Motor control device

Abstract

To provide a motor control device capable of detecting idling of a motor with a simple configuration while expanding a dynamic range.SOLUTION: A motor control device includes an inverter part, a current detection part, a control part, and an idling detection part. The control part generates a switching signal to be inputted to a drive circuit of the inverter part and for alternately turning on / off a first switching element and a second switching element based on detection results by the current detection part. The idling detection part includes: a voltage-dividing circuit having a first resistor whose one end is connected to the signal line and a second resistor connected to the other end of the first resistor; a comparator for comparing an output voltage of the voltage-dividing circuit and a reference voltage, and outputting a comparison result to the control part; and a removal part connected between a connection point of the first resistor and the second resistor of the voltage-dividing circuit and the comparator and for removing an offset voltage overlapped on the output voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor control device. [Background technology]

[0002] The outdoor unit of an air conditioner has a heat exchanger, a fan for the heat exchanger (hereinafter sometimes referred to as the "outdoor unit fan"), and a motor that rotates the outdoor unit fan (hereinafter sometimes referred to as the "fan motor"). The outdoor unit fan motor may rotate in the opposite direction to the normal rotation, i.e., in the reverse direction (hereinafter referred to as "reverse rotation"), when the outdoor unit fan is subjected to an external force such as wind and spins idly while the fan motor is stopped. Since the fan motor starts in the forward direction, if the outdoor unit fan is running idly before the fan motor starts, causing the fan motor to start while it is rotating in the reverse direction, the fan motor may fail to start or may be damaged.

[0003] Therefore, a motor control device has been proposed that includes a phase detector that determines the rotation direction of the fan motor when it is idling (for example, Patent Document 1). The control device disclosed in Patent Document 1 obtains the magnetic pole position and rotation frequency of the motor with a simple configuration while the switching operation of the inverter circuit is stopped. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-137106 Summary of the Invention [Problem to be solved by the invention]

[0005] The phase detection unit disclosed in Patent Document 1 is composed of a voltage divider circuit that divides the induced voltage output from the inverter circuit, and a comparator that receives the divided voltage output from the voltage divider circuit and outputs an H (high) level signal or an L (low) level signal as a phase detection signal to a CPU. With this configuration, the frequency during idling of the motor is calculated every time the signal level of the phase detection signal changes. However, comparators have a maximum allowable voltage. An offset voltage, which is a DC component, is superimposed on the induced voltage output from the inverter circuit, narrowing the dynamic range of the comparator by the amount of the offset voltage.

[0006] The present invention has been made in response to unresolved problems in the past, and aims to provide a motor control device that can detect motor slippage with a simple configuration while expanding the dynamic range. [Means for solving the problem]

