JP5370915B2 - Voltage limiting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage limit circuit for reducing power consumption while protecting a circuit for measuring a current flowing through a load or a voltage of a switching element. <P>SOLUTION: The voltage limit circuit 10 includes: a first resistor R1, a unipolar element S0 connected to the first resistor R1 in series, a Zener diode ZD having a cathode connected to the unipolar element S0 in series, a second resistor R2 connected to the unipolar element S0 in parallel, and a gate control circuit 12 inputting an on-signal or off-signal to a gate G of the unipolar element S0. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a voltage limiting circuit for protecting a voltage measuring circuit when measuring a current flowing through a load or the like or a voltage of a switching element.

  Conventionally, a current flowing through a load such as a motor is measured, and a switching element provided in an inverter or a converter is controlled. For example, as shown in FIG. 7, a shunt resistor Rs is connected to the output line of the inverter 2, and voltage dividing resistors r1 and r2 are connected to both ends of the shunt resistor Rs. The outputs of the voltage dividing resistors r1 and r2 are input to the voltage measuring circuit OP, and the potential difference of the shunt resistor Rs is differentially output. The differential output is input to the control circuit 4c, a current is obtained from the differential output, and the switching timing of the inverter 2 is controlled. A similar circuit is also disclosed in Patent Document 1. When the switching element S1 of the upper arm of the inverter 2 is turned on, a high voltage is output, but the voltage measuring circuit OP can be protected by the voltage dividing resistors r1 and r2.

  However, since the resistance value of the shunt resistor Rs is small, the potential difference to be measured is further reduced by dividing the voltage. For this reason, there exists a possibility that the detection accuracy of an electric current may fall.

  Further, when the switching element S1 of the upper arm of the inverter 2 is turned on, a high voltage is output. At that time, power consumption in the voltage dividing resistors r1 and r2 increases. In order to reduce power consumption, it is necessary to increase the impedance. However, if the impedance is increased, it becomes more susceptible to noise when a low voltage is output from the inverter 2.

JP 2004-309386 A

  An object of the present invention is to provide a voltage limiting circuit capable of reducing power consumption while protecting a circuit for measuring a current flowing in a load or the like and a voltage across a switching element.

The voltage limiting circuit of the present invention is connected in parallel with the switching element of the lower arm of the power conversion circuit having switching elements on the upper arm and the lower arm, and the voltage at both ends is smaller than a predetermined value or within a predetermined range. The same voltage as the both-end voltage is output, and when the both-end voltage is greater than a predetermined value, the same voltage as the predetermined value is output, or when the voltage is outside the predetermined range, The voltage limiting circuit includes a gate control circuit that has a resistance component between the switching element and the output and reduces the impedance of the resistance component, wherein the resistance component is a first resistor, series connected unipolar element to the first resistor, connected in parallel with said unipolar element, with a high second resistor impedance than the first resistor, zener the resistance component Over de are connected in series, the gate control circuit by outputting a signal to a unipolar device in the ON state when the switching element of the lower arm is on, the voltage across greater than a predetermined value, Alternatively, if it is outside the predetermined range, without reducing the impedance of the resistance component, causing the Zener diode to break down , and the voltage across the terminal is smaller than a predetermined value or within the predetermined range, The impedance of the resistance component is reduced.

The gate control circuit when the control circuit outputs a signal to turn on the switching elements of the lower arm, in response to the signal to turn on a unipolar device outputted from the control circuit to the gate control circuit, the gate control circuit An ON signal is sent to the unipolar element to control a decrease in impedance of the resistance component.

The resistive component, the unipolar element by being turned on from the off state to lower the impedance of the resistance component.

  The unipolar element is a normally-off unipolar element.

When the zener diode breaks down, the zener diode breaks so that the gate-source voltage value of the unipolar element is lower than the threshold voltage of the unipolar element regardless of the output voltage of the gate control circuit. The down voltage is set.

  The power conversion circuit is an inverter or a converter provided with a switching element on each of the upper arm and the lower arm, and the voltage limiting circuit is connected in parallel with the switching element on the lower arm.

