Motor drive device capable of discharging DC link voltage

Abstract

This motor drive device comprises: an inverter composed of a three-phase bridge circuit in which a switching element is provided to each of an upper arm and a lower arm in each of three phases; a smoothing capacitor provided to the DC-input side of the inverter; a dynamic brake circuit that closes a switch provided between the input terminals of the motor and short-circuits the input terminals via a dynamic brake resistor, thereby braking the motor; an inverter control unit that controls the on / off operation of the switching element; and a dynamic brake control unit that controls the opening / closing of the switch. The motor drive device closes the switch of the dynamic brake circuit and turns on only a switching element of the upper arm in one phase or two phases within the inverter and a switching element of the lower arm in the two phases or the one phase other than the aforementioned one phase or the aforementioned two phases, thereby discharging DC power of the smoothing capacitor.

Description

Motor drive device capable of discharging DC link voltage

[0001] The present disclosure relates to a motor drive device capable of discharging a DC link voltage.

[0002] A motor drive device that drives an AC motor is provided with a converter and an inverter. The converter and inverter are electrically connected via a DC link. The converter converts AC power supplied from an AC power source into DC power and outputs it. The inverter converts DC power in the DC link into AC power for driving the motor and outputs it. A smoothing capacitor is provided in the DC link between the converter and the inverter.

[0003] JP 2005-253213 A JP 2017-200337 A JP 07-245964 A JP 2014-155393 A JP 02-074419 A

[0004] The larger the capacity (capacitance value) of a smoothing capacitor installed in a DC link, the longer it takes to discharge. After a motor drive device is turned off or a power outage occurs, a charge remains in the smoothing capacitor for a while, posing a risk of electric shock during that time and making it impossible to perform maintenance, replacement, or restoration work, resulting in poor work efficiency. Therefore, there is a need for technology that can quickly discharge a smoothing capacitor installed in the DC link between the converter and inverter in a motor drive device.

[0005] According to one aspect of the present disclosure, a motor drive device includes an inverter including a three-phase bridge circuit in which a power element is provided in each of the upper arms on the high potential side and the lower arms on the low potential side of each of three phases, the power elements operating on and off to convert input DC power into AC power and output the AC power to the motor; a smoothing capacitor provided on the DC input side of the inverter; a dynamic braking circuit that generates deceleration torque in the motor by closing a switch provided between input terminals of the motor to short-circuit the input terminals via a dynamic braking resistor; an inverter control unit that controls the on and off operation of the power elements; and a dynamic braking control unit that controls the opening and closing of the switches, wherein a discharge process is performed to discharge the DC power from the smoothing capacitor by closing the switch using the dynamic braking control unit and by turning on only the power elements in the upper arms of one or two phases in the inverter and the power elements in the lower arms of two or one phase that are different from the one or two phases.

[0006] FIG. 1 is a diagram illustrating a motor drive device according to an embodiment of the present disclosure. FIG. 2 is a circuit diagram (part 1) illustrating a current flowing through a dynamic braking resistor when a discharge process is being executed. FIG. 3 is a circuit diagram (part 2) illustrating a current flowing through a dynamic braking resistor when a discharge process is being executed. FIG. 4 is a circuit diagram illustrating an equivalent circuit when the switching elements are performing on and off operations as shown in FIGS. 2A and 2B. FIG. 5 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a first embodiment of the present disclosure. FIG. 6 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a second embodiment of the present disclosure. FIG. 7 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a third embodiment of the present disclosure. FIG. 8 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a fourth embodiment of the present disclosure. FIG. 9 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a fifth embodiment of the present disclosure. FIG. 10 is a process illustrating an operation flow when discharging a smoothing capacitor in a motor drive device according to a sixth embodiment of the present disclosure. FIG. 11 is a waveform diagram illustrating an example of a relationship between current, a tolerance, and a threshold value. FIG. 12 is a diagram illustrating a motor drive device according to a seventh embodiment of the present disclosure. 2B is a circuit diagram illustrating an example of a temperature change in a dynamic braking resistor that occurs when the switching elements are turned on as shown in FIG. 2A during discharge processing. FIG. 2C is a circuit diagram illustrating an example of a current that flows through a dynamic braking resistor when the switching elements of the U-phase upper arm and the W-phase lower arm are turned on during discharge processing.2A, 2B, and 2C are circuit diagrams illustrating an example of a current flowing through a dynamic braking resistor when the switching elements of the upper arm of the V-phase and the lower arm of the W-phase are turned on during discharge processing. The figures also illustrate temperature changes in the dynamic braking resistor that occur when the switching elements are turned on during discharge processing as shown in FIGS. 2A, 20, and 21.

[0007] Hereinafter, an embodiment of a motor drive device capable of discharging a DC link voltage will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted. The scale of the drawings has been appropriately changed to facilitate understanding.

[0008] In the following description, "electrically connected" may be simply referred to as "connected." A converter that converts AC power supplied from a three-phase AC power source into DC power and outputs it is also called a "rectifier," "rectifier device," "rectifier circuit," or "forward converter." An inverter that converts DC power into AC power and outputs it is also called an "inverter." A "DC link" refers to a circuit portion that electrically connects the DC output side of a converter to the DC input side of an inverter. A "DC link" is also called a "DC link section," "DC link," "DC link section," "DC bus," or "DC intermediate circuit." A "DC link voltage" refers to the potential difference between the positive potential of the positive power line of the DC link and the negative potential of the negative power line. The "on" of a switching element means that the switching element is closed, thereby forming an electric path through the switching element. The "off" of a switching element means that the switching element is opened, thereby interrupting the electric path through the switching element. An "on command" refers to a command to turn on a switching element. An "off command" refers to a command to turn off a switching element. In the following description, when a phrase "a switching command is sent to the control terminal (gate terminal or base terminal) of a switching element" is used, "to the control terminal" may be omitted and simply expressed as "a switching command is sent to the switching element." "Motor current" refers to the current flowing through the motor windings. "Dynamic braking current" refers to the current flowing through the dynamic braking resistor. "Discharge processing" refers to the process of discharging DC power (charge) stored in a smoothing capacitor provided in the DC link between the converter and the inverter. Furthermore, the "position" of a motor refers to the "rotational position of the motor's rotor or rotating shaft." "Rotational position" refers to the "rotational angle of the rotor or rotating shaft." "Position control" of a motor refers to the "rotational angle position control relative to the motor's rotor or rotating shaft." "Speed" of a motor refers to the "speed of the motor's rotor or rotating shaft." "Rotational speed" refers to the rotational angular velocity of the rotor or rotating shaft.

[0009] <Overall Configuration of a Motor Drive Device According to an Embodiment of the Present Disclosure> Fig. 1 is a diagram showing a motor drive device according to an embodiment of the present disclosure. The diagram shown in Fig. 1 is applicable to first to twelfth embodiments described below.

[0010] In the embodiment of the present disclosure described below, a case is shown in which a motor 3 is driven by a motor drive device 1 connected to an AC power source 2. The number of phases of the AC power source 2 is not particularly limited in each embodiment and each modified example, and may be, for example, three-phase or single-phase. Examples of the AC power source 2 include a three-phase 400V AC power source, a three-phase 200V AC power source, a three-phase 600V AC power source, and a single-phase 100V AC power source. Here, as an example, the AC power source 2 is three-phase. Furthermore, the number of motors 3 is not particularly limited in each embodiment, and may be multiple. When multiple motors 3 are provided, the inverter 11, dynamic braking circuit 13, inverter control unit 14, dynamic braking control unit 15, and current detection unit 16 are provided for each motor 3. Here, as an example, there is one motor 3. Machines in which the motor 3 is provided include, for example, machine tools and robots.

[0011] A motor drive device 1 according to an embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits. Although not shown here, power lines that supply power to drive the inverter control unit 14, the dynamic braking control unit 15, the current detection unit 16, the switching control unit 18, and the voltage detection unit 19 are provided on a system separate from the power line that supplies power from the AC power source 2 to the converter 10.

[0012] The converter 10 converts AC power supplied from the AC power source 2 into DC power and outputs it to a DC link. In the example shown in FIG. 1 , the AC power source 2 is a three-phase AC power source, so the converter 10 is configured as a three-phase bridge circuit. If the AC power source 2 is a single-phase AC power source, the converter 10 is configured as a single-phase bridge circuit. Examples of the converter 10 include a diode rectifier, a PWM switching control rectifier, and a 120-degree conduction rectifier. For example, if the converter 10 is configured as a diode rectifier, it is configured as a three-phase bridge circuit of diodes. If the converter 10 is configured as a PWM switching control rectifier or a 120-degree conduction rectifier, it is configured as a three-phase bridge circuit of switching elements and diodes connected in reverse parallel to the switching elements. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other switching elements may also be used. An AC reactor, an AC line filter, and the like may be provided on the AC input side of the converter 10, but these are not shown here.

[0013] A smoothing capacitor 12 is electrically connected to the DC link between the converter 10 and the inverter 11. The smoothing capacitor 12 is sometimes referred to as a "DC link capacitor" or a "direct-current link capacitor." The smoothing capacitor 12 has the function of suppressing oscillations in the DC output of the converter 10 and the function of storing DC power used by the inverter 11 to generate AC power. Examples of the smoothing capacitor 12 include an electrolytic capacitor and a film capacitor. A pre-charging circuit for pre-charging the smoothing capacitor 12 may be provided, but is not shown here.

[0014] A switching unit 17 is provided between the AC power supply 2 and the AC input side of the converter 10. The switching unit 17 is configured by, for example, an electromagnetic contactor. The switching unit 17 opens and closes the electrical path between the AC power supply 2 and the converter 10 based on a switching command received from the switching control unit 18. When the switching command received from the switching control unit 18 is a close command, the switching unit 17 performs a closing operation to close the contacts, thereby forming an electrical path between the AC power supply 2 and the converter 10. When the switching command received from the switching control unit 18 is an open command, the switching unit 17 performs an opening operation to open the contacts, thereby interrupting the electrical path between the AC power supply 2 and the converter 10.

[0015] The switching control unit 18 controls the switching unit 17 to open or close the electrical path between the AC power supply 2 and the converter 10 .

[0016] The inverter 11 is connected to the converter 10 via a DC link. The inverter 11 is a three-phase bridge circuit in which a switching element is provided in each of the upper arms on the high potential side and the lower arms on the low potential side of each of the three phases. A diode is connected in antiparallel to each switching element. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other switching elements may also be used. In the illustrated example, for the U phase, a switching element SU is provided in the upper arm. U is provided in the lower arm, and the switching element SU L For the V phase, a switching element SV is provided in the upper arm. U is provided, and the lower arm is provided with a switching element SV L For the W phase, a switching element SW U is provided, and the lower arm is provided with a switching element SW L is provided.

[0017] The inverter 11 receives a drive command (on / off command) from the inverter control unit 14 and turns on / off the switching element SU U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. LBy turning on and off the inverter 11, the DC power in the DC link is converted into AC power for driving the motor, and this is output to the motor 3. As a result, the motor 3 is driven based on the AC power output from the inverter 11. Furthermore, the inverter 11 receives a drive command (on / off command) from the inverter control unit 14 and turns on and off the switching element SU U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L By turning on and off the inverter 11, the inverter 11 receives a drive command (on / off command) from the inverter control unit 14, converts the AC power regenerated during deceleration of the motor 3 into DC power, and outputs it to the DC link.

[0018] The inverter control unit 14 controls the switching elements SU in the inverter 11 based on the rotation speed of the motor 3 (rotation speed feedback), the current flowing through the windings of the motor 3 (current feedback), a rotation speed command, a torque command, a position command, and an operation program for the motor 3. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L The inverter control unit 14 generates a drive command (ON / OFF command) for controlling the ON / OFF operation of the switching element SU. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L The power conversion operation of the inverter 11 is controlled by the drive command generated by the inverter control unit 14, whereby the position, rotation speed, or torque of the rotor or rotating shaft of the motor 3 is controlled.

[0019] The dynamic braking circuit 13, under the control of the dynamic braking control unit 15, shorts the input terminals of the motor 3 via dynamic braking resistors 31U, 31V, and 31W, thereby generating a deceleration torque in the motor 3 and braking the motor 3.

[0020] The dynamic braking circuit 13 includes dynamic braking resistors 31U, 31V, and 31W, and a switch 32 connected in series with the dynamic braking resistors 31U, 31V, and 31W. As shown in the figure, a series circuit consisting of the dynamic braking resistors 31U, 31V, and 31W and the switch 32 is provided between the input terminals of the motor 3 (between the phases of the windings of the motor 3). The switch 32 is formed by a relay, a switching element, or the like, and its opening and closing is controlled by a brake command (opening / closing command) generated by the dynamic braking control unit 15.

