JP4168965B2 - AC motor controller - Google Patents

Description

  The present invention relates to an AC motor control device that controls an AC motor.

  2. Description of the Related Art Conventionally, as a current detection circuit for an electric motor, for example, there are a current detection element and an electric motor current detection means of an electric power steering apparatus disclosed in Japanese Patent Application Laid-Open No. 9-11918. The current detection element is a resistor connected in series with the DC motor. The motor current detection means is composed of conversion means and motor current signal conversion means. The conversion means is a differential amplifier circuit composed of an operational amplifier that operates with a single power supply with a power supply voltage of 5 V (VR). The virtual ground point of the operational amplifier is set to 2.5 V (VR / 2) by a bias resistor. The motor current signal conversion means is a circuit for converting the output voltage of the operational amplifier into a signal level corresponding to control means composed of a microprocessor operating at a power supply voltage of 5V.

  When a current flows through the DC motor, the current detection element generates a voltage corresponding to the direction and magnitude of the motor current. The voltage of the current detection element is amplified by the conversion means. Since the virtual ground point of the operational amplifier constituting the conversion means is set to 2.5V, when the motor current is 0A, the conversion means outputs 2.5V. On the other hand, when the motor current flows in the negative direction, the converting means has a voltage smaller than 2.5 V in proportion to the magnitude of the motor current, and when the motor current flows in the positive direction, the converting means becomes the magnitude of the motor current. A voltage greater than 2.5V is output in proportion.

The output voltage of the conversion means is converted into a signal level corresponding to the control means by the motor current signal conversion means. The output voltage of the motor current signal conversion means is A / D converted by a microprocessor constituting the control means. The microprocessor performs calculation according to a preset procedure using the A / D converted motor current value, and controls the DC motor via the motor driving means based on the calculation result.
Japanese Patent Laid-Open No. 9-11918

  By the way, the output voltage range of the operational amplifier is generally narrower than the power supply voltage range of the operational amplifier. For example, in the case of an operational amplifier that operates with a power supply voltage of 5V, the voltage range that can be output by the operational amplifier is in the range of 1.4 to 3.6V. On the other hand, the voltage range that can be input to the A / D conversion unit of the microprocessor is a range from 0 V to the power supply voltage. Convert to a digital value according to the number of bits. For example, in the case of a microprocessor that operates with a power supply voltage of 5 V, the input voltage range of the A / D conversion unit of the microprocessor is 0 to 5 V, and the A / D conversion unit sets the input voltage with 5 V as a full scale. Conversion to a digital value corresponding to the number of bits of the A / D converter.

  Therefore, in the above-described current detection element and motor current detection means, the output voltage range of the motor current detection means is considerably narrower than the voltage range that can be input to the A / D conversion unit. Can not reduce the error.

  The present invention has been made in view of such circumstances, and an AC motor that can reduce quantization error associated with A / D conversion of a voltage corresponding to the motor current of the AC motor and improve reliability. An object is to provide a control device.

  Therefore, as a result of intensive research and trial and error to solve this problem, the present inventors have amplified the voltage of the current detection element to a voltage whose output voltage range is wider than the input voltage range of the A / D converter, and thereafter The inventors have come up with the idea that the conversion error of the motor current can be reduced by converting the input voltage range of the A / D converter, and the present invention has been completed.

  That is, the AC motor control device according to claim 1 is an inverter circuit that converts DC power supplied from a DC power source into AC power and supplies the AC motor, and detects a motor current flowing in the AC motor to generate a voltage. AC motor control apparatus comprising: a current detection circuit that converts and outputs; and a control unit that has an A / D conversion unit and controls the inverter circuit based on the output voltage of the current detection circuit that has been A / D converted The current detection circuit includes a current detection element that detects and converts the motor current into a voltage, and the current detection circuit detects the voltage of the current detection element so that an output voltage range is wider than an input voltage range of the A / D conversion unit. A differential amplifier circuit that amplifies the voltage to a single polarity according to the polarity and magnitude of the voltage of the element, and a voltage change that converts the output voltage of the differential amplifier circuit into the input voltage range of the A / D converter. And having a circuit.

  The AC motor control device according to claim 2 is the AC motor control device according to claim 1, further comprising: a first power source for operating the control unit; and a voltage higher than an output voltage of the first power source. The differential amplifier circuit operates by being supplied with power from the second power source.

  The AC motor control device according to claim 3 is the AC motor control device according to claim 2, and further, the current detection circuit outputs a reference voltage that changes in proportion to an output voltage of the first power supply. It has a reference voltage circuit, The differential amplifier circuit amplifies the voltage of the current detection element on the basis of the reference voltage.

