KR20190051329A - Method for controlling dc-dc converter - Google Patents

Abstract

The present invention relates to a control method of a DC-DC converter, which reduces the consumption output of a converter charged with a low-voltage battery. The control method comprises the steps of: learning an efficient operation section so that the DC-DC converter operates at the optimum power conversion efficiency; collecting an input side voltage value and an output side voltage value of the DC-DC converter and a state of charge (SOC) value of a low voltage battery; determining an output power of the DC-DC converter such that the DC-DC converter performs a converting operation in the efficiency operation period corresponding to the input side voltage value and the output side voltage value taking into consideration the SOC value of the low voltage battery; and calculating a duty value corresponding to the determined output power so that the DC-DC converter performs the converting operation within the efficient operation period.

Description

METHOD FOR CONTROLLING DC-DC CONVERTER [0001]

The present invention relates to a control method of a DC-DC converter, and more particularly, to a control method of a DC-DC converter that efficiently operates a 48V DC-DC converter based on a battery state.

In general, a hybrid vehicle is a future type vehicle that travels by a combination of an engine and a motor. The hybrid vehicle is classified into a parallel type, a series type, and a hybrid type according to the driving method. Middle, and Hard types.

The mild hybrid system, which is classified as a mild type, is a system that utilizes a 48V battery through engine torque assist and regenerative braking for the purpose of improving fuel economy compared to a conventional internal combustion engine only.

In a mild hybrid system, the 48V battery is responsible for engine torque assist, regenerative braking and high load, while conventional 12V battle batteries are responsible for low loads.

A DC-DC converter that controls the flow of electrical energy between a 48V battery and a 12V battery should provide an electrical load connected to the 12V battery while maintaining the proper level of charge for the 12V battery.

Since the output voltage (or output power) of a conventional 48V DC-DC converter is set to a specific value and the voltage of the 12V battery is controlled to be constant, the output voltage of the converter (48V battery) The control considering the efficiency interval of the converter is not performed according to the variation and the output power.

An object of the present invention is to set the efficiency period of a DC-DC converter and to set the output power of the DC-DC converter and the 12V battery reference voltage in consideration of the state of charge (SOC) and voltage value of the low- And to reduce the power consumption of a converter charged with a low-voltage battery by increasing the power conversion efficiency of the DC-DC converter.

In order to accomplish the above object, a control method of a DC-DC converter of the present invention includes: learning an efficient operation period so that the DC-DC converter operates at an optimal power conversion efficiency; Collecting an input side and an output side voltage value of the DC-DC converter and an SOC value of the low voltage battery; Determining an output power of the DC-DC converter such that the DC-DC converter performs a converting operation in the efficient operation period corresponding to the input side and output side voltage values, taking into account the SOC value of the low voltage battery; And calculating a duty value corresponding to the determined output power so that the DC-DC converter performs a converting operation within the efficient operation interval.

According to the present invention, a DC-DC converter for charging a low-voltage battery in a power system using a high-voltage battery and a low-voltage battery utilizes the input side voltage, the voltage of the output side low-voltage battery, the SOC and the load power information, By operating in the region, it is possible to improve power conversion efficiency and further improve fuel economy. In addition, based on the SOC strategy of the low-voltage battery,

1 is a configuration diagram of a mild hybrid system according to an embodiment of the present invention.
2 is a functional block diagram of the converter controller shown in Fig.
3 is a flowchart illustrating a learning process of an efficient operation period according to an embodiment of the present invention.
4 is a flowchart illustrating an operation of a converter controller according to an exemplary embodiment of the present invention.
5 is a flowchart showing the detailed procedure of step S420 shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

1 is a configuration diagram of a mild hybrid system according to an embodiment of the present invention.

1, a mild hybrid system according to an embodiment of the present invention includes a high-voltage battery pack 100, a low-voltage battery pack 200, a DC-DC converter 300, an electric load 400, and a converter controller 500, . In Fig. 1, a dotted line in the form of an arrow indicates a CAN communication line.