[0021] When braking the motor 3 using the dynamic braking circuit 13, the inverter 11 cuts off the supply of drive power to the motor 3, and the dynamic braking control unit 15 outputs a brake command, closing the switch 32 in the dynamic braking circuit 13 and shorting the input terminals of the motor 3 via the dynamic braking resistors 31U, 31V, and 31W. Even though the motor 3 is electrically disconnected from the power supply, a field flux exists, and the motor 3, rotating by inertia, functions as a generator, generating a dynamic braking current. The dynamic braking current flows through the closed switch 32 into the dynamic braking resistors 31U, 31V, and 31W, where it is converted to Joule heat and consumed. As a result, a deceleration torque is generated in the motor 3. This deceleration torque brakes the motor 3, causing it to coast for a certain distance before finally coming to a stop. In one embodiment of the present disclosure, the dynamic braking circuit 13 is used not only to brake the motor 3 but also to discharge the smoothing capacitor 12.

[0022] The current detection unit 16 detects the value of the current output from the inverter 11 (hereinafter, sometimes referred to as the "output current from the inverter 11").

[0023] The voltage detection unit 19 detects the voltage applied between the positive and negative terminals of the smoothing capacitor 12 (hereinafter simply referred to as the "voltage of the smoothing capacitor 12"). The voltage of the smoothing capacitor 12 corresponds to the "DC link voltage" which is the potential difference between the positive potential appearing at the positive terminal of the DC output side of the converter 10 and the negative potential appearing at the negative terminal of the DC output side of the converter 10.

[0024] In the discharge process for discharging the DC power stored in the smoothing capacitor 12, first, the switching control unit 18 controls the switching unit 17 to open, thereby cutting off the flow of AC power from the AC power source 2 to the converter 10. Then, the dynamic braking control unit 15 controls the switch 32 to close.

[0025] Furthermore, in the discharge process, the inverter control unit 14 controls the upper arm switching elements of one or two phases in the inverter 11 and the lower arm switching elements of two or one phases different from the one or two phases to be turned on. More specifically, there are three switching patterns as follows. In the first switching pattern, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. In the second switching pattern, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. In the third switching pattern, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off. In the discharge process, the inverter control unit 14 may control the on / off of the switching elements in any one of the three switching patterns described above.

[0026] A series of discharge processes forms a closed circuit that runs from the smoothing capacitor 12 through the on-state switching elements in the inverter 11, via two or three of the dynamic braking resistors 31U, 31V, and 31W, and back to the smoothing capacitor 12. As a result, the DC power (charge) stored in the smoothing capacitor 12 flows through the inverter 11 into the dynamic braking resistors 31U, 31V, and 31W and is consumed as Joule heat.

[0027] In this way, when the discharge process is performed, the switching elements provided in the upper arm and the lower arm of different phases are turned on. Since six switching elements are provided in the inverter 11, there are a total of 12 combinations of switching elements to be turned on. That is, the switching elements SU U and SV L a first set consisting of switching elements SU U and SW L A second set consisting of switching elements SV U and SU L A third set consisting of switching elements SV U and SW L A fourth set consisting of a switching element SW U and SU L A fifth set consisting of a switching element SW U and SV L A sixth set consisting of switching element SU U and SV U and SW L A seventh set consisting of switching element SU U and SW U and SV L an eighth set consisting of switching elements SV U and SW U and SU L A ninth set consisting of switching elements SU L and SV L and SW U A tenth set consisting of switching elements SU L and SW L and SV U and an eleventh set consisting of a switching element SV L and SWL and SU U When the discharge process is performed, any one of the twelve sets of switching elements, such as the 12th set consisting of

[0028] <Calculation of dynamic braking current and motor current during discharge processing> Fig. 2A is a circuit diagram (part 1) illustrating the calculation of dynamic braking current and motor current during discharge processing. Fig. 2B is a circuit diagram (part 2) illustrating the calculation of dynamic braking current and motor current during discharge processing. In Figs. 2A and 2B, the AC power supply 2, converter 10, switching unit 17, and switching control unit 18 are not shown.

[0029] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, inverter control unit 14, dynamic braking control unit 15, current detection unit 16, switching unit 17, and switching control unit 18 are as described with reference to FIG. 1.

[0030] By providing a current calculation unit 21 in the motor drive device 1, the value of the current flowing through the dynamic braking resistor 31U, 31V or 31W when the discharge process is being performed can be calculated based on the resistance value of the dynamic braking resistor 31U, 31V or 31W, the inductance value of the motor 3 and the capacitance value of the smoothing capacitor 12.

[0031] In the discharge process, first, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power source 2 to the converter 10. Then, the dynamic braking control unit 15 controls the switch 32 to close. Furthermore, the inverter control unit 14 controls the upper arm switching element of one phase in the inverter 11 and the lower arm switching element of another phase different from the one phase to be turned on, while the other switching elements are turned off. Alternatively, the upper arm switching element of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, while the other switching elements are turned off. Alternatively, the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, while the other switching elements are turned off.

[0032] In the example shown in FIG. 2A, the upper arm switching element SV U and the U-phase lower arm switching element SU L Only the switching element SU is turned on. U , S.W. U , S.V. L , and S.W. L This series of processes turns off the smoothing capacitor 12 and the switching element SV U , dynamic brake resistor 31V, dynamic brake resistor 31U, switching element SU L A closed circuit is formed that passes through the inverter 11 and reaches the smoothing capacitor 12 again. As a result, the charge stored in the smoothing capacitor 12 flows into the dynamic braking resistors 31U and 31V through the inverter 11 and is consumed as Joule heat.

[0033] In the example shown in FIG. 2B, the upper arm switching element SV U , the upper arm switching element SW of the W phase U , and the U-phase lower arm switching element SU L Only the switching element SU is turned on. U , S.V. L , and S.W.L This series of processes turns off the smoothing capacitor 12 and the switching element SV U or SW U , dynamic brake resistor 31V or 31W, dynamic brake resistor 31U, switching element SU L A closed circuit is formed that leads back to the smoothing capacitor 12 via the inverter 11. As a result, the charge stored in the smoothing capacitor 12 flows into the dynamic braking resistors 31U, 31V, and 31W through the inverter 11 and is consumed as Joule heat.

[0034] Fig. 3 is a circuit diagram showing an equivalent circuit when the switching elements shown in Fig. 2A or 2B are turned on and off. In Fig. 3, the voltage of the smoothing capacitor 12 is V0 [V], and the capacitance value is C [F]. The dynamic brake resistors 31U and 31V in Fig. 2A are collectively represented as a dynamic brake resistor 31 in Fig. 3, with a resistance value of R [Ω]. The motor 3 in Fig. 2A is represented in Fig. 3 by an interphase reactor 61 of the motor 3, with an inductance value of L [H]. The output current from the inverter 11 is represented as I [A], and the dynamic brake current flowing through the dynamic brake resistor 31 is represented as I [A]. R [A], and the motor current flowing through the interphase reactor 61 of the motor 3 is I L Hereinafter, the units of each parameter may be omitted.

[0035] The current calculation unit 21 calculates the dynamic braking current I for the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12. R (hereinafter referred to as "current ratio"), and the motor current I to the output current I of the inverter 11 for each fixed time ΔT. L Then, the current ratio of the dynamic braking current I to the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. RSimilarly, the current value detected by the current detection unit 16 at every fixed time ΔT is multiplied by the motor current I to the output current I of the inverter 11 to calculate the dynamic braking current during the discharge process. L The motor current during discharge processing is calculated by multiplying the current ratio by the formula (1). Each calculation formula will be explained below, including the process of deriving it.

[0036] In the equivalent circuit of FIG. 3, the output current I from the inverter 11 detected by the current detection unit 16 and the dynamic braking current I R and the motor current I L The relational expression shown in Equation 1 holds between these.

[0037]

[0038] In the equivalent circuit of FIG. 3, the voltage relationships shown in Equation 2 and Equation 3 hold true.

[0039]

[0040]

[0041] Substituting Equation 3 into Equation 1, Equation 4 is obtained.

[0042]

[0043] By differentiating both sides of equation 2 with respect to t, equation 5 is obtained.

[0044]

[0045] Substituting Equation 5 into Equation 4, Equation 6 is obtained.

[0046]

[0047] By rearranging Equation 6, Equation 7 is obtained.

[0048]

[0049] I L Equation 7 is solved by setting as in Equation 8. In Equation 8, A is an integral constant. Equation 7 is L Since it is a second-order constant coefficient homogeneous ordinary differential equation, I LA general solution can be found from the solution of equation 9, which is the characteristic equation of the differential equation, as shown in equations 10 and 11. In equations 10 and 11, A, A, and B are integral constants.

[0050]

[0051]

[0052]

[0053]

[0054] Here, α shown in Equation 12, ω0 shown in Equation 13, and β shown in Equation 14 are introduced.

[0055]

[0056]

[0057]

[0058] By substituting equations 12 to 14 into equation 11, equation 15 is obtained.

[0059]

[0060] where α 2 -ω0 2 When 0, the motor current I L The formula for calculating is derived as follows: First, formula 15 is expressed as formula 16.

[0061]

[0062] When t=0, I L = 0, so Equation 17 is obtained.

[0063]

[0064] When t=0, Equation 18 holds true, and therefore Equation 19 is obtained.

[0065]

[0066]

[0067] By rearranging Equation 19, Equation 20 is obtained.

[0068]

[0069] The integral constant A1 is expressed as in Equation 21, and the integral constant A2 is expressed as in Equation 22.

[0070]

[0071]

[0072] Therefore, α 2 -ω0 2 When 0, the motor current I L [A] can be expressed as in Equation 23.

[0073]

[0074] On the other hand, α 2 -ω0 2 <0, the motor current I L The formula for calculating is derived as follows: First, α shown in formula 24, ω 0 shown in formula 25, and β shown in formula 26 are introduced.

[0075]

[0076]

[0077]

[0078] By substituting Equations 24 to 26 into Equation 15, Equation 27 is obtained.

[0079]

[0080] When t=0, I L = 0, so Equation 28 is obtained.

[0081]

[0082] When t=0, Equation 29 holds true, and Equation 30 is obtained.

[0083]

[0084]

[0085] By rearranging Equation 30, Equation 31 is obtained.

[0086]

[0087] The integral constant A1 is expressed as in Equation 32, and the integral constant A2 is expressed as in Equation 33.

[0088]

[0089]

[0090] Therefore, α 2 -ω0 2 <0, the motor current I L [A] can be expressed as in Equation 34.

[0091]

[0092] Also, α 2 -ω0 2 < 0, the dynamic braking current I R The formula for calculating is derived as follows: First, α shown in formula 35, ω 0 shown in formula 36, ​​and β shown in formula 37 are introduced.

[0093]

[0094]

[0095]

[0096] Substituting Equations 35 to 37 into Equation 3, α 2 -ω0 2 Dynamic braking current I when <0 R Equation 38 is obtained, which shows:

[0097]

[0098] Also, α 2 -ω0 2 When 0, the dynamic braking current I R The formula for calculating is derived as follows: First, α shown in formula 39, ω 0 shown in formula 40, and β shown in formula 41 are introduced.

[0099]

[0100]

[0101]

[0102] Substituting Equations 39 to 41 into Equation 3, α 2 -ω0 2 Dynamic braking current I when >0 R Equation 42 is obtained, which shows:

[0103]

[0104] To summarize, α 2 -ω0 2 When 0, the motor current I L is expressed by Equation 23, and the dynamic braking current I R is expressed by Equation 42. 2 -ω0 2 <0, the motor current I L is expressed by Equation 34, and the dynamic braking current I R is expressed by Equation 38.

[0105] The output current I from the inverter 11 detected by the current detection unit 16 is expressed as in Equation 1. Therefore, the motor current I relative to the output current I from the inverter 11 is L Current ratio D L is expressed as in Equation 43. Furthermore, the dynamic braking current I R Current ratio D R is expressed as in Equation 44.

[0106]

[0107]

[0108] When equations 23, 34, 38, and 42 are substituted into equations 43 and 44, V in each equation is eliminated, and the motor current I relative to the output current I from the inverter 11 is L Current ratio D L and the dynamic braking current I relative to the output current I from the inverter 11. R Current ratio D Rcan be expressed using the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor 61 of the motor 3, and the capacitance value C of the smoothing capacitor 12. From this, the motor current I L Current ratio D L and the dynamic braking current I relative to the output current I from the inverter 11. R Current ratio D R It can be seen that can be calculated in advance before the discharge process is performed.