  According to a fourth aspect of the present invention, there is provided the AC motor control device according to any one of the first to third aspects, further controlling an AC motor mounted on the vehicle.

  According to the AC motor control device of claim 1, the voltage of the current detection element in the differential amplifier circuit is set so that the output voltage range is wider than the input voltage range of the A / D converter, and the polarity of the voltage of the current detection element And can be amplified to a single polarity voltage depending on the magnitude. Furthermore, the voltage conversion circuit can convert the output voltage of the differential amplifier circuit into the input voltage range of the A / D converter. Therefore, the output voltage range of the current detection circuit can be expanded compared to the circuit including the current detection element and the motor current detection means described above, and the quantization error associated with A / D conversion can be reduced and the reliability can be improved.

  According to the AC motor control apparatus of the second aspect, the differential amplifier circuit can be operated by the second power source that outputs a voltage higher than the output voltage of the first power source that operates the control unit. Therefore, the differential amplifier circuit can reliably output a voltage in a range wider than the input voltage range of the A / D converter.

  According to the AC motor control apparatus of the third aspect, the reference voltage serving as a reference for amplification in the differential amplifier circuit can be changed in proportion to the output voltage of the first power supply in the reference voltage circuit. For this reason, it is possible to suppress an A / D conversion error associated with a change in the output voltage of the first power supply. By the way, the A / D conversion unit in the control unit operates by being supplied with power from the first power source, and A / D converts the input voltage using the output voltage of the first power source as a full scale. For this reason, when the output voltage of the first power supply fluctuates, the A / D conversion unit converts to a different digital value even if the input voltage is the same, and an error occurs. In the reference voltage circuit, the reference voltage that is the reference for amplification in the differential amplifier circuit is changed in proportion to the output voltage of the first power supply, so that the output of the differential amplifier circuit is synchronized with the change in the output voltage of the first power supply. The voltage can be changed. Thereby, the error of A / D conversion accompanying the fluctuation | variation of the output voltage of a 1st power supply can be reduced.

  According to the AC motor control apparatus of the fourth aspect, the reliability of the vehicle can be improved.

  The present embodiment shows an example in which the AC motor control device according to the present invention is applied to an electric compressor device for an air conditioner mounted on a hybrid vehicle.

(First embodiment)
FIG. 1 is a circuit diagram of the electric compressor device for an air conditioner according to the first embodiment, FIG. 2 shows the relationship between the current flowing through the current detection resistor and the output voltage of the current detection circuit, and FIG. The relationship of the output voltage is shown in FIG. Then, with reference to FIG. 1, FIG. 2 and FIG.

  First, a specific structure will be described with reference to FIG. As shown in FIG. 1, the electric compressor device 1 for an air conditioner includes a high voltage battery 2, an AC motor control device 3 (AC motor control device), an AC motor 4 (AC motor), and a compressor 5. ing.

  The high voltage battery 2 is, for example, a DC power supply with an output voltage of 300V, and the positive terminal 2a and the negative terminal 2b are connected to the AC motor control device 3, respectively.

  The AC motor control device 3 includes a smoothing capacitor 30, an inverter circuit 31, a current detection circuit power supply 32 (second power supply), a control circuit power supply 33 (first power supply), a current detection circuit 34, and a control. The circuit 35 (control part) is comprised.

  The smoothing capacitor 30 is a large-capacity capacitor for smoothing the voltage of the high-voltage battery 2, and is connected in parallel to the high-voltage battery 2.

  The inverter circuit 31 is a circuit that converts DC power supplied from the high-voltage battery 2 into AC power, and connects six IGBTs 31a to 31f having diodes connected in reverse parallel between the collector and the emitter in a three-phase bridge connection. Configured. The collectors of the three IGBTs 31a to 31c on the upper side of the inverter circuit 31 are connected to the positive terminal 2a of the high voltage battery 2, and the emitters of the three IGBTs 31d to 31f on the lower side are connected to the high voltage battery 2 via a current detection resistor 340 described later. Are respectively connected to the negative terminal 2b.

  The power source 32 for current detection circuit is a circuit that outputs, for example, 15V for stepping down the voltage of the high-voltage battery 2 and operating the current detection circuit 34. The input terminals of the current detection circuit power supply 32 are connected to the positive terminal 2a and the negative terminal 2b of the high voltage battery 2, respectively. The positive terminal 32 a and the negative terminal 32 b of the current detection circuit power supply 32 are connected to the current detection circuit 34 and the control circuit power supply circuit 33, respectively.

