阅读说明：本技术 升压转换器的控制方法以及控制装置 (Control method and control device for boost converter ) 是由 森宪一 大内敏生 近藤和洋 于 2018-04-10 设计创作，主要内容包括：升压转换器的控制方法,是将从电源输入的电压升压而向负载侧供给的升压转换器的控制方法。在该升压转换器的控制方法中,以如下方式对所述升压转换器进行控制,即,计算出确保根据与负载侧连接的电机的动作点而请求的输出电力、且使得升压转换器的输出电压不振荡的下限电压值,将升压转换器的目标输出电压设为大于或等于下限电压值的值,输出与目标输出电压相应的电压。(A method of controlling a boost converter is a method of controlling a boost converter that boosts a voltage input from a power supply and supplies the boosted voltage to a load. In the method for controlling the boost converter, the boost converter is controlled by calculating a lower limit voltage value at which the output voltage of the boost converter does not oscillate while ensuring the output power requested in accordance with the operating point of the motor connected to the load side, setting the target output voltage of the boost converter to a value equal to or greater than the lower limit voltage value, and outputting a voltage corresponding to the target output voltage.)

1. A method for controlling a boost converter for boosting a voltage input from a power supply and supplying the boosted voltage to a load,

The step-up converter is controlled by calculating a lower limit voltage value that ensures output power requested in accordance with an operating point of a motor connected to the load side and that prevents an output voltage of the step-up converter from oscillating,

setting a target output voltage of the boost converter to a value greater than or equal to the lower limit voltage value,

and outputting a voltage corresponding to the target output voltage.

2. The control method of a boost converter according to claim 1, wherein,

the lower limit voltage value is set to a value that increases as the output power of the motor increases.

3. The control method of a boost converter according to claim 1, wherein,

the lower limit voltage value is changed according to the magnitude of the current response lag of the motor.

4. The control method of a boost converter according to claim 3, wherein,

when electric power is supplied from the boost converter to the load side, the lower limit voltage value is set to a value that is larger as the current response lag of the motor is smaller.

5. The control method of a boost converter according to claim 3, wherein,

when the boost converter is supplied with electric power from the load side, the lower limit voltage value is set to a value that increases as the current response lag of the motor increases.

6. The control method of a boost converter according to claim 1, wherein,

the lower limit voltage value is corrected by adding a correction value calculated so that a frequency difference between a resonance frequency of the boost converter and an oscillation frequency of the motor becomes larger as the frequency difference becomes smaller.

7. The control method of a boost converter according to claim 6, wherein,

as the correction value, when the frequency difference is smaller than that before the correction and the resonance frequency of the boost converter is larger than the vibration frequency of the motor after the correction, a value calculated when the frequency difference is 0 is set.

8. The control method of a boost converter according to claim 6, wherein,

as the correction value, when the frequency difference is smaller than the frequency difference before the correction and the resonance frequency of the boost converter is smaller than the vibration frequency of the motor after the correction, a value obtained by adding a correction value calculated based on the frequency difference before the correction and a correction value calculated based on the frequency difference after the correction is set.

9. The control method of a boost converter according to any one of claims 1 to 8, wherein,

Calculating an optimum efficiency voltage value for ensuring output power requested according to an operating point of the motor and driving the motor at a maximum efficiency,

setting a larger voltage value of the lower limit voltage value and the optimum efficiency voltage value as the target output voltage.

10. A control device for a boost converter, comprising: a boost converter that boosts a voltage input from a power supply and supplies the boosted voltage to a load; and a controller that controls the boost converter, wherein,

the controller controls the boost converter to calculate a lower limit voltage value that ensures output power requested in accordance with an operating point of a motor connected to the load side and that causes an output voltage of the boost converter not to oscillate,

setting a target output voltage of the boost converter to a value greater than or equal to the lower limit voltage value,

and outputting the target output voltage.

Technical Field

The present invention relates to a method and a device for controlling a boost converter.

Background

JP2009-225634a discloses a technique related to setting of a target output voltage of a power conversion device (boost converter). In this step-up converter, the motor is connected to the load side, and the operation region of the motor is divided into a step-up region and a non-step-up region.

Disclosure of Invention

Here, when the motor is driven via the boost converter, the boosted voltage may oscillate due to the negative resistance characteristic accompanying the constant power control of the inverter when the motor is performing the power running. Further, when the motor performs the regenerative operation, the boosted voltage may oscillate due to a response delay of the current flowing into the inverter with respect to the boosted voltage.

However, in the technique disclosed in JP2009-225634a, the target output voltage of the boost converter is set in consideration of only the loss at the time of motor driving (at the time of powering), and therefore, there is a problem that the output voltage of the boost converter oscillates due to different factors at the time of powering and at the time of regenerative operation, respectively.

The purpose of the present invention is to provide a technique capable of suppressing output voltage oscillation of a boost converter regardless of the operating state (power running, regenerative running) of a motor.

A method of controlling a boost converter according to an aspect of the present invention is a method of controlling a boost converter that boosts a voltage input from a power supply and supplies the boosted voltage to a load. In the method for controlling the boost converter, the boost converter is controlled by calculating a lower limit voltage value at which the output voltage of the boost converter does not oscillate while ensuring the output power requested in accordance with the operating point of the motor connected to the load side, setting the target output voltage of the boost converter to a value equal to or greater than the lower limit voltage value, and outputting a voltage corresponding to the target output voltage.

The following detailed description of embodiments of the invention is provided in conjunction with the accompanying drawings.

Drawings

Fig. 1 is a system configuration diagram of a hybrid vehicle to which a control device of a boost converter according to the present invention is applied.

Fig. 2 is a system configuration diagram describing each configuration shown in fig. 1 in more detail.

Fig. 3 is a circuit configuration diagram for explaining a circuit configuration of the boost converter.

Fig. 4 is a block diagram of a structure used in determining the target output voltage V2.

Fig. 5 is a diagram for explaining linear approximation of the motor generator around the operating point.

Fig. 6 is a flowchart showing the setting process of the target output voltage V2.

FIG. 7 shows the lower limit voltage V2 in the case of the condition (a)_CA flowchart of the setting process of (1).

