JP6845655B2 - Electric work machine - Google Patents

Description

The present disclosure relates to a technique for PWM controlling a motor of an electric work machine.

Various electric working machines configured to PWM control the energization of the motor are known (see, for example, Patent Document 1). This type of electric work machine generally includes a bridge circuit having a plurality of switching elements. The bridge circuit consists of a plurality of switching elements (hereinafter referred to as high-side switches) provided between the positive electrode side of the DC power supply and each terminal of the motor, and between the negative electrode side of the DC power supply and each terminal of the motor. It has a plurality of provided switching elements (hereinafter, low-side switches).

In PWM control, a pair of high-side switches and low-side switches that form an energization path from the DC power supply to the motor are selected, one of which is kept on and the other is periodically turned on at a predetermined duty ratio. By turning it off, the current flowing through the motor is controlled.

Further, as PWM control, a control method called complementary PWM is known. Complementary PWM is to turn on another switching element connected to the motor terminal to which the switching element is connected during the off period of the switching element which is periodically turned on / off.

Japanese Unexamined Patent Publication No. 2011-101923

In complementary PWM, in order to prevent the high-side switch and low-side switch connected to the same motor terminal from being turned on at the same time, both are turned off and the other is turned on. It is common to have a dead time that keeps both off.

However, by providing a dead time, in complementary PWM, it may be difficult to appropriately adjust the duty ratio in a region where the duty ratio is close to 100%. As an example, it is assumed that the ratio of the dead time in the PWM carrier cycle is 7%. In this case, considering the dead time, it becomes difficult to perform PWM control with a duty ratio exceeding 93%. Therefore, in complementary PWM, if control is performed at a high duty ratio close to 100%, motor hunting and noise may occur.

One aspect of the present disclosure is to make it possible to appropriately perform PWM control at a set duty ratio in an electric work machine configured to PWM control the energization of a motor by using complementary PWM. To do.

One aspect of the present disclosure is an electric work machine, which includes a motor, a bridge circuit, and a control unit. The motor has a plurality of terminals for power input. The bridge circuit has a plurality of switching elements provided between the positive electrode side of the DC power supply and each of the plurality of terminals of the motor, and between the negative electrode side of the DC power supply and each of the plurality of terminals of the motor. .. The control unit keeps the first switching element of one of the pair of positive and negative switching elements forming the energization path of the motor from the positive side to the negative side of the DC power supply in the bridge circuit in the ON state, and the other second switching. By turning the element on and off according to the set duty ratio, PWM control for controlling the current flowing to the motor according to the duty ratio is executed.

Then, the control unit executes complementary PWM and non-complementary PWM as PWM control. Complementary PWM refers to the third switching element, which is another switching element connected to the terminal of the motor to which the second switching element is connected, while the second switching element is turned off each time the second switching element is turned off. It is configured to be turned on during a specific on-period in. The non-complementary PWM is configured to perform non-complementary PWM that keeps the third switching element in the off state regardless of whether the second switching element is on or off.

Then, the control unit executes complementary PWM when the set duty ratio is less than the threshold value, and executes complementary PWM when the set duty ratio is equal to or more than the threshold value.
According to such a configuration, when the set duty ratio is equal to or higher than the threshold value, non-complementary PWM is executed. Therefore, by appropriately setting the threshold value, PWM control is appropriately performed at the set duty ratio as a whole. It becomes possible to do.

In the complementary PWM, the third switching element is turned on after the dead time elapses after the second switching element is turned off in each PWM carrier cycle, and the second switching element is turned on after the turned on third switching element is turned off and after the dead time elapses. It may be configured to turn on the switching element. The PWM carrier cycle is a cycle when the second switching element is periodically turned on and off according to the duty ratio. The dead time is a time set to turn off both the second switching element and the third switching element.

Then, the threshold value may be a value of the ratio of the time obtained by subtracting a specific time at least twice the dead time from the PWM carrier cycle with respect to the PWM carrier cycle. That is, the ratio of the time obtained by subtracting a specific time at least twice the dead time from the PWM carrier cycle and the PWM carrier cycle may be used as the threshold value.

According to such a configuration, when the on-time of the second switching element indicated by the set duty ratio is at least the time obtained by subtracting twice the dead time from the PWM carrier period, the complementary PWM is not executed. The non-complementary PWM will be executed. Therefore, it is possible to set an appropriate threshold value in consideration of the dead time.

In the complementary PWM, when the minimum on-time, which is the minimum value of the on-period length of the third switching element, is determined and the on-period length is set to at least the minimum on-time or more, The specific time may be equal to or longer than the time obtained by adding the minimum on-time to twice the dead time.

According to such a configuration, the on-time of the second switching element indicated by the set duty ratio is at least the sum of twice the dead time and the minimum on-time of the third switching element reduced from the PWM carrier period. If it is more than the time, the complementary PWM is not executed and the non-complementary PWM is executed. Therefore, it is possible to set a more appropriate threshold value in consideration of the minimum on-time of the third switching element in addition to the dead time.

When the minimum on-time of the third switching element is set in the complementary PWM, the specific time may be a time obtained by adding the minimum on-time to twice the dead time. According to such a configuration, complementary PWM can be executed up to the maximum duty ratio that is not affected by the dead time and the minimum on-time of the third switching element. Therefore, it is possible to realize an appropriate PWM control as a whole, and to maximize the effect obtained by using the complementary PWM.