[0109] Therefore, the current value detected by the current detection unit 16 at every fixed time ΔT is calculated by subtracting the dynamic braking current I from the output current I of the inverter 11, which is expressed by Equation 43. R Similarly, the dynamic braking current for each fixed time ΔT can be calculated by multiplying the value of the current detected by the current detection unit 16 for each fixed time ΔT by the ratio of the motor current I to the output current I of the inverter 11, as shown in Equation 44. L By multiplying the current ratio of L Note that when the discharge process is executed, the discharge path via the dynamic braking resistors 31U, 31V, and 31W and the discharge path via the motor 3 change depending on the combination of switching elements that are turned on. Therefore, when the current calculation unit 21 calculates the dynamic braking current and the motor current, it should be noted that the resistance value R and inductance value L in the above equations are the resistance value of the combined resistance of the dynamic braking resistors 31U, 31V, and 31W and the inductance value L calculated from the motor phases under the discharge path determined by the combination of switching elements that are turned on.

[0110] First Embodiment of the Present Disclosure In the first embodiment of the present disclosure, the value of the dynamic braking current flowing through the dynamic braking resistor 31U, 31V, or 31W estimated during the discharge process is calculated, and execution and stop of the discharge process are controlled so that the dynamic braking current does not exceed the allowable value of the dynamic braking resistor 31U, 31V, or 31W.

[0111] The tolerance may be set to, for example, the maximum allowable current value or the continuous rated current value specified by the manufacturer or distributor of the dynamic braking resistor 31U, 31V, or 31W. Furthermore, for safety reasons, the tolerance may be set to a value that is several percent to several hundred percent smaller than the maximum allowable current value or the continuous rated current value of the dynamic braking resistor 31U, 31V, or 31W. The values ​​given here are merely examples, and other values ​​may also be used.

[0112] 1 , 2A, and 2B , a motor drive device 1 according to a first embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0113] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0114] The current calculation unit 21 calculates the dynamic braking current I for the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 38, 42, and 44. R Current ratio D R Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the above, the dynamic braking current for each fixed time ΔT is calculated sequentially.

[0115] When the discharge process is executed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the dynamic braking current calculated by the current calculation unit 21 does not exceed the allowable value. U , S.V.U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0116] FIG. 4 is a process showing an operation flow when discharging the smoothing capacitor in the motor drive device according to the first embodiment of the present disclosure.

[0117] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S101, the current calculation unit 21 calculates the value of the dynamic braking current.

[0118] In step S102, the inverter control unit 14 determines whether the value of the dynamic braking current calculated by the current calculation unit 21 is less than the allowable value.

[0119] If it is determined in step S102 that the value of the dynamic braking current is less than the allowable value, a discharge process is executed for a certain period of time in step S103. In the discharge process in step S103, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0120] In step S104 following step S103, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0121] If it is not determined in step S104 that the DC link voltage has become zero, the discharge process continues and the process returns to step S101.

[0122] If it is determined in step S104 that the DC link voltage has become zero, the process ends.

[0123] If it is determined in step S102 that the dynamic braking current value exceeds the allowable value, in step S105, the inverter control unit 14 controls all switching elements in the inverter 11 to turn off, thereby suspending the discharging process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S105, the process returns to step S101.

[0124] The processing of steps S101 to S105 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S101 to S105, the value of the dynamic braking current is calculated successively. The discharge processing continues while the process returns from step S103 to step S101 via No in step S104 and step S102 is executed again. On the other hand, the discharge processing remains suspended while the process returns from step S105 to step S101 and step S102 is executed again.

[0125] 10 is a waveform diagram illustrating the relationship between the current and the allowable value and threshold value, where the horizontal axis represents time and the vertical axis represents the dynamic braking current, the motor current, or the inverter output current.

[0126] In the first embodiment of the present disclosure, when the discharge process is started at time 0, for example, the dynamic braking current increases. If the dynamic braking current exceeds the allowable value at time t1, the discharge process is stopped for a certain period of time M. This reduces the dynamic braking current. If the discharge process is started at time t2, which is the certain period of time M after the discharge process was stopped, the dynamic braking current increases again.

[0127] According to the first embodiment of the present disclosure, the dynamic braking current flowing through the dynamic braking resistor during the discharge process can be suppressed to less than the allowable value, and therefore the dynamic braking resistor 31U, 31V, or 31W will not be damaged by the discharge process.

[0128] <Second embodiment of the present disclosure> In a second embodiment of the present disclosure, the value of the motor current flowing through the windings of the motor 3 estimated during the discharge process is calculated, and the execution and stop of the discharge process are controlled so that the motor current does not exceed the allowable value of the motor 3.

[0129] The allowable value may be set, for example, to the maximum allowable current value or continuous rated current value specified by the manufacturer or distributor of the motor 3. Furthermore, in consideration of safety, the allowable value may be set to a value that is several percent to several hundred percent smaller than the maximum allowable current value or continuous rated current value of the motor 3. Note that the numerical values ​​given here are merely examples, and other numerical values ​​may also be used.

[0130] 1 , 2A, and 2B , a motor drive device 1 according to a second embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0131] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, inverter control unit 14, dynamic braking control unit 15, current detection unit 16, switching unit 17, and switching control unit 18 are as described with reference to FIG. 1.

[0132] The current calculation unit 21 calculates the motor current I with respect to the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 23, 34, and 43. L Current ratio D L Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the current ratio, the motor current is calculated successively for each fixed time ΔT.

[0133] When the discharge process is performed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the motor current calculated by the current calculation unit 21 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0134] FIG. 5 is a process showing an operation flow when discharging a smoothing capacitor in the motor drive device according to the second embodiment of the present disclosure.

[0135] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power supply 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S201, the current calculation unit 21 calculates the value of the motor current.

[0136] In step S202, the inverter control unit 14 determines whether the value of the motor current calculated by the current calculation unit 21 is less than the allowable value.

[0137] If it is determined in step S202 that the motor current value is less than the allowable value, a discharge process is executed for a certain period of time in step S203. In the discharge process in step S203, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0138] In step S204 following step S203, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0139] If it is not determined in step S204 that the DC link voltage has become zero, the discharge process continues and the process returns to step S201.

[0140] If it is determined in step S204 that the DC link voltage has become zero, the process ends.

[0141] If it is determined in step S202 that the motor current value exceeds the allowable value, in step S205, the inverter control unit 14 controls all switching elements in the inverter 11 to turn off, thereby suspending the discharge process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S205, the process returns to step S201.

[0142] The processing of steps S201 to S205 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S201 to S205, the value of the motor current is calculated successively. The discharge processing continues while the process returns from step S203 to step S201 via No in step S204 and step S202 is executed again. On the other hand, the discharge processing remains suspended while the process returns from step S205 to step S201 and step S202 is executed again.

[0143] In the second embodiment, as shown in Figure 10, when the discharge process is started at time 0, for example, the motor current increases. If the dynamic braking current exceeds the allowable value at time t1, the discharge process is stopped for a certain period of time M. This causes the motor current to decrease. When the discharge process is started at time t2, which is the certain period of time M after the discharge process was stopped, the motor current increases again.

[0144] According to the second embodiment of the present disclosure, the motor current flowing through the windings of the motor 3 during the discharge process can be suppressed to less than the allowable value, so that the windings of the motor 3 are not damaged by the discharge process.

[0145] Third Embodiment of the Present Disclosure In a third embodiment of the present disclosure, execution and stop of a discharge process are controlled so that the output current from the inverter 11 detected by the current detection unit 16 does not exceed the allowable value of the dynamic braking resistor 31U, 31V, or 31W and / or the allowable value of the motor 3. The third embodiment of the present disclosure prevents the output current from the inverter 11 from exceeding the allowable value, which has the advantage of providing stronger protection for the dynamic braking resistor 31U, 31V, or 31W than the first embodiment of the present disclosure. The third embodiment of the present disclosure also has the advantage of reducing the computational load because it is not necessary to calculate the dynamic braking current. However, the third embodiment of the present disclosure may take longer to complete the discharge of the smoothing capacitor 12 than the first embodiment of the present disclosure.

[0146] 1 , a motor drive device 1 according to the second embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0147] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0148] When the discharge process is performed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the output current of the inverter 11 calculated by the current detection unit 16 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L For example, the inverter control unit 14 controls the on / off operation of the switching elements SU and SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed the allowable value of the dynamic braking resistors 31U, 31V, or 31W during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Further, for example, the inverter control unit 14 controls the on / off operation of the switching element SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed the allowable value of the motor 3 during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. LFurthermore, for example, the inverter control unit 14 controls the on / off operation of the switching elements SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed both the allowable value of the dynamic braking resistors 31U, 31V, or 31W and the allowable value of the motor 3 during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0149] FIG. 6 is a process showing an operation flow when discharging a smoothing capacitor in the motor drive device according to the third embodiment of the present disclosure.

[0150] Before the discharge of the DC power stored in the smoothing capacitor 12 starts, the switching control unit 18 controls the switching unit 17 to open, thereby blocking the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S301, the current detection unit 16 detects the value of the output current of the inverter 11.

[0151] In step S302, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value. For example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the dynamic braking resistor 31U, 31V, or 31W. Alternatively, for example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the motor 3. Alternatively, for example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the dynamic braking resistor 31U, 31V, or 31W and less than the allowable value of the motor 3.

[0152] If it is determined in step S302 that the value of the output current of the inverter 11 is less than the allowable value, a discharge process is executed for a certain period of time in step S303. In the discharge process in step S303, the inverter control unit 14 controls only the upper-arm switching elements of one phase in the inverter 11 and the lower-arm switching elements of another phase different from the one phase to be turned on, while the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper-arm switching elements of one phase in the inverter 11 and the lower-arm switching elements of two phases different from the one phase to be turned on, while the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper-arm switching elements of two phases in the inverter 11 and the lower-arm switching elements of one phase different from the two phases to be turned on, while the other switching elements are turned off.

[0153] In step S304 following step S303, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0154] If it is not determined in step S304 that the DC link voltage has become zero, the discharge process continues and the process returns to step S301.

[0155] If it is determined in step S304 that the DC link voltage has become zero, the process ends.

[0156] If it is determined in step S302 that the value of the output current of the inverter 11 exceeds the allowable value, in step S305, the inverter control unit 14 controls all switching elements in the inverter 11 to turn off, thereby suspending the discharge process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S305, the process returns to step S301.

[0157] The processing of steps S301 to S305 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S301 to S305, the value of the output current from the inverter 11 is successively detected. The discharge processing continues while the process returns from step S303 to step S301 via No in step S304 and step S302 is executed again. On the other hand, the discharge processing continues to be stopped while the process returns from step S305 to step S301 and step S302 is executed again.

[0158] In the third embodiment, as shown in Fig. 10, when the discharge process is started at time 0, for example, the output current of the inverter 11 increases. If the output current of the inverter 11 exceeds the allowable value at time t1, the discharge process is stopped for a certain time M. This causes the output current of the inverter 11 to decrease. When the discharge process is started at time t2, which is the certain time M after the discharge process was stopped, the output current of the inverter 11 increases again.

[0159] According to the third embodiment of the present disclosure, the output current from the inverter 11 flowing through the dynamic braking resistor during the discharge process can be kept below the allowable value, so that the dynamic braking resistor 31U, 31V, or 31W is not damaged by the discharge process.

[0160] In the first embodiment described above, if the dynamic braking current exceeds the allowable value of the dynamic braking resistor 31U, 31V, or 31W, the discharge process is stopped for a certain period of time (step S105), and then the process returns to step S101. In contrast, in the fourth embodiment of the present disclosure, if the dynamic braking current exceeds the allowable value of the dynamic braking resistor 31U, 31V, or 31W, the discharge process is stopped until the dynamic braking current reaches a value near 0 A. The value near 0 A is, for example, several mA to several tens of mA, but may be any other value.

[0161] 1 , 2A, and 2B , a motor drive device 1 according to a fourth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0162] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0163] The current calculation unit 21 calculates the dynamic braking current I for the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 38, 42, and 44. R Current ratio D R Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the above, the dynamic braking current for each fixed time ΔT is calculated sequentially.

[0164] When the discharge process is executed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the dynamic braking current calculated by the current calculation unit 21 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0165] FIG. 7 is a process showing an operation flow when discharging the smoothing capacitor in the motor drive device according to the fourth embodiment of the present disclosure.

[0166] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S401, the current calculation unit 21 calculates the value of the dynamic braking current.

[0167] In step S402, the inverter control unit 14 determines whether the value of the dynamic braking current calculated by the current calculation unit 21 in step S401 is less than the allowable value.

