Electric pump control device

Abstract

To provide a technology that increases the possibility of preventing the generation of vibration and noise caused by unnecessarily setting the carrier frequency in PWM control below a predetermined level. [Solution] An electric pump control device for controlling an electric pump comprises an inverter that converts power between a DC power supply and an AC motor that drives the electric pump, and an inverter that has a plurality of switching elements, and a control circuit that controls the inverter, wherein the control circuit comprises a processor that sets the carrier frequency in PWM control that switches the plurality of switching elements of the inverter based on the rotational speed of the motor and at least one of the voltage value applied from the DC power supply or the temperature of the working fluid pumped by the electric pump.

Description

Technical Field

[0001] The present invention relates to an electric pump control device.

Background Art

[0002] Conventionally, a drive device is known that includes an electric motor, an inverter having a plurality of switching elements for driving the electric motor, and control means for controlling the inverter to switch the plurality of switching elements of the inverter by a pulse width modulation (PWM) control method using a predetermined carrier frequency (for example, Patent Document 1). Patent Document 1 discloses that when the rotational speed of the motor is less than the threshold value Nref, the frequency Fc1 is used, and when the rotational speed of the motor is greater than or equal to the threshold value Nref, a frequency Fc2 higher than the frequency Fc1 is used (paragraph 0024, FIG. 4). By setting the carrier frequency low during low rotation of the motor in this way, good starting performance can be obtained. On the other hand, when the rotational speed of the motor increases, it is known that NV (noise and vibration) can be suppressed by setting the carrier frequency higher than when the motor is rotating slowly. However, at high motor speeds, if the carrier frequency is not set low, the switching elements of the inverter may overheat. Therefore, output limitation of the motor is also performed at high motor speeds to set the carrier frequency low. <​​​​​​​​​​​​​​​​​​​​​Conventionally, as described above, the carrier frequency was set low at low and high motor speeds, and high at all other speeds. As a result, noise and vibration can be suppressed when the motor is rotating at speeds other than low and high speeds.

[0005] However, conventional technology uniformly sets the carrier frequency in PWM control based solely on the motor's rotational speed. Therefore, when considering a motor that drives an electric pump, the set carrier frequency may not be appropriate depending on the conditions of the electric pump. In other words, even though it is possible to set a higher frequency than a predetermined level, the carrier frequency in PWM control may be unnecessarily set below the predetermined level.

[0006] This invention has been made in view of the above problems, and aims to provide a technology that can increase the possibility of preventing the generation of noise and vibration caused by unnecessarily setting the carrier frequency in PWM control to below a predetermined level. [Means for solving the problem]

[0007] To achieve the above objective, the electric pump control device for controlling the electric pump comprises an inverter that converts power between a DC power supply and an AC motor that drives the electric pump, and a control circuit that controls the inverter, wherein the control circuit includes a processor that sets the carrier frequency in PWM control for switching the plurality of switching elements of the inverter based on the rotational speed of the motor and at least one of the voltage value applied from the DC power supply or the temperature of the working fluid pumped by the electric pump.

[0008] In other words, the processor does not set the carrier frequency based solely on the motor's rotational speed, but also takes into account the voltage applied from the DC power supply and the temperature of the working fluid pumped by the electric pump. For example, if good startup performance and excessive heat generation of the switching elements can be ensured even when the carrier frequency is set above a predetermined level based on at least one of the rotational speed and voltage or the working fluid temperature, then the carrier frequency is set above the predetermined level. On the other hand, if good startup performance and excessive heat generation of the switching elements cannot be ensured unless the carrier frequency is set below a predetermined level based on at least one of the rotational speed and voltage or the working fluid temperature, then the carrier frequency is set below the predetermined level.

