JP4829915B2 - DC / DC converter device, fuel cell vehicle, and control method of DC / DC converter device - Google Patents

Description

  The present invention includes a multi-phase DC / DC converter that is connected between two power devices and includes a plurality of switching elements, and a control device that controls a switching operation of the plurality of switching elements using a drive signal. The present invention relates to a DC / DC converter device, a fuel cell vehicle including the same, and a method for controlling the DC / DC converter device. More specifically, the present invention relates to a DC / DC converter device capable of controlling a cycle for calculating a duty in switching control using pulse frequency modulation (PFM), a fuel cell vehicle including the same, and a method for controlling the DC / DC converter device. .

  There is known a DC / DC converter that can be used by switching between two modulation methods of pulse width modulation (PWM) and pulse frequency modulation (PFM) (Patent Documents 1 and 2). There is also a DC / DC converter that uses only PFM (Patent Document 3). Furthermore, some DC / DC converters are called multiphase DC / DC converters that perform voltage conversion using a plurality of phase switching elements (Patent Document 4).

Japanese Patent Laid-Open No. 06-311736 JP 2003-219637 A JP 2004-194484 A JP 2004-357388 A

  In Patent Documents 1 to 3, a DC / DC converter having a single-phase switching element is described, and use of PFM in a multiphase DC / DC converter is not studied. In Patent Document 4, only the use of PWM is disclosed.

  The present invention has been made in view of such problems, and includes a DC / DC converter device that includes a multiphase DC / DC converter having a plurality of switching elements and can suitably use a PFM. It is an object of the present invention to provide a control method for a fuel cell vehicle and the DC / DC converter device.

A DC / DC converter device according to the present invention is connected between a first power device and a second power device, and includes a multiphase DC / DC converter including a plurality of switching elements, and an output voltage of the DC / DC converter. A control device that controls a switching operation of the plurality of switching elements using a drive signal for controlling the value to a target value , wherein the control device has a duty used for generating the drive signal. It has a duty calculation function to carry out the duty calculation process of calculating a PFM drive signal generating function to implement the PFM drive signal generating process for generating a pulse frequency modulation (PFM) of the drive signal based on the duty, and The duty calculation process is repeated at a period of time n times a certain switching period (n is an integer of 2 or more). To the duty calculation process, when the switching period is long, characterized in that it is repeated in the cycle of the (n-1) times or less of the time of the certain switching period.

  According to the present invention, in the switching control using the PFM, as the switching period becomes longer, the duty calculation process is performed corresponding to a smaller number of switching periods. For this reason, even when the switching cycle becomes long, the operation of the switching element can be controlled in the same cycle (time) as when the switching cycle is short, and the DC / DC converter can be controlled more suitably. .

  That is, since the duty is used for generating the drive signal, it is preferable that the period for calculating the duty (duty calculation period) corresponds to the switching period indicating the period for generating the drive signal. Further, in the configuration in which the duty of a plurality of switching elements is calculated collectively, when the switching cycle is the minimum value, one duty calculation process corresponds to two or more switching cycles due to the limitation of the processing capability of the control device. There is. However, since the switching period is changed in the PFM, if the duty calculation process is always associated with the same number of switching periods, the time from the calculation of the duty to the output of the drive signal becomes longer as the switching period becomes longer. turn into. For example, when calculating the duty for three consecutive switching cycles collectively, the time taken from the time of calculating the duty until the output of the drive signal corresponding to the duty of the third switching cycle is the first and second switching cycles. As the switching period corresponding to the duty becomes longer, it becomes longer. In the present invention, as the switching period becomes longer, the duty calculation process is performed in association with a smaller number of switching periods. For this reason, even when the switching period becomes long, the duty calculation period (time) can be kept short. As a result, even if the switching cycle becomes longer, it is possible to calculate the duty reflecting the latest state, and it is possible to control the DC / DC converter more suitably.

In addition to the PFM drive signal generation function , the control device has a PWM drive signal generation function for performing PWM drive signal generation processing for generating the drive signal by pulse width modulation (PWM) based on the duty, The PWM drive signal generation process is used when the duty calculated in the duty calculation process can secure the minimum on-time required to turn on each switching element, and when the minimum on-time cannot be secured, the PFM drive signal is used. It is preferable to use a generation process.

  The control device includes a storage unit that stores a maximum value of a duty calculation process cycle that is a time from the start of a certain duty calculation process to the start of the next duty calculation process, and calculates when using the PFM drive signal generation process It is preferable to compare the switching cycle corresponding to the duty and the maximum value of the duty calculation processing cycle, and determine the number of switching cycles corresponding to each duty calculation processing based on the comparison result.

  The first power device can be a power storage device, the second power device can be a fuel cell, and the control device can control the power drawn from the fuel cell by controlling the DC / DC converter. is there.

  The fuel cell vehicle according to the present invention includes the DC / DC converter device, and the power of the fuel cell and the power storage device is supplied to a drive motor. Thereby, since the fuel cell is operated efficiently, a vehicle with good fuel efficiency can be realized.

The DC / DC converter device control method according to the present invention includes a multiphase DC / DC converter that is connected between a first power device and a second power device and includes a plurality of switching elements, and the DC / DC A control device for controlling a switching operation of the plurality of switching elements using a drive signal for controlling an output voltage value of the converter to a target value, the method for controlling the DC / DC converter device, A duty calculating step of calculating a duty used for generating a signal; and a PFM switching step of generating the drive signal by pulse frequency modulation (PFM) based on the duty and switching the plurality of switching elements using the drive signal. When, wherein the duty calculation process, time period (n n times of a switching period Repeated at least an integer), further, the duty calculation process, increasing the switching period, characterized in that it is repeated in the cycle of the (n-1) times or less of the time of the certain switching period.

  According to the present invention, in the switching control using the PFM, as the switching period becomes longer, the duty calculation process is performed corresponding to a smaller number of switching periods. For this reason, even when the switching cycle becomes long, the operation of the switching element can be controlled in the same cycle (time) as when the switching cycle is short, and the DC / DC converter can be controlled more suitably. .

A. Hereinafter, a fuel cell vehicle equipped with an embodiment of a DC / DC converter device according to the present invention will be described with reference to the drawings.

