JP2018164319A - Power conversion equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion equipment such as an on-vehicle step-down converter which is configured at low cost to detect an output voltage of a power converter with a small error.SOLUTION: To solve this problem, a power conversion equipment comprises a voltage-dividing resistor which is connected between an output terminal of a power converter and a reference GND and formed by serially connecting at least three or more odd numbers of resistors, and a voltage sensor circuit composed of two buffers and a differential amplifier. Each of voltages at both ends of a central resistor of the voltage-dividing resistor is input to the differential amplifier through the corresponding buffer. Output of the power converter is controlled on the basis of output of the differential amplifier.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a voltage converter used in the field of power electro, and more particularly to a voltage converter provided with an output voltage detection means for controlling the output voltage of a power converter such as an in-vehicle step-down converter. is there.

In power converters equipped with power converters such as in-vehicle step-down converters, in order to match the output value with the given target value, the difference between the output value and the target value, that is, the error is detected and the target value is detected. In order to amplify and attenuate the power converter, a method of performing feedback control of the power converter using a reference voltage and a PWM controller at the input stage of the error amplifier has been performed.
In order to execute such control, it is necessary to detect the voltage value on the power supply side, and a plurality of resistors connected in series are connected to the positive electrode terminal side of the power supply to form a positive voltage divider circuit. Connects a plurality of connected resistors to the negative terminal side of the power source to form a negative side voltage dividing circuit, and based on the divided voltage value divided by the positive side voltage dividing circuit and the negative side voltage dividing circuit, the positive and negative electrodes of the power source Patent Document 1 proposes to calculate a voltage value between the two.

  The voltage detection device proposed in Patent Document 1 includes a plurality of resistors connected in series and a positive voltage divider circuit unit connected to the positive electrode terminal side of the DC power supply, and a plurality of resistors connected in series. The positive and negative electrodes of the DC power source are connected to the negative terminal side of the DC power source based on the divided voltage values divided by the positive side voltage dividing circuit unit and the negative side voltage dividing circuit unit. An arithmetic circuit unit for calculating a voltage value between the two, a connection point between two adjacent resistors among the plurality of resistors constituting the positive voltage divider circuit unit, and the negative voltage divider circuit unit The capacitor includes a capacitor connected between the connection points of two adjacent resistors among the plurality of resistors.

  Here, the voltage detection method proposed in Patent Document 1 employs a method of sensing the voltage after resistance-dividing the high-voltage positive and negative terminals to be observed with respect to a reference ground. When such a configuration is adopted, since the GND serving as the reference potential on the main circuit side and the reference potential ground of the circuit on which the voltage detection device is mounted are connected via a fixed resistor in the casing, the power When the output current of the conversion device flows through an unintended circuit path in the casing, a so-called self-poisoning problem occurs in which the circuit is adversely affected.

JP 2011-64559 A

In a conventional power conversion device, when a configuration such as Patent Document 1 is used to detect a voltage value on the power supply side, GND that becomes a reference potential on the main circuit side via a fixed resistor in the housing Is connected to the reference potential ground of the circuit on which the voltage detection device is mounted, the output current of the power conversion device may flow through an unintended circuit path in the housing. This may cause malfunction of the control circuit and, in the worst case, fire or smoke of the product. For this reason, it is necessary to reduce the desired characteristics (input / output responsiveness, leakage current reduction, dynamic range) and sensor error required for the voltage sensor circuit in this power converter, and to establish a voltage detection method using a cheaper method. Met.
This invention solves the said subject and provides the power converter device comprised so that the output voltage of a power converter might be detected with a small error by a cheap structure in power converter devices, such as a step-down converter for vehicles. It is the purpose.

  The present invention has been made to solve such a problem, and in a power conversion device, a voltage sensor circuit comprising an odd number of voltage dividing resistors, two buffers, and a differential amplifier connected in series at least three or more. A shunt type in which the voltage dividing resistors and the like are connected in parallel to the output terminal of the power converter and the reference GND, and the voltage between both ends of the middle resistor is observed by the differential amplifier via each buffer. Using this voltage detection method, power conversion control is performed based on the differential amplifier output.