[0007] In order to achieve the above object, according to one aspect of the present invention, there is provided an inverter unit having a series circuit group in which at least three series circuits, each of which is connected in parallel and in which a first switching element constituting an upper arm and a second switching element constituting a lower arm are connected in series, a drive circuit that turns on / off the first and second switching elements, respectively, and a shunt resistor connected between the series circuit group and a reference potential, and which converts a DC voltage into an AC voltage based on an input PWM pulse and supplies the AC voltage to a motor, a current detection unit that detects a current flowing through the shunt resistor, and a current that is input to the drive circuit based on the detection result of the current detection unit and which controls the first switching element and the second switching element. a control unit that generates a switching signal that alternately turns on and off a switching element; a slip detection unit that is connected to a signal line that connects the motor and a junction between the first switching element and the second switching element and detects slippage of the motor, the slip detection unit comprising a voltage divider circuit having a first resistor whose one end is connected to the signal line and a second resistor connected to the other end of the first resistor; a comparator that compares the output voltage of the voltage divider circuit with a reference voltage and outputs the comparison result to the control unit; and a removal unit that is connected between the comparator and the junction between the first resistor and the second resistor of the voltage divider circuit and removes an offset voltage superimposed on the output voltage. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to obtain a motor control device that can detect idling of a motor with a simple configuration while expanding the dynamic range. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing the configuration of a motor control device 1 according to a first embodiment. [Figure 2] 1 is a block diagram showing a main configuration of an IPM according to a first embodiment. [Figure 3] 1 is a block diagram illustrating only a series circuit for one phase of an IPM according to a first embodiment. [Figure 4] FIG. 10 is a circuit diagram showing a comparative example of a slip detection circuit. [Figure 5] FIG. 10 is a waveform diagram showing the waveform of an induced voltage input to a slip detection circuit according to a comparative example. [Figure 6] FIG. 10 is an equivalent circuit diagram of a slip detection circuit in a comparative example. [Figure 7] 1 is a circuit diagram showing a spin detection circuit according to a first embodiment. [Figure 8A] FIG. 3 is a waveform diagram showing the waveform of an induced voltage after passing through a high-pass filter of the slip detection circuit according to the first embodiment. [Figure 8B] FIG. 3 is a waveform diagram showing the waveform of an induced voltage after passing through a superimposing section in the slip detection circuit according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of the components to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0011] First Embodiment FIG. 1 is a block diagram showing the configuration of a motor control device 1 according to the first embodiment. The motor control device 1 controls the rotation speed of the synchronous motor M by varying the voltage applied to the synchronous motor M (the output voltage of the inverter). The motor control device 1 includes an IPM (Intelligent Power Module) 11 (an example of an inverter unit), a current detection unit 12, a CPU 13 (an example of a control unit), a U-phase idling detection circuit 14 (an example of an idling detection unit), and a V-phase idling detection circuit 15 (an example of an idling detection unit). The IPM11 is an intelligent power module commonly used in inverters, and here it is configured in a full-bridge configuration with six built-in switching elements. A separate control power supply Vc of about 15V is supplied to the IPM11 to drive the internal control circuit. The IPM11 converts the DC voltage Vdc into AC voltage based on the input PWM (pulse width modulation) pulse, and supplies this AC voltage to the synchronous motor M.

[0012] 2 is a block diagram showing the main configuration of an IPM 11 according to the first embodiment. The IPM 11 has a U-phase series circuit 21, a V-phase series circuit 22, and a W-phase series circuit 23 connected in parallel, each of which has a first switching element Tr1 constituting an upper arm and a second switching element Tr2 constituting a lower arm connected in series. A shunt resistor R3 is connected between the U-phase series circuit 21, the V-phase series circuit 22, and the W-phase series circuit 23 connected in parallel and a reference potential.

[0013] A drive circuit 31 (31-1, 31-2) is connected to the U-phase series circuit 21. A drive circuit 32 (32-1, 32-2) is connected to the V-phase series circuit 22. A drive circuit 33 (33-1, 33-2) is connected to the W-phase series circuit 23. The drive circuit 31-1 turns on / off the first switching element Tr1 of the U-phase series circuit 21. The drive circuit 31-2 turns on / off the second switching element Tr2 of the U-phase series circuit 21. The drive circuit 32-1 turns on / off the first switching element Tr1 of the V-phase series circuit 22. The drive circuit 32-2 turns on / off the second switching element Tr2 of the V-phase series circuit 22. The drive circuit 33-1 turns on / off the first switching element Tr1 of the W-phase series circuit 23. The drive circuit 33-2 turns on / off the second switching element Tr2 of the W-phase series circuit 23.

[0014] A connection point between the first switching element Tr1 and the second switching element Tr2 of the U-phase series circuit 21 is connected to a U-phase terminal of the synchronous motor M via a signal line SL1. A connection point between the first switching element Tr1 and the second switching element Tr2 of the V-phase series circuit 22 is connected to a V-phase terminal of the synchronous motor M via a signal line SL2. A connection point between the first switching element Tr1 and the second switching element Tr2 of the W-phase series circuit 23 is connected to a W-phase terminal of the synchronous motor M via a signal line SL3.

[0015] A diode D1 constituting a bootstrap circuit is connected between the control power supply Vc and the drive circuit 31-1, and a capacitor C1 is connected in series to the diode D1. A diode D2 constituting a bootstrap circuit is connected between the control power supply Vc and the drive circuit 32-1, and a capacitor C2 is connected in series with the diode D2. A diode D3 constituting a bootstrap circuit is connected between the control power supply Vc and the drive circuit 33-1, and a capacitor C3 is connected in series with the diode D3.

