JP5370753B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter that drives a motor generator using a power conversion switching element such as an IGBT, and more particularly to a power converter that can detect a large load current flowing in the motor generator with an inexpensive configuration.

  FIG. 1 shows a circuit configuration of a conventional power converter capable of detecting a load current. Power conversion device 10 is mounted on a hybrid vehicle, and converts DC power from a DC power source (not shown) into U-phase / V-phase / W-phase three-phase AC power by inverter 11 to drive motor generator MG. Is. That is, the inverter 11 includes a U phase, a V phase, and a W phase, and the high voltage power supply line 12P and the high voltage ground line 12N of each phase are connected in parallel to the DC power supply. The U phase is formed by connecting an upper arm switching element T1 of the semiconductor element on the high voltage power supply line 12P side and a lower arm switching element T2 of the semiconductor element on the high voltage ground line 12N side in series. Similarly, the upper arm switching element T3 and the lower arm switching element T4 are connected in the V phase, and the upper arm switching element T5 and the lower arm switching element T6 are connected in series in the W phase.

  Between the collectors and emitters of the respective switching elements T1 to T6, diodes D1 to D6 that flow current from the emitter side to the collector side are respectively connected. However, each of the switching elements T1 to T6 is an IGBT (Insulated Gate Bipolar Transistor), and each of the diodes D1 to D6 is a free wheel diode.

  A control signal is input to the gate terminals of the switching elements T1 to T6 from the control microcomputer 15 to the SW (switching) element driving units 13b and 14b via the photocouplers 13a and 14a, so that the SW element driving unit 13b, Each switching element T1-T6 is driven by 14b. The intermediate points of the UVW phase switching elements T1 and T2, T3 and T4, and T5 and T6 are connected to phase coils (not shown) of the motor generator MG by load lines 16U, 16V, and 16W of the phases. . However, the control microcomputer 15 is connected to a low-voltage ground line GND connected to the vehicle body. The high-voltage ground line 12N is insulated from the low-voltage ground line GND and has a predetermined reference potential.

  In such a power conversion device 10, as a configuration for detecting a load current flowing between the inverter 11 and the motor generator MG on the motor generator MG side or the opposite side, the U-phase and V-phase load lines 16U and 16V are For example, a current sensor 17 having a magnetic core 17a and a hall element 17b as described in Patent Document 1 is incorporated in an insulated state, and a load current detected by the hall element 17b is supplied to the control microcomputer 15 as a voltage signal. It is designed to be entered. That is, the load current flowing between the inverter 10 and the motor generator MG can be detected by detecting the voltage from the current sensor 17 by the control microcomputer 15.

  In addition, FIG. 2 shows a configuration circuit for detecting a load current. In the power conversion device 10-1 shown in FIG. 2, the configuration for detecting the load current flowing between the inverter 11 and the motor generator MG on the motor generator MG side or the opposite side thereof is the U-phase and V-phase load line 16U. , 16V, and a shunt resistor Rs is inserted in each, and when a load current flows through the load lines 16U, 16V, 16W, the potential difference between both ends of the shunt resistor Rs is input to the differential amplifier 20 via the resistors R1, R2. In response to this input, the control microcomputer 15 detects the voltage output from the differential amplifier 20. In FIG. 2, the differential amplifier path on the shunt resistor Rs side inserted in the V-phase load line 16V is omitted.

  Further, a voltage dividing resistor R3 is connected between the resistor R1 and the inverting input terminal “−” of the differential amplifier 20, and the other end 21 of the resistor R3 is connected to the low-voltage ground line GND. . A voltage dividing resistor R4 is connected between the resistor R2 and the non-inverting input terminal “+” of the differential amplifier 20, and the other end 22 of the resistor R4 is connected to the low-voltage ground line GND. Further, a resistor R6 is connected between the resistor R2 and the non-inverting input terminal “+” of the differential amplifier 20, and a reference voltage Vf is applied to the other end 23 of the resistor R6. The inverting input terminal and the output terminal of the differential amplifier 20 are connected via a resistor R5.