  The control circuit power supply 33 is a circuit that outputs, for example, 5V for stepping down the 15V output voltage of the current detection circuit power supply 32 and operating the control circuit 35. The input terminal of the control circuit power supply 33 is connected to the positive terminal 32a and the negative terminal 32b of the current detection circuit power supply 32, respectively. The positive terminal 33 a and the negative terminal 33 b of the control circuit power source 33 are connected to the control circuit 35, respectively. Further, the positive terminal 33 a of the control circuit power supply 33 is connected to the current detection circuit 34, and the negative terminal 33 b is connected to the negative terminal 32 b of the current detection circuit power supply 32.

  The current detection circuit 34 is a circuit that detects a motor current flowing through the AC motor 4, converts it into a voltage, and outputs the voltage. A current detection resistor 340 (current detection element), a reference voltage circuit 341, a differential amplifier circuit 342, and the like. , And a voltage conversion circuit 343.

  The current detection resistor 340 is a low resistance element for converting a motor current flowing through the AC motor 4 into a voltage. One end of the current detection resistor 340 is connected to the emitters of the IGBTs 31 d to 31 f, and the other end is connected to the negative terminal 2 b of the high voltage battery 2.

  The reference voltage circuit 341 is a circuit that amplifies the output voltage of the control circuit power supply 33 and outputs a reference voltage serving as a reference for amplification in the differential amplifier circuit 342. The reference voltage circuit 341 includes a differential amplifier 341a, resistors 341b to 341d, and It is composed of The differential amplifier 341a is, for example, an operational amplifier that operates with a single power supply of 15V. The power supply terminal of the differential amplifier 341a is connected to the positive terminal 32a of the current detection circuit power supply 32, and the ground terminal is connected to the negative terminal 32b of the current detection circuit power supply 32. The inverting input terminal of the differential amplifier 341a is connected to the negative terminal 32b of the current detection circuit power source 32 via the resistor 341b, and is connected to the output terminal of the differential amplifier 341a via the resistor 341c. The non-inverting input terminal of the differential amplifier 341a is connected to the positive terminal 33a of the control circuit power supply 33 via the resistor 341d. Further, the output terminal of the differential amplifier 341 a is connected to the differential amplifier circuit 342.

  The differential amplifier circuit 342 is a circuit that amplifies the voltage of the current detection resistor 340 based on the reference voltage output from the reference voltage circuit 341, and includes a differential amplifier 342a and resistors 342b to 342e. The differential amplifier 342a is, for example, an operational amplifier that operates with a single power supply of 15V. The power terminal of the differential amplifier 342a is connected to the positive terminal 32a of the current detection circuit power source 32, and the ground terminal is connected to the negative terminal 32b of the current detection circuit power source 32. The inverting input terminal of the differential amplifier 342a is connected to the connection point between the current detection resistor 340 and the high voltage battery 2 through the resistor 342b, and is connected to the output terminal of the differential amplifier 342a through the resistor 342c. The non-inverting input terminal of the differential amplifier 342a is connected to the connection point between the current detection resistor 340 and the emitters of the IGBTs 31d to 31f via the resistor 342d, and is connected to the output terminal of the differential amplifier 341a via the resistor 342e. Yes. Further, the output terminal of the differential amplifier 342a is connected to the voltage conversion circuit 343.

  The voltage conversion circuit 343 is a circuit that converts the output voltage of the differential amplifier circuit 342 into a voltage range that can be input to an A / D input terminal of a microcomputer 35a, which will be described later, and includes resistors 343a and 343b. The resistor 343a and the resistor 343b are connected in series. One end of the resistor 343a is connected to the output terminal of the differential amplifier 342a, one end of the resistor 343b is connected to the negative terminal 32b of the power source 32 for the current detection circuit, and the connection point of the resistors 343a and 343b is connected to the control circuit 35.

  The control circuit 35 is a circuit that controls the inverter circuit 31 based on the motor current flowing through the AC motor 4, and includes a microcomputer 35a and an inverter drive circuit 35b.

  The microcomputer 35a is an element that outputs a drive signal of the IGBTs 31a to 31f based on a voltage corresponding to the motor current flowing through the AC motor 4 input via the current detection circuit 34, and includes an A / D conversion circuit. is doing. The power supply terminal of the microcomputer 35 a is connected to the positive terminal 33 a of the control circuit power supply 33, and the ground terminal is connected to the negative terminal 33 b of the control circuit power supply 33. The A / D input terminal of the microcomputer 35a is connected to the connection point of the resistors 343a and 343b of the voltage conversion circuit 343, and the output terminal is connected to the inverter drive circuit 35b.