[0168] If it is determined in step S402 that the value of the dynamic braking current is less than the allowable value, discharge processing is executed in step S403. In the discharge processing of step S403, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0169] In step S404 following step S403, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0170] If it is not determined in step S404 that the DC link voltage has become zero, the discharge process continues and the process returns to step S401.

[0171] If it is determined in step S404 that the DC link voltage has become zero, the process ends.

[0172] If it is determined in step S402 that the dynamic braking current value exceeds the allowable value, in step S405, the inverter control unit 14 controls all switching elements in the inverter 11 to be turned off, thereby stopping the discharge process. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored.

[0173] In step S406, the current calculation unit 21 calculates the value of the dynamic braking current.

[0174] In step S407, the inverter control unit 14 determines whether the value of the dynamic braking current calculated by the current calculation unit 21 in step S406 is close to 0 [A].

[0175] If it is determined in step S407 that the value of the dynamic braking current is close to 0 [A], the discharge process remains stopped and the process returns to step S401.

[0176] If it is determined in step S407 that the value of the dynamic braking current is not close to 0 [A], the process returns to step S406.

[0177] The processes of steps S406 and S407 are repeatedly executed until it is determined in step S407 that the value of the dynamic braking current is close to 0 [A]. This is because, when the current calculation unit 21 sequentially calculates the dynamic braking current for each fixed time ΔT, the dynamic braking current needs to be reset to 0 [A] at the start of step S401.

[0178] The processes of steps S401 to S407 are repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processes of steps S401 to S407, the value of the dynamic braking current is calculated successively. The discharge process continues while the process returns from step S403 to step S401 via No in step S404 and step S402 is executed again. On the other hand, the discharge process remains suspended while the process returns from step S405 to step S401 via Yes in steps S406 and S407 and step S402 is executed again.

[0179] In the fourth embodiment, as shown in FIG. 10 , when the discharge process is started at time 0, the dynamic braking current increases. When the dynamic braking current exceeds the allowable value at time t1 and the discharge process is stopped, the dynamic braking current decreases. When the dynamic braking current falls below the threshold at time t2, the discharge process is started. This causes the dynamic braking current to increase again.

[0180] According to the fourth embodiment of the present disclosure, the dynamic braking current flowing through the dynamic braking resistor during the discharge process can be suppressed to less than the allowable value, so that the dynamic braking resistor 31U, 31V, or 31W will not be damaged by the discharge process.

[0181] Fifth Embodiment of the Present Disclosure In the second embodiment described above, if the motor current exceeds the allowable value of the motor 3, the discharge process is stopped for a certain period of time (step S205), and then the process returns to step S201. In contrast, in the fifth embodiment of the present disclosure, if the motor current exceeds the allowable value of the motor 3, the discharge process is stopped until the motor current value reaches a value near 0 [A]. The value near 0 [A] is, for example, several [mA] to several tens [mA], but may be any other value.

[0182] 1 , 2A, and 2B , a motor drive device 1 according to a fifth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0183] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0184] The current calculation unit 21 calculates the motor current I with respect to the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 23, 34, and 43. L Current ratio D L Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the current ratio, the motor current is calculated successively for each fixed time ΔT.

[0185] When the discharge process is performed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the motor current calculated by the current calculation unit 21 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0186] FIG. 8 is a process showing an operation flow when discharging a smoothing capacitor in the motor drive device according to the fifth embodiment of the present disclosure.

[0187] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power supply 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S501, the current calculation unit 21 calculates the value of the motor current.

[0188] In step S502, the inverter control unit 14 determines whether the value of the motor current calculated by the current calculation unit 21 in step S501 is less than the allowable value.

[0189] If it is determined in step S502 that the motor current value is less than the allowable value, a discharge process is executed in step S503. In the discharge process in step S503, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0190] In step S504 following step S503, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0191] If it is not determined in step S504 that the DC link voltage has become zero, the discharge process continues and the process returns to step S501.

[0192] If it is determined in step S504 that the DC link voltage has become zero, the process ends.

[0193] If it is determined in step S502 that the motor current value exceeds the allowable value, in step S505, the discharge process is stopped by turning off all switching elements in the inverter 11 under the control of the inverter control unit 14. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored.

[0194] In step S506, the current calculation unit 21 calculates the value of the motor current.

[0195] In step S507, the inverter control unit 14 determines whether the value of the motor current calculated by the current calculation unit 21 in step S506 is close to 0 [A].

[0196] If it is determined in step S507 that the motor current value is close to 0 [A], the discharge process remains stopped and the process returns to step S501.

[0197] If it is determined in step S507 that the motor current value is not near 0 [A], the process returns to step S506.

[0198] The processing of steps S506 and S507 is repeatedly executed until it is determined in step S507 that the value of the motor current is close to 0 [A]. This is because, when the current calculation unit 21 sequentially calculates the motor current for each fixed time ΔT, it is necessary to reset the motor current to 0 [A] at the start of step S501.

[0199] The processing of steps S501 to S507 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S501 to S507, the value of the motor current is calculated successively. The discharge processing continues while the process returns from step S503 to step S501 via No in step S504 and step S502 is executed again. On the other hand, the discharge processing continues to be stopped while the process returns from step S505 to step S501 via Yes in step S506 and step S507 and step S502 is executed again.

[0200] In the fifth embodiment of the present disclosure, as shown in FIG. 10 , when the discharge process is started at time 0, the motor current increases. When the motor current exceeds the allowable value at time t1 and the discharge process is stopped, the motor current decreases. When the motor current falls below the threshold at time t2, the discharge process is started. This causes the motor current to increase again.

[0201] According to the fifth embodiment of the present disclosure, the motor current flowing through the windings of the motor 3 can be kept below the allowable value when the discharge process is performed, so that the windings of the motor 3 are not damaged by the discharge process.

[0202] Sixth Embodiment of the Present Disclosure In the third embodiment described above, if the output current from the inverter 11 exceeds the tolerance of the dynamic braking resistor 31U, 31V, or 31W and / or the tolerance of the motor 3, the discharge process is stopped for a certain period of time (step S305), and then the process returns to step S301. In contrast, in the sixth embodiment of the present disclosure, if the output current from the inverter 11 exceeds the tolerance of the dynamic braking resistor 31U, 31V, or 31W and / or the tolerance of the motor 3, the discharge process is stopped until the output current from the inverter 11 falls below a predetermined threshold. The threshold is set to a value smaller than the tolerance. A smaller threshold reduces the discharge efficiency, but reduces the load on the dynamic braking resistor 31U, 31V, or 31W and / or the load on the motor 3. A larger threshold improves the discharge efficiency, but increases the load on the dynamic braking resistor 31U, 31V, or 31W and / or the load on the motor 3, making them more susceptible to heat generation.

[0203] 1 , a motor drive device 1 according to the sixth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0204] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0205] When the discharge process is performed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the value of the output current of the inverter 11 calculated by the current detection unit 16 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W.L For example, the inverter control unit 14 controls the on / off operation of the switching elements SU and SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed the allowable value of the dynamic braking resistors 31U, 31V, or 31W during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Further, for example, the inverter control unit 14 controls the on / off operation of the switching element SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed the allowable value of the motor 3 during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Furthermore, for example, the inverter control unit 14 controls the on / off operation of the switching elements SU in the inverter 11 so that the value of the output current of the inverter 11 detected by the current detection unit 16 does not exceed both the allowable value of the dynamic braking resistors 31U, 31V, or 31W and the allowable value of the motor 3 during the discharge process. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0206] FIG. 9 is a process showing an operation flow when discharging a smoothing capacitor in a motor drive device according to the sixth embodiment of the present disclosure.

[0207] Before the discharge of the DC power stored in the smoothing capacitor 12 starts, the switching control unit 18 controls the switching unit 17 to open, thereby blocking the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S601, the current detection unit 16 detects the value of the output current of the inverter 11.

[0208] In step S602, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value. For example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the dynamic braking resistor 31U, 31V, or 31W. Alternatively, for example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the motor 3. Alternatively, for example, the inverter control unit 14 determines whether the value of the output current of the inverter 11 detected by the current detection unit 16 is less than the allowable value of the dynamic braking resistor 31U, 31V, or 31W and less than the allowable value of the motor 3.

[0209] If it is determined in step S602 that the value of the output current of the inverter 11 is less than the allowable value, a discharge process is executed in step S603. In the discharge process of step S603, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0210] In step S604 following step S603, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0211] If it is not determined in step S604 that the DC link voltage has become zero, the discharge process continues and the process returns to step S601.

[0212] If it is determined in step S604 that the DC link voltage has become zero, the process ends.

[0213] If it is determined in step S602 that the value of the output current of the inverter 11 exceeds the allowable value, in step S605, the inverter control unit 14 controls all switching elements in the inverter 11 to be turned off, thereby halting the discharge process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored.

[0214] In step S606 , the current detection unit 16 detects the value of the output current of the inverter 11 .

[0215] If it is determined in step S607 that the value of the output current of the inverter 11 exceeds the threshold value, the discharge process remains stopped, and the process returns to step S606.

[0216] If it is determined in step S607 that the value of the output current of the inverter 11 is less than the threshold value, the process proceeds to step S603, where a discharge process is executed.

[0217] The processing of steps S601 to S607 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S601 to S605, the value of the output current of the inverter 11 is successively calculated. The discharge processing continues while the process returns from step S603 to step S601 via No in step S604 and step S602 is executed again. On the other hand, the discharge processing remains suspended while the process returns from step S605 to step S601 via No in steps S606 and S607 and step S602 is executed again.

[0218] In the sixth embodiment, when the discharge process is started at time 0, for example, the output current of the inverter 11 increases. When the output current of the inverter 11 exceeds the allowable value at time t1 and the discharge process is stopped, the output current of the inverter 11 decreases. When the output current of the inverter 11 falls below the threshold at time t2, the discharge process is started. This causes the output current of the inverter 11 to increase again.

[0219] According to the sixth embodiment of the present disclosure, the output current from the inverter 11 flowing through the dynamic braking resistor during the discharge process can be kept below the allowable value, so that the dynamic braking resistor 31U, 31V, or 31W or the motor 3 will not be damaged by the discharge process.

[0220] Seventh Embodiment of the Present Disclosure In a seventh embodiment of the present disclosure, a discharge process is performed while preventing power consumption in a dynamic braking resistor from exceeding a predetermined allowable power value.

[0221] The allowable power value may be set, for example, to the maximum allowable power value or continuous rated power value specified by the manufacturer or distributor of the dynamic braking resistor 31U, 31V, or 31W. Furthermore, for safety reasons, the allowable power value may be set to a value that is several percent to several hundred percent smaller than the maximum allowable power value or continuous rated power value of the dynamic braking resistor 31U, 31V, or 31W. Note that the values ​​listed here are merely examples, and other values ​​may also be used. For example, if the dynamic braking resistor 31U, 31V, or 31W is configured as a cement resistor, the allowable power value may be set to the maximum allowable power value or continuous rated power value specified by the manufacturer or distributor of the cement resistor.

[0222] FIG. 11 is a diagram illustrating a motor drive device according to a seventh embodiment of the present disclosure.

[0223] 11 , a motor drive device 1 according to the seventh embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a power consumption calculation unit 22, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0224] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0225] The current calculation unit 21 calculates the dynamic braking current I for the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 38, 42, and 44. R Current ratio D R Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the above, the dynamic braking current for each fixed time ΔT is calculated sequentially.

[0226] The power consumption calculation unit 22 calculates the power consumption values ​​of the dynamic braking resistors 31U, 31V, and 31W based on the resistance values ​​of the dynamic braking resistors 31U, 31V, and 31W and the value of the current flowing through the dynamic braking resistors for each fixed time ΔT calculated by the current calculation unit 21.

[0227] The value of the current flowing through the dynamic braking resistors 31U, 31V, and 31W at each fixed time ΔT calculated by the current calculation unit 21 is expressed as I R (t), R × I for each fixed time ΔT as shown in Equation 45 R (t) 2The power consumption P of the dynamic braking resistors 31U, 31V, and 31W is calculated by integrating the power consumption P from the start time 0 of the discharge process to the time τ when the discharge process is temporarily stopped. R can be obtained.

[0228]

[0229] When the discharge process is executed, the inverter control unit 14 controls the switching element SU in the inverter 11 so that the power consumption at the dynamic braking current calculated by the power consumption calculation unit 22 does not exceed the allowable value. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Controls the on / off operation of the

[0230] FIG. 12 is a process showing an operation flow when discharging a smoothing capacitor in the motor drive device according to the seventh embodiment of the present disclosure.

[0231] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby interrupting the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S701, the current calculation unit 21 calculates the value of the dynamic braking current.