It is a perspective view which shows the structure of the electric work machine of embodiment. It is a block diagram which shows the electric structure of the electric work machine of embodiment. It is explanatory drawing which shows the outline of the PWM control of an embodiment. It is explanatory drawing which shows an example of PWM without complementation. It is explanatory drawing which shows an example of the complementary PWM of 1st Embodiment. It is explanatory drawing for demonstrating the current flow at the time of execution of complementary PWM. It is explanatory drawing for demonstrating that there is an upper limit of the set duty ratio which can perform complementary PWM normally. It is explanatory drawing for demonstrating the problem which occurs when the complementary PWM is used. It is explanatory drawing which shows the feature which the PWM control of 1st Embodiment has. It is a flowchart which shows the PWM control processing of 1st Embodiment. It is explanatory drawing which shows an example of the complementary PWM of the 2nd Embodiment. It is explanatory drawing for demonstrating the upper limit of the set duty ratio which can be set in the complementary PWM of 2nd Embodiment. It is explanatory drawing which shows the feature which the PWM control of 2nd Embodiment has. It is a flowchart which shows the PWM control process of 2nd Embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
[1. First Embodiment]
(1-1) Configuration of Electric Work Machine The electric work machine 1 shown in FIG. 1 is configured as a brush cutter mainly used for cutting objects to be cut such as grass and small-diameter trees. The electric work machine 1 of the present embodiment includes a main pipe 2, a rear end unit 3, a tip unit 4, and a handle 6.

The main pipe 2 is formed in the shape of a long and hollow rod. The tip unit 4 is provided on the front end side of both ends in the longitudinal direction of the main pipe 2. The rear end unit 3 is provided on the rear end side of both ends in the longitudinal direction of the main pipe 2.

A cutting blade 5 is detachably attached to the tip unit 4. The cutting blade 5 is a working element for cutting an object to be cut. A cover 13 is provided on the front end side of the main pipe 2. The cover 13 is provided to prevent the object to be cut cut by the cutting blade 5 from flying to the user of the electric work machine 1.

The tip unit 4 is equipped with a motor 25 for rotationally driving the cutting blade 5. The motor 25 is not shown in FIG. 1 and is shown in FIG. The rotational force of the motor 25 is transmitted to a drive shaft (not shown) via a reduction mechanism (not shown). A cutting blade 5 is mounted on the drive shaft, and when the motor 25 rotates, the rotational force is transmitted to the drive shaft, and the cutting blade 5 rotates together with the drive shaft. The rotation speed of the cutting blade 5 and the rotation speed of the motor 25 have a substantially linear relationship, and the higher the rotation speed of the motor 25, the higher the rotation speed of the cutting blade 5.

The handle 6 is formed in a U shape and is connected to the main pipe 2 in the vicinity of an intermediate position in the front-rear direction of the main pipe 2. A right grip 7 that the user grips with the right hand is provided on one end side of both ends of the handle 6, and a left grip 8 that the user grips with the left hand is provided on the other end side.

A forward / reverse switching lever 9, a lock-off button 10, and a trigger operation unit 11 are provided on the tip end side of the right grip 7. The forward / reverse switching lever 9 is a switch for switching the rotation direction of the motor 25, that is, the rotation direction of the cutting blade 5, to either forward rotation or reverse rotation.

The trigger operation unit 11 is an operation member that receives a drive operation for rotationally driving the motor 25 by the user of the electric work machine 1. The trigger operation unit 11 cannot be driven unless the lock-off button 10 is pressed. The lock-off button 10 is a button for suppressing a malfunction of the cutting blade 5.

Inside the right grip 7, a trigger switch 38 that operates in conjunction with the trigger operation unit 11 is built. The trigger switch 38 is not shown in FIG. 1 and is shown in FIG.

The trigger switch 38 turns on when the trigger operation unit 11 is driven (for example, pulled), and turns off when the trigger operation unit 11 is not driven. When the electric work machine 1 is activated by turning on the main switch 16 described later and the trigger switch 38 is turned on by the operator driving the trigger operation unit 11, the motor 25 is energized. The motor 25 rotates.

A wiring pipe 12 is provided between the right grip 7 and the rear end unit 3. The wiring pipe 12 is formed in the shape of a hollow rod, and inside, wiring for electrically connecting the trigger switch 38 and the forward / reverse switching lever 9 to the rear end unit 3 is arranged.

The rear end unit 3 is configured so that the battery pack 20 can be attached and detached on the surface on the rear end side. The battery pack 20 contains the battery 21. When the battery pack 20 is mounted on the rear end unit 3, the electric work machine 1 is configured so that the motor 25 can be rotationally driven by the battery power, which is the power supplied from the battery 21.

A speed change dial 15 and a main switch 16 are provided on the front side of the upper surface of the rear end unit 3 in a state in which an operator can operate the rear end unit 3, and a lamp 17 is further provided.
The main switch 16 is a switch for making the electric work machine 1 usable. When the operator turns on the main switch 16, each part in the rear end unit 3 is activated, and the motor 25 can be rotated by the driving operation to the trigger operation part 11.

The speed change dial 15 is a rotary type operating member operated by an operator to set a target rotation speed, which is a target value of the rotation speed of the motor 25. The lamp 17 is provided to display various states of the electric work machine 1.

The electrical configuration of the electric working machine 1 will be described with reference to FIG. As shown in FIG. 2, the electric work machine 1 includes a battery pack 20, a motor 25, and a controller 30.
The controller 30 is configured to receive power from the battery 21 in the battery pack 20 to drive and control the motor 25.

The motor 25 is a brushless motor configured to rotate by three-phase electric power in the present embodiment. The motor 25 has three windings 26, 27, 28. In this embodiment, as an example, these three windings 26, 27, 28 are delta-connected. Further, the motor 25 includes three terminals 25a, 25b, and 25c as terminals for power input.

The controller 30 includes a bridge circuit 31, a gate circuit 32, a control circuit 33, and a regulator 34. The bridge circuit 31 is a circuit for receiving electric power from the battery 21 and passing a current through the windings 26, 27, 28 of the motor 25. In the present embodiment, the bridge circuit 31 is configured as a three-phase full bridge circuit having six switching elements UH, VH, WH, UL, VL, and WL.