1. Configuration of Fuel Cell Vehicle 20 (1) Overall Configuration FIG. 1 is a circuit diagram of a fuel cell vehicle 20 equipped with a DC / DC converter device 23 according to this embodiment. The fuel cell vehicle 20 basically includes a hybrid electric power device including a fuel cell 22 and a power storage device (battery) 24 that is an energy storage, and a current (electric power) from the hybrid electric power device. Is supplied between the driving motor 26 supplied through the inverter 34, the primary side 1S to which the battery 24 is connected, and the secondary side 2S to which the fuel cell 22 and the motor 26 (inverter 34) are connected. DC / DC converter device for conversion (hereinafter referred to as “VCU” (Voltage Control Unit). } 23. The rotation of the motor 26 is transmitted to the wheel 16 through the speed reducer 12 and the shaft 14.

(2) Fuel cell 22
The fuel cell 22 has, for example, a stack structure in which cells formed by sandwiching a solid polymer electrolyte membrane between an anode electrode and a cathode electrode from both sides are stacked. A hydrogen tank 28 and an air compressor 30 are connected to the fuel cell 22 by piping. Pressurized hydrogen in the hydrogen tank 28 is supplied to the anode of the fuel cell 22. Further, air is supplied to the cathode of the fuel cell 22 by the air compressor 30. A power generation current If is generated by an electrochemical reaction between hydrogen (fuel gas), which is a reaction gas, and air (oxidant gas) in the fuel cell 22. The generated current If is supplied to the inverter 34 and / or the DC / DC converter 36 of the VCU 23 via a current sensor 32 and a diode (also referred to as a disconnect diode) 33.

(3) Battery 24
As the battery 24 connected to the primary side 1S, for example, a lithium ion secondary battery, a nickel hydride secondary battery, or a capacitor can be used. In this embodiment, a lithium ion secondary battery is used. The battery 24 supplies the motor current Im to the inverter 34 through the DC / DC converter 36 of the VCU 23.

(4) Inverter 34
The inverter 34 performs DC / AC conversion and supplies the motor current Im to the motor 26, while the motor current Im after AC / DC conversion accompanying the regenerative operation is transferred from the secondary side 2 </ b> S to the primary side through the DC / DC converter 36. Supply to 1S. In this case, the primary voltage V1 obtained by converting the regenerative voltage or the secondary voltage V2 that is the power generation voltage Vf of the fuel cell 22 into a low voltage by the DC / DC converter 36 charges the battery 24 as the battery current Ibat.

(5) VCU23
The VCU 23 includes a DC / DC converter 36 and a converter control unit 54 that drives and controls the DC / DC converter 36.

  The DC / DC converter 36 includes an upper arm composed of a switching element such as an IGBT between the battery 24 (first power device) and the second power device {the fuel cell 22 or the regenerative power source (inverter 34 and motor 26)}. Three phase arms {U-phase arm UA (81u, 82u) consisting of element 81 {81u, 81v, 81w (81u to 81w)} and lower arm element 82 {82u, 82v, 82w (82u to 82w)}, The V-phase arm VA (81v, 82v) and the W-phase arm WA (81w, 82w)} are configured as a three-phase arm connected in parallel.

  Diodes 83u, 83v, 83w, 84u, 84v, and 84w are connected in the reverse direction to the arm elements 81u, 81v, 81w, 82u, 82v, and 82w, respectively.

  In consideration of convenience of understanding and the like, in the present invention, it is assumed that the upper arm element 81 and the lower arm element 82 do not include the antiparallel diodes 83 and 84.

  When the voltage is converted between the primary voltage V1 and the secondary voltage V2 by the DC / DC converter 36, one reactor 90 for releasing and storing energy is provided for each phase arm (U phase). Arm UA, V-phase arm VA, W-phase arm WA) are inserted between the common connection point at the midpoint and battery 24.

  The upper arm elements 81 (81u to 81w) are respectively driven by gate drive signals (drive voltages) UH, VH, and WH (high levels thereof) output from the converter control unit 54, and the lower arm elements 82 (82u to 82w). ) Are driven by gate drive signals (drive voltages) UL, VL, WL (high levels thereof), respectively.

  The converter control unit 54 includes a microcomputer 72, a memory 74, and a timer 76, and controls the operation of the DC / DC converter 36. The control method will be described later.

(6) Capacitors 38 and 39
Smoothing capacitors 38 and 39 are provided on the primary side 1S and the secondary side 2S, respectively.

(7) Various control units (FC control unit 50, motor control unit 52, converter control unit 54, overall control unit 56)
The system including the fuel cell 22, the hydrogen tank 28 and the air compressor 30 is controlled by the FC control unit 50. The system including the inverter 34 and the motor 26 is controlled by a motor control unit 52 including an inverter driving unit (not shown). As described above, the system including the DC / DC converter 36 is controlled by the converter control unit 54.

  The FC control unit 50, the motor control unit 52, and the converter control unit 54 are higher-level control units, and are controlled by the overall control unit 56 that determines values such as the total load amount Lt of the fuel cell 22.

  The overall control unit 56 determines the total load request amount of the fuel cell vehicle 20 determined based on inputs (load requests) from various switches and various sensors in addition to the state of the fuel cell 22, the state of the battery 24, and the state of the motor 26. From Lt, the fuel cell shared load amount (required output) Lf that the fuel cell 22 should bear, the battery shared load amount (required output) Lb that the battery 24 should bear, and the regenerative power source shared load amount that the regenerative power source should bear Lr distribution (sharing) is determined while arbitrating, and commands are sent to the FC control unit 50, motor control unit 52, and converter control unit 54.

  The overall control unit 56, the FC control unit 50, the motor control unit 52, and the converter control unit 54 are respectively an input / output interface such as an A / D converter and a D / A converter in addition to a CPU, a ROM, a RAM, and a timer. In addition, a DSP (Digital Signal Processor) or the like is included as necessary.

  The overall control unit 56, the FC control unit 50, the motor control unit 52, and the converter control unit 54 are connected to each other through a communication line 70 such as a CAN (Controller Area Network) that is an in-vehicle LAN, and are connected to various switches and sensors. Input / output information is shared, and input / output information from these various switches and various sensors is input, and each CPU executes a program stored in each ROM to realize various functions.