  In such a configuration, the potential difference between both ends of the shunt resistor Rs disposed in the high voltage system is input to the differential amplifier 20 via the resistors R1 and R2, and output from the differential amplifier 20 according to this input. The input voltage is input to the control microcomputer 15 disposed in the low voltage system. For this reason, since it is necessary to insulate the high voltage system from the low voltage system in order to prevent an electric shock accident, the resistors R1 and R2 connected to the lead wires at both ends of the shunt resistor Rs have a high resistance value of several MΩ or more. The high pressure system and the low pressure system are insulated.

  There exists a thing of patent document 2 as this kind of power converter device.

JP-A-64-83154 Japanese Patent No. 3351330

  However, in the power converter 10 shown in FIG. 1 described above, the current sensor 17 is connected to the U-phase and V-phase load lines 16U and 16V in order to detect the load current flowing between the inverter 11 and the motor generator MG. However, since the current sensor 17 uses expensive parts such as the magnetic core 17a and the Hall element 17b, there is a problem that the power conversion device 10 becomes expensive.

  Further, in the power converter 10-1 shown in FIG. 2, in order to insulate the control microcomputer 15 arranged in the low voltage system from the high voltage system, the resistor R1 connected to the lead wires at both ends of the shunt resistor Rs. , R2 must have a high resistance value of several MΩ or more. Because of this high resistance value, it is easily affected by external noise, and when it is affected by noise, the input voltage to the differential amplifier 20 fluctuates and the control microcomputer 15 cannot accurately detect the load current. . That is, the resistors R1 and R2 connected to the lead wires at both ends of the shunt resistor Rs have to have a high resistance value of several MΩ or more, resulting in a problem that noise resistance is deteriorated.

  If an isolation amplifier is used for the differential amplifier 20, the resistors R1 and R2 need not have a high resistance value of several MΩ or more. However, since the isolation amplifier is expensive, the power converter 10-1 is expensive. End up.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a power conversion device that is inexpensive and has good noise resistance.

The invention according to claim 1, which has been made to achieve the above object, has an inverter that has a plurality of switching elements and converts high-voltage DC power of a DC power source into AC power, and generates AC power with the inverter. A load line through which a load current as the AC power or a load current as an AC power generated by the load device flows, and a control for detecting the load current and controlling the driving of the switching element Means, a current detecting resistor inserted in the load line, a voltage dividing resistor for dividing a potential difference between both ends of the current detecting resistor, and a voltage divided by the voltage dividing resistor The control means is connected to a high-voltage system ground line to which the inverter is connected, and is connected to both of the current detection resistors. Be one potential difference to detect the load current based on the voltage output from said frequency is divided by pressure resistor min and the differential amplifier, the reference voltage applied to the end of the voltage-dividing resistor and The reference voltage of the differential amplifier is the same voltage source voltage .

  According to this configuration, since the control means is connected to the high voltage system in the same manner as the current detection resistor, the voltage dividing resistor connected by being drawn from both ends of the current detection resistor can be provided as in the conventional case. As a high resistance value of several MΩ or more, there is no need to insulate the control means arranged in the low pressure system from the high pressure system. Conventionally, the control means is connected to a low-voltage ground line such as a vehicle body insulated from the high-voltage ground line and arranged in a low-pressure system. For this reason, it is necessary to insulate the low voltage control means from the high voltage system by setting the voltage dividing resistor to a high resistance value. Due to its high resistance value, it is easily affected by external noise, and when it is affected by noise, the input voltage to the differential amplifier fluctuates, making it impossible to accurately detect the load current by the control means. .

  However, in the present invention, since the control means is arranged in the high pressure system, it is not necessary to insulate from the high pressure system. For this reason, the resistance value of the voltage dividing resistor connected by being drawn from both ends of the current detecting resistor can be several tens KΩ, which is significantly lower than the conventional resistance value. This low resistance value makes it less susceptible to external noise and improves noise resistance. That is, since it is not affected by noise, the input voltage to the differential amplifier does not fluctuate, and the load current can be accurately detected by the control means.