[0232] In step S702, the power consumption calculation unit 22 calculates the value of the power consumption at the dynamic braking current.

[0233] In step S703, the inverter control unit 14 determines whether the value of the power consumption at the dynamic braking resistance calculated by the power consumption calculation unit 22 is less than the allowable power value.

[0234] If it is determined in step S703 that the power consumption value of the dynamic braking resistor is less than the allowable power value, a discharge process is executed for a certain period of time in step S704. In the discharge process in step S704, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0235] In step S705 following step S704, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0236] If it is not determined in step S705 that the DC link voltage has become zero, the discharge process continues and the process returns to step S701.

[0237] If it is determined in step S705 that the DC link voltage has become zero, the process ends.

[0238] If it is determined in step S703 that the power consumption value at the dynamic braking resistor exceeds the allowable power value, in step S706, the inverter control unit 14 controls all switching elements in the inverter 11 to turn off, thereby suspending the discharge process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S706, the process returns to step S701.

[0239] The processing of steps S701 to S706 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S701 to S706, the dynamic braking current value and the power consumption value at the dynamic braking resistor are successively calculated. The discharge processing continues while the process returns from step S704 to step S701 via No in step S705, and then to step S702 and step S703 again. On the other hand, the discharge processing remains suspended while the process returns from step S706 to step S701, and then to step S702 and step S703 again.

[0240] According to the seventh embodiment of the present disclosure, the power consumption in the dynamic braking resistor can be kept below the allowable power value during the discharge process, so that the dynamic braking resistor 31U, 31V, or 31W is not damaged by the discharge process.

[0241] Eighth Embodiment of the Present Disclosure In an eighth embodiment of the present disclosure, the value of the stored power in the smoothing capacitor 12 is calculated before discharging, and if the value of the stored power in the smoothing capacitor 12 does not exceed the allowable power value, a discharging process is performed while preventing the value of the dynamic braking current from exceeding the allowable value, and if the stored power in the smoothing capacitor 12 exceeds the allowable power value, a discharging process is performed while preventing the value of the dynamic braking current from exceeding the allowable value and preventing the value of power consumption in the dynamic braking resistor from exceeding the allowable power value.

[0242] FIG. 13 is a diagram illustrating a motor driving device according to an eighth embodiment of the present disclosure.

[0243] 13 , a motor drive device 1 according to an eighth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a power consumption calculation unit 22, an accumulated power calculation unit 23, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0244] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0245] The stored power calculation unit 23 calculates the value of stored power in the smoothing capacitor 12 based on the capacitance value of the smoothing capacitor 12 and the voltage of the smoothing capacitor 12 detected by the voltage detection unit 19. When the capacitance value of the smoothing capacitor 12 is C [F] and the voltage of the smoothing capacitor 12 detected by the voltage detection unit 19 is V0 [V], the stored power in the smoothing capacitor 12 is expressed by Equation 45.

[0246]

[0247] The current calculation unit 21 calculates the dynamic braking current I for the output current I of the inverter 11 for each fixed time ΔT from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12 in accordance with Equations 38, 42, and 44. R Current ratio D R Then, the dynamic braking current I for the output current I of the inverter 11 is calculated based on the current value detected by the current detection unit 16 at regular intervals ΔT. R By multiplying the current ratio by the above, the dynamic braking current for each fixed time ΔT is calculated sequentially.

[0248] The power consumption calculation unit 22 calculates the values ​​of power consumption at the dynamic braking resistors 31U, 31V, and 31W according to Equation 45, based on the resistance values ​​of the dynamic braking resistors 31U, 31V, and 31W and the value of the current flowing through the dynamic braking resistor for each fixed time ΔT calculated by the current calculation unit 21. The power consumption calculation unit 22 is as described in the seventh embodiment of the present disclosure.

[0249] If the value of the stored power does not exceed the allowable power value of the dynamic braking resistor, inverter control unit 14 controls the on / off operation of the switching elements during discharge processing so that the value of the dynamic braking current calculated by current calculation unit 21 does not exceed the allowable value. Furthermore, if the value of the stored power exceeds the allowable power value of the dynamic braking resistor, inverter control unit 14 controls the on / off operation of the switching elements during discharge processing so that the value of the dynamic braking current calculated by current calculation unit 21 does not exceed the allowable value and so that the value of the power consumption at the dynamic braking resistor calculated by power consumption calculation unit 22 does not exceed the allowable power value.

[0250] FIG. 14 is a process showing an operation flow when discharging a smoothing capacitor in the motor drive device according to the eighth embodiment of the present disclosure.

[0251] Before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby blocking the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, in step S801, the stored power calculation unit 23 calculates the value of the stored power in the smoothing capacitor 12.

[0252] In step S802, the inverter control unit 14 determines whether the value of the stored power in the smoothing capacitor 12 calculated by the stored power calculation unit 23 is less than the allowable power value.

[0253] If it is determined in step S802 that the value of the stored power is less than the allowable power value, the current calculation unit 21 calculates the value of the dynamic braking current in step S803.

[0254] In step S804 following step S803, the inverter control unit 14 determines whether the value of the dynamic braking current calculated by the current calculation unit 21 in step S803 is less than the allowable value.

[0255] If it is determined in step S804 that the value of the dynamic braking current is less than the allowable value, discharge processing is executed for a certain period of time in step S806. In the discharge processing in step S806, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of another phase different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of one phase in the inverter 11 and the lower arm switching elements of two phases different from the one phase to be turned on, and the other switching elements are turned off. Alternatively, the inverter control unit 14 controls the upper arm switching elements of two phases in the inverter 11 and the lower arm switching elements of one phase different from the two phases to be turned on, and the other switching elements are turned off.

[0256] If it is determined in step S804 that the dynamic braking current value exceeds the allowable value, the discharge process is stopped for a certain period of time in step S805. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S805, the process returns to step S803.

[0257] In step S807 following step S806, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0258] If it is not determined in step S807 that the DC link voltage has become zero, the discharge process continues and the process returns to step S803.

[0259] If it is determined in step S807 that the DC link voltage has become zero, the process ends.

[0260] If it is determined in step S802 that the value of the stored power exceeds the allowable power value, the current calculation unit 21 calculates the value of the dynamic braking current in step S808.

[0261] If it is determined in step S809 that the dynamic braking current value exceeds the allowable value, the discharge process is stopped for a certain period of time in step S814. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S814, the process returns to step S808.

[0262] In step S809, the inverter control unit 14 determines whether the value of the dynamic braking current calculated by the current calculation unit 21 in step S808 is less than the allowable value.

[0263] If it is determined in step S809 that the value of the dynamic braking current is less than the allowable value, the power consumption calculation unit 22 calculates the value of the power consumption at the dynamic braking current in step S810.

[0264] In step S811, the inverter control unit 14 determines whether the value of the power consumption at the dynamic braking resistance calculated by the power consumption calculation unit 22 is less than the allowable power value.

[0265] If it is determined in step S811 that the power consumption value of the dynamic braking resistor is less than the allowable power value, a discharge process is executed for a certain period of time in step S812. In the discharge process in step S812, only the upper arm switching element of one phase in the inverter 11 and the lower arm switching element of another phase different from the one phase are turned on under the control of the inverter control unit 14, and the other switching elements are turned off.

[0266] In step S813 following step S812, the inverter control unit 14 determines whether the DC link voltage has become zero. As described above, the DC link voltage corresponds to the voltage of the smoothing capacitor 12 and is detected by the voltage detection unit 19.

[0267] If it is not determined in step S813 that the DC link voltage has become zero, the discharge process continues and the process returns to step S808.

[0268] If it is determined in step S813 that the DC link voltage has become zero, the process ends.

[0269] If it is determined in step S811 that the power consumption value at the dynamic braking resistor exceeds the allowable power value, in step S814, the inverter control unit 14 controls all switching elements in the inverter 11 to turn off, thereby suspending the discharging process for a certain period of time. When all switching elements in the inverter 11 are turned off, no current flows from the DC side to the AC side via the inverter 11, so the charge in the smoothing capacitor 12 is not discharged and remains stored. After a certain period of time has elapsed from step S814, the process returns to step S808.

[0270] The processing of steps S801 to S814 is repeatedly executed at a predetermined cycle until the DC link voltage becomes zero, i.e., until the voltage of the smoothing capacitor 12 becomes zero. By repeatedly executing the processing of steps S801 to S814, the dynamic braking current value and the power consumption value at the dynamic braking resistor are sequentially calculated. The discharge processing is continuously executed while the process returns from step S806 to step S803 via a "No" in step S807 and step S804 is executed again. The discharge processing is continuously executed while the process returns from step S812 to step S808 via a "No" in step S813 and step S810 and step S811 are executed again. Meanwhile, the discharge processing is suspended while the process returns from step S805 to step S803 and step S804 is executed again. The discharge processing is suspended while the process returns from step S814 to step S808 and step S810 and step S811 are executed again.

[0271] As described above, in the eighth embodiment of the present disclosure, when the value of the stored power in the smoothing capacitor 12 does not exceed the allowable power value, the discharge process is performed while preventing the value of the dynamic braking current from exceeding the allowable value. As a modification of this embodiment, when the value of the stored power in the smoothing capacitor 12 does not exceed the allowable power value, the discharge process is performed while preventing the value of the motor current from exceeding the allowable value. However, even in this modification, the current calculation unit 21 needs to calculate the value of the dynamic braking current in order for the stored power calculation unit 23 to calculate the value of the stored power in the smoothing capacitor 12.

[0272] According to the eighth embodiment of the present disclosure, the dynamic braking current flowing through the dynamic braking resistor during the discharge process can be kept below the allowable value, and the power consumption of the dynamic braking resistor can be kept below the allowable power value. Therefore, the dynamic braking resistor 31U, 31V, or 31W will not be damaged by the discharge process.

[0273] Ninth Embodiment of the Present Disclosure In the first and second embodiments described above, the dynamic braking current I with respect to the output current I of the inverter 11 for each fixed time ΔT is calculated from the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12. R Current ratio D R or motor current I L Current ratio D L Calculate the current ratio D R or D L In the ninth embodiment of the present disclosure, the dynamic braking current is calculated sequentially for each fixed time ΔT based on the voltage value V of the smoothing capacitor 12 detected by the voltage detection unit 19, the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12, according to Equation 38 and Equation 42. Also, in the ninth embodiment of the present disclosure, the motor current is calculated sequentially for each fixed time ΔT based on the voltage value V of the smoothing capacitor 12 detected by the voltage detection unit 19, the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12, according to Equation 23 and Equation 34.

[0274] FIG. 15 is a diagram illustrating a motor drive device according to a ninth embodiment of the present disclosure.

[0275] 15 , a motor drive device 1 according to the ninth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a time zone calculation unit 24, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0276] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0277] The current calculation unit 21 sequentially calculates the value of the dynamic braking current for each fixed time ΔT based on the voltage value of the smoothing capacitor 12 before the discharge process is executed, the resistance value of the dynamic braking resistor, the inductance value of the motor 3, and the capacitance value of the smoothing capacitor 12. When the voltage value V0 of the smoothing capacitor 12 before the discharge process is substituted into Equation 38 and Equation 42, they become functions with t as the only variable. Therefore, by sequentially substituting t = ΔT × n (n is an integer equal to or greater than 0) into Equation 38 and Equation 42 after the voltage value V0 of the smoothing capacitor 12 is substituted, the value of the dynamic braking current for each fixed time ΔT can be calculated.

[0278] Alternatively, the current calculation unit 21 may sequentially calculate the motor current value for each fixed time ΔT based on the voltage value of the smoothing capacitor 12 before the discharge process is executed, the resistance value of the dynamic braking resistor, the inductance value of the motor 3, and the capacitance value of the smoothing capacitor 12. When the voltage value V0 of the smoothing capacitor 12 before the discharge process is substituted into Equation 23 and Equation 34, they become functions with t as the only variable. Therefore, by sequentially substituting t = ΔT × n (n is an integer equal to or greater than 0) into Equation 23 and Equation 34 after substituting the voltage value V0 of the smoothing capacitor 12, the motor current value for each fixed time ΔT can be calculated.

[0279] The time zone calculation unit 24 calculates a time zone during which the value of the current calculated by the current calculation unit 21 exceeds the allowable value. When the current calculation unit 21 calculates the value of the dynamic braking current, the time zone calculation unit 24 calculates a time zone during which the value of the dynamic braking current calculated by the current calculation unit 21 exceeds the allowable value. When the current calculation unit 21 calculates the value of the motor current, the time zone calculation unit 24 calculates a time zone during which the value of the motor current calculated by the current calculation unit 21 exceeds the allowable value.

