ระบบขับเคลื่อนมอเตอร์และเครื่องปรับอากาศ

Abstract

ระบบขับเคลื่อนมอเตอร์(100)ตามลักษณะของการประดิษฐ์นี้ประกอบด้วยอินเวอร์เตอร์(2)ซึ่งขับเคลื่อนมอเตอร์(30),ตัวตรวจจับกระแส(3)ซึ่งตรวจจับสัญญาณที่หนึ่งซึ่งเป็นค่ากระแสของกระแสที่ไหลผ่านอินเวอร์เตอร์(2)และส่งสัญญาณที่หนึ่งออกไปเป็นเอาต์พุต,วงจรกรองแบบผ่านต่ำที่หนึ่ง(4)ซึ่งขจัดส่วนประกอบที่มีความถี่รบกวนออกจากสัญญาณที่หนึ่งและส่งสัญญาณที่สองซึ่งเป็นค่ากระแสออกไปเป็นเอาต์พุตหลังจากขจัดส่วนประกอบที่มีความถี่รบกวนออกไปแล้ว,ตัวตัดสินกระแสการลบล้างอำนาจแม่เหล็ก(5)ซึ่งนำค่าจุดเริ่มเปลี่ยนของกระแสการลบล้างอำนาจแม่เหล็กซึ่งเป็นค่ากระแสการลบล้างอำนาจแม่เหล็กให้กับแม่เหล็กถาวรที่เป็นส่วนประกอบอยู่ในมอเตอร์(30)มาเปรียบเทียบกับสัญญาณที่สองและส่งสัญญาณปกป้องการลบล้างอำนาจแม่เหล็กออกไปเป็นเอาต์พุตเมื่อสัญญาณที่สองมีค่าที่มากกว่าค่าจุดเริ่มเปลี่ยนของกระแสการลบล้างอำนาจแม่เหล็กและตัวตัดสินวงจรลัด(7)ซึ่งนำสัญญาณที่สามที่ได้จากการรวมสัญญาณที่หนึ่งและสัญญาณปกป้องการลบล้างอำนาจแม่เหล็กเข้าด้วยกันมาเปรียบเทียบกับค่าจุดเริ่มเปลี่ยนของวงจรลัดซึ่งมีค่าน้อยกว่าหรือเท่ากับค่ากระแสของกระแสที่ไหลเมื่ออินเวอร์เตอร์(2)เกิดวงจรลัดและส่งสัญญาณความผิดปกติออกไปเป็นเอาต์พุตเพื่อหยุดการทำงานของอินเวอร์เตอร์(2)เมื่อสัญญาณที่สามมีค่าที่มากกว่าหรือเท่ากับค่าจุดเริ่มเปลี่ยนของวงจรลัด

Description

Motor drive system and air conditioner

[0001] The present invention relates to a motor drive system and an air conditioner that protect switching elements of an inverter.

[0002] A known motor drive system that reduces power consumption is one that uses a commutatorless motor, i.e., a brushless DC (Direct Current) motor, and an inverter as the motor drive unit that drives the motor. Commutatorless motors have a longer product life than commutator motors because the commutator does not wear out. Furthermore, commutatorless motors consume less power than induction motors because no current flows through the rotor. Because of this, commutatorless motors can reduce power consumption and are therefore used in a wide range of products, including air conditioners.

[0003] In order to protect the switching elements of the inverter, the motor connected to the inverter, and the power supply connected to the inverter, the inverter is generally provided with an overcurrent detection means for detecting overcurrent.

[0004] Patent Document 1 discloses a motor drive system that includes a protection means for protecting a switching element when a large current flows through an inverter, and a protection means for protecting a power supply from the large current.

[0005] Depending on the purpose of inverter protection, a motor drive system needs to be equipped with multiple overcurrent detection means. Among the overcurrents that can occur in an inverter, those caused by short circuits in the switching elements that make up the inverter are those that flow large currents in a short period of time. For this reason, when an overcurrent occurs due to a short circuit in a switching element, the inverter should be stopped as quickly as possible. Furthermore, when multiple overcurrent detection means are installed, it is considered best to combine protection against short circuits with protection against other currents.

[0006] JP 2013-81285 A

[0007] In conventional overcurrent protection, providing multiple overcurrent detection means requires multiple output lines for the abnormality signal. For example, when transmitting an abnormality signal to a gate drive signal generation circuit for a switching element, it may not be possible to connect multiple abnormality signal lines. Also, when transmitting an abnormality signal to a microcomputer, which is the control unit of the motor drive system, the number of ports on the microcomputer is limited, so it may be desirable to minimize the number of ports used.