[0009] Therefore, it is possible to increase the likelihood of preventing the generation of noise and vibration caused by unnecessarily setting the carrier frequency in PWM control below a predetermined level. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the overall configuration of the electric pump, including the electric pump control device. [Figure 2] This is a schematic cross-sectional view of an electric pump showing the cooling structure of a switching element. [Figure 3] This is a diagram showing the configuration of the working fluid circulation system. [Figure 4] This diagram shows the relationship between motor rotation speed and carrier frequency. [Figure 5] This diagram shows the relationship between motor rotation speed and carrier frequency. [Modes for carrying out the invention]

[0011] Here, embodiments of the present invention will be described in the following order. (1) Overall configuration of the electric pump, including the electric pump control device: (2) Detailed configuration of the electric pump: (3) Configuration of the working fluid circulation system: (4) Carrier frequency setting control: (5) Other embodiments:

[0012] (1) Configuration of the electric pump including the electric pump control device: The electric pump according to this embodiment will be described with reference to the drawings. Figure 1 is a diagram showing an electric pump including an electric pump control device according to one embodiment of the invention. The electric pump WP1 comprises a motor 40 that drives the electric pump WP1 and an electric pump control device 100 that controls the motor 40.

[0013] The electric pump control device 100 comprises an inverter 10 and a control circuit 20. The inverter 10 is equipped with multiple switching elements 11a to 11f. The inverter 10 converts power between the DC power supply 210 and the AC motor 40 that drives the electric pump WP1. In other words, the inverter 10 is a power conversion device that is connected to the DC power supply 210 and also to the motor 40, and converts power between the DC of the DC power supply 210 and the multi-phase AC (in this case, 3-phase AC) of the motor 40.

[0014] The control circuit 20 is a circuit that controls the inverter 10. The control circuit 20 comprises a drive circuit 24 and a processor 21 that sets the carrier frequency in PWM control for switching the multiple switching elements 11a to 11f of the inverter 10. PWM control means pulse width modulation control. The carrier frequency means the frequency that determines the pulse width modulation period in PWM control. In addition to the drive circuit 24 and the processor 21, the control circuit 20 may also include various circuits for controlling the inverter 10.

[0015] The processor 21 is connected to a voltmeter 211, a current sensor 41, a rotation sensor 42, and a higher-level control device 230. The voltmeter 211 is placed between the positive and negative terminals of the DC power supply 210 and detects the voltage applied from the DC power supply 210. The current sensor 41 detects the current flowing through the motor 40. The rotation sensor 42 is a resolver, etc., that detects the rotation angle of the rotor of the motor 40, and the processor 21 calculates the rotation speed of the motor 40 based on the detected rotation angle. Details of the current sensor 41 and the rotation sensor 42 will be described later. The higher-level control device 230 is a control device located above the electric pump control device 100, and when the electric pump control device 100 receives a command from the higher-level control device 230, it performs various controls based on that command. The higher-level control device 230 is, for example, a vehicle control unit that controls the operation of the vehicle when the electric pump WP1 is assumed to be mounted on a vehicle. The working fluid temperature sensor 231 is connected to the higher-level control device 230. The working fluid temperature sensor 231 detects the temperature of the working fluid (e.g., cooling water). The processor 21 obtains the working fluid temperature from the higher-level control unit 230. Based on the detection results from these sensors, the processor 21 sets the carrier frequency.

[0016] The DC power supply 210 supplies power to the electric pump WP1 and the other power-consuming units 220, and the voltage value applied to the electric pump WP1 (i.e., the voltage value detected by the voltmeter 211) fluctuates according to the power consumption of the power-consuming units 220. Assuming that the electric pump WP1 is installed in a vehicle, the power-consuming units refer to parts that consume power, such as the air conditioner, lighting, and car navigation system.

[0017] The DC power supply 210 is, for example, a fuel cell that obtains electrical energy through the chemical reaction of hydrogen and oxygen. The DC power supply 210 that supplies power to the motor 40 is a high-voltage and high-capacity DC power supply. Since the motor 40 is an AC motor, as described above, an inverter 10 for performing power conversion between DC and AC (here, three-phase AC) is provided between the DC power supply 210 and the motor 40. The DC power supply 210 can supply power to the motor 40 via the inverter 10.

