Current control apparatus for electric load

• US 7,312,969 B2
• Filed: 08/16/2005
• Issued: 12/25/2007
• Est. Priority Date: 02/28/2005
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Matsumoto, Shuuiti, Fujiwara, Takeshi, Nishizaki, Hiroyoshi
• Primary Examiner(s): Sherry; Michael
• Assistant Examiner(s): Nguyen; Danny
• Application Number:
  US11/204,221
• Publication Number:
  US 20060197508A1
• Time in Patent Office: 861 Days
• Field of Search: 361/23, 361/87, 361/93.9
• US Class Current: 361/93.9
• CPC Class Codes: F02D 2041/2027 Control of the current by pulse width modulation or duty cycle control
• CPC Class Codes: F02D 2041/2058 using information of the actual current value
• CPC Class Codes: F02D 2041/2093 detecting short circuits
• CPC Class Codes: F02D 41/20 Output circuits, e.g. for controlling currents in command coils
• CPC Class Codes: F02D 41/22 Safety or indicating devices for abnormal conditions in air/fuel ratio feedback systems F02D41/1495, in electric control linkage F02D11/107, in purge control systems F02M25/0809
• CPC Class Codes: H01F 7/1844 Monitoring or fail-safe circuits for relays H01H47/002
• CPC Class Codes: H03K 17/0826 in bipolar transistor switches
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A current control apparatus for an electric load can prevent burnout at a short-circuit accident with high control precision. A switching element is interrupted by an overcurrent detection circuit upon occurrence of a load short circuit, but is transitionally limited in current by a current detection resistor. A differential amplifier amplifies a difference voltage between voltages at opposite ends of the current detection resistor to generate a monitored voltage Ef corresponding to a load current. A microprocessor controls the energization rate of the switching element so as to make an estimated load current Ime calculated from the monitored voltage Ef coincide with a target load current Is, and it calculates, upon calibration operation, calibration constants and estimates, during actual operation, a load current Ime from the monitored voltage Ef using the calibration constants.

Claims

1. A current control apparatus for an electric load comprising:

a feeder circuit including a switching element and a current detection resistor both inserted in series between a drive power supply and an electric load for feeding electric power from said drive power supply to said electric load through said switching element and said current detection resistor;

a current control part that controls an on/off ratio of said switching element in such a manner that a load current detected by said current detection resistor is made to coincide with a target load current Is to be supplied to said electric load; and

said current control part including a microprocessor, a differential amplifier circuit part, a detected error calibration section, a conversion estimating section, and a feedback control section;

wherein said microprocessor includes a nonvolatile program memory, a nonvolatile data memory, a RAM memory for arithmetic operation, and a multichannel AD converter;

said differential amplifier circuit part amplifies a difference voltage between voltages at opposite ends of said current detection resistor to generate a monitored voltage Ef substantially proportional to said load current and to input it to said microprocessor;

said detected error calibration section stores a current proportional constant of said monitored voltage Ef, a voltage proportional constant of an error component, and an offset component, which are measured at the time of adjustment for shipment of said apparatus as a product, into said nonvolatile data memory as calibration constants;

said conversion estimating section calculates an estimated load current Ime based on said monitored voltage Ef and said calibration constants or calculates an estimated monitored voltage Es corresponding to said target load current Is;

said feedback control section controls an energization duty γ

, which is a closed circuit duration of said switching element divided by a switching period thereof, while setting said target load current Is as a target value of said current control part, and said estimated load current Ime as a feedback value, or setting said estimated monitored voltage Es as a target value of said current control part, and said monitored voltage Ef as a feedback value; and

said detected error calibration section, said conversion estimating section and said feedback control section are executed by said microprocessor based on a control program stored in said nonvolatile program memory.

2. The current control apparatus for an electric load as set forth in claim 1, wherein

said feeder circuit includes a commutating diode;

said differential amplifier circuit part includes a bias correction circuit;

said commutating diode is connected in parallel to said electric load in such a manner that it has a polarity to permit a continued transient-decay current due to the inductance of said electric load to return upon opening of said switching element; and

said bias correction circuit impresses a substantially equal, positive bias voltage to a first input and a second input of said differential amplifier so as to cancel a negative voltage impressed thereto due to a voltage drop of said commutating diode upon opening of said switching element, thereby inhibiting said negative voltage from being input to said differential amplifier.

