Ac / DC conversion device, rotary machine drive device, and refrigeration cycle use apparatus

Abstract

An AC / DC conversion device (2) includes: a rectifier circuit (20) that includes a switching element (215) and that rectifies a power supply voltage applied from an AC power supply (1); a capacitor (216) that is connected to DC buses (9a, 9b) and that smooths an output voltage of the rectifier circuit (20); a reactor (212) that is disposed more to the AC power supply (1) side than the capacitor (216); a current detection unit (211) that detects a power supply current flowing between the AC power supply (1) and the rectifier circuit (20); and a control unit (6) that generates a switching signal for controlling the switching element (215). The control unit (6) generates a switching signal so as to change the phase of the power supply current.

Description

AC / DC converters, rotating machine drives, and refrigeration cycle application equipment

[0001] The present disclosure relates to an AC / DC converter that converts AC power into desired DC power, and to a rotating machine drive device and refrigeration cycle equipment that are equipped with the AC / DC converter.

[0002] A power factor correction circuit is typically used to obtain DC voltage from an AC power source. A power factor correction circuit maintains a constant bus voltage and controls the power supply current to comply with harmonic standards. A power factor correction circuit and its control method, the "simple switching method" (also known as the "partial switching method"), performs switching at least once per half cycle of the power supply voltage, which is the voltage of the AC power supply. This method has the advantage of being able to control the bus voltage lower than the peak value of the power supply voltage. However, when the bus voltage is set lower than the peak value of the AC power supply using the simple switching method, the operating circuit switches from a boost chopper to a capacitor-input diode rectifier, which can distort the power supply current.

[0003] To address this issue, the prior art disclosed in Patent Document 1 below determines whether a combination of reactor capacity and switching timing complies with harmonic standards by repeating the design for each load power.

[0004] Japanese Patent Application Laid-Open No. 2000-125545

[0005] However, the conventional technology described in Patent Document 1 involves a method of checking whether compliance with harmonic standards can be achieved through repeated trials, which has the problem that the number of trials increases exponentially as the number of pulses increases. Furthermore, there is no clear guideline for quantitatively and uniquely designing control gains, which has the problem that it takes a long time to complete the design.

[0006] The present disclosure has been made in consideration of the above, and aims to shorten the time required for design by obtaining an AC-DC conversion device that can comply with harmonic standards without relying on trial-and-error adjustments.

[0007] In order to solve the above-mentioned problems and achieve the object, an AC / DC converter according to the present disclosure includes a rectifier circuit, a capacitor, a reactor, a current detection unit, and a control unit. The rectifier circuit has at least one switching element and rectifies a power supply voltage applied from an AC power supply. The capacitor is connected to a DC bus and smoothes the output voltage of the rectifier circuit. The reactor is arranged closer to the AC power supply than the capacitor. The current detection unit detects a power supply current flowing between the AC power supply and the rectifier circuit. When generating a switching signal for controlling the switching element arranged closer to the AC power supply than the capacitor, the control unit generates the switching signal so as to change the phase of the power supply current.

[0008] The AC-DC converter according to the present disclosure can comply with harmonic standards without relying on trial-and-error adjustments, thereby achieving the effect of reducing the time required for design.

[0009] 1 is a block diagram showing a configuration example of a rotary machine drive device according to embodiment 1; FIG. 2 is a circuit diagram showing a configuration example of an AC / DC converter according to embodiment 1; FIG. 3 is a block diagram showing a configuration example of a control unit according to embodiment 1; FIG. 4 is a block diagram showing a configuration example of a sine wave signal generator provided in the control unit according to embodiment 1; FIG. 5 is a diagram showing an example of an operation waveform when the AC / DC converter shown in FIG. 2 is passively operated; FIG. 6 is a diagram showing an example of an operation waveform when the AC / DC converter shown in FIG. 2 is operated with a fundamental wave power factor of 1;

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An AC-DC converter, a rotary machine drive device, and a refrigeration cycle application device according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0011] Embodiment 1. Fig. 1 is a block diagram showing an example of the configuration of a rotating machine driving device 8 according to Embodiment 1. The rotating machine driving device 8 is connected to an AC power source 1 and a load 4 including a motor 41. The rotating machine driving device 8 includes an AC-DC converter 2 and a DC-AC converter 3. When the rotating machine driving device 8 is used in an air conditioner, the load 4 is a compressor or a fan, and the motor 41 is a compressor motor or a fan motor.

