JP2008072802A - Power converter, and heat pump apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter which can reduce a high-frequency sound, is small in current variation, reduced in torque ripple, and low in vibration noise, and to provide a heat pump apparatus. <P>SOLUTION: A motor 205 installed at a compressor 201 is PWM-controlled by the power converter. This power converter can provide high efficiency and low noise with a torque ripple reduced by changing the pulse position and the pulse width of PWM with respect to a time by using a pulse position determination means 311 and a pulse width determination means 312. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power conversion device, and more particularly, to an inverter device that performs pulse width modulation (PWM) control, and a heat pump device using the inverter device.

  2. Description of the Related Art Generally, heat pump equipment having a compressor performs fine capacity control by changing the rotation speed of the compressor and the frequency of a power supply. In addition, power converters and inverters that control the frequency and voltage of the power supply by pulse width modulation control (PWM control) are widely used.

  In a device that controls frequency and voltage by such PWM control, a high frequency component (carrier frequency is a main component) generated by switching of a switching element provided in the device is present in its output component. When a power source having such a high-frequency component drives a compressor or an electric motor or a generator provided in an expander, the magnetic attraction force changes due to the harmonic component, and magnetic noise is generated.

  In order to solve this problem, an apparatus has been proposed in which the frequency distribution of magnetic noise is dispersed by changing the carrier frequency with time, the peak level is reduced, and magnetic noise is reduced. For example, in the PWM inverter control method and apparatus described in Patent Document 1, the PWM inverter whose output voltage is PWM-controlled has a function of temporally changing the frequency of the carrier wave that determines the frequency of the PWM signal. Is. As a result, the mechanical vibration of the iron core caused by the magnetic attraction force due to the harmonic current is not a large vibration that occurs when the excitation force is continuously applied at a constant frequency, and the frequency of the PWM signal is reduced. By changing with time, the frequency distribution is dispersed and the peak level of magnetic noise is reduced.

In addition, a control method has been proposed in which the generation of magnetic noise due to harmonic components is reduced by changing the output voltage generation timing with time without changing the carrier frequency. For example, in the method for controlling the power conversion device described in Patent Document 2, the average value of the output voltage during one period of the carrier signal is matched with the voltage command, and the pulse width determined by the pulse width modulation control is changed. The generation timing of the output voltage is changed with time without any problems. As a result, harmonics having the same frequency are not continuously applied to the load, and there is an effect that generation of magnetic sounds caused by the harmonic components can be reduced.
Japanese Patent Publication No. 3-79959 JP-A-7-177753

  In conventional power converters that perform PWM control, the frequency of the PWM signal is changed with time in order to reduce the peak level of magnetic noise, but the carrier frequency has been changed significantly in order to increase the magnetic noise reduction effect. In this case, the calculation cycle of control generally performed in synchronization with the carrier frequency also changes, and when the carrier frequency is high, the calculation time is shortened and the control calculation cannot be performed. there were. On the other hand, when the carrier frequency is low, the pulse interval becomes large and the current ripple increases, thereby increasing the torque ripple.

Also, in the conventional power converter, in order to reduce the generation of magnetic noise due to harmonic components, the output voltage generation timing is changed temporally without changing the carrier frequency and pulse width. However, in this case, when the generation timing of the output voltage fluctuates, the current flowing through the electric motor to be controlled also fluctuates, and the output torque of the electric motor fluctuates accordingly. As a result, there has been a problem that vibration noise caused by torque ripple increases and the drive efficiency of the electric motor decreases.

  The present invention has been made in view of such a point, and an object of the present invention is to provide high-frequency sound generated by a control device in a power conversion device that drives an electric motor and the like, and a heat pump device using the power conversion device. An object of the present invention is to provide a power converter device and a heat pump device that reduce noise, reduce torque ripple with less current fluctuation, and have low vibration noise.

  The power conversion device according to the present invention is based on pulse position determining means for temporally changing the output timing of the output pulse of pulse width modulation control, an output voltage command value, and the pulse position determined by the pulse position determining means. And a pulse width determining means for determining the width of the output pulse.

  Since the power converter changes the pulse width with the pulse position over time, it can be operated with low noise and high efficiency.

