JP7556696B2 - Motor drive control device and fan device - Google Patents

Description

This disclosure relates to a motor drive control device equipped with a current detection circuit, and a blower equipped with a motor drive control device.

In recent years, an increasing number of ventilation devices such as ventilation fans and blowers use permanent magnet synchronous motors with permanent magnets in the rotor for a wide range of variable speed control, power consumption savings, or low noise operation. Permanent magnet synchronous motors are driven by a motor drive circuit that includes an inverter circuit. Specifically, the motor drive circuit controls the inverter circuit with pulse width modulation (PWM) and applies the voltage obtained by PWM control to the permanent magnet synchronous motor, thereby driving the permanent magnet synchronous motor.

When driving a permanent magnet synchronous motor, it is necessary to detect the magnetic pole position of the permanent magnet, which is the rotor. Recently, however, position sensorless control methods have become mainstream, in which the magnetic pole position of the permanent magnet is estimated from information such as the motor current and controlled without directly detecting the magnetic pole position of the permanent magnet.

The following Patent Document 1 discloses a motor drive control device that drives a permanent magnet synchronous motor using a position sensorless control method.

Patent No. 4744505

In a position sensorless control method, to control the operation of a motor accurately and precisely, it is necessary to increase the resolution when detecting the motor current as much as possible. While the motor current is an analog quantity, the microcomputer (hereafter abbreviated as "microcomputer"), which is the processor installed in the motor drive control device, performs various processes using digital values. Therefore, when the motor current is detected and input into the microcomputer, the analog quantity is converted to a digital value. To convert the analog quantity to a digital value, an analog-to-digital (AD) conversion function provided in the microcomputer is used.

The quantization resolution when converting an analog quantity into a digital value is determined by the microcontroller, and the current value per digit is determined by the resolution of the microcontroller. For this reason, in order to increase the control accuracy within the motor's operating range, it is necessary to set the motor current detection range according to the motor's operating range. In other words, even with the same motor drive control device hardware, if the motor current detection range is not set to match the motor drive control device, the problem of fine operation control cannot be achieved. Conversely, if the motor current detection range cannot be set to match the motor drive control device, it becomes necessary to prepare current detection circuits with different specifications for each current detection range, which will result in a problem of reduced productivity. For this reason, it is desirable to expand the operating range of motors that can be controlled by the same current detection circuit.

The present disclosure has been made in consideration of the above, and aims to provide a motor drive control device that can expand the operating range of a motor that can be controlled by the same current detection circuit.

In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a motor drive control device that drives a motor using a position sensorless control method. The motor drive control device includes a current detection circuit that detects the motor current flowing through each phase of the motor, and a control unit that performs control to change the circuit configuration of the current detection circuit. The current detection circuit includes an amplifier that amplifies the detected value of the motor current, and an analog switch that switches the resistance value of a resistor that determines the amplification gain of the amplifier.

The motor drive control device according to the present disclosure has the advantage of being able to expand the operating range of a motor that can be controlled by the same current detection circuit.

FIG. 1 is a diagram showing a configuration of a motor drive control device according to a first embodiment; FIG. 2 is a block diagram showing an example of a hardware configuration for implementing the functions of the control unit shown in FIG. 1 . FIG. 1 is a diagram showing a configuration example of a current detection circuit according to a first embodiment; FIG. 2 is a diagram showing how the current detection range is expanded by the current detection circuit according to the first embodiment; FIG. 13 is a diagram showing a configuration example of a current detection circuit according to a second embodiment; Flowchart showing an operation flow in the third embodiment FIG. 13 is a perspective view illustrating a ventilation fan, which is an example of a blower according to a fourth embodiment.

The motor drive control device and the blower according to the embodiment of the present disclosure will be described in detail below with reference to the attached drawings. Note that in the following description, no distinction will be made between electrical connection and physical connection, and they will simply be referred to as "connection."

Embodiment 1.
Fig. 1 is a diagram showing the configuration of a motor drive control device 100 according to embodiment 1. As shown in Fig. 1, the motor drive control device 100 according to embodiment 1 includes a rectifier circuit 2, a smoothing capacitor 4, an inverter circuit 5, a control unit 9, and a current detection circuit 12. The control unit 9 includes a sensorless motor control unit 10 and a current calculation unit 11. Although the details will be described later, the control unit 9 performs control to change the circuit configuration of the current detection circuit 12. The current detection circuit 12 is a circuit that detects the motor current.