(8) Various switches and various sensors As various switches and various sensors for detecting the vehicle state, the primary voltage V1 (which is basically equal to the battery voltage Vbat) is detected in addition to the current sensor 32 for detecting the generated current If. A voltage sensor 61 for detecting a primary current I1 and a voltage sensor 63 for detecting a secondary voltage V2 (approximately equal to the generated voltage Vf of the fuel cell 22 when the disconnect diode 33 is conductive). There are a current sensor 64 for detecting the secondary current I2, an ignition switch 65 connected to the communication line 70, an accelerator sensor 66, a brake sensor 67, a vehicle speed sensor 68, and the like.

2. Various Controls / Processing (1) Basic Voltage Control in VCU 23 FIG. 2 shows a flowchart of the basic operation of the DC / DC converter 36 that is driven and controlled by the converter control unit 54.

  As described above, the overall control unit 56 determines the fuel cell vehicle 20 determined based on inputs (load requests) from various switches and various sensors in addition to the state of the fuel cell 22, the state of the battery 24, and the state of the motor 26. From the total load requirement Lt, the fuel cell shared load amount (required output) Lf that the fuel cell 22 should bear, the battery shared load amount (required output) Lb that the battery 24 should bear, and the regenerative power source should bear The distribution (sharing) of the regenerative power distribution load amount Lr is determined while arbitrating, and a command is sent to the FC control unit 50, the motor control unit 52, and the converter control unit 54. The command sent from the overall control unit 56 to the converter control unit 54 usually takes the form of a command value of the secondary voltage V2 (secondary voltage command value V2com).

  In step S1, when the overall control unit 56 determines (calculates) the total load request amount Lt from the electric power request of the motor 26, the electric power request of the air compressor 30, and the electric power request of an auxiliary machine (not shown), which are load requests. In step S2, the overall control unit 56 determines the distribution of the fuel cell shared load amount Lf, the battery shared load amount Lb, and the regenerative power source shared load amount Lr for outputting the determined total load request amount Lt. Here, when determining the fuel cell shared load Lf, the efficiency η (FIG. 3) of the fuel cell 22 is considered.

  Next, in step S3, the converter control unit 54 determines the power generation voltage Vf of the fuel cell 22, according to the secondary voltage command value V2com, here, the target value of the secondary voltage V2 (secondary voltage target value V2tar). The

  When the secondary voltage target value V2tar is determined, in step S4, the converter control unit 54 drives and controls the DC / DC converter 36 so as to be the determined secondary voltage target value V2tar. The DC / DC converter 36 performs a step-up operation, a step-down operation, and the like (details will be described later).

  The secondary voltage V <b> 2 and the primary voltage V <b> 1 are controlled by the converter control unit 54 by PID control in which the DC / DC converter 36 is combined with feedforward control and feedback control.

(2) Output Control of Fuel Cell 22 Next, output control of the fuel cell 22 by the VCU 23 will be described.

  During power generation in which fuel gas from the hydrogen tank 28 and compressed air from the air compressor 30 are supplied, the power generation current If of the fuel cell 22 is referred to as the characteristic 91 {function F (Vf) shown in FIG. } Is determined by setting the secondary voltage V2, that is, the generated voltage Vf, through the DC / DC converter 36 by the converter control unit 54. That is, the generated current If is determined as a function F (Vf) value of the generated voltage Vf. If If = F (Vf) and the generated voltage Vf is set to Vf = Vfa = V2, for example, the generated current Ifa as a function value of the generated voltage Vfa (V2) is determined. {Ifa = F (Vfa) = F (V2)}.

  Thus, since the fuel cell 22 determines the secondary voltage V2 (power generation voltage Vf), the power generation current If is determined. Therefore, when the fuel cell vehicle 20 is driven and controlled, the secondary voltage V2 (power generation voltage Vf) is determined. ) Is set to the target voltage (target value).

  In the system including the fuel cell 22 such as the fuel cell vehicle 20, the VCU 23 is basically controlled so that the secondary voltage V2 of the secondary side 2S of the DC / DC converter 36 becomes the target voltage, and the fuel cell 22 is controlled by the VCU 23. Output (generated current If) is controlled.

(3) Switching Control of DC / DC Converter 36 (a) Outline As switching control of the DC / DC converter 36 in the present embodiment, (i) upper arm elements 81u and 81v in a part of each switching cycle Tsw [μs]. , 81w, step-down chopper control to turn on, (ii) step-up chopper control to turn on one of the lower arm elements 82u, 82v, 82w in a part of each switching cycle Tsw, and (iii) step-down chopper control, There are direct connection control in which current is passed through the DC / DC converter 36 without performing any step-up chopper control, and (iv) stop control in which current is not passed through the DC / DC converter 36.

(B) Synchronous switching processing As shown in FIGS. 4 and 5, the step-down chopper control and the step-up chopper control described above are used in combination in each switching cycle Tsw. That is, in each switching cycle Tsw, the driving time of the upper arm elements 81u to 81w (hereinafter also referred to as “upper arm element driving time T1”) and the driving time of the lower arm elements 82u to 82w (hereinafter referred to as “lower arm element driving time T1”). Both of them appear, and the upper arm elements 81u to 81w and the lower arm elements 82u to 82w are driven alternately. In this manner, the process of alternately driving the upper arm elements 81u to 81w and the lower arm elements 82u to 82w every switching cycle Tsw is referred to as “synchronous switching process”.

  Further, between the upper arm element driving time T1 and the lower arm element driving time T2, the upper arm elements 81u to 81w and the lower arm elements 82u to 82w are simultaneously driven to prevent the secondary voltage V2 from being short-circuited. A dead time dt is arranged for this purpose. In the following, the dead time dt, which is arranged after the previous lower arm element driving time T2 and before the current upper arm element driving time T1, will be referred to as the first dead time dt1, A device disposed after the time T1 and before the current lower arm element driving time T2 is referred to as a second dead time dt2.

  In the synchronous switching process, the upper arm elements 81u to 81w and the lower arm elements 82u to 82w are alternately driven every switching cycle Tsw. However, because of the potential difference between the primary side 1S and the secondary side 2S, , Only one of them is turned on (not flowing).

(C) Step-down Chopper Control FIG. 4 shows a state in which the upper arm elements 81u to 81w are turned on and the lower arm elements 82u to 82w are not turned on by the step-down chopper control. In FIG. 4, in the waveforms of the drive signals UH, UL, VH, VL, WH, WL, the hatched period is an arm element to which the drive signals UH, UL, VH, VL, WH, WL are supplied (for example, , The arm element corresponding to the drive signal UH indicates a period during which the upper arm element 81u) is ON (a period during which current actually flows).