  It is preferable that the pulse width determining unit determines the pulse width so that the amount of change in the output current of the power converter generated by the change in the pulse position determined by the pulse position determining unit is minimized.

  This enables operation with high efficiency and low noise with less current fluctuation and torque ripple.

  In the power converter according to the present invention, when the pulse position determined by the pulse position determining unit is set earlier than the position synchronized with the carrier signal in the pulse width determining unit, the command value of the output voltage is set. On the other hand, the pulse width is set to be small, and when it is set late with respect to the position synchronized with the carrier signal, the pulse width is set to be large with respect to the output voltage command value. Is preferred.

  This enables high-efficiency, low-noise operation with little current fluctuation and torque ripple, regardless of changes in pulse position with respect to time.

  In the pulse width determining means, the pulse width change amount is preferably set in a proportional relationship with the change amount of the pulse position determined by the pulse position determining means relative to the position synchronized with the carrier signal.

  This makes it possible to operate with high efficiency and low noise with little torque ripple under any operating condition.

  A heat pump device according to the present invention includes a compressor that compresses a refrigerant with an electric motor, a radiator that cools the refrigerant, an expansion mechanism that expands the refrigerant, and an evaporator that evaporates the refrigerant. The compressor control means for driving and driving the electric motor is constituted by the power conversion device.

  This makes it possible to operate the heat pump device with high efficiency and low noise.

  The heat pump device according to the present invention includes a compressor that includes an electric motor to compress the refrigerant, a radiator that cools the refrigerant, an expander that includes a generator and expands the refrigerant, and an evaporator that evaporates the refrigerant. A generator control means for forming a refrigeration cycle and driving the generator is constituted by the power converter.

  This makes it possible to operate the heat pump device with high efficiency and low noise while performing power recovery by the expander.

  The refrigerant may be carbon dioxide.

  As described above, according to the present invention, a low-vibration, low-noise power conversion device and heat pump device with less torque ripple can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
The power converter of this embodiment controls the output voltage by pulse width modulation control based on the carrier signal. The power converter according to the present embodiment is characterized in that pulse position determining means for temporally changing the output timing of the output pulse of the pulse width modulation control, command value of output voltage and pulse determined by the pulse position determining means And pulse width determining means for determining the width of the output pulse based on the position. The features of the control method of the power conversion device of this embodiment will be described using FIG. 1 in comparison with the conventional control method.

  FIG. 1A shows, as Comparative Example 1, the characteristics of the output pulse by pulse width modulation control and the current change at that time when the carrier frequency is constant when the electric motor is driven by the power converter. For an output pulse that occurs evenly over time, the current value changes as an integral thereof, and changes with a uniform period. Since the noise generated by the motor is excited by the current flowing through the motor, the magnetic noise is also composed of uniform frequency components.

  FIG. 1B shows an output pulse by pulse width modulation control and current at that time when the generation timing of the output voltage is temporally changed without changing the carrier frequency and the pulse width as Comparative Example 2. The characteristic view which shows a change is represented. In this case, the position of the output pulse changes with time, and the current value that is the integral value also changes with a non-uniform period. Since the noise generated by the motor is excited by the current flowing through the motor, the magnetic noise is also composed of non-uniform frequency components, and the peak value of the noise is reduced. However, the current value change at this time is influenced by the position of the output pulse and fluctuates greatly. In the case of Comparative Example 2, the average current value is larger than the original average current value of 0 because the first and third pulses are output earlier than the time. In this way, when the generation timing of the output pulse is changed, current fluctuations are generated thereby, increasing torque ripple, increasing vibration noise, and further reducing efficiency due to fluctuation components.

  That is, as in Comparative Examples 1 and 2, simply changing the pulse position with respect to time increases current fluctuation and increases torque ripple. On the other hand, in the power converter of this embodiment, the pulse width is changed as shown in FIG. That is, by changing not only the pulse position but also the pulse width in a corresponding manner, the current fluctuation is reduced and the torque ripple is reduced. Thereby, in the case of FIG. 1C, the first and third pulse widths are changed, the average current becomes equivalent to that in FIG. 1A, and the current fluctuation is reduced.