The high voltage battery pack 100 and the low voltage battery pack 200 are charged or discharged with a constant voltage in accordance with the operation mode (electric mode or power generation mode) of the motor.

The high-voltage battery pack 100 is charged by supplying power to the motor 20 through the inverter 10 or by regenerative braking. The high voltage battery pack 100 may be, for example, a 48V battery pack. Here, the regenerative braking means that the motor 20 is operated as a generator to convert kinetic energy into electric energy.

This high voltage battery pack 100 may be configured to include a high voltage battery control unit 110 and a high voltage battery 120 composed of a 48 V cell.

The high voltage battery controller 110 provides the voltage value (or current value) and the state of charge (SOC) value of the high voltage battery 120 to the DC-DC converter 300. The manner of providing the voltage value and the SOC value includes a periodic and / or real-time providing method. The high voltage battery controller 110 may be referred to as a battery management system (BMS) that manages the temperature and voltage of the high voltage battery.

The inverter 10 is connected in series between the motor 20 and the high voltage battery pack 100. When the operation mode of the motor 20 is the motoring mode, the voltage applied from the high voltage battery pack 100 (Regenerative braking mode), converts the voltage applied from the motor 20 to direct current, and transmits the direct current to the high voltage battery pack 100.

The low voltage battery pack 200 supplies power to the load 400 in the vehicle. The load 400 may be a full-field system in the vehicle. The low-voltage battery pack 200 may be, for example, a 12V battery pack.

The low voltage battery pack 200 may be configured to include a low voltage battery control unit 210 and a low voltage battery 220 configured as a 12 V cell.

The low-voltage battery control unit 210 provides the voltage value (or current value) and the SOC value of the low-voltage battery 220 to the DC-DC converter 100. The low voltage battery control unit 210 may be sometimes referred to as a battery management system (BMS) that manages the temperature or voltage of a low voltage battery.

The DC-DC converter 300 may be connected in parallel between the high-voltage battery pack 100 and the low-voltage battery pack 200. Although not shown in detail, the DC-DC converter 300 may include a switching device, an inductor, a capacitor, and a diode for reflux.

The DC-DC converter 300 can operate in a boosting mode (BOOST) or a step-down mode (BUCK) according to the operation mode of the motor 20. [ For example, a step-up mode for stepping up the voltage of the low-voltage battery 220 to supply power to the motor 20 or a step-down mode for stepping down the voltage supplied from the motor 20 and supplying power to the low- Way DC-DC converter driven by a BUCK.

The converter controller 500 controls the DC-DC converter 300 to set an efficiency operation period with a high power conversion efficiency and perform a converting operation within the set efficiency operation period, thereby controlling the energy conversion of the DC-DC converter 300 Improve efficiency. This improvement in energy conversion efficiency can lead to additional fuel economy improvements.

Hereinafter, the converter controller 500 will be described in detail.

2 is a functional block diagram of the converter controller shown in Fig.

2, the converter controller 500 includes a collecting unit 510, an output power determining unit 520, a duty value calculating unit 530, an efficiency driving unit learning unit 540, and a storage 550 do.

The collecting unit 510 collects battery information from the two battery packs 100 and 200 and electric-charge-load information from the electric-field load 400.

The collected battery information includes voltage value (or current value) and SOC value.

The voltage value (or the current value) is the voltage value of the high-voltage battery 120 measured at the input terminal (302 in FIG. 1) of the DC-DC converter 300 connected to the high-voltage battery 120, And the voltage value of the low-voltage battery 220 measured at the output terminal (304 in FIG. 1) of the DC-DC converter.

The SOC value includes the SOC value of the low voltage battery 220 provided in the low voltage battery control unit 210 in the low voltage battery pack 200. At this time, the low-voltage battery control unit 210 may not be designed in the low-voltage battery pack 200 according to the design. In this case, the SOC value or the voltage value (or the current value) of the low-voltage battery 220 may be obtained from a voltage sensor (not shown) provided at the (-) terminal of the low-

The electrical field load information includes power values (hereinafter, referred to as " electric field load power values ") consumed (required or required) by each of a plurality of electric field loads.