In the bridge circuit 31, the three switching elements UH, VH, and WH as high-side switches are connected to the terminals 25a, 25b, and 25c of the motor 25 and the positive electrode side of the battery 21 (positive electrode side power supply line). It is provided between and each. Further, the three switching elements UL, VL, and WL as low-side switches are located between the terminals 25a, 25b, and 25c of the motor 25 and the ground line (negative electrode side power supply line) connected to the negative electrode side of the battery 21. , Each is provided.

That is, of the three terminals 25a, 25b, and 25c of the motor 25, the terminal 25a has a switching element UH as a high-side switch (hereinafter, also referred to as "U-phase high-side switch UH") and a switching element as a low-side switch. UL (hereinafter, also referred to as "U-phase low side switch UL") is connected. Further, the terminal 25b has a switching element VH as a high-side switch (hereinafter, also referred to as "V-phase high-side switch VH") and a switching element VL as a low-side switch (hereinafter, also referred to as "V-phase low-side switch VL"). Is connected. Further, the terminal 25c has a switching element WH as a high-side switch (hereinafter, also referred to as “W-phase high-side switch WH”) and a switching element WL as a low-side switch (hereinafter, also referred to as “W-phase low-side switch WL”). Is connected.

Each switching element UH, VH, WH, UL, VL, WL is an n-channel MOSFET in this embodiment. Therefore, a diode (so-called parasitic diode) in the forward direction from the source to the drain is connected in parallel between the drain and the source of each switching element UH, VH, WH, UL, VL, and WL. ..

The gate circuit 32 turns on / off each of the switching elements UH, VH, WH, UL, VL, and WL in the bridge circuit 31 according to the control signal output from the control circuit 33, so that each winding 26 of the motor 25, A current is passed through 27 and 28 to rotate the motor 25.

In the present embodiment, the control circuit 33 is mainly composed of a well-known microcomputer having a CPU 41, a memory 42, and the like. The memory 42 includes at least one of various semiconductor memories such as RAM, ROM, and flash memory. The control circuit 33 controls the drive of the motor 25 via the gate circuit 32.

Various functions of the control circuit 33 are realized by the CPU 41 executing a program stored in a non-transitional substantive recording medium. In this example, the memory 42 corresponds to a non-transitional substantive recording medium in which a program is stored. The number of microcomputers included in the control circuit 33 may be one or a plurality. Further, the functions of the control circuit 33 are not limited to those realized by software, and even if some or all of the functions are realized by using hardware in which a logic circuit, an analog circuit, or the like is combined. Good.

A trigger switch 38, a battery voltage detection unit 37, a current detection circuit 36, a rotor position detection circuit 35, a speed change dial 15, a main switch 16, and a lamp 17 are connected to the control circuit 33.

A signal indicating an on / off state of the trigger switch 38 is input from the trigger switch 38 to the control circuit 33. The trigger switch 38 may be configured to input a signal indicating the operation amount (pull amount) of the trigger operation unit 11 when it is turned on.

The battery voltage detection unit 37 is configured to detect the battery voltage input from the battery pack 20 to the controller 30. The current detection circuit 36 is provided on the energization path of the motor 25 from the bridge circuit 31 to the ground line, and is configured to output a signal indicating the value of the current flowing through the motor 25.

The rotor position detection circuit 35 detects the rotation position, that is, the rotation angle of the motor 25 by waveform-shaping the detection signal from the rotation sensor 29 provided in the motor 25. In the following description, when the rotation position or rotation angle of the motor 25 is specifically referred to, it means the electric angle of the rotor of the motor 25.

The rotation sensor 29 includes three Hall sensors arranged around the rotor of the motor 25. Then, from these three Hall sensors, Hall signals corresponding to the U phase, V phase, and W phase of the motor 25, whose increasing / decreasing directions are reversed each time the rotor rotates by an electric angle of 180 degrees, are output.

The rotor position detection circuit 35 waveform-shapes the hall signals of each of these phases U, V, and W to generate a pulse-shaped hall signal in which the positive and negative are inverted every 180 degrees of the electric angle of the rotor, and the rotor position detection circuit 35 generates a pulse-shaped hall signal in which the positive and negative are inverted. The rotation position of the motor 25 is detected at intervals of 60 degrees from the edge. Hall signals of each phase U, V, and W after waveform shaping are input from the rotor position detection circuit 35 to the control circuit 33.

The control circuit 33 detects the rotational position of the motor 25 from the signal level of each input Hall signal. Further, the control circuit 33 detects the rotation speed of the motor 25 based on at least one of the input Hall signals.

The regulator 34 receives power from the battery 21 and generates a DC operating power supply voltage. Each part in the controller 30, including the control circuit 33, operates using the operating power supply voltage from the regulator 34 as a power source.

A signal indicating the operation position of the speed change dial 15, that is, a signal indicating a set rotation speed (hereinafter referred to as a set speed signal) is input to the control circuit 33 from the speed change dial 15. The control circuit 33 performs rotation speed feedback control so that the rotation speed of the motor 25 becomes the rotation speed indicated by the set speed signal input from the speed change dial 15 while the trigger switch 38 is turned on.

(1-2) Explanation of PWM Control by Control Circuit The control circuit 33 is configured to control the drive of the motor 25 by PWM control. Specifically, the control circuit 33 forms a positive / negative pair that forms an energization path from the positive electrode side of the battery 21 to the negative electrode side via the motor 25 among the switching elements in the bridge circuit 31 based on the rotation position of the motor 25. Select the switching element of. For example, the U-phase high-side switch UH and the V-phase low-side switch VL are selected at the timing when a current that flows in from the terminal 25a and flows out from the terminal 25b should be applied to the motor 25.

Then, one of the selected positive and negative switching elements, the first switching element, is maintained in the ON state, and the other second switching element is periodically turned on and off in the PWM carrier cycle according to the set duty ratio. By performing such PWM control, the control circuit 33 controls the motor 25 so that a current corresponding to the duty ratio flows.