  The inverter drive circuit 35b is a circuit that drives the IGBTs 31a to 31f based on a drive signal from the microcomputer 35a. The inverter drive circuit 35 b has an input terminal connected to the microcomputer 35 a and an output terminal connected to the gates of the IGBTs 31 a to 31 f of the inverter circuit 31.

  The AC motor 4 is an electric motor that generates a driving force by being supplied with AC power via an inverter circuit 31. Three input terminals of the AC motor 4 are respectively connected to three output terminals of the inverter circuit 31.

  The compressor 5 is connected to the output shaft of the AC motor 4, and compresses and discharges the refrigerant by the driving force generated by the AC motor 4 to control the passenger compartment temperature.

  Next, a specific operation will be described with reference to FIGS. When the ignition switch (not shown) is turned on, the high voltage battery 2 is connected to the AC motor control device 3, the current detection circuit power supply 32 outputs 15V, and the control circuit power supply 33 outputs 5V. When 5V of the power supply 33 for the control circuit rises, the microcomputer 35a performs initial check and initial setting of each part of the circuit constituting the AC motor control device 3. Thereafter, when an air conditioner switch (not shown) is turned on, the microcomputer 35a drives the inverter circuit 31 via the inverter drive circuit 35b. The inverter circuit 31 converts the DC power supplied from the high voltage battery 2 into AC power and supplies it to the AC motor 4. The AC motor 4 is supplied with AC power from the inverter circuit 31 to generate driving force and start the compressor.

  When a motor current flows through AC motor 4, current detection resistor 340 generates a voltage corresponding to the direction and magnitude of the motor current.

  The reference voltage circuit 341 operates at 15V output from the current detection circuit power supply 32, and amplifies the output voltage of the control circuit power supply 33 by a factor of 1.5. When the output voltage of the control circuit power supply 33 is 5V, the reference voltage circuit 341 outputs a reference voltage of 7.5V. When the output voltage of the control circuit power supply 33 varies, the output voltage of the reference voltage circuit 34 also varies in proportion to the variation. The resistors 341b to 341d are set to resistance values so that the output voltage of the differential amplifier 341a is 1.5 times the output voltage of the control circuit power source 33.

  The differential amplifier circuit 342 operates at 15 V output from the current detection circuit power supply 32, and amplifies the voltage of the current detection resistor 340 with reference to the reference voltage output from the reference voltage circuit 341. When the output voltage of the control circuit power supply 33 is 5V, the differential amplifier circuit 342 amplifies the voltage of the current detection resistor 340 with reference to the 7.5V reference voltage. As shown in FIG. 2, in the differential amplifier circuit 342, a reference voltage of 7.5 V was passed when no current was flowing through the current detection resistor 340, 13.6 V was passed when 30 A was passed, and -30 A was passed. Sometimes 1.4V is output in proportion to the current. Here, a positive current indicates a current flowing from the inverter circuit 31 side to the high voltage battery 2 side, and a negative current indicates a current flowing from the high voltage battery 2 side to the inverter circuit 31 side. The current detection resistor 340 and the resistors 342b to 342e are set to such resistance values that the differential amplifier circuit 342 has the characteristics shown in FIG.

  The voltage conversion circuit 343 divides the output voltage of the differential amplifier circuit 342 by 1/3. When the output voltage of the control circuit power supply 33 is 5V, the output voltage of the differential amplifier circuit 342 amplified with reference to the 7.5V reference voltage is divided into 1/3. As shown in FIG. 3, the voltage conversion circuit 343 has a current of 2.5V, which is 1/3 of the output voltage 7.5V of the differential amplifier circuit 342 when no current flows through the current detection resistor 340, and 30A flows. When -30A flows, 4.5V is output in proportion to the current. The resistors 343a and 343b are set to resistance values that can divide the output voltage of the differential amplifier circuit 342 by 1/3.

  The microcomputer 35a operates with the output voltage of the control circuit power supply 33, and A / D converts the output voltage of the voltage conversion circuit 343. The input voltage range of the A / D conversion circuit built in the microcomputer 35a is a range from 0 V to the output voltage of the control circuit power supply 33. The A / D conversion circuit digitally converts a voltage that is ½ of the output voltage of the control circuit power supply 33 as a voltage corresponding to when no current flows through the current detection resistor 340. When the output voltage of the control circuit power supply 33 is 5V, the voltage range that can be input to the A / D conversion circuit is from 0V to 5V that is the output voltage of the control circuit power supply 33, and the A / D conversion circuit has 2 .5V is digitally converted as a corresponding voltage when no current flows through the current detection resistor 340. A voltage of 0.5 to 4.5 V, which is almost full of the input voltage range, is input to the A / D conversion circuit. The microcomputer 35a performs calculation according to a preset procedure using a voltage value corresponding to the motor current flowing through the A / D converted current detection resistor 340, and based on the calculation result, the microcomputer 35a performs alternating current via the inverter circuit 31. The motor 4 is controlled. As a result, the compressor connected to the AC motor 4 is controlled, and the vehicle interior temperature is comfortably controlled.

