JP4744565B2 - Brushless motor temperature detection device - Google Patents

Description

  The present invention relates to a brushless motor temperature detection device that detects the temperature of a brushless motor based on a voltage difference between both ends of an excitation coil of a resolver.

  The characteristics of a brushless motor change depending on its own temperature, and the characteristics are remarkably deteriorated at an excessively high temperature. Therefore, it is necessary to detect the temperature of the brushless motor and drive the motor so as to compensate for it. As a method for detecting the temperature of the brushless motor, a method for obtaining the temperature of the brushless motor from the temperature characteristic of the resolver has been conventionally proposed by paying attention to the temperature characteristic of the resolver that is attached to the brushless motor and detects the rotation angle.

  Focusing on the fact that the radius of the Lissajous circle formed by the sine signal and cosine signal, which are the outputs of the resolver, changes depending on the temperature, a method for obtaining the temperature from this radius has been proposed (see, for example, Patent Document 1). This method relies on the physical grounds that the amplitude of the output sine signal and cosine signal changes because the excitation current changes due to the temperature change of the excitation coil impedance of the resolver.

JP 2006-214969 A

  In the conventional method as described above, that is, the method of obtaining the temperature of the brushless motor from the radius of the Lissajous circle, the radius of the Lissajous circle is not determined only by the temperature characteristic of the impedance of the exciting coil of the resolver, but the mechanical tolerance of the resolver. There is a problem that the temperature obtained from the change in radius includes a large error because it is also affected by the temperature characteristics of the processing circuit and the temperature characteristics of the processing circuit for processing the resolver signal.

  In addition, the above-described conventional method has a problem in that the temperature detection process is performed by a calculation process by the CPU, so that the CPU load increases and an expensive CPU capable of high-speed processing is required. It was.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a temperature detection device for a brushless motor that does not include a detection error and does not become a calculation load of a CPU.

  A temperature detection device for a brushless motor according to the present invention is a brushless motor that detects a rotation angle by a resolver. An excitation circuit that outputs an AC signal, and a DC bias voltage is added to the AC signal to the excitation coil of the resolver. An adding circuit to be added; a low-pass filter that removes an AC component from a voltage difference between both ends of the exciting coil to extract a DC component; a differential amplifier that amplifies the DC component from the low-pass filter; and an output of the differential amplifier An A / D converter that performs A / D conversion of the voltage, and a temperature calculation unit that calculates the temperature of the brushless motor from the output of the A / D converter according to the proportional relationship between the DC component and the temperature are provided.

  The temperature detection device for a brushless motor according to the present invention has an effect that it does not include a detection error and does not become a calculation load of the CPU.

  In other words, the excitation coil is excited by an excitation signal obtained by adding a DC component to the resolver excitation coil, and the temperature is obtained from the DC component of the voltage difference between both ends of the excitation coil, so the impedance of the excitation coil can be detected directly, It does not include errors and does not become a computational load on the CPU.

Embodiment 1 FIG.
A temperature detection apparatus for a brushless motor according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a diagram showing a configuration of a temperature detection device for a brushless motor according to Embodiment 1 of the present invention. In the following, in each figure, the same reference numerals indicate the same or corresponding parts. In the following embodiments, a case where a brushless motor constitutes a part of an electric power steering apparatus will be described as an example.

  In FIG. 1, a temperature detection device for a brushless motor according to Embodiment 1 of the present invention is provided with a resolver 10 and an ECU 100.

  FIG. 1 shows a resolver 10 as an electric circuit. The resolver 10 includes a rotor 11, an excitation coil 13 wound around a stator (described later), and a coil wound around the stator. The two output coils 14 and 15 are configured.

  The ECU 100 is a two-stage CR low-pass filter composed of a DC power source Vcc, an excitation circuit 20, an adding circuit composed of resistors R1 and R2, and two resistors R3, R4 and two capacitors C1, C2. 30, a differential amplifier 40 including an operational amplifier 41 and two resistors R5 and R6, a CPU 50, a nonvolatile memory 60, and a differential amplifier 70 are provided.

