JP2012191805A - Inverter device and electric tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device and an electric tool.SOLUTION: An inverter device 1 has: an inverter circuit 16 for converting a DC power into an AC power depending on a conduction angle that is set, and outputting the AC power to an AC motor 31; a current detection resistance 17 for detecting a load applied to the AC motor 31; and a controller 19 for changing the conduction angle depending on a load detected by the current detection resistance 17. Thereby, the inverter device 1 can cope with a temporary overload applied to the AC motor 31.

Description

  The present invention relates to an inverter device and a power tool.

  Conventionally, an electronic device including an inverter circuit is known. Such an electronic device transforms AC power from a commercial power source with a transformer, rectifies and smoothes it into DC power with a rectifying / smoothing circuit, converts it to predetermined AC power with an inverter circuit, and outputs it to an AC motor or the like. (For example, refer to Patent Document 1).

JP 2009-278832 A

  However, for example, when the electronic device is a lawn mower, the AC motor may be overloaded due to grass jamming in the lawn mower. In such a case, the AC motor is locked and the work is performed. Will be interrupted.

  Then, an object of this invention is to provide the inverter apparatus and electric tool which can respond to the temporary overload concerning a motor.

  The present invention provides an inverter circuit that converts DC power into AC power according to a set conduction angle and outputs the AC power, a load detection unit that detects a load applied to the motor, and a load detected by the load detection unit. According to another aspect of the present invention, there is provided an inverter device comprising control means for changing the conduction angle in response.

  According to such a configuration, when an overload is applied to the motor, the temporarily increased power is supplied to the motor. Is prevented.

  Moreover, it is preferable that the said control means increases the said conduction angle, when the said load becomes more than predetermined value.

  Moreover, it is preferable that the said control means increases the said conduction angle, when the said load is more than the said predetermined value over 1st predetermined time.

  According to such a configuration, it is possible to accurately grasp that the motor is in the locked state or the state close to the locked state, and thus, the power is wasted by increasing the conduction angle in a state other than the locked state or the state close to the locked state. Is prevented.

  Moreover, it is preferable that the said control means reduces the said conduction angle after 2nd predetermined time progress, after increasing the said conduction angle.

  According to such a configuration, it is possible to prevent the motor from being damaged by supplying a large amount of power for a long time.

  Further, the control means decreases the conduction angle when the load detected by the load detection means is less than the predetermined value before the second predetermined time elapses after the conduction angle is increased. It is preferable.

  According to such a configuration, the period during which large electric power is supplied to the motor can be shortened, and the AC motor 31 is more appropriately prevented from being damaged.

  Moreover, according to another viewpoint of this invention, the electric tool provided with the motor and the said inverter apparatus is provided.

  According to the inverter device and the electric tool of the present invention, it is possible to cope with a temporary overload applied to the motor.

The circuit diagram of the inverter apparatus by embodiment of this invention Time chart explaining conduction angle control according to an embodiment of the present invention Flowchart for explaining conduction angle control according to an embodiment of the present invention

  The inverter apparatus 1 by embodiment of this invention is demonstrated using FIGS. 1-3.

  FIG. 1 is a circuit diagram of the inverter device 1. The inverter device 1 is connected between the battery pack 2 and the electric tool 3 in order to convert the DC power supplied from the battery pack 2 into AC power and supply it to the AC motor 31 of the electric tool 3. When the trigger switch 32 of the electric power tool 3 is operated, AC power is supplied to the AC motor 31 from the inverter device 1. Although the inverter apparatus 1 is detachable between the battery pack 2 and the electric tool 3, it demonstrates below as what is connected. In the present embodiment, a lawn mower is assumed as the electric tool 3, but other electric tools such as an electric drill may be used.

  The inverter device 1 includes a battery voltage detection unit 11, a power supply unit 12, a booster circuit 13, a rectification / smoothing circuit 14, a boost voltage detection unit 15, an inverter circuit 16, and a current detection resistor (load detection of the present invention). Means) 17, a PWM signal output section 18, and a control section (control means of the present invention) 19.

  The battery voltage detection unit 11 includes battery voltage detection resistors 111 and 112. The battery voltage detection resistors 111 and 112 are connected in series between the positive terminal 21 and the negative terminal 22 of the battery pack 2, and the battery voltage detection resistor 111 and the battery voltage detection resistor of the battery voltage of the battery pack 2 are connected. The voltage divided by 112 is output to the control unit 19. The battery pack 2 shown in FIG. 1 has four lithium battery cells of 3.6V / cell connected in series and outputs a rated voltage of 14.4V.