[0008] The present invention has been made in view of the above, and has as its object to provide a motor drive system that can transmit abnormality signals from a plurality of overcurrent detection means via a single abnormality signal output line.

[0009] In order to solve the above-mentioned problems and achieve the object, a motor drive system according to the present invention comprises an inverter that drives a motor, a current detection unit that detects a first signal that is the current value of a current flowing in the inverter and outputs the first signal, a first low-pass filter that removes noise frequency components from the first signal and outputs a second signal that is the current value from which the noise frequency components have been removed, a demagnetization current determination unit that compares the second signal with a demagnetization current threshold that is the current value at which a permanent magnet in the motor demagnetizes, and outputs a demagnetization protection signal if the second signal is greater than the demagnetization current threshold, and a short-circuit determination unit that compares a third signal, which is the combination of the first signal and the demagnetization protection signal, with a short-circuit threshold that is equal to or less than the current value of a current that flows when the inverter is short-circuited, and outputs an abnormality signal to stop the inverter if the third signal is equal to or greater than the short-circuit threshold.

[0010] According to the present invention, it is possible to obtain a motor drive system that can transmit abnormality signals from a plurality of overcurrent detection means using a single abnormality signal output line.

[0011] FIG. 1 is a diagram showing a motor drive system according to a first embodiment of the present invention; FIG. 2 is a diagram showing an example of the configuration of a control circuit according to a first embodiment of the present invention; FIG. 3 is a diagram showing a motor drive system according to a first embodiment of the present invention; FIG. 4 is a diagram showing a motor drive system according to a second embodiment of the present invention; FIG. 5 is a diagram showing a relationship between the magnitude relationship of the short-circuit current of the inverter, the demagnetization current of the motor, and the module overcurrent, and the time at which the inverter should be stopped, according to a second embodiment of the present invention; FIG. 6 is a diagram showing a current value of the inverter when the current value becomes larger than the short-circuit threshold value according to the second embodiment of the present invention;

[0012] A motor drive system and an air conditioner according to an embodiment of the present invention will be described in detail below with reference to the drawings, although the present invention is not limited to these embodiments.

[0013] 1 is a first diagram showing a motor drive system 100 according to a first embodiment of the present invention. The motor drive system 100 includes a rectifier circuit 1, an inverter 2, a current detection unit 3, a first low-pass filter 4, a demagnetizing current determination unit 5, a demagnetizing current threshold value holding unit 6, a short-circuit determination unit 7, and a short-circuit threshold value holding unit 8.

[0014] The rectifier circuit 1 has four bridge-connected diodes 11 to 14 and a capacitor 15. The rectifier circuit 1 rectifies the AC voltage output from the AC power supply 60 to a DC voltage using the diodes 11 to 14 and the capacitor 15, and applies the rectified DC voltage to the inverter 2. The inverter 2 has six switching elements 21 to 26, converts the DC voltage to an AC voltage, and applies the AC voltage to the motor 30. When the switching elements 21 to 26 are not distinguished from one another, they will be referred to as switching elements 20.

[0015] Although the switching elements 21-26 are illustrated as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) formed from silicon-based materials, the switching elements 21-26 are not limited to MOSFETs and may be MOSFETs formed from wide band gap (WBG) semiconductors such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), or diamond. Wide band gap semiconductors generally have higher voltage resistance and heat resistance than silicon semiconductors. Therefore, using a wide band gap semiconductor for at least one of the switching elements 21-26 increases the voltage resistance and allowable current density of the switching element, allowing for the miniaturization of semiconductor modules incorporating the switching elements.

[0016] The current detection unit 3 is connected to the inverter 2 and detects the value of a current flowing through the inverter 2. The current detection unit 3 also outputs information on the detected current value to the demagnetizing current determination unit 5 via a first low-pass filter 4. The current detection unit 3 also outputs information on the current value to the short-circuit determination unit 7 via a diode 16.

[0017] The first low-pass filter 4 removes noise frequency components from the current value information and outputs the current value information after the noise frequency components have been removed to the demagnetizing current determination unit 5. The demagnetizing current determination unit 5 uses the demagnetizing current threshold and the current value information, and if the current value information is greater than the demagnetizing current threshold, outputs a demagnetization protection signal to the short-circuit determination unit 7 via the diode 17. The demagnetizing current threshold holding unit 6 holds the demagnetizing current threshold. The demagnetizing current threshold is the value of the current that flows through the motor 30 when the permanent magnets of the motor 30 are demagnetized.