  When the upper arm elements 81u to 81w are turned on, a secondary current is supplied from the secondary side 2S to the primary side 1S {sinking. }, The step-down operation is executed by so-called step-down chopper control. For example, when the upper arm element 81u is turned on between time points t1 and t2 in FIG. 4, energy is stored in the reactor 90 by the secondary current I2 output from the capacitor 39, and the primary current I1 is transferred from the capacitor 38 to the battery 24. Supplied. Next, the diodes 84 u to 84 w are turned on as flywheel diodes, energy is released from the reactor 90, energy is stored in the capacitor 38, and the primary current I 1 is supplied to the battery 24. Next, between the time points t5 and t6, the upper arm element 81v is turned on, and the secondary current I2 is sunk to the battery 24 side as described above. Thus, in the present embodiment, the three upper arm elements 81u to 81w are turned on while rotating (such an operation is also referred to as “rotation switching”).

  When there is a regenerative voltage, the regenerative power source shared load Lr is added to the sunk secondary current I2 during this step-down operation. The driving time of the upper arm elements 81u to 81w and the lower arm elements 82u to 82w in the step-down operation is also determined so that the secondary voltage V2 is maintained.

  A timing chart of the primary current I1 during the step-down control of the VCU 23 is shown on the lower side of FIG.

  In FIG. 4, the sign of the primary current I1 flowing through the reactor 90 is a step-up current flowing from the primary side 1S to the secondary side 2S (source current flowing out from the secondary side 2S of the DC / DC converter 23 to the inverter 34). Positive (+), a step-down current flowing from the secondary side 2S to the primary side 1S (a sink current flowing from the fuel cell 22 or the inverter 34 to the secondary side 2S) is negative (−). This also applies to FIG.

(D) Boost Chopper Control FIG. 5 shows a state in which the lower arm elements 82u to 82w are turned on and the upper arm elements 81u to 81w are not turned on by the boost chopper control. The meaning of the hatched period is the same as that in FIG.

  When the lower arm elements 82u to 82w are turned on, a current flows from the primary side 1S to the secondary side 2S, and the boosting operation is executed by so-called boosting chopper control. For example, when the lower arm element 82u is turned on between time points t13 and t14 in FIG. 5, energy is stored in the reactor 90 by the primary current I1 as the battery current Ibat, and at the same time, the secondary current I2 is transferred from the capacitor 39 to the inverter 34 side. To supply {to say source. }. Next, the diodes 83u to 83w functioning as rectifier diodes are turned on, energy is discharged from the reactor 90, energy is stored in the capacitor 39, and it is sourced to the inverter 34 as the secondary current I2. Next, between time points t17 and t18, the lower arm element 82v is turned on, and the secondary current I2 is sourced to the inverter 34 side as described above. Similar to the three upper arm elements 81u to 81w, the three lower arm elements 82u to 82w also perform rotation switching.

  The upper arm element driving time T1 (time for driving the upper arm elements 81u to 81w) and the lower arm element driving time T2 (time for driving the lower arm elements 82u to 82w) are such that the secondary voltage V2 is maintained. To be determined.

(E) Modulation method In the present embodiment, pulse width modulation (PWM) and pulse frequency modulation are used as modulation methods for the drive signals UH, UL, VH, VL, WH, and WL generated by the converter control unit 54. (PFM: Pulse Frequency Modulation) can be used selectively.

  The PWM fixes the switching frequency Fsw [Hz] (1 / switching cycle Tsw [μs]), the upper arm element driving time T1, the lower arm element driving time T2, and the first dead time dt1 and the second second as necessary. By controlling the drive of the upper arm elements 81u to 81w and the lower arm elements 82u to 82w by changing the length of the dead time dt2, the step-up / step-down operation of the DC / DC converter 36 is controlled.

  The PFM fixes either the length of the upper arm element driving time T1 or the lower arm element driving time T2, and changes the switching cycle Tsw to turn on / off the upper arm elements 81u to 81w and the lower arm elements 82u to 82w. By controlling the off operation, the step-up / step-down operation of the DC / DC converter 36 is controlled.

(F) Generation of Drive Signals UH, UL, VH, VL, WH, WL In FIGS. 6 and 7, the process of generating the drive signals UH, UL, VH, VL, WH, WL in the converter control unit 54 is simplified. Has been shown. The converter control unit 54 determines a waveform of each drive signal UH, UL, VH, VL, WH, WL (calculates a timer set value TMR for setting each drive signal to a high level), a timer set value calculation process, and a calculation The timer set value TMR thus set is set in the timer 76, and drive signal output processing for outputting drive signals UH, UL, VH, VL, WH, WL corresponding to the timer set value TMR is performed. The timer set value calculation process and the drive signal output process are controlled by one microcomputer 72.

  In the present embodiment, the time Pcal required for one timer set value calculation process is, for example, 120 μs, and the time Pout required for one drive signal output process is, for example, 15 μs. When using PWM, the control cycle Tc (one of the calculation cycles in the microcomputer 72) is, for example, 60 μs, and when using PFM, the control cycle Tc is variable. The control cycle Tc indicates the cycle of the drive signal output process (the interval from the start of a certain drive signal output process to the start of the next drive signal output process). The control cycle Tc has the same length as the corresponding switching cycle Tsw (Tc = Tsw), and starts earlier by the time Pout related to the drive signal output process than the corresponding switching cycle Tsw.

  As shown in FIGS. 6 and 7, the drive signal output process is performed for a time Pout from the start of the control cycle Tc [μs]. In the present embodiment, the timer set value calculation process is performed with the remaining time Pr obtained by subtracting the drive signal output process time Pout from the control cycle Tc (Pr = Tc−Pout). For this reason, when PWM is used, the remaining time Pr is 45 μs (45 = 60−15), for example, and is shorter than the time Pcal (eg, 120 μs) required for the timer set value calculation process (Pr <Pcal). . For this reason, one timer set value calculation process is performed during a plurality of control cycles Tc (specifically, three control cycles Tc).