Fig. 8 is a diagram showing a relationship between the lower limit voltage correction value a and the vibration frequency of the motor generator.

Fig. 9 is a diagram showing a relationship between the lower limit voltage correction value B and the frequency difference.

FIG. 10 shows the lower limit voltage V2 in the case of the condition (b)_CA flowchart of the setting process of (1).

Fig. 11 is a diagram for explaining an effect of the method of controlling the boost converter according to the embodiment.

Detailed Description

(one embodiment)

Fig. 1 is a system configuration diagram showing a system configuration of a hybrid vehicle to which a control device of a boost converter according to the present invention is applied. Fig. 1 shows a configuration example in which a control device of a boost converter is applied to a hybrid vehicle equipped with two motor generators. As shown in the drawing, the hybrid vehicle of the present embodiment includes a battery 10, a boost converter 20, a 1 st inverter 30, a 2 nd inverter 40, a 1 st motor generator 50, a 2 nd motor generator 60, an engine 70, rotation speed detectors 51, 61, 71, an output shaft 80, and a control device 90.

Fig. 2 is a system configuration diagram describing each configuration shown in fig. 1 in more detail. Details of each configuration will be described with reference to fig. 2.

The battery 10 is a 2-time battery capable of being charged and discharged, and is, for example, a lithium ion 2-time battery.

The boost converter 20 is a power conversion device that boosts and outputs an input voltage. In the boost converter 20 of the present embodiment, the battery 10 as a power source is connected to the primary side (input side), and the 1 st inverter 30 and the 2 nd inverter 40 are connected in parallel to the 2 nd side (output side, load side). The configuration of the boost converter 20 will be described in detail with reference to fig. 3.

Fig. 3 is a circuit configuration diagram for explaining the circuit configuration of the boost converter 20. The boost converter 20 is mainly configured to include a capacitor 1, a reactor (inductor) 3, and switching elements 4a and 4 b. The boost converter 20 boosts an input voltage V1 of a direct current input from the battery 10, and outputs a boosted output voltage V2.

The capacitor 1 rectifies the input voltage V1 by absorbing a pulsating flow rate (voltage ripple) generated by the input voltage V1 due to switching of the switching elements 4a and 4 b.

The voltage sensor 2 is provided in the capacitor 1, detects the input voltage V1 of the boost converter 20, that is, the voltage of the capacitor 1, and transmits the detected voltage value to the control device 90.

The reactor 3 accumulates electric energy from the battery 10 when the switching element 4a is turned on and the switching element 4b is turned off, and releases the accumulated electric energy when the switching element 4a is turned off and the switching element 4b is turned on. Thereby, the boost converter 20 can boost the dc voltage from the battery 10. The boosted voltage value (the voltage value of the output voltage V2) can be arbitrarily adjusted by changing the ratio of the on time (the duty ratio D) of the switching element 4 a. The reactor 3 also has a function of suppressing current ripples generated by switching the switching elements 4a and 4 b.

The switching elements 4a and 4b are formed of power semiconductor elements such as IGBTs and MOS-FETs, for example. Further, diodes 5a and 5b are connected in parallel to the switching elements 4a and 4b, respectively.

The current sensor 6 detects the current flowing through the reactor 3, and sends the detected current value to the control device 90. In other words, the current sensor 6 can detect a direct current flowing from the battery 10 or flowing into the battery 10 via the boost converter 20.

The capacitor 7 rectifies the output voltage V2 by absorbing a pulsating flow rate (voltage ripple) generated in the output voltage V2 by switching the switching elements 4a and 4 b.

The voltage sensor 8 is provided in addition to the capacitor 7, detects the output voltage V2 of the boost converter 20, that is, the voltage of the capacitor 7, and transmits the detected voltage value to the control device 90. Next, the description is continued with returning to fig. 2.

The 1 st inverter 30 and the 2 nd inverter 40 are three-phase inverters capable of outputting three-phase ac power.

The 1 st inverter 30 converts the dc power (output voltage V2) input from the step-up converter 20 into the 1 st ac power of three phases and supplies the three phases to the 1 st motor generator 50. The 1 st inverter 30 converts the three-phase ac power generated by the 1 st motor generator 50 into dc power, and charges the battery 10 via the boost converter 20 or supplies the dc power to the 2 nd inverter 40.

The 2 nd inverter 40 converts the dc power input from the step-up converter 20 into the 2 nd ac power of three phases and supplies the three phases to the 2 nd motor generator 60. The 2 nd inverter 40 converts the three-phase 2 nd ac power (regenerative power) generated by the 2 nd motor generator 60 into dc power, and charges the battery 10 through the boost converter 20.

The current sensor 9a is additionally provided to an electric wire connecting the 1 st inverter 30 and the 1 st motor generator 50, and detects a current flowing through the electric wire and transmits the detected current to the control device 90. The current sensor 9b is additionally provided in an electric wire connecting the 2 nd inverter 40 and the 2 nd motor generator 60, detects a current flowing through the electric wire, and transmits the detected current value to the control device 90. The current sensors 9a and 9b of the present embodiment detect a current flowing from the inverter to the motor/generator side, that is, a current during the power running, as a positive value, and a current flowing from the motor/generator to the inverter side, that is, a current during the regenerative running, as a negative value.

In the present specification, the term "inverter" means at least one of the 1 st inverter 30 and the 2 nd inverter 40. In the present specification, the term "motor generator" or "motor" refers to at least one of the 1 st motor generator 50 and the 2 nd motor generator 60.

The 1 st motor generator 50 of the present embodiment is, for example, a generator. The 1 st motor generator 50 generates electric power by being rotated by the power from the engine 70. Further, the 1 st motor generator 50 is also driven by a motor that consumes electric power by cranking the engine 70 with the power of the 1 st motor generator 50 or by powering and rotating the engine 70 with the power of the 1 st motor generator 50 when the engine 70 is started.