The AC power supply 1 is connected to the input terminal of the motor drive control device 100, and the motor 7 is connected to the output terminal. The motor drive control device 100 is a device that drives the motor 7 using a position sensorless control method with power supplied from the AC power supply 1. An example of the motor 7 is a permanent magnet synchronous motor, but is not limited to this. Any motor that can be driven using a position sensorless control method may be used.

An example of the AC power source 1 is a commercial power source. In typical Japanese households, single-phase AC with a frequency of 50 Hz or 60 Hz and a voltage of 100 V is used. On the other hand, in other countries or when the motor drive control device 100 is for commercial use, single-phase AC with a voltage of 200 V or more may be used.

An example of the rectifier circuit 2 is a full-wave rectifier circuit shown in the figure. The rectifier circuit 2 includes four bridge-connected diodes 3a, 3b, 3c, and 3d (hereinafter referred to as "3a to 3d" as appropriate). The rectifier circuit 2 converts the AC voltage output from the AC power source 1 into a DC voltage. The rectifier circuit 2 and the inverter circuit 5 are connected by a high-potential DC bus 15 and a low-potential DC bus 16. The smoothing capacitor 4 is connected between the DC bus 15 and the DC bus 16, and smoothes the DC voltage output by the rectifier circuit 2.

The inverter circuit 5 is applied with a DC voltage that has been rectified by the rectifier circuit 2 and smoothed by the smoothing capacitor 4. The inverter circuit 5 performs PWM operation under the control of the control unit 9, and converts the applied DC voltage into a three-phase AC voltage of any voltage and any frequency.

The inverter circuit 5 includes six bridge-connected switching elements 6a, 6b, 6c, 6d, 6e, and 6f (hereinafter referred to as "6a to 6f" as appropriate). One example of the switching elements 6a to 6f is an insulated gate bipolar transistor (IGBT), and another example of the switching elements 6a to 6f is a metal-oxide-semiconductor field-effect transistor (MOSFET).

Each of the switching elements 6a to 6f has a diode connected in anti-parallel. Anti-parallel means that the diodes are connected so that the direction of the current flowing through them is opposite to the direction of the current flowing when the switching element is conductive. The current flowing through the diode is sometimes called a return current. In the case of a MOSFET, a parasitic diode exists inside the element. Therefore, when using a MOSFET, it is possible to omit the diode connected in anti-parallel by using the parasitic diode.

Switching elements 6a and 6b are connected in series to form the U-phase leg. Similarly, switching elements 6c and 6d are connected in series to form the V-phase leg, and switching elements 6e and 6f are connected in series to form the W-phase leg. The U-phase leg, V-phase leg, and W-phase leg are connected in parallel with each other. In each phase leg, the switching elements 6a, 6c, and 6e located on the high potential side are sometimes called the "upper arm switching elements" or simply the "upper arm." Also, the switching elements 6b, 6d, and 6f located on the low potential side are sometimes called the "lower arm switching elements" or simply the "lower arm."

A shunt resistor 8a is connected between the emitter of the switching element 6b and a terminal to which the low potential sides of the phase legs are commonly connected, and a shunt resistor 8b is connected between the switching element 6d and the terminal on the low potential side. In the example of FIG. 1, no shunt resistor is connected to the W-phase leg, but a shunt resistor may also be connected to the W-phase leg. Note that a method in which shunt resistors are provided in three legs of three phases is sometimes called a "three-shunt method," and a method in which shunt resistors are provided in two legs is sometimes called a "two-shunt method." In the case of the two-shunt method, the current of a phase without a shunt resistor can be calculated from the two currents of phases with shunt resistors.

The motor 7 includes a rotor 7a, a U-phase winding 7U, a V-phase winding 7V, and a W-phase winding 7W. One end of each phase winding is connected to each other, and the other end of each phase winding is connected to the connection point between the switching elements of the upper and lower arms in the legs of the corresponding phase.