  The CPU 50 includes an A / D converter 51, a temperature calculation unit 52, an A / D converter 53, a tangent calculation unit 54, and an inverse function calculation unit 55.

  FIG. 2 is a perspective view showing the configuration around the electric power steering apparatus including the brushless motor according to Embodiment 1 of the present invention.

  In FIG. 2, an electric power steering device 2 is provided in the vicinity of an axle 4, and controls a brushless motor 1 that generates an assist force for assisting rotation of the handle 3, and a current that is connected to the motor 1 and output to the motor 1. ECU100 which is a control means to do. The brushless motor 1 is installed in an engine room of a vehicle (not shown).

  FIG. 3 is a cross-sectional view showing the configuration of the brushless motor according to Embodiment 1 of the present invention.

  In FIG. 3, a magnet 82 for generating a magnetic field is attached to one end portion of a shaft 81 made of a magnetic material such as iron and rotatably supported, and a motor rotor 83 is provided. This motor rotor 83 is provided with a motor stator 85 fixed to the inner wall surface of the bottomed cylindrical frame 84. The motor stator 85 is formed by laminating silicon steel plates or the like, and a motor coil 87 is wound through a resin insulator 86. The motor coil 87 is composed of three phases, a U phase, a V phase, and a W phase, and is star-connected. A boss 88 that is a coupling made of a magnetic material such as iron and transmitting the driving force of the motor 1 to the outside is press-fitted to the other end of the shaft 81.

  The resolver 10 includes a rotor 11 and a stator 12. The rotor 11 is formed and attached by laminating silicon steel plates between the motor rotor 83 and the boss 88. The stator 12 is fixed to a housing 89 made of aluminum or the like so as to face the rotor 11. The aforementioned output coils 14 and 15 output an output signal in accordance with the rotation angle formed by the rotor 11 and the stator 12.

  Next, the operation of the temperature detection device for a brushless motor according to the first embodiment will be described with reference to the drawings.

  FIG. 4 is a waveform diagram showing an excitation signal for exciting the excitation coil of the resolver of the temperature detection device for a brushless motor according to Embodiment 1 of the present invention.

  In FIG. 4, the horizontal axis represents time, the vertical axis represents voltage, and the alternate long and short dash line in FIG. 4 represents zero volts as the reference voltage.

  The excitation circuit 20 outputs an AC signal shown in FIG. This AC signal is, for example, a sine wave signal having a frequency of 10 KHz and an amplitude of 4V. A direct current component shown in FIG. 4B is added to the alternating current signal to obtain an excitation signal in which the direct current component shown in FIG. 4C is superimposed, and this is added to the excitation coil 13 of the resolver 10 for excitation. To do.

  The resistors R1 and R2 are addition circuits for addition. One end of the resistor R1 is connected to the DC power source Vcc, and the other end is connected to the output terminal of the excitation circuit 20 via the resistor R2. By these two resistors R1 and R2, the AC signal from the excitation circuit 20 and the DC power source Vcc are added according to the ratio of the resistance values of the resistors R1 and R2, and a DC component (DC) shown in FIG. The excitation signal on which the bias voltage is superimposed is applied to the excitation coil 13.

  The impedance Zs of the exciting coil 13 of the resolver 10 is a series circuit of a resistance component Rs and an inductance component Ls.

  Considering only the DC component of the excitation signal applied to the excitation coil 13, the inductance component Ls is equal to zero with respect to the DC component, and the resistor R2 that transmits the AC signal is cut off. The voltage difference Vs between both ends is represented by the following formula (1).

  Here, when the resistor R1 is set to a sufficiently large value compared to the resistance component Rs, the equation (1) can be approximated by the following equation (2).

  Here, since the material of the winding of the exciting coil 13 is copper, if the temperature coefficient of copper is K, the equation (2) can be expressed by the following equation (3).

