JP2019004655A - Motor current detection circuit - Google Patents

Abstract

To provide a motor current detection circuit capable of eliminating influences of a forward voltage when clamping an overvoltage by using a diode.SOLUTION: A motor current detection circuit according to an embodiment comprises: a current detection resistor that detects a current flowing in a coil of a motor; a voltage-dividing circuit that shifts a level of a terminal voltage of the current detection resistor; a clamping diode that clamps a terminal of an A/D converter or an amplifier that receives the voltage whose level is shifted by the voltage-dividing circuit, to a power supply voltage and/or a ground potential; a potential adjustment circuit that gives the terminal a voltage obtained by dropping the power supply voltage by a forward voltage of the clamping diode, and/or that gives the terminal a voltage obtained by raising the ground potential by the forward voltage of the clamping diode.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a circuit that detects a current flowing through a winding of a motor.

  Conventionally, a circuit that detects a current flowing in a winding of a motor used in, for example, a washing machine or the like uses a combination of a current detection resistor and an A / D converter. Generally, in order to improve the current detection resolution and S / N ratio, the terminal voltage of the current detection resistor generated according to the normal current value range is adjusted when it is input to the A / D converter. .

  Further, for example, when a circuit malfunctions due to a step-out in the control of the DC brushless motor or other noise, an excessive current may be generated than usual. In such a case, it is necessary to protect the input section of the A / D converter from an overvoltage generated in response to an excessive current.

  For example, in Patent Document 1, a current limiting resistor 506a is connected between the output terminal of the operational amplifier 503a and the A / D converter input, and clamp diodes 507a and 508a are connected between the power supply and ground and the output terminal. Yes. In Patent Document 2, the electromotive voltage of the current detection resistor is level-shifted by a voltage dividing resistor, and positive and negative currents are converted into positive voltage that can be A / D converted.

Japanese Patent No. 4345553 Japanese Patent No. 5161502

  However, in the configuration using the clamp diode as in Patent Document 1, a voltage higher than the power supply voltage or a voltage lower than the ground potential is input by the forward voltage. For this reason, there is a problem that the input part of the A / D converter is damaged or malfunction is caused. In addition, a diode having a low forward voltage becomes expensive. Patent Document 2 does not specifically disclose protection against excessive current.

  Thus, a motor current detection circuit is provided that can eliminate the influence of forward voltage when clamping an overvoltage using a diode.

The motor current detection circuit of the embodiment is
A current detection resistor for detecting the current flowing in the motor winding;
A voltage dividing circuit for level shifting the terminal voltage of the current detection resistor;
A clamping diode for clamping a terminal of an A / D converter or amplifier to which a voltage level-shifted by the voltage dividing circuit is input to a power supply voltage and / or a ground potential;
A potential adjustment circuit that applies a voltage that is lowered by a forward voltage of the clamping diode to the power supply voltage and / or a forward voltage of the clamping diode with respect to the ground potential. And a potential adjusting circuit for applying a voltage increased by an amount corresponding to the voltage.

The motor current detection circuit of the embodiment is
A current detection resistor for detecting the current flowing in the motor winding;
A voltage dividing circuit for level shifting the terminal voltage of the current detection resistor;
A clamping diode for clamping a terminal of an A / D converter or amplifier to which a voltage level-shifted by the voltage dividing circuit is input to a power supply voltage and / or a ground potential;
A protective resistor inserted between the terminal and the clamping diode.

The circuit diagram which is one Embodiment and shows the electric constitution of a washing machine The figure which shows the comparison of the applied voltage of the input terminal for A / D conversion at the time of positive current generation | occurrence | production, and an injection current The figure which shows the comparison of the applied voltage of the input terminal for A / D conversion at the time of positive current generation | occurrence | production, and an injection current about a conventional structure. Partial longitudinal side view schematically showing the structure of the washing machine

  Hereinafter, an embodiment applied to a washing machine which is a laundry machine will be described with reference to the drawings. As shown in FIG. 4, in the washing machine 10, a bottomed cylindrical water tank 12 having an open upper surface is elastically supported by an elastic suspension mechanism 13 in an outer box 11 that constitutes an outline of the washing machine 10. Inside the water tank 12, a bottomed cylindrical rotating tank 14 having an open upper surface is rotatably provided. A reinforcing member 15 for reinforcing the bottom of the rotating tub 14 is provided at the bottom of the rotating tub 14. The rotating tub 14 is configured to rotate around a vertical axis, and serves as a washing tub for washing laundry, a washing tub for rinsing the laundry, and a dehydration tub for a dehydration stroke for dehydrating the laundry. It is also used. That is, the washing machine 10 is a so-called vertical washing machine in which the rotation center axis of the rotating tub 14 extends in the vertical direction.