  Next, the configuration of the power conversion device of the present embodiment and the heat pump device using the power conversion device will be described in more detail.

  FIG. 2 is a block diagram of an embodiment of a heat pump device using the power conversion device according to the present invention. This heat pump apparatus includes an electric motor 205 controlled by a power converter 206 and a compressor 201 that compresses refrigerant, a radiator 202 that cools the refrigerant, an expansion mechanism 203 that expands the refrigerant, and evaporation that evaporates the refrigerant. And a pipe 207 for circulating the refrigerant between the above elements to form a refrigeration cycle.

  The operating principle of the heat pump device is as follows. The pressure and temperature of the refrigerant vapor is increased by the compressor 201, which then enters the radiator 202 where it is cooled. Thereafter, the high-pressure refrigerant is reduced to the evaporating pressure by the expansion mechanism 203, is vaporized in the evaporator 204, and absorbs heat from the surroundings. Then, the refrigerant vapor returns to the compressor 201 through the outlet of the evaporator 204.

  On the other hand, FIG. 3 shows a block configuration diagram of the power conversion device 206 in the heat pump device in the present embodiment. As shown in this figure, the power conversion device 206 includes a circuit and a control unit for driving an electric motor 205 provided in a compressor 201 that is a fluid machine. The AC power supplied from the AC power supply 301 is converted into DC by the rectifier circuit 302 and the smoothing capacitor 303, and then the electric motor 205 is driven as a three-phase AC by the pulse width modulation (PWM) by the switching element 305. For example, an element such as an IGBT is used as the switching element 305. The control unit includes a rotation speed estimation means 307 that estimates the rotation speed of the motor using current value information that is an output of the current sensor 306 that detects a current flowing through the motor 205, and a rotation speed command given from the outside. And a rotational speed control means 308 for outputting a current command from the rotational speed estimated by the rotational speed estimation means, a current control means 309 for realizing the current command, a random number signal generating means 310, a pulse position determining means 311, a pulse width The determination unit 312 includes a switching control unit 313 for driving the switching element 305.

First, in the rotation speed estimation means 307, the rotation speed of the electric motor 205 is estimated using the detected current value. As this method, there is a method of estimating the induced voltage from current information and using the value for obtaining the rotational speed of the motor that realizes the estimated induced voltage, but the details are omitted. The rotational speed control means realizes the rotational speed command by comparing the estimated rotational speed of the electric motor 205 thus obtained with the rotational speed command value given from the outside in order to optimize the state of the heat pump device. Therefore, the current command I * is calculated from the error from the current rotational speed. As a calculation method, a general PI control method is used.
I * = Gpω × (ω * −ω) + Giω × Σ (ω * −ω)
... (Formula 1)
Where Gpω, Giω: speed control proportional gain, integral gain
ω: Number of rotations
ω *: Speed command
I *: Current command From the calculated current command I * and the current value detected by the current sensor, the current control means 309 determines the d-axis component of the component contributing to the magnetic flux and the q of the component contributing to the torque. Using the current commands Id * and Iq * and current values Id and Iq that are decomposed for each axis component, a control calculation is performed to realize the current command according to the following formula, and voltage commands Vd and Vq are output.
Vd = Gpd × (Id * −Id) + Gid × Σ (Id * −Id)
... (Formula 2)
Vq = Gpq × (Iq * −Iq) + Giq × Σ (Iq * −Iq)
... (Formula 3)
Where Vd, Vq: d-axis voltage command, q-axis voltage command
Gpd, Gid: d-axis current control proportional gain, integral gain
Gpq, Giq: q-axis current control proportional gain, integral gain From the obtained two-way output voltage commands Vd and Vq, the three-phase output voltages Vu, Vv, Vw are converted into a rotor so that the output waveform becomes a sine wave. Is obtained by conversion according to (Equation 4) and (Equation 5) by a general two-phase / three-phase conversion using the position θ.

Where Vu, Vv, Vw: U, V, W phase voltage
θ: Rotor position According to the pulse width modulation (PWM) method, the pulse position determining means 311, the pulse width determining means 312, and the switching control means 313 are implemented in accordance with the pulse width modulation (PWM) method so as to realize the three-phase voltage command for the electric motor thus obtained. Thus, the switching element 305 is controlled, and a voltage command is realized.

