JP2010197065A - Current detection device with variable resolution circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detection device, capable of detecting a current being supplied to a load with a desired resolution and having current detection resolution capable of reducing measurement errors, even when the operating environmental temperature is varied. <P>SOLUTION: The current detection device 20 with a variable resolution circuit includes a current detector (current sensor) 21, which outputs a voltage proportional to the value of the supply current being supplied to the load; and a variable resolution circuit 22, having an operational amplifier for inputting and amplifying the voltage output from this current detector, diodes, and resistors; and a conversion means (A/D converter) 23 for converting an input voltage value which is the output of the variable resolution circuit into a digital quantity. In the variable resolution circuit, the amplification factor of the operational amplifier is varied based on the output voltage of the current detector. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a current detection device in a motor control system.

  Conventionally, in the field of motor control technology, a current detection device that switches current detection resolution in accordance with the magnitude of a current command value has been disclosed (see, for example, Patent Document 1). This current detection device switches and compares the current command value and the level of the comparator so that when the current command value is large, the operational amplifier gain is set low so that a large current can be detected. Is small, the vibration of the motor is suppressed by setting the gain of the operational amplifier high to increase the current resolution. The gain of the operational amplifier is controlled by a short-circuit switch depending on whether or not a feedback resistor is inserted.

  Also, for switching the current detection resolution of the current detection device, an input gain switching unit that controls the amplification factor of the operational amplifier using an electronic volume and a fixed resistor is compared with the magnitude of the current command value and the gain of the current detection device. An apparatus provided with an input gain comparison / determination unit that is a comparator is also disclosed (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 10-132861 JP 11-274930 A

  However, in the conventional current detection device, in order to make the gain variable according to the magnitude of the current command value, the assumed resolution is that the current value measured when the current command value is output crosses the set threshold value. There was a problem that the current value at could not be obtained.

  In addition, even when the operating environment temperature varies, it has been desired to obtain a current detection device that has a small measurement error due to a temperature change and has a desired current detection resolution corresponding to the load operation.

In order to solve the above problems, the present invention detects a current supplied to a load with a desired resolution, and provides a current detection device having a current detection resolution with reduced measurement error even when the operating environment temperature varies. The purpose is to provide.

  In order to achieve the object, a current detector with a variable resolution circuit according to a first aspect of the present invention includes a current detector (current sensor) that outputs a voltage proportional to a supply current value supplied to a load, A variable resolution circuit having an operational amplifier, a diode, and a resistor for inputting and amplifying the voltage output from the current detector, and a conversion means (A) for converting a voltage value input to the output of the variable resolution circuit into a digital quantity. / D converter), wherein the variable resolution circuit makes the gain of the operational amplifier variable based on the voltage.

  With this configuration, the gain of the variable resolution circuit is determined based on the actual supply current value supplied to the load instead of the current command value, so that detection with unintended resolution does not occur. Further, since a comparator circuit for comparing with the current command value is not required, it is possible to reduce the size of the motor control system.

The variable resolution circuit of the current detector with a variable resolution circuit according to the second aspect of the present invention includes the operational amplifier, the first to sixth diodes as the diode, and the first to sixth resistors as the resistor. The voltage (Vi) is applied to one end of the first resistor (R1), the inverting input terminal of the operational amplifier is connected to the other end of the first resistor, and the input The terminal is grounded, one end of the second resistor (R2) is connected to the inverting input terminal, the anode of the third diode (D3) is connected to the other end of the second resistor, and the cathode Is connected to the output terminal of the operational amplifier, the fourth diode (D4) has a cathode connected to the other end of the second resistor, an anode connected to the output terminal, and the first diode (D1). ) , The anode is connected to the inverting input terminal, the third resistor (R3) has one end connected to the cathode of the first diode, the other end connected to the output terminal, and the second diode ( D2) has a cathode connected to the inverting input terminal, the fourth resistor (R4) has one end connected to the anode of the second diode, the other end connected to the output terminal, and the fifth resistor The resistor (R5) has one end connected to the cathode of the first diode (D1), the other end connected to the cathode of the fifth diode (D5), and the anode of the fifth diode connected to the anode of the fifth diode (D5). 1 voltage (V _H ) is applied, and the sixth resistor (R6) has one end connected to the anode of the second diode and the other end connected to the anode of the sixth diode (D6). The sixth die A second voltage (V _L ) is applied to the cathode of the Aode, and the output of the variable resolution circuit is a voltage (Vo1) at the other end of the second resistor.