[0280] When the discharge process is being executed, the inverter control unit 14 controls the upper arm switching elements of one or two phases in the inverter 11 and the lower arm switching elements of one or two phases that are different from the one or two phases to be turned on only during the time period when the value of the dynamic braking current calculated by the time period calculation unit 24 exceeds the allowable value. If the current calculation unit 21 calculates the value of the dynamic braking current, the inverter control unit 14 controls the upper arm switching elements of one or two phases in the inverter 11 and the lower arm switching elements of one or two phases that are different from the one or two phases to be turned on only during the time period when the value of the dynamic braking current calculated by the time period calculation unit 24 exceeds the allowable value, and controls the other switching elements to be turned off. When the current calculation unit 21 calculates the value of the motor current, the inverter control unit 14 controls the inverter 11 to turn on the upper arm switching elements of one or two phases in the inverter 11 and the lower arm switching elements of two or one phase that are different from the one or two phases in the inverter 11 during the time period in which the value of the motor current calculated by the time period calculation unit 24 exceeds the allowable value during the discharge process, and to turn off the other switching elements.

[0281] According to the ninth embodiment of the present disclosure, when the current calculation unit 21 calculates the value of the dynamic braking current, the dynamic braking current flowing through the dynamic braking resistor during the discharge process can be kept below the allowable value, so that the dynamic braking resistor 31U, 31V, or 31W will not be damaged by the discharge process.

[0282] Furthermore, according to the ninth embodiment of the present disclosure, when the current calculation unit 21 calculates the value of the motor current, the motor current can be kept below the allowable value when the discharge process is performed, so that the windings of the motor 3 will not be damaged by the discharge process.

[0283] Tenth Embodiment of the Present Disclosure In the seventh embodiment described above, the value of power consumption at the dynamic braking resistor is calculated based on the resistance values ​​of the dynamic braking resistors 31U, 31V, and 31W and the value of the current flowing through the dynamic braking resistor for each fixed time ΔT calculated by the current calculation unit 21. In contrast, in the tenth embodiment of the present disclosure, the value of power consumption at the dynamic braking resistor for each fixed time ΔT is calculated sequentially based on the voltage value V of the smoothing capacitor 12 detected by the voltage detection unit 19, the resistance value R of the dynamic braking resistor 31, the inductance value L of the interphase reactor of the motor 3, and the capacitance value C of the smoothing capacitor 12.

[0284] FIG. 16 is a diagram illustrating a motor drive device according to a tenth embodiment of the present disclosure.

[0285] 16 , a motor drive device 1 according to a tenth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current calculation unit 21, a time zone calculation unit 24, a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0286] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, switching control unit 18, and voltage detection unit 19 are as described with reference to FIG. 1.

[0287] The power consumption calculation unit 22 sequentially calculates the value of power consumption at the dynamic braking resistor for each fixed time ΔT based on the voltage value of the smoothing capacitor 12 before the discharge process is executed, the resistance value of the dynamic braking resistor, the inductance value of the motor 3, and the capacitance value of the smoothing capacitor 12. When the voltage value V0 of the smoothing capacitor 12 before the discharge process is substituted into Equation 45, it becomes a function with t as the only variable. Therefore, by sequentially substituting t = ΔT × n (n is an integer equal to or greater than 0) into Equation 45 after substituting the voltage value V0 of the smoothing capacitor 12, it is possible to calculate the value of power consumption at the dynamic braking resistor for each fixed time ΔT.

[0288] The time period calculation unit 24 calculates a time period in which the power consumption value calculated by the power consumption calculation unit 22 exceeds the allowable power value.

[0289] When performing a discharge process, the inverter control unit 14 controls the inverter 11 to turn on the upper arm switching elements of one phase and the lower arm switching elements of one phase different from the one phase, and to turn off the other switching elements, only during a time period when the power consumption value calculated by the time period calculation unit 24 exceeds the allowable power value. Alternatively, when performing a discharge process, the inverter control unit 14 controls the inverter 11 to turn on the upper arm switching elements of two phases and the lower arm switching elements of one phase different from the two phases, and to turn off the other switching elements, only during a time period when the power consumption value calculated by the time period calculation unit 24 exceeds the allowable power value. Alternatively, when performing a discharge process, the inverter control unit 14 controls the inverter 11 to turn on the upper arm switching elements of one phase and the lower arm switching elements of two phases different from the one phase, and to turn off the other switching elements, only during a time period when the power consumption value calculated by the time period calculation unit 24 exceeds the allowable power value.

[0290] According to the tenth embodiment of the present disclosure, the power consumption in the dynamic braking resistor can be kept below the allowable power value during the discharge process, so that the dynamic braking resistor 31U, 31V, or 31W is not damaged by the discharge process.

[0291] Eleventh Embodiment of the Present Disclosure In the first to tenth embodiments described above, current flows through the motor 3 even when the discharge process is being performed, which could cause the motor 3 to rotate. The discharge process is performed after the motor drive device is powered off or after a power outage occurs, so it is dangerous if the motor 3 rotates at this time. Therefore, in the eleventh embodiment of the present disclosure, the q-axis current component is prevented from flowing through the windings of the motor 3 to prevent the motor 3 from rotating when the discharge process is being performed.

[0292] 17 is a diagram illustrating a motor drive device according to an eleventh embodiment of the present disclosure, in which the AC power supply 2, the converter 10, the switching unit 17, and the switching control unit 18 are omitted from the illustration.

[0293] 17 , a motor drive device 1 according to an eleventh embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, and a dynamic braking control unit 15. The motor drive device 1 also includes a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits.

[0294] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, dynamic braking control unit 15, current detection unit 16, switching unit 17, and switching control unit 18 are as described with reference to FIG. 1.

[0295] The inverter control unit 14 includes a position detection unit 141 , a position control unit 142 , a current detection unit 16 , a three-phase dq current conversion unit 143 , a current control unit 144 , a dq three-phase voltage conversion unit 145 , and a switching control unit 146 .

[0296] The position detection unit 141 acquires position information (rotor phase angle) θ of the motor 3 from the encoder 51 attached to the motor 3 .

[0297] The position control unit 142 calculates the d-axis current command i on the dq coordinate system based on the position information. d * and d-axis current i d Generate.

[0298] The current detection unit 16 detects the three-phase AC current i output from the inverter 11. u , i v , and i w Detect.

[0299] The three-phase dq current converter 143 converts the current i in the three-phase coordinate system detected by the current detector 16 according to Equation 47. u , i v , and i w is the d-axis current i on the dq coordinate system. d and q-axis current i d Convert it to and output it.

[0300]

[0301] The current control unit 144 controls the d-axis current i d The d-axis current command i d * In order to make the d-axis current command i d * and d-axis current i d Based on the d-axis voltage command v d1 * In addition, the current control unit 144 generates the q-axis current i q The q-axis current command i q * In order to make the q-axis current command i q * and q-axis current i q Based on the q-axis voltage command v q1 * The d-axis voltage command v d1 * and q-axis voltage command v q1 * The method of generating the current control unit 144 does not limit the present embodiment, and may be realized by, for example, a known method. Note that the configuration of the current control unit 144 defined here is merely an example, and the configuration of the current control unit 144 may be defined using terms such as PI control and PID control.

[0302] The dq three-phase voltage converter 145 converts the d-axis voltage command v d * and q-axis voltage command v *is expressed as the U-phase voltage command v u * , V-phase voltage command v v * , and W-phase voltage command v w * Convert it to and output it.

[0303]

[0304] The switching control unit 146 outputs a three-phase voltage command v u * , v v * , and v w * Based on the switching element SU U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L and generates a drive command for controlling the on / off operation of the switching element SU. U , S.V. U , S.W. U , S.U. L , S.V. L , and S.W. L Send to.

[0305] When the discharge process is performed, before starting to discharge the DC power stored in the smoothing capacitor 12, the switching control unit 18 controls the switching unit 17 to open, thereby cutting off the flow of AC power from the AC power source 2 to the converter 10, and the dynamic braking control unit 15 controls to close the switch 32. Then, the position control unit 142 controls the q-axis current command i q * The current control section 144 sets the q-axis current i q The q-axis current command i q * Therefore, the q-axis current i q According to the eleventh embodiment of the present disclosure, when the discharge process is performed, the q-axis current i q Since the component of the current does not flow, no torque is generated in the motor 3, and therefore the motor 3 does not rotate.

[0306] <Twelfth embodiment of the present disclosure> In the first to tenth embodiments described above, current flows through the motor 3 even during the discharge process, which could cause the motor 3 to rotate. The discharge process is performed after the motor drive device is powered off or after a power outage occurs, so it is dangerous if the motor 3 rotates at this time. Therefore, in the twelfth embodiment of the present disclosure, a power cut-off unit is provided to cut off the AC power flowing from the inverter 11 to the motor 3 so that the motor 3 does not rotate during the discharge process.

[0307] FIG. 18 is a diagram illustrating a motor drive device according to a twelfth embodiment of the present disclosure.

[0308] 18 , a motor drive device 1 according to a twelfth embodiment of the present disclosure includes a converter 10, an inverter 11, a smoothing capacitor 12, a dynamic braking circuit 13, an inverter control unit 14, a dynamic braking control unit 15, a power cut-off unit 41, and a cut-off control unit 42. The motor drive device 1 also includes a current detection unit 16, a switching unit 17, a switching control unit 18, a voltage detection unit 19, and other circuits. Although not shown here, the power lines that supply power to drive the inverter control unit 14, the dynamic braking control unit 15, the current detection unit 16, the switching control unit 18, the voltage detection unit 19, and the cut-off control unit 42 are provided in a system separate from the power line that supplies power from the AC power source 2 to the converter 10.

[0309] The AC power supply 2, motor 3, converter 10, inverter 11, smoothing capacitor 12, dynamic braking circuit 13, inverter control unit 14, dynamic braking control unit 15, current detection unit 16, switching unit 17, and switching control unit 18 are as described with reference to FIG. 1.

[0310] The power cutoff unit 41 opens and closes the electrical path between the inverter 11 and (the windings of) the motor 3 (i.e., the three-phase power line electrically connecting the inverter 11 and the motor 3). The power cutoff unit 41 is composed of a relay, a switching element, etc.

[0311] The cutoff control unit 42 controls the power cutoff unit 41 to open and close the electrical path between the inverter 11 and the motor 3 .

[0312] When the discharge process is performed, before starting to discharge the DC power stored in the smoothing capacitor 12, the switch control unit 18 controls the switch 17 to open, thereby cutting off the flow of AC power from the AC power supply 2 to the converter 10, and the dynamic braking control unit 15 controls the switch 32 to close. Then, the cutoff control unit 42 controls the power cutoff unit 41 to open. According to the twelfth embodiment of the present disclosure, because no current flows through the windings of the motor 3 during the discharge process, no torque is generated in the motor 3, and therefore the motor 3 does not rotate.

[0313] <Relationship Between Switching Element Operation and Heat Generation in Dynamic Braking Resistors> As described above, in the first to twelfth embodiments, during discharge processing, the inverter control unit 14 controls the switching elements of the upper and lower arms of different phases to be turned on. That is, the inverter control unit 14 controls only the upper arm switching element of one phase in the inverter 11 and the lower arm switching element of another phase different from the upper arm switching element, while turning off the other switching elements. Current from the smoothing capacitor 12 flows into the dynamic braking resistors 31U, 31V, and 31W via the turned-on switching elements in the inverter 11 and is consumed as Joule heat, causing the dynamic braking resistors 31U, 31V, and 31W to generate heat. In addition, the current from the smoothing capacitor 12 also flows through the turned-on switching elements in the inverter 11, causing the conducting switching elements to generate heat.

[0314] 19 is a diagram illustrating temperature changes in the dynamic braking resistors that occur when the switching elements are turned on during discharge processing as shown in FIG. 19 shows, from top to bottom, the temperatures of the dynamic braking resistor 31U, the dynamic braking resistor 31V, and the dynamic braking resistor 31W.

[0315] For example, from time 0 to time t3, as shown in FIG. 2A, the upper arm switching element SV U and the U-phase lower arm switching element SU LOnly the switching element SU is turned on. U , S.W. U , S.V. L , and S.W. L This series of processes turns off the smoothing capacitor 12 and the switching element SV U , dynamic brake resistor 31V, dynamic brake resistor 31U, switching element SU L A closed circuit is formed, extending back to the smoothing capacitor 12 via the inverter 11. As a result, the charge stored in the smoothing capacitor 12 flows through the inverter 11 to the dynamic braking resistors 31U and 31V and is consumed as Joule heat. Therefore, between time 0 and time t3, the temperatures of the dynamic braking resistors 31U and 31V rise, but the temperature of the dynamic braking resistor 31W does not rise. In this way, if the switching elements to be turned on during the discharge process are fixed, the switching elements through which the dynamic braking current flows and the dynamic braking resistors 31U, 31V, and 31W are fixed, resulting in a bias in the heat-generating switching elements and the dynamic braking resistors 31U, 31V, and 31W. As a result, the lifespans of the switching elements and the dynamic braking resistors 31U, 31V, and 31W also become biased. Therefore, it is preferable to sequentially switch the phases of the upper-arm switching elements and the lower-arm switching elements that are turned on during the discharge process.

