Ground-fault resistance measurement circuit and ground-fault detection circuit

• US 7,560,935 B2
• Filed: 01/30/2007
• Issued: 07/14/2009
• Est. Priority Date: 01/30/2006
• Status: Expired due to Fees

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Morimoto, Naohisa
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US11/699,425
• Publication Number:
  US 20070176604A1
• Time in Patent Office: 896 Days
• Field of Search: 324/522, 324/503, 324/509, 324/525
• US Class Current: 324/525
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B60L 2250/30 by voice
• CPC Class Codes: B60L 3/0023 Detecting, eliminating, remedying or compensating for drive train abnormalities, e.g. failures within the drive train
• CPC Class Codes: B60L 3/0046 relating to electric energy storage systems, e.g. batteries or capacitors
• CPC Class Codes: B60L 3/0053 relating to fuel cells
• CPC Class Codes: B60L 3/0069 relating to the isolation, e.g. ground fault or leak current
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

There is a ground-fault resistance measurement circuit which measures a ground-fault resistance between a conductive frame body of electrical equipment and a charge section insulated from the frame body. This ground-fault resistance measurement circuit includes: a capacitor which is connected between the charge section and the frame body; a switch which opens and closes a connection path between the charge section and the capacitor; a charging unit which charges the capacitor to a predetermined voltage; a voltage measurement section which measures a charging voltage of the capacitor; a discharge control section which connects the capacitor and the charge section after the capacitor is charged, and discharges the capacitor; and a calculation section which calculates a resistance between the charge section and the frame body, based on a change in the charging voltage of the capacitor.

Claims

1. A ground-fault resistance measurement circuit which measures a resistance between a charge section insulated from a conductive frame body of an electrical apparatus and the frame body, comprising:

a capacitor which is connected between the charge section and the frame body;

a first switch which opens and closes a connection path between the charge section connected to the capacitor and the capacitor;

a charging power-source section which outputs a predetermined set voltage for charge;

a charging unit which charges the capacitor, using the predetermined set voltage output from the charging power-source section;

a voltage measurement section which measures a charging voltage of the capacitor;

a discharge control section which closes the first switch after charging the capacitor by the charging unit; and

a calculation section which calculates a resistance value between the charge section and the frame body, based on a change in the charging voltage measured by the voltage measurement section after closing the first switch by the discharge control section.

2. The ground-fault resistance measurement circuit according to claim 1, wherein the calculation section calculates a resistance value R_L between the charge section and the frame body, based on a value Vta indicative of a charging voltage of the capacitor as measured by the voltage measurement section at the time when the discharge control section closes the first switch and a value Vtb indicative of a charging voltage measured by the voltage measurement section at the time when a predetermined set time tb elapses after closing the first switch.

3. The ground-fault resistance measurement circuit according to claim 2, further comprising:

a first resistance having a first resistance value R₁ disposed on a path from the capacitor to the charge section via the first switch; and

second and third resistances having a second resistance value R₂ and a third resistance value R₃, respectively, which serve as voltage dividing resistances for dividing a charge voltage of said capacitor, wherein;

said voltage measurement section measures, as the charge voltage, a divided voltage divided by the voltage dividing resistances, and

said calculation section calculates the resistance value R_L based on the electrostatic capacity C₁ of the capacitor and from the following expression;

R_L=τ

×

(R₂+R₃)/{C₁×

(R₂+R₃)−

τ

}−

R₁,

where τ

=tb/(log Vta−

log Vtb).

4. The ground-fault resistance measurement circuit according to claim 1, wherein the calculation section calculates a resistance value R_L between the charge section and the frame body, based on a first charging voltage Vta measured by the voltage measurement section at the time when a predetermined first set time ta elapses after the discharge control section closes the first switch and a second charging voltage Vtb measured by the voltage measurement section at the time when a predetermined second set time tb elapses after a lapse of the predetermined first set time.

5. The ground-fault resistance measurement circuit according to claim 4, further comprising:

a first resistance having a first resistance value R₁ disposed on a path from the capacitor to the charge section via the first switch; and

second and third resistances having a second resistance value R₂ and a third resistance value R₃, respectively, which serve as voltage dividing resistances for dividing a charge voltage of said capacitor, wherein;

said voltage measurement section measures, as the charge voltage, a divided voltage divided by the voltage dividing resistances, and

said calculation section calculates the resistance value R_L based on the electrostatic capacity C₁ of the capacitor and from the following expression;

R_L=τ

×

(R₂+R₃)/{C₁×

(R₂+R₃)−

τ

}−

R₁,

where τ

=(ta−

tb)/(log Vta−

log Vtb).

6. The ground-fault resistance measurement circuit according to claim 1, further comprising:

a clock section which clocks time ta starting from a point of time when the discharge control section closes the first switch until a point of time the charging voltage measured by the voltage measurement section reaches a first predetermined set voltage V1 or below, and a time tb starting from a point of time when the discharge control section closes the first switch until a point of time the charging voltage measured by the voltage measurement section reaches a second predetermined set voltage V2 or below, said second predetermined set voltage V2 being lower than said first predetermined set voltage V1,

wherein,

the calculation section calculates a resistance value R_L between the charge section and the frame body, based on the time clocked by the clock section.

7. The ground-fault resistance measurement circuit according to claim 6, further comprising:

a first resistance having a first resistance value R₁ disposed on a path from the capacitor to the charge section via the first switch; and

second and third resistances having a second resistance value R₂ and a third resistance value R₃, respectively, which serve as voltage dividing resistances for dividing a charge voltage of said capacitor, wherein;

said voltage measurement section measures, as the charge voltage, a divided voltage divided by the voltage dividing resistances, and

said calculation section calculates the resistance value R_L based on the electrostatic capacity C₁ of the capacitor and from the following expression;

R_L=τ

×

(R₂+R₃)/{C₁×

(R₂+R₃)−

τ

}−

R₁,

where τ

=(tb−

ta)/(log V1−

log V2).

8. The ground-fault resistance measurement circuit according to claim 1, wherein,

the charging unit includes a second switch which opens and closes a connection path between the charging power-source section and the capacitor, and

the discharge control section closes the second switch so that the charging power-source section charges the capacitor, and thereafter opens the second switch.

9. The ground-fault resistance measurement circuit according to claim 1, wherein a resistance is disposed on a path from the capacitor through the first switch to the charge section.

10. The ground-fault resistance measurement circuit according to claim 1, further comprising:

a voltage-division resistance which divides a charging voltage of the capacitor;

wherein the voltage measurement section measures a division voltage obtained from the voltage division by the voltage-division resistance.

11. The ground-fault resistance measurement circuit according to claim 1, further comprising:

a display section which displays a resistance value calculated by the calculation section.

12. The ground-fault resistance measurement circuit according to claim 1, wherein:

the electrical apparatus includes a battery insulated from the frame body; and

the charge section is an electrode of the battery.

13. The ground-fault resistance measurement circuit according to claim 12, wherein:

the electrical apparatus is an electric automobile;

the battery supplies electric power to a mechanical-power motor of the electric automobile; and

the frame body is a body of the electric automobile.

14. A ground-fault detection circuit, comprising:

the ground-fault resistance measurement circuit according to claim 1; and

a decision section which decides that a ground fault is generated if the resistance value calculated by the calculation section is below a predetermined threshold value.

15. The ground-fault detection circuit according to claim 14, further comprising, a notification section which gives notice of a decision result by the decision section.