With this configuration, the variable resolution circuit has a limiter circuit configuration including one operational amplifier, six diodes, and six resistors, and a current (I _D1 ) flowing through the first diode (D1). ) And the current (I _D2 ) flowing through the second diode (D2), the input / output characteristics are limited to three regions. In particular, by appropriately setting the electrical characteristics of the diodes and resistors that are configured, the input / output characteristics of this variable resolution circuit are not dependent on the forward temperature characteristics of the diodes. The obtained input / output characteristics can be obtained.

In the variable resolution circuit of the current detector with a variable resolution circuit according to the third aspect of the present invention, the first to sixth diodes (D1 to D6) have the same standard forward voltage (V _F ). (V _F1 = V _F2 ... = V _F6 = V _F ) It is characterized by having electrical characteristics.

By doing so, it is possible to implement a variable resolution circuit having temperature compensated input / output characteristics that does not depend on the forward temperature characteristics of the diode. Further, since the diodes of the same standard are used, the effect of reducing the mounting cost is also achieved.

In the variable resolution circuit of the current detector with variable resolution circuit according to the fourth aspect of the present invention, the first to sixth diodes, which are constituent elements of the variable resolution circuit, are provided on the same substrate. It is characterized by being.

In this way, it is possible to implement a variable resolution circuit having input / output characteristics that are temperature-compensated, taking into account the mounting form on the same substrate.

Then, in the variable resolution circuit of a variable resolution with circuit current detection device according to a fifth aspect of the present invention, the second resistor (R2) to the sixth resistance value of the resistor (R6) of the (r ₂ ~r ₆₎ Are equal to each other.

In this way, by adopting resistors of the same model number with the same specification standard characteristics, there is an effect of further reducing the mounting cost of the variable resolution circuit having the temperature compensated input / output characteristics.

In the variable resolution circuit of the current detector with a variable resolution circuit according to the sixth aspect of the present invention, the absolute values of the first voltage (V _H ) and the second voltage (V _L ) are equal (| V _H | = | V _L |).

Thus, the first resistor (R1) and the second resistor in the variable resolution circuit having the temperature compensated input / output characteristics in consideration of the characteristics of the load (motor) and the current detector (current sensor). The resistance value (r ₁ , r ₂ ) of (R2) can be determined.

Furthermore, the current detector of the current detector with a variable resolution circuit according to the seventh aspect of the present invention includes a shunt resistor (Rs).

  By doing so, it is possible to implement a current detection device with a variable resolution circuit having a temperature-compensated variable resolution circuit in consideration of the input / output characteristics of the load (motor) and the variable resolution circuit.

A current detection device with a variable resolution circuit according to the present invention detects a current supplied to a load with a desired resolution, and has a current detection resolution with reduced measurement error even when the operating environment temperature varies. Is suitable for application to a motor control system.

It is a block diagram for demonstrating the structure of the motor control system containing the electric current detection apparatus with a variable resolution circuit of embodiment of this invention. It is a circuit diagram for demonstrating the structure of the variable resolution circuit of this embodiment. FIG. 6 is a circuit diagram (No. 1) for explaining the operation of the variable resolution circuit of the embodiment; FIG. 6 is a circuit diagram (No. 2) for explaining the operation of the variable resolution circuit of the embodiment. FIG. 6 is a circuit diagram (No. 3) for explaining the operation of the variable resolution circuit of the embodiment. It is a figure for demonstrating operation | movement of the current sensor of the current detection apparatus with a variable resolution circuit of this embodiment. It is a figure for demonstrating the input-output characteristic in the switching point and measurement limit of the variable resolution circuit of this embodiment. It is a circuit diagram for demonstrating operation | movement of the soft limit circuit of a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 7.
As shown in FIG. 1, the motor control system 1 includes a PID control unit 10, a PWM generator 11, and an inverter 12 as a motor drive system. As a drive detection system for the motor 13 that is a load, a current detection device 20 with a variable resolution circuit including a current sensor (current detector) 21, a variable resolution circuit 22, and an A / D converter (conversion means) 23. And a voltage-current converter 15.

As for the operation of the motor drive system, P (proportional), I (integral), and D (differential) control of the input signal is performed by the PID control unit 10, and the output signal is input to the PWM generator 11 and the pulse width As a result, a modulated pulse is generated as an output. Then, the inverter 12 by converting the pulse signal for driving the motor, the supply current I _M for driving the motor 13 as a load is supplied to the motor 13.