  In the present invention, a Zener diode can be limited to a desired voltage range, and a circuit connected to the voltage limiting circuit can be protected. Controlling on / off of the unipolar element increases the degree of freedom in circuit design. By connecting a high resistance in parallel with the unipolar element, the power consumption when the unipolar element is turned off can be reduced, and the Zener diode can be energized via the high resistance so that it operates stably. be able to. Since a voltage dividing resistor is not used as in the prior art, operation accuracy in a circuit connected to the voltage limiting circuit can be increased.

It is the figure which attached to the inverter in order to measure the electric current which flows into the load the voltage limiting circuit of this invention. It is a figure which shows the specific circuit structure of the voltage limiting circuit of this invention. It is the figure which attached the voltage limiting circuit of this invention to the inverter in order to measure the both-ends voltage of the switching element of an inverter. It is the figure which attached the diode and Zener diode for protection to the voltage limiting circuit of FIG. It is the figure which attached the voltage limiting circuit of this invention to the converter in order to measure the electric current input into a converter. It is the figure which attached the voltage limiting circuit of this invention to the converter in order to measure the both-ends voltage of the switching element of a converter. It is a figure which shows the structure for measuring the electric current which flows into load using the conventional voltage dividing resistance.

  The present invention will be described with reference to the drawings. The voltage limiting circuit of the present invention is connected in parallel to a switching element of a power conversion circuit such as an inverter or a converter. The voltage limiting circuit protects the voltage measurement circuit when measuring the current flowing through the load and the voltage of the switching element. First, a case where the current flowing from the inverter to the load is measured will be described.

  As shown in FIG. 1, a shunt resistor Rs for current measurement is connected in series to the output line of the inverter 2. A voltage limiting circuit 10 is connected to both ends of the shunt resistor Rs. A voltage measuring circuit OP that detects a potential difference is connected to the voltage limiting circuit 10. The control circuit 4 obtains a current flowing through the shunt resistor Rs based on the output of the voltage measurement circuit OP, and adjusts the switching timing of the inverter 2. The voltage measurement circuit OP may use, for example, a differential amplifier circuit or an instrumentation amplifier, or may be directly converted into a digital value by an A / D converter.

  In FIG. 1, the inverter 2 shows only one phase, and if it is a three-phase AC output inverter, a voltage limiting circuit 10 or the like is attached to at least two phases. A voltage limiting circuit 10 is appropriately attached according to the configuration of the inverter 2.

  In the inverter 2, switching elements S1 and S2 are connected to the power lines of the upper arm and the lower arm, and the switching elements S1 and S2 are alternately switched on and off. When the switching element S1 of the upper arm is turned on, a high voltage is output. When the switching element S2 of the lower arm is turned on, a low voltage is output. An example of the high voltage is 280V, and an example of the low voltage is −3 to + 3V. Since the output voltage from the inverter 2 varies greatly, the voltage limiting circuit 10 protects the voltage measuring circuit OP when a high voltage is output from the inverter 2.

  A specific configuration of the voltage limiting circuit 10 is shown in FIG. The voltage limiting circuit 10 includes a first resistor R1, a unipolar element S0 connected in series to the first resistor R1, a Zener diode ZD connected in series to the unipolar element S0, and a second connected in parallel to the unipolar element S0. A resistor R2 and a gate control circuit 12 for inputting an on or off signal to the gate G of the unipolar element S0 are provided.

  The first resistor R1 is connected to the output line of the inverter 2, and the anode A of the Zener diode ZD is connected to the lower arm of the inverter 2. Therefore, the voltage limiting circuit 10 is in parallel with the switching element S2 of the lower arm of the inverter 2. The drain D of the unipolar element S0 is connected to the first resistor R1, and the source S of the unipolar element S0 is connected to the voltage measuring circuit OP and the Zener diode ZD.

  The unipolar element S0 is a normally-off (enhancement) type element. For example, a MOSFET is used. By inputting an ON signal to the gate G of the unipolar element S0, the unipolar element S0 is turned ON.

