Patent Publication Number: US-2023139350-A1

Title: Controller for electrified vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-180202 filed on Nov. 4, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     A technology disclosed in the specification relates to a controller for an electrified vehicle. More specifically, the technology relates to a controller that controls a DC-DC converter in an electrified vehicle in which a motor generator used to drive a wheel is connected to a battery via the DC-DC converter. 
     2. Description of Related Art 
     A controller described in Japanese Unexamined Patent Application Publication No. 2017-051065 (JP 2017-051065 A) acquires a target value of reactor current flowing through a reactor of a DC-DC converter. The controller acquires a measured value of the reactor current. The controller executes feedback control in accordance with a deviation of the measured value from the acquired target value of the reactor current. 
     When the controller executes feedback control, the controller further determines whether the frequency of variations in the electric power of a motor generator of an electrified vehicle falls within resonant frequencies at which resonance occurs in a circuit of a DC-DC converter. The controller changes a feedback gain in accordance with whether the frequency of electric power variations is included in the resonant frequency. When the frequency of variations in the electric power falls within the resonant frequencies, the controller changes the frequency of variations in the electric power to a frequency outside the resonant frequencies by changing the feedback gain. Thus, it is possible to reduce occurrence of resonance in the circuit of the DC-DC converter. 
     SUMMARY 
     A reactor current flows through the reactor of the DC-DC converter in a direction that changes in accordance with an output direction of the DC-DC converter. In the controller described in JP 2017-051065 A, the feedback gain is similarly determined regardless of the direction of reactor current. However, the inventors found that harmful disturbance characteristics in feedback control changed depending on the direction of reactor current. The specification provides a technology for making it possible to accurately control the operation of a DC-DC converter by addressing disturbance characteristics that change in accordance with the direction of reactor current. 
     A controller disclosed in the specification is implemented in an electrified vehicle in which a motor generator used to drive a wheel is connected to a battery via a DC-DC converter. The controller is configured to be able to execute a process of acquiring a target value of output voltage of the DC-DC converter, a process of acquiring a measured value of the output voltage of the DC-DC converter, a process of acquiring a direction of reactor current flowing through a reactor of the DC-DC converter, and a process of executing feedback control over an operation of the DC-DC converter in accordance with a deviation of the measured value from the target value of the output voltage. The process of executing feedback control may include a process of determining a feedback gain that varies with the direction of the reactor current. 
     With the above configuration, the controller determines a feedback gain that varies with the direction of reactor current. Thus, it is possible to accurately control the operation of the DC-DC converter by addressing disturbance characteristics that change in accordance with the direction of reactor current. 
     The details of the technology disclosed in the specification and further improvement will be described in “Detailed Description of Embodiments”. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    schematically shows a circuit diagram of an electrified vehicle that includes a controller of an embodiment; 
         FIG.  2    is a flowchart of a process that the controller executes; and 
         FIG.  3    is a gain map that the controller uses to determine the value of a feedback gain. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In one embodiment of the technology, the reactor current may flow through the reactor in a first direction when electric power is supplied from the battery to the motor generator, and the reactor current may flow through the reactor in a second direction different from the first direction when electric power is supplied from the motor generator to the battery. In this case, in the process of determining the feedback gain, when the reactor current flows in the first direction with a first magnitude, the feedback gain may be determined at a first value, and, when the reactor current flows in the second direction with the first magnitude, the feedback gain may be determined at a second value greater than the first value. When electric power is supplied from the battery to the motor generator, that is, when the reactor current flows in the first direction, motoring for driving the motor generator is performed by stepping up the electric power of the battery by using the DC-DC converter. When electric power is supplied from the motor generator to the battery, that is, when the reactor current flows in the second direction, regeneration for charging the battery is performed by stepping down the electric power generated by the motor generator by using the DC-DC converter. The inventors found that, when regeneration was performed, the influence caused by disturbance during regeneration was reduced by using a feedback gain greater than a feedback gain during motoring. With such a configuration, it is possible to reduce the influence caused by disturbance during regeneration by using a feedback gain having the second value. 
     In one embodiment of the technology, the controller may be configured to be able to further execute a process of acquiring a measured value of the reactor current. In this case, in the process of determining the feedback gain, when the magnitude of the reactor current falls within a predetermined range and the reactor current flows in the second direction, the feedback gain may be determined so as to increase as the magnitude of the reactor current increases. In another embodiment, the feedback gain may be determined so as to change in a stepwise manner. 
