Drive device and drive method

Abstract

A drive device (100) that rotates an electric motor (2) on the basis of a rotational speed target value and has: a converter (3) that converts a voltage from an AC power supply (1) into a direct current; an inverter (5) that converts the direct current converted by the converter into an alternating current and supplies the alternating current to the electric motor (2); and an inverter circuit control unit (200) that has an instantaneous power calculation unit (8) and a power consumption amount calculation unit (10) and that, when a power consumption amount calculated by the power consumption amount calculation unit (10) exceeds a preset power consumption amount threshold value, causes the rotational speed of the drive device (100) to be lower than the rotational speed target value, said instantaneous power calculation unit (8) calculating instantaneous power for each calculation cycle from a voltage command to the inverter (5) and a current supplied from the inverter (5) to the electric motor (2), said power consumption amount calculation unit (10) calculating the power consumption amounts corresponding to the plurality of instantaneous powers calculated by the instantaneous power calculation unit (8). This makes it possible to enhance robustness for a steep load fluctuation.

Description

Driving device and driving method

[0001] The present disclosure relates to a driving device and a driving method.

[0002] The drive device is connected between a power supply and an electric motor, generates AC voltage from the power supply, and drives the electric motor. The drive device has an inverter circuit and an inverter circuit control unit, and the inverter circuit control unit controls the inverter circuit to control the electric motor.

[0003] For example, Patent Document 1 discloses that a drive device has a converter, an inverter circuit, an inverter circuit control unit, etc., in order to suppress the amount of heat generated by the electric motor, and calculates an actual power value based on the voltage of a capacitor connected in parallel with the converter and the measured value of the current supplied by the inverter to the electric motor, and reduces the rotation speed when the calculated actual power value exceeds a threshold value.

[0004] Here, in a drive device whose purpose is to control the rotation speed of an electric motor such as a fan or pump at a constant speed, it is important to be able to operate the device while suppressing changes in rotation speed as much as possible, even when a sudden load fluctuation occurs due to a disturbance such as the intrusion of foreign matter into the fan or pump.

[0005] International Publication No. 2020 / 188884

[0006] However, since the actual power fluctuates significantly when a sudden load change occurs, the rotation speed is changed every time a sudden load change occurs in Patent Document 1, which may cause the operation of the device itself to become unstable.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a drive device that is highly robust against sudden load fluctuations in a drive device that aims to control the rotation speed of an electric motor at a constant speed.

[0008] The drive device disclosed herein is a drive device that rotates an electric motor based on a rotational speed target value, and includes a converter that converts voltage from an AC power source into DC, an inverter that converts the DC converted by the converter into AC and supplies it to the electric motor, an instantaneous power calculation unit that calculates instantaneous power for each calculation period from a voltage command to the inverter and the current supplied from the inverter to the electric motor, and a power consumption calculation unit that calculates power consumption corresponding to the multiple instantaneous powers calculated by the instantaneous power calculation unit, and an inverter circuit control unit that reduces the rotational speed of the drive device below the rotational speed target value if the power consumption calculated by the power consumption calculation unit exceeds a predetermined power consumption threshold.

[0009] According to the present disclosure, high robustness can be maintained even against abrupt load fluctuations.

[0010] 1 is a schematic configuration diagram showing a drive device according to a first embodiment. FIG. 2 is a diagram showing the relationship between instantaneous power, a calculation period, unit period power consumption, a power consumption calculation value, and a power consumption upper limit value when the calculation period is a unit period in the drive device according to the first embodiment. FIG. 3 is a block diagram of a corrected rotation speed calculation unit according to the first embodiment. FIG. 4 is a flowchart showing the operation of the corrected rotation speed calculation unit according to the first embodiment. FIG. 5 is a block diagram of a Δω calculation unit according to the first embodiment. FIG. 6 is a diagram showing the current flowing in the electric motor when the rotation speed of the drive device according to the first embodiment is decelerated from ω1 to ω2. FIG. 7 is a schematic configuration diagram showing a drive device according to a second embodiment.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts.