In the formula (3), T is the current temperature (temperature of the brushless motor 1), _{T 0} is a reference temperature, _{R 0} represents a resistance value of the exciting coil 13 at a reference temperature _{T 0.}

For example, when the reference temperature T ₀ is 25 ° C. and the resistance value of the exciting coil 13 at 25 ° C. is R ₀ , the voltage difference Vs at both ends at 120 ° C. is expressed by the following equation (4).

  Therefore, conversely, it can be detected that the current temperature is 120 ° C. from the voltage difference Vs at both ends. As described above, the temperature T of the brushless motor 1 can be detected from the DC component Vs of the voltage difference between both ends of the exciting coil 13.

  In FIG. 1, the low-pass filter 30 removes the AC component from the voltage difference between both ends of the exciting coil 13 of the resolver 10 and extracts only the DC component Vs. As described above, when the value of the resistor R1 is set to a large value, the extracted voltage Vs becomes a small value from the equation (2).

  Therefore, the next-stage differential amplifier 40 amplifies the voltage Vs. From the above description, the output voltage Vo of the differential amplifier 40 is a value proportional to the temperature T.

  The A / D converter 51 of the CPU 50 performs A / D conversion and reads the output voltage Vo of the differential amplifier 40.

  The next-stage temperature calculation unit 52 calculates the temperature T of the brushless motor 1 according to the above equation (3).

  Thereafter, the processing unit of the CPU 50 (not shown) controls the energization to the three-phase motor coil 87 of the brushless motor 1 according to the temperature T. For example, when the temperature T is excessively high, measures such as reducing the energization current are performed in order to prevent deterioration of the characteristics of the brushless motor 1.

Incidentally, as shown by the formula (3), the resistance value R ₀ at a reference temperature T ₀ is, for example, because it contains variations that depend on the wire diameter variations in tool variation or windings, also across the voltage difference Vs Including variation, the temperature T determined from this also includes variation. Hereinafter, a method of correcting this variation will be described with reference to FIGS.

  FIG. 5 is a diagram showing the relationship between the voltage difference Vs at both ends and the temperature T of the temperature detection device for a brushless motor according to Embodiment 1 of the present invention.

  First, the resistance value Rr of the exciting coil 13 is obtained from the voltage difference Vs at the room temperature Tr (for example, 20 ° C.) according to the above equation (3), and the resistance value Rr of the room temperature Tr and the exciting coil 13 is provided outside the CPU 50. Stored in the non-volatile memory 60.

Once stored, the temperature calculation unit 52 calculates the temperature T on the basis of the stored room temperature Tr and resistance value Rr. In this case, the formula that is the basis for the calculation is the following formula (5) obtained by substituting R ₀ for Rr and T ₀ for Tr in the above formula (3).

  When the temperature T of the brushless motor 1 is obtained from this equation (5), it is expressed as the following equation (6).

  From equation (6), the temperature T is proportional to the voltage difference Vs between both ends. Here, when the voltage difference Vs between both ends is Vs = Rr · Vcc / R1, T = Tr. The above is represented by a graph as shown in FIG.

  As described above, the variation can be excluded by using the value measured and stored once as a reference.

  Next, a method of obtaining the rotation angle by processing the resolver signal will be described with reference to FIGS.

  FIG. 6 is a waveform diagram showing an output signal of the output coil of the resolver of the temperature detection device for a brushless motor according to Embodiment 1 of the present invention.

  In FIGS. 6A and 6B, in both FIGS. 6A and 6B, the horizontal axis represents time, the vertical axis represents voltage, and the alternate long and short dash line represents a reference voltage with an amplitude of zero.

  When the shaft 81 of the brushless motor 1 rotates, the rotor 11 of the resolver 10 fixed to the shaft 81 rotates together, and the amplitudes of both ends of the two output coils 14 and 15 depend on the rotation angle of the rotor 11. A modulated voltage waveform is output. A voltage waveform indicated by a thin line in FIGS. 6A and 6B is obtained at the output of the differential amplifier 70 that amplifies the voltage difference between both ends.

