JP6924080B2 - Motor current detection circuit - Google Patents

Description

An embodiment of the present invention relates to a circuit that detects a current flowing through a winding of a motor.

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

Further, for example, when the circuit is malfunctioning due to step-out in the control of the DC brushless motor or other noise, an excessive current than usual may be generated. In such a case, it is necessary to protect the input portion of the A / D converter from the overvoltage generated in response to the 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 input of the A / D converter, and clamp diodes 507a and 508a are connected between the power supply and ground and the output terminal. There is. Further, in Patent Document 2, the electromotive voltage of the current detection resistor is level-shifted by the voltage dividing resistor, and the positive and negative currents are converted into a positive voltage capable of A / D conversion.

Japanese Patent No. 43455553 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. Therefore, there is a problem that the input portion of the A / D converter is damaged or a malfunction is caused. Also, a diode with a low forward voltage becomes expensive. Further, Patent Document 2 does not particularly disclose protection measures in the event of an excessive current.

Therefore, we provide a motor current detection circuit 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 that detects the current flowing through the windings of the motor,
A voltage divider circuit that level-shifts the terminal voltage of this current detection resistor,
A power supply side clamp diode whose anode is connected to the terminal of the A / D converter or amplifier to which the level-shifted voltage is input by this voltage divider circuit .
A diode for clamping on the ground side to which the cathode is connected to the terminal,
A power supply side potential adjustment circuit consisting of a series circuit of a resistance element connected between the power supply and ground and a diode for voltage compensation in the forward direction,
It is equipped with a ground-side potential adjustment circuit consisting of a forward voltage compensation diode connected between the power supply and ground and a series circuit of resistance elements.
The cathode of the power supply side clamping diode is connected to the cathode of the voltage compensation diode of the power supply side potential adjustment circuit.
The anode of the ground-side clamp diode is connected to the anode of the voltage compensation diode of the ground-side potential adjustment circuit.

Further, the motor current detection circuit of the embodiment is
It comprises a pre-SL terminal between the anode of the power supply side clamping diode, and a protection resistor which are inserted between the cathode of the terminal and the ground-side clamping diode.

A circuit diagram showing an electrical configuration of a washing machine, which is an embodiment. The figure which shows the comparison between the applied voltage of the input terminal for A / D conversion and the injection current at the time of the positive current generation. The figure which shows the comparison between the applied voltage of the input terminal for A / D conversion and the injection current at the time of the positive current generation about the conventional structure. Partial vertical side view schematically showing the configuration of the washing machine

Hereinafter, an embodiment applied to a washing machine, which is a laundry device, 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 inside an outer box 11 constituting the outer shell of the washing machine 10. Inside the water tank 12, a bottomed cylindrical rotary tank 14 having an open upper surface is rotatably provided. The bottom of the rotary tank 14 is provided with a reinforcing member 15 for reinforcing the bottom of the rotary tank 14. The rotary tub 14 is configured to rotate about a vertical axis, and serves as a washing tub in a washing process for washing laundry and a washing process for rinsing laundry, and a dehydration tub in a dehydration process for dehydrating laundry. Also used. That is, the washing machine 10 is a so-called vertical axis type washing machine in which the rotation center axis of the rotary tub 14 extends in the vertical direction.

The rotary tank 14 has a large number of holes 16 in its peripheral wall portion. These holes 16 penetrate and allow water and ventilation. Note that FIG. 5 shows only a part of the large number of 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 rotary tank 14. At the bottom of the rotary tank 14, for example, a pulsator 18 made of synthetic resin is rotatably provided as a stirrer.

A drainage path 19 is provided in the lower part of the water tank 12. A drain valve 20 is provided in the drainage path 19, and when the drain valve 20 is opened, the water in the water tank 12 is discharged to the outside of the machine. Further, an air trap 21 for detecting the water level is provided at the bottom of the water tank 12.