     In one embodiment of the technology, in the process of determining the feedback gain, when the magnitude of the reactor current falls within a predetermined range and the reactor current flows in the first direction, the feedback gain may be determined at the same value regardless of the magnitude of the reactor current. In another embodiment, when the reactor current flows in the first direction, the feedback gain may be determined so as to reduce as the magnitude of the reactor current increases. 
     In one embodiment of the technology, in the process of determining the feedback gain, when the reactor current flows in the second direction, the feedback gain may be determined so as to increase for the reactor current with the same magnitude as the target value or the measured value reduces. The inventors particularly found that disturbance easily changed in a region in which the target value or the measured value was relatively small. With such a configuration, the controller is able to reduce the influence caused by disturbance that occurs in a region in which the target value or the measured value is relatively low. 
     In one embodiment of the technology, the controller may include a memory configured to store a map or a relational expression describing a relationship between a direction and magnitude of the reactor current and the feedback gain. With such a configuration, for example, in comparison with the case where the feedback gain is determined at a predetermined value when the magnitude of the reactor current exceeds a predetermined threshold, it is possible to minutely determine the feedback gain. 
     In one embodiment of the technology, the controller may be configured to be able to further execute a process of acquiring a target value of the reactor current. In this case, in the process of executing the feedback control, an operation of the DC-DC converter may be subjected to feedback control in accordance with a deviation of the measured value from the target value of the reactor current. With such a configuration, in comparison with a configuration that feedback control over the DC-DC converter is executed based on only a deviation of voltage, it is possible to increase the response of feedback control. 
     EMBODIMENT 
     A controller of an embodiment will be described with reference to the accompanying drawings. First, an electrified vehicle  100  equipped with a controller  20  of the embodiment will be described with reference to  FIG.  1   .  FIG.  1    mainly shows a circuit related to a drive-train of the electrified vehicle  100 . The electrified vehicle  100  includes a motor generator  2 , an inverter  4 , a high-voltage capacitor  6 , a high voltage sensor  8 , a DC-DC converter  10 , a low-voltage capacitor  36 , a low voltage sensor  38 , a system main relay  34 , a battery  32 , and the controller  20 . The electrified vehicle  100  runs by supplying the motor generator  2  with electric power stored in the battery  32 . In other words, the motor generator  2  drives a wheel (not shown) of the electrified vehicle  100 . The motor generator  2  also functions as a generator that generates electric power by using torque during braking. Electric power generated by the motor generator  2  is charged into the battery  32 . The motor generator  2  is connected to the battery  32  via the DC-DC converter  10 . 
     Each of the capacitors  6 ,  36  is a so-called smoothing capacitor and is provided to stabilize the voltage of the circuit. The high voltage sensor  8  measures the voltage between a high-voltage positive electrode  42   p  and a high-voltage negative electrode  42   n . The low voltage sensor  38  measures the voltage between a low-voltage positive electrode  43   p  and a low-voltage negative electrode  43   n.    
     The DC-DC converter  10  includes two switching elements  14 ,  16 , a current sensor  18 , and a reactor  19 . The DC-DC converter  10  changes the voltage by turning on or off the two switching elements  14 ,  16 . A technology that the DC-DC converter  10  changes the voltage is known, so the description thereof is omitted here. 
     The controller  20  is a computer that includes a memory  22 . Although not shown in the drawing, the controller  20  acquires running information related to running of the electrified vehicle  100 , including accelerator operation amount information, brake depression information, vehicle speed information, and the like. The controller  20  controls the DC-DC converter  10  based on the acquired running information. When an accelerator is depressed by a driver of the electrified vehicle  100  to drive the motor generator  2  at higher speed, the controller  20  supplies electric power from the battery  32  to the motor generator  2 . In this case, the controller  20  executes so-called motoring control. Thus, the DC-DC converter  10  converts electric power output from the battery  32  to high-voltage power and supplies the high-voltage power to the motor generator  2 . On the other hand, when a brake is depressed by the driver of the electrified vehicle  100  to perform regeneration by using the torque of the motor generator  2 , the controller  20  supplies electric power from the motor generator  2  to the battery  32 . In this case, the controller  20  executes so-called regenerative control. Thus, the DC-DC converter  10  converts electric power generated by the motor generator  2  to low-voltage power and supplies the low-voltage power to the battery  32 . 