  The rotating tank 14 has a large number of holes 16 in the peripheral wall portion. These holes 16 penetrate therethrough and allow water and air to pass therethrough. FIG. 5 shows only some of the many holes 16. A balance ring 17 made of synthetic resin in which a liquid such as salt water is sealed is attached to the upper part of the rotating tank 14. A pulsator 18 made of synthetic resin, for example, is rotatably provided as a stirring body at the bottom of the rotary tank 14.

  A drainage path 19 is provided in the lower part of the water tank 12. The drainage passage 19 is provided with a drainage valve 20, and when the drainage valve 20 is opened, the water in the water tank 12 is discharged outside the apparatus. An air trap 21 for detecting the water level is provided at the bottom of the water tank 12.

  A driving mechanism 23 is provided at the center of the lower part of the water tank 12. The drive mechanism unit 23 includes a motor 24 and a clutch mechanism unit (not shown). The drive mechanism 23 transmits the rotational force to the pulsator 18 by the clutch mechanism during the washing stroke or the rinsing stroke. For this reason, during the washing process or the rinsing process, the rotary tank 14 is not driven to rotate, and only the pulsator 18 is driven to rotate. In the washing process, for example, the rotation speed is controlled to about 100 to 150 rpm with a forward inversion operation of about 1 second.

  Further, the drive mechanism unit 23 transmits the rotational force of the motor 24 to the pulsator 18 and the rotary tank 14 by the clutch mechanism unit during the dehydration process. For this reason, the pulsator 18 is rotationally driven integrally with the rotary tank 14 during the dehydration process. In the dehydration process, the rotation speed is controlled to about 1300 to 1500 rpm, for example.

  A top cover 26 is provided on the top of the outer box 11. The top cover 26 is provided with, for example, a foldable lid 27 that can open and close the laundry doorway. A tank cover (not shown) is attached to the upper part of the water tank 12 so as to be openable and closable. An operation panel 28 is provided at the front portion of the top cover 26. A control unit 29 that controls the overall operation of the washing machine 10 is disposed on the back side of the operation panel 28.

  A water supply mechanism 30 that supplies water from the water source into the water tank 12 is provided at the rear portion of the top cover 26. The water supply mechanism 30 includes a water supply valve (not shown), a water supply path (not shown) that communicates with the water tank 12, and the water supply into the water tank 12 is controlled by the control unit 29 controlling the opening and closing of the water supply valve. The

  Next, an electrical configuration relating to the control system of the washing machine 10 will be described. As shown in FIG. 1, the control unit 29 includes an inverter circuit 50 that is a PWM control type inverter. The inverter circuit 50 is configured by connecting six IGBTs 51 in a three-phase bridge, and a flywheel diode 52 is connected between the collector and emitter of each IGBT 51. The IGBT 51 corresponds to a switching element. Each phase output terminal of the inverter circuit 50 is connected to each motor winding 24 a of the motor 24. In the present embodiment, for example, an outer rotor type three-phase brushless DC motor is employed as the motor 24.

  A shunt resistor 53, which is a current detection resistor, is connected in series between the emitter of the IGBT 51 on the lower arm side and the ground. The resistance value of the shunt resistor 53 is, for example, 0.18Ω. The common connection point between the emitter of the IGBT 51 on the lower arm side and the shunt resistor 53 is connected to a level shift circuit 64 constituted by an overcurrent detection circuit 54 and a resistance voltage dividing circuit. The same motor phase current as that of the motor winding 24a flows through the shunt resistor 53 at the timing when the IGBT 51 on the lower arm side is ON. Therefore, the terminal voltage indicates a level corresponding to the motor phase current. A switching leg corresponding to each phase is configured by connecting the IGBTs 51 of the upper arm and the lower arm in series.

  The overcurrent detection circuit 54 detects an overcurrent that occurs when the upper and lower arms of the inverter circuit 50 are short-circuited, and has three comparators (not shown) for detecting three phases. In any one or more of these three comparators, the output level changes when the input voltage exceeds a preset threshold value. Then, the control circuit 55 that has received the change in the comparator output immediately turns off the output of the PWM signal. Thereby, destruction of the circuit element or the like is prevented.