[0018] The inverter 10 includes a plurality of series circuits of upper-stage switching elements 11a to 11c and lower-stage switching elements 11d to 11f, and is a circuit that converts power between the DC power supply 210 and the AC motor 40. Specifically, among the plurality of switching elements, the switching elements electrically connected to the positive electrode of the DC power supply 210 are called upper-stage switching elements 11a, 11b, and 11c. Also, among the plurality of switching elements, the switching elements electrically connected to the negative electrode of the DC power supply 210 are called lower-stage switching elements 11d, 11e, and 11f.

[0019] It is preferable that power semiconductor elements capable of operating at high frequencies are used for the upper-stage switching elements 11a to 11c and the lower-stage switching elements 11d to 11f. Examples of such elements include IGBT (Insulated Gate Bipolar Transistor), power MOSFET (Metal Oxide Semiconductor Field Effect Transistor), SiC-MOSFET (Silicon Carbide - Metal Oxide Semiconductor FET), SiC-SIT (SiC - Static Induction Transistor), GaN-MOSFET (Gallium Nitride - MOSFET), and the like. In the present embodiment, the upper-stage switching elements 11a to 11c and the lower-stage switching elements 11d to 11f are IGBTs.

[0020] The inverter 10 is composed of a bridge circuit having a number of arms corresponding to each of the plurality of phases. The inverter 10 includes arms for three-phase alternating current, and each arm is composed of a series circuit of one of the upper switching elements 11a to 11c and one of the lower switching elements 11d to 11f. Specifically, as shown in FIG. 1, in the inverter 10, two switching elements are connected in series between the positive electrode side and the negative electrode side of the DC power supply 210 to form one arm.

[0021] For example, the upper switching element 11a and the lower switching element 11d form a series circuit to constitute one arm. Similarly, the upper switching element 11b and the lower switching element 11e form a series circuit to constitute one arm, and the upper switching element  11c and the lower switching element 11f form a series circuit to constitute one arm. In the case of three-phase alternating current, these series circuits (one arm) are connected in parallel in three lines (three phases). That is, a bridge circuit is configured in which a set of series circuits (arms) corresponds to each of the coils corresponding to the U-phase, V-phase, and W-phase of the motor 40.

[0022] The midpoints of the series circuits (arms) formed by the switching elements of the corresponding phases, that is, the connection points between the upper switching elements 11a to 11c and the lower switching elements 11d to 11f are electrically connected to each of the three-phase coils of the motor 40. In addition, for each switching element, the direction from the negative electrode to the positive electrode (the direction from the lower side to the upper side) is defined as the forward direction, and diodes 13a to 13f (freewheel diodes) are electrically connected in parallel to each switching element.

[0023] The control circuit 20 causes the switching elements constituting the inverter 10 to perform switching operations. The control circuit 20 includes a processor 21 and a drive circuit 24. The drive circuit 24 is a circuit for operating the power switching elements that constitute the inverter 10, which belongs to the high-voltage circuit. On the other hand, the processor 21 is an integrated circuit that performs various information processing. The processor 21 is an IC circuit that controls each part according to a predetermined procedure, and is composed of, for example, a microcomputer or a DSP (Digital Signal Processor).

[0024] The processor 21 controls the motor 40 via the inverter 10 by performing current feedback control using a vector control method, based on the target torque of the motor 40 provided as a request signal via CAN (Controller Area Network) from other control devices (higher-level control device 230), such as a vehicle control unit that controls the operation of the vehicle. Specifically, the processor 21 switches the upper switching elements 11a to 11c and the lower switching elements 11d to 11f of the inverter 10 via the drive circuit 24 using PWM control. In PWM control, the processor 21 changes the duty cycle of the rectangular pulse wave that turns the switching elements 11a to 11f of each phase on or off by comparing the carrier wave (triangular wave) of the carrier frequency with the signal waves of each phase of the motor 40 (signal waves of the AC voltage command signal, sine wave). The processor 21 can also change the carrier frequency.