  6A and 6B, when the peak points of the peaks or valleys of the two output waveforms of the differential amplifier 70 are sampled and connected, each rotates the rotor 11. A sine signal and a cosine signal with respect to the angle θ.

  The A / D converter 53 of the CPU 50 samples the peak point described above to obtain a sine value SINθ and a cosine value COSθ.

  The next stage tangent calculation unit 54 divides the sine value SINθ by the cosine value COSθ to obtain a tangent value TANθ.

  The inverse function calculation unit 55 in the next stage obtains the angle θ from the inverse function ArcTANθ of the tangent value TANθ.

  Through the above processing, the rotation angle θ of the rotor 11, that is, the rotation angle θ of the shaft 81 of the brushless motor 1 is obtained.

  The CPU 50 controls the energization of the three-phase motor coil 87 of the brushless motor 1 according to the calculated rotation angle θ by a subsequent processing unit (not shown) to generate an assist force.

It is a figure which shows the structure of the temperature detection apparatus of the brushless motor which concerns on Embodiment 1 of this invention. It is a perspective view which shows the structure of the periphery of the electric power steering apparatus containing the brushless motor which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the brushless motor which concerns on Embodiment 1 of this invention. It is a wave form diagram which shows the excitation signal which excites the excitation coil of the resolver of the temperature detection apparatus of the brushless motor which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the both-ends voltage difference Vs and the temperature T of the temperature detection apparatus of the brushless motor which concerns on Embodiment 1 of this invention. It is a wave form diagram which shows the output signal of the output coil of the resolver of the temperature detection apparatus of the brushless motor which concerns on Embodiment 1 of this invention.

Explanation of symbols

  1 brushless motor, 2 electric power steering device, 3 handle, 4 axles, 10 resolver, 11 rotor, 12 stator, 13 excitation coil, 14 output coil, 15 output coil, 20 excitation circuit, 30 low-pass filter, 40 difference Dynamic amplifier, 41 operational amplifier, 51 A / D converter, 52 temperature calculation unit, 53 A / D converter, 54 tangent calculation unit, 55 inverse function calculation unit, 60 nonvolatile memory, 70 differential amplifier, 81 shaft, 82 Magnet, 83 Motor rotor, 84 frame, 85 Motor stator, 86 Insulator, 87 Motor coil, 88 Boss, 89 Housing.

Claims (5)

In a brushless motor that detects the rotation angle with a resolver,
An excitation circuit that outputs an AC signal;
An adder circuit that adds a DC bias voltage to the AC signal and applies it to the exciting coil of the resolver;
A low-pass filter that removes an AC component from a voltage difference between both ends of the exciting coil and extracts a DC component;
A differential amplifier for amplifying a DC component from the low-pass filter;
An A / D converter for A / D converting the output voltage of the differential amplifier;
A temperature detection device for a brushless motor, comprising: a temperature calculation unit that calculates the temperature of the brushless motor from the output of the A / D converter according to a proportional relationship between the DC component and temperature. The adder circuit includes a first resistor connected to a DC power source and a second resistor connected to the excitation circuit, and receives the AC signal from the excitation circuit and the DC voltage from the DC power source. The temperature detection device for a brushless motor according to claim 1, wherein addition is performed according to a ratio of resistance values of the first resistor and the second resistor. 2. The temperature detection device for a brushless motor according to claim 1, wherein the low-pass filter includes two stages of CR filters each including a resistor and a capacitor connected in series. The brushless motor temperature detection device according to claim 1, wherein the differential amplifier includes an operational amplifier and a resistor network. It further comprises a non-volatile memory for storing the room temperature measured in advance and the resistance value of the exciting coil determined from the room temperature,
The temperature calculation unit is based on the temperature coefficient of the exciting coil, the resistance value of the first resistor, the DC voltage of the DC power supply, and the DC component with reference to the room temperature and the resistance value stored in the nonvolatile memory. The temperature detection device for a brushless motor according to claim 2, wherein the temperature of the brushless motor is calculated.

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