  The shunt resistor 53 generates a terminal voltage that is positive or negative with respect to the ground potential when the inverter circuit 50 operates. Therefore, the level shift circuit 64 uses the terminal voltage of the shunt resistor 53, that is, the voltage at the common connection point between the emitter of the IGBT 51 and the shunt resistor 53, to the input range of an A / D converter (not shown) built in the control circuit 55. Level shift to match. The power supply voltage of the level shift circuit 64 is generated from a 5V power supply by a 3.3V power supply circuit 70 which is a three-terminal regulator, for example.

  In FIG. 1, the ground symbol of the 3.3V power supply is marked with “0” to distinguish it from the 5V power supply ground symbol. The reason for dividing the two grounds in this way is to avoid the influence of noise generated in the 5V power supply system reaching the 3.3V power supply used for A / D conversion.

  The level shift circuit 64 includes three resistors 65a to 67a connected to the power supply voltage and three resistors 65b to 67b connected in series between the resistors 65a to 67a and the shunt resistor 53. Each of the terminal voltages of the resistors 53 is divided by resistors to shift the level. The level-shifted voltages are input to the A / D conversion input terminals “A / D input 2” to “A / D input 4” of the control circuit 55 through the protective resistors 68u to 68w, respectively. The resistance values of these resistors 65 to 68 are, for example, 1 kΩ. Capacitors 69u to 69w are connected between the input terminals “A / D input 2” to “A / D input 4” and the ground. The capacity of the capacitor 69 is, for example, 1000 pF. The capacitor 69 constitutes an RC filter together with the protective resistor 68.

  In order to detect the position of the rotor, the motor 24 is provided with a rotational position sensor 56 composed of, for example, a Hall IC, and a sensor signal output from the rotational position sensor 56 is input to the control circuit 55. The control circuit 55 controls the motor 24 by generating a PWM signal by feedback control, for example, vector control, based on the value of the current flowing through each motor winding 24 a of the motor 24 and applying it to the inverter circuit 50. As described above, the control circuit 55 is composed of a microcomputer incorporating an A / D converter and the like. The 3.3V power supply is also the reference voltage for the A / D converter.

  A driving power supply circuit 57 is connected to the input side of the inverter circuit 50. The driving power supply circuit 57 includes a full-wave rectification circuit 58 formed of a diode bridge connected to an AC power supply 61 having an input terminal of 100 V, and capacitors 59 a and 59 b connected between output terminals of the full-wave rectification circuit 58. It is composed of a circuit. A common connection point of the capacitors 59 a and 59 b is connected to one of input terminals of the full-wave rectifier circuit 58. The drive power supply circuit 57 supplies a DC voltage of about 280 V generated by voltage doubler full wave rectification to the inverter circuit 50.

  On the output side of the full-wave rectifier circuit 58, a power supply circuit 62 that generates power supply voltages used in the control unit 29, for example, two kinds of voltages of 5V and 15V, is provided. The power supply voltage of 5 V generated by the power supply circuit 62 is also used as the power supply voltage for the operation of the control circuit 55 and the power supply of the inverting buffer for inputting the sensor signal of the rotational position sensor 56 to the control circuit 55. When a user turns on a power-on switch (not shown), the driving power supply circuit 57 outputs a voltage to generate 15V and 5V power supplies, and the control circuit 55 starts operating. The 15V power supply is used for the gate drive voltage of the IGBT 51 as will be described later.

  A series circuit of resistors 71 and 72 is connected between the output terminal of the full-wave rectifier circuit 58 and the ground. The common connection point of the resistors 71 and 72 is connected to the A / D conversion input terminal “A / D input 1” of the control circuit 55. The resistance values of the resistors 71 and 72 are, for example, 2.2 MΩ and 13 kΩ, respectively.

  The control circuit 55 generates a PWM command for driving the motor 24. Further, the control circuit 55 selects, for each carrier wave period of the PWM signal, a phase corresponding to at least two phases, for example, a long lower arm ON time, near the middle of the timing when the lower arm IGBT 51 is turned ON, and the terminal voltage thereof A / D conversion is performed to obtain the motor phase current. The control circuit 55 acquires the position of the rotor based on the output of the rotational position sensor 56 accompanying the rotation of the motor 24 and adjusts the PWM signal so that the d-axis current and the q-axis current of the motor 24 have appropriate values. Vector control calculation is performed, and the drive of the motor 24 is controlled.