The motor current flowing through switching element 6b flows to shunt resistor 8a and is converted to a voltage by shunt resistor 8a. The motor current flowing through switching element 6d flows to shunt resistor 8b and is converted to a voltage by shunt resistor 8b. The voltages generated in shunt resistors 8a and 8b are input to current detection circuit 12. Current detection circuit 12 amplifies the input voltage. Current detection circuit 12 also performs level shift processing so that the amplified voltage becomes a voltage value suitable for the input range of control unit 9.

The current calculation unit 11 calculates the currents Id and Iq based on the information of the motor current output from the current detection circuit 12. The current Id is the d-axis current value in the dq coordinate system, and the current Iq is the q-axis current value in the dq coordinate system. The dq coordinate system is a coordinate system used in the internal processing of the control unit 9.

The sensorless motor control unit 10 determines the switching times of the switching elements 6a to 6f based on the currents Id and Iq calculated by the current calculation unit 11, thereby PWM-controlling the inverter circuit 5. This controls the current flowing through each phase winding of the motor 7, and the motor 7 is PWM-driven.

Figure 2 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 9 shown in Figure 1. When realizing the functions of the control unit 9 described above and the functions of the control unit 9 described below, as shown in Figure 2, the configuration can include a processor 300 that performs calculations, a memory 302 that stores programs read by the processor 300, and an interface 304 that inputs and outputs signals.

Processor 300 is an example of a calculation means. Processor 300 may be called a calculation device, a microprocessor, a microcomputer, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. Examples of memory 302 include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (registered trademark) (Electrically EPROM).

Specifically, memory 302 stores a program that executes the motor control function in control unit 9. Processor 300 exchanges necessary information via interface 304, executes the program stored in memory 302, and refers to the table stored in memory 302 to perform the motor control described below. The results of calculations by processor 300 can be stored in memory 302.

Next, the configuration and operation of the main parts in the first embodiment will be described. FIG. 3 is a diagram showing an example of the configuration of the current detection circuit 12 in the first embodiment. FIG. 3 shows an example of the circuit configuration for detecting the motor current Im flowing through the shunt resistor 8a via the switching element 6b of the lower arm of the U phase.

The current detection circuit 12 includes an amplifier 20, an analog switch 23, and resistors 21, 22, 24, 25, 26, and 27. The alphanumeric characters in parentheses shown with the symbol of each resistor indicate the resistance value of each resistor. The output of the current detection circuit 12 is input to a microcomputer 14 provided in the control unit 9. The microcomputer 14 includes an input port 14a, which is an input terminal, and an output port 14b, which is an output terminal.

In FIG. 3, the motor current Im is detected using a shunt resistor 8a. If the resistance value Rs of the shunt resistor 8a is increased, the loss due to heat generation by the shunt resistor 8a increases. For this reason, a small resistance value of 1 Ω or less is used as the resistance value Rs of the shunt resistor 8a. On the other hand, if the resistance value is small, the voltage of the shunt resistor 8a also becomes small. For this reason, a configuration is adopted in which the voltage amplified by the amplifier 20 is input to the microcomputer 14 as shown in FIG. 3. The power supply voltage VCC is applied to the microcomputer 14 and the amplifier 20.

The amplifier 20 has a positive input terminal 20a which is a non-inverting terminal, a negative input terminal 20b which is an inverting terminal, and an output terminal 20c. The analog switch 23 is a double-throw switch and has a common terminal 23a, a first contact 23b, and a second contact 23c. The analog switch 23 switches the contacts based on the input switch control signal.

One end of resistor 24 is connected to the power supply voltage VCC. The other end of resistor 24 is connected to one end of resistor 25, the negative input terminal 20b of amplifier 20, and the common terminal 23a of analog switch 23. The other end of resistor 25 is connected to ground (GND).

One end of resistor 26 is connected to the power supply voltage VCC. The other end of resistor 26 is connected to one end of resistor 27 and to the positive input terminal 20a of amplifier 20. The other end of resistor 27 is connected to the connection point between switching element 6b and shunt resistor 8a.

One end of resistor 21 is connected to output terminal 20c of amplifier 20 and one end of resistor 22. The other end of resistor 21 is connected to first contact 23b of analog switch 23. The other end of resistor 22 is connected to second contact 23c of analog switch 23. Output terminal 20c of amplifier 20 is connected to input port 14a of microcontroller 14.