3. The current control apparatus for an electric load as set forth in claim 1, wherein

said current control part includes a power supply voltage measuring circuit that measures a power supply monitoring voltage Vf;

said detected error calibration section includes a first, a second and a third data acquisition section, a calibration factor calculation section that calculates calibration factors from said data acquired by said first, second and third data acquisition sections, a power supply voltage calibration section that calibrates said power supply monitoring voltage Vf, and a transfer storage section that transfers and stores said calibration factors as calibration constants;

said power supply voltage measuring circuit inputs a divided voltage of a drive power supply voltage Vb from said drive power supply to said microprocessor as said power supply monitoring voltage Vf;

said first data acquisition section acts to write and store, in said RAM memory as a first error voltage Ef0, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element fully opened when a first calibration command is input upon impression of said drive power supply voltage Vb to said current control part;

said second data acquisition section acts, upon input of a second calibration command with wiring extending from said feeder circuit to said electric load being cut, to write and store, into said RAM memory as a second error voltage Ef1, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element being made fully conductive, and at said same time to write and store into said RAM memory the value of said drive power supply voltage Vb externally measured;

said third data acquisition section acts, upon input of a third calibration command with wiring extending from said feeder circuit to said electric load being connected, to write and store, into said RAM memory as a measured voltage Ef2, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element being made fully conductive, and at the same time to write and store the value of an external load current Im measured on the outside into said RAM memory;

when a voltage drop Vd of said commutating diode is made substantially equal to 1 [V] (Vd≈

1 [V]), said calibration factor calculation section calculates and stores a voltage proportional constant A of the error component, a current proportional constant B and an offset component C in such a manner that said monitored voltage Ef, said drive power supply voltage Vb, said energization duty γ and

said external load current Im of said differential amplifier circuit part satisfy the following relation;

Ef=A×

(Vb+Vd)×

γ

+B×

Im+C

said offset component C coincides with said first error voltage Ef0 stored in said first data acquisition section;

said voltage proportional constant A is calculated from data acquired by said first and second data acquisition sections as follows;

A=(Ef1−

Ef0)/(Vb+Vd)

said current proportional constant B is calculated from data acquired by said second and third data acquisition sections as follows;

B=(Ef2−

Ef1)/Im

said power supply voltage calibration section is executed in said first, second and third data acquisition sections to write and store said power supply monitoring voltage Vf into said RAM memory, and to calculate a power supply voltage calibration factor Kv as Kv=Vb/Vf, or apply a fixed constant which is preset as the reciprocal of a voltage division ratio of said drive power supply voltage Vb; and

said transfer storage section transfers and stores, into said nonvolatile data memory as calibration constants, the respective values of said voltage proportional constant A, said current proportional constant B, said offset component C, and said power supply voltage calibration factor Kv, all of which are the calculation results of said calibration factor calculation section.

4. The current control apparatus for an electric load as set forth in claim 1, wherein

said current control part includes an average voltage measuring circuit for measuring an average monitored voltage Va that is an average value of the voltage impressed to said electric load;

said detected error calibration section includes a first, a second and a third data acquisition section, a calibration factor calculation section that calculates calibration factors from data acquired by said first, second and third data acquisition sections, an average voltage calibration section that calibrates said average monitored voltage Va, and a transfer storage section that transfers and stores said calibration factors as calibration constants;

said average voltage measuring circuit inputs a divided voltage obtained by dividing a voltage across said opposite ends of said electric load to said microprocessor as said average monitored voltage Va;

said first data acquisition section acts to write and store, in said RAM memory as a first error voltage, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element fully opened when a first calibration command is input upon impression of said predetermined drive power supply voltage Vb to said current control part;

said second data acquisition section acts, upon input of a second calibration command with wiring extending from said feeder circuit to said electric load being cut, to write and store, into said RAM memory as a second error voltage Ef1, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element being made fully conductive, and at the same time to write and store said average monitored voltage Va into said RAM memory;

said third data acquisition section acts, upon input of a third calibration command with wiring extending from said feeder circuit to said electric load being connected, to write and store, into said RAM memory as a measured voltage Ef2, the value of a monitored voltage that is generated from said differential amplifier circuit part with said switching element being made fully conductive, and at the same time to write and store the value of an external load current Im measured at the outside into said RAM memory;

said calibration factor calculation section calculates and stores a voltage proportional constant D of an error component, a current proportional constant B and a offset component C in such a manner that a monitored voltage Ef of said differential amplifier circuit part 150, said average monitored voltage Va and said external load current Im satisfy the following relation;