[0012] 2 is a circuit diagram showing an example of the configuration of the AC-DC converter 2 according to the first embodiment. The AC-DC converter 2 according to the first embodiment mainly includes a control unit 6, a rectifier circuit 20, a reactor 212, and a capacitor 216. The AC-DC converter 2 also includes a current detection unit 211 and voltage detection units 217a and 217b as means for detecting voltage or current. In this document, when the voltage detection units 217a and 217b are distinguished from each other without reference numerals, the voltage detection unit 217b will be referred to as a "first voltage detection unit" and the voltage detection unit 217a will be referred to as a "second voltage detection unit."

[0013] The rectifier circuit 20 includes single-phase diode bridge cells 213a and 213b, each of which has four diodes bridge-connected, and a switching element 215 connected in parallel across the single-phase diode bridge cell 213b. The single-phase diode bridge cells 213a and 213b are connected in parallel to each other across the AC power supply 1. The rectifier circuit 20 shown in FIG. 2 is called a "simple switching circuit." The single-phase diode bridge cell 213b and the switching element 215 constitute a switching cell 225. The switching element 215 performs a switching operation at least once per half cycle of the power supply voltage.

[0014] The capacitor 216 is connected between the DC bus 9a and the DC bus 9b. The reactor 212 is arranged closer to the AC power supply than the capacitor 216. The rectifier circuit 20 receives the power supply voltage applied from the AC power supply 1 via the reactor 212 and rectifies the received power supply voltage. The capacitor 216 smoothes the output voltage of the rectifier circuit 20.

[0015] The voltage detector 217b detects a bus voltage, which is the voltage of a DC bus to which the capacitor is connected. The voltage detector 217a detects a power supply voltage. The current detector 211 detects a power supply current flowing between the AC power supply 1 and the rectifier circuit 20.

[0016] The control unit 6 receives the detection values ​​of the voltage detection units 217a and 217b and the current detection unit 211. The control unit 6 generates a switching signal for controlling the on / off of the switching element 215 based on the detection values.

[0017] An example of the switching element 215 is an insulated gate bipolar transistor (IGBT) as shown in the figure, but is not limited to an IGBT. Any element capable of switching operation may be used as the switching element 215. Another example of the switching element 215 is a metal-oxide-semiconductor field-effect transistor (MOSFET).

[0018] 2 is configured as a closed loop using the detected values ​​of the voltage detectors 217a, 217b and the current detector 211, but may be configured as an open loop using a target value, an estimated value, etc. When the AC-DC converter 2 is configured as an open loop, it is also possible to control the switching element 215 without using the detected values ​​of the voltage detectors 217a, 217b and the current detector 211.

[0019] 3 is a block diagram showing an example configuration of the control unit 6 according to embodiment 1. The control unit 6 includes a subtractor 611, a voltage controller 612, a multiplier 613, a subtractor 614, a current controller 615, a switching signal generator 616, and a sine wave signal generator 617.

[0020] The subtractor 611 generates a voltage deviation, which is the difference between the first voltage command value and the bus voltage detected by the voltage detection unit 217b. The first voltage command value is a command value for the bus voltage. The voltage controller 612 generates a first current command value using the voltage deviation output from the subtractor 611. The voltage controller 612 can be configured, for example, by a PI (Proportional Integral) controller.

[0021] The transfer function G when the voltage controller 612 is configured as a PI controller ＡＶＲ（ｓ） can be expressed by the following equation (1).

[0022]

[0023] Here, the transfer function G ＡＶＲ（ｓ） "AVR" in the above is an abbreviation for "Automatic Voltage Regulator." Also, in the above formula (1), K ｐＡＶＲ is the proportional gain, and K ｉＡＶＲ is the integral gain and s is the Laplace operator. In the PI controller, the proportional gain K ｐＡＶＲ and integral gain K ｉＡＶＲ can be determined arbitrarily. ｐＡＶＲ may be set to zero and configured as an I controller, or the integral gain K ｉＡＶＲ may be set to zero and configured as a P controller.

[0024] The sine wave signal generator 617 generates a sine wave signal as an excitation signal based on the first voltage command value and the detected value of the power supply voltage. The multiplier 613 multiplies the first current command value by the sine wave signal. The sine wave signal is a sine wave synchronized with the phase of the power supply voltage. The output of the multiplier 613 is input to the subtractor 614 as a second current command value. The subtractor 614 generates a current deviation, which is the difference between the second current command value and the detected value of the power supply current detected by the current detection unit 211. The current controller 615 generates a second voltage command value using the current deviation output from the subtractor 614. The current controller 615 can be configured, for example, by a PI controller. The switching signal generator 616 generates a switching signal using the second voltage command value.

