JP3622906B2 - DC-DC converter device for battery charging - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery charging DC-DC converter device.
[0002]
[Prior art and problems to be solved by the invention]
For example, in a hybrid vehicle or the like, two high and low power systems each having a battery are provided, and a DC-DC converter device is arranged to supply power from a high voltage side battery to a low voltage side battery.
[0003]
This type of dual power supply type vehicle power supply device is equipped with overload detection circuits 300 and 400 shown in FIGS. 3 and 4 in order to prevent a failure due to overload of the DC-DC converter device. 3 and 4, 100 is a DC-DC converter, and 200 is a low-voltage battery. Vi is a DC input voltage of about 300 V, and is formed by rectifying the power generation voltage of a vehicle-mounted high voltage generator (not shown). Vo is a DC output voltage of about 14 V, and is fed to the low voltage battery 200 and a low voltage on-vehicle electric load (not shown). In order to float the high-voltage power supply system from the ground voltage, the DC-DC converter 100 includes a step-down transformer, an inverter on the input side of the step-down transformer, and a rectifier circuit on the output side of the step-down transformer.
[0004]
The overload detection unit 300 shown in FIG. 3 includes a voltage comparison circuit 302 that inputs an input signal voltage proportional to the DC input voltage Vi of the DC-DC converter 100 through a photocoupler 301. The voltage comparison circuit 302 is an input signal. The voltage is compared with a predetermined reference voltage, and if the input signal voltage falls below the reference voltage, it is determined that the load is overloaded, and the comparison result is output as an output signal voltage based on the ground voltage.
[0005]
4 includes a magnetic current sensor 401 that detects the output current of the DC-DC converter 100 in a non-contact manner, and a voltage comparison circuit 402 that compares the output signal voltage with a predetermined reference voltage. The voltage comparison circuit 402 determines that the sensor 401 is overloaded if the output signal voltage of the sensor 401 is greater than the reference voltage.
[0006]
However, in the overload detection method for detecting an overload due to a decrease in the input voltage of the DC-DC converter shown in FIG. 3 described above, the circuit configuration is complicated and there is a limit to the reduction in manufacturing cost due to the expensive photocoupler. .
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a battery-charging DC-DC converter device capable of reducing the manufacturing cost with a simple configuration.
[0008]
[Means for Solving the Problems]
The DC-DC converter device for charging a battery according to claim 1 is a DC-DC converter that converts input DC power into a voltage and supplies power to the battery, and a first value corresponding to a value obtained by multiplying a predetermined target voltage Vp by a predetermined gain G1. A constant voltage circuit unit for generating one reference voltage Vs1 = G1 · Vp, and a first voltage V1 = G1 · Vo corresponding to a value obtained by multiplying the output voltage Vo of the DC-DC converter by the predetermined gain G1 and the first voltage A control unit for intermittently controlling the switching element built in the DC-DC converter based on a comparison result with reference voltage Vs = G1 · Vp to converge the output voltage Vo to the target voltage Vp, and the DC-DC converter In a DC-DC converter device for battery charging comprising an overload determination unit for detecting an overload state,
The overload detection unit includes a second reference voltage Vs2 that is linked to a predetermined overload determination threshold voltage Vth that is smaller by a predetermined small value than a lower limit value of an allowable output voltage range including the target voltage Vp, and the DC-DC Based on the comparison result with the second voltage V2 linked to the output voltage Vo of the converter, the DC-DC converter is in an overload state when the output voltage Vo falls below the overload determination threshold voltage Vth. It is characterized by determining that there is.
[0009]
Each gain is preferably less than 1, more preferably 0.5, but setting the gain to 1 or more is not prohibited.
[0010]
That is, in the DC-DC converter device having the above configuration, feedback control is performed to converge the output voltage Vo to the target voltage Vp. Therefore, if there is a predetermined input voltage or if there is no overload, the output voltage Vo is the target. When the voltage is within the allowable output voltage range including the voltage Vp and becomes lower than a predetermined input voltage or becomes overloaded, the output voltage Vo rapidly decreases due to an overcurrent limiting circuit and insufficient input voltage.
[0011]
The present invention has been made paying attention to the above phenomenon, and a predetermined overload determination threshold voltage Vth in which the output voltage Vo or the second voltage V2 that is the interlocking voltage thereof is smaller than the lower limit value of the allowable output voltage range. Or it compares with the 2nd reference voltage Vs2 linked | related to it, and if it becomes small, it will determine with an overload.
[0012]
Thereby, all the problems of the above-described conventional overload detection method can be solved, and overload detection excellent in practicality can be performed.
[0013]
Further, in the configuration of claim 1, wherein the overload determination threshold voltage Vth is characterized in that it is set higher than the open circuit voltage of the battery.
[0014]
As a result, it is possible to prevent erroneous determination that the DC-DC converter is not overloaded when the DC-DC converter is not charged and is discharging.
[0015]
Structure of claim 2 further in the battery DC-DC converter device for charging according to claim 1, wherein the overload determination threshold voltage Vth, it is almost intermediate value between the open-circuit voltage and the lower limit value It is characterized by. Note that the substantially intermediate value designates a range of the open circuit voltage + 0.4 · ΔV to the open circuit voltage + 0.6 · ΔV, where ΔVx is a voltage difference between the lower limit value and the open circuit voltage.