     The controller  20  acquires a measured value of the current sensor  18  of the DC-DC converter  10 . Thus, the controller  20  acquires a current flowing through the reactor  19  (hereinafter, the current may be referred to as reactor current IL) from the current sensor  18 . As shown in  FIG.  1   , when the controller  20  executes motoring control, the reactor current IL flows in a first direction D 1 . When the controller  20  executes regenerative control, the reactor current IL flows in a second direction D 2 . 
     A process that the controller  20  executes to control the DC-DC converter  10  will be described with reference to  FIG.  2   . The controller  20  constantly executes the process of  FIG.  2    during running of the electrified vehicle  100 . Here, a process that the controller  20  executes during motoring control will be described. The controller  20  acquires a target value Vt of output voltage of the DC-DC converter  10  by calculating the target value Vt from the running information (S 2 ). The controller  20  acquires a measured value Vm of output voltage of the DC-DC converter  10  from the high voltage sensor  8  (see  FIG.  1   ) (S 4 ). Subsequently, the controller  20  acquires a measured value ILm of the reactor current IL from the current sensor  18  (see  FIG.  1   ) (S 6 ). The controller  20  executes feedback control over the operation of the DC-DC converter  10  such that the output voltage of the DC-DC converter  10  is equal to the target value Vt. Although not limited, proportional-plus-integral control is adopted for feedback control in the present embodiment, and the operation of the DC-DC converter  10  is controlled in accordance with an instantaneous value of a deviation of the measured value Vm from the target value Vt and an integrated value obtained by integrating the deviation. Alternatively, feedback control over the DC-DC converter  10  may be executed based on only an instantaneous value of the deviation, as in the case of so-called proportional control. Hereinafter, for the sake of clear description, a proportional term (feedback control based on an instantaneous value of the deviation) in proportional-plus-integral control will be mainly described. 
     The controller  20  determines a feedback gain GV based on the measured value ILm of the reactor current IL, acquired in the process of S 6  (S 8 ). The details that the controller  20  determines the feedback gain GV will be described later with reference to  FIG.  3   . 
     The controller  20  determines a first operation amount (Vt−Vm)×GV for the DC-DC converter  10  by multiplying a deviation between the target value Vt acquired in the process of S 2  and the measured value Vm acquired in the process of S 4  by the feedback gain GV determined in the process of S 8  (S 10 ). 
     The controller  20  acquires a target value ILt of the reactor current IL by calculating the target value ILt from the target value Vt of the output voltage (S 12 ). Subsequently, the controller  20  determines a feedback gain GI based on the measured value ILm of the reactor current IL, acquired in the process of S 6  (S 14 ). Although not shown in the drawing, the controller  20  stores a table for a feedback gain GI associated with a target value ILt and a measured value ILm in the memory  22  (see  FIG.  1   ). The controller  20  determines the value of the feedback gain GI from the table in the memory  22 . 
     The controller  20  determines a second operation amount (ILt−ILm)×GI for the DC-DC converter  10  by multiplying a deviation of the target value ILt acquired in the process of S 12  from the measured value ILm acquired in the process of S 6  by the feedback gain GI determined in the process of S 14  (S 16 ). 
     The controller  20  determines a duty ratio for turning on or off the switching elements  14 ,  16  (see  FIG.  1   ) of the DC-DC converter  10  by using the first operation amount (Vt−Vm)×GV calculated in S 10  and the second operation amount (ILt−ILm)×GI calculated in S 16  (S 20 ). In this way, the controller  20  executes feedback control over the operation of the DC-DC converter  10 . 
     When regenerative control is executed, the controller  20  acquires the measured value Vm from the low voltage sensor  38  in the process of S 4  and executes feedback control over the operation of the DC-DC converter  10 . 
     A process that the controller  20  determines the feedback gain GV in the process of S 8  of  FIG.  2    will be described with reference to  FIG.  3   .  FIG.  3    shows a gain map M 1  stored in the memory  22  of the controller  20 . The gain map M 1  is a map that describes the value of the feedback gain GV used to reduce disturbance, such as resonance, that occurs at the time of executing feedback control over the DC-DC converter  10  in the electrified vehicle  100  by measuring the disturbance. 
     As shown in  FIG.  3   , the gain map M 1  describes a relationship between a measured value ILm of the reactor current IL and a feedback gain GV for each measured value Vm of the output voltage, acquired in S 4  of  FIG.  2   . Therefore, in  FIG.  3   , the line type of a graph is changed for each measured value Vm. In a modification, the gain map M 1  may describe a relationship between a measured value ILm of the reactor current IL and a feedback gain GV for each target value Vt of the output voltage, acquired in S 2  of  FIG.  2   . 