In PWM control, it is appropriately determined which of the selected positive / negative pair of switching elements is kept on as the first switching element and which is turned on / off as the second switching element according to the duty ratio. May be good.

Further, the control circuit 33 compares the actual rotation speed of the motor 25 with the target rotation speed indicated by the set speed signal from the speed change dial 15, and determines the duty ratio for matching the actual rotation speed with the target rotation speed. calculate. Then, the calculated duty ratio is set to the duty ratio for driving the bridge circuit 31.

The control circuit 33 executes PWM control via the gate circuit 32 by outputting a control signal indicating a selected pair of positive and negative switching elements and a set duty ratio (hereinafter, set duty ratio) to the gate circuit 32.

Further, the PWM control of the present embodiment has two types of control methods, a complementary PWM and a non-complementary PWM, more specifically. The complementary PWM is another switching element connected to each terminal of the motor 25 to which the second switching element is connected during the off period of the second switching element to be turned on / off according to the set duty ratio. The third switching element is turned on.

That is, in the complementary PWM, every time the second switching element is turned off, the third switching element is turned on during a specific on period during the off period. For example, it is assumed that the U-phase high-side switch UH and the V-phase low-side switch VL are selected as a pair of positive and negative switching elements as in the above example. Further, it is assumed that the V-phase low-side switch is maintained in the ON state as the first switching element, and the U-phase high-side switch UH is periodically turned on / off as the second switching element in the PWM carrier cycle. In this case, every time the U-phase high-side switch UH is turned off, the U-phase low-side switch UL as the third switching element is turned on during the off period.

The on period for turning on the third switching element may be appropriately set during the off period for the second switching element. For example, the third switching element may be turned on for the entire off period of the second switching element. However, if this is done, there is a possibility that when the second switching element and the third switching element are switched on and off, a state in which both are temporarily turned on at the same time may occur.

Therefore, in the complementary PWM of the present embodiment, the third switching element is turned on after the dead time elapses after the second switching element is turned off for each PWM carrier cycle. Then, after the third switching element that has been turned on is turned off, the second switching element is turned on after the dead time has elapsed. That is, in the present embodiment, the on period of the third switching element during the off period of the second switching element is the timing at which the second switching element is turned on again from the timing when the dead time has elapsed after the second switching element is turned off. It is set to the timing before the dead time. The dead time is the period from turning off the second switching element to turning on the third switching element, and from turning off the third switching element to turning on the second switching element in the complementary PWM. It is a time set in between to turn off both the second switching element and the third switching element.

When the U-phase high-side switch UH and the V-phase low-side switch VL are selected as a pair of positive and negative switching elements for energization as in the above example, the U-phase high as the second switching element is selected for each PWM carrier cycle. After the side switch UH is turned off and the dead time elapses, the U-phase low side switch UL as the third switching element is turned on. Then, after the U-phase low-side switch UL is turned off and the dead time elapses, the U-phase high-side switch UH is turned on.

The non-complementary PWM is to maintain the third switching element in the off state without turning it on regardless of whether the second switching element is turned on or off. That is, the switching elements turned on in the non-complementary PWM are only the selected positive / negative pair of switching elements.

The control circuit 33 is configured to control the motor 25 by using either complementary PWM or non-complementary PWM as PWM control. Specifically, when the set duty ratio is less than the threshold value, the control circuit 33 of the present embodiment executes complementary PWM as PWM control. On the other hand, when the set duty ratio is equal to or higher than the threshold value, PWM without complement is executed as PWM control.

The set duty ratio that can be set by the control circuit 33 has an upper limit value of, for example, 100% and a lower limit value of, for example, 0%. Therefore, in the present embodiment, complementary PWM is performed when the set duty ratio is 0% or more and less than the threshold value, and non-complementary PWM is performed when the set duty ratio is the threshold value or more and 100% or less.

The lower limit value and the upper limit value of the set duty ratio may be appropriately determined. For example, the lower limit value may be a value larger than 0%, and the upper limit value may be a value smaller than 100%. .. Then, within the settable duty ratio range, the threshold value is appropriately determined, and when a duty ratio equal to or higher than the threshold value is set, non-complementary PWM is performed, and when a duty ratio less than the threshold value is set, complementary PWM is performed. You just have to do it.

Further, in the range below the threshold value, it is not essential to uniformly perform complementary PWM, and depending on the value of the set duty ratio, non-complementary PWM may be executed. That is, at least when the set duty ratio is equal to or higher than the specific duty ratio and is within the range below the threshold value, the complementary PWM is executed, but in the range below the specific duty ratio, the complementary PWM is executed or the non-complementary PWM is executed. It may be decided as appropriate. In the range less than a specific duty ratio, for example, one of them may be determined for each range by dividing into a plurality of ranges, and indicates an operating state such as a motor rotation speed, a motor current value, and a battery voltage value. It may be configured to determine which to perform depending on the values of the various parameters. Further, the specific duty ratio may be appropriately determined within the range of less than the threshold value.

FIG. 3 shows an operation example of each switching element UH, VH, WH, UL, VL, and WL of the bridge circuit 31 PWM-controlled by the control circuit 33. In FIG. 3, "deg" means "degree" which is a unit of electric angle.

FIG. 3 illustrates, as an example, a state in which complementary PWM is always executed. That is, for example, in the section A where the rotation angle (that is, the electric angle) of the motor 25 is 0 to 60 degrees, the U-phase high-side switch UH and the V-phase low-side switch VL are selected as a pair of positive and negative switching elements. In this section A, the U-phase high-side switch UH is periodically turned on and off in the PWM carrier cycle.