[0025] The drive circuit 24 is a circuit for switching the on and off states of the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, respectively. The drive circuit 24 only needs to be able to control the on and off states of each switching element. When each switching element is an IGBT or FET, the control terminal is the gate terminal, so the drive circuit 24 generates a drive signal that is applied to the gate terminal of each switching element. Here, this drive signal is called the gate drive signal.

[0026] The motor 40 is equipped with a current sensor 41 and a rotation sensor 42. The actual current flowing through the coils of each phase of the motor 40 is detected by the current sensor 41, and the processor 21 acquires the detection result. In addition, the magnetic pole position of the motor 40's rotor at each point in time is detected by the rotation sensor 42, such as a resolver, and the processor 21 acquires the detection result. The processor 21 performs current feedback control using the detection results of the current sensor 41 and the rotation sensor 42. The processor 21 is configured with various functional units for current feedback control, and each functional unit is realized through the cooperation of hardware such as a microcomputer or DSP and software (program). Current feedback control is a control method that performs PWM control so that the current flowing through the windings of the motor 40 approaches the current command value. Since current feedback control is well known, a detailed explanation is omitted here.

[0027] The processor 21 identifies the switching elements to be turned on or off in order to perform the current feedback control described above, and instructs the drive circuit 24 corresponding to each switching element to turn each switching element on or off. In response to this instruction, the drive circuit 24 generates gate drive signals to drive the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, respectively.

[0028] (2) Detailed configuration of the electric pump: Figure 2 is a schematic cross-sectional view of an electric pump showing the cooling structure of the switching elements. Here, the direction parallel to the rotation axis Ax is referred to as the axial direction. As described above, the electric pump WP1 comprises a motor 40 and an electric pump control device 100. The motor 40 and the electric pump control device 100 are housed inside a housing 110. On one axial side inside the housing 110, the electric pump control device 100 is arranged, which includes an inverter 10 containing a plurality of switching elements 11a to 11f and a control circuit 20 for controlling the inverter 10. Adjacent to the other axial side of the electric pump control device 100, a motor drive unit 43 including a rotor and stator is arranged. Furthermore, on the other axial side of the motor drive unit 43, a pumping unit 140 for pumping the working fluid W1 is provided. The pumping unit 140 includes an inlet 141 for taking in the working fluid W1, a discharge port (not shown) for discharging the working fluid W1 to the outside, and an impeller 142 for pumping the working fluid W1 taken in from the inlet 141 through the discharge port. The impeller 142 rotates due to the driving force of the motor drive unit 43 and pumps the working fluid. For example, the impeller 142 is part of the rotor that constitutes the motor drive unit 43, and the impeller 142 rotates in conjunction with the rotation of the rotor.

[0029] A heat conduction member 120 extends between the switching elements 11a to 11f of the inverter 10 and the internal space of the pressurized section 140 adjacent to the working fluid. The heat conduction member 120 is made of a material with high thermal conductivity, such as aluminum. As a result, heat generated by the switching elements 11a to 11f of the inverter 10 is transferred to the working fluid via the heat conduction member 120, making it possible to adjust the temperature of the switching elements 11a to 11f.

[0030] (3) Configuration of the working fluid circulation system: Figure 3 shows the configuration of the working fluid circulation system. The working fluid circulation system in this embodiment includes an electric pump WP1, a working fluid temperature sensor 231, a fuel cell stack FC1, a rotary valve 240, a radiator 250, and a flow path 260 connecting them.

[0031] In this embodiment, the electric pump WP1 is used to cool the fuel cell stack FC1, and the fuel cell stack FC1 is the same as the DC power supply 210 described above. If the electric pump WP1 is used to cool something other than the fuel cell stack FC1, then in Figure 3, the block for the fuel cell stack FC1 (DC power supply 210) will be replaced with a block other than the fuel cell stack FC1.

[0032] The rotary valve 240 is a valve for switching which of the branched passages the working fluid flowing from the upstream of the passage 260 flows into. In this embodiment, the rotary valve 240 is connected to a higher-level control device 230, and the higher-level control device 230 switches which of the branched passages the working fluid flows into based on the temperature of the working fluid from the working fluid temperature sensor 231. Alternatively, the passage may be switched mechanically according to the temperature of the working fluid, similar to a thermostat used in a typical automobile. The radiator 250 is a device for cooling by dissipating heat by passing the working fluid through its interior.