Ef=D×

Va+B×

Im+C

said offset component C coincides with said first error voltage Ef0 stored in said first data acquisition section;

said voltage proportional constant D is calculated from data acquired by said first and second data acquisition sections as follows;

D=(Ef1−

Ef0)Va

said current proportional constant B is calculated from data acquired by said second and third data acquisition sections as follows;

B=(Ef2−

Ef1)/Im

said average voltage calibration section is executed in said second or third data acquisition section to take in the value of a drive power supply voltage Vb measured on the outside to write and store it into said RAM memory, and at the same time said average voltage calibration section calculates an average voltage calibration factor Ka between an average monitored voltage Va when said switching element becomes fully conductive and said drive power supply voltage Vb as Ka=Vb/Va, or applies a fixed constant which is preset as the reciprocal of a voltage division ratio to a voltage across opposite ends of said electric load; and

said transfer storage section transfers and stores, into said nonvolatile data memory as said calibration constants, the respective values of said voltage proportional constant D, said current proportional constant B, said offset component C, and said average voltage calibration factor Ka, all of which are the calculation results of said calibration factor calculation section.

5. The current control apparatus for an electric load as set forth in claim 3, wherein

said current control part includes a serial communication interface circuit that connects between said microprocessor and an external tool for calibration operation;

and

at the time of calibration operation, a calibration command, voltage information on said drive power supply, and current information on said electric load input from said external tool through said serial communication interface circuit are transferred to and stored into said RAM memory.

6. The current control apparatus for an electric load as set forth in claim 3, wherein

said current control part includes an input interface circuit that connects between said microprocessor, a switch input group, and an analog input group through a bus;

at the time of calibration operation, at least one of said first, second and third calibration commands is input from an input terminal of a predetermined number in said switch input group; and

voltage information on said drive power supply and current information on said electric load are input as analog inputs of predetermined numbers in said analog input group, transferred to and stored into said RAM memory.

7. The current control apparatus for an electric load as set forth in claim 3, wherein

said nonvolatile program memory includes a conversion estimating section that calculates said estimated load current Ime or said estimated monitored voltage Es, and a switching control output generation section that constitutes said feedback control section;

said conversion estimating section calculates said estimated load current Ime from said monitored voltage Ef generated from said differential amplifier circuit part and the present value of the energization duty γ

of said switching element as follows;

Ime=[Ef−

A×

(Vb+Vd)×

γ

−

C]/B

alternatively, said conversion estimating section calculates said estimated monitored voltage Es generated from said differential amplifier circuit part when said target load current Is flows at the energization duty γ

of said switching element as follows; and

Es=A×

(Vb+Vd)×

γ

+B×

Is+C

said switching control output generation section gradually increases or decreases the energization duty γ

of said switching element in response to a deviation between said target load current Is and said estimated load current Ime, or in response to a deviation between said estimated monitored voltage Es and said actual monitored voltage Ef.

8. The current control apparatus for an electric load as set forth in claim 7, wherein

said nonvolatile program memory includes a program that constitutes an initial setting section;

said initial setting section calculates a roughly estimated value γ

0 of said energization duty of said switching element from a relation among a minimum power supply voltage Vmin, a reference load current Ir, said power supply monitoring voltage Vf and said target load current Is by using the following expression, and sets it as an energization duty immediately after starting of the energization;

γ

0=(Vmin/Vb)×

(Is/Ir)(here, Vb=Kv×

Vf)

said reference load current Ir is calculated by using a standard resistance value Rc, which is determined within a resistance value variation range (Rmin-Rmax) of said electric load as follows;

Ir=Vmin/Rc.

9. The current control apparatus for an electric load as set forth in claim 4, wherein

said nonvolatile program memory includes a conversion estimating section that calculates said estimated load current Ime or said estimated monitored voltage Es, and a switching control output generation section that constitutes said feedback control section;

said conversion estimating section calculates said estimated load current Ime from said monitored voltage Ef generated from said differential amplifier circuit part and the present value of said average monitored voltage Va as follows;

Ime=[Ef−

D×

Va−

C]/B

alternatively, said conversion estimating section calculates said estimated monitored voltage Es generated from said differential amplifier circuit part when said target load current Is flows as follows; and

Es=D×

Va+B×

Is+C

said switching control output generation section gradually increases or decreases the energization duty γ

of said switching element in response to a deviation between said target load current Is and said estimated load current Ime, or in response to a deviation between said estimated monitored voltage Es and said actual monitored voltage Ef.

