JP5818600B2 - Motor driving device and refrigeration cycle device - Google Patents

Description

  The present invention relates to an electric motor driving device for driving a compressor or the like included in a refrigeration cycle device at a variable speed, for example.

  Conventionally, in a compressor constituting a refrigeration cycle apparatus such as an air conditioner, in order to perform variable speed driving of the rotational speed (output) of an electric motor included in the compressor, an electric motor driving apparatus that performs power conversion is provided with a power source and an electric motor. Often placed between. The motor driving device has, for example, an inverter main circuit, converts the power of the AC power source into DC, converts it again into AC, and supplies it to the motor.

  When power conversion is performed in such a motor driving apparatus, it is necessary to prevent heat generation or the like due to an excessive ripple current flowing through a DC smoothing capacitor that is an element of the inverter main circuit. Therefore, for example, when the pulsation voltage (ΔV) of the DC bus voltage exceeds a predetermined value (hereinafter referred to as a threshold value), the inverter output is limited to protect the DC smoothing capacitor (element) (hereinafter referred to as protection). An air conditioner having an electric motor driving device having a control) has been proposed (for example, see Patent Document 1).

JP 2007-259629 A (FIG. 1)

  In the protection control as described above, conventionally, the ripple current value is derived from the pulsation (ΔV) of the voltage across the DC smoothing capacitor (DC bus voltage), and the core temperature rise value of the capacitor is estimated from the value. Then, the inverter output is controlled so as to set the threshold of the pulsating voltage (ΔV) such that the core temperature value obtained from the estimated core temperature rise value is within the allowable temperature range of the DC smoothing capacitor, and the DC smoothing is controlled. The heat generation of the capacitor was suppressed. At this time, in the conventional protection control, a simulation or the like is performed in advance to determine the relationship between the pulsating voltage (ΔV) and the ripple current, and the relationship is set, for example, as data in a table.

  However, if at least one of the power supply frequency and the inverter output power (power supplied to the electric motor) fluctuates, even if the pulsation voltage (ΔV) is the same, the fluctuation pattern of the DC bus voltage is different and the ripple current cannot be uniquely determined. Therefore, from the viewpoint of DC smoothing capacitor protection, it is actually necessary to set a value with allowance as the threshold value of the pulsating voltage (ΔV) at which protection control operates. For this reason, for example, there is a high possibility that the inverter output is limited by the margin of the threshold, and there is a possibility that appropriate power supply cannot be performed.

  The present invention has been made in order to solve the above-described problems. An electric motor driving device or the like that can more accurately derive a ripple current flowing through a DC smoothing capacitor and can perform appropriate protection control is provided. The purpose is to provide.

An apparatus for driving an electric motor according to the present invention includes a rectifier, a DC reactor, a DC smoothing capacitor, and an inverse converter, and detects an inverter main circuit for converting electric power from a power source to supply the electric motor and a DC bus voltage. DC bus voltage detecting means, pulsating voltage detecting means for detecting the pulsating voltage of the DC bus voltage, output current detecting means for detecting the output current of the inverter main circuit, and power supply frequency detecting means for detecting the power supply frequency in the power supply The output power calculation means for calculating the inverter output power based on the output current, the ripple current is calculated from the power supply frequency and the pulsation voltage, the inverter output power is compared with a predetermined reference value, and the inverter output power is If it is larger than the value, a predetermined correction amount is added to the ripple current. A ripple current calculation means for subtracting a correction amount determined beforehand from the ripple current, based on the ripple current ripple current calculation unit is corrected, and the correction processing of the output frequency of the inverter main circuit is set, an output frequency command Output frequency correcting means, and inverse converter driving means for sending a drive signal to the inverse converter based on the output frequency command.

  According to the present invention, when calculating the ripple current flowing in the DC smoothing capacitor from the pulsation voltage, the pulsation is based on the power supply frequency related to the detection by the power supply frequency detection means and the inverter output power related to the calculation by the output power calculation means. Since the ripple current is calculated from the voltage, the accuracy of the ripple current according to the calculation can be improved. For this reason, the motor drive device which can prevent that protection control operates excessively can be obtained. For example, it is possible to obtain an effect that a compressor can be operated by appropriate power supply without restricting power supply to the refrigeration cycle apparatus unnecessarily.

