     In one implementation, the current adjustment computation module  195  can include a first current adjustment computation sub-module  199 -A, a second current adjustment computation sub-module  199 -B and a scaling block (K)  199 -C. The current adjustment computation sub-modules  199 -A,  199 -B compute a derivative [dIq/dId] of the q-axis current (Tq) with respect to the d-axis current (Id). The partial derivative [dIq/dId] with torque constant is calculated using the equation. 
             T   =       3   2     ·     P   2     ·     [         k   e     ·     I   qs       -       (       L   q     -     L   d       )     ·     I   qs     ·     I   ds         ]             
for I ph ≦I max  and V ph ≦K·V max , where I ph =√{square root over (I ds   2 +I qs   2 )}, the Ids and Iqs currents are calculated such that torque per ampere is maximized with machine parameters and stored in a look-up table as function of the first torque command signal (Te*_ 1 )  136 -A and the first new d-axis current command signal (IdsNew_e*_ 1 )  156 -A. In one exemplary implementation, the first current adjustment computation sub-module  199 -A receives the first adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196  and multiplies it by the partial derivative [dIq/dId], and use these to generate the first adjusted q-axis current command signal (Iqs_e*_Adj_ 1 )  197 . The scaling block (K) receives the first adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196  and multiply it by a K factor to obtain the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194 . The second current adjustment computation sub-module  199 -B can receive the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194 , the second torque command signal (Te*_ 2 )  136 -B and the second new d-axis current command signal (Ids New_e*_ 2 )  156 -B and use these to generate the second adjusted q-axis current command signal (Iqs_e*_Adj_ 2 )  198 . The first adjusted d-axis current command signal (Ids_e*_Adj_ 1 )  196 , the first adjusted q-axis current command signal (Iqs_e*_Adj_ 1 )  197 , the second adjusted q-axis current command signal (Iqs_e*_Adj_ 2 )  198  and the second adjusted d-axis current command signal (Ids_e*_Adj_ 2 )  194  are used to modify the original current command signals (i.e., the first d-axis current command signal (Ids_e*_ 1 )  142 -A, the first q-axis current command signal (Iqs_e*_ 1 )  144 -A, the second d-axis current command signal (Ids_e*_ 1 )  142 -B and the second q-axis current command signal (Iqs_e*_ 2 )  144 -B) to allow machines  120 -A,  120 -B to output a given mechanical power with less phase voltage (i.e. it allows sharing the voltage available between both machines without compromising output power).
 
       FIGS. 2A-C  illustrate block diagrams of a torque control system  200  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention. 
     As illustrated in  FIG. 2A , this embodiment differs from that illustrated in  FIG. 1  in that the system  200  includes two five-phase AC machines  220 -A,  220 -B instead of two three-phase AC machine  120 -A,  120 -B. The two five-phase AC machines  220 -A,  220 -B are coupled to each other, and the five-phase PWM inverter module  110  is connected to one of the five-phase AC machines  220 -A, which is in turn coupled to the other one of the two five-phase AC machines  220 -B. The system  200  includes a first control loop  204  and a second control loop  205 . The first control loop  204  and the second control loop  205  are both coupled to the five-phase PWM inverter module  110  via synchronous to stationary block  203  and SVPWM block  209 . 
     The five-phase PWM inverter module  110  is coupled to the Space Vector (SV) PWM module  209 . The five-phase PWM inverter module  110  receives a first switching vector signal (Sa)  109 -A, a second switching vector signal (Sb)  109 -B, a third switching vector signal (Sc)  109 -C, a fourth switching vector signal (Sd)  109 -D, and a fifth switching vector signal (Se)  109 -E. The five-phase PWM inverter module  110  includes a first inverter pole  111  that outputs a first sinusoidal voltage (Va_*), a second inverter pole  112  that outputs a second sinusoidal voltage (Vb_*), a third inverter pole  113  that outputs a third sinusoidal voltage (Vc_*), a fourth inverter pole  114  that outputs a fourth sinusoidal voltage (Vd_*), and a fifth inverter pole  115  that outputs a fifth sinusoidal voltage (Ve_*). 