[0316] FIG. 20 is a circuit diagram illustrating an example of the current flowing through the dynamic braking resistor when the switching elements of the U-phase upper arm and the W-phase lower arm are turned on during the discharge process.

[0317] In FIG. 20, the upper arm switching element SU U and the W-phase lower arm switching element SW L Only the switching element SV is turned on. U , S.W. U , S.U. L , and S.V. L At this time, the smoothing capacitor 12 is turned off. U, dynamic brake resistor 31U, dynamic brake resistor 31W, switching element SW L A closed circuit is formed that extends from the inverter 11 to the smoothing capacitor 12 again. As a result, the charge stored in the smoothing capacitor 12 flows into the dynamic braking resistors 31U and 31W through the inverter 11 and is consumed as Joule heat, causing the temperatures of the dynamic braking resistors 31U and 31W to rise.

[0318] FIG. 21 is a circuit diagram illustrating an example of a current flowing through a dynamic braking resistor when the switching elements of the V-phase upper arm and the W-phase lower arm are turned on during the discharge process.

[0319] In FIG. 21, the upper arm switching element SV U and the W-phase lower arm switching element SW L Only the switching element SU is turned on. U , S.W. U , S.U. L , and S.V. L At this time, the smoothing capacitor 12 is turned off. U , dynamic brake resistor 31V, dynamic brake resistor 31W, switching element SW L A closed circuit is formed that extends from the inverter 11 to the smoothing capacitor 12 again. As a result, the charge stored in the smoothing capacitor 12 flows into the dynamic braking resistors 31V and 31W through the inverter 11 and is consumed as Joule heat, causing the temperatures of the dynamic braking resistors 31V and 31W to rise.

[0320] FIG. 22 is a diagram illustrating temperature changes in the dynamic braking resistor that occur when the switching elements are turned on as shown in FIGS. 2A, 20, and 21 during the discharge process.

[0321] From time 0 to time t1, as shown in FIG. 2A, the upper arm switching element SV U and the U-phase lower arm switching element SU L Only the switching element SU is turned on. U , S.W.U , S.V. L , and S.W. L When the dynamic braking resistors 31U and 31V are turned off, a dynamic braking current flows through the dynamic braking resistors 31U and 31V. Therefore, the temperatures of the dynamic braking resistors 31U and 31V rise, but the temperature of the dynamic braking resistor 31W does not rise.

[0322] As shown in FIG. 20, from time t1 to time t2, the upper arm switching element SU U and the W-phase lower arm switching element SW L Only the switching element SV is turned on. U , S.W. U , S.U. L , and S.V. L When the dynamic braking resistors 31U and 31W are turned off, a dynamic braking current flows through the dynamic braking resistors 31U and 31W. Therefore, the temperatures of the dynamic braking resistors 31U and 31W rise, and the temperature of the dynamic braking resistor 31V falls.

[0323] From time t2 to time t3, as shown in FIG. 21, the upper arm switching element SV U and the W-phase lower arm switching element SW L Only the switching element SU is turned on. U , S.W. U , S.U. L , and S.V. L When the dynamic braking resistors 31V and 31W are turned off, a dynamic braking current flows through the dynamic braking resistors 31V and 31W. Therefore, the temperatures of the dynamic braking resistors 31V and 31W rise, and the temperature of the dynamic braking resistor 31U falls.

[0324] In this way, by sequentially switching the phases of the upper arm switching elements and the lower arm switching elements that are turned on during discharge processing, it is possible to distribute the conductive switching elements and the heat-generating dynamic braking resistors 31U, 31V, and 31W, respectively, thereby leveling out the lifespans of the switching elements and dynamic braking resistors 31U, 31V, and 31W.

[0325] As described above, it is preferable that the inverter control unit 14 performs control to sequentially switch the phases of the upper arm switching elements and the lower arm switching elements to be turned on when the discharge process is performed.

[0326] <Processor and Memory> The motor drive device 1 includes at least one processor, which is a processing unit. Examples of the processing unit include an IC, an LSI, a CPU, an MPU, and a DSP. The processing unit includes an inverter control unit 14, a dynamic braking control unit 15, a current detection unit 16, a switching control unit 18, a voltage detection unit 19, a current calculation unit 21, a power consumption calculation unit 22, an accumulated power calculation unit 23, a time zone calculation unit 24, a shutoff control unit 42, and other processing units. Each of these units included in the processing unit is a functional module implemented, for example, by a program executed on the processor. For example, if the inverter control unit 14, the dynamic braking control unit 15, the current detection unit 16, the switching control unit 18, the voltage detection unit 19, the current calculation unit 21, the power consumption calculation unit 22, the accumulated power calculation unit 23, the time zone calculation unit 24, the shutoff control unit 42, and other processing units are implemented in the form of a program, the functions of each unit can be realized by operating the processing unit in accordance with the program. The programs for executing the processes in the inverter control unit 14, dynamic braking control unit 15, current detection unit 16, switching control unit 18, voltage detection unit 19, current calculation unit 21, power consumption calculation unit 22, stored power calculation unit 23, time zone calculation unit 24, shutdown control unit 42, and other processing units may be provided in the form of being recorded on a computer-readable recording medium such as a semiconductor memory, a magnetic recording medium, or an optical recording medium. Alternatively, the inverter control unit 14, dynamic braking control unit 15, current detection unit 16, switching control unit 18, voltage detection unit 19, current calculation unit 21, power consumption calculation unit 22, stored power calculation unit 23, time zone calculation unit 24, shutdown control unit 42, and other processing units may be realized as semiconductor integrated circuits into which programs for realizing the functions of the respective units are written.

[0327] The motor drive device 1 also includes at least one memory serving as a storage device. The memory includes the inverter control unit 14, the dynamic braking control unit 15, the current detection unit 16, the switching control unit 18, the voltage detection unit 19, the current calculation unit 21, the power consumption calculation unit 22, the stored power calculation unit 23, the time zone calculation unit 24, the shutdown control unit 42, and various other storage units within the processing units. Examples of the memory include electrically erasable and recordable nonvolatile memory such as EEPROM (registered trademark), and high-speed read / write random access memory such as DRAM and SRAM. The storage unit may also be configured as a hard disk drive (HDD) or solid state drive (SSD). The memory stores programs for operating the inverter control unit 14, the dynamic braking control unit 15, the current detection unit 16, the switching control unit 18, the voltage detection unit 19, the current calculation unit 21, the power consumption calculation unit 22, the stored power calculation unit 23, the time zone calculation unit 24, the shutdown control unit 42, and other processing units. The memory also stores the value of the output current of the inverter 11 detected by the current detection unit 16 and the value of the voltage of the smoothing capacitor 12 detected by the voltage detection unit 19. The memory also stores the value of the current calculated by the current calculation unit 21, the value of the power consumption calculated by the power consumption calculation unit 22, and the value of the stored power calculated by the stored power calculation unit 23. The memory also stores allowable values, allowable power values, and thresholds. The memory also stores various programs and data related to the inverter control unit 14. The memory also stores various programs and data related to the motor drive device 1.

[0328] <Advantages of the embodiments and modifications thereof of the present disclosure> According to the embodiments and modifications thereof of the present disclosure, it is possible to quickly discharge a smoothing capacitor provided in a DC link between a converter and an inverter in a motor drive device.

[0329] After a motor drive device is powered off or a power outage occurs, charge remains in the smoothing capacitor for a while, posing a risk of electric shock during that time and preventing maintenance, replacement, or recovery work, resulting in poor work efficiency. According to each embodiment and its modified examples of the present disclosure, the charge accumulated in the smoothing capacitor is dissipated as heat by a dynamic braking resistor in a dynamic braking circuit, allowing the smoothing capacitor to be quickly discharged. Depending on the capacitance value of the smoothing capacitor, each embodiment and its modified examples of the present disclosure completes the discharge of the smoothing capacitor in several seconds to several tens of seconds. According to each embodiment and its modified examples of the present disclosure, the discharge time of the smoothing capacitor can be shortened, thereby reducing the risk of electric shock and improving work efficiency.

[0330] In addition, in the past, a discharge circuit having a discharge resistor and a switch has been provided in the DC link, and when discharging the smoothing capacitor, the switch in the discharge circuit is operated to consume the charge stored in the smoothing capacitor through the discharge resistor. However, providing a discharge circuit in the DC link is undesirable because it increases the circuit mounting area, the number of components, and costs. In contrast, according to the embodiments and their modifications of the present disclosure, there is no need to add a discharge circuit and the dynamic braking circuit that was previously provided can be reused, thereby reducing costs and reducing the circuit mounting area and number of components.

[0331] Furthermore, according to the first, fourth, eighth, and ninth embodiments of the present disclosure, the dynamic braking current flowing through the dynamic braking resistor during the discharge process can be suppressed to less than the allowable value, and therefore the dynamic braking resistor will not be damaged by the discharge process.

[0332] Furthermore, according to the second, fifth, and ninth embodiments of the present disclosure, the motor current flowing through the motor windings during the discharge process can be suppressed to less than the allowable value, so that the motor windings will not be damaged by the discharge process.

[0333] Furthermore, according to the third and sixth embodiments of the present disclosure, the output current from the inverter flowing through the dynamic braking resistor during the discharge process can be suppressed to less than the allowable value, so that the dynamic braking resistor is not damaged by the discharge process.

[0334] Furthermore, according to the seventh, eighth, and tenth embodiments of the present disclosure, the power consumption in the dynamic braking resistor can be kept below the allowable power value when the discharge process is performed, and therefore the dynamic braking resistor is not damaged by the discharge process.

[0335] Furthermore, according to the eleventh embodiment of the present disclosure, since no q-axis current component flows through the motor windings when the discharge process is performed, no torque is generated in the motor, and therefore the motor does not rotate, making it safe.

[0336] Furthermore, according to the twelfth embodiment of the present disclosure, no current flows through the motor windings when the discharge process is performed, so no torque is generated in the motor 3 and therefore the motor 3 does not rotate, making it safe.

[0337] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments and individual variations described above. Various additions, substitutions, modifications, partial deletions, etc. are possible for these embodiments and variations within the scope of the gist of the present disclosure, or within the scope of the gist of the present disclosure derived from the content of the claims and their equivalents. These embodiments and variations can also be implemented in combination. For example, in the above-described embodiments and variations, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical formulas are used in the description of the above-described embodiments and variations.

[0338] <Supplementary Notes> The following supplementary notes are further disclosed regarding the above-described embodiment and modifications.