The collector 510 for collecting the voltage value (or the current value), the SOC value, and the electric field load power value may be referred to as a sensor that performs a monitoring function. For example, converter controller 500 may monitor the operational status of electrical loads, request electrical load power values for the operational electrical loads, and provide electrical load power values from operational electrical loads in response to the request Can receive.

The output power determining unit 520 comprehensively analyzes the voltage value (or the current value), the SOC value, and the electric field load power value provided from the collecting unit 510 and performs a conversion operation within the pre- To-DC converter (300).

The efficient operation section is previously learned by the efficient operation section learning section 540, and the learned efficiency operation section is stored in the storage 550 in the form of a table.

The efficiency operation section table stored in the storage 550 is loaded into the output power determining section 520 at the request of the output power determining section 520 and the efficiency operation section table loaded into the output power determining section 520 is stored in the DC- DC converter 300. In this case, as shown in FIG.

The duty value calculation unit 530 receives the output power value determined in the efficiency operation period having the excellent power conversion efficiency from the output power determination unit 520, calculates a duty value corresponding to the received output power value, To-DC converter (300).

The various switching elements in the DC-DC converter 300 perform the switching operation in accordance with the duty value calculated from the output power value determined in the efficiency operation period having the excellent power conversion efficiency, so that the DC-DC converter 300 basically performs the switching operation, The converting operation can be performed within the efficient operation section having excellent power conversion efficiency.

Also, since the converting operation of the DC-DC converter 300 reflects the power value of the running electric load 400, the DC-DC converter 300 converts the low voltage battery that supplies electric power to the electric load 400 It is possible to reduce the power consumption and further improve the durability of the low voltage battery.

Hereinafter, the operation process performed by the converter controller 500 shown in FIG. 2 will be described in detail.

3 is a flowchart illustrating a learning process of an efficient operation period according to an embodiment of the present invention. The execution subject of each step described below is assumed to be the efficiency driving section learning unit 540 shown in FIG. 2 unless otherwise specified.

Referring to FIG. 3, in step S310, a process of measuring an input-side learning voltage and an output-side learning voltage of the DC-DC converter 300 is performed. The learning voltage is used as learning data for learning the efficient operation period of the DC-DC converter. The learning voltage on the input side is the voltage level (or voltage value) of the high voltage battery measured for learning on the input side terminal 302 of the DC-DC converter 300, 304 is a voltage level (voltage value) of the low-voltage battery measured for learning.

Next, in step S320, a process of learning the optimal output power value (OOP) of the DC-DC converter 300 using the currently measured input side learning voltage and the output side learning voltage is performed. Various learning methods such as machine learning can be utilized as a method of learning the optimum output power value.

Next, in step S330, an efficiency operation section including an upper output power value (UOP) and a lower output power value (LOP) centered on the learned optimal output power value (OOP) A determination process is performed.

This efficient operation section is made up of the upper limit interval between the optimum output power value OOP and the upper limit output power value and the lower limit interval between the optimum output power value OOP and the lower limit output power value LOP.

The upper limit interval and the lower limit interval may be set the same or may be set differently. In order to avoid the complexity of the design, it would be desirable to set the upper and lower spacings equally.

The efficiency operation section is determined according to a certain ratio (%) of the optimum output power value (OOP) learned for each input / output side voltage.

Specifically, the efficiency operation period is determined based on the learned optimal output power value OOP for each input / output side voltage of the DC-DC converter 300, within a certain ratio of the optimal output power value OOP, The value LOP and the upper limit output power value UOP can be set.

