KR20190084681A - Method of efficiently controlling battery chargers and a battery charger adopting the same - Google Patents

Abstract

An objective of the present invention is to provide a method of controlling a switching frequency by finding a maximal efficiency point of switching driving of a slow charger of battery, etc., and a battery charger adopting the same. The present invention provides a switching frequency control method of a battery charger (hereinafter, referred to as ′charger′) including a resonant converter driven at a switching frequency f0. The method comprises the steps of: sensing an output voltage and an output current of the charger to obtain an output voltage sensing value and an output current sensing value; acquiring a voltage condition gain value based on the output voltage sensing value; determining a switching frequency candidate f1 based on the voltage condition gain value; acquiring a load condition gain value based on the output current sensing value; determining a switching frequency candidate f2 based on the load condition gain value; performing a switching process with each of the switching frequency candidate f1 and switching frequency candidate f2 to operate the charger; and determining a frequency of which power values are less deviated as the optimal switching frequency by respectively comparing output and input power values in case of f0, output and input power values in case of f1 and output and input power values in case of f2 in order to determine an optimal switching frequency from the switching frequency candidate f1 and the switching frequency candidate f2.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of controlling an optimum efficiency of a battery charger, and a charger employing the same.

The present invention relates to a control method for optimum efficiency of a charger which improves the charging efficiency of a battery charger including a resonant converter (for example, a slow charging charger, etc.) .

A conventional electric vehicle battery charger consists of an AC-DC stage that boosts power from the AC utility line to 400 VDC and a DC-DC stage that converts DC to the required voltage level. These two stages may include separate DC-DC converters. In order to improve the efficiency and controllability of this DC-DC converter, LLC resonant converter is widely used.

1 is an example of such an LLC resonant converter circuit (Korean Patent Laid-Open No. 10-2016-0070820, published on June 20, 2016). The LLC resonant converter 800 includes a power input stage 502, a resonant tank 504, and a power output stage 506. The sensing unit 808 includes a rectifier (consisting of a capacitor C1, a capacitor C2, a diode D1 and a diode D2), a DC blocking capacitor C4, a load resistor R1, / Filter circuit. An efficient point tracking control mechanism is applied to these LLC resonant converters with an internal Q value to automatically track the maximum efficiency point.

Thus, in the conventional resonant converter, a separate circuit (for example, the detector 808 in FIG. 1) for sensing the voltage and current applied to both ends of the resonant inductor (for example, Lr in FIG. 1) The threshold value is adjusted by setting the threshold value according to the level of the load current. Since the range of the threshold value may vary depending on the distribution of the constituent circuit components, there is a disadvantage in that the efficiency point tracking control mechanism can not reach the maximum efficiency point . In addition, conventional resonant converters can produce switching losses due to zero voltage switching and zero current switching.

Accordingly, it is an object of the present invention to provide a method of controlling the switching frequency by finding the maximum efficiency point of switching operation of a battery full charging charger (hereinafter referred to as a 'charger') and a battery charger employing the method.

Another object of the present invention is to provide a method of adjusting a switching frequency in consideration of dispersion (tolerance range) of circuit components in a charger and a battery charger employing the method.

The prior art requires a separate circuit configuration for checking and controlling the waveform form through the detection of the resonance waveform. However, in the present invention, the switching frequency is varied through the tracking algorithm for the current sensing value and the gain control, .

And has an additional function of defining a threshold value to further determine whether the component is abnormal and delivering information to the user.

According to an aspect of the present invention, there is provided a method of controlling a switching frequency of a battery charger (hereinafter 'charger') including a resonant converter driven with a switching frequency f0, the method comprising the steps of: Sensing an output voltage and an output current of the charger; Obtaining a voltage condition gain value based on the output voltage sensing value; Determining a switching frequency candidate f1 based on the voltage condition gain value; Obtaining a load condition gain value based on the output current sensing value; Determining a switching frequency candidate f2 based on the load condition gain value; Operating the charger by switching to the switching frequency candidate f1 and the switching frequency candidate f2, respectively; In order to determine an optimum switching frequency among the first switching frequency candidate and the second switching frequency candidate, an output and input power value at f0, an output and input power value at f1, and an output at f2 and an input And comparing the power values with each other to determine a frequency having a small deviation of the power value as an optimum switching frequency.