[0339] (Supplementary Note 1) A motor drive device comprising: an inverter comprising a three-phase bridge circuit in which switching elements are provided in each of the upper arms on the high potential side and the lower arms on the low potential side of each of three phases, the switching elements operating on and off to convert input DC power into AC power and output the AC power to a motor; a smoothing capacitor provided on the DC input side of the inverter; a dynamic braking circuit that generates deceleration torque in the motor by closing a switch provided between input terminals of the motor to short-circuit the input terminals via a dynamic braking resistor; an inverter control unit that controls the on and off operation of the switching elements; and a dynamic braking control unit that controls the opening and closing of the switches, wherein the dynamic braking control unit closes the switch, and the inverter control unit turns on only the switching elements of the upper arms of certain one or two phases in the inverter and the switching elements of the lower arms of two or one phases that are different from the certain one or two phases, thereby performing a discharge process to discharge the DC power of the smoothing capacitor. (Supplementary Note 2) The motor drive device according to Supplementary Note 1, comprising: a current detection unit that detects the value of a current output from the inverter; and a current calculation unit that calculates at least one of the value of a current flowing through a dynamic braking resistor and the value of a current flowing through the motor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor, wherein the inverter control unit controls the on / off operation of the switching elements during discharge processing so that the value of the current calculated by the current calculation unit does not exceed an allowable value. (Supplementary Note 3) The motor drive device according to Supplementary Note 1, comprising: a current detection unit that detects the value of a current output from the inverter; and the inverter control unit controls the on / off operation of the switching elements during discharge processing so that the value of the current detected by the current detection unit does not exceed an allowable value of the current flowing through the motor.(Supplementary Note 4) A motor drive device according to Supplementary Note 1, comprising: a current detection unit that detects the value of a current output from the inverter; a current calculation unit that calculates the value of a current flowing through a dynamic braking resistor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of a smoothing capacitor; and a power consumption calculation unit that calculates the value of power consumption at the dynamic braking resistor based on the resistance value of the dynamic braking resistor and the value of the current flowing through the dynamic braking resistor calculated by the current calculation unit, wherein the inverter control unit controls the on / off operation of the switching elements so that the value of power consumption does not exceed an allowable power value during discharge processing. a current calculation unit that calculates the value of the current flowing through the dynamic braking resistor and the value of the current flowing through the motor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; and a power consumption calculation unit that calculates the value of the power consumption at the dynamic braking resistor based on the resistance value of the dynamic braking resistor and the value of the current flowing through the dynamic braking resistor calculated by the current calculation unit, wherein the inverter control unit controls the on / off operation of the switching elements during discharge processing if the value of the stored power does not exceed the allowable power value at the dynamic braking resistor, and controls the on / off operation of the switching elements during discharge processing if the value of the stored power exceeds the allowable power value at the dynamic braking resistor.(Supplementary Note 6) A motor drive device according to Supplementary Note 1, comprising: a current calculation unit that calculates at least one of the value of the current flowing through the dynamic braking resistor and the value of the current flowing through the motor based on the voltage value of the smoothing capacitor before execution of a discharge process, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; a time period calculation unit that calculates a time period during which the value of the current calculated by the current calculation unit exceeds an allowable value; and an inverter control unit that, during execution of a discharge process, controls to turn on a switching element of an upper arm of one phase in the inverter and a switching element of a lower arm of one phase different from the one phase, only during the time period during which the value of the current calculated by the time period calculation unit exceeds the allowable value. (Supplementary Note 7) A motor drive device according to Supplementary Note 1, comprising: a power consumption calculation unit that calculates a value of power consumption at a dynamic brake resistor based on a voltage value of a smoothing capacitor before execution of a discharge process, a resistance value of the dynamic brake resistor, an inductance value of the motor, and a capacitance value of the smoothing capacitor; a time period calculation unit that calculates a time period during which the value of power consumption calculated by the power consumption calculation unit exceeds an allowable power value; and an inverter control unit that, during execution of a discharge process, controls an upper arm switching element of one phase in the inverter and a lower arm switching element of a phase different from the one phase to be turned on only during the time period during which the value of power consumption calculated by the time period calculation unit exceeds the allowable power value.a current control unit that converts the current on the three-phase coordinate system detected by the current detection unit into d-axis current and q-axis current on the dq coordinate system and outputs them; a current control unit that generates a d-axis voltage command based on the d-axis current command and the d-axis current, and generates a q-axis voltage command based on the q-axis current command and the q-axis current; a dq three-phase voltage conversion unit that converts the d-axis voltage command and the q-axis voltage command into three-phase voltage commands on the three-phase coordinate system and outputs them; and a switching control unit that controls the on / off operation of switching elements based on the three-phase voltage commands, wherein the q-axis current command is set to zero in the position control unit, thereby preventing a q-axis current component from flowing through the motor when a discharge process is performed. (Supplementary Note 9) The motor drive device according to Supplementary Note 1, further comprising: a power cut-off unit that opens and closes an electric path between the inverter and the motor; and a cut-off control unit that controls the power cut-off unit to open and close the electric path, wherein the cut-off control unit opens the power cut-off unit when a discharge process is performed. (Supplementary Note 10) The motor drive device according to any one of Supplementary Notes 1 to 9, wherein the inverter control unit sequentially switches the phases of the upper arm switching elements and the lower arm switching elements that are turned on when a discharge process is performed. (Supplementary Note 11) The motor drive device according to any one of Supplementary Notes 1 to 9, further comprising: a converter that is provided on the DC input side of the inverter via a smoothing capacitor, and converts input AC power into DC power and outputs the DC power to the inverter, a switching unit that is provided between the AC power source and the converter, and opens and closes the electric path between the AC power source and the converter, and a switching control unit that controls the switching unit to open and close the electric path, wherein the switching control unit opens the switching unit when a discharge process is performed. (Appendix 12) The motor drive device according to any one of appendices 1 to 9, wherein, during discharge processing, the inverter control unit turns on only the upper arm switching element of one phase in the inverter and the lower arm switching element of one phase different from the one phase, and turns off the other switching elements.(Supplementary Note 13) The motor drive device according to any one of Supplementary Notes 1 to 9, wherein, during discharge processing, the inverter control unit turns on only the upper arm switching elements of certain two phases in the inverter and the lower arm switching elements of a phase different from the certain two phases, and turns off the other switching elements. (Supplementary Note 14) The motor drive device according to any one of Supplementary Notes 1 to 9, wherein, during discharge processing, the inverter control unit turns on only the upper arm switching elements of certain one phase in the inverter and the lower arm switching elements of two phases different from the certain one phase, and turns off the other switching elements.

[0340] REFERENCE SIGNS LIST 1 Motor drive device 2 AC power supply 3 Motor 10 Converter 11 Inverter 12 Smoothing capacitor 13 Dynamic braking circuit 14 Inverter control unit 15 Dynamic braking control unit 16 Current detection unit 17 Switching unit 18 Switching control unit 19 Voltage detection unit 21 Current calculation unit 22 Power consumption calculation unit 23 Stored power calculation unit 24 Time period calculation unit 31, 31U, 31V, 31W Dynamic braking resistor 32 Switch 41 Power cut-off unit 42 Cut-off control unit 51 Encoder 61 Interphase reactor 141 Position detection unit 142 Position control unit 143 Three-phase dq current conversion unit 144 Current control unit 145 dq three-phase voltage conversion unit 146 Switching control unit SU L , S.V. L , S.W. L , S.U. U , S.V. U , S.W. U Switching element

Claims

1. A motor drive device comprising: an inverter comprising a three-phase bridge circuit in which switching elements are provided in each of the upper arms on the high potential side and the lower arms on the low potential side of each of three phases, the switching elements operating on and off to convert input DC power into AC power and output it to a motor; a smoothing capacitor provided on the DC input side of the inverter; a dynamic braking circuit that generates deceleration torque in the motor by closing a switch provided between the input terminals of the motor to short-circuit the input terminals via a dynamic braking resistor; an inverter control unit that controls the on and off operation of the switching elements; and a dynamic braking control unit that controls the opening and closing of the switches, wherein a discharge process is performed to discharge the DC power of the smoothing capacitor by closing the switch using the dynamic braking control unit and by the inverter control unit turning on only the switching elements of the upper arms of one or two phases in the inverter and the switching elements of the lower arms of two or one phases that are different from the one or two phases.

2. A motor drive device as described in claim 1, comprising: a current detection unit that detects the value of the current output from the inverter; and a current calculation unit that calculates at least one of the value of the current flowing through the dynamic braking resistor and the value of the current flowing through the motor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor, wherein the inverter control unit controls the on / off operation of the switching element so that the value of the current calculated by the current calculation unit does not exceed an allowable value when the discharge process is performed.

3. A motor drive device as described in claim 1, further comprising a current detection unit that detects the value of the current output from the inverter, and wherein the inverter control unit controls the on / off operation of the switching element so that the value of the current detected by the current detection unit does not exceed an allowable value when the discharge process is being performed.

4. A motor drive device as described in claim 1, comprising: a current detection unit that detects the value of the current output from the inverter; a current calculation unit that calculates the value of the current flowing through the dynamic brake resistor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic brake resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; and a power consumption calculation unit that calculates the value of power consumption at the dynamic brake resistor based on the resistance value of the dynamic brake resistor and the value of the current flowing through the dynamic brake resistor calculated by the current calculation unit, wherein the inverter control unit controls the on / off operation of the switching elements so that the value of power consumption does not exceed an allowable power value during the discharge process.

5. A motor drive device according to claim 1, comprising: a current detection unit that detects the value of the current output from the inverter; an accumulated power calculation unit that calculates the value of the accumulated power of the smoothing capacitor; a current calculation unit that calculates the value of the current flowing through the dynamic braking resistor and the value of the current flowing through the motor based on the value of the current output from the inverter detected by the current detection unit, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; and a power consumption calculation unit that calculates the value of power consumption at the dynamic braking resistor based on the resistance value of the dynamic braking resistor and the value of the current flowing through the dynamic braking resistor calculated by the current calculation unit, wherein the inverter control unit controls the on / off operation of the switching element during execution of the discharge process if the value of the accumulated power does not exceed the allowable power value of the dynamic braking resistor, and controls the on / off operation of the switching element during execution of the discharge process if the value of the accumulated power exceeds the allowable power value of the dynamic braking resistor, so that the value of power consumption calculated by the power consumption calculation unit does not exceed the allowable power value.

6. The motor drive device of claim 1, further comprising: a current calculation unit that calculates at least one of the value of the current flowing through the dynamic braking resistor and the value of the current flowing through the motor based on the voltage value of the smoothing capacitor before execution of the discharge process, the resistance value of the dynamic braking resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; a time period calculation unit that calculates a time period during which the value of the current calculated by the current calculation unit exceeds an allowable value; and the inverter control unit, when executing the discharge process, controls the upper arm switching element of one phase in the inverter and the lower arm switching element of one phase different from the one phase to be turned on only during the time period during which the value of the current calculated by the time period calculation unit exceeds the allowable value.

7. The motor drive device of claim 1, further comprising: a power consumption calculation unit that calculates the value of power consumption at the dynamic brake resistor based on the voltage value of the smoothing capacitor before execution of the discharge process, the resistance value of the dynamic brake resistor, the inductance value of the motor, and the capacitance value of the smoothing capacitor; a time period calculation unit that calculates a time period during which the power consumption value calculated by the power consumption calculation unit exceeds an allowable power value; and the inverter control unit, when executing the discharge process, controls the upper arm switching element of one phase in the inverter and the lower arm switching element of one phase different from the one phase to be turned on only during the time period during which the power consumption value calculated by the time period calculation unit exceeds the allowable power value.

8. The motor drive device according to claim 1, wherein the inverter control unit comprises: a position detection unit that acquires position information of the motor from an encoder attached to the motor; a position control unit that generates a d-axis current command and a q-axis current command on a dq coordinate system based on the position information; a current detection unit that detects three-phase AC current output from the inverter; a three-phase dq current conversion unit that converts the current on the three-phase coordinate system detected by the current detection unit into a d-axis current and a q-axis current on the dq coordinate system and outputs them; a current control unit that generates a d-axis voltage command based on the d-axis current command and the d-axis current, and generates a q-axis voltage command based on the q-axis current command and the q-axis current; a dq three-phase voltage conversion unit that converts the d-axis voltage command and the q-axis voltage command into three-phase voltage commands on a three-phase coordinate system and outputs them; and a switching control unit that controls on / off operations of the switching elements based on the three-phase voltage commands, wherein the q-axis current command is set to zero in the position control unit, thereby preventing the q-axis current component from flowing through the motor when the discharge process is performed.

9. The motor drive device according to claim 1, further comprising: a power cut-off unit that opens and closes an electric circuit between the inverter and the motor; and a cut-off control unit that controls the opening and closing of the electric circuit by the power cut-off unit, wherein the cut-off control unit opens the power cut-off unit when the discharge process is performed.

10. A motor drive device according to any one of claims 1 to 9, wherein the inverter control unit sequentially switches the phase of the upper arm switching element and the phase of the lower arm switching element to be turned on when the discharge process is performed.

11. A motor drive device according to any one of claims 1 to 9, further comprising: a converter provided on the DC input side of the inverter via the smoothing capacitor, converting input AC power into DC power and outputting the DC power to the inverter; a switching unit provided between an AC power source and the converter, opening and closing an electric circuit between the AC power source and the converter; and a switching control unit controlling the opening and closing of the electric circuit by the switching unit, wherein the switching control unit opens the switching unit when the discharge process is performed.

12. A motor drive device according to any one of claims 1 to 9, wherein, when the discharge process is performed, the inverter control unit turns on only the upper arm switching element of one phase in the inverter and the lower arm switching element of one phase different from the one phase, and turns off the other switching elements.

13. A motor drive device according to any one of claims 1 to 9, wherein, when the discharge process is performed, the inverter control unit turns on only the upper arm switching elements of two phases in the inverter and the lower arm switching element of one phase different from the two phases, and turns off the other switching elements.

14. A motor drive device according to any one of claims 1 to 9, wherein, when the discharge process is performed, the inverter control unit turns on only the upper arm switching elements of one phase in the inverter and the lower arm switching elements of two phases different from the one phase, and turns off the other switching elements.

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