Next, the operation of the current detection circuit 12 will be described. A divided voltage of the power supply voltage VCC divided by resistors 24 and 25 is applied to the negative input terminal 20b of the amplifier 20. When the motor current Im does not flow, the resistance value of the shunt resistor 8a is small, so that a divided voltage of the power supply voltage VCC divided by resistors 26 and 27 is applied to the positive input terminal 20a of the amplifier 20. On the other hand, when the motor current Im flows, a voltage obtained by superimposing the voltage of the shunt resistor 8a on the divided voltage when the motor current Im does not flow is applied to the positive input terminal 20a of the amplifier 20. This voltage is amplified by the amplifier 20. The output voltage of the amplifier 20 is represented by Vo, as follows:

Vo=[(Rf1/R0)+(1/2)]×Rs×Im+(1/2)×VCC…(1)

In the above formula (1), R0 is the resistance value of resistors 24 and 25. Furthermore, the above formula (1) represents the output voltage when analog switch 23 is connected to first contact 23b. When analog switch 23 is connected to second contact 23c, Rf1 is replaced with Rf2. There is a relationship between Rf1 and Rf2: Rf1>Rf2. The contacts of analog switch 23 are switched by a switch control signal output from output port 14b of microcontroller 14.

As mentioned above, the output voltage Vo is input to the input port 14a of the microcontroller 14. Inside the microcontroller 14, an AD conversion process is performed to convert an analog quantity into a digital value. For this reason, in the current detection circuit 12, the output voltage Vo of the amplifier 20 must be suppressed so that it falls within the range of 0 to VCC [V] where AD conversion is possible. For this reason, in the first embodiment, the amplification gain of the amplifier 20 is adjusted. Specifically, in FIG. 3, the resistor that determines the amplification gain of the amplifier 20 is switched from resistor 21 to resistor 22. This switching can be achieved by switching the contact of the analog switch 23 from the first contact 23b to the second contact 23c.

Figure 4 is a diagram showing how the current detection range is expanded by the current detection circuit 12 in embodiment 1. The horizontal axis of Figure 4 represents the motor current Im, and the vertical axis represents the output voltage Vo of the amplifier 20. Figure 4 shows that when the resistance value is Rf1, the motor current value is Im1 when the output voltage Vo is VCC, which is the maximum value of the input range. Also, when the resistance value is Rf2, the motor current value is Im2 (>Im1) when the output voltage Vo is VCC, which is the maximum value of the input range.

When using the same current detection circuit to handle motors ranging from small capacity motors with a small maximum value of the motor current Im to large capacity motors with a large maximum value of the motor current Im, it is necessary to expand the current detection range to match the large capacity motor. In this case, the resolution of the data in the small current range of a small capacity motor is insufficient, resulting in a large current value per digit and making it impossible to perform fine operation control. For this reason, the conventional solution was to prepare current detection circuits with different specifications to match the operating current range of the motor.

In contrast, the current detection circuit 12 of embodiment 1 is configured such that the resistance value that determines the amplification gain of the amplifier 20 is switched by the analog switch 23. For this reason, for example, when controlling a small capacity motor, the contact of the analog switch 23 is controlled so that resistor 21 is connected, and when controlling a large capacity motor, the contact of the analog switch 23 is controlled so that resistor 22 is connected. This makes it possible to detect currents in motors of both small and large capacity using the same current detection circuit. It also makes it possible to expand the operating range of motors that can be controlled by the same current detection circuit.

The analog switch 23 that switches the resistance value is preferably connected to the negative input terminal 20b of the amplifier 20 as shown in FIG. 3. A voltage of (1/2)×VCC, which is the power supply voltage VCC divided by 1/2, is applied to the negative input terminal 20b of the amplifier 20 by a resistor 24 with a resistance value of R0, one end of which is connected to the power supply voltage VCC, and a resistor 25 with a resistance value of R0, the other end of which is connected to ground (GND). This voltage is stable because it does not depend on the motor current Im. Therefore, there is no large fluctuation in the voltage applied to the common terminal 23a of the analog switch 23. As a result, the current detection circuit 12 shown in FIG. 3 can apply a stable potential to the analog switch 23 even when the resistance value is switched.

