JP2008304290A - Earth leakage detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric leak detector capable of measuring the insulating resistance of a fuel cell with high precision. <P>SOLUTION: The electric leak detector 70 is equipped with a measuring part 72 for measuring response voltage when AC voltage for measuring insulating resistance is applied to the fuel cell 20, and an arithmetic part 73 for correcting and calculating the value Z2 of the insulating resistance Z of the fuel cell 20 on the basis of the value Z1 measured in the past of the insulating resistance Z of the fuel cell 20, the ratio (V2/V1) of the AC voltage V1 and the response voltage V2 and the voltage change ΔVf of the fuel cell 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a leakage detector for measuring the insulation resistance of a fuel cell with high accuracy.

  A fuel cell is an energy conversion system for causing an electrochemical reaction by supplying a fuel gas and an oxidizing gas to a membrane-electrode assembly and converting chemical energy into electric energy. Among them, a solid polymer electrolyte fuel cell using a solid polymer membrane as an electrolyte is expected to be used as an in-vehicle power source because it is low-cost and easy to downsize and has a high output density.

A fuel cell for in-vehicle power supply generates a high voltage of about 300V to 400V by connecting several hundred cells in series, so that sufficient measures against electric leakage are required. For example, in Japanese Patent Laid-Open No. 2003-250201, a difference between response voltages measured when a high-level voltage and a low-level voltage are respectively applied to a power supply terminal of an in-vehicle high-voltage power supply via a coupling capacitor is predetermined. A ground fault detection device that detects a ground fault when it falls below a threshold is disclosed. Japanese Patent Application Laid-Open No. 2004-286523 discloses a leakage determination device that detects voltage fluctuations of an on-vehicle high-voltage power supply and measures the insulation resistance of the high-voltage power supply when the voltage fluctuation is small.
JP 2003-250201 A JP 2004-286523 A

  However, when a voltage for measuring the insulation resistance is applied to the power supply terminal of the fuel cell via the coupling capacitor, charging / discharging occurs in the coupling capacitor due to the voltage fluctuation of the fuel cell, which affects the response voltage. In some cases, the insulation resistance of a fuel cell cannot be accurately measured.

  In view of the above problems, an object of the present invention is to provide a leakage detector capable of measuring the insulation resistance of a fuel cell with high accuracy.

  In order to solve the above-described problems, an earth leakage detector according to the present invention includes a measurement unit that measures a response voltage when an AC voltage for measuring insulation resistance is applied to a fuel cell, and a fuel cell insulation measured in the past. A calculation unit for correcting and calculating the insulation resistance of the fuel cell based on the resistance value, the ratio between the AC voltage and the response voltage, and the voltage fluctuation of the fuel cell. According to such a configuration, since the insulation resistance is corrected and calculated in consideration of the voltage fluctuation of the fuel cell, the measurement accuracy can be improved.

  According to the present invention, the insulation resistance of a fuel cell can be measured with high accuracy.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration of a power system of a fuel cell system 10 according to the present embodiment, and illustration of a reaction gas supply system, a cooling system, and the like is omitted.
The fuel cell system 10 includes a fuel cell stack 20, a traction inverter 30, a traction motor 40, a DC / DC converter 50, a secondary battery 60, a leakage detector 70, and a control unit (ECU) 80.

  The fuel cell stack 20 is a solid polymer electrolyte cell stack formed by stacking a plurality of cells in series. In the fuel cell stack 20, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the cathode electrode. The fuel cell stack 20 as a whole undergoes an electromotive reaction of the formula (3).

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  A voltage sensor 90 for detecting the output voltage of the fuel cell stack 20 is attached to the fuel cell stack 20.

  The DC / DC converter 50 boosts the DC voltage supplied from the secondary battery 60 and outputs it to the traction inverter 30 and the DC power generated by the fuel cell stack 20 or the traction motor 40 recovers by regenerative braking. It is a power conversion means having a function of reducing the regenerative power and charging the secondary battery 60. The charge / discharge of the secondary battery 60 is controlled by these functions of the DC / DC converter 50. Further, the operation point (output voltage, output current) of the fuel cell stack 20 is controlled by voltage conversion control by the DC / DC converter 50.