     In the current sensor  18 , when the reactor current IL flows in the first direction D 1 , a measured value ILm is measured as a positive value. In the current sensor  18 , when the reactor current IL flows in the second direction D 2 , a measured value ILm is measured as a negative value. In other words, when the controller  20  executes motoring control, the measured value ILm is a positive value; whereas, when the controller  20  executes regenerative control, the measured value ILm is a negative value. In this way, the controller  20  is able to acquire the direction of the reactor current IL by acquiring the measured value ILm of the reactor current IL from the current sensor  18  and determining the sign of the measured value ILm. 
     When the controller  20  acquires the measured value ILm in the process of S 6  of  FIG.  2   , the controller  20  applies the acquired measured value ILm to the graph for the measured value Vm. When, for example, the measured value Vm acquired in S 4  of  FIG.  2    is 300 V indicated by the narrow dashed line, the reactor current IL flows in the first direction D 1 , and the measured value ILm is 100 A, the controller  20  determines the value of the feedback gain GV at a first value GV 1  from the gain map M 1 . On the other hand, when the measured value Vm is 300 V, the reactor current IL flows in the second direction D 2 , and the measured value ILm is −100 A, the controller  20  determines the value of the feedback gain GV at a second value GV 2  from the gain map M 1 . 
     As is understood from  FIG.  3   , the second value GV 2  is greater than the first value GV 1 . Even when the value of the reactor current IL is 100 A, the second value GV 2  that is determined when the reactor current IL flows in the second direction D 2  is different from the first value GV 1  that is determined when the reactor current IL flows in the first direction D 1 . With the existing technology, the value of the feedback gain GV does not depend on the direction of the reactor current IL, and is, for example, similarly determined based on the value of the reactor current IL. However, as shown in  FIG.  1   , the circuit in which the DC-DC converter  10  is disposed has an asymmetric structure between the motor generator  2  side and the battery  32  side. The inventors found that the harmful disturbance characteristics in feedback control could change depending on the direction of the reactor current IL. As shown in  FIG.  2    and  FIG.  3   , the controller  20  of the specification acquires the direction of the reactor current IL before determining the feedback gain GV and determines a feedback gain GV that varies with the direction. Thus, it is possible to accurately control the operation of the DC-DC converter  10  by addressing disturbance characteristics that change in accordance with the direction of the reactor current IL. 
     As shown in  FIG.  3   , in the region within a first range A 1  of the gain map M 1 , the feedback gain GV of which the measured value Vm is 300 V increases as the magnitude of the measured value ILm of the reactor current IL flowing in the second direction D 2  increases (that is, toward the left side in  FIG.  3   ). As a result, for example, a third value GV 3  that is determined when the measured value Vm is 300 V and the value of the measured value ILm is −150 A is greater than the second value GV 2 . 
     On the other hand, in the region within a second range A 2  of the gain map M 1 , regardless of the magnitude of the measured value ILm of the reactor current IL flowing in the first direction D 1 , the value of the feedback gain GV is held at the first value GV 1 . In the region within the second range A 2 , the graphs in the case where the measured values Vm are respectively 200 V, 300 V, 400 V, 500 V, and 600 V are shown so as to overlap one another. In other words, in the region within the second range A 2 , regardless of the magnitude of the measured value Vm, the value of the feedback gain GV is determined at the first value GV 1 . 
     In the region within the first range A 1  of the gain map M 1 , in a state where the measured value ILm of the reactor current IL is −100 A, the measured value Vm of the output voltage is 300 V, the feedback gain GV is determined at the second value GV 2 . However, in a state where the measured value ILm of the reactor current IL is the same −100 A, when the measured value Vm of the output voltage is 200 V, the feedback gain GV is determined at a fourth value GV 4 . As shown in  FIG.  3   , the fourth value GV 4  is greater than the second value GV 2 . Similarly, in a state where the measured value ILm of the same reactor current IL is −150 A, a fifth value GV 5  that is determined when the measured value Vm of the output voltage is 200 V is greater than the fourth value GV 4  that is determined when the measured value Vm of the output voltage is 300 V. In other words, when the reactor current IL flows in the second direction D 2 , the controller  20  determines the feedback gain GV such that the feedback gain GV increase as the measured value Vm of the output voltage decreases for the reactor current IL with the same magnitude. The inventors found that, particularly, in a region in which the measured value Vm of the output voltage is low, disturbance during regenerative control had a tendency to differ from disturbance during motoring control. The controller  20  determines the feedback gain GV such that the feedback gain GV increases as the measured value Vm of the output voltage decreases. Thus, it is possible to reduce the influence on feedback control due to disturbance during regenerative control in a region in which the measured value Vm of the output voltage is low. 