[0018] The short circuit determination unit 7 uses the current value information and the short circuit threshold, and if the current value information is equal to or greater than the short circuit threshold, outputs an abnormality signal to a drive signal generation unit (not shown) or a control unit (not shown) that controls the motor drive system 100. The abnormality signal is a signal that controls the operation of the switching elements 21 to 26 of the inverter 2, and by the short circuit determination unit 7 outputting the abnormality signal, the operation of the inverter 2 can be stopped in the event of an abnormality in the motor drive system 100. The short circuit threshold holding unit 8 holds the short circuit threshold. The short circuit threshold is a value equal to or less than the current value of the current that flows when the inverter 2 is short-circuited.

[0019] The following describes the hardware configurations of the current detection unit 3, demagnetization current determination unit 5, demagnetization current threshold holding unit 6, short circuit determination unit 7, and short circuit threshold holding unit 8 according to an embodiment of the present invention. The demagnetization current determination unit 5 and short circuit determination unit 7 are realized by resistors, capacitors, diodes, comparators, or combinations of these. The short circuit threshold holding unit 8 and demagnetization current threshold holding unit 6 are realized by processing circuits, which are electronic circuits that perform each process.

[0020] The processing circuit according to the first embodiment of the present invention may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit) that executes a program stored in the memory. Here, the memory may be, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), or a flash memory. FIG. 2 is a diagram showing an example configuration of a control circuit 500 according to the first embodiment of the present invention. When the processing circuit is dedicated hardware, the processing circuit may be, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0021] As shown in Fig. 2, the control circuit 500 includes a processor 500a, which is a CPU, and a memory 500b. When the demagnetizing current determination unit 5, demagnetizing current threshold holding unit 6, short circuit determination unit 7, and short circuit threshold holding unit 8 are realized by the control circuit 500 shown in Fig. 2, the processor 500a reads and executes programs corresponding to each process stored in the memory 500b. The memory 500b is also used as a temporary memory for each process performed by the processor 500a. The demagnetizing current determination unit 5 and the short circuit determination unit 7 may be realized by the control circuit 500. The current detection unit 3 is, for example, a current sensor.

[0022] The operation of short circuit determination will now be described. When any of the switching elements 21 to 26 is short-circuited, for example, when both switching elements 21 and 22 are turned on simultaneously due to a malfunction, the DC voltage applied by the rectifier circuit 1 is short-circuited. As a result, the current flowing through the inverter 2 increases at a high speed. There are two paths for transmitting current value information to the short circuit determination unit 7: a path via the first low-pass filter 4 and a path via the backflow prevention diode 16. A delay occurs in the path via the first low-pass filter 4. Therefore, the short circuit determination unit 7 performs short circuit determination based on the current information received from the path via the diode 16, which does not cause a delay.

[0023] The short circuit determination unit 7 compares the current value information with the short circuit threshold, and if the current value information is equal to or greater than the short circuit threshold, outputs an abnormality signal to the drive signal generation unit or control unit to turn off all of the switching elements 21 to 26 of the inverter 2 and suddenly stop the operation of the inverter 2. The short circuit threshold is set to a value within a range in which it is guaranteed that the switching elements will not fail, known as the short circuit safe operating area (SOA). This operation prevents the switching element 20 from being destroyed when an unintended short circuit occurs.

[0024] Next, we will explain the operation of the demagnetizing current determination unit 5. Because the motor 30 has inductance, the rate at which the current flowing through the motor 30 increases is slower than the rate at which the current flowing when the switching elements 21 to 26 are short-circuited. Therefore, by passing the current value information output by the current detection unit 3 through the first low-pass filter 4, erroneous detection due to noise in the current value information is suppressed.

[0025] 3 is a diagram showing the relationship between the short-circuit current value of the switching element 20 and the overcurrent value of the motor 30 according to the first embodiment of the present invention. In FIG. 3, the vertical axis represents the current value, and the horizontal axis represents the time. As shown in FIG. 3, the inverter short-circuit current generated by the switching element 20 shorting increases at a faster rate than the motor overcurrent value flowing through the motor 30. It can also be seen that the short-circuit threshold is greater than the demagnetization current threshold.

[0026] If the information on the current value that has passed through the first low-pass filter 4 is greater than the demagnetizing current threshold, the demagnetizing current determination unit 5 outputs a demagnetization protection signal to the short-circuit determination unit 7 via the diode 17. Here, the demagnetization protection signal is output as a value greater than the short-circuit threshold and input to the short-circuit determination unit 7. As a result, the short-circuit determination unit 7 outputs an abnormality signal, turns off all of the switching elements 21 to 26 of the inverter 2, and suddenly stops the operation of the inverter 2. The demagnetizing current threshold is set to be equal to or less than the demagnetizing current value of the motor 30. This operation protects the permanent magnets of the motor 30 from unintentional demagnetization.