  By the way, when a load fluctuation occurs in another electric load connected to the high voltage battery 2, the output voltage of the control circuit power source 33 also fluctuates. For example, when the output voltage of the control circuit power supply 33 fluctuates from 5 V to 5.5 V, the output voltage of the reference voltage circuit 34 is 1.5 times the output voltage 5.5 V of the control circuit power supply 33. 25V. When no current flows through the current detection resistor 340, the differential amplifier circuit 342 outputs the reference voltage of 8.25V, and the voltage conversion circuit 343 is 1/3 of the output voltage of 8.25V of the differential amplifier circuit 342. .75V is output. The A / D conversion circuit digitally converts 2.75 V, which is 1/2 of the output voltage 5.5 V of the power supply 33 for the control circuit, as a voltage corresponding to when no current flows through the current detection resistor 340. Therefore, even if the output voltage of the control circuit power supply 33 fluctuates, there is no error in the voltage value corresponding to the motor current flowing through the A / D converted current detection resistor 340.

  Finally, specific effects will be described. According to the first embodiment, the AC motor control device 3 uses the differential amplifier circuit 342 to set the voltage of the current detection resistor 340 so that the output voltage range is wider than the input voltage range of the A / D conversion circuit, and the current The voltage can be amplified to a single polarity voltage according to the polarity and magnitude of the voltage of the detection resistor 340. Further, the voltage conversion circuit 343 can convert the output voltage of the differential amplifier circuit 342 into a voltage range that can be input to the A / D conversion circuit. Therefore, the output voltage range of the current detection circuit 34 can be expanded, and the quantization error accompanying A / D conversion can be reduced and the reliability can be improved.

  The AC motor control device 3 can operate the differential amplifier circuit 343 with the current detection circuit power source 32 that outputs a voltage higher than the output voltage of the control circuit power source 33 that operates the microcomputer 35a. Therefore, the differential amplifier circuit 342 can reliably output a voltage in a wider range than the voltage range that can be input by the A / D converter circuit.

  Further, the AC motor control device 3 can change the reference voltage serving as a reference for amplification in the differential amplifier circuit 342 in proportion to the output voltage of the control circuit power supply 33 by the reference voltage circuit 341. For this reason, it is possible to suppress an A / D conversion error caused by a change in the output voltage of the control circuit power supply 33. By the way, the A / D conversion circuit built in the microcomputer 35a operates when power is supplied from the control circuit power supply 33, and the input voltage is A / D converted using the output voltage of the control circuit power supply 33 as a full scale. To do. For this reason, when the output voltage of the control circuit power supply 33 fluctuates, the A / D converter circuit converts even the same input voltage into a different digital value, resulting in an error. In synchronization with the change in the output voltage of the control circuit power supply 33, the reference voltage circuit 341 changes the reference voltage that is the reference for amplification in the differential amplifier circuit 342 in proportion to the output voltage of the control circuit power supply 33. The output voltage of the differential amplifier circuit 342 can be changed. Thereby, the error of A / D conversion accompanying the fluctuation | variation of the output voltage of the power supply 33 for control circuits can be reduced.

  Furthermore, according to the AC motor control device 3, it is possible to improve the reliability of the electric compressor device for an air conditioner mounted on the hybrid vehicle.

(Second Embodiment)
Next, FIG. 4 shows a circuit diagram of an electric compressor device for an air conditioner according to the second embodiment. Here, only a different part from the electric compressor apparatus for air conditioners in 1st Embodiment is demonstrated, and description except a required part is abbreviate | omitted about a common part. In addition, the same code | symbol is attached | subjected and demonstrated to the element same as the said embodiment.

  First, a specific structure will be described with reference to FIG. As shown in FIG. 4, the inverter circuit 31 is configured by connecting six IGBTs 31 a to 31 f having diodes connected in antiparallel between the collector and the emitter in a three-phase bridge connection. The collectors of the three IGBTs 31a to 31c on the upper side of the inverter circuit 31 are connected to the positive terminal 2a of the high-voltage battery 2, and the emitters of the three IGBTs 31d to 31f on the lower side are connected to the high voltage via current detection resistors 340a to 340c described later. The voltage battery 2 is connected to the negative terminal 2b.