  The PWM signal generated by the PWM output unit of the control circuit 55 is input to the gate of each IGBT 51 via the drive circuit 86 and further on the upper arm side via the high-voltage driver 87. The input terminal of the drive circuit 86 is pulled down by a resistor 85. The resistance value of the resistor 85 is, for example, 4.7 kΩ.

  A bootstrap capacitor 88 is connected between the emitter of each IGBT 51 and the high voltage driver 87. The control circuit 55 charges the bootstrap capacitor 88 to generate a power supply voltage for the high voltage driver 87 to drive the gate of the upper IGBT 51. When the lower phase IGBT 51 is turned on and the upper phase IGBT 51 is turned off, the bootstrap capacitor 88 is charged with 15V. Even when the lower phase IGBT 52 is turned off and the upper phase IGBT 51 is turned on, the voltage is maintained until the capacitor 88 is discharged, so that it can be used as a gate drive power supply.

  Between the 3.3V power supply and the ground, a series circuit of a forward diode 73 and a resistor 74 and a series circuit of a resistor 75 and a forward diode 76 are connected. The resistance values of the resistors 74 and 75 are, for example, 1 kΩ. Between the cathode of the diode 73 and the input terminals of the control circuit 55: “A / D input 2” to “A / D input 4”, diodes 77u, 77v and 77w for voltage clamping are opposite to the diode 73, respectively. Connected in the direction. Voltage clamping diodes 78u, 78v, and 78w are connected in the opposite direction to the diode 76 between the input terminals: “A / D input 2” to “A / D input 4” and the anode of the diode 76. ing. The two series circuits correspond to a potential adjustment circuit. The diodes 73 and 76 correspond to voltage compensating diodes.

  Next, the operation of this embodiment will be described. The voltage applied to the A / D conversion input terminal of the control circuit 55 should basically not exceed the range of the A / D conversion reference voltage; 0V to 3.3V. Therefore, the voltage applied to the input terminal is clamped to the power supply voltage of 3.3V and the ground potential of 0V by the clamping diodes 77 and 78, respectively. However, a forward voltage of about 0.6 to 0.7 V is generated in the diodes 77 and 78 when conducting. Therefore, when clamping is performed with only the diodes 77 and 78 as in the prior art, the actual clamping voltages are 4.0 V and −0.7 V, respectively.

  Therefore, in this embodiment, a series circuit of the diode 73 and the resistor 74 and a series circuit of the resistor 75 and the diode 76 are provided between the 3.3V power supply and the ground. Then, by connecting the cathode of the diode 77 to the common connection point of the diode 73 and the resistor 74, the potential of the cathode becomes (3.3-0.7 =) 2.6V. Further, by connecting the anode of the diode 77 to the common connection point of the resistor 75 and the diode 76, the potential of the anode becomes (0 + 0.7 =) 0.7V.

  Thus, if the voltage applied to the A / D conversion input terminal is clamped by the diodes 77 and 78, the forward voltage is offset by the forward voltages of the diodes 73 and 76, respectively. The voltage can be clamped so that the upper limit is 3.3V and the lower limit is 0V. Therefore, even when an overvoltage occurs, it is possible to prevent the current injected into the input terminal from becoming excessive.

  Further, even if the clamp voltage may exceed the power supply voltage 3.3V by about 0.1V or the ground potential 0V by about 0.1V due to variations in the forward voltage of the diodes 73 and 76, it may be used for A / D conversion. Since the protective resistor 68 is connected to the input terminal, the current injected to the input terminal is suppressed so as not to become excessive.

  FIG. 3 is a graph showing a comparison between the voltage applied to the input terminal for A / D conversion and the injection current when a positive current is generated in a conventional configuration in which voltage clamping is performed only by the diodes 77 and 78. In the conventional configuration, a large current of up to about 40 A is generated due to the occurrence of an abnormality such as a short circuit, and the input terminal voltage in that case is saturated at about 3.9 V exceeding the reference voltage 3.3 V. For example, in the Renesas RL78 / G14 microcomputer, the rated voltage of the input terminal of the built-in A / D converter is defined as +0.3 V or less with respect to the positive side of the A / D conversion reference voltage. , Its rated value is exceeded. Further, the injection current to the terminal is regulated to 0.8 mA or less and the motor current equivalent value is 21 A, which exceeds the prescribed value.

  On the other hand, in the configuration of the present embodiment shown in FIG. 2, the terminal voltage is suppressed to about + 0.1V with respect to the reference voltage 3.3V, and satisfies the rating within + 0.3V. Also, the injection current is significantly below the specified 0.8 mA or less, which satisfies the regulations.