  According to the present invention, since the offset error of the voltage to be observed can be reduced and the voltage sensing with high accuracy can be realized with an inexpensive configuration, the controllability of the power converter is improved.

It is a block diagram which shows the basic composition of this invention. It is a block diagram which shows Embodiment 1 of this invention. FIG. 3 is a configuration diagram illustrating an output voltage of a step-down converter and a circuit resistance between the step-down converter and a load in the first embodiment. It is a block diagram which shows the structure which applied the protection component to Embodiment 1 of this invention. It is a block diagram which shows Embodiment 2 of this invention. It is a block diagram which shows Embodiment 3 of this invention. It is a block diagram which shows replacement of Embodiment 3 of this invention.

  As an example of the power conversion device of the present invention, an in-vehicle step-down converter that is connected between a high-voltage battery and a low-voltage battery and steps down the power of the high-voltage battery and supplies the low-voltage battery will be described as an example.

FIG. 1 is a diagram showing a basic configuration of the present invention. In addition, the same code | symbol in a figure shows the same part or an equivalent part respectively.
As shown in the figure, in the in-vehicle step-down converter 1, a voltage sensor circuit comprising a voltage dividing resistor 2, two buffers 3, and a differential amplifier 4 in which at least three or more odd-numbered resistors are connected in series. The voltage dividing resistor 2 is connected between the output terminal 5 of the step-down converter 1 for vehicle mounting and the reference GND 6, and the voltages across the resistors in the center of the plurality of resistors of the voltage dividing resistor 2 are respectively buffered. 3, a shunt-type voltage detection method observed by the differential amplifier 4 is performed, the control unit 7 controls the power conversion unit 8 based on the output of the differential amplifier 4, and the control as an in-vehicle step-down converter is performed. The power is supplied to the load. The control unit 7 includes a control controller IC, a microcontroller, and the like. The power conversion unit 8 includes a switching element such as a MOSFET, IGBT, or wide gap semiconductor such as SiC or GaN.

Further, the control system GND9 in the in-vehicle step-down converter 1 is harness-connected to a reference potential of the load (for example, a negative terminal of a lead battery).
On the other hand, the casing of the step-down converter 1 is at the same potential as the negative side of the output terminal 5 of the step-down converter 1, and the casing and the negative terminal side of the load are different metal bodies (for example, , The vehicle body earth) 10. That is, the reference GND of the buffer and the differential amplifier is connected to the reference potential of the load by the first member, and the casing of the power converter is at the same potential as the negative side of the output terminal and the negative terminal side of the load Are connected by the second member.

Here, the in-vehicle step-down converter 1 is a power conversion device for charging a low-voltage side lead battery from a high-voltage battery (lithium-in battery) mounted on the vehicle side, and drives the step-down converter 1. The control power supply is supplied with power directly or boosted or lowered from a low-voltage lead battery as a load.
In this configuration, if the casing potential and the control system GND are connected inside the casing, the output current path of the step-down converter 1 and the GND of the sensing line are shared, thereby accompanying the switching operation in the power converter. Since switching noise is superimposed on other control signal lines, it becomes a symptom of so-called self-poisoning that malfunctions due to the operation of the product itself.

  Alternatively, when the casing potential of the step-down converter 1 and the negative electrical connection between the lead battery are disconnected, a large current output from the step-down converter 1 may flow instantaneously through the control system GND inside the product. At this time, in order to prevent the output current from flowing through an unintended circuit path in the casing, the control system GND and the casing potential are grounded outside the casing of the step-down converter 1.

Embodiment 1
Hereinafter, the configuration of the first embodiment to which the present invention is applied will be described with reference to the drawings.
FIG. 2 is a diagram showing Embodiment 1 of the present invention.
In the in-vehicle step-down converter 1, in order to amplify and attenuate to a desired voltage, a method of performing converter control using a reference voltage and a PWM controller or the like at the input stage of the error amplifier is taken. A part or all of the circuit portion is included as a function of the control unit 7 such as a control controller IC or a microcontroller provided in the step-down converter 1.

  The voltage sensor circuit includes a voltage dividing resistor 2, two buffers 3, and a differential amplifier 4. The buffer 3 here is assumed to be a single power supply operational amplifier.