Further, as shown in FIG. 3, in PWM control, every time the rotation of the motor 25 advances by 60 degrees, one of the currently selected positive / negative pair of switching elements is deselected, and another switching element is newly selected. Be selected. For example, when the rotation position is 120 degrees, as shown in FIG. 3, the U-phase high-side switch UH and the W-phase low-side switch WL were selected as a pair of positive and negative switching elements before reaching 120 degrees, whereas 120 When the time comes, the V-phase high-side switch VH is selected in place of the U-phase high-side switch UH. Then, each time the selected switching element is switched, the newly selected switching element is periodically turned on as the second switching element from the switching timing to the rotation of 60 degrees to the next switching timing.・ It is turned off.

When each switching element is selected as a pair of positive and negative switching elements for energization, the selected state is maintained from the selected timing until the rotation is 120 degrees. However, the selected switching element is periodically turned on and off as the second switching element until it is rotated by 60 degrees in the first half of the period of 120 degrees, and 60 degrees in the latter half. , The ON state is maintained as the first switching element.

In section A of FIG. 3, if non-complementary PWM is executed, only the U-phase high-side switch UH is turned on and off at each PWM carrier cycle, and the U-phase low-side switch UL is turned off. Be maintained. In the section A, the V-phase low-side switch VL is maintained in the ON state.

On the other hand, in the case of complementary PWM, as shown in FIG. 3, in addition to turning on / off the U-phase high-side switch UH at each PWM carrier cycle, the U-phase low-side switch UL also has the U-phase high-side switch UH. Each time it is turned off, it is turned on for a specific on period during that off period.

A more specific operation content of the section A will be described with reference to FIGS. 4 and 5 by taking, for example, a case where the PWM carrier cycle is 50 μs, the set duty ratio is 50%, and the dead time is 3.5 μs. To do. In addition, "μs" indicates microseconds.

If non-complementary PWM is executed as the PWM control, the V-phase low-side switch VL as the first switching element is maintained in the ON state in the section A as shown in FIG. Then, the U-phase high-side switch UH as the second switching element is periodically turned on and off. In the example of FIG. 4, the off time and the on time of the U-phase high-side switch UH in the PWM carrier cycle are both 25 μs.

On the other hand, when complementary PWM is executed as PWM control, in section A, as shown in FIG. 5, the positive and negative pair of positive and negative switching elements of the U-phase high-side switch UH and the V-phase low-side switch VL are the same as the non-complementary PWM. In addition, the U-phase low-side switch UL as the third switching element is turned on and off.

That is, while the U-phase high-side switch UH is on, the U-phase low-side switch UL is turned off. In this case, an energization path as shown by the solid arrow in FIG. 6 is formed. That is, an energization path is formed from the positive electrode of the battery 21 to the negative electrode of the battery 21 via the U-phase high-side switch UH, the winding 26 of the motor 25, and the V-phase low-side switch VL.

Then, when the U-phase high-side switch UH is turned off, the U-phase low-side switch UL is turned on after the dead time of 3.5 μs has elapsed after the U-phase high-side switch UH is turned off. Then, at the timing 3.5 μs before the dead time before the U-phase high-side switch UH is turned on again, that is, at the timing when the on-period of 18 μs has elapsed since the U-phase low-side switch UL was turned on, the U-phase is U-phase. The low side switch UL is turned off.

While the U-phase low-side switch UL is on, a current path as shown by the dashed arrow in FIG. 6 is formed. That is, a current path is formed from the winding 26 of the motor 25 to the winding 26 via the U-phase low-side switch UL.

In the example of FIG. 5, the length of the on-period during which the U-phase low-side switch UL is turned on during the off-period of the U-phase high-side switch UH is 18 μs. The length of the on-period of the U-phase low-side switch UL, that is, the length of the on-period of the third switching element in the complementary PWM depends on the length of the dead time in the present embodiment. That is, the on-time of the third switching element is the length obtained by subtracting twice the dead time from the length of the off period of the second switching element that is turned on / off according to the set duty ratio.

The length of the dead time may be appropriately determined. Further, in the example of FIG. 5, the dead time from when the second switching element is turned on until the third switching element is turned on and from when the third switching element is turned off until the second switching element is turned on. The dead times were the same 3.5 μs, but they may have different lengths.

By the way, in the case of complementary PWM, since the dead time is provided as described above in the present embodiment, it is difficult to set a desired duty ratio in a high region where the set duty ratio is close to 100%.

That is, in the present embodiment, since the dead time is set to, for example, 3.5 μs, the second switching element cannot be turned on for 7 μs, which is at least twice the dead time, in the PWM carrier cycle of 50 μs. That is, the time during which the second switching element can be turned on is limited to 43 μs at the maximum per cycle.

Further, in the present embodiment, in the complementary PWM, the minimum value of the length, that is, the minimum on-time is set with respect to the on-period of the third switching element. Specifically, in this embodiment, the minimum on-time is set to, for example, 0.5 μs. Therefore, in the present embodiment, the second switching element cannot be turned on for at least 7.5 μs in which the minimum on-time is added to twice the dead time during the PWM carrier cycle. That is, the time during which the second switching element can be turned on is limited to 42.5 μs at the maximum per cycle.

FIG. 7 shows an operation example when the maximum 42.5 μs is set to the on-time of the second switching element, that is, when the set duty ratio is set to 85%. In the present embodiment, even if a set duty ratio such that the on-time of the U-phase high-side switch UH as the second switching element exceeds 42.5 μs, that is, a desired set duty exceeding 85% is set, the desired setting duty is set. It becomes difficult to energize according to the set duty ratio. Even if there is no restriction on the minimum on-time of the third switching element, considering the dead time, the length obtained by subtracting twice the dead time from the length of one cycle is 43 μs. In complementary PWM, the second switching element cannot be turned on for 43 μs or more.

For this reason, conventionally, when complementary PWM is used as PWM control, for example, when the set duty ratio is equal to or higher than the upper limit value at which complementary PWM can be normally executed, the set duty ratio is set as illustrated in FIG. Regardless of the value of, the motor 25 may be driven with a duty ratio of substantially 100% without turning off the second switching element. That is, conventionally, in complementary PWM, it has been difficult to energize the motor 25 according to the set duty ratio in a region where the set duty ratio is close to 100%.