  The current detection circuit 34 is a circuit that detects motor currents flowing through the AC motor 4 via the IGBTs 31d to 31f, converts them into voltages, and outputs the voltages. The current detection circuit 34 includes current detection resistors 340a to 340c, a reference voltage circuit 341, differential amplifier circuits 344 to 346, and voltage conversion circuits 347 to 349.

  The current detection resistors 340a to 340c are low resistance elements for converting motor currents flowing through the AC motor 4 through the IGBTs 31d to 31f into voltages, respectively. One end of each of the current detection resistors 340 a to 340 c is connected to the emitters of the IGBTs 31 d to 31 f, and the other end is connected to the negative terminal 2 b of the high voltage battery 2.

  The reference voltage circuit 341 is a circuit that outputs a reference voltage that is a reference for amplification in the differential amplifier circuits 344 to 346, and includes a differential amplifier 341a and resistors 341b to 341d. The output terminal of the differential amplifier 341a is connected to the differential amplifier circuits 344 to 346.

  The differential amplifier circuits 344 to 346 are circuits that amplify the voltages of the current detection resistors 340a to 340c on the basis of the reference voltage output from the reference voltage circuit 341. The differential amplifier circuit 344 includes a differential amplifier 344a and resistors 344b to 344e. The differential amplifier 344a is, for example, an operational amplifier that operates with a single power supply of 15V. The power terminal of the differential amplifier 344 a is connected to the positive terminal 32 a of the current detection circuit power supply 32, and the ground terminal is connected to the negative terminal 32 b of the current detection circuit power supply 32. The inverting input terminal of the differential amplifier 344a is connected to the connection point between the current detection resistor 340a and the high voltage battery 2 via the resistor 344b, and is connected to the output terminal of the differential amplifier 344a via the resistor 344c. The non-inverting input terminal of the differential amplifier 344a is connected to the connection point between the current detection resistor 340a and the emitter of the IGBT 31d via the resistor 344d, and is connected to the output terminal of the differential amplifier 341a via the resistor 344e. Further, the output terminal of the differential amplifier 344a is connected to the voltage conversion circuit 347. The differential amplifier circuits 335 and 336 have the same configuration as the differential amplifier circuit 334. The power supply terminal is connected to the positive terminal 32a of the current detection circuit power supply 32, and the ground terminal is connected to the negative terminal 32b of the current detection circuit power supply 32. It is connected. The input terminal of the differential amplifier circuit 335 is connected to the connection point between the current detection resistor 340b and the high voltage battery 2, and the other input terminal is connected to the connection point between the current detection resistor 340b and the emitter of the IGBT 31e. Further, another input terminal of the differential amplifier circuit 335 is connected to the output terminal of the differential amplifier 341a. Further, the output terminal of the differential amplifier circuit 335 is connected to the voltage conversion circuit 348. The input terminal of the differential amplifier circuit 336 is connected to the connection point between the current detection resistor 340c and the high voltage battery 2, and the other input terminal is connected to the connection point between the current detection resistor 340c and the emitter of the IGBT 31f. Further, another input terminal of the differential amplifier circuit 336 is connected to the output terminal of the differential amplifier 341a. Further, the output terminal of the differential amplifier circuit 336 is connected to the voltage conversion circuit 349.

  The voltage conversion circuits 347 to 349 are circuits that convert the output voltage of the differential amplifier circuits 344 to 346 into a voltage range that can be input to the A / D input terminal of the microcomputer 35a. The voltage conversion circuit 347 includes resistors 347a and 347b. The resistor 347a and the resistor 347b are connected in series. One end of the resistor 347a is connected to the output terminal of the differential amplifier 344a, one end of the resistor 347b is connected to the negative terminal 32b of the power source 32 for the current detection circuit, and the connection point of the resistors 347a and 347b is connected to the control circuit 35. The voltage conversion circuits 348 and 349 have the same configuration as the voltage conversion circuit 347. One end of the voltage conversion circuit 348 is connected to the output terminal of the current detection circuit 345, the other end is connected to the negative terminal 2b of the power supply 32 for the current detection circuit, and the connection point between the two resistors constituting the voltage conversion circuit 348 is connected to the control circuit 35. It is connected. One end of the voltage conversion circuit 349 is connected to the output terminal of the current detection circuit 346, the other end is connected to the negative terminal 2b of the power supply 32 for the current detection circuit, and the connection point of the two resistors constituting the voltage conversion circuit 349 is connected to the control circuit 35. It is connected.

