JP2011244635A - Control method of inverter device for driving brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate current detection method even when using a current transformer in which the method solves problems in an existing control method of an inverter device, since the current transformer has temperature characteristics, a deviation between an actual current value and a detected current value is measured when a temperature is high, that is, the actual current value differs from the detected current value by a drift caused by temperature characteristics of a current detecting element.SOLUTION: A control method of an inverter device estimates a temperature difference between an ambient temperature and a device temperature warmed by self-heating to correct a detected current value, thereby realizing a highly accurate current detection even if a temperature of the current transformer varies significantly.

Description

  The present invention relates to a method for controlling an inverter device used for sensorless driving of a brushless motor.

  The conventional technique will be described with reference to FIG. FIG. 5 is a diagram showing an embodiment of a motor control apparatus according to a conventional invention.

  This motor control device is supplied with the output of a rectifier circuit 32 having an AC power supply 31 as an input, a three-phase inverter circuit (power device) 33 having a DC output of the rectifier circuit 32 as an input, and the three-phase inverter circuit 33. An OCP unit 35b that performs OCP provided at a predetermined position of a DC link that connects the motor 34, the rectifier circuit 32, and the three-phase inverter circuit 33; a phase current calculation unit 36 that calculates the phase current of the motor 34; A driver 39 for supplying a switching signal to the switching element of the phase inverter circuit 33 and outputting output voltage information is provided.

  Further, the motor control device receives a phase current and an output voltage as inputs, a position / speed detector 37 for detecting the rotation position and rotation speed of the rotor of the motor 34, and a rotation speed command and a detected rotation speed as inputs. A speed control unit 38 that performs control calculation and outputs an output current command; a current command limiting unit 40 that receives the output current command and clamps the output current command to be a current command equal to or less than OCP; and a current command limiting unit A current control unit 41 that compares the output current command output from 40 and the detected phase current, creates a voltage command so that the phase current becomes the output current command, and supplies the voltage command to the driver 39; .

  The OCP unit 35b receives a shunt resistor 35a inserted in the DC link and a voltage across the shunt resistor 35a as a predetermined threshold (a value corresponding to the maximum current set from the limit current of the power device or the motor). And an OCP unit 35b for outputting a DC link current Idc.

  The phase current calculation unit 36 receives the DC link current Idc and calculates the phase current. The calculation of the phase current is conventionally known.

  If the motor controller with the above configuration is used, the output current command is limited to a current command below the overcurrent protection, so that the motor can be driven without causing an overcurrent protection stop due to an instantaneous overload. Can continue. In addition, hardware for current detection can be simplified.

  Furthermore, for example, when an error in DC link current detection that becomes the OCP lower limit value occurs, the error is set to the phase current limit lower limit value in phase current detection due to sharing of current detection. As a result, it is possible to prevent the OCP from being applied before the phase current is limited.

  As a result, the mutual variation (the variation that one is large and the other is small) that occurs when two current detection units are provided is eliminated, and the phase current lower limit value that is the lower limit of the maximum output of the three-phase inverter circuit 33 Thus, the range up to the OCP upper limit value, which is the maximum current during protection, can be narrowed. As a result, the capacity of the power device of the three-phase inverter circuit 33 and the capacity of the motor 34 can be reduced.

  Furthermore, current detection imbalance between phases can be prevented.

JP 2003-111479 A

  However, the conventional configuration has a problem that the detected current value is different from the flowing current by the variation due to the temperature characteristic of the current detection element.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a highly accurate current detection method using a current transformer 3a.

  In order to solve the above-described conventional problems, the inverter device of the present invention corrects the detected current value by estimating the temperature difference due to the ambient temperature and self-heating.

  The inverter device of the present invention can realize accurate current detection even when the temperature of the current transformer 3a varies greatly.

Circuit block diagram in Embodiment 1 of the present invention Temperature characteristic value graph of current transformer in Example 1 of the present invention Graph of motor current and temperature rise value in Example 1 of the present invention The graph of the time change of the temperature rise value in Example 1 of this invention Circuit block diagram of conventional example

  According to a first aspect of the present invention, the current value output from the current transformer is estimated and corrected by the temperature characteristics of the current transformer, the output of the ambient temperature detection circuit, the operating current, and the operating time, thereby correcting the temperature characteristics depending on the ambient temperature. It is possible to perform control with an output value closer to reality than the output fluctuation of minutes.

(Embodiment 1)
The embodiment of the present invention will be described with reference to FIGS. 1, 2, 3, and 4. FIG.

  In FIG. 1, a DC power source 1 is made by rectifying an AC power source and becomes a power source for an inverter. The three-phase full bridge circuit 2 is connected to the DC power source 1 on the input side and is driven by a command from the control unit 4. The current transformer 3a transmits the current flowing through the primary winding, which is the main line, to the secondary side by the action of mutual induction of the transformer. As a result, the primary side current, the current determined by the turn ratio of the primary side and secondary side windings, or the current is converted into a voltage and output. The control unit 4 performs an operation based on the output value from the current transformer 3a and outputs a drive command of a predetermined pattern to the three-phase full bridge circuit 2. It also has a function to measure the operating time.