Therefore, in the present embodiment, the control circuit 33 executes complementary PWM as PWM control when the set duty ratio is less than the threshold value, with the upper limit value at which the complementary PWM can be normally executed as a threshold value, and the set duty ratio is equal to or higher than the threshold value. In this case, it is configured to execute PWM without complement as PWM control. In this embodiment, the threshold is 85%. Strictly speaking, since complementary PWM can be normally executed up to a set duty ratio of 85%, complementary PWM is executed when the set duty ratio is below the threshold value, and non-complementary PWM is performed when the threshold value is exceeded. You may want to do it. Further, if there is no restriction on the minimum on-time of the third switching element, up to 86% can be energized according to the set duty ratio by complementary PWM, so the threshold value may be set to 86%. ..

The threshold value is not necessarily set to the upper limit value at which complementary PWM can be normally executed as described above, and may be set to a value lower than the upper limit value. For example, in the above example, a predetermined value lower than 85% may be set as the threshold value. If there is no restriction on the minimum on-time of the third switching element, a predetermined value lower than 86% may be set as the threshold value.

By switching the PWM control method as described above, in the present embodiment, as illustrated in FIG. 9, when the set duty ratio is less than 85%, complementary PWM is performed, whereby the bridge circuit 31 is set. It operates according to the duty ratio. On the other hand, when the set duty ratio is 85% or more, PWM without complementation is performed, so that the bridge circuit 31 operates according to the set duty ratio also in this case. That is, in the present embodiment, the bridge circuit 31 can be operated according to the set duty ratio regardless of the value of the set duty ratio, whereby a current corresponding to the set duty ratio can be passed through the motor 25.

(1-3) PWM Control Process Next, the PWM control process executed by the control circuit 33 will be described with reference to FIG. When the trigger switch 38 is turned on after the control circuit 33 is started, the CPU 41 selects a pair of positive and negative switching elements that form an energization path based on the rotation position of the motor 25 as described above. More specifically, as illustrated in FIG. 3, the switching element to be selected is switched every time the rotation position of the motor 25 advances by 60 degrees.

Then, the CPU 41 periodically executes the PWM control process of FIG. 10 every time the rotation position advances by 60 degrees and the switching element to be selected is switched. The execution cycle of the PWM control process is sufficiently shorter than the above-mentioned PWM carrier cycle. Further, the PWM control processing program of FIG. 10 is stored in the memory 42.

When the CPU 41 of the control circuit 33 starts the PWM control process of FIG. 10, the CPU 41 calculates the set duty ratio Ds by constant rotation control in S110. The constant rotation control here means so-called speed feedback control. Specifically, the CPU 41 calculates the set duty ratio Ds so that the difference becomes 0 based on the difference between the target rotation speed corresponding to the set position of the speed change dial 15 and the actual rotation speed of the motor 25.

In S120, it is determined whether or not the set duty ratio Ds is equal to or greater than the threshold value. When the set duty ratio Ds is less than the threshold value, complementary PWM control is executed as PWM control in S140.
When the set duty ratio Ds is equal to or greater than the threshold value, PWM without complement is executed as PWM control in S130. The set duty ratio Ds calculated in S110 may be 100% or more. When the set duty ratio Ds calculated in S110 is 100% or more, energization with a duty ratio of 100% is performed in S130. That is, the second switching element is always turned on during the PWM carrier cycle.

(1-4) Effects of First Embodiment According to the first embodiment described above, the following effects (1a) to (1c) are exhibited.
(1a) The control circuit 33 executes complementary PWM when the set duty ratio is less than the threshold value, and executes non-complementary PWM when the set duty ratio is equal to or more than the threshold value. Therefore, by appropriately setting the threshold value, it is possible to appropriately perform PWM control at the set duty ratio as a whole.

(1b) Even when the set duty ratio is less than the threshold value, the non-complementary PWM may be executed in a part of the region, but in the present embodiment, the complementary PWM is uniformly executed when the set duty ratio is less than the threshold value. It is configured to do. Therefore, it is possible to enjoy more effects obtained by using complementary PWM as PWM control, that is, more excellent effects than when using non-complementary PWM.

(1c) The threshold value is a value of the ratio of the time obtained by subtracting the specific time from the PWM carrier cycle to the PWM carrier cycle. The specific time in the present embodiment is a time obtained by adding the minimum on-time of the third switching element to twice the dead time. Therefore, the complementary PWM can be executed up to the maximum set duty ratio that is not affected by the dead time and the minimum on-time of the third switching element. As a result, it is possible to realize an appropriate PWM control as a whole, and to maximize the effect obtained by using the complementary PWM.

(1-5) Correspondence with the wording of the claims Here, the correspondence between the wording of the first embodiment and the wording of the claims will be supplementarily described. The battery 21 corresponds to an example of a DC power supply. The control circuit 33 corresponds to an example of a control unit.

[2. Second Embodiment]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, the differences will be described below. The same reference numerals as those in the first embodiment indicate the same configurations, and the preceding description will be referred to.

First, regarding the method of calculating the duty ratio, in the first embodiment, the duty ratio is calculated by so-called rotation speed feedback control, but in the second embodiment, the feedback control is not performed and the duty ratio is calculated by an open loop. Specifically, the duty ratio corresponding to the set speed signal input from the speed change dial 15 is calculated. Therefore, the higher the rotation speed set by the speed change dial 15, the larger the calculated duty ratio. The duty ratio calculated by the open loop is also hereinafter referred to as an calculated duty ratio.

Further, in the complementary PWM in the first embodiment described above, as described with reference to FIG. 5, the on-time of the second switching element to be turned on / off in the PWM carrier cycle is the same as the time corresponding to the set duty ratio. there were. That is, as in the example of FIG. 5, when the set duty ratio is 50%, the on-time of the U-phase high-side switch, which is the second switching element, is 25 μs, which is the time corresponding to the set duty ratio. ..