  On the other hand, when the PFM is used, the remaining time Pr changes according to the length of the control cycle Tc (Pr∝Tc). As a result, it is possible to perform a single timer set value calculation process with a control cycle Tc that is smaller than that in PWM. For example, if the remaining time Pr is 60 μs or more, the timer setting value calculation process can be performed once every two control cycles Tc. If the remaining time Pr is 120 μs or more, one timer setting value calculation process can be performed for each control cycle Tc. In this embodiment, paying attention to this point, as shown in FIGS. 6 and 7, the use of PFM increases the switching cycle Tsw, and the control cycle Tc increases accordingly, and the smaller the number. The timer setting value calculation process is performed once corresponding to the switching period Tsw (control period Tc).

  Switching between PWM and PFM is performed according to the duty DUT. The duty DUT indicates the ratio of the sum of the upper arm element driving time T1 and the first dead time dt1 in the switching period Tsw {DUT = (T1 + dt1) / Tsw}. Therefore, the ratio of the sum of the lower arm element driving time T2 and the second dead time dt2 to the switching cycle Tsw is obtained by 1−DUT {(T2 + dt2) / Tsw = 1−DUT}. In addition, a fixed value (for example, 5 μs) is normally used for the first dead time dt1 and the second dead time dt2. Therefore, by mapping the correspondence relationship between the duty DUT and the upper arm element driving time T1 and the lower arm element driving time T2 in advance, the upper arm element driving time T1 and the lower arm element driving are based on the duty DUT. Time T2 can be selected.

  In the present embodiment, PWM is normally used as the modulation method, and PFM is used when the duty DUT approaches 1 (100%) or 0 (0%). Specifically, PFM is used when the duty DUT approaches 100% and the lower arm element drive time T2 is less than the minimum on-time T2on_min of the lower arm elements 82u to 82w. Further, when the duty approaches 0% and the upper arm element driving time T1 is less than the minimum on-time T1on_min of the upper arm elements 81u to 81w, PFM is used. In the present embodiment, the minimum on-time T1on_min of the upper arm elements 81u to 81w and the minimum on-time T2on_min of the lower arm elements 82u to 82w are the same length.

  8 and 9, as a comparative example of FIGS. 6 and 7, the case where the number of switching periods Tsw corresponding to one timer setting value calculation process is the same is shown regardless of whether PWM or PFM is used. Has been. Comparing the present embodiment with the comparative example, in the comparative example (FIGS. 8 and 9), when the PFM is used, as the switching cycle Tsw (control cycle Tc) becomes longer, the cycle of the timer set value calculation process Tcal (interval from the start of one timer set value calculation process to the start of the next timer set value calculation process) becomes longer.

  On the other hand, in the present embodiment (FIGS. 6 and 7), when the PFM is used, even if the switching cycle Tsw (control cycle Tc) becomes long, the timer setting value calculation processing cycle Tcal does not become long (rather short). In some cases.). For this reason, it is possible to increase the number of times of the timer set value calculation process, and as a result, it is possible to calculate the timer set value TMR corresponding to the most recent situation. Therefore, the DC / DC converter 36 can be controlled more suitably.

  FIG. 10 is a flowchart for executing the timer setting calculation process and the drive signal output process of the present embodiment, and FIG. 11 is an explanatory diagram simply showing the flow of data and signals in FIG.

  In step S <b> 11 of FIG. 10, the microcomputer 72 of the converter control unit 54 performs one timer setting value calculation process. In subsequent step S12, the microcomputer 72 performs one drive signal output process. Details of the timer set value calculation process and the drive signal output process will be described later.

  In step S13, the microcomputer 72 starts the next timer set value calculation process. In a succeeding step S14, it is determined whether or not there is an interrupt request Rint for performing the drive signal output process. Details of the interrupt request Rint will be described later. When there is an interrupt request Rint (S14: Yes), in step S15, the microcomputer 72 performs one drive signal output process in the same manner as in step S12, and returns to step S14. If there is no interrupt request (S14: No), in step S16, the microcomputer 72 continues the timer set value calculation process. In subsequent step S <b> 17, the microcomputer 72 determines whether or not the timer set value calculation process has been completed. If the timer set value calculation process has not been completed (S17: No), the process returns to step S14. If the timer set value calculation process has been completed (S17: Yes), in step S18, the microcomputer 72 determines whether a predetermined number of drive signal output processes have been completed (details will be described later). If the predetermined number of drive signal output processes have not been completed (S18: No), step S18 is repeated. If the predetermined number of drive signal output processes have been completed (S18: Yes), the process returns to step S13, and the microcomputer 72 starts the next timer set value calculation process.

  FIG. 12 shows a flowchart of the timer set value calculation process. In step S21, the microcomputer 72 of the converter control unit 54 calculates the duty DUT. The calculation of the duty DUT is performed as follows. That is, the reference duty DUTs is calculated by dividing the primary voltage V1 detected by the voltage sensor 61 by the secondary voltage command value V2com received from the overall control unit 56 (DUTs = V1 / V2com). In parallel with this, a correction duty ΔDUT that is the difference between the secondary voltage command value V2com and the secondary voltage V2 detected by the voltage sensor 63 is calculated (ΔDUT = V2com−V2). Then, the duty DUT is calculated as the sum of the reference duty DUTs and the correction duty ΔDUT (DUT = DUTs + ΔDUT).

  In subsequent step S22, the microcomputer 72 calculates the timer set value TMR (upper arm element driving time T1, lower arm element driving time T2, first dead time dt1 and second dead time dt2) based on the calculated duty DUT. calculate. The calculated timer set value TMR is temporarily stored in the memory 74.

  In the present embodiment, the timer set value TMR calculated in step S22 is used for each of the phase arms UA, VA, WA. That is, the three-phase timer set value TMR is the same. Instead, the timer setting values TMR of the respective phase arms UA, VA, WA can be obtained by other methods, such as obtaining the three timer setting values TMR by repeating the steps S21, S22.

  In step S23, the microcomputer 72 calculates the next timer set value based on the total Ttotal of the control periods Tc (substantially equal to the switching period Tsw) for three phases (U phase, V phase, W phase). Next calculation process call control cycle number Ntc [Tc] (hereinafter also referred to as “control cycle number NTc”) indicating the number of control cycles Tc until the process is selected. For example, when the control cycle number Nt is “0”, it indicates that the next timer set value calculation process is performed in the next control cycle Tc. When the control cycle number Ntc is “1”, the next timer set value calculation process is performed in the control cycle Tc two times after the control cycle Tc in which the current timer set value calculation process is performed. A timer set value calculation process is performed once for each cycle Tc. When the control cycle number Ntc is “2”, the timer set value calculation process is performed once every three control cycles Tc. The calculated control cycle number Ntc is temporarily stored in the memory 74.