Here, the step of acquiring the voltage condition gain value of the charger based on the output voltage sensing value may use a gain table for defining a gain value with respect to the output voltage sensing value for the charger. In another embodiment, the step of acquiring the voltage condition gain value of the charger based on the output voltage sensing value comprises the steps of: determining a gain trend line algorithm represented by a voltage trend line of y = f (x) (y = gain, x = sensing voltage) Can be used.

Also, the step of obtaining the load condition gain value of the charger based on the output current sensing value may use a gain table that defines a gain value with respect to the output current sensing value for the charger. In another embodiment, the step of acquiring the load condition gain value of the charger based on the output current sensing value comprises the steps of: determining a gain trend line algorithm represented by a current trend line of y = f (x) (y = gain, x = Can be used.

The switching frequency control method may further include determining that the resonant component included in the charger is an abnormal component if the optimum switching frequency is equal to or higher than the limit value. In this step, an algorithm for varying the optimum switching frequency by adjusting the gain value with respect to the tolerance range of the resonance component may be used.

According to another aspect of the present invention, there is provided a battery charger optimum efficiency control apparatus configured to execute the battery charger optimum efficiency control method configured as described above.

According to another aspect of the present invention, there is provided a battery charger including the battery charger optimum efficiency control device.

The structure and effect of the present invention described above will become more apparent from the following detailed description of the invention together with the drawings.

According to the present invention, it is possible to improve the charging efficiency by improving the efficiency of the charger by the switching control technique for the optimum efficiency, and to shorten the charging time and the charging cost of the user by improving the charging efficiency.

In the prior art, it is necessary to have a separate circuit configuration for checking and controlling the shape of the waveform through the detection of the resonance waveform. However, in the present invention, the switching frequency is changed through the tracking algorithm for the current sensing value and the gain control, . And has an additional function of defining a threshold value to further determine whether the component is abnormal and delivering information to the user.

1 is a circuit diagram of a conventional LLC resonant converter
2 is a block diagram of a resonant converter to which a charger optimum efficiency control method according to the present invention is applied
3 is an example of a circuit diagram in which the block diagram shown in Fig. 2 is actually constructed.
4 is a flow chart of a charger optimum efficiency control method according to one embodiment of the present invention.
5 is an exemplary diagram of a gain table;
6 is a flow chart of a method for controlling optimum charger efficiency according to another embodiment of the present invention.
FIG. 7 is an illustration of a table of change in minimum, medium, maximum values and switching frequency of an inductor and a capacitor; FIG.

Before describing specific embodiments for carrying out the present invention, charging of an electric vehicle, one technical field to which the present invention may be applied, will be briefly described first. An electric vehicle is a vehicle in which a battery is used as a main driving source of a vehicle. In order to charge the battery, a vehicle-mounted charger OBC (On Board Charger) is connected to the charging port, and the household AC power is converted into DC to charge the battery. The OBC receives electricity using electric vehicle supply equipment (EVSE). When receiving electricity, EVSE checks the voltage command value included in the control pilot (CP) do. Battery management system that controls OBC The BMS (Battery Management System) determines whether or not the battery is charged according to the input voltage command value. OBC and BMS communicate by CAN method.

2 is a block diagram of a resonant converter to which a charger optimum efficiency control method according to the present invention is applied. This resonant converter is configured in an OBC (vehicle battery charger). Components of the resonant converter of FIG. 2 include resonant inductors L and resonant capacitors C, which are basically resonant converters, and a transformer 5; There are a primary side circuit 10 located at the primary side of the transformer 5 and a secondary side circuit 20 located at the secondary side.