The 2 nd motor generator 60 of the present embodiment is, for example, a drive motor that functions as a drive source of the vehicle. The 2 nd motor generator 60 generates a driving force using the ac power supplied from the 2 nd inverter 40, and transmits the driving force to the output shaft 80. Further, when the vehicle is rotated by the drive wheels during deceleration or coasting, regenerative drive force is generated, and the kinetic energy of the vehicle is recovered as electric energy.

That is, the control device of the boost converter 20 according to the present embodiment is applied to a so-called series hybrid vehicle in which the 1 st motor/generator 50 (generator) for power generation and the 2 nd motor/generator 60 (drive motor) for driving are mounted.

The engine 70 is connected to a rotation shaft of the 1 st motor generator 50 via a gear not shown, and transmits power for generating the 1 st motor generator 50 to the 1 st motor generator 50. Further, since the vehicle to which the control device of the step-up converter 20 of the present embodiment is applied is of a series system, the engine 70 of the present embodiment is basically used only as a drive source for rotationally driving the 1 st motor generator 50. However, a known torque transmission device may be disposed between the engine 70 and the output shaft 80 so as to be able to transmit the output torque of the engine 70 to the output shaft 80.

The rotation speed detectors 51, 61, 71 are, for example, resolvers. The rotation speed detectors 51 and 61 are respectively provided in the 1 st motor generator 50 and the 2 nd motor generator 60, detect the rotation angle or the rotation speed of the rotor of each of the 1 st motor generator 50 and the 2 nd motor generator 60, and output the detected rotation angle or rotation speed to the control device 90. The rotation speed detector 71 is provided in the engine 70, detects a rotation angle or a rotation speed of a crankshaft of the engine 70, and outputs the detected rotation angle or rotation speed to the control device 90.

The control device 90 controls driving of the step-up converter 20, the 1 st inverter 30, the 2 nd inverter 40, the 1 st motor generator 50, the 2 nd motor generator 60, and the engine 70. The control device 90 is constituted by 1 or more controllers. The controller is configured by, for example, a Central Processing Unit (CPU), a Read Only Memory (ROM), a Random Access Memory (RAM), and an input/output interface (I/O interface).

More specifically, the control device 90 is provided with a switching pattern according to a torque command for the 1 st motor generator 50, a motor rotation speed (a detection value of the rotation speed detector 51) of the 1 st motor generator 50, an input/output current value (a detection value of the current sensor 9 a), and an input voltage (a detection value of the voltage sensor 8), and transmits the switching pattern as a gate signal to the 1 st inverter 30. The control device 90 is provided with a switching pattern according to a torque command for the 2 nd motor generator 60, the motor rotation speed of the 2 nd motor generator 60 (the detection value of the rotation speed detector 61), the input/output current value (the detection value of the current sensor 9 b), and the input voltage (the detection value of the voltage sensor 8), and transmits the switching pattern to the 2 nd inverter 40 as a gate signal. The torque command here refers to a command value (torque request value) for outputting a desired torque (requested torque) to the motor, and is calculated based on, for example, an accelerator opening degree or the like.

The control device 90 calculates an input voltage required for the 1 st motor generator 50 based on a torque command for the 1 st motor generator 50 and the motor rotation speed of the 1 st motor generator 50. Further, the control device 90 calculates an input voltage required for the 2 nd motor generator 60 based on a torque command for the 2 nd motor generator 60 and the motor rotation speed of the 2 nd motor generator 60. Then, the control device 90 sets a voltage value determined based on each input voltage obtained by the calculation as the target output voltage V2 of the boost converter 20. The control device 90 is provided with a switching pattern (duty ratio D) for outputting the target output voltage V2, and transmits the duty ratio D as a gate signal to the boost converter 20.

Next, a method of setting the target output voltage V2 of the present embodiment will be described with reference to fig. 4.

Fig. 4 is a block diagram of the control device 90 when determining the target output voltage V2. The control device 90 of the present embodiment determines the target output voltage V2 using the efficiency optimum voltage operators 401 and 402, the multipliers 403 and 404, the oscillation avoidance voltage operator 405, and the selector 406.

The efficiency optimum voltage calculator 401 sets the efficiency optimum voltage obtained from the torque command for the 1 st motor/generator 50 and the motor rotation speed of the 1 st motor/generator 50 as the 1 st efficiency optimum voltage V2 for the 1 st motor/generator 50 _{_m1}And output to the selector 406. The efficiency optimum voltage here is a voltage that is input to the 1 st inverter 30 to output a desired torque to the 1 st motor generator 50 most efficiently while ensuring an output power requested according to the operating point of the 1 st motor generator 50, and is obtained by a known method based on a torque command for the 1 st motor generator 50 and the like.

The efficiency optimum voltage calculator 402 uses the efficiency optimum voltage obtained from the torque command for the 2 nd motor generator 60 and the motor rotation speed of the 2 nd motor generator 60 as the 2 nd efficiency optimum voltage V2 for the 2 nd motor generator 60_{_m2}And output to the selector 406. Here, the efficiency optimum voltage is to secure the output power requested according to the operating point of the 2 nd motor generator 60 and output the desired torque to the 2 nd motor generator with the highest efficiency60, the voltage input to the 2 nd inverter 40 is obtained by a known method based on a torque command for the 2 nd motor generator 60 and the like.

The multiplier 403 multiplies the torque command for the 1 st motor generator 50 by the motor rotation speed of the 1 st motor generator 50 to calculate a requested output (requested electric power P1) for the 1 st motor generator 50, and outputs the requested output to the hunting voltage calculator 405. The requested electric power P1 is a positive value (P1 > 0) when the 1 st motor/generator 50 is in power operation, and a negative value (P1 < 0) when the 1 st motor/generator 50 is in regeneration operation.

The multiplier 404 multiplies the torque command for the 2 nd motor generator 60 by the motor rotation speed of the 2 nd motor generator 60 to calculate a requested output (requested electric power P2) for the 2 nd motor generator 60, and outputs the requested output to the hunting voltage calculator 405. The requested electric power P2 is a positive value (P2 > 0) when the 2 nd motor/generator 60 is in power running, and a negative value (P2 < 0) when the 2 nd motor/generator 60 is in regeneration running.