[0012] 1 is a schematic diagram showing a drive device 100 for an electric motor 2 according to a first embodiment. The drive device 100 is provided between an AC power supply 1 and an electric motor 2, and has a converter circuit unit 3, a smoothing capacitor 4, an inverter circuit unit 5, a current detection unit 6, and an inverter circuit control unit 200. The converter circuit unit 3, the smoothing capacitor 4, the inverter circuit unit 5, and the current detection unit 6 are provided in parallel between the AC power supply 1 and the electric motor 2.

[0013] The driving device 100 rotates the electric motor 2 with the rotational speed target value ω1* as a target, that is, the driving device 100 rotates the electric motor 2 based on the rotational speed target value ω1*.

[0014] The converter circuit unit 3 converts the voltage from the AC power supply 1 into DC, which is smoothed by a smoothing capacitor 4. The inverter circuit unit 5 converts the smoothed DC voltage into a three-phase voltage in accordance with a gate signal from an inverter circuit control unit 200, and supplies the converted three-phase voltage to the electric motor 2. The inverter circuit unit 5 is an inverter. The converter circuit unit is a converter. The inverter converts the DC converted by the converter into AC, and supplies it to the electric motor 2.

[0015] The current detection unit 6 detects three-phase currents (Iu, Iv, Iw) from the converted three-phase voltages and outputs them to the inverter circuit control unit 200 .

[0016] Inverter circuit control unit 200 has a current coordinate conversion unit 7, an instantaneous power calculation unit 8, a power consumption calculation unit 10, a memory 11, a corrected rotational speed calculation unit 12, an integral calculation unit 13, a voltage command calculation unit 14, a voltage coordinate conversion unit 15, and a PWM signal generation unit 16. Instantaneous power calculation unit 8, power consumption calculation unit 10, memory 11, and corrected rotational speed calculation unit 12 constitute a power consumption suppression calculation unit 300.

[0017] In the inverter circuit control unit 200, the current coordinate conversion unit 7 converts the three-phase current (Iu, Iv, Iw) from the current detection unit 6 into a two-phase current (Id 、 Here, the phase θ used in the coordinate transformation is the phase calculated by the integration calculation unit 13, which will be described later.

[0018] The instantaneous power calculation unit 8 calculates the two-phase current (Id 、 The instantaneous power P[n] is calculated from the voltage command (Vd*, Vq*) and the two-phase voltage command (Vd*, Vq*) calculated by the voltage command calculation unit 14 described later, according to Equation 1. Here, P[n] is the power consumption in the nth calculation cycle. The instantaneous power is also the power consumption of the driving device 100 at the timing of the calculation. The instantaneous power calculation unit calculates the instantaneous power for each calculation cycle from the voltage command to the inverter and the current supplied from the inverter to the electric motor 2.

[0019]

[0020] The power consumption calculation unit 10 calculates a power consumption calculation value West[n] for multiple calculation periods (n0) from the instantaneous power P[n] calculated by the instantaneous power calculation unit 8 according to Equation 2. The power consumption calculation value West[n] is the power consumption. Here, T0 is the calculation period and is set in advance in the memory 11. Furthermore, W[n] is the unit period power consumption of the drive unit 100 for one period for which the instantaneous power was calculated.

[0021]

[0022] The power consumption calculation unit 10 calculates the unit period power consumption W[n] by multiplying the instantaneous power P[n] by the calculation period T0 obtained from the memory 11. The power consumption calculation unit 10 stores the calculated unit period power consumption W[n] for the nth calculation period in the memory 11. The power consumption calculation unit 10 obtains the unit period power consumptions W[n] to W[n-(n0-1)] from the memory 11 and calculates the calculated power consumption value West[n] for the most recent multiple times (n0 times). In other words, the power consumption calculation unit 10 calculates the power consumption corresponding to the multiple instantaneous powers calculated by the instantaneous power calculation unit 8.

[0023] Here, the method by which the power consumption calculation unit 10 calculates the power consumption calculation value West[n] is not limited to this. For example, the memory 11 may store not only the unit period power consumption W[n] but also the power consumption calculation value West[n], and calculate the power consumption calculation value West[n] by subtracting the unit period power consumption W[n-(n0-1)] of the oldest period out of n0 cycles from the power consumption calculation value West[n-1] of the previous cycle, and adding the unit period power consumption W[n] of the current cycle.