It is a figure which shows the structure of the refrigerating-cycle apparatus in Embodiment 1 of this invention. It is a figure which shows the relationship between a power supply frequency and the waveform of DC bus-line voltage. It is a figure which shows the relationship between inverter output electric power, a pulsation voltage, and a ripple current. It is a figure which shows the flowchart which concerns on the protection control in this Embodiment. It is a figure which shows the structure of the refrigerating-cycle apparatus in Embodiment 2 of this invention. It is a figure for demonstrating calculation of the power supply frequency of the power supply frequency calculating means.

Embodiment 1 FIG.
1 is a diagram showing a configuration of a refrigeration cycle apparatus centering on an electric motor driving apparatus according to Embodiment 1 of the present invention. In the present embodiment, an air conditioner will be described as an example of the refrigeration cycle apparatus. As shown in FIG. 1, the air-conditioning apparatus according to the present embodiment connects a compressor 1, a condenser 2, a throttling device 3, and an evaporator 4 in a ring shape with refrigerant piping to form a refrigerant circuit.

  The compressor 1 having an electric motor sucks refrigerant, compresses it, and discharges it in a high temperature / high pressure state. Here, the compressor 1 is constituted by a compressor of a type that can adjust the discharge amount of the refrigerant by, for example, controlling the rotation speed (output frequency) of the motor by an inverter circuit. The condenser 2 is a heat exchanger that performs heat exchange between, for example, air and the refrigerant, and condenses and liquefies the refrigerant. In addition, the blower 2 </ b> A sends air to the condenser 2, for example, and promotes heat exchange with the refrigerant flowing through the condenser 2. The expansion device 3 expands the refrigerant by decompressing it. The evaporator 4 is a heat exchanger that evaporates a refrigerant by heat exchange.

  Here, when the motor driving device performs protection control, in the refrigeration cycle device, the opening amount of the expansion device 3 is decreased to reduce the amount of refrigerant circulating in the refrigerant circuit, and the pressure on the discharge side of the compressor 1 is increased. Try to reduce. Moreover, the air volume of the blower 2A can be increased, the heat exchange amount in the condenser 2 can be increased, and the pressure on the discharge side of the compressor 1 can be reduced.

  In addition, the motor driving device for supplying power to the compressor 1 includes a rectifier 5, a DC reactor 6 for power factor improvement, a DC smoothing capacitor 7, and an inverse converter 8 as an inverter main circuit. The rectifier 5 is configured by bridge-connecting rectifier elements such as diodes, for example, and is provided for rectifying power by an AC power source 9 that is a commercial power source, for example. The DC reactor 6 for power factor improvement is connected to the output side of the rectifier 5 and is provided to suppress harmonics. The DC smoothing capacitor 7 is provided to smooth the voltage related to the rectification of the rectifier 5 and to supply power to the load-side inverter 8 by applying a DC voltage (output voltage). The inverse converter 8 drives the compressor 1 by applying a voltage obtained by converting the DC voltage to the electric motor of the compressor 1. In the present embodiment, the inverse converter 8 applies a PWM voltage obtained by converting a DC voltage into a PWM (Pulse Width Modulation).

  Further, the DC bus voltage detecting means 11 detects the voltage across the DC smoothing capacitor 7 (hereinafter referred to as DC bus voltage). Further, the pulsation voltage detection means 12 detects the pulsation voltage (ΔV) applied to the DC smoothing capacitor 7 based on the DC bus voltage detected by the DC bus voltage detection means 11. Furthermore, the output current detection means 13 detects the output current output from the inverter main circuit.