[0025] The transfer function G when the current controller 615 is configured as a PI controller ＡＣＲ（ｓ） can be expressed by the following equation (2).

[0026]

[0027] Here, the transfer function G ＡＣＲ（ｓ） "ACR" in the above expression is an abbreviation for "Automatic Current Regulator." ｐＡＣＲ is the proportional gain, and K ｉＡＣＲis the integral gain and s is the Laplace operator. In the PI controller, the proportional gain K ｐＡＣＲ and integral gain K ｉＡＣＲ can be determined arbitrarily. ｐＡＣＲ may be set to zero and configured as an I controller, or the integral gain K ｉＡＣＲ may be set to zero and configured as a P controller.

[0028] 4 is a block diagram showing an example of the configuration of the sine wave signal generator 617 provided in the control unit 6 according to the first embodiment. The sine wave signal generator 617 outputs a sine wave synchronized with the phase and frequency of the power supply voltage. To achieve this function, the sine wave signal generator 617 includes a PLL (Phase Locked Loop) calculator 6171, a subtractor 6172, a sine wave calculator 6173, and a phase shift amount calculator 6174.

[0029] The PLL calculator 6171 generates and outputs a sine wave phase synchronized with the phase and frequency of the power supply voltage. The phase shift amount calculator 6174 calculates a phase shift amount based on the detected value of the power supply voltage and a first voltage command value which is a command value for the bus voltage. The subtractor 6172 calculates the difference between the output of the PLL calculator 6171 and the output of the phase shift amount calculator 6174. The sine wave calculator 6173 calculates a sine wave signal using the difference output from the subtractor 6172.

[0030] Next, a method for calculating the amount of phase shift will be described using some drawings and formulas.

[0031] 5 is a diagram showing an example of operating waveforms when the AC-DC converter 2 shown in FIG. 2 is operated passively. Passive operation refers to operation in passive mode. Passive mode is a mode in which the rectifier circuit 20 operates without switching the switching element 215. In the upper part of FIG. 5, the waveform of the absolute value of the power supply voltage is shown by a dashed line, and the waveform of the bus voltage is shown by a solid line. In the lower part of FIG. 5, the waveform of the power supply current is shown by a dashed line, and the waveform of the fundamental wave component of the power supply current is shown by a solid line. The power supply current shown in the lower part is the detected waveform of the power supply current detected by the current detection unit 211.

[0032] In the passive mode, when the power supply voltage exceeds the bus voltage, a current flows, exciting the reactor 212. The current flow start phase γ, which is the phase at which this current starts to flow, is the intersection at which the power supply voltage increases and becomes equal to the bus voltage, and can be calculated by the following equation (3).

[0033]

[0034] In the above formula (3), V ｄｃ is the bus voltage, and v ｓ is the effective value of the power supply voltage. The power supply current continues to increase until the power supply voltage and the bus voltage cross again, and this intersection point is the peak value of the power supply current. The current peak phase φ, which is the phase of the peak value of the power supply current, can be expressed by the following equation (4), using the peak value of the power supply voltage as the reference.

[0035]

[0036] When the power supply voltage falls below the bus voltage, the current decreases and finally becomes 0. Due to the above circuit operation, the power supply current has an approximate shape as shown by the line in FIG.

[0037] Furthermore, during passive operation, the fundamental component of the power supply current has a waveform that lags in phase with respect to the power supply voltage, as shown in Figure 5. Due to this characteristic during passive operation, if an attempt is made to achieve a fundamental power factor of 1 when the bus voltage is below the peak value of the power supply voltage, low-order harmonics will be superimposed on the power supply current. The reason for this is as follows. First, if an attempt is made to achieve a fundamental power factor of 1 during passive operation, multiple switching operations are required after the zero crossing of the power supply voltage. However, this switching control distorts the power supply current. Therefore, if an attempt is made to achieve a fundamental power factor of 1 when the bus voltage is below the peak value of the power supply voltage, the power supply current will be distorted, resulting in low-order harmonics being superimposed on the power supply current.

[0038] Therefore, in the control method of this paper, when the bus voltage is equal to or lower than the peak value of the power supply voltage, the fundamental power factor is not set to 1, but the phase of the sine wave signal that oscillates the first current command value is controlled to be synchronized with the fundamental phase of the power supply current during passive operation. In this way, it is possible to reduce current distortion caused by fundamental control of the power supply current, and therefore it is possible to suppress harmonic components that may be contained in the power supply current when the bus voltage is equal to or lower than the peak value of the power supply voltage.