An output voltage sensing unit 22 for sensing the output voltage of the secondary side circuit 20 and an output current sensing unit 24 for sensing the output current may be included. An input voltage sensing unit 12 for sensing an input voltage of the primary side circuit 10 and an input current sensing unit 14 for sensing an input current may be further included.

Fig. 3 is an example of a circuit diagram in which the block diagram shown in Fig. 2 is actually constructed. Fig.

The primary side circuit 10 is a chopper circuit including four FETs driven at a predetermined switching frequency to convert a DC input into an AC signal. The alternating current waveform chopped at a specific frequency in the primary circuit 10 is outputted to the transformer 5 through the resonant inductor L and the resonant capacitor C. On the secondary side of the transformer 5, an AC waveform of another voltage that has been stepped up or stepped down by electromagnetic induction appears, and this AC waveform is rectified by a rectifying circuit composed of a diode constituting the secondary circuit 20, _L as a DC voltage.

3, the input voltage sensing unit 12 may be a voltmeter or a voltage sensing circuit or an element, and the input current sensing unit 14 may be an ammeter or a current sensing circuit or an element. Similarly, the output voltage sensing unit 22 may be a voltmeter or a voltage sensing circuit or element, and the output current sensing unit 24 may be implemented as an ammeter or current sensing circuit or device.

4 is a flowchart of a method of controlling optimum efficiency of a charger according to an embodiment of the present invention. Describe in numerical order.

102: Receiving voltage command value for charging based on battery voltage condition (voltage value) between OBC controller and BMS controller through CAN message.

The OBC and BMS are the same as described above, and the CAN (Controller Area Network), which is a communication method between the OBC controller and the BMS controller, is a communication protocol between the automotive network systems, and is a serial network communication method designed for communication between microcontrollers. It provides an economical and stable network to communicate with each other. By controlling multiple ECUs with a single CAN interface, the overall cost and weight of the vehicle can be reduced and the speed and safety of the system can be improved. In addition, since each device has a CAN controller chip, each system can be efficiently controlled.

The command value means the target voltage of the battery charge. For example, in the case of a 3.3 kW charger, 330 V can be included in the CAN message as a command value.

104: Calculating the output power value based on the received voltage command value.

The output power value at this time means the power capacity of the battery charger driven and switched to the basic switching frequency f0. For example, for a 3.3kW charger, the output power is 3.3kW. In this case, if the battery voltage is 330V, the output current becomes 10A. The present invention performs the following calculation process to control the current to the rated output current.

106, and 108: sensing the output voltage and the output current by the output voltage sensing unit 22 and the output current sensing unit 24 described in FIG. 2 (voltage, current actual measurement).

110: calculating the power value of the output and the input based on the sensed value

The actual output power value is calculated from the sensing value of the output voltage and the output current using the formula of [power = voltage x current (P = VI)]. For example, when the sensing voltage is 360 V and the sensing current is 9 A, the output power is 360 V × 9 A = 3.24 kW.

The input power can be calculated inversely using a preset efficiency table. The efficiency table is a table for the efficiency calculated by the output voltage for a particular charger. For example, when the output voltage of a specific charger of 3.3 kW is sensed at 360 V, the efficiency table of Table 1 below shows an efficiency value of 95% corresponding to 360 V, which is 3.3 kW / 95% = 3.473 kW The input power can be calculated.

Output voltage 330V 340V 350V 360V ... efficiency 94% 95% 95% 95% ...

On the other hand, the input power can also be calculated using the formula of [power = voltage x current (P = VI)] from the sensing value of the input voltage and the input current.

The above steps are the preceding steps necessary for the operation of the battery charger, and in particular, are the steps used in connection with an external system of a vehicle, for example, EVSE (electric vehicle charging power supply). The method of controlling optimum efficiency of the charger of the present invention proceeds from now on.