  The output frequency setting means 15 sets the frequency (output frequency) of the inverter output power (inverter output current) supplied by the inverter main circuit based on the temperature set by the user for the air conditioner. Here, the motor driving device has the output frequency setting means 15, but in some cases, a control device (not shown) for controlling the equipment constituting the refrigeration cycle device sets the output frequency. You may make it have a function. When the output frequency correction means 16 calculates the core temperature of the DC smoothing capacitor 7 and determines that the protection control is to be performed, the output frequency correction means 16 reduces the output frequency set by the output frequency setting means 15 and outputs the output frequency command. The signal is sent to the PWM signal calculation unit 10.

  FIG. 2 is a diagram showing the relationship between the power supply frequency and the waveform of the DC bus voltage. FIG. 2A shows the case where the power supply frequency is 50 Hz. FIG. 2B shows the case where the power supply frequency is 60 Hz. FIG. 2 shows that even if the pulsating voltage (ΔV) is the same value, a difference occurs in the ripple current flowing in the DC smoothing capacitor because the voltage fluctuation pattern is different. For this reason, it is necessary to accurately determine the power supply frequency in order to accurately derive the ripple current. Therefore, the power supply frequency detection means 18 detects the power supply frequency of the AC power supply 9. Here, for example, when the power supply frequency is detected in the external device, the power supply frequency detection means 18 may receive a signal for detection of the external device. In the present embodiment, the AC power supply 9 is a commercial power supply. For this reason, the power supply frequency is 50 Hz or 60 Hz.

  FIG. 3 is a diagram showing the relationship between inverter output power, pulsation voltage (ΔV), and ripple current. As shown in FIG. 3, it can be seen that if the power supplied to the electric motor of the compressor 1 is different, the ripple current is different from the pulsating voltage (ΔV). For this reason, in order to accurately derive the ripple current, it is necessary to accurately calculate the power supplied from the inverter main circuit (inverter output power). Therefore, the output power calculation means 17 calculates the inverter output power. Further, the ripple current calculation means 14 calculates a ripple current from the pulsation voltage (ΔV) based on the power supply frequency of the AC power supply 9 and the output power of the inverter main circuit. The power calculation of the output power calculation means 17 and the operation of the ripple current calculation means 14 will be described later. The storage unit 20 stores data used when the ripple current calculation unit 14 or the like performs ripple current calculation or the like.

  Further, the PWM signal calculation unit 10 serving as the inverse converter driving means outputs the required air conditioning capability of the air conditioner from the output voltage, phase, and frequency to be applied to the compressor 1 based on the output frequency command. A PWM signal (PWM duty signal) that is a command value of a PWM voltage applied to the compressor 1 is generated. Then, a PWM signal as a drive signal is sent to the inverse converter 8 to be driven, and a PWM voltage is applied to the compressor 1.

  FIG. 4 is a diagram showing a flowchart according to protection control in the present embodiment. Based on FIG. 4, the operation of each means for determining whether or not to perform protection control of the motor driving device in the present embodiment will be described.

For example, the output power calculation means 17 is based on the following expression based on the output current detection means 13 for detecting the inverter output current and the output voltage command value of the PWM signal calculation unit 10 for calculating the PWM voltage applied to the compressor 1. The inverter output power is calculated by applying (1) (S1). Here, the inverter output power is calculated before the ripple current calculation by the ripple current calculation means 14, but the processing order is not particularly limited as long as it is before the process of S6 described later. In equation (1), P is the inverter output power, V is the output line voltage, I is the output current, and cos θ is the power factor.
P = 3 ^1/2 × V × I × cos θ (1)

  On the other hand, the pulsation voltage detection means 12 detects the pulsation voltage (ΔV) of the DC bus voltage based on the DC bus voltage related to the detection by the DC bus voltage detection means 11 (S2). Then, the ripple current calculation means 14 calculates the ripple current flowing through the DC smoothing capacitor 7 based on the pulsation voltage (ΔV) of the DC bus voltage detected by the pulsation voltage detection means 12. Here, data relating to the relationship between the pulsation voltage (ΔV) and the ripple current, which is data used when the ripple current calculation means 14 calculates the ripple current, is stored in the storage means 20 in the form of a table, for example. For example, for table creation, two types of tables at power supply frequencies of 50 Hz and 60 Hz are prepared in advance by simulation or the like, and the table is used properly according to the power supply frequency detected by the power supply frequency detection means 18. For this reason, the ripple current calculation means 14 determines the power supply frequency related to the detection by the power supply frequency detection means 18 (S3). If it is determined that the power supply frequency is 60 Hz, a ripple current is calculated based on a table for 60 Hz (S4). If it is determined that the power supply frequency is 50 Hz, a ripple current is calculated based on a table for 50 Hz (S5).