In addition, since a current detection resistor such as a shunt resistor, a voltage dividing resistor, and a differential amplifier, which are low in material cost, may be used for load current detection, the power conversion device can be configured at low cost.
Furthermore, when the reference voltage at the end of the voltage dividing resistor and the reference voltage of the differential amplifier are determined separately, even if the reference voltage of the voltage dividing resistor varies, the reference voltage of the differential amplifier varies. Therefore, the output voltage of the differential amplifier fluctuates, but according to this configuration, the reference voltage of the voltage dividing resistor and the reference voltage of the differential amplifier are set to the same voltage source voltage. Even if the reference voltage of the voltage resistor fluctuates, the reference voltage of the differential amplifier also fluctuates in the same manner, so that the fluctuation of the output voltage of the differential amplifier is eliminated.

  According to a second aspect of the present invention, the control means includes an A / D conversion circuit that converts an analog signal into a digital signal, and an output voltage of the differential amplifier is input to the A / D conversion circuit. The differential amplifier amplifies a voltage resulting from a potential difference between both ends of the current detection resistor divided by the voltage dividing resistor into a voltage that can be directly input to the A / D conversion circuit. It has an amplification factor.

  According to this configuration, since control means such as a standard specification My computer can be used, a special specification control means or a circuit configuration that requires a voltage amplifier on the input side of the control means is not adopted. Therefore, the cost of the power conversion device can be reduced accordingly.

  The invention according to claim 3 is characterized in that the reference voltage of the differential amplifier is ½ of the input side voltage of the A / D conversion circuit of the control means.

  According to this configuration, the load current flowing through the current detection resistor may flow to the load device side or vice versa, so the voltage due to the potential difference across the current detection resistor is a sine wave. . The upper half-wave waveform of the center potential of the sine wave is, for example, a load current flowing on the load device side, and the lower half-wave waveform is a half-wave waveform flowing on the opposite side. Here, when the reference voltage of the differential amplifier is the lowest voltage (for example, 0 V) of the A / D conversion circuit, the waveform of the voltage output from the differential amplifier and input to the A / D conversion circuit is a sine wave. Only the upper half-wave waveform from the center of. For this reason, the control means can detect only the load current flowing to the load device side. Therefore, as in the present invention, the reference voltage is set to 1/2 (for example, 2.5 V) of the input side voltage of the A / D conversion circuit, and the center potential of the sine wave output from the differential amplifier is changed to the A / D conversion circuit. If the center potential is set to (for example, 2.5 V), the control means can easily determine the voltage between the upper side and the lower side of the center potential of the sine wave. That is, it is possible to easily determine the load current flowing on the load device side and the load current flowing on the opposite side.

  The invention according to claim 4 is characterized in that the reference voltage of the differential amplifier is ½ of the potential difference from the ground of the inverter to the power supply potential.

  According to this configuration, for example, when the potential difference from the ground of the inverter to the power supply potential is 650 V, the reference voltage becomes 325 V, which is a half of the reference voltage. For example, an output voltage of 0 to 5 V is obtained by a differential amplifier using 325 V as a reference voltage. As a result, compared with the case where an output voltage of 0 to 5 V is obtained from 650 V, the potential difference converted into the output voltage is 325 V, which is 1/2 of the original potential difference 650 V, so that it is less affected by the voltage due to external noise. Become. That is, noise resistance can be improved.

The invention according to claim 5 is characterized in that the control means is connected via a photocoupler to a low-voltage system device that operates by receiving a power supply from a low-voltage source different from the DC power source. And

  According to this configuration, even if the control means is arranged in the high-pressure system, the low-pressure system device separated from the high-pressure system can be controlled.

This is a circuit configuration of a conventional power conversion device capable of detecting a load current. This is a circuit configuration of another conventional power conversion device capable of detecting a load current. It is a figure which shows the circuit structure of the power converter device which can detect the load current which concerns on embodiment of this invention. It is a figure which shows the modification of the circuit structure of the power converter device which can detect the load current which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. However, parts corresponding to each other in all the drawings in this specification are denoted by the same reference numerals, and description of the overlapping parts will be omitted as appropriate.

  FIG. 3 is a diagram illustrating a circuit configuration of a power conversion device capable of detecting a load current according to the embodiment of the present invention.

  The power converter 10-2 shown in FIG. 3 is different from the power converter 10-1 shown in FIG. 2 in that the control microcomputer (control means) 15 is connected to the high-voltage ground line 12N and arranged on the high-voltage system side. There is.