The oscillation avoidance voltage operator 405 has as inputs the requested electric power P1 for the 1 st motor generator 50 and the requested electric power P2 for the 2 nd motor generator 60. The oscillation avoidance voltage calculator 405 calculates a lower limit voltage V2 as a lower limit value based on the requested powers P1 and P2_cThat is, if greater than or equal to this value, the output voltage V2 can be prevented from oscillating. In other words, the oscillation avoidance voltage calculator 405 calculates the lower limit voltage V2 of the output voltage V2 that does not oscillate the output voltage V2 of the boost converter 20 based on the request powers P1, P2_c. The calculated lower limit voltage V2_cOutput to the selector 406. Hereinafter, the lower limit voltage V2_cThe details of the calculation method (2) will be described.

The selector 406 selects and outputs the maximum value (select high) from the input 3 voltage values. That is, the selector 406 operates from the 1 st efficiency optimum voltage V2 _{_m1}2 nd efficiency optimum voltage V2_{_m2}And the highest voltage of the lower limit voltages V2c is selected, thereby determining the target output voltage V2 of the final boost converter 20. The control device 90 is used in a control module not shown in the figure to controlThe boost converter 20 outputs a duty ratio D of a voltage corresponding to the target output voltage V2 to the boost converter 20 as a gate signal. Further, if the efficiency of the motor generator is not considered, the lower limit voltage V2c calculated in the avoidance oscillation voltage calculator 405 may be set to the target output voltage V2 without the efficiency optimum voltage calculators 401 and 402 and the selector 406.

Here, the principle of oscillation of the output voltage V2 of the boost converter 20 will be explained.

The boost converter 20 has electric power that is, in principle, a value obtained by adding the requested electric power P1 and the requested electric power P2 (hereinafter, this value is referred to as "requested electric power P1+ P2"). When the requested power P1+ P2 is positive, the output voltage V2 oscillates mainly due to the negative resistance characteristic accompanying the constant power control of at least one of the 1 st and 2 nd inverters 30 and 40. On the other hand, when the requested electric power P1+ P2 is negative, the output voltage V2 oscillates mainly due to a response delay when a current flows through at least one of the 1 st and 2 nd motor generators 50 and 60. That is, the cause of the oscillation of the output voltage V2 differs depending on the positive and negative of the electric power requested by the boost converter 20. Hereinafter, the term "inverter" will be used to refer to at least one of the 1 st and 2 nd inverters 30 and 40, and the term "motor generator" will be used to refer to at least one of the 1 st and 2 nd motor generators 50 and 60.

First, a description will be given of conditions for stably supplying the output voltage V2 without oscillating when the requested electric power P1+ P2 is positive, that is, when the electric power is taken out from the boost converter 20 (when the powering operation is performed).

Output power V2 of boost converter 20 and output current (I) of boost converter 20₁+I₂) The relationship (2) is represented by the following formula (1). Wherein, V in the formula₂₀Represents the value, I, of the output voltage V2 of the boost converter 20₁₀Represents the value of the current I1 flowing through the 1 st inverter 30, I₂₀Which indicates the value of the current I2 flowing through the 2 nd inverter 40. In addition, R in the formula₀The voltage V2 output from the boost converter 20 is shown as the voltage V2₀The 1 st and 2 nd inverters 30, 40 are connected to the 1 st and 2 nd motor generators50. 60 controls the impedance of the motor generator at a constant power (requested power P1+ P2). Hereinafter, reference I with reference to FIG. 5_ofsThe description will be made.

[ mathematical formula 1]

Fig. 5 is a diagram for explaining a case where linear approximation is performed around an operating point when the 1 st and 2 nd inverters 30 and 40 control the 1 st and 2 nd motor generators 50 and 60 to be constant electric power in order to derive the above expression (1). The horizontal axis represents the output voltage V2 of the boost converter 20, and the vertical axis represents the output current (I) of the boost converter 20 ₁+I₂). In addition, the curves shown by the thick lines in the figure represent constant power lines when the 1 st and 2 nd inverters 30 and 40 control the 1 st and 2 nd motor generators 50 and 60 to be constant electric power. The operating points of the 1 st and 2 nd motor generators 50 and 60 are on the constant power line, and the horizontal axis is set to V2₀The vertical axis is set to the position of I10+ I20.

As shown, by being at the action point (V)₂₀、I₁₀+I₂₀) The periphery is linearly approximated to derive the above expression (1) (see the dotted line in the figure). Further, as shown by the broken line in the figure, Iofs in the formula (1) is determined at the operating point (V)₂₀、I₁₀+I₂₀) The intercept of the line when a linear approximation is made. In addition, R represents the impedance of the motor generator₀The positive value is set when the requested power P1+ P2 is positive, and the negative value is set when the requested power P1+ P2 is negative. In the illustrated state, the transfer characteristic from the input voltage V1 to the output voltage V2 of the boost converter 20 is represented by the following expression (2).

[ mathematical formula 2]

In the formula (2), L represents the inductance [ H ] of the reactor 3, C represents the capacitance [ F ] of the capacitor 7, and R represents the circuit resistance [ Ω ] of the boost converter 20 when the switching element 4b is turned on.

As described above, the R is set to be the power received by the boost converter 20 (the requested power P1+ P2) when it is positive ₀Is greater than 0. Therefore, R for stabilizing the output voltage V2 supplied to the boost converter 20₀The condition (2) is expressed by the following equation (3) in consideration of the value of R, L, C when the boost converter 20 is actually designed. Also, if the following formula (3) is collated with the following formula (4) and in accordance with the output voltage V2 of the boost converter 20 and the requested power P1+ P2, the condition represented by the following formula (5) can be obtained.

[ mathematical formula 3]

[ mathematical formula 4]

[ math figure 5]

Equation (5) defines conditions for stably supplying the output voltage V2 of the boost converter 20. As can be seen from equation (5), in order not to oscillate the output voltage V2 of the boost converter 20 when the requested power P1+ P2 for the boost converter 20 is positive, the output voltage V2 needs to be increased as the requested power P1+ P2 is increased. In the present embodiment, the lower limit voltage V2 of the output voltage V2 of the boost converter 20 is set so as not to oscillate the output voltage V2 of the boost converter 20_CThe formula (5) is satisfied.