  Next, operations of the random number signal generating unit 310, the pulse position determining unit 311 and the pulse width determining unit 312 will be described. The random number signal generation means 310 outputs a random number in the range of 0 to 1 by a random number generation method that can be easily realized by a microcomputer such as a pseudo random number calculation. The pulse position determining unit 311 determines the pulse position using a predetermined carrier frequency and the random number output from the random number signal generating unit 310. The purpose of this is to change the pulse position with time and to disperse the carrier frequency component in frequency in order to reduce electromagnetic noise caused by the carrier frequency.

  4A and 4B are timing charts showing an example of the timing of the pulse voltage and the current flowing through the motor. FIG. 4A shows the case of the configuration of Comparative Example 1 in which the pulse position and width are not changed, and FIG. 4B shows the case where the pulse position and width in this embodiment are changed. The period in which the pulses are output is the same for all c. That is, the carrier frequency does not change. FIG. 4A shows a pulse pattern obtained by general PWM pulse generation. That is, the pulse width is a value d1 including a duty for realizing the output voltage, and the value is constant as long as the output voltage does not change. Further, since the position of the pulse is set to the center position and set to the center of the carrier period c, the interval between the start of the carrier period and the pulse center position is p1, and this value is also always constant. .

FIG. 4B is a timing chart showing an example of pulse positions and widths in the power conversion device 206 according to this embodiment. Similarly, the period in which the pulse is output does not change with c. In the first carrier period, the pulse position is set at a position p2 from the start time of the carrier period. This is set by a random value output from the random number signal generating means. That is, the random number signal generating means outputs a random value r2 (this random value is a value in the range of 0 to 1). Accordingly, the value of the pulse position p2 is set according to (Equation 6) in the pulse position determining means. This is performed for the purpose of frequency dispersion of the carrier frequency component.

p2 = c × r2 (Formula 6)
In the period following the carrier period in which the pulse position is corrected, the pulse position is set to the center. That is, the pulse position is not corrected. That is, in this embodiment, the pulse position is set at the center every other carrier cycle. Further, in the next carrier cycle, the value of the pulse position p4 is set in accordance with (Equation 7) in the pulse position determining means in accordance with the random value r4 output from the random number signal generating means, as in the previous carrier cycle.

p4 = c × r4 (Expression 7)
As described above, the pulse position p (n) of the carrier period n is set to the position of (Equation 8).

p (n) = c × r (n): n = 2m (m = 0, 1,...)
p (n) = c / 2: n = 2m + 1 (m = 0, 1,...)
r (n): the output value of the random number signal generating means with carrier period n
... (Formula 8)
Next, the operation principle of the pulse width determination unit 312 will be described. For the pulse position determined by the pulse position determining means 311, an optimum pulse width is set so that the current ripple is minimized. In order to minimize the current ripple, here, the pulse width is set so that the average value of the current becomes the same value as when the pulse position is not corrected. As shown in FIG. 1B (Comparative Example 2), when the pulse width is not changed with respect to the change of the pulse position, FIG. 1A when the pulse position and the width are not changed. The average current value varies as compared with the case of Comparative Example 1). In this case, the current value increases because the position of the first pulse is moved to a position earlier in time. Therefore, the pulse position determining means 312 corrects the pulse width in a form corresponding to the change of the pulse position. FIG.1 (c) is a characteristic view which shows an example which changed the pulse position and the width | variety in the power converter device 206 in a present Example. By reducing the width of the first pulse in this way, the current fluctuation is reduced.

  FIG. 5 shows an example of a characteristic diagram showing a pulse width change amount for minimizing the current ripple. With respect to the change amount of the pulse position on the horizontal axis, the optimum voltage change amount that minimizes the current ripple on the vertical axis, that is, the pulse width change amount is a linear voltage as shown in the figure in each case of the output voltage 50V, 100V, 150V. You can see that there is a relationship. Thus, it can be seen that the slope changes depending on the output voltage amount, that is, the output duty. However, this relationship is not affected by the inductance of the motor. Accordingly, the value of the optimum voltage change amount with respect to the output voltage and pulse position calculated in advance by simulation is recorded in the pulse width determining means in the form of a table or a linear function, and the voltage command and the pulse are recorded using this information. By determining the pulse width from the position, the optimum pulse width for always minimizing the current ripple is determined. As described with reference to the pulse position determining means, the pulse position is changed every other carrier cycle, and the pulse width is changed corresponding to the pulse position in accordance with the relationship shown in FIG. Further, in the carrier period after the change period, the pulse width is set so as to compensate for the previous pulse width correction.