Then, the operation of the detection system, the variable resolution with circuit current detection device 20 of the present invention, by a current sensor 21 as a current detector, a voltage proportional to the supply current value of the supply current I _M to the motor 13 as a load Is generated as an output, the input voltage of the variable resolution circuit 22 is input as Vi, and the output voltage is output as Vo1. Then, the output voltage Vo1 of the variable resolution circuit 22 is converted and output by the A / D converter 23 which is a conversion means. Further, the feedback current _IFB is fed back via the voltage-current conversion 15 that converts the output voltage from the current detector 20 with a variable resolution circuit into a current. Then, an error signal E between the current command value and the feedback current _IFB is fed back to the drive system PID controller 10.

One feature of this embodiment is based on the supply current value of the supply current I _M to the motor 13 in the detection system, a variable resolution with circuit current detecting device 20 is to perform the current detection.
That is, the supply current I _M supplied to the motor (load) 13 can be detected with a desired resolution. Further, since a comparator circuit for comparing with the current command value is not required, it is possible to reduce the size of the motor control system.

Next, the variable resolution circuit 22 that is a component of the current detection device 20 with a variable resolution circuit of the present embodiment will be described with reference to FIGS. Here, regarding the second to seventh embodiments, the six diodes as the constituent elements have the same characteristics and are mounted on the same substrate, so that the variable resolution has the temperature compensated input / output characteristics. The implementation of the circuit 22 will be described. Of the six resistors, the resistance values of the second to sixth resistors are the same, the absolute values of the first and second voltages (V _H and V _L ), and the components of the current sensor The shunt resistance will be further described.

FIG. 2A is a circuit diagram showing a configuration of the variable resolution circuit 22 of the present embodiment.
The variable resolution circuit 22 has a configuration of a kind of limiter circuit including one operational amplifier, six diodes D1 to D6, and six resistors R1 to R6. The output voltage of the current sensor 21 is input as an input voltage Vi from one end of the resistor R1 and output as an output voltage Vo1 from the other end of the resistor R2, and becomes an input voltage to the A / D converter 23.

  The resistor R1 has one end applied with the voltage from the current sensor 21 shown in FIG. 1 as the input voltage Vi. The operational amplifier has its inverting input terminal connected to the other end of the resistor R1 and its input terminal grounded. . The resistor R2 has one end connected to the inverting input terminal of the operational amplifier, the diode D3 has its anode connected to the other end of the resistor R2, its cathode connected to the output terminal of the operational amplifier, and the diode D4 has its cathode connected to the cathode. The other end of the resistor R2 is connected, and its anode is connected to the output terminal of the operational amplifier.

The anode of the diode D1 is connected to the inverting input terminal of the operational amplifier, the resistor R3 has one end connected to the cathode of the diode D1, the other end connected to the output terminal of the operational amplifier, and the diode D2 has its cathode connected to the cathode. Connected to the inverting input terminal of the operational amplifier, the resistor R4 has one end connected to the anode of the diode D2 and the other end connected to the output terminal of the operational amplifier.

Furthermore, one end of the resistor R5 is connected to the cathode of the diode D1, the other end is connected to the cathode of the diode D5, and the first voltage _VH is applied to the anode of the diode D5. The resistor R6 has one end connected to the anode of the diode D2, the other end connected to the anode of the diode D6, and the second voltage _VL is applied to the cathode of the diode D6.

The output of the variable resolution circuit 22 is output as a voltage value Vo1 at the other end of the resistor R2, and becomes an input voltage to the A / D converter 23 of FIG.

  An input / output characteristic diagram (Vi-Vo1 characteristic) of the variable resolution circuit 22 having such a configuration is shown in FIG. Although the details will be described later, the input / output characteristics of the variable resolution circuit 22 are as follows. The output voltage Vo1 with respect to the input voltage Vi is an area (1), area (2), In addition, the input / output characteristics limited to the three regions (3) are shown.

The variable resolution circuit 22 of this embodiment has a kind of limiter circuit configuration using an operational amplifier, a diode, and a resistor. With this configuration, the temperature does not depend on the forward temperature characteristics of the diode described later. This is a second feature of the present invention that implements a compensated variable resolution circuit.

Next, the operation of the variable resolution circuit 22 of the present embodiment will be described with reference to FIGS.
When the circuit shown in FIG. 2A is operated, there are two cases in which the currents flowing through the two diodes D1 and D2 are in the forward direction (in the case of I _D1 > 0 and I _D2 > 0). ) And the case where no current flows (I _D1 = I _D2 = 0).