  A configuration of the power conversion device 10-2 will be described. The power conversion device 10-2 is mounted on a hybrid vehicle and includes an inverter 11 composed of a U phase, a V phase, and a W phase. Inverter 11, high-voltage power supply line 12P and high-voltage ground line 12N for each phase are connected in parallel to a DC power supply (not shown), and DC power from this DC power supply is converted into three-phase AC power to drive motor generator MG. . Further, when the motor generator MG functions as a generator, AC power output from the motor generator MG is converted into DC by the inverter 11 and regenerated to a DC power source.

  The U phase is formed by connecting a switching element T1 for the upper arm of the semiconductor element on the high voltage power supply line 12P side and a switching element T2 for the lower arm of the semiconductor element on the high voltage grounding line 12N side. The upper arm switching element T3, the lower arm switching element T4, and the W phase are formed by connecting an upper arm switching element T5 and a lower arm switching element T6 in series.

  Between the collectors and emitters of the respective switching elements T1 to T6, diodes D1 to D6 that flow current from the emitter side to the collector side are respectively connected. A drive control signal of the SW element drive unit 13b according to the control of the control microcomputer 15 via the photocoupler 13a is input to the gate terminals of the switching elements T1, T3, T6 for the upper arm on the high-voltage power supply line 12P side. The arm switching elements T2, T4, and T6 are directly input with a drive control signal of the SW element driving unit 14b according to the control of the control microcomputer 15, thereby controlling the driving of the switching elements T1 to T6. The intermediate points of the UVW phase switching elements T1 and T2, T3 and T4, and T5 and T6 are connected to phase coils (not shown) of the motor generator MG by load lines 16U, 16V, and 16W of the phases. . However, the control microcomputer 15 is connected to a low-voltage ground line GND connected to the vehicle body. The high-voltage ground line 12N is insulated from the low-voltage ground line GND and has a predetermined reference potential such as 5V.

  Further, in the power conversion device 10-2, the configuration for detecting the load current (for example, 500A) flowing between the inverter 11 and the motor generator MG on the motor generator MG side or the opposite side thereof is a load of U phase and V phase. A shunt resistor (current detection resistor) Rs is inserted in each of the lines 16U and 16V, and a potential difference (for example, 50 mV) at both ends of the shunt resistor Rs is resisted when a load current flows through the load lines 16U, 16V, and 16W. The voltage is input to the differential amplifier 20a via the devices R1a and R2a, and the voltage (for example, 0 to 5V) output from the differential amplifier 20 in response to this input is input to the control microcomputer 15. In FIG. 3, the differential amplifier path on the shunt resistor Rs side inserted in the V-phase load line 16V is omitted.

  Further, a voltage dividing resistor R3a is connected between the resistor R1a and the inverting input terminal “−” of the differential amplifier 20a, and the other end 21a of the resistor R3a is connected to the high voltage ground line 12N. . A voltage dividing resistor R4a is connected between the resistor R2a and the non-inverting input terminal “+” of the differential amplifier 20a, and the other end 22a of the resistor R4a is connected to the high voltage ground line 12N. Further, a resistor R6a is connected between the resistor R2a and the non-inverting input terminal “+” of the differential amplifier 20a, and a reference voltage Vf is applied to the other end 23a of the resistor R6a. Further, the inverting input terminal and the output terminal of the differential amplifier 20a are connected via a resistor R5a. Furthermore, a vehicle communication device 30 disposed on the low-voltage ground line GND side is connected to the control microcomputer 15 via photocouplers 31 and 32.

  According to the power conversion device 10-2 having this configuration, when a load current flows through the load lines 16U, 16V, and 16W of the respective phases, the potential difference between both ends of the shunt resistor Rs becomes a voltage dividing resistor by the resistors R1a and R3a. And the voltage dividing resistors by the resistors R2a and R4a and input to the inverting input terminal and the non-inverting input terminal of the differential amplifier 20a, and the voltage output from the differential amplifier 20 in response to this input Input to the control microcomputer 15. Thereby, the control microcomputer 15 can detect a load current flowing between the inverter 11 and the motor generator MG on the motor generator MG side or the opposite side.