  The power supply unit 12 includes a power switch 121 and a constant voltage circuit 122 connected in series between the plus side terminal 21 of the battery pack 2 and the control unit 19. The constant voltage circuit 122 includes a three-terminal regulator 122a and oscillation preventing capacitors 122b and 122c. When the power switch 121 is turned on by the user, the voltage from the battery pack 2 is changed to a predetermined DC voltage (for example, 5V) and supplied to the control unit 19 as drive power. Note that when the power switch 121 is turned off, the driving power is not supplied to the control unit 19, so that the entire inverter device 1 is turned off.

  The booster circuit 13 includes a transformer 131 and an FET 132, and the transformer 131 includes a primary side winding 131a and a secondary side winding 131b.

  The primary side winding 131a is connected between the plus side terminal 21 and the minus side terminal 22 of the battery pack 2, and an FET 132 is further provided between the primary side winding 131a and the minus side terminal 22 of the transformer 131. Has been placed. A first PWM signal for turning on / off the FET 132 is input to the gate of the FET 132 from the control unit 19, and the DC power supplied from the battery pack 2 is converted into AC power by turning on / off the FET 132. The voltage is output to the primary winding 131a of the transformer 131. The AC power input to the primary side winding 131a is transformed according to the turn ratio between the primary side winding 131a and the secondary side winding 131b and output from the secondary side winding 131b.

  The rectifying / smoothing circuit 14 includes rectifying diodes 141 and 142, and a smoothing capacitor 143. With these, the AC power boosted by the transformer 131 is rectified and smoothed and output as DC power.

  The boosted voltage detection unit 15 includes resistors 151 and 152 connected in series with each other, detects a DC boosted voltage (smoothing capacitor voltage, for example, 140 V) output from the rectifying / smoothing circuit 14, and detects the boosted voltage. The voltage divided by the resistor 151 and the resistor 152 is output to the control unit 19.

  The inverter circuit 16 includes four FETs 161 to 164, and FETs 161 and 162 connected in series and FETs 163 and 164 connected in series are connected in parallel to the smoothing capacitor 143. Specifically, the drain of the FET 161 is connected to the cathodes of the rectifier diodes 141 and 142, and the source of the FET 161 is connected to the drain of the FET 162. The drain of the FET 163 is connected to the cathodes of the rectifier diodes 141 and 142, and the source of the FET 163 is connected to the drain of the FET 164.

  Further, the source of the FET 161 and the drain of the FET 162, the source of the FET 163 and the drain of the FET 164 are connected to the output terminals 165 and 166, respectively, and the output terminals 165 and 166 are connected to the AC motor 31. A second PWM signal for turning on / off the FET 161-164 is input from the PWM signal output unit 18 to the gate of the FET 161-164, and is output from the rectifying / smoothing circuit 14 by turning on / off the FET 161-164. The direct current power is converted into alternating current power and output to the electric power tool 3 (AC motor 31).

  The first current detection resistor 17 is connected between the source of the FET 162 and the source of the FET 164 and the negative side terminal 22 of the battery pack 2, and the high voltage side terminal of the first current detection resistor 17 is controlled. The unit 19 is connected. With such a configuration, the first current detection resistor 17 detects the current flowing through the AC motor 31 and outputs it as a voltage to the control unit 19.

  Based on the boosted voltage detected by the boosted voltage detection unit 15, the control unit 19 outputs a first PWM signal such that AC power having a target effective value (for example, 141 V) is output from the secondary side of the transformer 131. Output to the gate of the FET 132. In addition, the control unit 19 outputs a second PWM signal such that AC power having a target effective value (for example, 100 V) is output to the AC motor 31 to the gates of the FETs 161 to 164 via the PWM signal output unit 18. To do. In the present embodiment, at the normal time, the control unit 19 sets the FET 161 and the FET 164 (hereinafter referred to as the first set), the FET 162 and the FET 163 (hereinafter referred to as the second set) as one set, and the first set. And a second PWM signal for alternately turning on and off the second set at a duty ratio of 50%.

  In addition, the control unit 19 determines overdischarge of the battery pack 2 based on the battery voltage detected by the battery voltage detection unit 11. Specifically, when the battery voltage detected by the battery voltage detection unit 11 is smaller than a predetermined overdischarge voltage, it is determined that the battery pack 2 is overdischarged and the output to the AC motor 31 is stopped. The first PWM signal and the second PWM signal for outputting are output. Further, the battery pack 2 includes a protection IC and a microcomputer inside, and has a function of detecting overdischarge by itself and outputting an overdischarge signal to the control unit 19. The control unit 19 is connected to the signal terminal LD. Even when the overdischarge signal is received, the first PWM signal and the second PWM signal for stopping the output to the AC motor 31 are output. With such a configuration, it is possible to prevent the life of the battery pack 2 from being shortened.