[0024] The corrected rotation speed calculation unit 12 calculates the rotation speed correction amount Δω from the power consumption excess amount ΔW[n] expressed by Equation 3. Here, Wmax is the power consumption upper limit value, which is set in advance in the memory 11. The power consumption upper limit value is the power consumption threshold value.

[0025]

[0026] 2 shows the relationship between instantaneous power P[n], unit-period power consumption W[n], calculated power consumption value West[n], and power consumption upper limit Wmax when the calculation period is a unit period. The calculated power consumption value West[n] is calculated by adding up the unit-period power consumption W[n] multiple times.

[0027] 1, a specific method for calculating the rotation speed correction amount Δω in the corrected rotation speed calculation unit 12 will be described later. The corrected rotation speed calculation unit 12 calculates the corrected rotation speed command ω2* according to Equation 4.

[0028]

[0029] The integral calculation unit 13 calculates the phase θ by integrating the corrected rotation speed command ω2*. The voltage command calculation unit 14 calculates two-phase voltage commands (Vd*, Vq*) on the rotating coordinate system according to the corrected rotation speed command ω2*.

[0030] The voltage coordinate conversion unit 15 converts the two-phase voltage commands (Vd*, Vq*) calculated by the voltage command calculation unit 14 into three-phase voltage commands (Vu*, Vv*, Vw*). The phase used in the coordinate conversion is the phase θ calculated by the integral calculation unit 13.

[0031] The PWM signal generating unit 16 outputs a gate signal to the inverter circuit unit 5 based on the three-phase voltage commands (Vu*, Vv*, Vw*) calculated by the voltage coordinate converting unit 15. Here, the gate signal is a pulse width modulated signal.

[0032] That is, if the power consumption calculated by the power consumption calculation unit 10 exceeds a preset power consumption threshold, the inverter circuit control unit 200 reduces the rotation speed of the drive device 100 below the rotation speed target value ω1*.

[0033] 3 is a block diagram of the corrected rotational speed calculation unit 12. The corrected rotational speed calculation unit 12 includes a comparison unit 1201, a rotational speed correction flag setting unit 1202, a Δω calculation unit 1203, and a previous value storage unit 1204.

[0034] The comparator 1201 compares the power consumption excess amount ΔW[n] with 0. The rotation speed correction flag setting unit 1202 sets the rotation speed correction flag for the current calculation cycle based on the power consumption excess amount ΔW[n], the rotation speed correction flag for the previous calculation cycle, and the rotation speed correction amount Δω for the previous calculation cycle. The Δω calculation unit 1203 calculates the rotation speed correction amount Δω based on the power consumption excess amount ΔW[n] and the rotation speed correction amount Δω for the previous cycle. The previous value storage unit 1204 stores the rotation speed correction amount Δω for the previous cycle and the rotation speed correction flag for the previous cycle.

[0035] 4 is a flowchart showing the operation of the corrected rotational speed calculation unit 12. The corrected rotational speed calculation unit 12 calculates the rotational speed correction amount Δω from the power consumption excess amount ΔW[n], the rotational speed correction amount Δω for the previous cycle, and the rotational speed correction flag for the previous cycle. In step ST1, the comparison unit 1201 determines whether the power consumption excess amount ΔW[n] is greater than 0. If it is greater than 0 (Yes in step ST1), the process proceeds to step ST2, where the rotational speed correction flag setting unit 1202 sets the rotational speed correction flag to 1 (ON). Next, the process proceeds to step ST3, where the Δω calculation unit 1203 calculates the rotational speed correction amount Δω, as described below.