In practice, the lower limit voltage V2c may be calculated by obtaining the transfer characteristic from the input voltage V1 to the output voltage V2 in consideration of the response characteristic of the current flowing through the 1 st and 2 nd motor generators 50 and 60 when the output voltage V2 of the boost converter 20 is applied to the input unit (dc unit) of the 1 st and 2 nd inverters 30 and 40. More specifically, it is considered that when the output voltage V2 of the boost converter 20 is applied to the 1 st motor generator 50, the current I1 is at the 1 st level corresponding to the requested power P1 The response characteristic of the current flowing through the dynamo-electric machine 50 and the response characteristic of the current flowing through the 2 nd motor-generator 60 according to the requested power P2 are at least one of the current I2 when the output voltage V2 of the boost converter 20 is applied to the 2 nd motor-generator 60 and the lower limit voltage V2_cAnd (6) performing calculation. This makes it possible to more accurately calculate the lower limit voltage V2c that does not cause the output voltage V2 to oscillate.

However, the lower limit voltage V2 shown on the right side of equation (5) is not considered in consideration of the response characteristic of the current_CIs calculated, and is therefore essentially the value calculated under the most stringent conditions. Therefore, the lower limit voltage V2 shown on the right side of equation (5)_CThe value of (b) is larger than that in the case of calculation in consideration of the response characteristic of the current. Therefore, when the oscillation is mainly suppressed, it is not always necessary to set the lower limit voltage V2_CThe calculation takes into account the response characteristics of the current. By applying a lower limit voltage V2_CThe output voltage V2 of the boost converter 20 can be reliably suppressed from oscillating when equation (5) is satisfied.

Next, conditions for stably supplying the output voltage V2 without oscillating when the requested power P1+ P2 is negative, that is, when the regenerative operation for supplying power to the boost converter 20 is performed will be described.

Next, as an example, a case where the 2 nd motor generator 60 performs the regenerative operation in a state where the step-up converter 20 is stopped will be described. If the transfer characteristic from the input voltage V1 to the output voltage V2 of the boost converter 20 in this case is calculated, it is represented by the following expression (7). In the following equation (7), when the output voltage V2 of the boost converter 20 is applied to the input unit (dc unit) of the 2 nd inverter 40, the response characteristic of the current when the current I2 flows through the 2 nd motor generator 60 according to the requested power P2 is considered. The current response characteristic is represented by a 2-order hysteresis system of the following equation (6). ζ in the formula (6)₂The attenuation coefficient of the 2-time lag system is shown. Omega₂The natural frequency indicating the natural frequency of the 2 nd order lag system is f2, and is a value determined at the operating point of the 2 nd motor generator 60. In addition, pleaseSince the power P1+ P2 is negative, P0 < 0 is set.

[ mathematical formula 6]

[ math figure 7]

R for stabilizing the transfer characteristics from the input voltage V1 to the output voltage V2 of the boost converter 20 is obtained based on the equation (7)₀The conditions of (1). Specifically, R is obtained such that the real part of the solution in which the characteristic equation of the denominator polynomial of equation (7) is 0 is negative ₀The conditions of (1). Based on the output voltage V2 of the boost converter and the request power P1+ P2, R obtained by the above equation (4)₀The conditions are collated, and the conditions relating to the output voltage V2 are calculated. Also, the output voltage V2 of the boost converter 20 is set to be greater than or equal to the lower limit voltage V2_CSo as to satisfy this condition, thereby the oscillation of the output voltage V2 can be suppressed.

In addition to the above conditions, there are also conditions under which the output voltage V2 is easily oscillated. For example, regardless of the positive or negative of the requested power P1+ P2 for the boost converter 20, when the resonance frequency of the boost converter 20 and the vibration frequency of the motor generator (at least one of the 1 st motor generator 50 and the 2 nd motor generator 60) are close to each other, the output voltage V2 of the boost converter 20 is likely to oscillate due to the interference between the two. Therefore, in the present embodiment, the lower limit voltage V2 of the output voltage V2 is set to be closer to the resonance frequency of the boost converter 20 and the vibration frequency of the motor generator_CThe higher the setting. This increases the output voltage of the boost converter 20, and improves the stability, so that the oscillation of the output voltage V2 can be further suppressed.

Next, a method of setting the target output voltage V2 of the boost converter 20 according to the present embodiment will be described with reference to fig. 6 to 10.

Fig. 6 is a flowchart showing a process of setting the target output voltage V2 of the boost converter 20 executed by the control device 90 according to the present embodiment. The flow described below is programmed in such a manner that the control device 90 always executes at constant intervals during startup of the vehicle system.

In step S1, the control device 90 acquires torque commands for the 1 st motor generator 50 and the 2 nd motor generator 60, respectively, and the respective rotation speeds of the 1 st motor generator 50 and the 2 nd motor generator 60.

In step S2, the control device 90 acquires the current response characteristic parameter values of the 1 st motor generator 50 and the 2 nd motor generator 60. The current response characteristic parameter value is an index indicating the current response characteristic of the motor generator, and includes information on the vibration frequency of the motor generator. The current response characteristic parameter value of the present embodiment is acquired by referring to a map storing the relationship between the operating point and the current response characteristic, in accordance with the operating point of the motor generator specified from the torque command value or the like acquired in step S1.

In step S3, the control device 90 sets the lower limit voltage V2 for stably supplying the boost converter 20 without oscillating_C. Lower limit voltage V2 in the present embodiment_CThe setting method of (2) differs depending on the following two conditions. The two conditions are (a) a case where the response characteristic of the current flowing into the inverter includes an unknown parameter, and (b) a case where the response characteristic of the current flowing into the inverter is known. In the present embodiment, the case where the response characteristic of the current is unknown means the case where the response characteristic cannot be described by the above equation (6), and the case where the response characteristic of the current is known means the case where the response characteristic can be described by the above equation (6).