[0016]
According to a third aspect of the present invention, in the battery-charging DC-DC converter device according to the first or second aspect , the overload detection unit is formed by multiplying the output voltage Vo by a predetermined gain G2 greater than the predetermined gain G1. Based on the comparison result between the second voltage V2 = G2 · Vo and the second reference voltage Vs2 set equal to the first reference voltage Vs1, the second voltage V2 = G2 · Vo is When the reference voltage Vs1 is lower than the second reference voltage Vs2, it is determined that the overload state is established.
[0017]
According to this configuration, the first reference voltage Vs1 for converging the output voltage Vo of the DC-DC converter to the target voltage Vp and the first load voltage for determining overload depending on whether the output voltage Vo has decreased by a predetermined value or more. The two reference voltages Vs2 can be created by the same constant voltage circuit, and the circuit configuration can be simplified.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the DC-DC converter device for battery charging according to the present invention will be described below with reference to FIGS.
[0019]
FIG. 1 shows a circuit diagram of a battery-charging DC-DC converter device for a dual power-source hybrid vehicle.
[0020]
1 is a high-voltage battery having a rated voltage of about 300V, 2 is a DC-DC converter, 3 is a low-voltage battery having a rated voltage of about 12V, 4 is a control circuit, and the DC-DC converter 2 and the control circuit 4 are battery charging in the present invention. The DC-DC converter apparatus for a vehicle is comprised.
[0021]
The DC-DC converter 2 includes a smoothing capacitor 21, an inverter circuit 22, a step-down transformer 23, a pair of rectifying diodes 24 and 25, a smoothing choke coil 26, and a smoothing capacitor 27.
[0022]
The inverter circuit 22 is formed by bridge-connecting four MOS transistors, and the output AC voltage of the inverter circuit 22 is stepped down by the step-down transformer 23. The connection ends of the pair of secondary coils of the step-down transformer 23 are grounded through an intermediate tap, and the other ends of both secondary coils are low-voltaged through diodes 24 and 25 forming a single-phase full-wave rectifier circuit, and further through a smoothing choke coil 26. Power is supplied to the battery 3.
[0023]
Each MOS transistor of the inverter circuit 22 is PWM controlled (only the MOS transistor on the upper arm side or the lower arm side may be PWM controlled, and the remaining MOS transistor may be intermittently controlled at a predetermined timing), and the duty of the MOS transistor to be PWM controlled The ratio is feedback-controlled by the comparison result between the voltage of the low-voltage battery 3, that is, the output voltage Vo of the DC-DC converter 2 and the constant target voltage Vp, so that the output voltage Vo is converged to the target voltage Vp. Since the circuit configuration and operation of the DC-DC converter 2 are well known, further detailed description is omitted.
[0024]
The control circuit 4 forms a constant voltage circuit section, a control section, and an overload determination section referred to in the present invention, and is actually configured integrally with the DC-DC converter 2.
[0025]
Reference numeral 41 denotes a voltage control resistor voltage dividing circuit, 42 denotes a voltage control comparator, 43 denotes a gate voltage generation circuit, 44 denotes an overload detection resistor voltage dividing circuit, 45 denotes an overload detection comparator, and 46 denotes a constant voltage circuit. . The voltage control resistance voltage dividing circuit 41, the voltage control comparator 42, and the gate voltage generation circuit 43 constitute a control unit referred to in the present invention, and the overload detection resistance voltage dividing circuit 44 and the overload detection comparator 45 are the present invention. And the constant voltage circuit 46 constitutes a constant voltage circuit unit according to the present invention.
[0026]
The voltage control resistor voltage dividing circuit 41 is formed by connecting resistance elements r1 and r2 in series. The output voltage Vo of the DC-DC converter 2 is divided by the voltage control resistor voltage dividing circuit 41 and input to the comparator 42. Input at the end.
[0027]
The constant voltage circuit 46 applies the voltage of the low voltage battery 3 (substantially equal to the output voltage Vo of the DC-DC converter 2) to, for example, a series circuit of a resistance element and a Zener diode, and the lower end is grounded. The high-order end potential of the Zener diode is applied to the + input ends of the comparators 42 and 45 as the reference voltage Vref.
[0028]
The comparator 42 compares the divided voltage V1 of the output voltage Vo input from the voltage control resistance voltage dividing circuit 41 with the reference voltage Vref, and outputs the comparison result to the gate voltage generating circuit 43.
[0029]
The gate voltage generation circuit 43 creates a PWM gate voltage having a predetermined carrier frequency and applies it to each MOS transistor of the inverter circuit 22. The gate control circuit 43 controls the on-time of the MOS transistor by controlling the duty ratio of the PWM gate voltage based on the comparison result inputted, and controls the average amplitude of the output voltage outputted from the inverter circuit 22. Thus, the output voltage Vo is converged to the target voltage Vp. In the feedback control by the comparator 42 described above, the output voltage Vo of the DC-DC converter 2 fluctuates by a predetermined width above and below the target voltage Vp, that is, within the allowable output voltage range referred to in the present invention.