[0033] The electric pump WP1, the working fluid temperature sensor 231, the fuel cell stack FC1, and the rotary valve 240 are arranged in this order and connected by the flow path 260, forming a closed flow path. Downstream of the rotary valve 240, the flow path branches into a flow path R1 leading to the electric pump WP1 and a flow path R2 leading to the radiator 250. Therefore, the electric pump WP1, the working fluid temperature sensor 231, the fuel cell stack FC1, the rotary valve 240, and the radiator 250 are arranged in this order and connected by the flow path 260, forming a closed flow path. Thus, by switching the rotary valve 240, it is possible to select either of the two flow paths R1 or R2.

[0034] Here, P1 is defined as the point where the flow path R1 from the rotary valve 240 to the electric pump WP1 and the flow path R2 from the radiator 250 to the electric pump WP1 merge. P2 is defined as the position of the flow path 260 just before it flows into the fuel cell stack FC1. In this embodiment, the working fluid temperature sensor 231 is positioned between the electric pump WP1 and the fuel cell stack FC1, but it may be set at any position between P1 and P2. This is because the temperature of the working fluid in this section is approximately the same as the temperature of the working fluid passing through the electric pump WP1.

[0035] The electric pump WP1 pumps the working fluid, and the working fluid cools the fuel cell stack FC1 as it passes through it. In this embodiment, even if the working fluid passes through the fuel cell stack FC1, if the working fluid does not reach a temperature above a predetermined value, flow path R1 is selected; if it reaches a temperature above a predetermined value, flow path R2 is selected. The rotary valve 240 may be configured to select either flow path R1 or R2 depending on other conditions.

[0036] (4) Carrier frequency setting control: Figure 4 shows the relationship between motor speed and carrier frequency. Figure 4A shows the control mode of the carrier frequency in the low-speed range of motor 40, Figure 4B shows the control mode of the carrier frequency in the high-speed range of motor 40, and Figure 4C shows the control mode of the carrier frequency in both the low-speed and high-speed ranges of motor 40.

[0037] The processor 21 sets the carrier frequency in the PWM control that switches the plurality of switching elements 11a to 11f of the inverter 10 based on the rotational speed of the motor 40 and at least one of the voltage value V applied from the DC power supply 210 or the temperature T of the working fluid pumped by the electric pump WP1. In other words, the processor 21 does not set the carrier frequency based only on the rotational speed N of the motor 40, but also takes into account the voltage value V applied from the DC power supply 210 and the temperature T of the working fluid pumped by the electric pump WP1 when setting the carrier frequency. Specifically, the processor 21 obtains the rotational speed N from the rotation sensor 42 and compares it with threshold values ​​N1 and N2 for the rotational speed N. If the rotational speed N is lower than N1, it obtains the voltage value V from the voltmeter 211 and sets the carrier frequency based on the voltage value V. On the other hand, if the rotational speed N is higher than N2, it obtains the working fluid temperature T from the working fluid temperature sensor 231 and sets the carrier frequency based on the temperature T.

[0038] Specifically, as shown in Figure 4A, the processor 21 sets the carrier frequency to a first frequency f1 if the voltage value V is less than a first threshold Vt1 in the rotational speed range of the motor 40 that is lower than a predetermined first rotational speed N1, and sets the carrier frequency to a second frequency f2 that is lower than the first frequency f1 if the voltage value V is greater than or equal to the first threshold Vt1. The first frequency f1 is a predetermined value as the carrier frequency at which noise and vibration are below an acceptable level. The second frequency f2 is a predetermined value as the carrier frequency at which malfunctions such as step loss do not occur during startup.