The switching of the contacts of the analog switch 23 may be selected according to the model to be connected. If the storage device that holds the program that operates the microcomputer 14 is a writable and erasable storage device, the output of a signal that controls the switching of the contacts of the analog switch 23 may be written into the program.

As described above, according to the motor drive control device of embodiment 1, the current detection circuit that detects the motor current includes an amplifier that amplifies the detected value of the motor current, and an analog switch. The control unit controls switching of the resistance value of the resistor that determines the amplification gain of the amplifier by switching the contacts of the analog switch. This allows the same current detection circuit to handle current detection for motors with small to large capacities, making it possible to expand the operating range of motors that can be controlled by the same current detection circuit.

Embodiment 2.
Fig. 5 is a diagram showing a configuration example of a current detection circuit 12A in embodiment 2. In the current detection circuit 12A, the analog switch 23 is replaced with an analog switch 23A and the resistor 22 is replaced with a resistor 22A in the configuration of the current detection circuit 12 in embodiment 1 shown in Fig. 3. The analog switch 23A is a single-throw switch and includes a common terminal 23Aa and a contact 23Ab. The analog switch 23A switches the circuit on and off based on an input switch control signal.

The common terminal 23Aa of the analog switch 23A is connected to the negative input terminal 20b of the amplifier 20, the other end of the resistor 21, and one end of the resistor 25. One end of the resistor 22A is connected to one end of the resistor 21 and the output terminal 20c of the amplifier 20. The other end of the resistor 22A is connected to the contact 23Ab of the analog switch 23A. The other configuration is the same as or equivalent to the configuration of the current detection circuit 12 shown in FIG. 3, and the same reference numerals are used for the same or equivalent components. Hereinafter, explanations of overlapping contents will be omitted as appropriate.

The current detection circuit 12A in the second embodiment, like the first embodiment, is designed to adjust the amplification gain of the amplifier 20 according to the capacity of the motor. In the second embodiment, the resistor 21 is left connected, and the analog switch 23A switches between the connection and non-connection of the resistor 22A. If the circuit operation of the second embodiment is to be the same as that of the first embodiment, the resistance value Rf3 of the resistor 22A should be set to a value that satisfies the following formula.

Rf3=(Rf1×Rf2)/(Rf1-Rf2)…(2)

Note that the above formula (2) can be transformed to Rf3 = Rf2/[1-(Rf2/Rf1)], so there is a relationship between Rf2 and Rf3: Rf3>Rf2.

In the second embodiment, the analog switch 23A is not a two-way switch, but a simple switch with only short-circuit and open functions can be used. This allows the cost per part to be reduced compared to the first embodiment.

As described above, according to the motor drive control device of embodiment 2, the current detection circuit that detects the motor current includes an amplifier that amplifies the detected value of the motor current, and an analog switch. The control unit controls switching the resistance value of the resistor that determines the amplification gain of the amplifier by switching the analog switch on and off. This allows the same current detection circuit to handle current detection for motors with small to large capacities, making it possible to expand the operating range of motors that can be controlled by the same current detection circuit.

Embodiment 3.
Fig. 6 is a flowchart showing an operation flow in the third embodiment. In the third embodiment, the amplification gain of the amplifier 20 is switched using the motor current Im. The flowchart shown in Fig. 6 can be implemented by using either the current detection circuit 12 of the first embodiment shown in Fig. 3 or the current detection circuit 12A of the second embodiment shown in Fig. 5. Fig. 6 illustrates the case where the current detection circuit 12 shown in Fig. 3 is used.

If the motor current Im is smaller than the judgment value Im0 (step S101, Yes), the connection of resistor 21 is selected (step S102). On the other hand, if the motor current Im is equal to or greater than the judgment value Im0 (step S101, No), the connection of resistor 22 is selected (step S103). After completing the processes of steps S102 and S103, the process returns to step S101 and repeats the process of FIG. 6. As described above, the operation flow of FIG. 6 is constantly activated and executed while the motor 7 is in operation.