[0016] 1, the current detection unit 12 detects the current flowing through the shunt resistor R3. Based on the detection result by the current detection unit 12, the CPU 13 generates a drive signal (an example of a switching signal) that alternately turns on / off the first switching element Tr1 and the second switching element Tr2, and outputs the drive signal to each of the drive circuits 31-1, 31-2, 32-1, 32-2, 33-1, and 33-2. The U-phase signal line SL1 is connected to a U-phase idling detection circuit 14. The V-phase signal line SL2 is connected to a V-phase idling detection circuit 15. The U-phase idling detection circuit 14 and the V-phase idling detection circuit 15 each detect idling of the synchronous motor M and output the detection results to the CPU 13.

[0017] (To detect wheel slip) During normal operation, the motor control device 1 converts the DC voltage Vdc into an AC voltage using six drive signals from the CPU 13, and supplies the AC voltage to the synchronous motor M to continuously rotate it. When the synchronous motor M is stopped, the first switching element Tr1 and the second switching element Tr2 of each of the U-phase series circuit 21, the V-phase series circuit 22, and the W-phase series circuit 23 are turned off, and the terminals of the synchronous motor M enter a high impedance state. Therefore, when outside wind rotates the load propeller fan, an induced voltage is generated at each terminal due to idling. Therefore, the U-phase idling detection circuit 14 and the V-phase idling detection circuit 15 detect the idling state of the propeller fan using the induced voltage.

[0018] There are two main purposes for detecting the idling state. The first is to predict the air volume hitting the heat exchanger of the outdoor unit from the idling rotation speed. The heat exchanger is part of the refrigerant circuit that exchanges thermal energy between the inside and outside of the room for heating and cooling, and the amount of heat exchange is controlled by the amount of air passing through the heat exchanger. When the outside wind is strong enough, heat exchange can be carried out without driving the fan, so the refrigeration cycle is operated by driving only the compressor without starting the fan. In other words, to control the refrigeration cycle, it is necessary to know the idling rotation speed of the fan as an indicator of air volume.

[0019] Another purpose of detecting the idling state is to enable sensorless driving of the synchronous motor M, which is particularly necessary for small synchronous motors M of around 25W that have high winding resistance. Such small motors have a slow current rise time and relatively weak torque, so they cannot be started against the outside wind unless braking and starting patterns are devised. The information required at start-up is the idling rotation speed and direction of rotation (forward or reverse).

[0020] (Bootstrap circuit explanation) 3 is a block diagram illustrating only one phase of the series circuit of the IPM 11 according to the first embodiment. This is a simplified diagram for understanding the operation and does not show the actual circuit configuration. Here, the U-phase series circuit 21 will be described as a representative example. This technology is particularly applicable to small motors that perform sensorless control by detecting one shunt current, and is targeted at devices that have a bootstrap circuit built into the upper arm power supply as an IPM to drive them.

[0021] The bootstrap circuit is made up of a diode D1 and a capacitor C1, and supplies power to the drive circuit 31. The drive circuit 31 includes drivers Tr1-1 and Tr1-2, control circuits A1 and A2, and a capacitor C1-1. When the second switching element Tr2 is on, the bootstrap circuit charges the capacitor C1 from the control power supply voltage Vc referenced to the control ground, and controls the first switching element Tr1 using this charged power as the power supply for the drive circuit 31. On the other hand, when the first switching element Tr1 is on, the bootstrap circuit reverse-biases the control power supply Vc using the diode D1, thereby separating the control power supply Vc and the DC voltage Vdc, thereby inexpensively realizing the power charging function of the upper arm drive circuit.