  FIG. 13 shows a flowchart for calculating the control cycle number Ntc. In step S231, the microcomputer 72 calculates the total Ttotal of the three control periods Tc corresponding to the phase arms UA, VA, WA. In subsequent step S232, the microcomputer 72 determines whether or not the total Ttotal is less than the cycle threshold THcyc. The cycle threshold value THcyc is, for example, a value obtained by doubling the remaining time Pr obtained by subtracting the time Pout required for the drive signal output processing from the control cycle Tc (substantially equal to the switching cycle Tsw). It is set to a value that is longer than the time Pcal required for the calculation process (THcyc ≧ 2 × (Tc−Pout) = 2 × Pr> Pcal). For example, if the time Pout required for the drive signal output process is 15 μs and the time Pcal required for the timer set value calculation process is 120 μs, the period threshold THcyc can be 75 μs or more.

  When the total Ttotal of the three control cycles Tc is less than the cycle threshold THcyc (S232: Yes), in step S233, the microcomputer 72 sets the switching cycle number Ntc to “2”. When the total Ttotal of the three control cycles Tc is equal to or greater than the cycle threshold THcyc (S232: No), the process proceeds to step S234.

  In step S234, the microcomputer 72 calculates the total Tsub of the two control periods Tc. For example, the sum of the control periods Tc corresponding to the U-phase arm UA and the W-phase arm WA can be used as the total Tsub. In subsequent step S235, the microcomputer 72 determines whether or not the total Tsub is less than the cycle threshold THcyc. The cycle threshold THcyc is the same as that used in step S232.

  When the total Tsub of the two control cycles Tc is less than the cycle threshold THcyc (S235: Yes), in step S236, the microcomputer 72 sets the number of control cycles Ntc to “1”. When the total Tsub of the two control cycles Tc is equal to or greater than the cycle threshold THcyc (S235: No), in step S237, the microcomputer 72 sets the number of control cycles Ntc to “0”.

  FIG. 14 is a characteristic diagram schematically showing an example of a method for determining the control cycle number Ntc. In FIG. 14, when the switching frequency Fsw [kHz] (inversely proportional to the switching period Tsw substantially equal to the control period Tc) exceeds about 6 kHz, the time Pcal [μs] required for the timer set value calculation processing is set to the timer setting. Even if the value calculation processing is made to correspond to the three control cycles Tc, the value falls below the cycle threshold THcyc. In other words, the cycle Tcal of the timer set value calculation process cannot be ensured unless there are three control cycles Tc. Therefore, the control cycle number Ntc is set to “2”.

  When the switching frequency Fsw exceeds about 4 kHz and becomes about 6 kHz or less, the time Pcal required for the timer set value calculation process exceeds the period threshold THcyc when the timer set value calculation process is associated with three control periods Tc, and the timer setting If the value calculation process is associated with two control periods Tc, the value falls below the period threshold value THcyc. In other words, the time Pcal required for the timer set value calculation process can be secured if there are two control cycles Tc. Therefore, the control cycle number Ntc is set to “1”.

  When the switching frequency Fsw is about 4 kHz or less, the time Pcal required for the timer set value calculation process exceeds the cycle threshold value THcyc when the timer set value calculation process is associated with two or three control cycles Tc, and the timer set value calculation is performed. If the process is associated with one control cycle Tc, it falls below the cycle threshold THcyc. In other words, the time Pcal required for the timer set value calculation process can be secured if there is one control cycle Tc. Therefore, the control cycle number Ntc is set to “0”.

  Returning to FIG. 12, in step S <b> 24, the microcomputer 72 determines whether this is the first timer setting value calculation process. This determination is performed by, for example, the calculation processing determination flag FLGcal stored in the memory 74. When the calculation process determination flag FLGcal is “0”, it indicates that the timer set value calculation process has not been performed so far, and when it is “1”, the timer set value calculation process has been performed so far. Indicates. The initial value of the calculation process determination flag FLGcal is “0”. When the timer set value calculation process is performed once, the calculation process determination flag FLGcal is changed to “1”. If this is the first timer set value calculation process (S24: Yes), the process returns to step S21. If this is not the first timer set value calculation process (S24: No), in step S25, the microcomputer 72 uses the new timer set value TMR calculated in step S22 and the new control cycle number Ntc determined in step S23. It is determined whether there is a transmission request REQ to be requested. This transmission request REQ is made in step S35 in the drive signal output process (details will be described later). If there is no transmission request REQ (S25: No), step S25 is repeated. If there is a transmission request REQ (S25: Yes), the process returns to step S21.

  FIG. 15 shows a flowchart of the drive signal output process. In step S31, microcomputer 72 of converter control unit 54 selects phase arms UA, VA, WA for setting timer set value TMR in timer 76. This selection is performed by the phase selection flag FLGph stored in the memory 74. When the phase selection flag FLGph is “0”, it indicates that the next object is the phase arm UA, when it is “1”, it indicates that the next object is the phase arm VA, and when it is “2”, Indicates that the next object is the phase arm WA.

  In step S 32, the microcomputer 72 inputs the timer set value TMR to the timer 76. For example, when the phase arm UA is selected in step S31, the timer 76 sets the timer set value TMR (upper arm element driving time T1, lower arm element driving time T2, first dead time dt1, second dead time dt2). In response, the drive signals UH and UL are set to be output.

  In step S33, the microcomputer 72 stores a value obtained by adding 1 to the value of the current phase selection flag FLGph in the memory 74 as a new phase selection flag FLGph. When the current phase selection flag FLGph is “2”, the new phase selection flag FLGph is set to “0”.

  In step S <b> 34, the microcomputer 72 determines whether or not the next calculation process call control cycle number Ntc stored in the memory 74 is “0”. When the call control cycle number Ntc is “0” (S34: Yes), in step S35, a request signal REQ requesting a new timer set value TMR and a new next calculation process call control cycle number Ntc is transmitted. The request signal REQ permits execution of the next timer set value calculation process. When the call switching cycle number Ntsw is “1” or “2” (S34: No), in step S36, the microcomputer 72 sets the number obtained by subtracting “1” from the current call switching cycle number Nsw as a new call. This is set as the switching period number Ntsw and stored in the memory 74.