[0036] On the other hand, if the power consumption excess amount ΔW[n] is equal to or less than 0 (No in step ST1), the process proceeds to step ST4, where the rotation speed correction flag setting unit 1202 determines whether the rotation speed correction flag for the previous cycle is ON. If the rotation speed correction flag for the previous cycle is ON (Yes in step ST4), the process proceeds to step ST5. In step ST5, the rotation speed correction flag setting unit 1202 determines whether the rotation speed correction amount Δω for the previous cycle is not 0. If the rotation speed correction amount Δω for the previous cycle is not 0 (Yes in step ST5), the process proceeds to step ST6.

[0037] In step ST6, the rotation speed correction flag setting unit 1202 sets the rotation speed correction flag to 1 (ON). Next, the process proceeds to step ST7, where the Δω calculation unit 1203 calculates the rotation speed correction amount Δω as described below.

[0038] If it is determined in step ST4 that the rotation speed correction flag for the previous cycle is not 1 (ON) (No in step ST4), the process proceeds to step ST8. Also, if it is determined in step ST5 that the rotation speed correction amount Δω for the previous cycle is 0 (No in step ST5), the process also proceeds to step ST8, where the rotation speed correction flag setting unit 1202 sets the rotation speed correction flag to 0 (OFF). Next, the process proceeds to step ST9, where the Δω calculation unit 1203 sets the rotation speed correction amount Δω to 0 and ends the process.

[0039] The rotation speed correction amount Δω is a correction amount for reducing the rotation speed at which the inverter circuit control unit 200 drives the drive unit 100 below the rotation speed target value ω1*. In other words, even if the power consumption calculated by the power consumption calculation unit 10 does not exceed a preset power consumption threshold, if the rotation speed of the drive unit 100 was reduced below the rotation speed target value ω1* in the previous calculation cycle, the inverter circuit control unit 200 reduces the rotation speed of the drive unit 100 below the rotation speed target value ω1* in the current calculation cycle.

[0040] Fig. 5 is a block diagram of the Δω calculation unit 1203 corresponding to step ST3 or step ST7 in Fig. 4. The rotation speed correction amount Δω is calculated by performing PI control from the power consumption excess amount ΔW[n], which is the difference between the power consumption calculation value West[n], the power consumption excess amount ΔW[n], and the power consumption upper limit value Wmax.

[0041] 6 is a diagram showing the current flowing through the electric motor 2 when the rotational speed is reduced from ω1 to ω2. In the case of an electric motor 2 having a reduced torque load characteristic, the output current of the driving device 100 is proportional to the square of the rotational speed. Therefore, particularly in the high-speed range, even if the rotational speed correction amount Δω is small, the output current of the driving device 100 can be significantly reduced, and the driving device 100 can achieve a high energy-saving effect.

[0042] As described above, according to this embodiment, the instantaneous power calculation unit 8 calculates the calculated power consumption value West[n] for a certain interval using the current output from the inverter circuit unit 5 and the voltage command input to the inverter circuit unit 5, and reduces the rotation speed when the calculated power consumption value West[n] exceeds the power consumption upper limit value Wmax. The actual voltage output from the inverter circuit unit 5 fluctuates significantly when a sudden load change occurs due to a disturbance such as the inclusion of foreign matter. In this embodiment, the voltage command is used instead of the actual voltage output from the inverter circuit unit 5, so that the drive device 100 can be realized with high robustness that is not affected by sudden load changes, compared to when the calculated power consumption value is calculated using the actual voltage.

[0043] Furthermore, in this embodiment, the rotation speed is corrected when the power consumption calculation value West[n] exceeds the power consumption upper limit Wmax, and even if the power consumption calculation value West[n] does not exceed the power consumption upper limit Wmax, the rotation speed correction amount Δω is corrected if the rotation speed correction amount Δω for the previous cycle is not 0. This further improves the robustness of the output of the drive device 100 compared to correcting the rotation speed regardless of the rotation speed correction amount Δω for the previous cycle when the power consumption calculation value West[n] does not exceed the power consumption upper limit Wmax.

[0044] Second Embodiment Fig. 7 is a schematic diagram showing a drive device 100 according to a second embodiment. Explanation of the same parts as in the first embodiment will be omitted. The drive device 100 according to the second embodiment will be explained based on Fig. 7. The difference from the first embodiment is that an average power calculation unit 9 is added. Other aspects are the same as those of the first embodiment.