  In the configuration shown in FIG. 1, an overcurrent detection circuit 54 is provided. However, it takes a time on the order of microseconds until the control circuit 55 detects the occurrence of overcurrent via the detection circuit 54 and stops the operation of the inverter circuit 50. Thereby, the IGBT 51 and the like can be protected from overcurrent, but the A / D converter built in the control circuit 55 may not be guaranteed in terms of time. Therefore, if the voltage clamp circuit using the diodes 73 and 76 to 78 is applied, the A / D converter can be reliably protected.

  As described above, according to the present embodiment, the current flowing through the winding of the motor 24 is detected by the shunt resistor 53, and the terminal voltage of the shunt resistor 53 is level-shifted by the level shift circuit 64. When the A / D conversion input terminal of the control circuit 55 to which the level-shifted voltage is applied is clamped to the power supply voltage and the ground potential by the diodes 77 and 78, the diode is connected to the power supply voltage at the terminal. And a potential adjusting circuit that applies a voltage that is decreased by the forward voltage of 77 and a potential adjusting circuit that applies a voltage that is increased by the forward voltage of the diode 78 with respect to the ground potential.

  Specifically, a series circuit of a diode 73 and a resistor 74 and a series circuit of a resistor 75 and a diode 76 are provided between the 3.3V power supply and the ground, and a diode is connected to a common connection point of the diode 73 and the resistor 74. The cathode of 77 is connected, and the anode of the diode 77 is connected to the common connection point of the resistor 75 and the diode 76.

  With this configuration, a larger current than usual is generated during a malfunction, and the voltage applied to the A / D conversion input terminal becomes larger than the reference voltage, resulting in circuit damage and further malfunction. Can be blocked. Since a general element can be used without using an expensive diode whose forward voltage is lower than a normal value, a countermeasure can be taken at low cost. Further, since the protective resistor 68 is connected to the A / D conversion input terminal, the current value injected to the input terminal can be suppressed even if the forward voltages of the diodes 73 and 76 vary.

(Other embodiments)
Instead of the A / D converter, the voltage applied to the input terminal of the amplifier may be clamped with the same configuration.
Depending on the specifications of the microcomputer constituting the control circuit, voltage clamping may be performed for only one of the power supply side and the ground side.
Only one of the series circuit including the diodes 73 and 76 and the protective resistor 68 may be provided.

The potential adjustment circuit is not limited to the one using the diodes 73 and 76, and may be any circuit that adjusts the voltage so as to cancel out the influence of the forward voltage.
What is necessary is just to change about each power supply voltage, resistance value, etc. according to individual design. The same applies to the frequency, period, and specific values for each period.
The switching element is not limited to the IGBT 51, and may be a MOSFET, a power transistor, or the like.
You may apply to laundry machines, such as a drum type washing machine, a washing dryer, and a dryer. Moreover, you may apply to the inverter apparatus used not only for a laundry machine but for other products.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the drawing, 10 is a washing machine, 50 is an inverter circuit, 51 is an IGBT, 55 is a control circuit, 53 is a shunt resistor, 68 is a protective resistor, 73 and 76 are voltage compensation diodes, and 77 and 78 are clamping diodes. .

Claims (3)

A current detection resistor for detecting the current flowing in the motor winding;
A voltage dividing circuit for level shifting the terminal voltage of the current detection resistor;
A clamping diode for clamping a terminal of an A / D converter or amplifier to which a voltage level-shifted by the voltage dividing circuit is input to a power supply voltage and / or a ground potential;
A potential adjustment circuit that applies a voltage that is lowered by a forward voltage of the clamping diode to the power supply voltage and / or a forward voltage of the clamping diode with respect to the ground potential. A motor current detection circuit comprising a potential adjustment circuit that applies a voltage increased by an amount corresponding to the voltage.   2. The motor current detection circuit according to claim 1, wherein the potential adjustment circuit includes a voltage compensation diode connected in a reverse direction to the diode between the power source and / or the ground and the clamping diode. A current detection resistor for detecting the current flowing in the motor winding;
A voltage dividing circuit for level shifting the terminal voltage of the current detection resistor;
A clamping diode for clamping a terminal of an A / D converter or amplifier to which a voltage level-shifted by the voltage dividing circuit is input to a power supply voltage and / or a ground potential;
A motor current detection circuit comprising a protective resistor inserted between the terminal and the clamping diode.

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