Here, the voltage dividing resistor 2 is composed of at least three resistors in order to detect a voltage to be observed in a shunt type based on a current effect.
The voltage dividing resistor 2 is connected between the output terminal 5 of the in-vehicle step-down converter 1 and the reference GND 6, and is connected in parallel to the output terminal 5 and the reference GND 6. Converter control is performed based on the output of the differential amplifier 4 using a shunt-type voltage detection method in which the voltage across the buffer 3 is observed by the differential amplifier 4 via the respective buffers 3.

Normally, a method of detecting a voltage after resistance-dividing a high-voltage positive and negative terminal to be observed with respect to a reference ground is used. Here, the control system GND is a reference potential of a load, for example, a lead battery. And a control system GND in the in-vehicle step-down converter is connected to a reference potential of a load (for example, a negative terminal of a lead battery) while a housing of the in-vehicle step-down converter is connected to the in-vehicle step-down converter. Configuration having the same potential as the output terminal minus side of the converter, and the casing and the minus terminal side of the load are connected via a metal body (for example, car body ground) different from the harness It is said.
In addition, a voltage offset error due to a parasitic resistance component between the control system GND and the casing potential can be reduced.

The voltage observation range of the voltage sensor circuit is set by the voltage dividing resistor 2. For example, the output maximum voltage of the in-vehicle step-down converter 1 is _Vout, and the return current of the output of the step-down converter 1 and the frame When the voltage drop due to GND (hereinafter referred to as R _FG ) is V _N , the observation voltage range is −V _N from V _out .

Here, reference numeral minus Nanoha of V _N, when relative to the negative terminal of the low-pressure battery, the voltage drop due to the parasitic resistance of the return current and the housing or the vehicle chassis ground to buck converter 1 occurs, the original observation It shows that a negative bias is applied from the control system GND which is a potential with respect to the potential.
That is, the voltage sensor circuit on the observation side performs sensing with the buffer 3 and the differential amplifier 4 in the control system GND.
On the other hand, when the negative terminal of the low voltage battery is used as a reference, the control system GND is lower than the control system GND because the casing potential drops depending on the casing potential depending on the output current of the in-vehicle step-down converter.

The differential amplifier 4 is for amplifying / attenuating the voltage level so as to be within a desired voltage range in order to remove the offset and drive the in-vehicle step-down converter.
The differential amplifier 4 in FIG. 2 is shown as an example composed of one operational amplifier and a resistor. However, the differential amplifier 4 is not limited to this configuration, and may be realized by using an instrumentation amplifier and a plurality of operations. good.

Next, conditions for determining the voltage dividing resistor 2 (R1, R2, R3) will be described.
The output voltage _Vout of the in-vehicle step-down converter 1 and the circuit resistance R _FG 11 between the in-vehicle step-down converter and the load are conceptually represented in FIG. In the drawing, the circuit resistance R _FG 11 is arranged on the reference potential side, but parasitic resistance inherently exists on the output terminal side. However, when determining each constant, it is more difficult to place it on the reference potential side under the following conditions.

When balancing the potential difference of the voltage drop V _N due to the output current at the circuit resistance R _FG 11 with the voltage dividing resistor 2 of R1, R2 and R3, either the upper or lower buffer input voltage V ₁ 12, V on the basis of the control system GND. ₂ 13 should be greater than or equal 0V to the control system GND reference, since the circuit operation is satisfied, it is necessary to the following conditional expression is satisfied.

From this equation (1), the following equation (3) can be derived.

Here, V _out is _generated when the in-vehicle step-down converter outputs a maximum output current as a voltage lower limit value that can be output by the in-vehicle step-down converter 1 at a value V _{out_min that} is the minimum V _out. Voltage-dividing resistors R1, R2, and R3 that satisfy the above relational expression in terms of voltage drop (maximum value) are selected.

As for V _N , constants of voltage dividing resistors R1, R2, and R3 that satisfy the above relational expression are selected by a voltage drop (maximum value) generated when the on-vehicle step-down converter outputs the maximum output current _Iout. To do. V _N can be expressed by the following equation (4) when the round resistance (frame resistance) R _FG between the loads is assumed.