112: Obtaining the voltage condition gain value based on the output voltage sensing value

There are two ways to obtain the voltage condition gain value.

One is a method of reading the gain corresponding to the output voltage sensing value in the predetermined gain table shown in FIG. In FIG. 5, since the gain corresponding to 360V in the voltage condition column is '1', it is acquired.

Another method uses a gain trend line algorithm represented by a voltage trend line as shown in Equation (1). Since y = gain and x = sensing voltage in Equation 1 below, substituting x = 360 for this equation yields a gain value of y = 1.000778 (= 1).

114: Determining the switching frequency candidate f1 based on the voltage condition gain value obtained in step 112. [

The switching frequency candidate f1 can be determined in the gain table shown in Fig. That is, the switching frequency when the voltage condition gain value is 1 is 150 kHz. The gain-to-switching frequency presented as a discrete value in FIG. 5 can be obtained continuously from a predetermined preset function. The equation defining the function can be used to determine the switching frequency relative to the gain.

116: Obtaining the load condition gain value based on the output current sensing value.

Similar to the above-described acquisition of the voltage condition gain value in step 112, the gain corresponding to the output current sensing value is read from the predetermined gain table shown in FIG. (Each row is not shown in detail in Fig. 5).

Alternatively, a method using a gain trend line algorithm represented by a current trend line as shown in Equation (2) may be used. Since y = gain and x = sensing current in the following Equation 2, substituting x = 9 for this equation gives a gain value of y = 0.9466. This gain trend line algorithm is an algorithm that changes the gain value by learning and learning switching based on a predefined trend line.

118: Determining the switching frequency candidate f2 on the basis of the load condition gain value obtained in step 116.

Here, the switching frequency candidate f2 can be determined in the gain table shown in Fig. 5 or can be acquired continuously from a separately set function, in the same manner as the above-mentioned switching frequency candidate f1.

120: Switching f1 and f2, respectively, to operate the charger.

By operating the switching elements (for example, the FETs in the primary circuit of FIG. 3) of the charger with the determined switching frequency candidates f1 and f2, the charger is operated.

122: Recalculate the power values of the input and output stages and compare them with the previous values.

As the output power value and the input power value are calculated when the charger is operated at the basic switching frequency f0 in steps 106, 108 and 110, the switching frequency candidates f1 and f2 are set to the sensing values of the output voltage / The output power value and the input power value are calculated and compared with the values at f0.

124: Determining the optimal switching frequency from f1 and f2.

The output and input power values at f0, the output and input power values at f1, and the output and input power values at f2 are compared with each other to determine a frequency having a small variation in power value as a switching frequency. The switching frequency thus determined results in a switching frequency generated based on the gain value of the charger. Now, when the charger is operated at this determined frequency, the charger can perform the power conversion with maximum efficiency.

Fig. 6 is a diagram showing another example of the embodiment of the present invention. In Fig. 2 and Fig. 3, a step of determining whether the inductor L or the capacitor C, which is a resonant part between the primary circuit 10 and the transformer 5, As shown in Fig. Since steps 102 to 124 are the same as those described in Fig. 4, the following steps will be described. The essence of this embodiment is an algorithm for determining the switching frequency change range and gain according to the tolerance values of the resonance inductor L and the resonance capacitor C.

126: If the switching frequency is above the limit value, judge the part as an inductor or a capacitor component is out of tolerance range.

128: a step of generating a 'fault flag' for a part judged as a component abnormality.

If the optimum switching frequency determined in step 124 in FIG. 4 is a predetermined limit range or more, it is determined that the inductor L or the capacitor C is out of the tolerance range (scatter), and the component fault flag is generated and processed by the control logic.