[0039] It is generally known that setting a higher carrier frequency can reduce noise and vibration. On the other hand, it is known that setting a lower carrier frequency in the low rotational speed range of the motor 40 can provide good starting performance. Therefore, the applicant focused on the fact that if the voltage value V applied from the DC power supply 210 is low, good starting performance can be obtained even if the carrier frequency is set high.

[0040] Therefore, when the voltage value V is less than the first threshold Vt1, setting the carrier frequency to the first frequency f1, which is higher than the second frequency f2, increases the likelihood of preventing noise and vibration while maintaining a similar level of good startup performance compared to setting the carrier frequency to the second frequency f2. On the other hand, when the voltage value V is equal to or greater than the first threshold Vt1, setting the carrier frequency to the first frequency f1 may result in poor startup performance. For this reason, setting the carrier frequency to the second frequency f2, which is lower than the first frequency f1, reduces the noise and vibration prevention effect compared to setting the carrier frequency to the first frequency f1, but still ensures good startup performance.

[0041] On the other hand, the processor 21 sets the carrier frequency to at least a frequency higher than the second frequency f2 in the rotational speed range of the motor 40 above the first rotational speed N1. In this embodiment, the processor 21 sets the carrier frequency in the rotational speed range of the motor 40 above the first rotational speed N1 to the first frequency f1, which is the carrier frequency set when the voltage value V is less than the first threshold Vt1 in the rotational speed range of the motor 40 below the first rotational speed N1. This increases the possibility of preventing noise and vibration even in the rotational speed range of the motor 40 above the first rotational speed N1.

[0042] On the other hand, as shown in Figure 4B, in the rotational speed range of the motor 40 that is higher than a predetermined second rotational speed N2, the processor 21 sets the carrier frequency to a third frequency f3 if the temperature T of the working fluid is less than the second threshold Tt2, and sets the carrier frequency to a fourth frequency f4 that is lower than the third frequency f3 if the temperature T is greater than or equal to the second threshold Tt2.

[0043] In this case, at high rotational speeds of the motor 40, if the carrier frequency is not set low, the switching elements 11a to 11f of the inverter 10 may overheat. However, in this embodiment, the heat generated by the switching elements 11a to 11f of the inverter 10 is transferred to the working fluid via the heat conduction member 120, making it possible to adjust the temperature of the switching elements 11a to 11f (see Figure 2). On the other hand, since the temperature of the working fluid W1 fluctuates, there are cases where the heat from the switching elements 11a to 11f can be sufficiently removed and cases where it cannot.

[0044] When the working fluid temperature T is below the second threshold Tt2, setting the carrier frequency to the third frequency f3, which is higher than the fourth frequency f4, can prevent excessive heat generation of the switching elements 11a to 11f and increase the likelihood of preventing noise and vibration. On the other hand, when the working fluid temperature T is above the second threshold Tt2, setting the carrier frequency to the fourth frequency f4, which is lower than the third frequency f3, reduces the noise and vibration prevention effect, but reliably prevents excessive heat generation of the switching elements 11a to 11f.

[0045] On the other hand, in the rotational speed range of the motor 40 below the second rotational speed N2, the carrier frequency is set to a frequency at least higher than the fourth frequency f4. In this embodiment, the processor 21 sets the carrier frequency in the rotational speed range of the motor 40 below the second rotational speed N2 to the third frequency f3, which is the carrier frequency set when the working fluid temperature T is less than the second threshold Tt2 in the rotational speed range of the motor 40 above the second rotational speed N2. This increases the possibility of preventing noise and vibration even in the rotational speed range of the motor 40 below the second rotational speed N2.

[0046] Of course, as shown in Figure 4C, the processor 21 may perform the carrier frequency setting control according to the present invention described above in both the low-speed and high-speed ranges of the motor 40. In this case, the first rotational speed N1 is lower than the second rotational speed N2. On the other hand, the processor 21 sets the carrier frequency to a frequency higher than at least the second frequency f2 and the fourth frequency f4 in the rotational speed range of the motor 40 that is above the first rotational speed N1 and below the second rotational speed N2. In this embodiment, the processor 21 sets the carrier frequency in the rotational speed range of the motor 40 that is above the first rotational speed N1 and below the second rotational speed N2 (medium rotational speed range) to a frequency that is the same as both the first frequency f1, which is the carrier frequency set when the voltage value V is less than the first threshold Vt1 in the rotational speed range below the first rotational speed N1 of the motor 40, and the third frequency f3, which is the carrier frequency set when the working fluid temperature T is less than the second threshold Tt2 in the rotational speed range above the second rotational speed N2 of the motor 40.