First, the lower limit voltage V2 in the case of (a) above, that is, in the case where the response characteristic of the current flowing into the inverter includes an unknown parameter and cannot be described by the above equation (6)_CThe method of setting (2) will be explained. FIG. 7 is a diagram showing the lower limit voltage V2 executed in step S3 in the case of the condition (a)_CA flowchart of the setting process of (1).

In step S301, the control device 90 sets the lower limit voltage V2 to the right of the above expression (5)_C0And (6) performing calculation. Thus, the lower limit voltage V2 for preventing the output voltage V2 from oscillating is set without considering the response characteristic of the current flowing in the inverter _CAnd (6) performing calculation. At this time, as shown in equation (5), the lower limit voltage V2 is set as the requested output P1+ P2 for the boost converter 20 is larger_C0The larger. In principle, the larger the output of the motor generator is, the more easily the output voltage of the boost converter 20 oscillates. Therefore, the output of the motor generator, i.e., the request output P1+ P2, is set to be larger as the output voltage V2 is larger, whereby increase in oscillation with respect to the output voltage V2 can be suppressed.

In step S302, control device 90 sets lower limit voltage V2 in consideration of the current response delay of the motor generator_C0The value of (c) is changed. The current response lag of the motor generator affects the stability of the boost converter system constituted by the boost converter 20, the motor generator, and the inverter. Therefore, by changing the value of the lower limit voltage V2 in accordance with the current response delay of the motor generator, both the stability and the efficiency of the boost converter system can be achieved.

How the lower limit voltage V2 is changed differs depending on whether the requested power P1+ P2 is positive or negative. Specifically, when the requested power P1+ P2 is positive, that is, when power is supplied from the boost converter 20 to the load side (1 st and 2 nd inverters 30 and 40) (when power is taken out from the boost converter 20), the control device 90 calculates the response lag of the current with respect to the lower limit voltage V2 _C0Lower limit voltage V2 with smaller value and larger value_C1. When the requested power P1+ P2 is positive, the stability of the boost converter system is degraded mainly due to the influence of the negative resistance characteristic of the constant power control of the inverter. Since the influence of the negative resistance characteristic is stronger as the current response delay of the motor generator is smaller, the oscillation of the output voltage V2 can be suppressed by setting the lower limit voltage V2 to be larger as the current response delay is smaller.

On the other hand, when the requested power P1+ P2 is negative, that is, when the requested power is negative, the requested power is boosted from the load side (1 st and 2 nd inverters 30 and 40)When the converter 20 supplies electric power, the response delay of the current with respect to the lower limit voltage V2 is calculated_C0The higher the lower limit voltage V2, the larger the value_C1. When the requested electric power P1+ P2 is negative, the stability of the boost converter system decreases as the current response lag of the motor generator increases. Therefore, the lower limit voltage V2 is set to be larger as the current response lag is larger, whereby the oscillation of the output voltage V2 can be suppressed. However, in the following description, the requested power P1+ P2 is assumed. For the lower limit voltage V2 calculated in step S301_C0The lower limit voltage V2C1 is calculated by adding the lower limit voltage correction value a shown in fig. 8, for example.

Fig. 8 is a diagram showing a relationship between the lower limit voltage correction value a and the vibration frequency of the motor generator in the case where the requested power P1+ P2 is positive. As shown in the figure, the lower limit voltage correction value a is a negative value and is a value that tends to be more negative as the vibration frequency of the motor generator is smaller. The smaller the vibration frequency of the motor generator is, the larger the response lag of the current is. That is, the lower limit voltage V2 in the case where the request power P1+ P2 is positive is larger in response delay of the current_C1Relative to the lower limit voltage V2_C0The smaller the value is set.

In step S303, control device 90 calculates resonance frequency fc of boost converter 20. The resonance frequency fc is calculated by the following equation (8).

[ mathematical formula 8]

Where L in the formula (8) is an inductance [ H ] of the reactor 3, C is a capacitance [ F ] of the capacitor 7, and D is a duty ratio at which the switching element 4a is turned on. The reciprocal of D is a boosting ratio of the boost converter 20.

In step S304, the control device 90 compares the resonance frequency fc of the step-up converter 20 obtained in step S303 with the vibration frequency of the motor generator obtained in step S2 of fig. 6, and determines whether or not the absolute value of the difference (hereinafter referred to as "frequency difference") is smaller than a predetermined value a. The predetermined value A is based on the ratio of the utilization basis to the predetermined value A Lower limit voltage V calculated by comparing results_2CThe viewpoint of whether or not the oscillation of the output voltage V2 can be suppressed is predetermined by an experiment or the like. The predetermined value a in the present embodiment is set to, for example, 50 Hz. If the absolute value of the frequency difference is smaller than the prescribed value a, the subsequent processing of step 305 is performed. If the frequency difference is greater than or equal to the prescribed value A, the lower limit voltage V2 calculated in step S302 is determined_C1Set to the lower limit voltage V2_CThe process of step S3 is ended, and the subsequent process of step S4 is executed (see fig. 6).

In step S305, the lower limit voltage V2 is increased based on the frequency difference acquired in step S304_C1The value of (c). Specifically, the control device 90 controls the voltage V2 with respect to the lower limit voltage_C1And the lower limit voltage V2 with the smaller frequency difference and the larger value_CAnd (6) performing calculation. The lower limit voltage V2 calculated in this step_CBy comparing the lower limit voltage V2 calculated in step S302_C1For example, the lower limit voltage correction value B shown in fig. 9 is added to the calculated value. In other words, in this step, the lower limit voltage V2 is corrected by the lower limit voltage correction value B calculated based on the frequency difference.

Fig. 9 is a diagram showing a relationship between the lower limit voltage correction value B and the frequency difference. As shown in the figure, lower limit voltage correction value B is a positive value in a region smaller than prescribed value a of the frequency difference, and is a value that decreases as the frequency difference approaches 0. That is, in this step, the lower limit voltage V2 calculated in step S302 is corrected _C1The lower limit voltage V2 is calculated by adding the lower limit voltage correction value B which becomes larger as the frequency difference becomes smaller_C。

As a result of the voltage addition in step S305, the frequency difference decreases, and the voltage may need to be added further. More specifically, the lower limit voltage V2 is made by adding the lower limit voltage correction value B_CIf the duty ratio D is set to a smaller value in order to increase the output voltage V2, the frequency difference between the resonance frequency fc and the vibration frequency of the motor generator may be further reduced. In this case, lower limit voltage V2 is generated by adding lower limit voltage correction value B (see fig. 9) corresponding to the frequency difference that is further reduced_CResetting to a larger value.