  Finally, the switching control means 313 generates a drive signal for the switching element 305 in order to realize the pulse position and pulse width determined in the above processing. By driving each of the three-phase bridge type switching elements with a necessary pulse width, a voltage for realizing the target rotational speed can be applied to each of the three phases.

  FIG. 6 shows (a) current ripple, motor rotation speed (corresponding to the number of rotations), and (b) current frequency in the case of Comparative Example 1, that is, when the motor is driven by the conventional power conversion device at a constant carrier frequency. An example of the simulation result of a component is shown. On the other hand, FIG. 7 shows an example of simulation results of (a) current ripple, motor rotation speed (corresponding to the number of rotations), and (b) current frequency components when the motor is driven by the power conversion device of the present embodiment. Thus, in the case of the conventional power conversion device with a constant carrier frequency, the current ripple is also generated in the same pattern with a constant period, and the frequency component is based on about 5 KHz and has a high peak composed of its harmonic component. However, in the case of the power conversion device of this embodiment, since the output pulse position is dispersed, it can be seen that the current ripple also has its period changed, the frequency component is also dispersed, and the peak is lowered. Thereby, the actual hearing feeling of the noise at the time of a drive is improved.

  Further, FIG. 8 shows a simulation result of the power conversion device of Comparative Example 2, that is, the current ripple at the time of driving the motor and the motor rotation speed (corresponding to the rotation speed) when the output pulse position is dispersed but the pulse width is not changed. An example is shown. As described above, since the period of the current ripple changes, the noise audibility due to the carrier frequency is reduced. However, the pulse width corresponding to the output pulse position is set as in the power converter of the present invention. As a result, the current ripple associated therewith increases and a large fluctuation occurs in the rotational speed. As a result, a decrease in efficiency and an increase in noise occur. On the other hand, when the electric motor is driven by the power conversion apparatus according to the present embodiment shown in FIG. 7, the fluctuation of the electric motor speed is small, thereby realizing high efficiency and low noise.

  As described above, in the heat pump device according to the present embodiment, the pulse width as well as the pulse position of the power converter that drives the compressor are changed with respect to time, so that noise is low, current fluctuation, torque ripple, There is little fluctuation in the motor rotation speed, thereby realizing high efficiency and further low noise.

In the present embodiment, the pulse position is changed every other carrier cycle. However, it goes without saying that the same effect can be obtained by changing the pulse position every carrier cycle.
(Second Embodiment)
FIG. 9 is a configuration diagram of a heat pump device using the power conversion device according to the second embodiment. The heat pump apparatus includes an electric motor 905 that compresses a refrigerant, a compressor 901 that cools the refrigerant, a radiator 902 that cools the refrigerant, an electric generator 907 that expands the refrigerant, and an evaporator that evaporates the refrigerant. 904 and a pipe 909 that circulates the refrigerant between the above elements form a refrigeration cycle.

  The operating principle of the heat pump device is as follows. The pressure and temperature of the refrigerant vapor is increased by the compressor 901 and the refrigerant vapor then enters the radiator 902 where it is cooled. Thereafter, the high-pressure refrigerant is reduced to the evaporation pressure by the expander 903, vaporizes in the evaporator 904, and absorbs heat from the surroundings. Then, the refrigerant vapor returns to the compressor 901 through the outlet of the evaporator 904. When the refrigerant expands, a power generator 907 provided in the expander 903 generates power, thereby recovering power, and a heat pump device with high energy efficiency.

  The motor 905 provided in the compressor 901 has its rotation speed controlled by an electric motor control device 906. Further, the electric motor control device 906 is a PWM converter similar to the power conversion device described in the first embodiment. By changing the pulse position and pulse width with respect to time, the apparatus has a function of realizing high efficiency and low noise with little torque ripple.