  In subsequent step S <b> 37, the microcomputer 72 determines whether or not an interrupt request Rint for performing the next drive signal output process should be performed. This determination can be performed, for example, by using the timer 76. Specifically, when starting the current drive signal output process, the time until the next drive signal output process is performed is input to the timer 76 as a count value, and when the count value becomes zero, It is determined that the interrupt request Rint is necessary. If the interrupt request Rint is not necessary (S37: No), step S37 is repeated. When the interrupt request Rint is necessary (S37: Yes), the microcomputer 72 performs the interrupt request Rint and prioritizes the drive signal output process even when the timer set value calculation process is being performed. . After making the interrupt request Rint, the process returns to step S31.

3. As described above, in the present embodiment, in the switching control using the PFM, the control cycle Tc (substantially the same length as the switching cycle Tsw) becomes smaller as the control cycle Tc becomes longer. Timer setting value calculation processing (such as calculation of duty DUT) is performed in correspondence with a number of control cycles Tc (switching cycle Tsw). For this reason, even when the control cycle Tc becomes long, it becomes possible to control the operations of the upper arm elements 81u to 81w and the lower arm elements 82u to 82w with the same cycle (time) as when the control cycle Tc is short, Even if the control cycle Tc becomes longer, it is possible to prevent the deviation between the secondary voltage target value V2tar and the secondary voltage V2 from increasing. Therefore, the DC / DC converter 36 can be controlled more suitably.

  That is, since the timer set value calculation process is used to generate the drive signals UH, UL, VH, VL, WH, and WL, the period Tcal of the timer set value calculation process is a period (drive) for generating each drive signal. It is preferable to correspond to a control cycle Fc (switching cycle Tsw) indicating a signal output processing cycle. In the configuration in which the duty DUTs of the upper arm elements 81u to 81w and the lower arm elements 82u to 82w are calculated together, when the control cycle Tc is the minimum value, one timer is required due to the processing capacity of the microcomputer 72. The set value calculation process may be associated with two or more control cycles Tc. However, in the PFM, since the switching cycle Tsw (control cycle Tc) is changed, if the timer set value calculation process is always associated with the same number of switching cycles Tsw, the drive signals UH, UL, VH, The time until the output of VL, WH, WL becomes longer as the switching period Tsw becomes longer. For example, when the duty DUTs for three consecutive switching periods Tsw are calculated together, the time taken from the calculation of the duty DUT to the output of the drive signal corresponding to the duty DUT of the third switching period Tsw is the first and The switching period Tsw corresponding to the duty DUT of the second switching period Tsw becomes longer as it becomes longer. In the present embodiment, as the control cycle Tc (switching cycle Tsw) becomes longer, the timer set value calculation process is performed in association with a smaller number of control cycles Tc (switching cycle Tsw). For this reason, even when the control cycle Tc becomes longer, the cycle Tcal (time) of the timer set value calculation process can be kept short. As a result, even if the control cycle Tc becomes longer, it becomes possible to calculate the duty DUT reflecting the more recent state, and the DC / DC converter 36 can be controlled more suitably.

  In this embodiment, it is possible to switch between PWM and PFM. Further, when using PFM, the number of control cycles Tc (switching cycle Tsw) corresponding to one timer set value calculation process is controlled for each control. It can be adjusted according to the increase / decrease of the period Tc (time). In PWM, since the switching cycle Tsw (control cycle Tc) is fixed, the cycle Tcal of the timer set value calculation processing does not change, while in PFM, the switching cycle Tsw (control cycle Tc) is variable, so that the timer set value calculation is performed. It is difficult to fix the processing cycle Tcal (time). According to the present embodiment, when using the PFM, the number of control cycles Tc (switching cycle Tsw) corresponding to one timer set value calculation process is changed according to the length of the control cycle Tc. It is also possible to cope with a change in the control cycle Tc accompanying switching from PWM to PFM. Therefore, the timer set value calculation process used in PWM can be easily used in PFM.

  In the present embodiment, the total Ttotal of the three control cycles Tc (switching cycle Tsw) actually used, the total Tsub of the two control cycles Tc (switching cycle Tsw), and the cycle threshold THcyc stored in the memory 74 in advance And the number of control periods Tc (switching periods Tsw) corresponding to each timer set value calculation process is determined based on the comparison result. For this reason, the number of control cycles Tc corresponding to each timer set value calculation process can be determined by a relatively simple calculation.

  In the present embodiment, the converter control unit 54 can control the power drawn from the fuel cell 22 by controlling the DC / DC converter 36. According to the present embodiment, the number of control cycles Tc (switching cycles Tsw) corresponding to the timer set value calculation process is determined according to the length of each control cycle Tc (switching cycle Tsw). Therefore, the fuel cell 22 can be operated efficiently because the electric power drawn from the fuel cell can be precisely and accurately controlled.

  In the present embodiment, the electric power of the fuel cell 22 and the battery 24 is supplied to the motor 26. Thereby, since a fuel cell is operated efficiently, the fuel cell vehicle 20 with good fuel efficiency can be realized.

B. Modifications It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted based on the contents described in this specification. For example, the following configurations (1) to (5) can be employed.

(1) Target for mounting VCU 23 In the above embodiment, the VCU 23 is mounted on the fuel cell vehicle 20, but the present invention is not limited to this. For example, it can also be mounted on a battery-powered vehicle (electric vehicle). Of course, it can also be mounted on a so-called parallel or series-parallel hybrid vehicle equipped with an engine, a battery and a motor.

(2) Phase arm UA, VA, WA
In the above embodiment, the three-phase phase arms UA, VA, and WA are used, but two or more phases may be used.

(3) Switching control In the above embodiment, each switching cycle Tsw includes both switching of the upper arm elements 81u to 81w (step-down chopper control) and switching of the lower arm elements 82u to 82w (step-up chopper control). However, the present invention is not limited to this, and the present invention can be applied to only one of the step-down chopper control and the step-up chopper control.