  The control circuit 35 is a circuit that controls the inverter circuit 31 based on the motor current flowing through the AC motor 4 via the IGBTs 31d to 31f, and includes a microcomputer 35a and an inverter drive circuit 35b.

  The microcomputer 35a is an element that outputs drive signals for the IGBTs 31a to 31f based on a voltage corresponding to the motor current flowing through the AC motor 4 input via the current detection circuit 34, and includes three A / D conversion circuits. Built in. The three A / D input terminals of the microcomputer 35a are respectively connected to connection points of two resistors constituting the voltage conversion circuits 337 to 349.

  Next, a specific operation will be described with reference to FIG. When a motor current flows through the AC motor 4, the current detection resistors 340a to 340c generate a voltage corresponding to the direction and magnitude of the flowing current.

  The differential amplifier circuits 344 to 346 operate at 15 V output from the current detection circuit power supply 32, and amplify the voltages of the current detection resistors 340a to 340c with reference to the reference voltage output from the reference voltage circuit 341, respectively. When the output voltage of the control circuit power supply 33 is 5V, the differential amplifier circuits 344 to 346 amplify the voltages of the current detection resistors 340a to 340c, respectively, with a reference voltage of 7.5V as a reference. As in the first embodiment, the differential amplifier circuits 344 to 346 have a reference voltage of 7.5 V when no current flows through the current detection resistors 340 a to 340 c, and 13.6 V when 30 A flows. When -30 A flows, 1.4 V is output in proportion to the current. Here, the positive current indicates the current flowing from the IGBTs 31d to 31f to the high voltage battery 2 side, and the negative current indicates the current flowing from the high voltage battery 2 to the IGBTs 31d to 31f side.

  The voltage conversion circuits 347 to 349 divide the output voltages of the differential amplifier circuits 344 to 346 by 1/3, respectively. When the output voltage of the power supply 33 for the control circuit is 5V, the output voltages of the differential amplifier circuits 344 to 346 amplified based on the reference voltage of 7.5V are respectively divided into 1/3. Similarly to the first embodiment, the voltage conversion circuits 347 to 349 are 2.5V that is 1/3 of the output voltage 7.5V of the differential amplifier circuits 344 to 346 when no current flows through the current detection resistors 340a to 340c. When 30A flows, 4.5V is output, and when -30A flows, 0.5V is output in proportion to the current.

  The microcomputer 35a operates with the output voltage of the control circuit power supply 33, and A / D converts the output voltages of the voltage conversion circuits 347 to 349, respectively. The input voltage range of the three A / D conversion circuits built in the microcomputer 35a is the range from 0V to the output voltage of the control circuit power supply 33. The A / D conversion circuit digitally converts a voltage that is ½ of the output voltage of the control circuit power supply 33 as a voltage corresponding to when no current flows through the current detection resistors 340a to 340c. When the output voltage of the control circuit power supply 33 is 5V, the voltage range that can be input to the A / D conversion circuit is from 0V to 5V that is the output voltage of the control circuit power supply 33, and the A / D conversion circuit has 2 .5V is digitally converted as a corresponding voltage when no current flows through the current detection resistors 340a to 340c. A voltage of 0.5 to 4.5 V, which is almost full of the input voltage range, is input to the A / D conversion circuit. The microcomputer 35a performs an operation according to a preset procedure using a voltage value corresponding to the motor current flowing through the A / D converted current detection resistors 340a to 340c, and passes through the inverter circuit 31 based on the operation result. Then, the AC motor 4 is controlled. As a result, the compressor connected to the AC motor 4 is controlled, and the vehicle interior temperature is comfortably controlled.

  By the way, when a load fluctuation occurs in another electric load connected to the high voltage battery 2, the output voltage of the control circuit power source 33 also fluctuates. For example, when the output voltage of the control circuit power supply 33 fluctuates from 5 V to 5.5 V, the output voltage of the reference voltage circuit 34 is 1.5 times the output voltage 5.5 V of the control circuit power supply 33. 25V. When no current flows through the current detection resistors 340a to 340c, the differential amplifier circuits 344 to 346 output the reference voltage of 8.25V, and the voltage conversion circuits 347 to 349 output the output voltage 8 of the differential amplifier circuits 344 to 346. 2.75V that is 1/3 of 25V is output. The A / D conversion circuit digitally converts 2.75 V, which is 1/2 of the output voltage 5.5 V of the power supply 33 for the control circuit, as a voltage corresponding to when no current flows through the current detection resistors 340 a to 340 c. Therefore, even if the output voltage of the control circuit power supply 33 fluctuates, no error occurs in the voltage value corresponding to the motor current flowing through the A / D converted current detection resistors 340a to 340c.