  Further, the ripple current calculation means 14 determines whether or not the value of the inverter output power calculated by the output power calculation means 17 is larger than the reference value (inverter output power value> reference value) (S6). Here, as the reference value, for example, the value of the inverter output power at the time of creating the table described above is used. When it is determined that the value of the inverter output power is larger than the reference value, the correction amount is added to the calculated ripple current (S7), and a signal is sent to the output frequency correction means 16. If it is determined that the inverter output power is below the reference value, the correction amount is subtracted (S8), and a signal is sent to the output frequency correction means 16. Here, the value of the correction amount to be added or subtracted differs depending on the inverter output power and the pulsation voltage (ΔV). For example, a correction amount value obtained in advance by simulation or the like is stored in the storage unit 20 as, for example, tabulated data, and used when performing addition / subtraction.

Then, the output frequency correction unit 16 performs a correction process based on the ripple current calculated by the ripple current calculation unit 14. For the correction process, first, the following equation (2) is applied to calculate the core temperature increase value ΔT of the DC smoothing capacitor 7. Here, I is the ripple current [Arms], R is the equivalent series resistance ESR [Ohm] of the DC smoothing capacitor 7, β is the heat dissipation constant [W / ° C. · cm ² ], and A is the surface area [cm ² ].
ΔT = (I ² × R) / (β × A) (2)

  Then, the output frequency correction means 16 further calculates the core temperature based on the core temperature increase value ΔT (S9). Then, it is determined whether the core temperature is equal to or higher than the allowable temperature of the element (DC smoothing capacitor 7) (S10).

  When it is determined that the core temperature is equal to or higher than the allowable temperature of the element, the output frequency set in the output frequency setting means 15 is reduced by a predetermined frequency (for example, 1 Hz) (S11), and an output frequency command signal related to the process is obtained. This is sent to the PWM signal calculation unit 10. Then, the inverter 8 is driven to operate the compressor 1 so as to limit the inverter output power (S13). As a result, the ripple current flowing through the DC smoothing capacitor 7 can be reduced and heat generation can be suppressed. On the other hand, if it is determined that the temperature is lower than the permissible temperature, the process is not performed (S12), and an output frequency command signal for maintaining the output frequency is sent to the PWM signal calculation unit 10 to drive the inverse converter 8, and the inverter output power is increased. While maintaining the supply, the compressor 1 is operated (S13).

  As described above, according to the motor driving device of the present embodiment, when the ripple current calculation means 14 calculates the ripple current from the pulsation voltage (ΔV), the power supply frequency and output detected by the power supply frequency detection means 18 are output. Since the calculation based on the inverter output power related to the calculation of the power calculation means 17 is performed, the ripple current can be calculated corresponding to the fluctuation of the power supply frequency and the inverter output power, and the accuracy is improved. Can be improved. For this reason, calculation of the core temperature used as the reference | standard of whether to perform protection control can be performed appropriately. Therefore, for example, it is possible to prevent the protection control from operating excessively. And the refrigerating-cycle apparatus which can perform the driving | operation of the compressor 1 by appropriate electric power supply can be obtained, without restrict | limiting the electric power supply to a refrigerating-cycle apparatus unnecessarily.

Embodiment 2. FIG.
FIG. 5 is a diagram showing a configuration of a refrigeration cycle apparatus centering on an electric motor driving apparatus according to Embodiment 2 of the present invention. In FIG. 5, the devices having the same reference numerals as those in FIG. 1 perform the same operation as described in the first embodiment. In the present embodiment, when there is no external device or the like and the power supply frequency cannot be detected, the power supply frequency calculation means 19 having a microprocessor or the like is provided instead of the power supply frequency detection means 18 so that the pulsating voltage (ΔV) is obtained. The power supply frequency is calculated.