  The gate control circuit 12 controls on / off of the unipolar element S0. By this on / off control, the impedance of the resistance component of the voltage control circuit 10 is controlled. The reason for controlling the impedance together with the operation of the Zener diode and the specific control will be described below.

  As described above, since the inverter 2 alternately outputs a high voltage and a low voltage, the voltage across the switching element S2 of the lower arm varies greatly. When the voltage across the voltage limiting circuit 10 connected in parallel with the switching element S2 is larger than a predetermined value or outside a predetermined range, the voltage measurement circuit OP needs to be protected. That is, the voltage input to the voltage measurement circuit OP when the high voltage is output from the inverter 2 only needs to be lower than the allowable voltage of the voltage measurement circuit OP. When a value higher than the allowable voltage of the voltage measuring circuit OP is applied to the Zener diode ZD, the voltage measuring circuit OP is protected if the Zener diode ZD breaks down. Therefore, the breakdown voltage of the Zener diode ZD is lower than the allowable voltage of the voltage measurement circuit OP.

  When the voltage across the voltage limiting circuit 10 connected in parallel with the switching element S2 is smaller than a predetermined value or enters a predetermined range, the voltage measuring circuit OP operates normally and the shunt resistor Rs What is necessary is just to differentially output the potential difference between both ends. Therefore, the Zener diode ZD is prevented from being broken down when the switching element S2 of the lower arm of the inverter 2 is turned on. When the Zener diode ZD does not break down, no current flows through the Zener diode ZD. Therefore, the potential of the output terminal of the voltage limiting circuit 10 is the same as that of both terminals of the shunt resistor Rs, and the voltage measuring circuit OP sets the shunt resistor Rs. The potential difference between both ends, that is, the value of current flowing through the shunt resistor Rs can be measured.

  In summary, the Zener diode ZD breaks down when the switching element S1 of the upper arm of the inverter 2 is turned on, and the Zener diode ZD breaks down when the switching element S2 of the lower arm is turned on. Don't go down. It is assumed that the breakdown voltage of the Zener diode ZD is, for example, 15V. When the switching element S1 of the upper arm is turned on, a reverse bias is applied to the Zener diode ZD, and a voltage of 15 V is input to the voltage measurement circuit OP. When the switching element S2 of the lower arm is turned on, the voltage across the shunt resistor Rs is input. The actual breakdown voltage of the Zener diode ZD is a negative voltage, but since it is connected to a reverse bias, the breakdown voltage is a positive voltage.

  A second resistor R2 is connected in parallel with the unipolar element S0. The resistance value of the second resistor R2 is higher than the internal resistance when the unipolar element S0 is in the ON state. As described above, the unipolar element S0 is a normally-off type. When the switching element S2 of the upper arm of the inverter 2 is turned on, the unipolar element S0 is always turned off, the current is reduced by the second resistor R2, and the power consumption is reduced. Therefore, the gate signal may be controlled so that the unipolar element S0 is always turned off when the switching element S1 of the upper arm of the inverter 2 is turned on, or when the zener diode ZD breaks down, the unipolar element is controlled. The breakdown voltage may be set so that the gate-source voltage value of the element S0 is lower than the threshold voltage of the unipolar element S0. For example, the breakdown voltage of the Zener diode ZD is made the same as the voltage of the ON signal to the gate G of the unipolar element S0.

  When the breakdown voltage of the zener diode ZD is set to the same voltage value as the voltage of the ON signal to the gate G of the unipolar element S0, and the ON signal is applied to the gate G of the unipolar element S0, a high voltage is output from the inverter 2 Assume that the Zener diode ZD is broken down. In this case, the gate voltage and the source voltage of the unipolar element S0 are the same. The unipolar element S0 is turned off, and a current flows through the second resistor R2 instead of the unipolar element S0. If no ON signal is applied to the gate G of the unipolar element S0, the unipolar element S0 remains off. Therefore, regardless of whether the unipolar element S0 is on or off, the unipolar element S0 is always turned off when a high voltage is output from the inverter 2. When a high voltage is output from the inverter 2, a current always flows through the second resistor R2, and power consumption can be reduced. In other words, when the unipolar element S0 is turned off, the impedance of the resistance component of the voltage limiting circuit 10 is increased, and the power consumption is reduced.