From the maximum output current value of the in-vehicle step-down converter applied to the vehicle and the grounding condition of the product, the circuit resistance (frame resistance) R _FG is assumed to be in the range of 0.1 mΩ to 30 mΩ, and the voltage dividing resistors R1, R2, What is necessary is just to determine R3.
Incidentally, the R _FG resistance is determined by the resistivity of the physical property values, because no problem in general replaced by the arrangement relative distance of the vehicle converter and the load, is adapted in the range of 30cm to 3m.

Further, the voltage dividing resistors R1, R2, R3 and the desired output voltage V _out, a voltage drop V _N by the output _current, when the differential amplifier gain G, the output V0 of the voltage sensor circuit, the table as follows: Is done.

When the in-vehicle step-down converter output terminal is connected to a lead battery as a load, a leak current is generated due to the output impedance of the converter. In the case of this configuration, this occurs due to a series combined resistance value of the voltage dividing resistors R1, R2, and R3 in addition to factors such as a rectifier diode provided on the main circuit side. Accordingly, the lower limit value of the combined resistance value is determined to be equal to or less than a desired leakage current value.
Further, if the voltage dividing resistance value is excessively increased due to the input terminal parasitic capacitance (several 1 pF to several 100 pF) in the buffer 3, band limitation occurs. Therefore, considering the responsiveness as the voltage sensor, the combined resistance value of the voltage dividing resistors and the like is suitably in the range of 10 kΩ to 100 kΩ.

As described above, in order to control the output voltage in the in-vehicle step-down converter, the sensing harness directly connected to the load terminal of the converter is used. Or, the output voltage of the in-vehicle step-down converter was measured with a single end, but there was a problem that the reference potential shifted and an offset error occurred.
According to the first embodiment, a voltage sensing harness generally used as an offset error countermeasure is not required in an in-vehicle step-down converter, and the offset error of a voltage to be observed can be reduced by a low-cost method, with high accuracy. Therefore, controllability of the in-vehicle step-down converter can be improved.

  Further, the reference potential (control system GND) of the buffer and differential amplifier in the in-vehicle step-down converter is harness-connected to the reference potential of the load (for example, the negative terminal of the lead battery), so that the control system GND harness and the in-vehicle The reference potential of the step-down converter for the vehicle is electrically insulated in the casing, while the casing of the in-vehicle step-down converter has the same potential as the negative side of the output terminal of the in-vehicle step-down converter, and the casing and the load Is connected to the negative terminal side via a metal body different from the harness (for example, car body ground), so that the circuit configuration of the in-vehicle step-down converter can be reduced. Isolation can be ensured with a high impedance between the reference potential of the control system and the main circuit system.

Thereby, it is possible to prevent the output current of the in-vehicle step-down converter from flowing through an unintended circuit path in the housing. Further, it is possible to reduce malfunction of the control circuit accompanying the main circuit operation, or to prevent the product from being ignited or smoked due to the malfunction.
In addition, a dedicated harness for return current is not required for the load of the in-vehicle step-down converter, and the output voltage can be monitored by an inexpensive method.
In addition, since the voltage drop can be reduced by using the vehicle chassis GND having a low parasitic resistance component in the return path of the large current output from the on-vehicle step-down converter, the on-board step-down converter can increase the voltage by the voltage drop. There is no need to output. Therefore, a margin between the normal output range and the overvoltage detection range of the in-vehicle step-down converter can be ensured.

  In addition, the input / output response required for the voltage sensor circuit can be realized, the voltage monitoring range of the voltage sensor circuit can be ensured in an appropriate range, and the regulation performance of the in-vehicle step-down converter can be improved.

According to the present invention, since the circuit constant can be set in an appropriate range, the output voltage of the in-vehicle step-down converter can be monitored and power conversion can be realized without impairing the input / output response of the voltage sensor circuit.
Further, when the on-vehicle step-down converter as described above is stopped, leakage current from the lead battery as a load can be reduced.

  Further, as shown in FIG. 4, an ESD or surge protection component such as a diode or a varistor may be arranged before the input of the buffer 3. At this time, the ground potential of the protection element is connected to the control system GND which is the same potential as the buffer element.