[0047] In this embodiment, the first frequency f1 in the low rotational speed range, the frequency in the medium rotational speed range, and the third frequency f3 in the high rotational speed range are assumed to be the same, but they only need to be higher than the second frequency f2 in the low rotational speed range and the fourth frequency f4 in the high rotational speed range, and these frequencies may be different. Similarly, in this embodiment, the second frequency f2 in the low rotational speed range and the fourth frequency f4 in the high rotational speed range are assumed to be the same, but at least the second frequency f2 in the low rotational speed range may be lower than the first frequency f1, and the fourth frequency f4 in the high rotational speed range may be lower than the third frequency f3, and these frequencies may be different.

[0048] As described above, conventionally, the carrier frequency in PWM control was uniformly set based solely on the rotational speed N of the motor 40. In contrast, in this embodiment, the carrier frequency is set based on the rotational speed N of the motor 40 and at least one of the voltage value V applied from the DC power supply 210 or the temperature T of the working fluid pumped by the electric pump WP1. Specifically, the processor 21 determines whether it is necessary to set the carrier frequency below a predetermined level based on this information, and sets the carrier frequency based on the determination result. Therefore, it is possible to avoid unnecessarily setting the carrier frequency below a predetermined level and increase the possibility of preventing the generation of noise and vibration.

[0049] (5) Other embodiments: The above embodiments are just examples of how to implement the present invention, and various other embodiments can be adopted. For example, in the above embodiments, the motor 40 is provided with a rotation sensor 42 such as a resolver for detecting the rotation angle of the rotor, and the rotation speed of the motor 40 is calculated, but the present invention can also be applied to a sensorless type without a rotation sensor. In this case, the rotation speed is calculated from the zero-crossing of the U-phase, V-phase, and W-phase voltages of the motor 40.

[0050] In the above embodiment, the DC power supply 210 is a fuel cell, and the voltage value applied to the electric pump WP1 (i.e., the voltage value detected by the voltmeter 211) is described as fluctuating according to the power consumption in the power consumption unit 220. However, the DC power supply 210 may be composed of a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery, or an electric double-layer capacitor. In this case, the voltage value applied to the electric pump WP1 hardly fluctuates according to the power consumption in the power consumption unit 220. Even in this case, the present invention can be applied. For example, as shown in Figure 4B, when the processor 21 sets the carrier frequency f based on the rotational speed N of the motor 40 and the temperature T of the working fluid pumped by the electric pump WP1, it is independent of whether the voltage value V is constant or not. Therefore, the present invention is valid even when the voltage value V does not fluctuate. In the above embodiment, as shown in Figure 4A, a first threshold Vt1 is set as a threshold for the voltage value V, and one carrier frequency is selected from two carrier frequencies f1 and f2 depending on whether the voltage value V is less than the first threshold. However, it is also possible to set multiple (A) thresholds for the voltage value V, and one carrier frequency is selected from multiple (A+1) carrier frequencies f depending on which of the voltage value ranges defined by those thresholds the voltage value V falls within. For example, as shown in Figure 5A, in addition to the first threshold Vt1, a third threshold Vt3 greater than the first threshold Vt1 may be set as a threshold for the voltage value V. If the voltage value V is less than the first threshold Vt1, the carrier frequency may be set to the first frequency f1. If the voltage value V is greater than or equal to the first threshold Vt1 and less than the third threshold Vt3, the carrier frequency may be set to the fifth frequency f5, which is lower than the first frequency f1. If the voltage value V is greater than or equal to the third threshold Vt3, the carrier frequency may be set to the second frequency f2, which is lower than the fifth frequency f5. In the above embodiment, as shown in Figure 4B, a second threshold Tt2 is provided as a threshold for the working fluid temperature T, and one carrier frequency is selected from two carrier frequencies f3 and f4 depending on whether the working fluid temperature T is less than the second threshold Tt2. However, it is also possible to provide multiple (B) thresholds for the working fluid temperature T, and one carrier frequency is selected from multiple (B+1) carrier frequencies f depending on which of the ranges of working fluid temperature T the working fluid temperature T falls within. For example, as shown in Figure 5B, in addition to the second threshold Tt2, a fourth threshold Tt4 greater than the second threshold Tt2 may be set as a threshold for the working fluid temperature T. If the working fluid temperature T is less than the second threshold Tt2, the carrier frequency may be set to the third frequency f3. If the working fluid temperature T is greater than or equal to the second threshold Tt2 and less than the fourth threshold Tt4, the carrier frequency may be set to the sixth frequency f6, which is lower than the third frequency f3. If the working fluid temperature T is greater than or equal to the fourth threshold Tt4, the carrier frequency may be set to the fourth frequency f4, which is lower than the sixth frequency f6. Of course, as shown in Figure 5C, the processor 21 may be controlled to perform the carrier frequency setting according to the present invention described above using Figures 5A and 5B in both the low-speed and high-speed ranges of the motor 40. In this example, the fifth frequency f5 in the low-speed range and the sixth frequency f6 in the high-speed range are the same, but at least the fifth frequency f5 in the low-speed range can be predetermined between the first frequency f1 and the second frequency f2, and the sixth frequency f6 in the high-speed range can be predetermined between the third frequency f3 and the fourth frequency f4, and these frequencies can be different.