Therefore, in the present embodiment, the processing in step S305 can be implemented in the following manner. That is, when the frequency difference after adding the lower limit voltage correction value B (see fig. 9) calculated based on the frequency difference acquired in step S304 is smaller than that before the addition, the processing according to the following two conditions may be performed. The two conditions are (c) a case where the frequency difference decreases and the resonance frequency fc of the boost converter 20 is greater than the vibration frequency of the motor generator (resonance frequency fc > vibration frequency), and (d) a case where the frequency difference decreases and the resonance frequency fc of the boost converter 20 is less than the vibration frequency of the motor generator (resonance frequency fc < vibration frequency).

In the case of (c) above, the control device 90 sets the lower limit voltage V2 calculated in step S302 to the lower limit voltage V2_C1A lower limit voltage correction value B (see fig. 9) when the frequency difference is zero is added. In the case of (d) above, the control device 90 sets the lower limit voltage V2 calculated in step S302 to the lower limit voltage V2_C1A value obtained by adding a lower limit voltage correction value B based on the frequency difference before addition to the lower limit voltage correction value B and a lower limit voltage correction value B based on the frequency difference after addition to the lower limit voltage correction value B is added. By doing so, the lower limit voltage V2 that causes the output voltage V2 not to oscillate can be set immediately_CTherefore, the lower limit voltage V2 can be shortened_CThe operation time of (2).

This is the lower limit voltage V2 in the case of the condition (a) of step S3 in fig. 6, that is, in the case where the response characteristic of the current flowing into the inverter includes an unknown parameter_CDetails of the setting method of (1). Next, referring to fig. 10, the lower limit voltage V2 in the case of the condition (b) of step 3 in fig. 6, that is, in the case where the response characteristic of the current flowing into the inverter is known_CThe method of setting (2) will be explained.

FIG. 10 is a diagram showing the lower limit voltage V2 executed in step S3 in the case of the condition (b)_CA flowchart of the setting process of (1). Note that the same processing as in the flowchart shown in fig. 7 is denoted by the same step numbers, and description thereof is omitted.

In step S311, the control device 90 sets the lower limit voltage V2 to the lower limit voltage V2 based on the above expressions (6) and (7)_C0And (6) performing calculation. Specifically, when the response characteristic of the current flowing into the inverter when the output voltage V2 of the boost converter 20 is applied to the inverter can be described by equation (6), the lower limit voltage V2 of the output voltage V2 that stabilizes the transfer characteristic (equation (7)) of the input voltage V1 to the output voltage V2 is obtained_CAnd (6) performing calculation. Further, the attenuation coefficient ζ shown in the formula (6) may be obtained in advance₂Natural frequency f2, input voltage V1 of the boost converter 20 and requested power P1+ P2 for the boost converter 20, and lower limit voltage V2 that stabilizes the output voltage V2_CA corresponding map, the lower limit voltage V2 being set according to the operating point of the motor generator by referring to the map_CAnd (6) performing calculation.

In subsequent steps S304 to S305, control device 90 executes the same processing as the processing denoted by the same step number in fig. 6, and sets lower limit voltage V2_C. Thus, when the current response characteristic is known, the lower limit voltage V2 in consideration of the current response characteristic can be immediately applied_CAnd (6) performing calculation.

As described above, the lower limit voltage V2 calculated by the flow shown in fig. 7 and 10 _CBecomes the following value. That is, the higher the requested power P1+ P2 for the boost converter 20 is, the lower limit voltage V2_CThe larger the value of (c). When the requested power P1+ P2 is positive, the lower limit voltage V2 increases as the response delay of the current flowing into the inverter increases_CThe smaller the value of (c). Further, when the requested power P1+ P2 is negative, the lower limit voltage V2 increases as the response delay of the current flowing into the inverter increases_CThe larger the value of (c). The lower limit voltage V2 is smaller as the difference (frequency difference) between the resonance frequency fc of the step-up converter 20 and the vibration frequency of the motor generator is smaller_CThe larger the value of (c). In addition, the lower limit voltage V2 may be set in consideration of a calculated value accompanying calculation, fluctuation of a detected value, and the like_CThe value obtained by adding a margin (margin) of, for example, 10% is set as the final lower limit voltage V2_C. If the lower limit voltage V2 is set_CThe control device 90 then executes the processing of step S4 shown in fig. 6. Lower partThe description is continued with reference to fig. 6.

In step S4, the control device 90 sets the 1 st efficiency optimum voltage V2_{_m1}And 2 nd efficiency optimum voltage V2_{_m2}And (6) performing calculation. More specifically, the control device 90 calculates the 1 st efficiency optimum voltage V2 for the 1 st motor generator 50 based on the torque command for the 1 st motor generator 50 and the motor rotation speed of the 1 st motor generator 50 _{_m1}And a 2 nd efficiency optimum voltage V2 for the 2 nd motor generator 60 is calculated based on the torque command for the 2 nd motor generator 60 and the motor rotation speed of the 2 nd motor generator 60_{_m2}。

In step S5, the controller 90 determines the lower limit voltage V2 from step S3_CThe 1 st efficiency optimum voltage V2 obtained in step S4_{_m1}And the 2 nd efficiency optimum voltage V2_{_m2}The maximum voltage value among the 3 voltage values is selected, and the selected voltage value is set as a target output voltage V2 (target output voltage command value V2). Thereby, the output voltage V2 satisfying the requested power P1+ P2 and having suppressed oscillation can be output to the boost converter 20.

An effect of the method for controlling the boost converter 20 according to the present embodiment will be described with reference to fig. 11.

Fig. 11 is a timing chart illustrating a change in the output voltage V2 in the case where the control method of the boost converter 20 according to the present embodiment is applied. Fig. 11(a) shows the output voltage of the boost converter 20, and fig. 11(b) shows the requested electric power P1+ P2 for the boost converter 20. The horizontal axis of both figures represents time.