  When the switching element S1 of the upper arm of the inverter 2 is turned on, the voltages input to the voltage measuring circuit OP are all the breakdown voltage of the Zener diode ZD, and the voltage measuring circuit OP is the breakdown voltage of the Zener diode ZD. Output potential difference. For this reason, the control circuit 4 cannot obtain the current flowing through the shunt resistor Rs. The control circuit 4 waits. In this case, the second resistor R2 reduces the power consumption as described above, and the power consumption during standby is reduced in the present invention.

  Further, the second resistance R2 is made larger than the first resistance R1. For example, the first resistor R1 is 1 kΩ and the second resistor R2 is 27 kΩ. Since the second resistor R2 increases, the current flowing through the Zener diode ZD can be reduced when the Zener diode ZD breaks down. In addition, since the current flows through the Zener diode ZD via the second resistor R2, the voltage of the Zener diode ZD can be stabilized. This stabilization can prevent oscillation of the unipolar element S0.

  In order to accurately measure the potential difference between the voltages across the shunt resistor Rs when a low voltage is output from the inverter 2, it is necessary to reduce the impedance of the voltage limiting circuit 10 and reduce the influence of the voltage limiting circuit 10. is there. For this purpose, an ON signal is applied to the gate G of the unipolar element S0 so that the unipolar element S0 is turned on when a low voltage is output from the inverter 2. If the Zener diode ZD does not break down, no current flows through the Zener diode ZD, and only the current flowing through the voltage measurement circuit OP flows through the first resistor R1 and the unipolar element S0. Since the input impedance of the voltage measuring circuit OP is generally large, the power consumption is small. Further, it is desirable that the impedance of the first resistor R1 is selected so as to be sufficiently smaller than the input impedance of the voltage measurement circuit OP. By selecting in this way, it is possible to measure accurately without using a highly accurate resistor for the first resistor R1.

  When the switching element S2 of the lower arm of the inverter 2 is turned on, the unipolar element S0 is also turned on. Therefore, when an ON signal is output from the control circuit 4 to the transistor Snu in the lower arm of the inverter 2, a signal is transmitted from the control circuit 4 to the gate control circuit 12, and the unipolar element S0 is transmitted from the gate control circuit 12. To output an ON signal. Alternatively, an ON signal may be output to the unipolar element S0 when all the switching elements of the lower arm of the inverter 2 are turned on. Note that the gate signal of the unipolar element S0 does not need to be switched in synchronization with the switching of the ON / OFF state of the switching element, and an ON signal may be output to the unipolar element S0 only during the period of voltage measurement. Even when S2 is off, an on signal may be output to the unipolar element S0.

  If the unipolar element S0 is off when a low voltage is output from the inverter 2, the impedance of the voltage limiting circuit 10 increases. The control circuit 4 uses a differential output from the voltage measurement circuit OP when a low voltage is output from the inverter 2 and the unipolar element S0 is on.

  The output of the voltage measuring circuit OP is input to the control circuit 4 and used to determine the switching timing of the inverter 2 and the like.

  In the present invention, when the output from the inverter 2 is a low voltage and an ON signal is input to the gate G of the unipolar element S0, the voltage measurement circuit OP outputs the potential difference between the both ends of the shunt resistor Rs as a differential output. To do. The voltage measurement circuit OP can be protected by appropriately selecting the breakdown voltage of the Zener diode ZD. Since the second resistor R2 is connected in parallel to the unipolar element S0, power consumption can be reduced when current measurement is not performed. By controlling on / off of the unipolar element S0, the impedance can be lowered, so that the degree of freedom in circuit design can be increased.

  Since the shunt resistor Rs is connected in series to the output line of the inverter 2, if the load is an inductance load, the current tends to flow from the inverter 2 even after the transistor Spu of the upper arm is turned off. In this case, a current flows from the load to the load via the free wheel diode Dnu connected in parallel to the lower arm transistor Snu and the lower arm transistor of the other phase. At this time, the current flowing through the shunt resistor Rs can also be detected.