10. The current control apparatus for an electric load as set forth in claim 9, wherein

said nonvolatile program memory includes a program that constitutes an initial setting section;

said initial setting section calculates a roughly estimated value Vaa of said average monitored voltage Va from a relation among a minimum power supply voltage Vmin, a maximum power supply voltage Vmax, a reference load current Ir, and said target load current Is as follows;

Vaa=/2

at the same time, said initial setting section calculates a roughly estimated value γ

0 of said energization duty by using said roughly estimated value Vaa according to the following expression, and sets it as an energization duty immediately after starting of the energization; and

γ

0=x

said reference load current Ir is calculated by using a standard resistance value Rc, which is determined within a resistance value variation range of said electric load as follows;

Ir=Vmin/Rc.

11. A current control apparatus for an electric load comprising:

a feeder circuit including a switching element and a current detection resistor both inserted in series between a drive power supply and an electric load for feeding electric power from said drive power supply to said electric load through said switching element and said current detection resistor;

a current control part that controls an on/off ratio of said switching element in such a manner that a load current detected by said current detection resistor is made to coincide with a target load current Is to be supplied to said electric load; and

said current control part includes a microprocessor, a control power supply, a differential amplifier circuit part, a conversion estimating section, a feedback control section, an overcurrent detection circuit, a voltage limiting diode, an output stop section, and an abnormality warning section;

wherein said microprocessor includes a nonvolatile program memory, a nonvolatile data memory, a RAM memory for arithmetic operation, and a multichannel AD converter;

said control power supply is fed with power from said drive power supply, generates a stabilized control power supply voltage Vcc, which is lower than a drive power supply voltage Vb, and supplies it to said microprocessor;

said differential amplifier circuit part amplifies a difference voltage between voltages at opposite ends of said current detection resistor to generate a monitored voltage Ef substantially proportional to said load current and to input it to said microprocessor;

said conversion estimating section calculates an estimated load current Ime based on said monitored voltage Ef, or calculates an estimated monitored voltage Es corresponding to said target load current Is;

said feedback control section controls an energization duty γ

, which is equal to a closed circuit duration of said switching element divided by a switching period thereof, while setting said target load current Is as a target value of said current control part, and said estimated load current Ime as a feedback value, or setting said estimated monitored voltage Es as a target value of said current control part, and said actual monitored voltage Ef as a feedback value;

when the value of a prestage voltage E0 of said monitored voltage Ef obtained from said differential amplifier circuit part exceeds a predetermined value that is equal to or greater than said controlled power supply voltage Vcc, said overcurrent detection circuit generates an overcurrent determination warning signal indicative of an excessive large state of said load current and inputs it to said microprocessor;

said voltage limiting diode is connected to said overcurrent detection circuit for limiting said monitored voltage Ef to be input to said microprocessor to the level of said controlled power supply voltage Vcc; and

said output stop section and said abnormality warning section stop a feedback control output PWM from said feedback control section to said switching element, and provide a warning indication of an abnormally stopped state in response to said overcurrent determination signal.

12. The current control apparatus for an electric load as set forth in claim 11, wherein

said overcurrent determination signal is impressed to an interrupt input terminal of said microprocessor;

and

said output stop section stops said feedback control output in immediate response to the generation of said overcurrent determination signal.

13. The current control apparatus for an electric load as set forth in claim 11, wherein

said overcurrent state detection circuit includes a warning signal input circuit connected to an input terminal of said microprocessor and an abnormality occurrence storage circuit;

and

said abnormality occurrence storage circuit is set by said overcurrent determination signal to stop the conduction of said switching element, and is reset when power is turned on.

14. The current control apparatus for an electric load as set forth in claim 11, wherein

said nonvolatile program memory includes a program which constitutes an average voltage estimation section that estimates an average monitored voltage Va, which is an average value of the voltage impressed to said electric load, an abnormality determination section comprising at least one of an overcurrent state detection section and an undercurrent state detection section, said output stop section, and said abnormality warning section;

said average voltage estimation section calculates the product of the energization duty γ

of said switching element and said drive power supply voltage Vb as said average monitored voltage Va;

when a relative relation between said monitored voltage Ef and said average monitored voltage Va varies exceeding an allowable variation range, said abnormality determination section generates an abnormality determination warning signal indicating that said monitored voltage Ef is excessively large or small; and

said output stop section and said abnormality warning section stop said feedback control output PWM, and provide a warning indication of an abnormally stopped state in response to said overcurrent determination signal.