For example, assuming that the optimum output power value OOP learned from the specific input side / output side voltage of the DC-DC converter 300 is 100 (W), a certain ratio is 10%, and the upper limit interval and the lower limit interval Since the width of the effective operation section is 10, which corresponds to 10% of 100, and the upper limit interval and the lower limit interval are the same, the lower limit output power value (LOP) is 95 and the upper limit output power The value (UOP) becomes 105. Therefore, in this example, the optimum output power value OOP can be determined to be 95 (W) to 105 (W) around 100 (W) in the efficiency operation period. The numerical values set forth herein assume an excessively high value to aid understanding of the description.

The thus determined efficiency operation period is utilized as a reference index for determining the output power of the converter 300 so as to operate at an excellent power conversion efficiency in the output power determination unit 520 (FIG. 2).

On the other hand, the efficiency of the DC-DC converter 300 may be affected by the temperature. This is because the characteristics of the elements (for example, resistors, capacitors, inductors, MOSFETs, diodes, etc.) constituting the converter 300 depend on the temperature.

As described above, since the efficiency operation section obtained through learning does not consider the influence of temperature, its reliability may be deteriorated. Therefore, in order to increase the reliability, the efficiency operation section needs to be adjusted in consideration of the current temperature at which the converter operates.

As the temperature rises, the resistance value of the resistor increases and the power loss increases accordingly. Thus, it is known that the power conversion efficiency can be expected to decrease and the actual measurement results also match the expectations.

Thus, since the temperature and the power conversion efficiency are in inverse proportion, the width of the learned efficiency operation section should be adjusted to be small as the converter temperature rises. That is, a certain ratio (%, upper limit output power value and lower limit output power value) of the optimum output power (OOP) for determining the effective operation interval by temperature should be corrected to an appropriate value.

The power loss ( P _loss ) calculated from an arbitrary input side learning voltage (input side learning current) and an arbitrary output side learning voltage (output side learning current) is calculated for each operating temperature of the converter and then an arbitrary input side learning voltage (Learning current on the input side) and an arbitrary output-side learning voltage (output-side learning current) using a power loss ( P _loss ) calculated at each operating temperature.

In the case where the operating temperature of the DC-DC converter 300 is t , the power loss can be calculated by the following equation (1).

Here, V _in and I _in are input side learning voltage and input side learning current of the converter, respectively, and V _out and I _out are respectively an output side learning voltage corresponding to the input side learning voltage of the DC-DC converter and an output side learning Current.

In the case where the operating temperature of the DC-DC converter 300 is t , the corrected efficiency operation period can be calculated by the following equation (2).

&Quot; (2) "

LOP - P _loss ≤ OOP ≤ UOP - P _loss .

Here, LOP is the lower limit output power value, UOP is the upper limit output power value, and OOP is the optimal output power value.

 As described above, the efficiency operation period corrected for each operating temperature of the DC-DC converter 300 is configured in a table form and stored in the storage (550 in FIG. 2).

The following table is an example of the efficiency operation section table corrected by the operating temperature of the converter.

Temperature 1 ( P _loss1 ) Temperature 2 ( P _loss2 ) Temperature 3 ( P _loss3 ) Temperature 4 ( P _loss4 ) Calibrated efficiency
Driving section LOP - P _loss1 ? OOP? UOP - P _loss1 LOP - P _loss2 ? OOP? UOP - P _loss2 LOP - P _{loss 3} ≤ OOP ≤ UOP - P _loss3 LOP - P _{loss 4} ≤ OOP ≤ UOP - P _loss4

4 is a flowchart illustrating an operation of a converter controller according to an exemplary embodiment of the present invention.

Referring to FIG. 4, first, in S410, a process of collecting a plurality of pieces of information by the collecting unit 510 in the converter controller 510 is performed. The plurality of pieces of information includes the current input side voltage value (or current input side current value), the current output side voltage value (current output side current value) of the DC-DC converter 300, the SOC value of the low voltage battery, And the current temperature value of the DC-DC converter 300.

In step S420, the output power determination unit 520 in the converter controller 510 analyzes the collected information and determines the output power of the DC-DC converter 300 so as to perform a conversion operation in the efficient operation period Is performed.