On the other hand, in the complementary PWM of the second embodiment, the second switching element is not turned on immediately at the timing when it should be turned on (hereinafter, PWM on timing), but is turned on after the dead time elapses from the PWM on timing.

A specific example is shown in FIG. FIG. 11 shows an example in which the PWM carrier period is 50 μs, the set duty ratio is 50%, the dead time is 3.5 μs, and the U-phase high-side switch UH is selected as the second switching element.

As shown in FIG. 11, in the second embodiment, the U-phase low-side switch UL is turned on after the dead time has elapsed after the U-phase high-side switch UH is turned off. Up to this point, it is the same as the first embodiment. Then, the U-phase low-side switch UL is turned on until the PWM on timing according to the set duty ratio, that is, until 25 μs has elapsed in the PWM carrier cycle, and is turned off at the PWM on timing. Incidentally, in the first embodiment, the U-phase low-side switch UL is turned off at a timing before the dead time before the PWM on timing.

Then, after the U-phase low-side switch UL is turned off at the PWM on timing, the timing after the dead time elapses, that is, the timing when 28.5 μs has passed since the U-phase high-side switch UH was turned off, the U-phase high-side switch UH Is turned on again.

Therefore, the actual on-time of the U-phase high-side switch UH is shorter than the regular on-time according to the set duty ratio by the dead time. That is, the actual duty ratio, which is the ratio of the actual on-time to the PWM carrier cycle, is lower than the set duty ratio by the duty ratio corresponding to the dead time. In the example of FIG. 11, when the dead time of 3.5 μs is converted into the duty ratio, it becomes 7%. Therefore, even if the set duty ratio is 50%, the actual duty ratio is 43%, which is 7% lower than the set duty ratio.

Therefore, in the second embodiment, in order to match the set duty ratio with the actual duty ratio, the control circuit 33 does not set the calculated calculated duty ratio as it is as the set duty ratio, but sets the calculated calculated duty ratio as the dead time. It is offset by a minute, and the duty ratio after the offset is set as the set duty ratio.

In the case of the example of FIG. 11, when a value of 50% is calculated as the calculated duty ratio required to drive the motor 25, the duty ratio for the dead time is used instead of setting the 50% as the set duty ratio as it is. 57%, which is the sum of 7%, is set as the set duty ratio.

As a result, the U-phase low-side switch UL is turned off at a timing 21.5 μs after the U-phase high-side switch UH is turned off. Then, after a dead time of 3.5 μs elapses from the time of turning off, that is, 25 μs after the U-phase high-side switch UH is turned off, the U-phase high-side switch UH is turned on again and then turned on for 25 μs. become. That is, although the set duty ratio itself is set to 57%, which is offset from the originally required duty ratio of 50%, as a result, the actual duty ratio becomes 50%, which is the originally required duty ratio.

Also in the second embodiment, as an example, it is assumed that the dead time is 3.5 μs and the minimum on time of the third switching element is set to 0.5 μs. Therefore, in the complementary PWM, a maximum actual duty ratio of 85% can be realized.

Therefore, in the complementary PWM of the second embodiment, as shown in FIG. 12, the set duty ratio can be set up to 92%. This is because even if it is set to 92%, the actual duty ratio becomes 85% due to the influence of the dead time. Conversely, on the premise that the calculated calculated duty ratio is offset and set to the set duty ratio, complementary PWM is performed until the calculated calculated duty ratio is up to 85%, as in the first embodiment. It can be executed normally.

Therefore, in the second embodiment, as illustrated in FIG. 13, when the calculated calculated duty ratio is less than 85%, the complementary PWM is executed with the value obtained by offsetting the calculated calculated duty ratio as the set duty ratio. To do. As a result, in the region where the calculated duty ratio is less than 85%, the actual duty ratio becomes the same value as the calculated duty ratio.

Then, when the calculated calculated duty ratio is 85% or more, the non-complementary PWM is executed with the calculated duty ratio as the set duty ratio. Therefore, even in the region where the calculated duty ratio is 85% or more, the actual duty ratio is the same value as the calculated duty ratio. That is, as a whole, the calculated duty ratio and the actual duty ratio can be matched.

Next, the PWM control process of the second embodiment will be described with reference to FIG. When the CPU 41 starts the PWM control process of FIG. 14, in S210, the duty ratio D1 by the open loop, that is, the calculated duty ratio D1 is calculated.

In S220, the offset duty ratio D2 is calculated by adding the offset amount Doff to the calculated duty ratio D1 calculated in S210. The offset amount Doff is the ratio of the dead time to the PWM carrier cycle as described above, and is 7% in the present embodiment.

In S230, it is determined whether or not the offset duty ratio D2 calculated in S220 is 100% or more. If it is not 100% or more, the process proceeds to S250, and if it is 100% or more, the process proceeds to S240. In S240, the offset duty ratio D2 is set to 100%, and the process proceeds to S250.

In S250, it is determined whether or not the calculated duty ratio D1 calculated in S210 is equal to or greater than the threshold value. The threshold is the same as in the first embodiment, for example 85%. When the calculated duty ratio D1 is less than the threshold value, the offset duty ratio D2 is set as the set duty ratio Ds in S280. Then, in S290, complementary PWM is executed according to the set duty ratio Ds set in S280.

If the calculated duty ratio D1 is equal to or greater than the threshold value in S250, the calculated duty ratio D1 is set as the set duty ratio Ds in S260. When the calculated duty ratio D1 is 100% or more, 100% is set as the set duty ratio Ds in S260. Then, in S270, the non-complementary PWM is executed according to the set duty ratio Ds set in S260. When the set duty ratio Ds is 100%, energization is performed with a duty ratio of 100%. That is, the second switching element is always turned on during the PWM carrier cycle.