  By the way, for example, when the electric power tool 3 is a lawn mower, the AC motor 31 may be overloaded due to grass caught in the lawn mower. In such a case, the AC motor 31 is locked. The work will be interrupted.

  Therefore, in the inverter device 1 according to the present embodiment, the control unit 19 changes the ON period of the first set and the second set, that is, the conduction angle, according to the current detected by the current detection resistor 17. .

  Specifically, the second PWM signal for increasing the conduction angle when the current detected by the current detection resistor 17 exceeds a predetermined value (5.8 A in the present embodiment) is supplied to the FETs 161-164. Output to the gate.

  Normally, the ON period of the first set and the second set is controlled with a conduction angle of 90 degrees as shown in FIG. As shown in FIG. 2 (c), (1) in FIG. 2 (a) is a period in which only the first set is on, and (3) in FIG. 2 (a) is the second set. 2 is a period in which only both are on, and (2) and (4) in FIG. 2A are periods in which both are off.

  On the other hand, in the present embodiment, the conduction angle is increased to 150 when the current detected by the current detection resistor 17 exceeds a predetermined value. Specifically, as shown in FIG. 2B, the period remains constant and only the first set is on (1) and only the second set is on (3). And decrease the period when both are off.

  As shown in FIG. 2 (d), when considering the case where AC power with a frequency of 50 Hz (period 20 ms) is output, when the conduction angle is set to 90 degrees, the first set and the second The on time of the set is 5 ms, but when the conduction angle is 150 degrees, it increases to 8.3 ms.

  As a result, for example, when the AC motor 31 is overloaded due to grass caught in the lawn mowing portion of the electric power tool 3, the temporarily increased power is supplied to the AC motor 31. Therefore, it becomes possible to remove the jammed grass from the lawn mowing unit, and the AC motor 31 is prevented from being locked and the work being interrupted.

  Further, the current detected by the current detection resistor 17 may temporarily increase due to noise or the like. However, if the conduction angle is increased to such a case, power is wasted.

  Therefore, in the present embodiment, the conduction angle is increased when the current detected by the current detection resistor 17 is equal to or greater than the predetermined value over a first predetermined time (2 s in the present embodiment). As a result, it is possible to accurately grasp that the AC motor 31 is in the locked state or the state close to the locked state. Therefore, it is possible to waste power by increasing the conduction angle in a state other than the locked state or the state close to the locked state. Is prevented.

  In addition, there may be a case where entangled grass cannot be removed from the lawn mowing unit by increasing the conduction angle. In such a case, if a large amount of power is supplied to the AC motor 31, the AC motor 31 is damaged. There is a fear.

  Therefore, in the present embodiment, the conduction angle is decreased after the second predetermined time (3 s in the present embodiment) has elapsed since the conduction angle was increased. Thus, it is possible to prevent the AC motor 31 from being damaged by supplying a large amount of power for a long time.

  Furthermore, in the present embodiment, when the load detected by the current detection resistor 17 becomes less than the predetermined value before the second predetermined time elapses, the conduction angle is decreased at that time. Thereby, the period during which large electric power is supplied to the AC motor 31 can be shortened, and the AC motor 31 is more appropriately prevented from being damaged.

  Next, the operation of the control unit 19 will be described using the flowchart of FIG.

  In the flowchart of FIG. 3, when the power switch 121 is turned on while the battery pack 2 is attached to the inverter device 1, or the battery pack 2 is attached to the inverter device 1 while the power switch 121 is turned on. Start when When the power switch 121 is turned on, a voltage is supplied from the voltage of the battery pack 2 to the constant voltage circuit 122, whereby the drive voltage of the control unit 19 is generated and the control unit 19 operates. In this flowchart, the control unit 19 acquires the current detected by the current detection resistor 17 every predetermined sampling period (hereinafter, detected current).

  First, after setting the conduction angle to 90 degrees as an initial value (S301), the control unit 19 determines whether or not the detected current is equal to or greater than a predetermined value (5.8 A in the present embodiment). (S302).

  If the detected current is greater than or equal to a predetermined value (S302: YES), then, for the first predetermined time (2 s in the present embodiment) after first being determined as “YES” in S302. It is determined whether or not the detected current is greater than or equal to a predetermined value (S303). Here, for example, the time at which “YES” is first determined in S302 is stored, and whether or not all of the plurality of detected currents detected from the time until the first predetermined time elapses are equal to or greater than the predetermined value. It may be determined whether or not.

  If the detected current is equal to or greater than the predetermined value for the first predetermined time (S303: YES), the conduction angle is increased to 150 degrees (S304).

  Subsequently, in order to determine whether or not grass jammed in the lawn mower has been removed by increasing the conduction angle in S304, it is determined whether or not the detected current has decreased to the predetermined value or less (S305). ).