First, the case where I _D1 > 0 will be described as a first case with reference to FIG. 3A and 3B illustrate a case where the forward current I _D1 flows through the diode D1 (when I _D1 > 0). In this case, the diode D2 is reverse-biased and no current flows (I _D2 = 0).
Therefore, in FIG. 3 (a), the current flowing through the resistor R1 and the resistor R2 direction as I ₁ and I _2, including taking into account the same manner current direction below, the diode D1, D3 to be forward biased, In D5, the forward voltages of the respective diodes are V _F1 , V _F3 , and V _F5, and in this case, the currents flowing through the resistors R3 and R5 including the direction are I ₃ and I ₅ . Here, will be the resistance value of the resistors Rn described in r _n.

Now, when the cathode voltage of the diode D1 and _{V 3,} for the diode D1 to operate forward _is when the _{I D1>} 0,
V ₃ <−V _F1 (1)
That is,
_{V 3 = Vo + ((V} H -V F5) -Vo) (r 3 / (r 3 + r 5))
= (R ₃ / (r ₃ + r ₅ )) (r ₅ Vo + r ₃ (V _H −V _F5 )) <− V _F1 (2)
And
Vo <− (r ₃ + r ₅ ) V _F1 / r ₅ − (V _H −V _F5 ) r ₃ / r ₅ (3)
Is established. On the other hand, considering that the diode D3 is inserted,
Vo1 = Vo + V _F3 (4)
As a condition for I _D1 > 0,
Vo1 <− (r ₃ + r ₅ ) V _F1 / r ₅ − (V _H −V _F5 ) r ₃ / r ₅ + V _F3 (5)
It becomes. This region is a straight line (1) in FIG.

Next, when the input / output relationship in the first case is analyzed, in the current,
I _D1 = I ₁ −I ₂ (6)
Is established, and
I _D1 + I ₅ = I ₃ (7)
Therefore, if expressed in terms of voltage, the relationship between the input and output voltages from (6) and (7) is
Vo1 = (− Vi / r ₁ −V _H / r ₅ − (1 / r ₃ + 1 / r ₅ ) V _F1
+ V _F3 / r ₃ + V _F5 / r ₅ ) r ₂ r ₃ / (r ₂ + r ₃ ) (8)
It becomes. What should be considered in the relational expression (8) of the input / output voltage is that the output voltage Vo1 includes factors of the forward voltages V _F1 , V _F3, and V _F5 of the diodes D1, D3, and D5.

Therefore, when the current is very small, assuming that the forward voltage is substantially the same in a diode having similar characteristics,
V _F1 = V _F3 = V _F5 (9)
When,
Vo1 = (− Vi / r ₁ −V _H / r ₅ ) r ₂ r ₃ / (r ₂ + r ₃ ) (10)
Thus, the term including the forward voltage of the diode that must take into account the change due to temperature disappears, and the output voltage Vo1 becomes independent of temperature.

Due to the characteristics of the diode, the relationship between the forward current _IF and the forward voltage V _F may change depending on the operating temperature. However, the characteristics of the forward current I _F and the forward voltage V _F of the substrate to implement the same model number with the same specification standard characteristics diode, since it can be said to be the same, equation (10) is satisfied.

Next, the case of I _D2 > 0 will be described as a second case with reference to FIG. 4A and 4B illustrate a case where forward current _ID2 flows through diode D2 (when _ID2 > 0). In this case, a reverse bias is applied to the diode D1, and no current flows (I _D1 = 0).
Thus, in FIG. 4 (a), the current flowing through the resistor R1 and the resistor R2 direction as I ₁ and I _2, including taking into account the same manner current direction below, the diode D2, D4 to be forward biased, The forward voltages of the diodes in D6 are V _F2 , V _F4 , and V _F6, and in this case, the currents that flow in the resistors R4 and R6 are I ₄ and I ₆ including the direction. As with the first, will be the resistance value of the resistors Rn described in r _n.

Now, when the cathode voltage of the diode D2 and _{V 4,} because the diode D2 is operated forward _is when the _{I D2>} 0,
V ₄ > V _F2 (11)
That is,
_{V 4 = Vo- (Vo- (V} L -V F6)) (r 4 / (r 4 + r 6))
= (1 / (r ₄ + r ₆ )) (r ₆ Vo + r ₄ (V _L + V _F6 ))> V _F2 (12)
And
Vo> − (V _L + V _F6 ) r ₄ / r ₆ + (r ₄ + r ₆ ) V _F2 / r ₆ (13)
Is established. On the other hand, considering that the diode D4 is inserted,
Vo = Vo1 + V _F4 (14)
As a condition for I _D2 > 0,
Vo1> − (V _L + V _F6 ) r ₄ / r ₆ + (r ₄ + r ₆ ) V _F2 / r ₆ −V _F4 (15)
It becomes. This region is a straight line (2) in FIG.