  In such a power converter 10-2 of this embodiment, since the control microcomputer 15 is connected to the high voltage system in the same manner as the shunt resistor Rs, the resistor connected to the lead wires at both ends of the shunt resistor Rs. It is not necessary to insulate the low-voltage control microcomputer 15 from the high-voltage system by setting R1a and R2a to a high resistance value of several MΩ or more as in the prior art. Therefore, the resistance values of the resistors R1a and R2a connected to the lead wires at both ends of the shunt resistor Rs can be several tens KΩ, which is much lower than the conventional resistance value.

  This low resistance value makes it less susceptible to external noise and improves noise resistance. That is, since it is not affected by noise, the input voltage to the differential amplifier 20a does not fluctuate, and the control microcomputer 15 can accurately detect the load current. Further, since the load current detection requires only the shunt resistor Rs, the differential amplifier 20a, and the plurality of resistors R1a to R6a, which are inexpensive in material cost, the power converter 10-2 can be configured at low cost. That is, since there is no current sensor or an isolation amplifier as a differential amplifier as in the prior art, the power converter 10-2 can be configured at a lower cost. Therefore, according to the present embodiment, the power conversion device 10-2 can be made inexpensive and have good noise resistance.

  The voltage input circuit from the differential amplifier 20a in the control microcomputer 15 is composed of an A / D (analog / digital) conversion circuit. Therefore, the differential amplifier 20a amplifies the voltage resulting from the potential difference across the shunt resistor Rs divided by the voltage dividing resistors R1a to R4a into a voltage that can be directly input to the A / D conversion circuit. It is good also as an amplification factor. In this way, since the standard specification control microcomputer 15 can be used, it is not necessary to adopt a circuit configuration such as a special specification control microcomputer or a voltage amplifier further required on the input side of the control microcomputer. Therefore, the apparatus cost can be reduced accordingly.

  The reference voltage Vf applied to the end 23a of the resistor R6a connected to the non-inverting input terminal “+” of the differential amplifier 20a is ½ of the input side voltage of the A / D conversion circuit of the control microcomputer 15. (For example, 2.5 V) may be used.

  Here, the load current flowing through the shunt resistor Rs may flow to the motor generator MG side or vice versa. For this reason, the voltage by the electric potential difference of the both ends of shunt resistor Rs turns into a sine wave of 0-5V, for example. That is, the upper half-wave waveform of the center potential of the sine wave is, for example, a load current that flows on the motor generator MG side, and the lower half-wave waveform is a half-wave waveform that flows on the opposite side.

  Here, when the reference voltage Vf of the differential amplifier 20a is the lowest voltage (for example, 0V) of the A / D conversion circuit, the waveform of the voltage output from the differential amplifier 20a and input to the A / D conversion circuit is as follows. Only the upper half-wave waveform from the center of the sine wave is obtained. For this reason, the control microcomputer 15 can detect only the load current flowing to the motor generator MG side.

  Therefore, as described above, the reference voltage Vf is set to 1/2 (for example, 2.5 V) of the input side voltage of the A / D conversion circuit, and the center potential of the sine wave output from the differential amplifier 20a is A / D converted. By setting the center potential of the circuit (for example, 2.5 V), it is possible to easily determine the voltage between the upper side and the lower side of the center potential of the sine wave. That is, it is possible to easily determine the load current flowing on the motor generator MG side and the load current flowing on the opposite side.

  Next, as in the power converter 10-3 shown in FIG. 4, the reference voltage Vf of the differential amplifier 20a may be ½ of the voltage of the potential difference from the high-voltage ground line 12N to the high-voltage power line 12P. This is because the high-voltage ground line 12N and the high-voltage power supply line 12P are connected via two resistors R11 and R12, and between the resistors R11 and R12 and to the non-inverting input terminal “+” of the differential amplifier 20a. This is realized by connecting the end 23a of the connected resistor R6a. However, the potentials at the ends 21a and 22a of the voltage dividing resistors R3a and R4a are also the same as the reference voltage Vf.