  The secondary battery 60 is subjected to charge / discharge control in order to adjust excess or deficiency of electric power supplied from the fuel cell stack 20 to an external load (such as the traction motor 40 or auxiliary machinery). The secondary battery 60 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle. As the secondary battery 60, for example, a nickel / cadmium storage battery, a nickel / hydrogen storage battery, a lithium secondary battery, or the like is suitable.

  The traction inverter 30 is, for example, a PWM inverter driven by a pulse width modulation method, and converts the DC voltage output from the fuel cell stack 20 or the secondary battery 60 into a three-phase AC voltage in accordance with a control command from the control unit 80. The rotational torque of the traction motor 40 is controlled by conversion. The traction motor 40 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

  The control unit 80 is a computer system including a CPU, a ROM, a RAM, an input / output interface, and the like, and is output from an accelerator position signal output from an accelerator sensor (not shown) or a vehicle speed sensor (not shown). The required power of the entire system is obtained based on the vehicle speed signal.

  The required power of the entire system is the total value of the vehicle running power and the auxiliary machine power. Auxiliary power is the power consumed by in-vehicle accessories (humidifiers, air compressors, hydrogen pumps, cooling water circulation pumps, etc.), and equipment required for vehicle travel (transmissions, wheel control devices, steering devices, and suspensions) Power consumed by devices, etc., and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.

  Then, the control unit 80 determines the distribution of output power between the fuel cell stack 20 and the secondary battery 60, calculates a power generation command value, and makes the power generation amount of the fuel cell stack 20 coincide with the target power. In addition, the supply of the reaction gas to the fuel cell stack 20 is controlled. Further, the control unit 80 controls the operating point (output voltage, output current) of the fuel cell stack 20 by controlling the DC / DC converter 50 and adjusting the output voltage of the fuel cell stack 20. The control unit 80 outputs, for example, each U-phase, V-phase, and W-phase AC voltage command value to the traction inverter 30 as a switching command so that the target vehicle speed corresponding to the accelerator opening is obtained, and the traction motor 40 output torque and rotation speed are controlled.

  The leakage detector 70 measures the insulation resistance Z between the power terminal of the fuel cell stack 20 and the ground (vehicle body), and determines that leakage has occurred if the insulation resistance Z falls below a predetermined threshold. Then, the control unit 80 is notified of the occurrence of electric leakage. The control unit 70 that has received the notification of the occurrence of the electric leakage stops the power generation of the fuel cell stack 20 and opens the relays L1 and L2 to ensure the safety of the vehicle.

  The leakage detector 70 includes an AC power supply 71, a measurement unit 72, a calculation unit 73, a resistor R, and a coupling capacitor C. The AC power supply 71 applies an AC voltage for measuring insulation resistance to the power supply terminal of the fuel cell stack 20 via the resistor R and the coupling capacitor C. The measuring unit 72 measures the voltage (hereinafter referred to as response voltage) of the measurement part A (the part between the resistance R and the coupling capacitor C) when an AC voltage for measuring insulation resistance is applied to the power supply terminal of the fuel cell stack 20. Is measured). The calculation unit 73 calculates the value Z1 of the insulation resistance Z measured in the past, the voltage fluctuation ΔVf of the fuel cell stack 20 measured by the voltage sensor 90, and the ratio (V2) between the AC voltage V1 for measuring the insulation resistance and the response voltage V2. / V1), the value Z2 of the insulation resistance Z is calculated. Here, the influence of the voltage fluctuation ΔVf on the calculation of the insulation resistance Z is obtained theoretically or experimentally in advance, and the calculation unit 73 takes into account the correction calculation based on the voltage fluctuation ΔVf and then calculates the insulation resistance Z. The value Z2 is calculated.

  According to this embodiment, since the insulation resistance Z is calculated in consideration of the voltage fluctuation of the fuel cell stack 20, the measurement accuracy can be improved.

It is a schematic block diagram of the fuel cell system concerning this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell stack 30 ... Traction inverter 40 ... Traction motor 50 ... DC / DC converter 60 ... Secondary battery 70 ... Electric leakage detector 80 ... Control unit 90 ... Voltage sensor

Claims (1)

An earth leakage detector for measuring an insulation resistance between a fuel cell and a ground,
A measurement unit for measuring a response voltage when an AC voltage for measuring insulation resistance is applied to the fuel cell;
A calculation unit for correcting and calculating the insulation resistance based on a value of the insulation resistance measured in the past, a ratio between the AC voltage and the response voltage, and a voltage variation of the fuel cell;
A ground fault detector.

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