The second embodiment described above can also obtain the same effect as that of the first embodiment. Further, in the second embodiment, the complementary PWM method is different from that in the first embodiment, and the actual duty ratio is smaller than the set duty ratio by the amount corresponding to the dead time. Therefore, instead of setting the calculated duty ratio as it is as the set duty ratio, the value obtained by offsetting the calculated duty ratio by the amount corresponding to the dead time is set as the set duty ratio. As a result, even in the complementary PWM, the actual duty ratio can be matched with the calculated duty ratio.

[3. Other embodiments]
Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and can be implemented in various modifications.

(3-1) In PWM control, for a switching element newly selected as a pair of positive and negative switching elements to be turned on, only the first half 60 degree section of 120 degrees from the selection to the turning off state again. It is not essential to turn on / off according to the PWM carrier cycle. For example, the low-side switch of the selected pair of positive and negative switching elements may be kept on at all times, and the high-side switch may be always turned on / off according to the PWM carrier cycle.

(3-2) In the above embodiment, the set speed signal from the speed change dial is used as the information to be referred to when calculating the duty ratio, but this is only an example. For example, the target speed may be set according to the operation amount of the trigger operation unit 11, and the required duty ratio may be calculated based on the target speed.

(3-3) The threshold value may have hysteresis. Specifically, for example, it is assumed that the threshold value for switching from complementary PWM to non-complementary PWM is 85%. In this case, it is assumed that the PWM control method is switched from complementary PWM to non-complementary PWM when the set duty ratio is changed from less than 85% to 85% or more. Then, when the set duty ratio decreases again after that, instead of switching to complementary PWM when it becomes less than 85%, complementary PWM when it becomes less than a predetermined boundary value lower than 85%. You may switch to.

(3-4) In the present disclosure, the motor is not limited to a brushless motor. Further, the number of power input terminals of the motor is not limited to three. For example, the present disclosure may be applied to an electric working machine having a brushed DC motor having two terminals for power input.

As for the bridge circuit, the configuration having six switching elements as in the above embodiment is only an example, and the number of switching elements included in the bridge circuit is not limited. For example, when the motor is a DC motor, a so-called H-bridge circuit having four switching elements may be used as the bridge circuit.

(3-5) The technique of the present disclosure can be applied to various electric working machines such as horticultural working machines other than brush cutters, and electric tools for masonry, metalworking, and woodworking. More specifically, electric hammers, electric hammer drills, electric drills, electric drivers, electric wrenches, electric grinders, electric circular saws, electric reciprocal saws, electric jigsaws, electric hammers, electric cutters, electric chainsaws, electric cannaes, electric nail cutters ( (Including studs), electric hedge trimmers, electric lawn mowers, electric lawn wrench, electric brush cutters, electric cleaners, electric blowers, electric sprayers, electric sprayers, electric dust collectors, etc. ..

(3-6) A plurality of functions possessed by one component in the above embodiment may be realized by a plurality of components, or one function possessed by one component may be realized by a plurality of components. May be good. Further, a plurality of functions possessed by the plurality of components may be realized by one component, or one function realized by the plurality of components may be realized by one component. Further, a part of the configuration of the above embodiment may be omitted. In addition, at least a part of the configuration of the above embodiment may be added or replaced with the configuration of the other above embodiment. It should be noted that all aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

1 ... Electric work machine, 11 ... Trigger operation unit, 15 ... Shift dial, 20 ... Battery pack, 21 ... Battery, 25 ... Motor, 25a, 25b, 25c ... Terminal, 26, 27, 28 ... Winding, 29 ... Rotation Sensor, 30 ... controller, 31 ... bridge circuit, 32 ... gate circuit, 33 ... control circuit, 34 ... regulator, 35 ... rotor position detection circuit, 38 ... trigger switch, 41 ... CPU, 42 ... memory, UH, VH, WH , UL, VL, WL ... Switching element.

Claims (3)

A motor with multiple terminals for power input,
A bridge circuit having a plurality of switching elements provided between the positive electrode side of the DC power supply and each of the plurality of terminals, and between the negative electrode side of the DC power supply and each of the plurality of terminals.
One of the positive and negative switching elements forming the energization path of the motor from the positive side to the negative side of the DC power supply in the bridge circuit is maintained in the on state, and the other second switching element is maintained. A control unit that executes PWM control that controls the motor so that a current corresponding to the duty ratio flows through the motor by turning the element on and off according to a set duty ratio.
With
When the duty ratio is less than the threshold value, the control unit performs the PWM control for each PWM carrier cycle, which is a cycle when the second switching element is periodically turned on and off according to the duty ratio. turns on the third switching element and the second switching element is in addition to the switching elements that are connected to the terminals of the motor connected to the on period of the specific, is configured to perform a complementary PWM Ori ,
The on period is a period from the timing at which the second switching element is turned off and the first dead time elapses to the timing before the timing at which the second switching element is turned on again by the second dead time. Yes,
The first dead time and the second dead time are times set so as to turn off both the second switching element and the third switching element, respectively.
The threshold value is a value of the ratio of the time obtained by subtracting the specific time from the PWM carrier cycle to the PWM carrier cycle.
The specific time is equal to or greater than the sum of the first dead time and the second dead time.
When the duty ratio is equal to or higher than the threshold value, the control unit executes, as the PWM control, non-complementary PWM that keeps the third switching element in the off state regardless of whether the second switching element is on or off. Is configured to
Electric work machine. The electric work machine according to claim 1.
The complementary PWM has a minimum on-time that is a minimum value of the length of the on-period, and is configured to set the length of the on-period to at least the minimum on-time or more.
The specific time is equal to or greater than the time obtained by adding the minimum on-time to the sum of the first dead time and the second dead time.
Electric work machine. The electric work machine according to claim 2.
The specific time is a time obtained by adding the minimum on-time to the sum of the first dead time and the second dead time.

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