[0022] During operation, the first switching element Tr1 and the second switching element Tr2 are not simultaneously turned on but alternately turned on and off in a complementary manner. When the second switching element Tr2 constituting the lower arm is turned on, the phase terminal 34 is shorted to approximately the control ground. As a result, the capacitor C1 is charged to approximately the control power supply voltage Vc by current passing through the diode D1. This charged power drives the control circuit A1 and drivers Tr1-1 and Tr1-2. In other words, to drive the first switching element Tr1 of the upper arm, the second switching element Tr2 of the lower arm must be periodically turned on to charge the capacitor C1. When a drive signal is received from the CPU 13 or a higher-level control device, the first switching element Tr1 of the upper arm and the second switching element Tr2 of the lower arm switch the phase terminal 34 of the synchronous motor M to Vdc or ground, thereby supplying power to the synchronous motor M in the form of PWM pulses. Furthermore, when the synchronous motor M is stopped, the IPM 11 is turned off. When an off signal from the CPU 13 is transmitted to the control circuit A1 via the control circuit A2, the control circuit A1 raises the base potentials of the drivers Tr1-1 and Tr1-2 to a high level as an off signal.

[0023] Because driver Tr1-1 is a PNP type and driver Tr1-2 is an NPN type, driver Tr1-1 is off and driver Tr1-2 is on. Therefore, the gate terminal of first switching element Tr1 falls to the negative side of the potential reference of capacitor C1. As a result, the collector-emitter of first switching element Tr1 is turned off. The first switching elements Tr1 in V-phase series circuit 22 and W-phase series circuit 23 are also turned off by the same logic. Furthermore, the second switching elements Tr2 in U-phase series circuit 21, V-phase series circuit 22, and W-phase series circuit 23 are driven directly by control power supply Vc and turned off. In the all-phase OFF state, the impedance of each phase terminal 34 of the synchronous motor M is high. Therefore, the synchronous motor M easily spins freely due to external forces such as wind, and an induced voltage proportional to the rotation speed is generated in the synchronous motor M.

[0024] <Comparative example of a slip detection circuit> 4 is a circuit diagram showing a comparative example of the idling detection circuit B14 according to the first embodiment. The idling detection circuit B14 includes a voltage dividing circuit 41 and a comparator 42. The voltage dividing circuit 41 has a first resistor R1 connected to a signal line SL1 at one end and a second resistor R2 connected to the other end of the first resistor R1. The comparator 42 compares the output voltage of the voltage dividing circuit 41 with a reference voltage Vref and outputs the comparison result to the CPU 13. Since the induced voltage of the synchronous motor M is AC, the rotation speed can be determined by measuring the voltage period, and the rotation direction can be inferred from the magnitude relationship by detecting the voltage of two of the three phases. For this detection, the idling detection circuit B14 is provided with a voltage divider circuit 41 that reduces the induced voltage to the voltage level of the CPU 13.

[0025] (Operation of the idling detection circuit B14) FIG. 5 is a waveform diagram showing the waveform of the induced voltage Ve input to the slip detection circuit B14. FIG. 5(a) shows the waveform of the induced voltage Ve before voltage division, and FIG. 5(b) shows the waveform of the induced voltage Ve' after voltage division. In FIG. 5, the vertical axis represents the voltage level, and the horizontal axis represents time. When the waveform of the induced voltage Ve input to the slip detection circuit B14 is monitored with respect to the ground, as shown in FIG. 5(a), it is observed as a half-wave rectified waveform with an upper hip on which a DC offset voltage Vofst is superimposed. The superimposition of the DC offset voltage Vofst narrows the dynamic range of the comparator 42, thereby degrading the signal-to-noise (SN) characteristics and increasing the risk of false detection.

[0026] (The reason why an offset voltage is added to the induced voltage Ve, resulting in an upper hip waveform) Since the synchronous motor M is stopped, an OFF command (logic signal) is input to the control circuit A1 from the CPU 13. However, it is assumed that the capacitor C1 has already been charged. When the OFF command is input, the control circuit A1 outputs a high-level signal. The high-level signal output from the control circuit A1 is input to drivers Tr1-1 and Tr1-2, turning driver Tr1-1 off and driver Tr1-2 on. As a result, the gate terminal of the first switching element Tr1 becomes low-level, turning the first switching element Tr1 off. Using the same logic, the second switching element Tr2 is also turned off by an OFF command from the CPU 13.