     The first five-phase AC machine  220 -A is coupled to the five-phase PWM inverter module  110  via the first inverter pole  111 , the second inverter pole  112 , the third inverter pole  113 , the fourth inverter pole  114  and the fifth inverter pole  115 . The first five-phase AC machine  220 -A generates output mechanical power (torque×speed) based on the first sinusoidal voltage (Va*), the second sinusoidal voltage (Vb*), the third sinusoidal voltage (Vc*), the fourth sinusoidal voltage (Vd*) and the fifth sinusoidal voltage (Ve*). In addition, a first shaft position output (θ_r 1 )  121 -A can be measured from the first five-phase AC machine  220 -A. The first five-phase AC machine  220 -A also includes a first output link (a 1 )  222  that outputs a first output voltage, a second output link (b 1 )  224  that outputs a second output voltage, a third output link (c 1 )  225  that outputs a third output voltage, a fourth output link (d 1 )  226  that outputs a fourth output voltage, and a fifth output link (e 1 )  227  that outputs a fifth output voltage. Each output link (a 1  . . . e 1 ) is coupled to a motor winding of the second five-phase AC machine  220 -B so that the second five-phase AC machine  220 -B is coupled to the first five-phase AC machine  220 -A via the first output link (a 1 )  222 , the second output link (b 1 )  224 , the third output link (c 1 )  225 , the fourth output link (d 1 )  226 , and the fifth output link (e 1 )  227 . 
     The second five-phase AC machine  220 -B outputs its own mechanical power output based on voltage at output links  222  . . .  227 . Links (a 2  . . . e 2 ) that are coupled together to form a star connection in second five-phase AC machine  220 -B. The shaft is part of each machine, the machine function is convert electrical power to mechanical power or vice-versa. The second five-phase AC machine  220 -B outputs a second shaft position output (θ_r 2 )  121 -B. 
     As in the first embodiment described with reference to  FIG. 1B , the first control loop  204  includes a first torque-to-current mapping module  140 -A, a second summing junction  152 -A, a third summing junction  162 -A, a fourth summing junction  154 -A, a fifth summing junction  164 -A, a first current controller module  170 -A, and a first modulation index computation module  175 -A, as illustrated in  FIG. 2B . Likewise, as illustrated in  FIG. 2C , the second control loop  205  includes a second torque-to-current mapping module  140 -B, a sixth summing junction  152 -B, a seventh summing junction  162 -B, an eighth summing junction  154 -B, a ninth summing junction  164 -B, a second current controller module  170 -B, and a second modulation index computation module  175 -B. Each of these junctions and modules operates as described with reference to  FIG. 1  and for sake of brevity the description of their operation will not be described here again. Moreover, the current command adjustment module  106  operates in the same manner as in the first embodiment ( FIGS. 1A-D ), and for sake of brevity, the operation of the current command adjustment module  106  will not be repeated here. 
     The embodiment of  FIG. 2A  also differs from the embodiment illustrated in  FIG. 1A  in that the first control loop  204  and the second control loop  205  of the system  200  share a stationary-to-synchronous conversion module  231 , and a synchronous-to-stationary conversion module  203 . Operation of these modules will now be described. 
     The stationary-to-synchronous conversion module  231  is coupled to the five-phase PWM inverter module  110  so that it receives a first resultant stator current (I_as)  122 , a second resultant stator current (I_bs)  123 , a third resultant stator current (I_cs)  124 , a fourth resultant stator current (I_ds)  126 , a fifth resultant stator current (I_es)  127 , a first shaft position output (θ_r 1 )  121 -A, and a second shaft position output (θ_r 2 ). The stationary-to-synchronous conversion module  231  is designed to convert these stator currents  122 ,  123 ,  124 ,  126 ,  127  to generate current feedback signals  132 -A,  132 -B,  134 -A,  134 -B. In particular, the stationary-to-synchronous conversion module  231  generates a first feedback d-axis current signal (Ids_e_ 1 )  132 -A, a first feedback q-axis current signal (Iqs_e_ 1 )  134 -A, a second feedback d-axis current signal (Ids_e_ 1 )  132 -B and a second feedback q-axis current signal (Iqs_e_ 1 )  134 -B, based on the first resultant stator current (I_as)  122 , the second resultant stator current (I_bs)  123 , the third resultant stator current (I_cs)  124 , the fourth resultant stator current (I_ds)  126 , the fifth resultant stator current (I_es)  127 , the first shaft position output (θ_r 1 )  121 -A, and the second shaft position output (θ_r 2 ) by using equations (1) through (3) below. 