Next, as in the first case, when the input / output relationship for the second case is analyzed, in the current,
I _D2 + I ₂ = I ₁ (16)
Is established, and
I ₄ + I _D2 = I ₆ (17)
Therefore, if expressed in terms of voltage, the relationship between the input and output voltages from (6) and (7) is
Vo1 = (− Vi / r ₁ + (1 / r ₄ + 1 / r ₆ ) V _F2 −V _F4 / r ₄
− (V _L + V _F6 ) / r ₆ ) r ₂ r ₄ / (r ₂ + r ₄ ) (18)
It becomes. What should be considered in the relational expression (18) of the input / output voltage is that the output voltage Vo1 is equal to the forward voltages V _F2 , V6 of the diodes D2, D4 and D6, as in the relational expression (8) in the first case. _{It includes F4} and V _F6 factors.

Therefore, as the same consideration as in the first case, in the case where the current is very small, assuming that the forward voltage is substantially the same in the diode having the same characteristic, in the relational expression (18),
V _F2 = V _F4 = V _F6 (19)
When,
Vo1 = (− Vi / r ₁ −V _L / r ₆ ) r ₂ r ₄ / (r ₂ + r ₄ ) (20)
Thus, the term including the forward voltage of the diode that must take into account the change due to temperature disappears, and the output voltage Vo1 becomes independent of temperature.

Due to the characteristics of the diode, the relationship between the forward current _IF and the forward voltage V _F may change depending on the operating temperature. However, the characteristics of the forward current I _F and the forward voltage V _F of the substrate to implement the same model number with the same specification standard characteristics diode, since it can be said to be the same, equation (20) is satisfied.

Next, the case where I _D1 = I _D2 = 0 will be described as a third case with reference to FIG. 5A and 5B illustrate a case where no current flows through the diode D1 and the diode D2 (when I _D1 = I _D2 = 0). In this case, from the relational expression (5) and the relational expression (15), the region of the output voltage Vo1 is − (r ₃ + r ₅ ) V _F1 / r ₅ − (V _H −V _F5 ) r ₃ / r ₅ + V. _F3 ≦ Vo1
≦ − (V _L + V _F6 ) r ₄ / r ₆ + (r ₄ + r ₆ ) V _F2 / r ₆ −V _F4 (21)
It becomes. This region is a straight line (3) in FIG.

In addition, since the input / output relationship in the third case is I _D1 = I _D2 = 0,
I ₁ = I ₂ (22)
From the fact that
Vo1 = −r ₂ Vi / r ₁ (23)
Thus, the relational expression (23) of the input / output voltage does not include the factors of the diodes D1 to D6 and the factors of the resistors 3 to R6, unlike the first case and the second case. Therefore, the output voltage Vo1 in this case does not depend on the temperature.

As described above, in the variable resolution circuit 22 of the present embodiment, in the same substrate for mounting, the forward current I _F and the forward voltage V _F of the same model number of the diode having the same in specification Characteristics Characteristic By using a diode having the above, it is possible to implement a variable resolution circuit that does not depend on the forward temperature characteristics of the diode, that is, temperature compensated.

Furthermore, the first to sixth resistors (R1 to R6), which are components other than the first to sixth diodes (D1 to D6) of the variable resolution circuit 22 of the present embodiment, and the first and second resistors Consider the voltages (V _H and V _L ). In this case, first to sixth diodes presupposes the use of a diode having a characteristic of the forward current I _F and the forward voltage V _F of the same model number of the diode having the same specification standard characteristics.

As described above, the first to third cases are conceivable, but the case where current does not flow through the diode D1 and the diode D2 (when I _D1 = I _D2 = 0), which is the third case, is described. Omitted.