[0039] To calculate the phase of the power supply current during passive operation, it is possible to use a Fourier series expansion that formulates the time equation for the power supply current during passive operation. However, with this method, it is not possible to calculate the timing at which the current becomes zero using algebraic operations, so the calculation of the fundamental wave can only be done analytically. Therefore, in this paper, the phase shift amount δ is determined approximately.

[0040] The lower part of Figure 5 shows the phase shift amount δ. The phase shift amount δ is the phase of the peak value of the power supply current with respect to the peak value of the power supply voltage. Meanwhile, the upper part of Figure 5 shows the current peak phase φ described above. The current peak phase φ is the phase of the peak value of the power supply current during passive operation. Both the phase shift amount δ and the current peak phase φ are based on the peak value of the power supply voltage. Furthermore, as shown in Figure 5, the two are close to each other and have the characteristic that they have close values.

[0041] Therefore, in this paper, the phase shift amount δ is considered to be approximately equal to the current peak phase φ, and the phase shift amount δ is defined by the following equation (5).

[0042]

[0043] It should be noted that the above formula (5) is merely an example, and the phase shift amount δ in this paper is not limited to only the above formula (5).

[0044] The phase shift amount calculator 6174 outputs the phase shift amount δ generated based on the above equation (5) to the subtractor 6172. The sine wave phase output from the PLL calculator 6171 is calculated as θ ｖｓ is input to the sine wave calculator 6173. ｖｓ−δ″ is input. Therefore, the sine wave calculator 6173 outputs a sine wave signal f expressed by the following equation (6).

[0045]

[0046] The sinusoidal signal f is a signal that excites the first current command value, and shifting the phase of the power supply current also shifts the phase of the sinusoidal signal f. In this paper, this control is appropriately referred to as "phase shift control."

[0047] Fig. 6 is a diagram showing an example of operating waveforms when the AC-DC converter 2 shown in Fig. 2 is operated with a fundamental power factor of 1. In the upper part of Fig. 6, the waveform of the absolute value of the power supply voltage is shown by a dashed line, and the waveform of the bus voltage is shown by a solid line. In the lower part of Fig. 6, the waveform of the power supply current is shown by a solid line, and the waveform of the fundamental wave component of the power supply current is shown by a dashed line.

[0048] 6, the switching control for the switching element 215 is concentrated in the period from when the power supply voltage passes the zero-cross point until before the absolute value of the power supply voltage reaches its peak value. In other words, when the fundamental wave power factor of the power supply current is set to 1 without using phase shift control, the switching control for the switching element 215 is concentrated in a certain period, resulting in distortion of the power supply current.

[0049] Fig. 7 is a diagram showing an example of operational waveforms when phase shift control is performed on the AC-DC converter 2 shown in Fig. 2. In the upper part of Fig. 7, the waveform of the absolute value of the power supply voltage is shown by a dashed line, and the waveform of the bus voltage is shown by a solid line. In the lower part of Fig. 7, the waveform of the power supply current is shown by a solid line.

[0050] Looking at the waveform in the lower part of Figure 7, it can be seen that although slight current fluctuations are observed, the waveform of the power supply current itself changes in agreement with the waveform of the fundamental wave of the power supply current. Therefore, by operating the AC-DC converter 2 using the phase shift control of this paper, it is possible to control the power supply current to a sinusoidal waveform. Therefore, by using the phase shift control of this paper, it is possible to operate the AC-DC converter 2 in a manner that complies with harmonic standards without relying on trial-and-error adjustments that require repeated trials to confirm whether or not compliance with harmonic standards is achieved.

[0051] As described above, the AC-DC converter according to the first embodiment includes a rectifier circuit that rectifies a power supply voltage applied from an AC power supply, a capacitor that smooths the output voltage of the rectifier circuit, a reactor that is disposed closer to the AC power supply than the capacitor, and a current detection unit that detects a power supply current flowing between the AC power supply and the rectifier circuit. The rectifier circuit has at least one switching element that is disposed closer to the AC power supply than the capacitor. When generating a switching signal for controlling the switching element, the control unit generates the switching signal so as to change the phase of the power supply current. The AC-DC converter according to the first embodiment can control the power supply current to a sinusoidal waveform. This enables harmonic components contained in the power supply current flowing between the AC power supply and the rectifier circuit to comply with harmonic standards without relying on trial-and-error adjustment. Furthermore, the AC-DC converter according to the first embodiment can comply with harmonic standards while improving the input power factor, even under operating conditions in which the bus voltage is equal to or lower than the peak absolute value of the power supply voltage.