  Although the above description is the detection of the current flowing from the inverter 2 to the load, the voltage limiting circuit 10 of the present application can be used to detect the voltage of the switching element S2 of the inverter 2. As shown in FIG. 3, a voltage limiting circuit 10 is connected to the inverter 2 in parallel. The voltage limiting circuit 10 is the same as the circuit 10 in FIG. The voltage measuring circuit OP and the lower arm of the inverter 2 are connected to the voltage measuring circuit OP.

  When the switching element S2 of the lower arm of the inverter 2 is turned on, the Zener diode ZD does not break down. At this time, the voltage across the switching element S2 is input to the voltage measurement circuit OP.

  When the switching element S2 of the lower arm of the inverter 2 is on and the unipolar element S0 is on, the differential output of the voltage measuring circuit OP is used for switching control of the inverter 2.

  When the switching element S1 of the upper arm of the inverter 2 is turned on, the Zener diode ZD breaks down. Regardless of whether an ON or OFF signal is input to the gate G of the unipolar element S0, the unipolar element S0 is automatically turned off. The same potential is input to the voltage measuring circuit OP, and the differential output becomes zero. At this time, a current flows through the second resistor R2, but the power consumption is reduced because the resistance value of the second resistor R2 is high.

  Further, as shown in FIG. 4, a diode Do or a Zener diode ZDo for circuit protection may be provided as necessary. In the circuit 10b of FIG. 4, a protection diode Do is attached in parallel to the unipolar element S0, and a Zener diode ZDo is attached in series to the Zener diode ZD. When a low voltage is output, no current flows through the voltage limiting circuit 10b, so there is no change in impedance. In terms of the circuit configuration, the protection diode Do or the like does not affect the operation of the voltage measurement circuit OP. When the Zener diode ZDo is provided, the lower limit value of the output voltage of the voltage limiting circuit 10 changes from the forward voltage of the Zener diode ZD to the breakdown voltage of the Zener diode ZDo, and the measurable voltage range can be expanded.

  Although the embodiment in which the voltage limiting circuit 10 of the present invention is applied to the inverter 2 has been described, it can also be applied to the converter 6. As shown in FIG. 5, a shunt resistor Rs is connected to the input line of the converter 6, and a voltage limiting circuit 10 is attached to both ends thereof. A voltage measuring circuit OP is connected to the voltage limiting circuit 10, and the voltage measuring circuit OP differentially outputs the potential difference between the voltages at both ends of the shunt resistor Rs. The differential output is input to the control circuit 8 and used to determine the timing at which the control circuit 8 performs switching control of the converter 6.

  The converter 6 in FIG. 5 has only one phase, but if it is a three-phase input converter, the voltage limiting circuit 10 is attached to at least two phases.

  The circuit configuration of the voltage limiting circuit 10 is the same as that of the circuit 10 of FIG. A first resistor R1, a unipolar element S0 connected in series to the first resistor R1, a Zener diode ZD having a cathode C connected in series to the unipolar element S0, and a second resistor R2 connected in parallel to the unipolar element S0. And a gate control circuit 12 for inputting an on or off signal to the gate G of the unipolar element S0. The anode A of the Zener diode ZD is connected to the lower arm of the converter 6.

  When the switching element S2 of the lower arm of the converter 6 is turned on, the Zener diode ZD does not break down. When an ON signal is input to the gate G of the unipolar element S0, the potential difference between the both ends of the shunt resistor Rs output from the voltage measurement circuit OP is used for switching control of the converter 6.

  When the switching element S1 of the upper arm of the converter 6 is turned on, the Zener diode ZD breaks down. Regardless of the signal to the gate G of the unipolar element S0, the unipolar element S0 is turned off. The voltage measurement circuit OP receives the same potential from the two voltage limiting circuits 10 and the differential output becomes zero. At this time, a current flows through the second resistor R2, but the power consumption is reduced because the resistance value of the second resistor R2 is high.