First, Vo1 = (− Vi / r ₁ −V _H / r ₅ − (1 / r ₃ + 1 / r) from the relational expression (8) of the input / output voltages for I _D1 > 0 and I _D2 = 0 in the first case. ₅ ) V _F1
+ V _F3 / r ₃ + V _F5 / r ₅ ) r ₂ r ₃ / (r ₂ + r ₃ ) (8)
Is established. Here, in FIG. 3A,
−Vo = r ₂ I ₂ + V _F3 (24)
In the loop of the diode D1,
−Vo = r ₃ I ₃ + V _F1 = r ₃ (I _D1 + I ₅ ) + V _F1 (25)
It becomes. Here, when R5 is set so that I _D1 = I ₅ , the relational expression (25) becomes as follows.
−Vo = r ₃ (I _D1 + I ₅ ) + V _F1 = 2r ₃ I _D1 + V _F1 (26)
Therefore, from relational expressions (24) and (26), r ₂ I ₂ + V _F3 ≡2r ₃ I _D1 + V _F1 (27)
It becomes.

As described above, in the present embodiment, since the use of diode having a characteristic of the forward current I _F and the forward voltage V _F of the same model number of the diode having the same specification standard characteristics, for use in certain operating temperature a plurality of diodes, in the linear region in the forward current-voltage characteristics I _F -V _F is
r ₂ I ₂ + K _D I ₂ ≡2r ₃ I _D1 + K _D I _D1 (28)
Is guided. Here, the _{K D} and _constant, and the V _{F =} K D _{I F.} Actually, the forward current-voltage characteristic I _F -V _F characteristic of the diode is V _F = K _D log I _F , but the characteristic in the linear region is considered here. Therefore, the relational expression (28) is transformed and
(R ₂ + K _D ) I ₂ ≡ (2r ₃ + K _D ) I _D1 (29)
It becomes. Further, here, if the resistance values of the resistors R2 and R3 are set to r ₂ = 2r ₃ , the influence of the forward voltage of the diodes when all the diodes exist on the same substrate, that is, at the same environmental temperature. The input / output characteristics of the variable resolution circuit 22 can be obtained without being subjected to the above. That is, in relational expression (10),
Vo1 = (− Vi / r ₁ −V _H / r ₅ ) r ₂ r ₃ / (r ₂ + r ₃ )
_{= (- Vi / r 1 -V} H / r 5) r 2/3 (30)
It becomes.

Similarly, in the second case, when I _D1 = 0 and I _D2 > 0, R6 is set so that I _D2 >> I _D6 , and the resistance values of the resistors R2 and R4 are set to r ₂ = r If set to ₄ , the relational expression (20) becomes
Vo1 = (− Vi / r ₁ −V _L / r ₆ ) r ₂ r ₄ / (r ₂ + r ₄ )
_{= (- Vi / r 1 -V} H / r 6) r 2/3 (31)
It becomes.

Therefore, in the components of the variable resolution circuit 22 of the present embodiment, the resistance value (r ₂ ) of the second to sixth resistors (R2 to R6) among the resistors of the first to sixth resistors (R1 to R6). To r ₆ ) are made equal. That is, the requirement of the invention of the variable resolution circuit 22 of the present invention can be made more reliable by using resistors of the same model number having the same specification standard characteristics.

  Next, a method for determining each resistance of the variable resolution circuit 22 of the present embodiment in consideration of the rated current of the motor 13 as a load will be described with reference to FIG.

  In general, in motor control systems, high resolution is set near the rated current at which the motor is used, and detection is possible with a certain degree of resolution in the large current band to achieve instantaneous high load operation. Then, the current detection device is set so as to achieve a low resolution that the feedback control can be realized.

  If it is desired to obtain a high resolution at any current value, the variable resolution circuit of this embodiment can be applied to the difference between the target value and the measured location. At this time, if the error is large, the control is performed with low resolution, not the control performance, but close to the target value (pseudo bang-bang control). On the other hand, when the error is small, the control performance can be improved because the control can be performed with high resolution. Therefore, it is considered that higher resolution current detection can be realized in any current band. It can also be used effectively as an amplifier for a force sensor.

  A current sensor 21 that is a current detector of the current detector 20 with a variable resolution circuit according to the present embodiment will be described with reference to FIG. The current sensor 21 includes a shunt resistor Rs 211, an insulation amplifier 212, and a non-inverting amplifier circuit 213 having a gain of −1.

Here, it is assumed that the rated current value of the motor 13 is I _r (I _r ≧ 0), the peak current is I _p , the resistance value of the shunt resistor Rs 211 is R _s , and the output gain of the insulation amplifier 212 is C _iso . Then, if the switching point of the current n times of the rated current I _r, the current value I _sw at this switching point is as follows.
| I _sw | = nI _r (32)
The input voltage Vi to the variable resolution circuit 22 at that time is
Vi = −R _s C _iso | I _sw | (I ≧ 0), Vi = R _s C _iso | I _sw |
(I <0) (33)
It becomes. The input voltage Vi to the variable resolution circuit 22 when I _p flows through the shunt resistor Rs211 as the peak current is as follows.
Vi = −R _s C _iso I _p (I ≧ 0), Vi = R _s C _iso I _p (I <0) (34)
However, in this case, I _p ≧ 0.