A drive mechanism unit 23 is provided in the central portion of the lower portion of the water tank 12. The drive mechanism unit 23 includes a motor 24, a clutch mechanism unit (not shown), and the like. The drive mechanism unit 23 transmits the rotational force to the pulsator 18 by the clutch mechanism unit during the washing stroke or the rinsing stroke. Therefore, the rotary tank 14 is not rotationally driven during the washing stroke or the rinsing stroke, and only the pulsator 18 is rotationally driven. In the washing process, the rotation speed is controlled to about 100 to 150 rpm by, for example, a forward / reverse 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 stroke. Therefore, during the dehydration stroke, the pulsator 18 is rotationally driven integrally with the rotary tank 14. In the dehydration stroke, the rotation speed is controlled to, for example, about 1300 to 1500 rpm.

A top cover 26 is provided on the upper part of the outer box 11. The top cover 26 is provided with, for example, a two-fold type lid 27 that can be opened and closed to open and close the laundry entrance. 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 on the front portion of the top cover 26. On the back side of the operation panel 28, a control unit 29 that controls the overall operation of the washing machine 10 is arranged.

At the rear part of the top cover 26, a water supply mechanism portion 30 for supplying water from the water source into the water tank 12 is provided. The water supply mechanism unit 30 includes a water supply valve (not shown), a water supply path (not shown) communicating with the water tank 12, and the like, and the control unit 29 controls the opening and closing of the water supply valve to control the water supply into the water tank 12. NS.

Next, the electrical configuration related 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 which is a PWM control type inverter. The inverter circuit 50 is configured by connecting six IGBTs 51 with a three-phase bridge, and a flywheel diode 52 is connected between the collector and the 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 24a of the motor 24. In the present embodiment, for example, an outer rotor type three-phase brushless DC motor is adopted as the motor 24.

A shunt resistor 53, which is a current detection resistor, is connected in series to the emitter of the IGBT 51 on the lower arm side with the ground. The resistance value of the shunt resistor 53 is, for example, 0.18Ω. Further, 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 composed of an overcurrent detection circuit 54 and a resistance voltage divider circuit, respectively. 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 turned on. Therefore, the terminal voltage indicates a level corresponding to the motor phase current. By connecting the IGBTs 51 of the upper arm and the lower arm in series, switching legs corresponding to each phase are configured.

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 output of the PWM signal is immediately turned off by the control circuit 55 that receives the change in the comparator output. As a result, destruction of the circuit element or the like is prevented.

When the inverter circuit 50 operates, the shunt resistor 53 generates positive and negative terminal voltages with respect to the ground potential. Therefore, the level shift circuit 64 sets the terminal voltage of the shunt resistor 53, that is, the voltage of the common connection point between the emitter of the IGBT 51 and the shunt resistor 53, into the input range of an A / D converter (not shown) built in the control circuit 55. Level shift according to. The power supply voltage of the level shift circuit 64 is generated from a 5V power supply by, for example, a 3.3V power supply circuit 70 which is a 3-terminal regulator.

In FIG. 1, "0" is added to the ground symbol of the 3.3V power supply to distinguish it from the ground symbol of the 5V power supply. The reason why the two grounds are separated in this way is to prevent the influence of noise generated in the 5V power supply system from affecting the 3.3V power supply side used for A / D conversion.

The level shift circuit 64 is shunted by three resistors 65a-67a connected to the power supply voltage and three resistors 65b-67b connected in series between these resistors 65a-67a and the shunt resistor 53. The terminal voltage of the resistor 53 is divided by the resistor and the level is shifted. The level-shifted voltage is input to the A / D conversion input terminals "A / D input 2" to "A / D input 4" of the control circuit 55 via the protection resistors 68u to 68w, respectively. The resistance value of these resistors 65 to 68 is, for example, 1 kΩ. Further, capacitors 69u to 69w are connected between the input terminals "A / D input 2" to "A / D input 4" and the ground. The capacitance of the capacitor 69 is, for example, 1000 pF. The capacitor 69 constitutes an RC filter together with the protection resistor 68.