15. A current control apparatus for an electric load comprising:

a feeder circuit including a switching element and a current detection resistor both inserted in series between a drive power supply and an electric load for feeding electric power from said drive power supply to said electric load through said switching element and said current detection resistor;

a current control part that controls an on/off ratio of said switching element in such a manner that a load current detected by said current detection resistor is made to coincide with a target load current Is to be supplied to said electric load; and

said current control part includes a microprocessor, a differential amplifier circuit part, a conversion estimating section, a feedback control section, an average voltage measuring circuit, an abnormality determination section, an output stop section, and an abnormality warning section;

wherein said microprocessor includes a nonvolatile program memory, a nonvolatile data memory, a RAM memory for arithmetic operation, and a multichannel AD converter;

said differential amplifier circuit part amplifies a difference voltage between voltages at opposite ends of said current detection resistor to generate a monitored voltage Ef substantially proportional to said load current and to input it to said microprocessor;

said conversion estimating section calculates an estimated load current Ime based on the value of said monitored voltage Ef, or calculates an estimated monitored voltage Es corresponding to said target load current Is;

said feedback control section controls an energization duty γ

, which is a closed circuit duration of said switching element divided by a switching period thereof, while setting said target load current Is as a target value of said current control part, and said estimated load current Ime as a feedback value, or setting said estimated monitored voltage Es as a target value of said current control part, and said actual monitored voltage Ef as a feedback value;

said average voltage measuring circuit divides and smoothens a voltage impressed to said electric load to generate an average measured voltage Ea proportional to an average impressed voltage to said electric load;

said abnormality determination section generates an abnormality determination signal when a relative relation between said monitored voltage Ef and said average measured voltage Ea varies exceeding an allowable variation range; and

said output stop section and said abnormality warning section stop a feedback control output PWM from said feedback control section to said switching element, and provide a warning indication of an abnormally stopped state in response to said overcurrent determination signal.

16. The current control apparatus for an electric load as set forth in claim 15, wherein

said abnormality determination section includes at least one of an overcurrent state detection circuit and an undercurrent state detection circuit;

said overcurrent state detection circuit comprises a comparison circuit for determination of an excessively large current, and supplies an abnormality determination signal in the form of a warning signal to said microprocessor when said relative relation between said monitored voltage Ef and said average measured voltage Ea varies exceeding an allowable variation range to indicate an excessive large state of said monitored voltage Ef;

said undercurrent state detection circuit comprises a comparison circuit for determination of an excessively small current, and supplies an abnormality determination signal in the form of a warning signal to said microprocessor when said relative relation between said monitored voltage Ef and said average measured voltage Ea varies exceeding an allowable variation range to indicate an excessive small state of said monitored voltage Ef; and

said output stop section and an abnormality warning section stop, in response to a warning signal from said overcurrent state detection circuit or said undercurrent state detection circuit, said feedback control output PWM and at said same time indicate a warning of said abnormally stopped state.

17. The current control apparatus for an electric load as set forth in claim 16, wherein

said warning signal is impressed to an interrupt input terminal of said microprocessor;

and

said output stop section stops said feedback control output PWM in immediate response to the generation of said abnormality determination signal.

18. The current control apparatus for an electric load as set forth in claim 16, wherein

said overcurrent state detection circuit or said undercurrent state detection circuit includes a warning signal input circuit connected to said input terminal of said microprocessor and an abnormality occurrence storage circuit;

and

said abnormality occurrence storage circuit is set by said warning signal to stop the conduction of said switching element, and is reset when power is turned on.

19. The current control apparatus for an electric load as set forth in claim 15, wherein

said abnormality determination section includes at least one of an overcurrent state detection section and an undercurrent state detection section;

said average measured voltage Ea generated by said average voltage measuring circuit is input to said microprocessor as said average monitored voltage;

said overcurrent state detection section generates an abnormality determination signal when said relative relation between said monitored voltage Ef and said average monitored voltage Va varies exceeding an allowable variation range to indicate an excessively large state of said monitored voltage Ef;

said undercurrent state detection section generates an abnormality determination signal when said relative relation between said monitored voltage Ef and said average monitored voltage Va varies exceeding an allowable variation range to indicate an excessively small state of said monitored voltage Ef; and

said output stop section and said abnormality warning section serve to stop, in response to an abnormality determination signal from said overcurrent state detection section or said undercurrent state detection section, said feedback control output PWM and at said same time indicate a warning of said abnormally stopped state.