Next, in step S430, a duty value calculation unit 530 in the converter controller 510 calculates a duty value corresponding to the determined output power of the DC-DC converter 300. [

In step S440, the DC-DC converter performs the converting operation in the efficient operation period according to the calculated duty value.

FIG. 5 is a flowchart showing the detailed procedure of step S420 shown in FIG. 4. Unless otherwise specified, the execution subject of each of the following steps is assumed to be the output power determining unit 520. FIG. In the following description of each step, contents overlapping with those described in Figs. 1 to 4 will be described briefly or omitted.

Referring to FIG. 5, first, in step S420-1, the efficiency operation section table stored in the storage (550 in FIG. 2) is inquired and a dictionary corresponding to the current input side / current output side voltage value of the DC- The learned efficiency section is searched for. At this time, the current temperature value of the DC-DC converter 300 may be further utilized to increase the reliability of the efficient operation period. That is, an efficiency operation section corresponding to the current input side / current output side voltage value of the DC-DC converter 300 and the current temperature value of the DC-DC converter 300 can be searched.

Next, in step S420-3, a process of comparing the SOC value of the low-voltage battery with the first reference SOC value is performed. The first reference value may be variously set as a criterion for determining the degree of fullness of the low-voltage battery (220 in FIG. 1), and may be set at a value between 75 and 100%, for example.

In step S420-5, if the SOC value of the low-voltage battery (220 in FIG. 1) is equal to or greater than the first reference SOC value, the output power of the DC-DC converter 300 is determined to be OFF. Voltage battery 220 is not required to be charged and the low-voltage battery 220 can supply electric power to the electric-field load 400 alone in a state where the charging state of the low-voltage battery is sufficient, the DC-DC converter 300 Is stopped in terms of power conversion efficiency.

Next, in step S420-7, when the output power OFF of the DC-DC converter 300 is determined in step S420-5, a process of determining the duty value so that the converting operation of the DC-DC converter 300 is stopped is performed .

On the other hand, if the SOC value of the low-voltage battery is less than the first reference SOC value in the comparison process of step S420-3, the process proceeds to step S420-9.

In step S420-9, a process of comparing the SOC value of the low-voltage battery with the second reference SOC value is performed. The second reference SOC value may be set to a value smaller than the first reference SOC value, for example, between 40 and 65%. If the SOC value of the low-voltage battery is equal to or greater than the second reference SOC value, the process proceeds to step S420-11. If the SOC value of the low-voltage battery is smaller than the second reference SOC value, the process proceeds to step S420-17.

If the SOC value of the low-voltage battery is equal to or greater than the second reference SOC value, in step S420-11, both the optimum output power value OOP and the electric power value of the electric field load 400 in the efficiency safety interval searched in step S420-1 A process of comparing the absolute value of the difference of the summed values with the allowable reference value is performed. If the absolute value is smaller than the allowable reference value, the process proceeds to step S440-13; otherwise, the process proceeds to step S440-15.

In step S440-13, the process of determining the output power of the DC-DC converter 300 as the optimal output power value OOP is performed.

When the output power of the DC-DC converter 300 is determined as the optimum output power value OOP, the DC-DC converter 300 sets the optimum output power value OOP to the optimum output power value OOP so that the DC- The process of determining the corresponding duty value (S420-7) is performed.

If the absolute value is equal to or greater than the allowable reference value, in step S420-15, the output power of the DC-DC converter 300 is converted into an output power value corresponding to the power value of the current running load 400 in the efficient operation period A determination process is performed. Thereafter, a step S420-7 is performed in which the DC-DC converter 300 determines a duty value corresponding to the output power value corresponding to the power value of the electric field load 400 currently in operation.

If the SOC value of the low-voltage battery 220 is smaller than the second reference SOC value, the process proceeds to step S420-17. If the SOC value of the low-voltage battery 220 is smaller than the second reference SOC value, , The charging state of the low-voltage battery 220 is extremely unstable. In this case, a process of determining the output power of the DC-DC converter 300 as the upper limit output power value UOP of the efficiency safety section is performed. Depending on the design, the output power of the DC-DC converter 300 may be determined as an output power value that is larger than the upper limit output power value UOP. Then, in step S420-7, a step S420-7 of determining a duty value corresponding to the output power value larger than the upper limit output power value UOP or the upper limit output power value UOP is performed.