  In this way, by arranging ESD or surge protection components such as diodes or varistors before the input of the buffer 3, even if excessive surge or static electricity occurs at the input end of the voltage sensor circuit, the surge protection components Therefore, the voltage sensor circuit is protected by clamping to a predetermined voltage. Therefore, the surge resistance of the voltage sensor circuit portion can be improved.

Embodiment 2
FIG. 5 is a diagram showing a second embodiment of the present invention.
In the first embodiment, the configuration of the voltage sensor circuit is the buffer 3 and the differential amplifier 4, but instead, in this second embodiment, an insulation amplifier is applied as shown in FIG. . Thereby, since the number of parts can be reduced, the circuit scale can be reduced.

Embodiment 3
FIG. 6 is a diagram showing a third embodiment of the present invention.
In the first embodiment, the configuration of the voltage sensor circuit is the buffer 3 and the differential amplifier 4, but instead of this, in the third embodiment, as shown in FIG. The instrumentation amplifier that is configured is applied. Thereby, since the number of parts can be reduced, the circuit scale can be reduced.
In the third embodiment, as shown in FIG. 7, the same effect can also be achieved as an instrumentation amplifier including two or more operational amplifiers as the voltage sensor circuit 17. Also by this, the number of parts can be reduced similarly, so that the circuit scale can be reduced.

  The first embodiment, the second embodiment, and the third embodiment have been described by taking an in-vehicle converter as an example for the sake of simplicity, but an in-vehicle charger, an AC / DC converter, and The same effect can be exhibited even when applied to a voltage sensor circuit in a power converter such as an inverter.

  In the present invention, for the sake of simplicity, for example, the resistors constituting the voltage dividing resistor 2 and the like are described as constants composed of the minimum number of members. However, the voltage dividing resistors R1, R2, and R3 are each desired. In order to realize the constant, a plurality of resistors may be connected in various combinations in series or in parallel.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

1 Automotive buck converter, 2 voltage divider resistor, 3 buffer, 4 differential amplifier,
5 Output terminal, 6 Reference GND, 7 Control unit, 8 Power conversion unit, 9 Control system GND,
10 Metal body, 11 Circuit resistance R _FG , 12 Buffer input terminal voltage V ₁ ,
13 Buffer input terminal voltage V ₂ , 14 Protection component, 15 Insulation amplifier,
16, 17 Voltage sensor

Claims (9)

  A power converter, a voltage dividing resistor connected between an output terminal of the power converter and a reference GND of the power converter, and having at least three odd-numbered resistors connected in series in the device; two buffers; A voltage sensor circuit comprising a differential amplifier, and the voltage across the resistor in the middle of the voltage dividing resistor is input to the differential amplifier via the buffer, and the voltage based on the output of the differential amplifier. A power conversion device characterized in that power conversion control of a power converter is performed.   The reference GND of the buffer and the differential amplifier is connected to the reference potential of the load by a first member, and the casing of the power converter is at the same potential as the minus side of the output terminal and the minus of the load The power converter according to claim 1, wherein the power converter is connected to the terminal side by a second member.   The power converter according to claim 2, wherein a circuit resistance of a current path from the output terminal to the load is in a range of 0.1 mΩ to 30 mΩ.   The power converter according to claim 2, wherein a relative distance between the power converter and the load is in a range of 30 cm to 3 m.   The power conversion device according to claim 1, wherein a resistance constant of the voltage dividing resistor is determined based on an upper limit of an output current of the power converter and a minimum voltage value to be detected.   6. The power converter according to claim 5, wherein a combined resistance value of the voltage dividing resistor is in a range of 10 kΩ to 100 kΩ.   The power converter according to claim 1, wherein a protection element for surge protection is provided before the input of the buffer.   The power converter according to claim 1, wherein an insulation amplifier is used instead of the buffer and the differential amplifier of the voltage sensor circuit.   The power conversion apparatus according to claim 1, wherein an instrumentation amplifier including a gain resistor and two or more operational amplifiers is used instead of the buffer and the differential amplifier of the voltage sensor circuit.

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