Furthermore, the expander 903 is provided with a generator 907, and the generator 907 is controlled in its rotational speed by a generator control device 908, and the generated power is collected. In the present embodiment, the generator control device 908 also has the same function as the motor control device 906. The details of the motor control device 906 and the generator control device 908 are the same as those of the power conversion device described in the first embodiment, and are omitted.

  As described above, in the heat pump device according to the present embodiment, the motor control device 906 that controls the motor 905 provided in the compressor 901 and the generator control device 908 that controls the power generator 907 provided in the expander 903 are provided. It has a function as a heat pump and realizes low noise and high efficiency by optimally controlling the rotation of the compressor 901 and the expander 903.

  As described above, the present invention is useful for a power conversion device that performs pulse width modulation control and a heat pump device using the same.

Characteristics diagram showing output pulse and current change by power conversion device (a) Diagram for Comparative Example 1, (b) Diagram for Comparative Example 2, (c) Diagram for the first embodiment Block configuration diagram of the heat pump device according to the first embodiment The block block diagram of the power converter device in the heat pump apparatus which concerns on 1st Embodiment. Timing chart showing an example of timing of pulse voltage and current flowing through motor in power converter in heat pump device (a) Timing chart in comparative example 1, (b) Timing chart in first embodiment Characteristic diagram showing the amount of pulse width change to minimize current ripple (A) (b) The characteristic view showing an example of the current ripple at the time of the motor drive by the power converter device of the comparative example 1, an electric motor rotational speed, and the frequency component of an electric current. (A) (b) The characteristic view showing an example of the current ripple at the time of the motor drive by the power converter device of 1st Embodiment, an electric motor rotational speed, and the frequency component of an electric current. The characteristic diagram showing an example of the current ripple at the time of the motor drive by the power converter device of the comparative example 2, and a motor rotational speed The block diagram of the heat pump apparatus using the power converter device which concerns on 2nd Embodiment.

Explanation of symbols

201 Compressor 206 Power Converter 307 Rotational Speed Estimation Unit 308 Rotational Speed Control Unit 309 Current Control Unit 310 Random Number Signal Generation Unit 311 Pulse Position Determination Unit 312 Pulse Width Determination Unit 313 Switching Control Unit

Claims (7)

In a power converter for controlling an output voltage by pulse width modulation control based on a carrier signal, pulse position determining means for temporally changing an output timing of an output pulse of the pulse width modulation control, an output voltage command value, and the pulse And a pulse width determining means for determining the width of the output pulse based on the pulse position determined by the position determining means. 2. The pulse width determining unit according to claim 1, wherein the pulse width determining unit determines the amount of change in the output current of the power converter generated by the change in the pulse position determined by the pulse position determining unit to be a minimum. Power converter In the pulse width determining means, when the pulse position determined by the pulse position determining means is set earlier than the position synchronized with the carrier signal, the pulse is determined so as to be smaller than the command value of the output voltage. 2. The pulse width is set so as to be larger than the command value of the output voltage when the width is set and when it is set late with respect to the position synchronized with the carrier signal. -2 power converter The pulse width change amount in the pulse width determination means is set in a proportional relationship with the change amount of the pulse position determined by the pulse position determination means relative to the position synchronized with the carrier signal. 1-3 of the power converter In a heat pump device that forms a refrigeration cycle from a compressor that includes an electric motor and compresses the refrigerant, a radiator that cools the refrigerant, an expansion mechanism that expands the refrigerant, and an evaporator that evaporates the refrigerant.
The compressor control means which drives the said electric motor is comprised by the power converter device of Claims 1-4, The heat pump apparatus characterized by the above-mentioned. A heat pump that forms a refrigeration cycle from a compressor that includes an electric motor to compress the refrigerant, a radiator that cools the refrigerant, an expander that includes a generator and expands the refrigerant, and an evaporator that evaporates the refrigerant In the equipment
A heat pump device, wherein the generator control means for driving the generator is constituted by the power conversion device according to claim 1.   The heat pump device according to any one of claims 5 to 6, wherein the refrigerant is carbon dioxide.

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