The motor 24 is provided with a rotation position sensor 56 composed of, for example, a Hall IC, in order to detect the position of the rotor, and a sensor signal output by the rotation 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 current value flowing through each motor winding 24a of the motor 24, and giving the PWM signal to the inverter circuit 50. As described above, the control circuit 55 is composed of a microcomputer having an A / D converter or the like built-in. The 3.3V power supply is also the reference voltage of the A / D converter.

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

On the output side of the full-wave rectifier circuit 58, a power supply circuit 62 that generates two types of power supply voltages, for example, 5V and 15V, used by the control unit 29 by chopping is provided. The 5V power supply voltage generated by the power supply circuit 62 is also used as the operating power supply voltage of the control circuit 55 and the power supply of the inverting buffer for inputting the sensor signal of the rotation position sensor 56 to the control circuit 55. When a power-on switch (not shown) is operated by the user, the drive power supply circuit 57 outputs a voltage to generate 15V and 5V power supplies, and the control circuit 55 starts operation. Further, the 15V power supply is used for the gate drive voltage of the IGBT 51 as 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 points of the resistors 71 and 72 are 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 at least two phases, for example, phases having a long ON time of the lower arm near the middle of the timing at which the IGBT 51 on the lower arm side is ON for each carrier period of the PWM signal, and their terminal voltages. Is A / D converted to obtain the motor phase current. The control circuit 55 acquires the position of the rotor based on the output of the rotation 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 become appropriate values. Vector control calculation is performed to drive and control the motor 24.

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 the upper arm side via the high voltage driver 87. The input terminal of the drive circuit 86 is pulled down by the 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 these bootstrap capacitors 88 to generate a power supply voltage for the high voltage driver 87 to drive the gate of the upper IGBT 51. If the lower phase IGBT 51 is turned on and the upper phase IGBT 51 is turned off, the boot strap capacitor 88 is charged with 15 V. Even if the lower phase IGBT 52 is off and the upper phase IGBT 51 is on, the voltage is maintained until the capacitor 88 is discharged, so that it can be used as a gate drive power supply.

A series circuit of the forward diode 73 and the resistor 74 and a series circuit of the resistor 75 and the forward diode 76 are connected between the 3.3V power supply and the ground. The resistance values of the resistors 74 and 75 are, for example, 1 kΩ. Between the cathode of the diode 73 and the input terminal of the control circuit 55: "A / D input 2" to "A / D input 4", the diodes 77u, 77v and 77w for voltage clamping are opposite to those of the diode 73, respectively. Connected in the direction. Further, between the input terminals: "A / D input 2" to "A / D input 4" and the anode of the diode 76, diodes 78u, 78v and 78w for voltage clamping are connected in the opposite direction to the diode 76. ing. The two series circuits correspond to a potential adjustment circuit. The diodes 73 and 76 correspond to voltage compensation 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 basically must 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 by the clamping diodes 77 and 78 to the power supply voltage of 3.3 V and the ground potential of 0 V, respectively. However, the diodes 77 and 78 generate a forward voltage of about 0.6 to 0.7 V when conducting. Therefore, if the clamp is performed only with the diodes 77 and 78 as in the conventional case, the actual clamping voltages will be 4.0 V and −0.7 V, respectively.

Therefore, in the present 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 3.3 V 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.

As a result, if the voltage applied to the input terminal for A / D conversion is clamped by the diodes 77 and 78, the forward voltage component is canceled by the forward voltage of the diodes 73 and 76, respectively, so that the voltage is applied as expected. It can be clamped so that the upper limit of the voltage is 3.3V and the lower limit is 0V. Therefore, even when an overvoltage is generated, it is possible to suppress the current injected into the input terminal from becoming excessive.