(f_sw = 스위칭주파수, L = 인덕터 제한범위값, C = 커패시터 제한범위값)이므로, 스위칭 주파수가 해당 제한범위를 벗어나면 인덕터와 커패시터에 문제가 있음을 확인하여 부품 FAULT를 생성한다. 도 7은 10% 허용오차범위(산포)의 인덕터와 5% 허용오차범위의 커패시터의 각 산포에 따른 부품값의 최소허용값, 정상값, 최대허용값을 나타내는 것으로 각 값에 따른 스위칭 주파수의 변화를 예시하고 있다. Specifically, when the device has a limit of 10%, the switching limit range is calculated to be 5% of the inductor and 10% of the capacitor (limit range: [-10% inductor value * -5% capacitance value] Inductor value * + 5% capacitance value]).

(f _sw = switching frequency, L = inductor limit value, and C = capacitor limit value). If the switching frequency falls outside this range, it is confirmed that there is a problem with the inductor and capacitor. FIG. 7 shows the minimum allowable value, the steady value, and the maximum allowable value of the component value according to each dispersion of the inductor of the 10% tolerance range (scatter) and the capacitor of the 5% tolerance range. .

An algorithm for varying the switching frequency by adjusting the gain value for the component having such a tolerance range may be included in the control logic. For example, in this algorithm, when the calculated gain value is 1, switching is made to 150 kHz to check the deviation of the current value, and then the gain value is adjusted to 0.97 and 1.05 to reaffirm the deviation of the current value, So that the charger can be operated.

The present invention has been described above by way of specific examples and embodiments. However, the technical scope of the present invention is not limited by these embodiments but is determined by a reasonable interpretation of the following claims.

L: resonant inductor, C: resonant capacitor, transformer 5, primary circuit 10, input voltage sensing unit 12, input current sensing unit 14, secondary circuit 20, output voltage sensing unit 22, an output current sensing unit 24,

Claims (8)

A method of controlling a switching frequency of a battery charger (hereinafter 'charger') including a resonant converter driven by a switching frequency f0,
Sensing an output voltage and an output current of the charger;
Obtaining a voltage condition gain value based on the output voltage sensing value;
Determining a switching frequency candidate f1 based on the voltage condition gain value.
Obtaining a load condition gain value based on the output current sensing value;
Determining a switching frequency candidate f2 based on the load condition gain value;
Operating the charger by switching to the switching frequency candidate f1 and the switching frequency candidate f2, respectively;
In order to determine an optimum switching frequency among the first switching frequency candidate and the second switching frequency candidate, an output and input power value at f0, an output and input power value at f1, and an output at f2 and an input And comparing the power values with each other to determine a frequency having a small deviation of the power value as an optimum switching frequency. The method of claim 1, wherein the step of acquiring the voltage condition gain value of the charger based on the output voltage sensing value uses a gain table that defines a gain value with respect to the output voltage sensing value for the charger. 2. The method of claim 1, wherein the step of obtaining a voltage condition gain value of the charger based on the output voltage sensing value comprises the steps of: determining a gain trend line algorithm represented by a voltage trend line of y = f (x) (y = A method for controlling an optimum efficiency of a battery charger using a battery charger. The method as claimed in claim 1, wherein the step of acquiring the load condition gain value of the charger based on the output current sensing value uses a gain table that defines a gain value with respect to the output current sensing value for the charger. 2. The method of claim 1, wherein the step of obtaining a load condition gain value of the charger based on the output current sensing value comprises the steps of: determining a gain trend line algorithm represented by a current trend line of y = f (x) (y = A method for controlling an optimum efficiency of a battery charger using a battery charger. The method of claim 1, further comprising: determining that the resonant component included in the charger is an abnormal component if the optimal switching frequency is not less than the limit value,
Wherein an algorithm for varying the optimal switching frequency by adjusting a gain value with respect to a tolerance range of the resonant component is used in this step. A battery charger optimum efficiency control apparatus configured to execute the battery charger optimum efficiency control method according to any one of claims 1 to 6. A battery charger comprising the battery charger optimum efficiency control device according to claim 7.

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