[0045] In the first embodiment, the power consumption for a certain interval is calculated by adding up the unit period power consumption (instantaneous power P[n] x calculation period T0) for the certain interval. In the second embodiment, the average value of the instantaneous power P[n] for the certain interval is calculated, and the calculated power consumption value West[n] for the certain interval is calculated by multiplying the average value by the duration of the certain interval.

[0046] The average power calculation unit 9 acquires the instantaneous power P[n] calculated by the instantaneous power calculation unit 8 and the instantaneous powers (P[n-1] to P[n-(n0-1)]) from the memory for the previous and previous periods. The average power calculation unit 9 calculates the average power Pave[n], which is the average value of the instantaneous powers for the most recent n0 calculation periods. The average power calculation unit 9 calculates the average value of the instantaneous powers for multiple calculation periods.

[0047] The power consumption calculation unit 10 acquires the time length Tdef for n0 calculation cycles and the average power Pave[n] output by the average power calculation unit 9 from the memory 11. The power consumption calculation unit 10 calculates the power consumption calculation value West by multiplying the average power Pave[n] by the time length Tdef. The power consumption calculation unit calculates the power consumption using the average value of the instantaneous power. The subsequent processing is the same as in the first embodiment.

[0048] As described above, according to this embodiment, similarly to the first embodiment, the instantaneous power calculation unit 8 calculates the power consumption for a certain period using the current that is the output of the inverter circuit unit 5 and the voltage command that is the input to the inverter circuit unit 5. Even in this case, the same effects as those of the first embodiment can be achieved.

[0049] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and can be combined with other known technologies, or the above embodiments can be combined, or parts of the configurations can be omitted or modified within the scope of the gist of the present disclosure.

[0050] REFERENCE SIGNS LIST 1 AC power supply, 2 Electric motor, 3 Converter circuit unit, 5 Inverter circuit unit, 6 Current detection unit, 7 Current coordinate conversion unit, 8 Instantaneous power calculation unit, 9 Average power calculation unit, 10 Power consumption calculation unit, 11 Memory, 12 Corrected rotation speed calculation unit, 13 Integration calculation unit, 14 Voltage command calculation unit 15 Voltage coordinate conversion unit, 16 PWM signal generation unit, 100 Drive device, 200 Inverter circuit control unit.

Claims

1. A drive device that rotates an electric motor based on a rotational speed target value, comprising: a converter that converts voltage from an AC power source into DC; an inverter that converts the DC converted by the converter into AC and supplies it to the electric motor; an instantaneous power calculation unit that calculates instantaneous power for each calculation period from a voltage command to the inverter and a current supplied from the inverter to the electric motor; and an inverter circuit control unit that calculates power consumption corresponding to multiple instantaneous powers calculated by the instantaneous power calculation unit, and that reduces the rotational speed of the drive device below the rotational speed target value when the power consumption calculated by the power consumption calculation unit exceeds a predetermined power consumption threshold.

2. The drive device according to claim 1, characterized in that the inverter circuit control unit further has an average power calculation unit, which calculates the average value of the instantaneous power for multiple times, and the power consumption calculation unit calculates the power consumption using the average value of the instantaneous power.

3. The drive device according to claim 1 or 2, characterized in that, even if the power consumption calculated by the power consumption calculation unit does not exceed a preset power consumption threshold, if the rotation speed of the drive device was reduced below the rotation speed target value in the previous calculation cycle, the inverter circuit control unit reduces the rotation speed of the drive device below the rotation speed target value in the current calculation cycle.

4. A method for driving a drive device that rotates an electric motor based on a rotational speed target value, comprising: a step of converting voltage from an AC power source into DC; a step of converting the converted DC into AC and supplying it to the electric motor; a step of calculating instantaneous power for each calculation period from a voltage command to an inverter and a current supplied from the inverter to the electric motor; a step of calculating power consumption corresponding to a plurality of the instantaneous powers; and a step of reducing the rotational speed of the drive device below the rotational speed target value when the power consumption exceeds a predetermined power consumption threshold.

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