[0027] The slip detection circuit B14 is connected to the phase terminal 34 of the synchronous motor M. In this case, as shown in the equivalent circuit diagram of Fig. 6, a closed circuit is formed by the path of the control power supply Vc, diode D1, control circuit A1, the base terminal of driver Tr1-2, first resistor R1 and second resistor R2 of the slip detection circuit B14, and control ground. Since driver Tr1-2 is an NPN type, when viewed from the base terminal, it is equivalent to a PN junction element (called diode D1-2) being connected between the base and emitter, that is, it is equivalent to diode D1-2 being connected in forward bias to the output of control circuit A1.

[0028] For these reasons, a DC offset voltage Vofst is superimposed on the induced voltage Ve. In the section where the DC offset voltage Vofst is superimposed on the other two phases, the induced voltage Ve becomes an upper-hip voltage, similar to two-phase modulation. Measuring the voltage at phase terminal 34 reveals that the DC offset voltage Vofset appearing at phase terminal 34 is approximately 13 V when the control power supply Vc is 15 V. This corresponds to a voltage drop in the control power supply Vc equivalent to the forward voltage of two diodes.

[0029] As a result, as shown in FIG. 5(a), an induced voltage Ve′ obtained by superimposing a DC offset voltage Vofst (e.g., 13 V) obtained by subtracting the voltage drop due to the switching element from the DC voltage Vdc on the upper hip induced voltage is applied to the spin detection circuit B14. The DC offset voltage Vofst' in Fig. 5(b) is the DC offset voltage Vofst divided by the voltage divider circuit 41 of the spin detection circuit B14. If the upper limit voltage for use of the comparator 42 of the spin detection circuit B14 is set to +V, the Vofst' portion of the induced voltage Ve' to which the DC offset voltage Vofst' has been added becomes unusable.

[0030] <Solution according to the first embodiment> Figure 7 is a circuit diagram showing a U-phase slip detection circuit 14 according to the first embodiment. In Figure 7, the same parts as those in Figure 4 above are given the same reference numerals, and detailed explanations will be omitted. Here, the U-phase slip detection circuit 14 will be explained as a representative example. In the first embodiment of the present disclosure, a removal unit 43 that removes the DC offset voltage Vofst is provided between the connection point between the first resistor R1 and the second resistor R2 of the voltage divider circuit 41 and the comparator 42. In the first embodiment of the present disclosure, for example, a high-pass filter (HPF) 431 is connected as the removal unit 43. In addition, in the first embodiment of the present disclosure, a superposition unit 44 is connected between the high-pass filter 431 and the comparator 42.

[0031] High-pass filter 431 removes the DC component from the output voltage of voltage divider circuit 41 and extracts only the AC component. FIG. 8A shows the waveform of induced voltage Ve' after passing through high-pass filter 431. A superimposing unit 44 is provided on the output side of high-pass filter 431. Superimposing unit 44 superimposes an arbitrary offset voltage V0 on the output voltage of high-pass filter 43 and outputs the result to one input terminal of comparator 42.

[0032] FIG. 8B shows the waveform of the induced voltage Ve′ after passing through the superimposing unit 44, and is a waveform diagram conceptually illustrating the comparison state of input values ​​at the comparator 42 of the U-phase idle detection circuit 14 according to the first embodiment. In FIGS. 8A and 8B, the vertical axis represents the voltage level, and the horizontal axis represents time. The high-pass filter 431 removes the DC component from the induced voltage divided by the voltage-dividing circuit 41. As a result, the output voltage of the high-pass filter 431 has a waveform such that the average voltage Vave of the induced voltage becomes the reference voltage (control ground) for control, as shown in FIG. 8A. The superimposing unit 44 then superimposes an offset voltage on the output voltage of the high-pass filter 43. In this case, if the offset voltage V0 of the induced voltage Ve′ is the average voltage Vave, the entire induced voltage waveform falls within the dynamic range, as shown in FIG. 8B, and the comparator 42 can be generated independent of component variations in the IPM 11. Note that Vref can also be set to the same value as the offset voltage V0. In this case, the comparator 42 can easily detect the change in the induced voltage value, and the idling state of the fan can be reliably detected.