[0027] FIG. 4 is a second diagram showing a motor drive system 100a according to the first embodiment of the present invention. In the motor drive system 100a, a demagnetizing current determination unit 5, a demagnetizing current threshold value holding unit 6, a short circuit determination unit 7, and a short circuit threshold value holding unit 8 are provided in an inverter module 40 including an inverter 2. The demagnetizing current determination unit 5 outputs an abnormality signal to a drive signal generation unit 41, rather than outputting a demagnetization protection signal to the short circuit determination unit 7. FIG. 5 is a third diagram showing a motor drive system 100b according to the first embodiment of the present invention. In the motor drive system 100b, the short circuit determination unit 7 and the short circuit threshold value holding unit 8 are provided in the inverter module 40. Thus, in the first embodiment, as shown in FIGS. 4 and 5, both or either one of the short circuit determination unit 7 and the demagnetizing current determination unit 5 may be provided in the inverter module 40. Note that in FIGS. 4 and 5, the short circuit determination unit 7 is configured to output an abnormality signal to the drive signal generation unit 41. The drive signal generating unit 41 generates a drive signal under the control of the control unit 42 .

[0028] As described above, in the first embodiment of the present invention, the motor drive system 100 includes the inverter 2 that drives the motor 30, the current detection unit 3 that detects a first signal that is the current value of the current flowing through the inverter 2 and outputs the first signal, the first low-pass filter 4 that removes noise frequency components from the first signal and outputs a second signal that is the current value from which the noise frequency components have been removed, the demagnetization current determination unit 5 that compares the second signal with a demagnetization current threshold that is the current value at which the permanent magnets of the motor 30 demagnetize, and outputs a demagnetization protection signal if the second signal is greater than the demagnetization current threshold, and the short-circuit determination unit 7 that compares a third signal, which is a combination of the first signal and the demagnetization protection signal, with a short-circuit threshold that is equal to or less than the current value that flows when the inverter is short-circuited, and outputs an abnormality signal that stops the inverter 2 if the third signal is equal to or greater than the short-circuit threshold. Thus, the motor drive system 100 can protect the switching element 20 in the event of a short circuit and protect the motor 30 from demagnetization by outputting a single abnormality signal.

[0029] Embodiment 2. In embodiment 1, the motor drive system 100 was protected from short-circuit current and demagnetizing current, but in embodiment 2, in addition to these, the motor drive system 100c protects the inverter module including the inverter 2 from overcurrent. Note that components having the same functions as those in embodiment 1 are given the same reference numerals as in embodiment 1, and redundant explanations will be omitted.

[0030] FIG. 6 is a diagram illustrating a motor drive system 100c according to a second embodiment of the present invention. In addition to the configuration of the first embodiment, the motor drive system 100c further includes a second low-pass filter 31, a module overcurrent determination unit 32, and a module overcurrent threshold holding unit 33. The module overcurrent determination unit 32 uses current value information and a module overcurrent threshold. If the current value information is greater than the module overcurrent threshold, the module overcurrent determination unit 32 determines that an overcurrent is flowing through the inverter module 40 and outputs an overcurrent signal to the short-circuit determination unit 7 via a diode 18. The module overcurrent threshold is a current value used to determine that an overcurrent is flowing through the inverter module 40. The module overcurrent threshold holding unit 33 holds the module overcurrent threshold. The second low-pass filter 31 is connected before the module overcurrent determination unit 32. The time constant of the second low-pass filter 31 is greater than the time constant of the first low-pass filter 4.

[0031] The operation of the module overcurrent determination unit 32 will now be described. The inverter module has a rated current value, which is the upper limit of the current at which operation is guaranteed. Basically, a current below this rated current value must be passed through the inverter module. However, the inverter module can withstand a current that momentarily exceeds the rated current value. For this reason, the rated current value of the inverter module is smaller than the demagnetizing current value. When the current suddenly rises and reaches the demagnetizing current value, a period occurs during which the rated current of the module is exceeded. However, if this period is short, the inverter module can withstand the current. However, if the period during which the rated current of the module is exceeded is longer than the predetermined period, the power supply to the inverter 2 must be stopped.

[0032] 7 is a diagram showing the relationship between the magnitude relationship of the short-circuit current of the inverter 2, the demagnetizing current of the motor 30, and the module overcurrent, and the time at which the inverter 2 should be stopped, according to the second embodiment of the present invention. As shown in FIG. 7, the module overcurrent increases at a slower rate than the motor overcurrent. It is also clear that the overcurrent threshold is smaller than the demagnetizing current threshold.