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

FIG. 3 graphically shows a comparison between the applied voltage of the A / D conversion input terminal and the injection current when a positive current is generated in the conventional configuration in which the voltage is clamped only by the diodes 77 and 78. In the conventional configuration, a large current of up to about 40 A is generated due to an abnormality such as a short circuit, and the input terminal voltage in that case is saturated at about 3.9 V, which exceeds the reference voltage of 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 specified to be + 0.3V or less with respect to the positive side of the A / D conversion reference voltage. , The rated value is exceeded. Further, the injection current to the terminal is specified to be 0.8 mA or less and the motor current equivalent value is 21 A, but the specified value is exceeded.

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 of 3.3V, which satisfies the rated value of + 0.3V or less. In addition, the injection current is well below the specified 0.8mA or less, which meets the regulations.

In the configuration shown in FIG. 1, an overcurrent detection circuit 54 is provided. However, it takes time on the order of μs until the control circuit 55 detects the occurrence of an overcurrent via the detection circuit 54 and stops the operation of the inverter circuit 50. This makes it possible to protect the IGBT 51 and the like from overcurrent, but there is a possibility that the protection of the A / D converter built in the control circuit 55 cannot be guaranteed in terms of time. Therefore, if a voltage clamp circuit using diodes 73, 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. Then, 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 terminal is connected to the diode with respect to the power supply voltage. A potential adjusting circuit for applying a voltage lowered by the forward voltage of 77 and a potential adjusting circuit for applying a voltage increased by the forward voltage of the diode 78 with respect to the ground potential are provided.

Specifically, a series circuit of the diode 73 and the resistor 74 and a series circuit of the resistor 75 and the resistor 76 are provided between the 3.3V power supply and the ground, and the diode is provided at the common connection point of the diode 73 and the resistor 74. The cathode of 77 is connected, and the anode of 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, causing damage to the circuit and further malfunction. Can be stopped. Then, since a general element can be used without using an expensive diode whose forward voltage is lower than the normal value, countermeasures can be taken at low cost. Further, since the protection resistor 68 is connected to the A / D conversion input terminal, the current value injected into the input terminal can be suppressed even if the forward voltage of the diodes 73 and 76 varies.

(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 that constitutes the control circuit, voltage clamping may be performed on 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 protection resistor 68 may be provided.

The potential adjustment circuit is not limited to the one using the diodes 73 and 76, and may be similarly used as long as it adjusts the voltage so as to cancel the influence of the forward voltage.
Each power supply voltage, resistance value, etc. may be changed according to the 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.
It may be applied to laundry equipment such as a drum type washing machine, a washer / dryer, and a dryer. Further, the present invention is not limited to laundry equipment, and may be applied to inverter devices used in other products and the like.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope 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 protection resistor, 73 and 76 are voltage compensation diodes, and 77 and 78 are clamping diodes. ..

Claims (2)

A current detection resistor that detects the current flowing through the windings of the motor,
A voltage divider circuit that level-shifts the terminal voltage of this current detection resistor,
A power supply side clamp diode whose anode is connected to the terminal of the A / D converter or amplifier to which the level-shifted voltage is input by this voltage divider circuit .
A diode for clamping on the ground side to which the cathode is connected to the terminal,
A power supply side potential adjustment circuit consisting of a series circuit of a resistance element connected between the power supply and ground and a diode for voltage compensation in the forward direction,
It is equipped with a ground-side potential adjustment circuit consisting of a forward voltage compensation diode connected between the power supply and ground and a series circuit of resistance elements.
The cathode of the power supply side clamping diode is connected to the cathode of the voltage compensation diode of the power supply side potential adjustment circuit.
The anode of the ground-side clamping diode is a motor current detection circuit connected to the anode of the voltage compensation diode of the ground-side potential adjustment circuit. Between the anode of the terminal and the power supply side clamping diode, and the motor current detecting circuit according to claim 1, further comprising a protection resistor which are inserted between the cathode of the terminal and the ground-side clamping diode.

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