  If the detected current has fallen below the predetermined value (S305: YES), it is considered that grass or the like stuck in the lawn mower has been removed by increasing the conduction angle. Is reset to 90 degrees (S307).

  On the other hand, if the detected current has not decreased below the predetermined value (S305: NO), it is considered that the grass stuck in the lawn mower is not removed even if the conduction angle is increased. Then, it is determined whether or not the detected current is larger than the predetermined value over a second predetermined time (3 s in the present embodiment) after it is initially determined “NO” in S305 (S306). Also here, for example, the time when “NO” is first determined in S305 is stored, and the plurality of detected currents detected from the time until the second predetermined time elapses are all larger than the predetermined value. It may be determined whether or not.

  If the detected current is larger than the predetermined value over the second predetermined time (S306: YES), the grass stuck in the lawn mower is not removed, but the conduction angle is increased further. The AC motor 31 may be damaged. Accordingly, in this case, the conduction angle is reset to the initial value of 90 degrees (S307).

  Subsequently, the control unit 19 outputs a first PWM signal such that AC power having a target effective value (for example, 141) is output from the secondary side of the transformer 131 to the gate of the FET 132 (S308). Based on the voltage detected by the voltage detector 15, it is determined whether or not the effective value of the voltage boosted by the transformer 131 is larger than the target effective value (S309).

  When the boosted voltage is larger than the target effective value (S309: YES), the duty ratio of the FET 132 is decreased (S311). When the boosted voltage is less than the target effective value (S309: NO), the FET 132 Is increased (S310).

  Subsequently, based on the voltage detected by the battery voltage detector 11, it is determined whether or not the battery voltage of the battery pack 2 is smaller than a predetermined overdischarge voltage (S312). When the voltage is smaller than the predetermined overdischarge voltage (S312: YES), it is determined that the battery pack 2 is in an overdischarge state, and the first PWM signal and the second PWM for stopping the output to the AC motor 31 are determined. A signal is output (S314). Thereby, the operation of the booster circuit 13 and the inverter circuit 16 is stopped, and the output from the inverter device 1 to the AC motor 31 is stopped.

  If the battery voltage of the battery pack 2 is equal to or higher than the predetermined overdischarge voltage (S312: NO), it is determined whether or not an overdischarge signal is input from the battery pack 2 via the LD terminal (S313). If an overdischarge signal has been input (S313: YES), it is determined that the battery pack 2 is in an overdischarge state, and the first PWM signal and the second PWM signal for stopping output to the AC motor 31 are determined. A PWM signal is output (S314).

  As described above, in the inverter device 1 according to the present embodiment, the ON period of the first set and the second set, that is, the conduction angle is changed in accordance with the current detected by the current detection resistor 17. When the motor 31 is temporarily overloaded, it is possible to prevent the AC motor 31 from being locked and interrupting the work.

  The power tool of the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made within the scope described in the claims.

  For example, in the above embodiment, 90 degrees and 150 degrees are used as the conduction angles, but the present invention is not limited to these.

  Further, in the flowchart of FIG. 3, the control of the boosted voltage in S308-S311 and the overdischarge detection in S312 to S313 may be performed at any position in the flowchart of FIG. It may be done.

  Further, when the current (voltage) detected by the current detection resistor 17 is equal to or larger than a second predetermined value larger than the predetermined value, the control unit 19 determines an overcurrent and changes the conduction angle. The power supply to the AC motor 31 may be stopped without performing the above.

  In the above-described embodiment, the load applied to the AC motor 31 is determined based on the current applied to the AC motor 31, but may be determined based on other factors such as the voltage applied to the AC motor 31, for example. Good.

DESCRIPTION OF SYMBOLS 1 Inverter apparatus 3 Electric tool 16 Inverter circuit 17 Current detection resistance 19 Control part 31 AC motor

Claims (6)

An inverter circuit that converts DC power into AC power according to the set conduction angle and outputs the AC power to the motor;
Load detecting means for detecting a load applied to the motor;
Control means for changing the conduction angle according to the load;
An inverter device comprising:   The inverter device according to claim 1, wherein the control unit increases the conduction angle when the load becomes a predetermined value or more.   The inverter device according to claim 2, wherein the control unit increases the conduction angle when the load is equal to or greater than the predetermined value for a first predetermined time.   4. The inverter device according to claim 2, wherein the control unit decreases the conduction angle after a second predetermined time has elapsed after increasing the conduction angle. 5.   The control means decreases the conduction angle when the load detected by the load detection means is less than the predetermined value before the second predetermined time elapses after increasing the conduction angle. The inverter apparatus according to claim 4. The motor;
An inverter device according to any one of claims 1 to 5;
An electric tool comprising:

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