     
       
         
           
             
               
                 
                   
                     
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     The synchronous-to-stationary conversion module  203  receives the first d-axis voltage command signal (Vds_e*_ 1 )  172 -A, the first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A, the second d-axis voltage command signal (Vds_e*_ 1 )  172 -B, the second q-axis voltage command signal (Vqs_e*_ 1 )  174 -B, the first shaft position output (θ_r 1 )  121 -A and the second shaft position output (θ_r 2 )  121 -B. Using these inputs and equations (1), (2) and (4) above, the synchronous-to-stationary conversion module  203  generates a first sinusoidal voltage command (Va)  103 -A 1 , a second sinusoidal voltage command (Vb)  103 -A 2 , a third sinusoidal voltage command (Vc)  103 -A 3 , a fourth sinusoidal voltage command (Vd)  103 -A 4 , and a fifth sinusoidal voltage command (Ve)  103 -A 5 . 
     The Space Vector (SV) PWM module  209  is coupled to the synchronous-to-stationary conversion module  203  and receives the first sinusoidal voltage command (Va)  103 -A 1 , the second sinusoidal voltage command (Vb)  103 -A 2 , the third sinusoidal voltage command (Vc)  103 -A 3 , the fourth sinusoidal voltage command (Vd)  103 -A 4 , and the fifth sinusoidal voltage command (Ve)  103 -A 5 . Based on these inputs, the SV PWM module  209  generates a first switching vector signal (Sa)  109 -A, a second switching vector signal (Sb)  109 -B, a third switching vector signal (Sc)  109 -C, a fourth switching vector signal (Sd)  109 -D, and a fifth switching vector signal (Se)  109 -E. 
       FIGS. 3A-3D  illustrate block diagrams of a torque control system  300  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention. 
     As illustrated in  FIG. 3A , the system  300  comprises a first control loop  304 , a second control loop  305 , the five-phase PWM inverter module  110 , a first three-phase AC machine  120 -A coupled to the five-phase PWM inverter module  110 , a second three-phase AC machine  120 -B coupled to the five-phase PWM inverter module  110 , and a voltage boost command control loop  306  coupled to the first control loop  304  and the second control loop  305 . The three-phase AC machines are three-phase AC powered motors. 
     The five-phase PWM inverter module  110  is coupled to SVPWM module  108 . The SVPWM module  108  is coupled to the first control loop  304  and the second control loop  305  such that the SVPWM module  108  receives modulation voltage commands Va* . . . Ve*, which are compared with a carrier to generate switching vector signals Sa . . . Se  109 . The five-phase PWM inverter module  110  receives switching vector signals  109  and generates sinusoidal voltage signals. In the particular embodiment, the five-phase PWM inverter module  110  receives a first switching vector signal (Sa)  109 -A, a second switching vector signal (Sb)  109 -B, a third switching vector signal (Sc)  109 -C, a fourth switching vector signal (Sd)  109 -D, and a fifth switching vector signal (Se)  109 -E. The five-phase PWM inverter module  110  includes a plurality of inverter poles including a first inverter pole  111  that outputs a first sinusoidal voltage (Va_*), a second inverter pole  112  that outputs a second sinusoidal voltage (Vb_*), a third inverter pole  113  that outputs a third sinusoidal voltage (Vc_*), a fourth inverter pole  114  that outputs a fourth sinusoidal voltage (Vd_*), and a fifth inverter pole  115  that outputs a fifth sinusoidal voltage (Ve_*). 
     The first three-phase AC machine  120 -A is coupled to the five-phase PWM inverter module  110  via the first inverter pole  111 , the second inverter pole  112  and the third inverter pole  113 . The first three-phase AC machine  120 -A generates mechanical power (torque×speed) and a first shaft position output (θ_r 1 ) based on the first sinusoidal voltage (Va_*), the second sinusoidal voltage (Vb_*) and the third sinusoidal voltage (Vc_*). 
     The second three-phase AC machine  120 -B is coupled to the five-phase PWM inverter module  110  via the third inverter pole  113 , the fourth inverter pole  114  and the fifth inverter pole  115 . In other words, the second three-phase AC machine  120 -B and the first three-phase AC machine  120 -A share the third inverter pole  113 . The second three-phase AC machine  120 -B generates mechanical power (torque×speed) and a second shaft position output (θ_r 2 ) based on the third sinusoidal voltage (Vc_*), the fourth sinusoidal voltage (Vd_*) and the fifth sinusoidal voltage (Ve_*). 