The three-phase brushless motor 5 is a three-phase brushless motor that mechanically rotates in response to a predetermined pattern of power supplied from the three-phase full bridge circuit 2. The thermistor 6 detects the ambient temperature of the apparatus. The fan motor 7 is used for cooling the apparatus. Or if it is the inverter apparatus for compressors of an air conditioner, it may be used also for cooling of a control apparatus, using for the structure of a refrigerating cycle. The control device is housed in the case 8 of the inverter device. These organically relate to each other and constitute an inverter device for driving the three-phase brushless motor 5 sensorlessly.

  A method for correcting the current transformer output of the inverter driving apparatus configured as described above will be described below.

  FIG. 2 shows the output fluctuation value due to the temperature of the current transformer 3a as a solid line. This value is usually provided as a part specification. If the output voltage V25 when the temperature is 25 ° C. is used as a reference, if the temperature fluctuates by ΔT1, the output fluctuates by ΔV1. This indicates that the output increases or decreases in proportion to the temperature, and that the effect on the output increases as the temperature difference from the reference increases. Therefore, when power is supplied from the three-phase full bridge circuit 2 to the three-phase brushless motor 5 through the current transformer 3a under a certain operating condition, heat is generated due to power loss due to the current and component impedance. If the ambient temperature of the current transformer 3a in the case 8 fluctuates due to this heat generation, it will be affected by the output fluctuation as shown in FIG.

  For this reason, a more accurate current detection is performed by estimating a temperature change due to operating conditions and performing a correction by adding a temperature change outside the case 8 to this. The method is shown below.

  The temperature rise value ΔTr of the current transformer is obtained from the power loss P0 and the thermal resistance Rt, and is expressed by the following equation which is the product of this and the time constant depending on time. Ct represents heat capacity.

  Here, when there is a rise in space temperature due to a rise in the temperature of components around the current transformer, it is necessary to consider the value. When the total temperature rise value is expressed as ΔT,

  Here, Rp1,... Rpn represents thermal resistance of peripheral components, Ppn1... Ppn represents power loss of peripheral components, and Ctp1,. Pp1 × Rp1 +... Ppn × Rpn in Equation 2 is considered as a temperature rise value of the surrounding space other than the current transformer 3a and is set as ΔTpn, and Rt + Rp1.

  Can be expressed as

  Here, the power loss P0 of the current transformer 3a is expressed by the product of the square of the output current I0 to the motor and the impedance Z0 of the path, and is given by the following equation.

  The temperature rise value ΔTr can be modified as follows, except for the time constant term of the equation (1).

  Here, if Z0 × Rt is a constant K,

  The constant K can be calculated from the known current I0 by the control unit 4 from the temperature rise value ΔTr at the stable time and the output value of the motor control, and needs to be stored in advance. FIG. 3 shows the relationship between ΔT, ΔTr, ΔTpn and motor current I0 when the change in ΔTpn is considered to be dominated by the influence of the motor current.

  The term [1-exp {−t / (Rt0 × Ct0)}] representing the time constant is obtained by measuring the time during which the temperature rise value ΔT is 63.2% of the stable time. This is shown in FIG. Rt0 and Ct0 take predetermined values depending on the physical structure. However, when the fan motor 7 is driven by an inverter, it varies depending on the flow rate. Therefore, it is necessary to measure in advance in the system use state and store it in the control unit 4. is there.

  The actual control value is calculated from the above values as follows. A correction value ΔVs based on the difference ΔTs between the temperature Ta detected by the thermistor 6 and the reference temperature T25 is employed. Since the surrounding heat generation has not occurred for a while at the start of operation, the ambient temperature of the current transformer 3 a can be regarded as equivalent to the outside air temperature Ta detected by the thermistor 6. Here, ΔVs corresponding to ΔTs can be calculated from ΔTs, whereby an initial correction value is determined, and an output corresponding to 0 A is set to Vos = V25 + ΔVs.

  The correction value ΔT1 is obtained from FIG. 3 based on the operating current I1 of the three-phase brushless motor 5. ΔTs + ΔT1 is the final temperature rise value. Further, more accurate control can be performed by selecting the time constant of temperature change from 2c and updating the correction value according to the operation time.

  Note that since the temperature rise is relatively slow with respect to the motor control, it is sufficient to update the correction value once every few minutes.

  The present invention can be widely applied to inverter drive circuits.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 3 phase full bridge circuit 3a Current transformer 4 Control part 5 3 phase brushless motor 6 Thermistor 7 Fan motor 8 Case 31 AC power supply 32 Rectifier circuit 33 Three phase inverter circuit 35b OCP part 35a Shunt resistance 36 Phase current calculation part 37 Position / speed detector 38 Speed controller 39 Driver 40 Current command limiter 41 Current controller

Claims (2)

A motor, an inverter circuit composed of a three-phase full-bridge circuit for driving the motor, a current transformer for detecting a current flowing through the inverter circuit, an outside air temperature detection circuit for detecting an ambient temperature of the current transformer, In the inverter drive circuit configured by the control unit, the control unit corrects the current value detected by the current transformer based on the temperature characteristics of the current transformer, the output of the outside air temperature detection circuit, the operation time, and the operation current. And a method for controlling an inverter device for driving a brushless motor, characterized by being used for inverter control. The inverter drive circuit according to claim 1, further comprising a current transformer temperature detection circuit for measuring a temperature of the current transformer, wherein the temperature detected by the current transformer temperature detection circuit is corrected based on a temperature characteristic and used for control. A control method for an inverter device for driving a brushless motor.