     The controller  20  executes not only feedback control over the operation of the DC-DC converter  10  based on a deviation of the output voltage but also feedback control over the operation of the DC-DC converter  10  based on a deviation of the reactor current IL as shown in S 12 , S 14 , S 16  of  FIG.  2   . Thus, in comparison with a configuration that feedback control based on only a deviation of the output voltage is executed, it is possible to execute feedback control over the operation of the DC-DC converter  10  more quickly. In other words, with such a configuration, it is possible to improve the response of feedback control. As a result, for example, it is possible to reduce the capacitance of each of the capacitors  6 ,  36 . 
     Specific examples of the technology disclosed in the specification have been described in detail; however, these are only illustrative and are not intended to limit the scope of the appended claims. The technology described in the appended claims also encompasses various modifications and changes from the specific examples illustrated above. Modifications of the above-described embodiment will be described below. 
     First Modification 
     In the above-described embodiment, the controller  20  determines the value of the feedback gain GV by using the gain map M 1  associated with an instantaneous value of a deviation of a measured value Vm of the output voltage from a target value Vt of the output voltage. In a modification, the controller  20  may store an additional gain map associated with an integrated value obtained by integrating a deviation of a measured value Vm from a target value Vt of the output voltage in the memory  22  and determine the value of the feedback gain GV by using the additional gain map in addition to the gain map M 1 . In other words, in the present modification, the value of the feedback gain GV may be determined by using a gain map in an integral term (feedback control based on an integrated value of a deviation) of proportional-plus-integral control. 
     Second Modification 
     A gain map that the controller  20  uses to determine the feedback gain GV is not limited to the gain map M 1 . The controller  20  may determine a feedback gain GV by using another gain map calculated based on the resonant frequencies of the configuration of the drive-train of the electrified vehicle  100  instead of the gain map M 1 . In this case, for example, in the other gain map, in a state where the measured value ILm of the reactor current IL is the same 100 A, when the reactor current IL flows in the second direction D 2  (that is, when regenerative control is executed), the feedback gain GV may be determined at the first value GV 1 . In this case, when the reactor current IL flows in the first direction D 1  (that is, when motoring control is executed), the feedback gain GV may be determined at the second value GV 2  greater than the first value GV 1 . In further another modification, the controller  20  may store a relational expression that describes the relationship between the direction and magnitude of a reactor current IL and a feedback gain GV in the memory  22  instead of the gain map M 1 . 
     Third Modification 
     The controller  20  may determine the feedback gain GV at a certain predetermined value when the direction of the reactor current IL is the first direction D 1  and determine the feedback gain GV at another predetermined value when the direction of the reactor current IL is the second direction D 2 . In other words, the controller  20  may determine the feedback gain GV regardless of a change in the magnitude of the reactor current IL. 
     Fourth Modification 
     In the gain map M 1 , in the first range A 1 , the feedback gain GV does not need to continuously change as shown by the graphs of  FIG.  3   . For example, the feedback gain GV may change in a stepwise manner. 
     Fifth Modification 
     The controller  20  may determine the same value of the feedback gain GV when the measured value ILm of the reactor current IL is the same regardless of the measured value Vm of the output voltage in the first range A 1 . 
     Sixth Modification 
     The controller  20  does not need to execute feedback control over the operation of the DC-DC converter  10  in accordance with a deviation of a measured value ILm of the reactor current IL from a target value ILt of the reactor current IL. In the present modification, the processes of S 12 , S 14 , and S 16  of  FIG.  2    may be omitted. 
     Seventh Modification 
     The controller  20  may, for example, acquire the direction of the reactor current IL from the output torque of the motor generator  2  instead of the measured value ILm of the reactor current IL, acquired from the current sensor  18 . In this case, the DC-DC converter  10  does not need to include the current sensor  18 . In further another modification, the current sensor  18  may be disposed between the DC-DC converter  10  and the system main relay  34 . 
     The technical elements described in the specification or the drawings exhibit technical usability solely or in various combinations and are not limited to combinations of the appended claims at the time of filing the application. The technology illustrated in the specification and drawings can achieve multiple purposes at the same time and has technical usability by achieving one of those purposes.