     As in the embodiment described with respect to  FIG. 1A , the five-phase PWM inverter module  110  can be used to control two three-phase AC machines  120 . However, this embodiment differs from that illustrated in  FIG. 1A  since the system  300  in  FIG. 3A  further includes a boost converter  340  coupled to the five-phase PWM inverter module  110  so that a DC input voltage (Vdc)  139  can be “boosted” or increased to a boosted DC input voltage (Vdc_high)  330  when the two three-phase AC machines  120  require additional voltage that exceeds the DC input voltage (Vdc)  139 . The boosted DC input voltage (Vdc_high)  330  can be provided to the five-phase PWM inverter module  110  when the boost converter  340  coupled to the five-phase PWM inverter module  110  receives a boost command signal (VBoost_command)  320 . The five-phase PWM inverter module  110  can then use the boosted DC input voltage (Vdc_high)  330  to provide sinusoidal voltages (Va_* . . . Ve_*) that have an increased voltage to the two three-phase AC machines  120 . As will be explained in greater detail below, the voltage boost command control loop  306  receives a first modulation index (Mod. Index  1 )  177 -A and a second modulation index (Mod. Index  2 )  177 -B from the first control loop  304  and the second control loop  305  and generates a modulation index feedback signal input  179  based on the first modulation index (Mod. Index  1 )  177 -A and the second modulation index (Mod. Index  2 )  177 -B. 
     Prior to describing the operation of the voltage boost command control loop  306 , operation of the first control loop  304  and the second control loop  305  will be described. This embodiment differs from that illustrated in  FIGS. 1B and 1C  since the first control loop  304  and the second control loop  305  of system  300  are somewhat simplified and use fewer summing junctions, as will now be described below. 
     As illustrated in  FIG. 3B , the first control loop  304  includes a first stationary-to-synchronous conversion module  130 -A, a first torque-to-current mapping module  140 -A, a summing junction  152 -A, a summing junction  154 -A, a first current controller module  170 -A, a first modulation index computation module  175 -A, and a first synchronous-to-stationary conversion module  102 -A. Operation of the first control loop  304  will now be described. 
     The first stationary-to-synchronous conversion module  130 -A and the first torque-to-current mapping module  140 -A operate in the same manner described above with respect to  FIG. 1  and for sake of brevity their respective operation will not be described again. 
     In this embodiment, upon receiving the first d-axis current command signal (Ids_e*_ 1 )  142 -A and the first feedback d-axis current signal (Ids_e_ 1 )  132 -A, the summing junction  152 -A subtracts the first feedback d-axis current signal (Ids_e_ 1 )  132 -A from the first d-axis current command signal (Ids_e*_ 1 )  142 -A to generate a first error d-axis current signal (Idserror_e_ 1 )  166 -A. Similarly, upon receiving the first q-axis current command signal (Iqs_e*_ 1 )  144 -A and the first feedback q-axis current signal (Iqs_e_ 1 )  134 -A, the summing junction  154 -A subtracts the first feedback q-axis current signal (Iqs_e_ 1 )  134 -A from the first q-axis current command signal (Iqs_e*_ 1 )  144 -A to generate a first error q-axis current signal (Iqserror_e_ 1 )  168 -A. 
     The first current controller module  170 -A receives the first error d-axis current signal (Idserror_e_ 1 )  166 -A and the first error q-axis current signal (Iqserror_e_ 1 )  168 -A and uses these signals to generate a first d-axis voltage command signal (Vds_e*_ 1 )  172 -A and a first q-axis voltage command signal (Vqs_e*_ 1 )  174 -A. 
     The first modulation index computation module  175 -A, and the first synchronous-to-stationary conversion module  102 -A operate in the same manner described above with respect to  FIG. 1  and for sake of brevity their respective operation will not be described again. 
     As illustrated in  FIG. 3C , the second control loop  305  includes similar blocks or modules as the first control loop  304 . The second control loop  305  includes a second stationary-to-synchronous conversion module  130 -B, a second torque-to-current mapping module  140 -B, a summing junction  152 -B, summing junction  154 -B, a second current controller module  170 -B, a second modulation index computation module  175 -B, and a second synchronous-to-stationary conversion module  102 -B. As will now be described, the second control loop  305  operates in a similar manner as the first control loop  304 . 
     The second stationary-to-synchronous conversion module  130 -B, and the second torque-to-current mapping module  140 -B operate in the same manner described above with respect to  FIG. 1  and for sake of brevity their respective operation will not be described again. 
     The summing junction  152 -B receives the second d-axis current command signal (Ids_e*_ 2 )  142 -B and the second feedback d-axis current signal (Ids_e_ 1 )  132 -B, and subtracts the second feedback d-axis current signal (Ids_e_ 1 )  132 -B from the second d-axis current command signal (Ids_e*_ 2 )  142 -B to generate a second error d-axis current signal (Idserror_e_ 2 )  166 -B. 