[0052] To achieve the above functions, the AC-DC converter according to the first embodiment includes a current detector that detects a power supply current, and a controller that generates a switching signal to change the phase of the power supply current based on the fundamental wave of the power supply current detected when the switching element is turned off and the rectifier circuit is in passive operation. Controlling the switching element of the rectifier circuit using the switching signal thus generated allows the power supply current to be controlled to a sinusoidal waveform. This enables compliance with harmonic standards while improving the input power factor, even under operating conditions where the bus voltage is equal to or less than the peak absolute value of the power supply voltage. The switching signal can be generated by changing the phase of the power supply current depending on the magnitude relationship between the bus voltage detected by the first voltage detector and the power supply voltage detected by the second voltage detector.

[0053] Embodiment 2 Fig. 8 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to embodiment 2. The refrigeration cycle-applied device 900 according to embodiment 2 includes the rotating machine drive device 8 described in embodiment 1. The refrigeration cycle-applied device 900 according to embodiment 2 can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters.

[0054] The refrigeration cycle device 900 includes a compressor 42 incorporating the motor 41 of the first embodiment, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, all of which are attached via refrigerant piping 912. Inside the compressor 42, there are provided a compression mechanism 904 that compresses the refrigerant, and a motor 41 that operates the compression mechanism 904. The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902.

[0055] The compression mechanism 904 is driven by a variable-speed controlled motor 41. During heating operation, as indicated by the solid arrows, the refrigerant is pressurized by the compression mechanism 904 and discharged, passes through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910, and the four-way valve 902, and returns to the compression mechanism 904. During cooling operation, as indicated by the dashed arrows, the refrigerant is pressurized by the compression mechanism 904 and discharged, passes through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906, and the four-way valve 902, and returns to the compression mechanism 904. During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant and causes it to expand.

[0056] 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, or part of the configuration may be omitted or modified without departing from the spirit of the invention. For example, the above-described control method may also be applied to a DC-AC converter.

[0057] 1 AC power source, 2 AC / DC converter, 3 DC / AC converter, 4 Load, 6 Control unit, 8 Rotating machine drive unit, 9a, 9b DC bus, 20 Rectifier circuit, 41 Motor, 42 Compressor, 211 Current detection unit, 212 Reactor, 213a, 213b Single-phase diode bridge cell, 215 Switching element, 216 Capacitor, 217a, 217b Voltage detection unit, 225 Switching cell, 611, 614, 6172 Subtractor, 612 Voltage controller, 613 Multiplier, 615 Current controller, 616 Switching signal generator, 617 Sine wave signal generator, 900 Refrigeration cycle applied equipment, 902 Four-way valve, 904 Compression mechanism, 906 Indoor heat exchanger, 908 Expansion valve, 910 Outdoor heat exchanger, 912 Refrigerant piping, 6171 PLL calculator, 6173 sine wave calculator, 6174 phase shift amount calculator.

Claims

1. An AC / DC conversion device comprising: a rectifier circuit having at least one switching element and rectifying a power supply voltage applied from an AC power supply; a capacitor connected to a DC bus and smoothing the output voltage of the rectifier circuit; a reactor located on the AC power supply side of the capacitor; a current detection unit that detects the power supply current flowing between the AC power supply and the rectifier circuit; and a control unit that generates a switching signal for controlling the switching element, wherein the switching element is located on the AC power supply side of the capacitor, and the control unit generates the switching signal so as to change the phase of the power supply current.

2. The AC-DC converter according to claim 1, characterized in that the control unit generates the switching signal so as to change the phase of the power supply current based on the fundamental wave of the power supply current detected when the switching element is turned off and the rectifier circuit is operated passively.

3. An AC-DC converter as described in claim 2, further comprising: a first voltage detection unit that detects a bus voltage, which is the voltage of the DC bus; and a second voltage detection unit that detects the power supply voltage, wherein the control unit generates the switching signal so as to change the phase of the power supply current depending on the magnitude relationship between the detected value of the bus voltage and the detected value of the power supply voltage.

4. A rotary machine drive device comprising an AC / DC converter according to any one of claims 1 to 3.

5. A refrigeration cycle device comprising an AC / DC converter as claimed in any one of claims 1 to 3.

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