As described above, in the present invention, the efficiency safety interval is learned in advance according to the input / output side voltage value of the DC-DC converter 300 which fluctuates from time to time, and the DC-DC converter 300 performs the conversion operation in the efficiency safe interval So that the power conversion efficiency performance of the DC-DC converter 300 can be improved.

Further, not only does the DC-DC converter perform the conversion operation in the efficiency safety interval, but also determines the optimum output power value in the efficiency safety interval according to the SOC value of the low-voltage battery 220, the DC-DC converter 300 It is possible to reduce the power consumption and further improve the durability of the low-voltage battery 220 in a state of operating in a mode of charging the low-voltage battery.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications not illustrated in the drawings are possible. For example, each component specifically shown in the embodiments of the present invention can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (11)

Learning an efficient operation period so that the DC-DC converter operates at an optimum power conversion efficiency;
Collecting an input side and an output side voltage value of the DC-DC converter and an SOC value of the low voltage battery;
Determining an output power of the DC-DC converter such that the DC-DC converter performs a converting operation in the efficient operation period corresponding to the input side and output side voltage values, taking into account the SOC value of the low voltage battery; And
Calculating a duty value corresponding to the determined output power so that the DC-DC converter performs a converting operation within the efficient operation interval;
The DC-DC converter comprising:
2. The method of claim 1,
Measuring an input-side learning voltage and an output-side learning voltage of the DC-DC converter;
Learning the optimal output power value of the DC-DC converter using the measured input-side learning voltage and the output-side learning voltage;
Determining an efficiency operation period including an upper limit output power value and a lower limit output power value about the optimum output power value
The DC-DC converter comprising:
3. The method of claim 2,
Wherein the output power of the DC-DC converter is determined according to a certain ratio of the optimum output power value.
3. The method of claim 2,
A step of correcting the efficiency operation period using the power loss according to the operating temperature of the DC-DC converter
Further comprising the step of controlling the DC-DC converter.
2. The method of claim 1,
Searching the efficiency operation section corresponding to the input side and output side voltage values with reference to the efficiency operation section table generated in the learning step; And
Determining an output power of the DC-DC converter to perform a converting operation within the searched efficiency operation period;
Wherein the DC-DC converter comprises a DC-DC converter.
The method according to claim 5,
Wherein the DC-DC converter includes a plurality of efficient operation periods according to an operating temperature of the DC-DC converter.
6. The method of claim 5,
DC converter according to claim 1, wherein the current operation temperature value of the DC-DC converter is further considered in addition to the input side and output side voltage values to search the efficiency operation section in the efficiency operation section table.
2. The method of claim 1,
And turns off the output power of the DC-DC converter when the SOC value of the low-voltage battery is equal to or greater than a first reference SOC value.
2. The method of claim 1,
When the SOC value of the low-voltage battery is less than the first reference SOC value and is equal to or greater than a second reference SOC value less than the first reference SOC value, an optimal output power value corresponding to the center of the efficiency- Comparing a difference value between the power values of the connected electric field loads with an allowable reference value; And
Determining an output power of the DC-DC converter as the optimal output power value when the difference value is smaller than the allowable reference value
Wherein the DC-DC converter comprises a DC-DC converter.
10. The method of claim 9, further comprising: determining an output power of the DC-DC converter as an output power value corresponding to a power value of a currently operating electric field load when the difference value is equal to or greater than the allowable reference value
Further comprising the step of controlling the DC-DC converter.
The method as claimed in claim 9, further comprising: determining an output power of the DC-DC converter as an upper limit output power value corresponding to an upper limit value of the efficiency operation section when the SOC value of the low-voltage battery is less than the second reference SOC value
Further comprising the step of controlling the DC-DC converter.

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