In step S101 of the operation flow shown in FIG. 6, when the motor current Im is equal to the judgment value Im0, the result is determined as "No", but the result may be determined as "Yes". In other words, when the motor current Im is equal to the judgment value Im0, the result may be determined as either "Yes" or "No".

According to the motor drive control device of the third embodiment, the resistance value that determines the amplification gain of the amplifier is switched based on the magnitude of the motor current, and the amplification gain of the amplifier is automatically switched according to the magnitude of the motor current. Therefore, it is not necessary to determine in advance whether the analog switch is on or off, and it is not necessary to write the initial value of the analog switch state in the program. This eliminates the need to select a program according to the model, making it possible to share and standardize programs.

Embodiment 4.
7 is a perspective view for explaining a ventilation fan 150, which is an example of a blower according to embodiment 4. If the motor drive control device according to any one of embodiments 1 to 3 is mounted on the ventilation fan 150, it is possible to standardize the control circuit and control software that drive the ventilation fan 150. This allows the same specification control circuit and control software to be used for various types of products, thereby reducing the cost of the product.

The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. In addition, parts of the configurations may be omitted or modified without departing from the spirit of the invention.

1 AC power supply, 2 Rectifier circuit, 3a, 3b, 3c, 3d Diode, 4 Smoothing capacitor, 5 Inverter circuit, 6a, 6b, 6c, 6d, 6e, 6f Switching element, 7 Motor, 7a Rotor, 7U U-phase winding, 7V V-phase winding, 7W W-phase winding, 8a, 8b Shunt resistor, 9 Control unit, 10 Sensorless motor control unit, 11 Current calculation unit, 12, 12A Current detection circuit, 14 Microcomputer, 14a Input port, 14b Output port, 15, 16 DC bus, 20 Amplifier, 20a Positive input terminal, 20b Negative input terminal, 20c Output terminal, 21, 22, 22A, 24, 25, 26, 27 Resistor, 23, 23A Analog switch, 23a, 23Aa Common terminal, 23b First contact, 23c second contact, 23Ab contact, 100 motor drive control device, 150 ventilation fan, 300 processor, 302 memory, 304 interface.

Claims (5)

A motor drive control device that drives a motor using a position sensorless control method,
An inverter circuit that converts an applied DC voltage into a three-phase AC voltage of an arbitrary voltage and an arbitrary frequency;
Two shunt resistors, each having a resistance value of 1 Ω or less, are inserted in only two of the three phase legs of the inverter circuit;
a current detection circuit that detects a motor current flowing through each phase of the motor based on a current flowing through the two shunt resistors;
A control unit that performs control to change a circuit configuration of the current detection circuit;
Equipped with
The current detection circuit includes:
an amplifier having a positive input terminal, a negative input terminal and an output terminal, and amplifying the detected value of the motor current;
a resistor group including two or more resistors each having one end connected to the output terminal and each of which determines an amplification gain of the amplifier;
an analog switch having a common terminal and at least one contact, the common terminal being connected to the negative input terminal, the contact being connected to one resistor included in the resistor group at the other end side of the resistor group, and changing a connection between the resistor included in the resistor group and the contact to switch a resistance value that determines an amplification gain of the amplifier;
a first resistor having one end connected to a power supply voltage and the other end connected to the negative input terminal;
a second resistor having one end connected to ground and the other end connected to the other end of the first resistor, the negative input terminal, and the common terminal of the analog switch;
a third resistor having one end connected to a power supply voltage and the other end connected to the positive input terminal;
a fourth resistor having one end connected to the other end of the third resistor and the positive input terminal and having the other end connected to a connection point between the switching element of the inverter circuit and the shunt resistor;
Equipped with
the first, second, third and fourth resistors all have equal resistance values;
The motor drive control device according to claim 1, wherein the resistance value is switched based on the magnitude of the motor current. 2. The motor drive control device according to claim 1, wherein the resistance value is changed by changing a contact of the analog switch. 2. The motor drive control device according to claim 1, wherein the resistance value is changed by turning on and off the analog switch. 4. The motor drive control device according to claim 2, wherein the amplification gain is automatically switched in accordance with the magnitude of the motor current. A blower comprising the motor drive control device according to any one of claims 1 to 4 .

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