     The summing junction  154 -B receives the second q-axis current command signal (Iqs_e*_ 2 )  144 -B and the second feedback q-axis current signal (Iqs_e_ 2 )  134 -B, and subtracts the second feedback q-axis current signal (Iqs_e_ 2 )  134 -B from the second q-axis current command signal (Iqs_e*_ 2 )  144 -B to generate a second error q-axis current signal (Iqserror_e_ 2 )  168 -B. 
     The second current controller module  170 -B receives the second error d-axis current signal (Idserror_e_ 2 )  166 -B and the second error q-axis current signal (Iqserror_e_ 2 )  168 -B, and generates a second d-axis voltage command signal (Vds_e*_ 1 )  172 -B and a second q-axis voltage command signal (Vqs_e*_ 1 )  174 -B. 
     The second modulation index computation module  175 -B, and the second synchronous-to-stationary conversion module  102 -B operate in the same manner described above with respect to  FIG. 1  and for sake of brevity their respective operation will not be described again. 
     Operation of the voltage boost command control loop  306  will now be described with reference to  FIG. 3D . As illustrated in  FIG. 3D , the voltage boost command control loop  306  includes a summing junction  180 , a voltage controller  312 , and a negative limiter module  360 . The voltage boost command control loop  306  operates as follows. The summing junction  180  receives a modulation index reference signal input  101  and a modulation index feedback signal input  179 , and subtracts the modulation index reference signal input  101  from the modulation index feedback signal input  179  from to generate a modulation index error signal  181 . The voltage controller  312  receives the modulation index error signal  181 , and generates a first output command signal  186  based on the modulation index error signal  181  using a Proportional-Integral (PI) controller. The positive limiter module  316  receives the first output command signal  186 , and allows the first output command signal  186  to pass when it is in the range from zero to a positive value. The output of the positive limiter module  316  becomes the voltage boost command signal (V_Boost_Cmd)  320  based on the first output command signal  186 . 
     When the voltage boost command signal (V_Boost_Cmd)  320  is generated by the voltage command controller  310 , it is supplied to the boost converter  340 . When the voltage boost command signal (V_Boost_Cmd)  320  received by the boost converter  340  is equal to zero, the boost converter provides the normal DC input voltage (Vdc)  139  to the five-phase PWM inverter module  110 . When the two three-phase AC machines  120  require additional voltage that exceeds the DC input voltage (Vdc)  139  required to meet a combined target mechanical power required by the two three-phase AC machines  120 , the voltage command controller  310  will generate the voltage boost command signal (V_Boost_Cmd)  320  that controls the boost converter  340  such that the boost converter  340  generates the new boosted DC input voltage (Vdc_high) in response to the voltage boost command signal (V_Boost_Cmd)  320  that has a value greater than the normal DC input voltage (Vdc)  139 . When the voltage boost command signal (V_Boost_Cmd)  320  received by the boost converter  340  is greater than zero, it increases or “boosts” the DC input voltage (Vdc)  139  and provides a boosted DC input voltage (Vdc_high)  330  to the five-phase PWM inverter module  110 . The five-phase PWM inverter module  110  can then use the boosted DC input voltage (Vdc_high)  330  to provide sinusoidal voltages (Va_* . . . Ve_*) that have an increased voltage to the two three-phase AC machines  120 . 
     Thus, the five-phase PWM inverter module  110  receives the switching vector signals  109  and the boosted DC input voltage (Vdc_high)  330 , which can be equal to the normal DC input voltage (Vdc)  139  or higher, and uses it to generate sinusoidal voltage waveforms on links  111 - 115  that drive the first three-phase AC machines  120 -A,  120 -B at varying speeds. 
     Although not illustrated in  FIG. 3A , the system  300  also includes a gear coupled to and driven by the first three-phase AC machine  120 -A shaft and the second three-phase AC machine  120 -B shaft. 
       FIGS. 4A-4C  illustrate block diagrams of a torque control system  400  architecture implemented in a motor drive system of a hybrid/electric vehicle (HEV) according to one exemplary implementation of the present invention. 