Therefore, FIG. 7 shows input / output relation values of the variable resolution circuit 22 at the switching point and the measurement limit from the relational expressions (20), (30), and (31). In FIG. 7, the resistance values of the resistor R5 and the resistor R6 are made equal, and the first voltage V _H and the second voltage V so that the characteristics of the output voltage Vo1 are equal depending on whether the input voltage Vi of the input / output characteristics is positive or negative. _{So that} the absolute values of _L are equal,
r ₅ = r ₆ (35)
| V _H | = | V _L | (36)
Then, from the relationship at the switching point,
R _s C _iso nI _r = r ₁ V _H / r ₅ (37)
Is satisfied. Also, from the relationship at the measurement limit,
R _s C _iso nI _p = (1-1 / 2r ₅ ) 2r ₁ V _H / r ₂ (38)
It becomes the relationship.

In the present embodiment, since the desired minimize the current flowing through the respective diodes, it is necessary to increase the resistance value r ₅ of the resistor R2 or the resistor R5. Then, since the input voltage Vi with respect to the first voltage V _H small, to the current flowing through the diode D5 to the minute, increasing the resistance value r ₅ of the resistor R5.

Therefore, if determined resistance value _{r 5} of the resistor R5, the relational expression (37) and 38, the resistance value _{r 2} the following relational expression of the resistance value _{r 1} and a resistance R2 of the resistor R1 (39) and ( 40).
_{r 1 = r 5 R s C} iso nI r / V H (39)
_{r 2 = (1-r 2} / 3r 5) 3r 1 V H / R s C iso nI p (40)

(Comparative example)
A comparative example of the variable resolution circuit 22 of the present invention will be described with reference to FIGS. 8 (a) to 8 (b). This circuit is a circuit called a soft limit circuit, and is a typical circuit used for a feedback loop of an AM modulation circuit (for example, EDN Japan, December 2007, p. 93, Read Business). (See Information Inc.)

  As shown in FIG. 8A, the circuit configuration includes one operational amplifier, two diodes D1 and D2, and six resistors R1 to R6. An input voltage Vi is applied to one end of the resistor R1, an inverting input terminal of the operational amplifier is connected to the other end of the resistor R1, and one end of the resistor R2 is connected in parallel to the inverting input terminal of the operational amplifier. It is connected to the output terminal of the operational amplifier. The anode of the diode D1 is connected in parallel to the inverting input terminal of the operational amplifier, the resistor R3 has one end connected to the cathode of the diode D1, the other end connected to the output terminal of the operational amplifier, and the diode D2 The cathode is connected in parallel to the inverting input terminal of the operational amplifier, and the resistor R4 has one end connected to the anode of the diode D2 and the other end connected to the output terminal of the operational amplifier.

Furthermore, one end of the resistor R5 is connected to the cathode of the diode D1, and the first voltage _VH is applied from the other end. In addition, one end of the resistor R6 is connected to the anode of the diode D2, and the second voltage _VL is applied from the other end. The output of the soft limit circuit is output as the voltage value Vo at the other end of the resistor R2.

As shown in FIG. 8B, the input / output characteristics of this circuit are the same as the characteristics of the variable resolution circuit 22 of the present invention. However, the circuit diagram of FIG. From the regions (1), (2), and (3) to the region (3), that is, the regions (1) and (2) are input except when no current flows through the two diodes D1 and D2. The output characteristics are as follows when ID1> 0 and ID2> 0. Note that will be the resistance value of the resistors Rn described in r _n.
Vo = (− Vi / r ₁ −V _H / r ₅ − (1 / r ₃ + 1 / r ₅ ) V _F1 ) r ₂ r ₃ / (r ₂ + r ₃ )
(41)
And Vo = (− Vi / r ₁ −V _L / r ₆ − (1 / r ₄ + 1 / r ₆ ) V _F2 ) r ₂ r ₄ / (r ₂ + r ₄ )
(42)
Thus, the factors of the forward voltages V _F1 and V _F2 of the two diodes D1 and D2 remain. Therefore, in the comparative example, since temperature compensation cannot be performed due to the occurrence of a temperature change of the forward voltage of the diode, even if two diodes D1 and D2 having the same specification standard characteristic are used, the environment as in the present invention. It cannot be applied to technical fields where temperature changes.