  In this way, for example, when the voltage of the potential difference from the high-voltage ground line 12N to the high-voltage power supply line 12P is 650V, the reference voltage Vf becomes 325V that is 1/2 of that. For example, an output voltage of 0 to 5V is obtained by the differential amplifier 20a with 325V as a reference voltage Vf. As a result, compared with the case where an output voltage of 0 to 5 V is obtained from 650 V, the potential difference converted into the output voltage is 325 V, which is 1/2 of the original potential difference 650 V, so that it is less affected by the voltage due to external noise. Become. That is, noise resistance can be improved.

  In FIG. 3, the reference voltage applied to the ends 21a and 22a of the voltage dividing resistors R3a and R4a and the reference voltage Vf of the differential amplifier 20a may be the same voltage source. As in the power converters 10-2 and 10-3 in FIG. 3 described above, the voltage dividing resistors R3a and the ends 21a and 22a of R4a are connected to the high-voltage ground line 12N to determine the reference voltage. If the reference voltage Vf of the differential amplifier 20a is set separately, even if the reference voltages of the resistors R3a and R4a change, the reference voltage Vf does not change, so that the output voltage of the differential amplifier 20a changes. Become.

  However, when the reference voltage applied to the ends 21a and 22a of the voltage dividing resistors R3a and R4a and the reference voltage Vf of the differential amplifier 20a are the same voltage source voltage, the reference voltages of the resistors R3a and R4a are Even if it fluctuates, the reference voltage Vf also fluctuates in the same manner, so that fluctuations in the output voltage of the differential amplifier 20a can be eliminated.

  Further, the control microcomputer 15 is connected via a photocoupler 31 and 32 to a low-voltage system device (for example, the communication device 30) that operates by receiving a power supply from a low voltage source different from the DC power source. As a result, even if the control microcomputer 15 is arranged in the high-pressure system, it is possible to control the low-pressure apparatus separated from the high-pressure system.

10-2, 10-3 Power converter 11 Inverter 12P High voltage power line 12N High voltage ground line 13a, 14a, 31, 32 Photocoupler 13b, 14b SW element drive unit 15 Control microcomputer 16U, 16V, 16W Load line 20a Differential amplifier 30 Communication device T1, T3, T5 Upper arm switching element T2, T4, T6 Lower arm switching element D1-D6 Diode MG Motor generator Rs Shunt resistor R1a-R6a, R11, R12 Resistor Vf Reference voltage of differential amplifier GND Low voltage grounding wire

Claims (5)

An inverter that has a plurality of switching elements and converts high-voltage DC power of a DC power source into AC power, and the inverter and a load device that generates AC power are connected, and the load current as the AC power or the load A load line through which a load current as AC power generated in the apparatus flows, a control means for detecting the load current and controlling the driving of the switching element, a current detection resistor inserted in the load line, In a power converter having a voltage dividing resistor that divides a potential difference between both ends of the current detecting resistor, and a differential amplifier that amplifies and outputs a voltage divided by the voltage dividing resistor,
The control means is connected to a high-voltage ground line to which the inverter is connected, and a potential difference between both ends of the current detection resistor is divided by the voltage dividing resistor and output from the differential amplifier. be one that detects the load current on the basis of that voltage,
The power converter according to claim 1, wherein a reference voltage applied to an end of the voltage dividing resistor and a reference voltage of the differential amplifier are set to the same voltage source . The control means includes an A / D conversion circuit that converts an analog signal into a digital signal, and is configured such that an output voltage of the differential amplifier is input to the A / D conversion circuit,
The differential amplifier has an amplification factor for amplifying a voltage resulting from a potential difference between both ends of the current detection resistor divided by the voltage dividing resistor into a voltage within a range that can be directly input to the A / D conversion circuit. The power conversion apparatus according to claim 1.   The power converter according to claim 2, wherein the reference voltage of the differential amplifier is ½ of the input side voltage of the A / D converter circuit of the control means.   The power converter according to claim 1, wherein a reference voltage of the differential amplifier is set to ½ of a potential difference from a ground of the inverter to a power supply potential. Wherein, with respect to low-voltage devices which operate by receiving power supply from the different low voltage source and the DC power supply, one of the claims 1-4, characterized in that it is connected via the photocoupler The power converter device of Claim 1.

Images