As shown, the requested electric power P1+ P2 represents a constant value of a positive value, and the vehicle is in power running. At this time, in the case of calculating the target output voltage for the boost converter 20 from the requested power P1+ P2, if only the efficiency is considered as it is, the target output voltage shown by the chain line in fig. 11(a) is calculated. As a result, as shown by the broken line in the figure, the actual output voltage output from the target output voltage considering only the efficiency oscillates.

In contrast, according to the present embodimentThe control device of the boost converter 20 of the embodiment controls the target output voltage (the 1 st efficiency optimum voltage V2) in which only the efficiency is considered as in the conventional case_{_m1}2 nd efficiency optimum voltage V2_{_m2}) A calculation is made, and a lower limit voltage V2 that causes the actual output voltage not to oscillate is applied_CAnd (6) performing calculation. Then, the highest voltage value is set as the target output voltage V2 by the high selection of the voltage values. As shown in the drawing, the lower limit voltage V2 calculated by the control method of the boost converter 20 according to the present embodiment_CGreater than the target output voltage calculated as currently considering efficiency alone. Therefore, according to the present embodiment, the lower limit voltage V2 is selected by high selection_CLower limit voltage V2_CSet to the target output voltage V2. As a result, the actual output voltage oscillation of the boost converter 20 can be suppressed more greatly than in the past.

As described above, the method of controlling the boost converter 20 according to the embodiment is a method of controlling the boost converter 20 that boosts a voltage input from a power supply and supplies the boosted voltage to a load side, and the boost converter is controlled by calculating a lower limit voltage value (lower limit voltage V2c) that ensures output power (request power P1+ P2) requested in accordance with an operating point of a motor (1 st and 2 nd motor generators 50 and 60) connected to the load side and prevents the output voltage V2 of the boost converter 20 from oscillating, setting the target output voltage V2 of the boost converter 20 to a value greater than or equal to the lower limit voltage V2c, and outputting a voltage corresponding to the target output voltage. This can suppress oscillation of the output voltage V2 of the boost converter 20. As a result, it is possible to prevent the output voltage V2 from oscillating, thereby preventing the generation of an overvoltage, an overcurrent, and torque oscillation of the motor generator.

In addition, according to the control method of the boost converter 20 of one embodiment, the lower limit voltage V2c is set to a value that is larger as the output power of the motor generator (the requested output P1+ P2) is larger. Accordingly, the output voltage V2 is set to be larger as the output P1+ P2 is larger, and therefore, an increase in oscillation can be suppressed with respect to the output voltage V2. As a result, it is possible to prevent the output voltage V2 from oscillating, thereby preventing the generation of an overvoltage, an overcurrent, and torque oscillation of the motor generator.

In addition, according to the control method of the boost converter 20 of the embodiment, the lower limit voltage V2c is changed according to the magnitude of the current response delay of the motor generator. This makes it possible to achieve both stability and efficiency of the boost converter system.

In the method of controlling the boost converter 20 according to the embodiment, when the electric power is supplied from the boost converter 20 to the load side (1 st and 2 nd inverters 30 and 40), the lower limit voltage V2c is set to a value that is larger as the current response delay of the motor generator is smaller. This can reduce the influence of the constant power control of the inverter on the negative resistance characteristic, and therefore can suppress the oscillation of the output voltage V2.

In the method of controlling the boost converter 20 according to the embodiment, when the electric power is supplied from the load side (1 st and 2 nd inverters 30 and 40) to the boost converter 20, the lower limit voltage V2 is set to a value that increases as the current response delay of the motor generator increases. This can suppress oscillation of the output voltage V2.

In addition, according to the control method of the boost converter 20 of the embodiment, the lower limit voltage V2 is corrected by adding the correction value (the lower limit voltage correction value B) calculated so that the frequency difference between the resonance frequency of the boost converter 20 and the vibration frequency of the motor generator becomes larger as the frequency difference becomes smaller. This increases the output voltage of the boost converter 20, and improves the stability, so that the oscillation of the output voltage V2 can be further suppressed.

In addition, according to the control method of the boost converter 20 of one embodiment, the correction value (lower limit voltage correction value B) is set to a value calculated when the frequency difference is smaller than the frequency difference before correction and the resonance frequency fc of the boost converter 20 is larger than the vibration frequency of the motor generator after correction, and the frequency difference is 0. This can shorten the calculation time and calculate the target output voltage V2, which does not oscillate the output voltage, more quickly.

In addition, according to the control method of the boost converter 20 of one embodiment, the correction value (lower limit voltage correction value B) is set to a value obtained by adding the correction value (lower limit voltage correction value B) calculated based on the frequency difference before correction and the correction value (lower limit voltage correction value B) calculated based on the frequency difference after correction when the frequency difference is smaller than before correction and the resonance frequency fc of the boost converter 20 is smaller than the vibration frequency of the motor generator after correction. This can shorten the calculation time and calculate the target output voltage V2, which does not oscillate the output voltage, more quickly.

In addition, according to the control method of the boost converter 20 of the embodiment, the optimal efficiency voltage value (1 st and 2 nd efficiency optimal voltages V2) for driving the motor generator most efficiently while ensuring the output power (the requested power P1 and P2) requested according to the operating point of the motor generator is calculated_{_m1}、V2_{_m2}) The larger voltage value of the lower limit voltage V2c and the optimum efficiency voltage value is set as the target output voltage V2. As a result, particularly when the optimum efficiency voltage value is larger than the lower limit voltage V2c, the output voltage V2 that can drive the motor generator most efficiently can be output to the boost converter 20 while suppressing hunting.

The present invention is not limited to the above-described embodiments, and various modifications and applications can be realized.

For example, although the description has been given of the case where the vehicle to which the control method of the boost converter 20 of the present embodiment is applied is a series hybrid vehicle, the present invention is not limited to this. The method of controlling the boost converter 20 according to the present invention can be suitably applied to a boost converter system in which at least one set of an inverter and a motor is connected to the load side of the boost converter 20.