As described above, the variable resolution with circuit current detection device 20 of the present embodiment can detect a supply current I _M to be supplied to the motor (load) 13 at the desired resolution. Further, since a comparator circuit for comparing with the current command value is not required, it is possible to reduce the size of the motor control system. Furthermore, even when there is a change in the operating environment temperature, etc., it is possible to obtain a current detection device having a temperature compensation with a small measurement error caused by the temperature change and having a desired current detection resolution corresponding to the load operation. .

DESCRIPTION OF SYMBOLS 1 ... Motor control system 10 ... PID controller 11 ... PWM generator 12 ... Inverter 13 ... Motor (load)
DESCRIPTION OF SYMBOLS 15 ... Current-voltage conversion 20 ... Current detector with variable resolution circuit 21 ... Current sensor (current detector)
22... Variable resolution circuit 23... A / D converter (conversion means)
211 ... Shunt resistor 212 ... Insulation amplifier 213 ... Non-inverting amplifier circuit Vi ... Input voltage Vo1, Vo ... Output voltage D1, D2, D3, D4, D5, D6 ... Diode I _{D1, I D2} forward current _I 1 of ... diodes D1 and _{D2, I 2, I 3,} I 4, I 5, I 6 ··· current value _{V F, V F1, V F2} , V F3, V _{F4, V} F5, _{V F6} forward voltage of ... diode _I F forward current ... diodes R1, R2, R3, R4, R5, R6, Rn ··· resistance _{r 1,} r 2, _{r 3 , r 4, r 5, r} 6, r n ··· resistance _V H · · · first voltage _V L · · · second voltage _I M · · · supply current _{I FB} · · · feedback current E ... error signal Rs ··· shunt resistor _R s ··· resistance value of the shunt resistor Current value at the output gain _{I SW} · · · switching point of I _r · · · motor rated current value _I p · · · peak current value _{C iso} · · · Isolation Amplifier motor

Claims (7)

A current detector that outputs a voltage proportional to the supply current value supplied to the load;
An operational amplifier that inputs and amplifies the voltage output from the current detector, a diode, and a variable resolution circuit having a resistor;
A current detection device with a variable resolution circuit, comprising: a conversion means for converting a voltage value input to the output of the variable resolution circuit into a digital quantity;
The variable resolution circuit-equipped current detection device with a variable resolution circuit, wherein the gain of the operational amplifier is variable based on the voltage. The variable resolution circuit includes the operational amplifier, first to sixth diodes as the diodes, and first to sixth resistors as the resistors,
The voltage is applied to one end of the first resistor,
The operational amplifier has its inverting input terminal connected to the other end of the first resistor, its input terminal grounded,
One end of the second resistor is connected to the inverting input terminal,
The third diode has an anode connected to the other end of the second resistor, a cathode connected to the output terminal of the operational amplifier,
The fourth diode has a cathode connected to the other end of the second resistor, an anode connected to the output terminal,
The first diode has an anode connected to the inverting input terminal;
The third resistor has one end connected to the cathode of the first diode and the other end connected to the output terminal.
The second diode has a cathode connected to the inverting input terminal;
The fourth resistor has one end connected to the anode of the second diode and the other end connected to the output terminal.
The fifth resistor has one end connected to the cathode of the first diode and the other end connected to the cathode of the fifth diode.
A first voltage is applied to an anode of the fifth diode;
The sixth resistor has one end connected to the anode of the second diode and the other end connected to the anode of the sixth diode.
A second voltage is applied to the cathode of the sixth diode;
The current detection device with a variable resolution circuit according to claim 1, wherein the output of the variable resolution circuit is a voltage at the other end of the second resistor. In the variable resolution circuit,
The current detection device with a variable resolution circuit according to claim 2, wherein the first to sixth diodes have electrical characteristics having equal forward voltages in accordance with a standard. In the variable resolution circuit,
4. The current detection device with a variable resolution circuit according to claim 2, wherein the first to sixth diodes are provided on the same substrate. In the variable resolution circuit,
5. The current detection device with a variable resolution circuit according to claim 2, wherein resistance values of the second resistor to the sixth resistor are equal. 6. In the variable resolution circuit,
6. The current detection device with a variable resolution circuit according to claim 2, wherein absolute values of the first voltage and the second voltage are equal. The current detector with a variable resolution circuit according to claim 1, wherein the current detector includes a shunt resistor.

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