  In the above embodiment, the rotation switching is performed in the order of the U-phase arm UA → the V-phase arm VA → the W-phase arm WA, but is not limited to this order. It is also possible to drive the upper arm elements 81u to 81w and the lower arm elements 82u to 82w of a plurality of phase arms in one control cycle Fc.

(4) Modulation method In the above embodiment, PWM and PFM are used by switching, but it is also possible to use only PFM. Also, PFM can be used in combination with a modulation method other than PWM.

  In the above embodiment, the PWM is used when the duty DUT can secure the minimum on-time required to turn on the upper arm elements 81u to 81w and the lower arm elements 82u to 82w, and PFM when the minimum on-time cannot be secured. However, it is also possible to switch between PWM and PFM based on other criteria.

(5) Others In the above embodiment, the next calculation process call control cycle number Ntc is selected using the flowchart of FIG. 13, but other methods can also be used. For example, when the timer setting value TMR calculated in one timer setting value calculation process is the same in each phase, the control cycle number Ntc can be directly selected from the duty DUT.

1 is a circuit diagram of a fuel cell vehicle equipped with a DC / DC converter device according to an embodiment of the present invention. It is a flowchart of the basic control of the DC / DC converter mounted in the fuel cell vehicle. It is explanatory drawing of the current-voltage characteristic of a fuel cell. It is a timing chart used for operation | movement description of the pressure | voltage fall operation of a DC / DC converter. It is a timing chart used for operation | movement description of the pressure | voltage rise operation of a DC / DC converter. 4 is a part of a timing chart used for explaining an operation when the modulation method is switched from PWM to PFM in the embodiment. In the embodiment, the remaining part of the timing chart used for explaining the operation when the modulation method is switched from PWM to PFM. In a comparative example, it is a part of timing chart used for operation | movement description at the time of switching a modulation system from PWM to PFM. In a comparative example, it is the remaining part of the timing chart used for operation | movement description at the time of switching a modulation system from PWM to PFM. 4 is a flowchart for switching between a timer set value calculation process and a drive signal output process in the embodiment. It is explanatory drawing which shows simply the flow of the data and signal in FIG. It is a flowchart of a timer set value calculation process. It is a flowchart which selects the number of control periods after the timer setting value calculation process this time until the next timer setting value calculation process. It is a characteristic view which shows simply an example of the method of determining the number of control periods of FIG. It is a flowchart of a drive signal output process.

Explanation of symbols

20 ... Fuel cell vehicle 22 ... Fuel cell (second power device)
23 ... DC / DC converter unit (VCU)
24 ... Battery (first power device) 26 ... Motor (second power device)
34 ... Inverter 36 ... DC / DC converter 54 ... Converter control part 81 (81u-81w) ... Upper arm element 82 (82u-82w) ... Lower arm element 83u, 83v, 83w, 84u, 84v, 84w ... Diode 90 ... Reactor 91 ... Fuel cell output characteristics (current-voltage characteristics)
DUT ... Duty Ntc ... Next calculation process call control cycle number T1 ... Upper arm element drive time T2 ... Lower arm element drive time Tc ... Control cycle Tcal ... Timer set value calculation process period Tout ... Drive signal calculation process period Tsw ... Switching Period UA ... U-phase arm VA ... V-phase arm WA ... W-phase arm UH, UL, VH, VL, WH, WL ... Drive signal

Claims (7)

A multiphase DC / DC converter connected between the first power device and the second power device and comprising a plurality of switching elements;
A control device for controlling switching operations of the plurality of switching elements using a drive signal for controlling an output voltage value of the DC / DC converter to a target value ;
A DC / DC converter device comprising:
The controller is
A duty calculation function for performing a duty calculation process for calculating a duty used to generate the drive signal;
A PFM drive signal generation function for performing a PFM drive signal generation process for generating the drive signal by pulse frequency modulation (PFM) based on the duty;
Have
The duty calculation process is repeated in a period of time n times a certain switching period (n is an integer of 2 or more),
Furthermore, the duty calculation process, when the switching period is long, the certain switching cycle DC / DC converter apparatus characterized by repeated with a period of n-1 time or less time. The DC / DC converter device according to claim 1, wherein
The controller is
In addition to the PFM drive signal generation function , a PWM drive signal generation function for performing PWM drive signal generation processing for generating the drive signal by pulse width modulation (PWM) based on the duty,
The PWM drive signal generation process is used when the duty calculated in the duty calculation process can secure the minimum on-time necessary to turn on each switching element, and the PFM drive when the minimum on-time cannot be secured. A DC / DC converter device using signal generation processing. The DC / DC converter device according to claim 1 or 2,
The controller is
A storage unit that stores a maximum value of a duty calculation process period that is a time from the start of a certain duty calculation process to the start of the next duty calculation process;
When the PFM drive signal generation process is used, the switching period corresponding to the calculated duty is compared with the maximum value of the duty calculation process period, and the switching period corresponding to each duty calculation process is based on the comparison result. A DC / DC converter device characterized by determining a number. The DC / DC converter device according to claim 2 or claim 3 dependent on claim 2,
When performing the PWM drive signal generation processing, the duty is collectively calculated for a plurality of switching periods,
When the PFM drive signal generation process is performed, the duty is calculated for a switching cycle that is smaller than when the PWM drive signal generation process is performed.
A DC / DC converter device characterized by that. In the DC / DC converter device according to any one of claims 1 to 4 ,
The first power device is a power storage device, and the second power device is a fuel cell;
The control device controls the electric power drawn from the fuel cell by controlling the DC / DC converter. The DC / DC converter device, wherein: 6. A fuel cell vehicle comprising the DC / DC converter device according to claim 5, wherein electric power of the fuel cell and the power storage device is supplied to a drive motor. A multiphase DC / DC converter having a plurality of switching elements connected between the first power device and the second power device, and a drive for controlling the output voltage value of the DC / DC converter to a target value A control device for controlling switching operations of the plurality of switching elements using a signal, and a control method for a DC / DC converter device comprising:
A duty calculating step for calculating a duty used for generating the drive signal;
A PFM switching step of generating the drive signal by pulse frequency modulation (PFM) based on the duty and switching the plurality of switching elements using the drive signal;
With
The duty calculation step is repeated with a period of time n times a certain switching period (n is an integer of 2 or more),
Furthermore, the duty calculation process, increasing the switching period, the control method of the DC / DC converter apparatus characterized by repeated with a period of n-1 time or less time the certain switching period.

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