[0033] <Effects of the First Embodiment> As described above, according to the first embodiment, in the U-phase idling detection circuit 14 and the V-phase idling detection circuit 15, a high-pass filter 43 is inserted between the voltage dividing circuit 41 and the comparator 42, and the offset (DC) from the IPM 11 is removed from the induced voltage value to extract only the AC component. An arbitrary offset voltage is superimposed on the output voltage of the high-pass filter 43 in the superimposing unit 44, and the superimposed voltage is input to one input terminal of the comparator 42. Therefore, the comparator 42 can be generated independent of variations in the components of the IPM 11, and the comparator 42 can easily detect the rotation speed and rotation direction.

[0034] Furthermore, according to the first embodiment, when the second switching element Tr2 constituting the lower arm is on, the control power supply voltage referenced to the control ground is charged from the control power supply Vc to the capacitor C1, and this charged power is used as the power supply for the drive circuit 31 to control the first switching element Tr1 constituting the upper arm, thereby making it possible to provide an inexpensive idling detection circuit for a small motor that performs sensorless control by detecting a single shunt current.

[0035] <Other embodiments> As described above, the present invention has been described using the first embodiment. However, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Upon understanding the gist of the technical content disclosed in the above embodiment, those skilled in the art will understand that various alternative embodiments, examples, and operational techniques can be included in the present invention. Furthermore, the configurations disclosed in the first embodiment can be appropriately combined within a range that does not cause contradictions. For example, configurations disclosed in multiple different embodiments can be combined, or configurations disclosed in multiple different modified examples of the same embodiment can be combined. [Explanation of symbols]

[0036] 1. Motor control device 12 Current detection section 14 U-phase idle detection circuit 15 V-phase idle detection circuit 21 U-phase series circuit 22 V-phase series circuit 23 W-phase series circuit 31(31-1, 31-2), 32(32-1, 32-2), 33(33-1, 33-2) Drive circuit 34 phase terminal 41 Voltage divider circuit 42 Comparator 43 Removal part 431 High Pass Filter 44 Overlapping section B14 Idling detection circuit R1 First resistor R2 Second resistor R3 shunt resistor

Claims

1. an inverter unit having a series circuit group, in which at least three series circuits are connected in parallel, each series circuit being a first switching element constituting an upper arm and a second switching element constituting a lower arm connected in series, a drive circuit for turning on / off the first and second switching elements, respectively, and a shunt resistor connected between the series circuit group and a reference potential, and converting a DC voltage into an AC voltage based on an input PWM pulse and supplying the AC voltage to a motor; a current detection unit that detects a current flowing through the shunt resistor; a control unit that generates a switching signal that is input to the drive circuit based on a detection result by the current detection unit and that alternately turns on / off the first switching element and the second switching element; a idling detection unit connected to a signal line connecting the motor to a connection point between the first switching element and the second switching element, the idling detection unit detecting idling of the motor; Equipped with The slip detection unit a voltage divider circuit having a first resistor connected to the signal line at one end and a second resistor connected to the other end of the first resistor; a comparator that compares the output voltage of the voltage divider circuit with a reference voltage and outputs the comparison result to the control unit; a removal unit that is connected between the comparator and a connection point between the first resistor and the second resistor of the voltage divider circuit and that removes an offset voltage superimposed on the output voltage; A motor control device comprising:

2. The motor control device according to claim 1 , wherein the removing unit has a high-pass filter that removes a DC component from the output voltage.

3. The motor control device according to claim 1 , wherein the slip detection unit is provided corresponding to at least two of the series circuits in the group of series circuits.

4. 2. The motor control device according to claim 1, wherein the inverter unit has a diode connected between a control power supply and the drive circuit and a capacitor connected in parallel to the diode, and when the second switching element is on, power from the control power supply is charged to the capacitor via the diode, and when the second switching element is off, the power charged in the capacitor is supplied to the drive circuit.

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