[0030]
Here, V1 = G1 · Vo, G1 = r1 / (r1 + r2), and Vref = G1 · Vp are set.
[0031]
The overload detection resistance voltage dividing circuit 44 is formed by connecting resistance elements r3 and r4 in series. The output voltage Vo of the DC-DC converter 2 is divided by the voltage control resistance voltage dividing circuit 44 and Input to the input terminal.
[0032]
The comparator 45 compares the divided voltage V2 of the output voltage Vo input from the overload detection resistor voltage dividing circuit 44 with the reference voltage Vref, and when the divided voltage V2 of the output voltage Vo is lower than the reference voltage Vref, The DC-DC converter 2 determines that it is in an overload state, and outputs a high level potential signal as an overload alarm signal.
[0033]
Here, V2 = G2 · Vo, G2 = r3 / (r3 + r4), and Vref = G1 · Vp are set. In particular, G2 is set larger than G1 by a predetermined value. Accordingly, when the output voltage Vo decreases to the lower limit value of the allowable output voltage range when the target voltage Vp decreases, the comparator 42 is first inverted, and duty ratio up control for increasing the output voltage Vo is started. At this time, the second voltage V2 input to the comparator 45 is still higher than the reference voltage Vref, and the comparator 45 is not inverted and does not output an overload alarm signal.
Thereafter, when the output voltage Vo further decreases, the second voltage V2 input to the comparator 45 becomes smaller than the reference voltage Vref, and the comparator 45 is inverted and outputs an overload alarm signal.
[0034]
FIG. 2 shows the relationship between the output current of the DC-DC converter 2 and the output voltage Vo, and FIG. 3 shows an equivalent block circuit of the DC-DC converter 2.
[0035]
In this embodiment, the reference voltage Vref corresponds to the first reference voltage Vs1 and the second reference voltage Vs2 referred to in the present invention.
[0036]
Here, V1 = G1 · Vo, G1 = r1 / (r1 + r2), and Vref = G1 · Vp are set. Also, V2 = G2 · Vo, G2 = r3 / (r3 + r4), and Vref = G1 · Vp are set. In particular, G2 is set larger than G1 by a predetermined value.
[0037]
In this embodiment, the overload determination threshold voltage Vth equal to the value of the output voltage Vo when the comparator 45 is inverted is set higher than the open-circuit voltage of the battery, so that erroneous determination is prevented. Can do.
[0038]
In this embodiment, the target voltage Vp is set to 14.4V, the open voltage of the low voltage battery 3 is 12.8V, and the overload determination threshold voltage Vth is 13.5V.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a DC-DC converter device for battery charging according to the present invention.
FIG. 2 is a characteristic diagram showing an output current-output voltage relationship of the DC-DC converter shown in FIG.
FIG. 3 is a block circuit diagram showing a conventional battery charging DC-DC converter device.
FIG. 4 is a block circuit diagram showing a conventional battery charging DC-DC converter device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 High voltage battery 2 DC-DC converter 3 Low voltage battery (battery)
4 Control circuit (constant voltage circuit part, control part and overload judgment part)

Claims (3)

A DC-DC converter that converts the input DC power into a voltage and supplies it to the battery;
A constant voltage circuit unit for generating a first reference voltage Vs1 = G1 · Vp corresponding to a value obtained by multiplying a predetermined target voltage Vp by a predetermined gain G1;
Based on the comparison result between the first voltage V1 = G1 · Vo and the first reference voltage Vs = G1 · Vp corresponding to the value obtained by multiplying the output voltage Vo of the DC-DC converter by the predetermined gain G1. A controller for intermittently controlling a switching element built in the DC converter to converge the output voltage Vo to the target voltage Vp;
An overload determination unit for detecting an overload state of the DC-DC converter;
In a DC-DC converter device for battery charging comprising:
The overload detection unit includes a second reference voltage Vs2 that is linked to a predetermined overload determination threshold voltage Vth that is smaller than a lower limit value of an allowable output voltage range including the target voltage Vp by a predetermined small value, and the DC-DC Based on the comparison result with the second voltage V2 linked to the converter output voltage Vo, the DC-DC converter is in an overload state when the output voltage Vo falls below the overload determination threshold voltage Vth. Judge that there is ,
The battery overload DC-DC converter device characterized in that the overload determination threshold voltage Vth is set higher than an open circuit voltage of the battery. The battery-charging DC-DC converter device according to claim 1 ,
The overload determination threshold voltage Vth is set to a substantially intermediate value between the lower limit value and the open-circuit voltage. In the DC-DC converter device for battery charging according to claim 1 or 2 ,
The overload detector is
Comparison between the second voltage V2 = G2 · Vo formed by multiplying the output voltage Vo by a predetermined gain G2 larger than the predetermined gain G1 and the second reference voltage Vs2 set equal to the first reference voltage Vs1 Based on the result, when the second voltage V2 = G2 · Vo is lower than the first reference voltage Vs1 = the second reference voltage Vs2, it is determined that the battery is overloaded. DC-DC converter device.

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