  Finally, specific effects will be described. According to the second embodiment, the AC motor control device 3 uses the differential amplifier circuits 344 to 346 to increase the voltage of the current detection resistors 340 a to 340 c so that the output voltage range is wider than the voltage range that can be input to the A / D converter circuit. And it can amplify to the voltage of the single polarity according to the polarity and magnitude | size of the voltage of current detection resistance 340a-340c. Furthermore, the voltage conversion circuits 347 to 349 can convert the output voltages of the differential amplifier circuits 344 to 346 into a voltage range that can be input to the A / D conversion circuit. Therefore, the output voltage range of the current detection circuit 34 can be expanded, and the quantization error accompanying A / D conversion can be reduced and the reliability can be improved.

  The AC motor control device 3 can operate the differential amplifier circuits 344 to 346 with the current detection circuit power source 32 that outputs a voltage higher than the output voltage of the control circuit power source 33 that operates the microcomputer 35a. Therefore, the differential amplifier circuits 344 to 346 can reliably output a voltage in a wider range than the voltage range that can be input by the A / D conversion circuit.

  Further, AC motor control device 3 can change the reference voltage, which is the reference for amplification in differential amplifier circuits 344 to 346, in proportion to the output voltage of control circuit power supply 33 by reference voltage circuit 341. For this reason, it is possible to suppress an A / D conversion error caused by a change in the output voltage of the control circuit power supply 33.

  Furthermore, according to the AC motor control device 3, it is possible to improve the reliability of the electric compressor device for an air conditioner mounted on the hybrid vehicle.

The circuit diagram of the electric compressor for air-conditioners in 1st Embodiment is shown. The relationship between the electric current which flows into the electric current detection resistance in 1st Embodiment, and the output voltage of a electric current detection circuit is shown. The relationship between the electric current which flows into the electric current detection resistance in 1st Embodiment, and the output voltage of a voltage converter circuit is shown. The circuit diagram of the electric compressor apparatus for air conditioners in 2nd Embodiment is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric compressor apparatus for air conditioners, 2 ... High voltage battery, 3 ... AC motor control apparatus (AC motor control apparatus), 30 ... Smoothing capacitor, 31 ... Inverter circuit, 31a 31 f... IGBT, 32... Current detection circuit power source (second power source), 33... Control circuit power source (first power source), 34... Current detection circuit, 340, 340 a, 340 b, 340c: current detection resistor (current detection element), 341: reference voltage circuit, 341a: differential amplifier, 341b to 341d: resistance, 342, 344, 345, 346: differential amplification Circuit, 342a, 344a ... Differential amplifier, 342b-342e, 344b-344e ... Resistance, 343, 347, 348, 349 ... Voltage conversion circuit, 343a, 343b, 34 a, 347b.. resistor, 35 ... control circuit (control unit), 35a ... microcomputer, 35b ... inverter driving circuit, 4 ... AC motor (AC motor), 5 ... compressor

Claims (4)

An inverter circuit that converts DC power supplied from a DC power source into AC power and supplies it to the AC motor, a current detection circuit that detects and converts the motor current flowing through the AC motor into voltage, and A / D conversion An AC motor control device comprising: a control unit that controls the inverter circuit based on an output voltage of the current detection circuit that has an A / D converter
The current detection circuit includes a current detection element that detects the motor current and converts it into a voltage, and the output voltage range of the voltage of the current detection element is wider than the input voltage range of the A / D conversion unit. A differential amplifier circuit that amplifies the voltage to a single polarity voltage according to the polarity and magnitude of the voltage, and a voltage converter circuit that converts an output voltage of the differential amplifier circuit into an input voltage range of the A / D converter. An AC motor control device comprising: A first power source for operating the control unit; and a second power source that outputs a voltage higher than an output voltage of the first power source,
2. The AC motor control apparatus according to claim 1, wherein the differential amplifier circuit is operated by being supplied with power from the second power source. The current detection circuit further includes a reference voltage circuit that outputs a reference voltage that changes in proportion to the output voltage of the first power supply,
3. The AC motor control apparatus according to claim 2, wherein the differential amplifier circuit amplifies the voltage of the current detection element based on the reference voltage.   4. The AC motor control apparatus according to claim 1, wherein the AC motor is mounted on a vehicle.

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