[0051] An inverter comprises multiple series circuits of upper and lower switching elements, and these elements should be able to convert power between a DC power source and an AC motor. In other words, an inverter should be a circuit capable of converting DC voltage and AC voltage using known PWM control. The switching elements consist of upper and lower switching elements, and power conversion between DC and AC should be performed by controlling the switching timing of these elements. When the motor is driven by multiphase AC, there will be multiple series circuits combining upper and lower switching elements. For example, in the case of three-phase AC, there will be three combinations of upper and lower switching elements. [Explanation of symbols]

[0052] 10...Inverter, 11a~11c...Upper switching element, 11d~11f...Lower switching element, 13a~13f...Diode, 20...Control circuit, 21...Processor, 24...Drive circuit, 40...Motor, 41...Current sensor, 42...Rotation sensor, 100...Electric pump control device, 210...DC power supply, 211...Voltmeter, 220...Power consumption unit, 230...Higher-level control device, 231...Working fluid temperature sensor, WP1...Electric pump

Claims

1. An electric pump control device for controlling an electric pump, An inverter equipped with multiple switching elements that converts power between a DC power supply and an AC motor that drives the electric pump, The system comprises a control circuit for controlling the inverter, The control circuit includes a processor that sets the carrier frequency in PWM control for switching a plurality of switching elements of the inverter based on the rotational speed of the motor and at least one of the voltage value applied from the DC power supply or the temperature of the working fluid pumped by the electric pump. Electric pump control device.

2. The processor sets the carrier frequency to a first frequency if the voltage value is less than a first threshold in a rotational speed range lower than a predetermined first rotational speed of the motor, and sets the carrier frequency to a second frequency lower than the first frequency if the voltage value is equal to or greater than the first threshold. The electric pump control device according to claim 1.

3. The processor sets the carrier frequency to a third frequency if the temperature of the working fluid is below a second threshold in a rotational speed range higher than a predetermined second rotational speed of the motor, and sets the carrier frequency to a fourth frequency lower than the third frequency if the temperature is above the second threshold. The electric pump control device according to claim 1 or 2.

4. The DC power supply provides power to the electric pump and other power-consuming components. The voltage value fluctuates according to the power consumption in the power consumption unit. The electric pump control device according to claim 1 or 2.

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