     As illustrated in  FIG. 4A , this embodiment differs from that illustrated in  FIG. 3A  in that the system  400  includes two five-phase AC machines  220 -A,  220 -B instead of two three-phase AC machines  120 -A,  120 -B. The two five-phase AC machines  220 -A,  220 -B are coupled to each other, and the five-phase PWM inverter module  110  is connected to one of the five-phase AC machines  220 -A, which is in turn coupled to the other one of the five-phase AC machines  220 -B. The system  400  includes a first control loop  304  and a second control loop  305 . The first control loop  304  and the second control loop  305  are both coupled to the five-phase PWM inverter module  110 . The embodiment of  FIG. 4A  also differs from the embodiment illustrated in  FIG. 3A  in that the first control loop  304  and the second control loop  305  of the system  400  share a stationary-to-synchronous conversion module  231 , and a synchronous-to-stationary conversion module  203 . Operation of these modules is the same as described above with respect to  FIGS. 2A-2C  and for sake of brevity their respective operation will not be described again. 
     The five-phase PWM inverter module  110  is coupled to the Space Vector (SV) PWM module  209 . The five-phase PWM inverter module  110  receives a first switching vector signal (Sa)  109 -A, a second switching vector signal (Sb)  109 -B, a third switching vector signal (Sc)  109 -C, a fourth switching vector signal (Sd)  109 -D, and a fifth switching vector signal (Se)  109 -E. The five-phase PWM inverter module  110  includes a first inverter pole  111  that outputs a first sinusoidal voltage (Va_*), a second inverter pole  112  that outputs a second sinusoidal voltage (Vb_*), a third inverter pole  113  that outputs a third sinusoidal voltage (Vc_*), a fourth inverter pole  114  that outputs a fourth sinusoidal voltage (Vd_*), and a fifth inverter pole  115  that outputs a fifth sinusoidal voltage (Ve_*). 
     The first five-phase AC machine  220 -A is coupled to the five-phase PWM inverter module  110  via the first inverter pole  111 , the second inverter pole  112 , the third inverter pole  113 , the fourth inverter pole  114  and the fifth inverter pole  115 . The first five-phase AC machine  220 -A generates output mechanical power (torque×speed) based on the first sinusoidal voltage (Va_*), the second sinusoidal voltage (Vb_*), the third sinusoidal voltage (Vc_*), the fourth sinusoidal voltage (Vd_*) and the fifth sinusoidal voltage (Ve_*). In addition, a first shaft position output (θ_r 1 )  121 -A can be measured from the first five-phase AC machine  220 -A. The first five-phase AC machine  220 -A also includes a first output link (a 1 )  222  that outputs a first output voltage, a second output link (b 1 )  224  that outputs a second output voltage, a third output link (c 1 )  225  that outputs a third output voltage, a fourth output link (d 1 )  226  that outputs a fourth output voltage, and a fifth output link (e 1 )  227  that outputs a fifth output voltage. Each output link (a 1  . . . e 1 ) is coupled to a motor winding of the second five-phase AC machine  220 -B so that the second five-phase AC machine  220 -B is coupled to the first five-phase AC machine  220 -A via the first output link (a 1 )  222 , the second output link (b 1 )  224 , the third output link (c 1 )  225 , the fourth output link (d 1 )  226 , and the fifth output link (e 1 )  227 . 
     The second five-phase AC machine  220 -B outputs its own output mechanical power based on voltage at output links  222  . . .  227 . Links (a 2  . . . e 2 ) that are coupled together to form a star connection in machine  220 -B. The second five-phase AC machine  220 -B outputs a second shaft position output (θ_r 2 )  121 -B. 
     As in the third embodiment described with reference to  FIG. 3B , the first control loop  304  includes a first torque-to-current mapping module  140 -A, a summing junction  152 -A, a summing junction  154 -A, a first current controller module  170 -A, and a first modulation index computation module  175 -A, as illustrated in  FIG. 4B . Likewise, as illustrated in  FIG. 4C , the second control loop  305  includes a second torque-to-current mapping module  140 -B, a summing junction  152 -B, a summing junction  154 -B, a second current controller module  170 -B, and a second modulation index computation module  175 -B. Each of these junctions and modules operates as described with reference to  FIGS. 3B and 3C  and for sake of brevity the description of their operation will not be described here again. Moreover, the voltage boost command control loop  306  operates in the same manner as in the third embodiment ( FIG. 3D ), and for sake of brevity, the operation of the voltage boost command control loop  306  will not be repeated here. 
     Some of the embodiments and implementations are described above in terms of functional and/or logical block components and various processing steps. However, it should be appreciated that such block components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment of a system or a component may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments described herein are merely exemplary implementations. 
     In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.