  The voltage limiting circuit 10 of the present invention can also be used to measure the voltage across the switching element S2 of the lower arm of the converter 6 (FIG. 6). The voltage limiting circuit 10 is connected in parallel with the switching element S2. The voltage measuring circuit OP outputs a differential output of the lower arm of the voltage limiting circuit 10 and the converter 6.

  As in the case of the inverter 2, when the switching element S2 of the lower arm of the converter 6 is turned on, the Zener diode ZD does not break down. At this time, if the unipolar element S0 is turned on, the control circuit 8 uses the potential difference of the voltage across the switching element S2 output from the voltage measurement circuit OP for switching of the converter. When the switching element S1 of the upper arm of the converter 6 is turned on, the Zener diode ZD breaks down. The unipolar element S0 is turned off regardless of the signal to the gate G. The same potential is input to the voltage measuring circuit OP, and the differential output becomes zero.

  Even when the voltage limiting circuit 10 of the present invention is used for the converter 6, a protection diode Do or a Zener diode ZDo as shown in FIG. 4 may be attached.

  As described above, even when the voltage limiting circuit 10 of the present invention is applied to the converter 6, the voltage measuring circuit OP can be protected by the Zener diode ZD. The voltage across the shunt resistor Rs is input to the voltage measurement circuit OP, and a differential output is output. This differential output is used for switching control of the converter 6. The degree of freedom in circuit design is increased by the on / off control of the unipolar element S0.

  In addition, the present invention can be carried out in a mode in which various improvements, modifications, and changes are added based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

2: Inverters 4, 4b, 8, 8b: Control circuit 6: Converters 10, 10b: Voltage limiting circuit 12: Gate control circuit S0: Unipolar element Rs: Shunt resistors R1, R2: Resistor OP: Voltage measuring circuits ZD, ZDo: Zener diodes S1, S2, S3, S4: switching elements Spu, Snu, Spr, Snr: transistors Dpu, Dnu, Dpr, Dnr, Do: diodes

Claims (6)

Connected in parallel with the switching element of the lower arm of the power conversion circuit having a switching element on the upper arm and the lower arm,
When the voltage at both ends is smaller than the predetermined value or within the predetermined range, the same voltage as the voltage at both ends is output,
If the voltage across the both ends is greater than a predetermined value, the same voltage as the predetermined value is output, or if it is outside the predetermined range, a voltage within the predetermined range is output,
Having a resistance component between the switching element and the output;
A voltage limiting circuit including a gate control circuit for reducing the impedance of the resistance component,
The resistance component includes a first resistance, a unipolar element connected in series to the first resistance, a second resistance connected in parallel to the unipolar element and having a higher impedance than the first resistance ,
A Zener diode is connected in series to the resistance component,
The gate control circuit outputs a signal for turning on the unipolar element when the switching element of the lower arm is on,
When the voltage across the both ends is greater than a predetermined value or outside the predetermined range, the impedance of the resistance component is not lowered , the Zener diode is broken down ,
A voltage limiting circuit for reducing the impedance of the resistance component when the voltage between both ends is smaller than a predetermined value or within the predetermined range. The gate control circuit when the control circuit outputs a signal to turn on the switching elements of the lower arm, in response to the signal to turn on a unipolar device outputted from the control circuit to the gate control circuit, the gate control circuit The voltage limiting circuit according to claim 1, wherein the voltage limiting circuit is configured to send an ON signal to a unipolar element to control a decrease in impedance of the resistance component. The voltage limiting circuit according to claim 1, wherein the resistance component reduces impedance of the resistance component when the unipolar element is turned on from an off state. 4. The voltage limiting circuit according to claim 1, wherein the unipolar element is a normally-off unipolar element. When the zener diode breaks down, the zener diode breaks so that the gate-source voltage value of the unipolar element is lower than the threshold voltage of the unipolar element regardless of the output voltage of the gate control circuit. 5. The voltage limiting circuit according to claim 4, wherein a down voltage is set. The power converter circuit, respectively the upper arm and the lower arm is an inverter or converter including a switching element, the voltage limiting circuit of any of claims 1 to 5 are connected in parallel with the switching element of the lower arm Voltage limiting circuit.

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