[0033] FIG. 8 is a diagram showing the current value of the inverter 2 when the current value according to the second embodiment of the present invention is greater than the short-circuit threshold. FIG. 9 is a diagram showing the current value of the inverter 2 when the current value according to the second embodiment of the present invention is greater than the demagnetizing current threshold. FIG. 10 is a diagram showing the current value of the inverter 2 when the current value according to the second embodiment of the present invention is greater than the overcurrent threshold. In each of FIGS. 8 to 10, the vertical axis represents the current value and the horizontal axis represents the time. As shown in FIG. 8, in the event of a short circuit, the current value of the inverter 2 increases rapidly and quickly reaches the same value as the short-circuit threshold. As shown in FIG. 9, when the current value exceeds the demagnetizing current threshold, the current value of the inverter 2 increases more slowly than in the event of a short circuit, but exceeds the demagnetizing current threshold. As shown in FIG. 10, when the current value exceeds the overcurrent threshold, the current value of the inverter 2 increases more slowly and exceeds the overcurrent threshold.

[0034] The second low-pass filter 31 will now be described. The time constant of the second low-pass filter 31 is longer than the time constant of the first low-pass filter 4. By doing so, the module overcurrent determination unit 32 does not output an abnormality signal when the current flowing through the inverter 2 exceeds the module overcurrent threshold for a short period of time, but if the time that the module overcurrent threshold is exceeded becomes longer, the short-circuit determination unit 7 outputs an abnormality signal.

[0035] The overcurrent signal output by the module overcurrent determination unit 32 is greater than the threshold value of the short circuit determination unit 7. Therefore, when the overcurrent signal is input, the short circuit determination unit 7 outputs an abnormality signal, turns off all switching elements 20 of the inverter 2, and suddenly stops operation. In addition to short circuit protection and demagnetization protection, the module can be protected from overcurrent.

[0036] As described above, the motor drive system 100c according to the second embodiment of the present invention comprises, in addition to the configuration of the motor drive system 100, a second low-pass filter 31 having a longer time constant than the first low-pass filter 4 that removes noise frequency components from the first signal and outputs a fourth signal which is the current value from which the noise frequency components have been removed, and a module overcurrent determination unit 32 that compares the fourth signal with a module overcurrent threshold which is the upper limit of current at which operation of the inverter module 40 including the inverter 2 is guaranteed, and outputs an overcurrent signal if the fourth signal is greater than the module overcurrent threshold, and the short-circuit determination unit 7 uses the overcurrent signal to output an abnormality signal to stop the inverter 2.

[0037] In the first and second embodiments, the module overcurrent determination unit 32, the demagnetizing current determination unit 5, and the short-circuit determination unit 7 may be configured as circuits on an electronic board. Alternatively, the module overcurrent determination unit 32, the demagnetizing current determination unit 5, and the short-circuit determination unit 7, or at least one of these determination units, may be configured within the microcomputer that serves as the control unit 42 or within the inverter module 40. Configuring the module overcurrent determination unit 32, the demagnetizing current determination unit 5, and the short-circuit determination unit 7, or at least one of these determination units, within the inverter module 40 can reduce the circuit area. Configuring the module overcurrent determination unit 32, the demagnetizing current determination unit 5, and the short-circuit determination unit 7, or at least one of these determination units, within the inverter module 40 can suppress the influence of noise from outside the inverter module 40, thereby improving noise resistance.

[0038] In the first and second embodiments, the motor 30 connected to the inverter 2 may be one that operates a compressor or a fan of an air conditioner.

[0039] The configurations shown in the above embodiments are examples of the content of the present invention, and may be combined with other known technologies, and some of the configurations may be omitted or modified within the scope of the gist of the present invention.

[0040] 1 Rectifier circuit, 2 Inverter, 3 Current detection unit, 4 First low-pass filter, 5 Demagnetization current determination unit, 6 Demagnetization current threshold holding unit, 7 Short circuit determination unit, 8 Short circuit threshold holding unit, 11 to 14, 16 to 18 Diodes, 15 Capacitor, 20 to 26 Switching elements, 30 Motor, 31 Second low-pass filter, 32 Module overcurrent determination unit, 33 Module overcurrent threshold holding unit, 40 Inverter module, 41 Drive signal generation unit, 42 Control unit, 60 AC power supply, 100, 100a, 100b, 100c Motor drive system, 500 Control circuit, 500a Processor, 500b Memory.