  FIG. 6 is a diagram for explaining the calculation of the power supply frequency by the power supply frequency calculation means 19. It is known that when the AC power supply 9 which is a three-phase AC is rectified by the rectifier 5, the DC bus voltage at both ends of the DC smoothing capacitor 7 pulsates at a frequency six times the power supply frequency. Therefore, as shown in FIG. 6, the power source frequency calculation means 19 calculates the time of one cycle based on the pulsation voltage (ΔV) related to the detection by the pulsation voltage detection means 12, for example, multiplied by 6 to obtain the inverse. The value is the power supply frequency.

  Then, as in the first embodiment, the ripple current calculated from the pulsation voltage (ΔV) is corrected based on the values of the power supply frequency calculation means 19 and the output power calculation means 17, and a threshold value is set.

  As described above, according to the second embodiment, the power supply frequency calculation means 19 calculates the power supply frequency based on the pulsation voltage (ΔV), so that the ripple current can be more accurately obtained even in an environment where the power supply frequency cannot be detected. Can be derived.

Embodiment 3 FIG.
In the above-described embodiment, the ripple current calculation unit 14 calculates the ripple current based on the power supply frequency and the inverter output power, but is not particularly limited. In some cases, even if the ripple current is calculated based on either the power supply frequency or the inverter output power, the accuracy in calculating the ripple current can be improved as compared with the conventional case. Basically, the accuracy improvement effect is higher based on the power supply frequency.

  In the above-described embodiment, the case where the motor driving device is applied to the compressor 1 of the air conditioner has been described. However, the invention is not limited to the cooling device, but a refrigerant circuit such as a refrigeration device, a heat pump device such as a water heater, etc. It can apply also to the other refrigeration cycle apparatus which comprises.

  DESCRIPTION OF SYMBOLS 1 Compressor, 2 Condenser, 2A Blower, 3 Throttling device, 4 Evaporator, 5 Rectifier, 6 DC reactor, 7 DC smoothing capacitor, 8 Inverter, 9 AC power supply, 10 PWM signal calculating part, 11 DC bus voltage Detection means, 12 pulsation voltage detection means, 13 output current detection means, 14 ripple current calculation means, 15 output frequency setting means, 16 output frequency correction means, 17 output power calculation means, 18 power supply frequency detection means, 19 power supply frequency calculation means 20 Storage means.

Claims (6)

An inverter main circuit having a rectifier, a DC reactor, a DC smoothing capacitor, and an inverter, for converting electric power from a power source and supplying the electric motor;
DC bus voltage detection means for detecting the DC bus voltage;
Pulsation voltage detection means for detecting the pulsation voltage of the DC bus voltage;
Output current detecting means for detecting the output current of the inverter main circuit;
Power supply frequency detection means for detecting a power supply frequency in the power supply;
Output power calculation means for calculating inverter output power based on the output current;
A ripple current is calculated from the power supply frequency and the pulsation voltage, the inverter output power is compared with a predetermined reference value, and if the inverter output power is larger than a reference value, a predetermined correction amount is calculated as the ripple current. Ripple current calculation means for subtracting the predetermined correction amount from the ripple current if the inverter output power is below a reference value ,
Output frequency correction means for correcting the output frequency of the set inverter main circuit based on the ripple current corrected by the ripple current calculation means and outputting an output frequency command;
Inverter drive means for sending a drive signal to the inverse converter based on the output frequency command.   The output frequency correction means calculates the core temperature of the DC smoothing capacitor based on the ripple current, and determines that the core temperature exceeds an allowable temperature, and outputs an output frequency command having a frequency lower than the output frequency. The motor driving device according to claim 1, wherein the motor driving device is output.   The apparatus for driving an electric motor according to claim 1 or 2, further comprising power supply frequency calculation means for calculating the power supply frequency from the pulsating voltage instead of the power supply frequency detection means. A compressor that compresses and discharges the refrigerant; a condenser that condenses the refrigerant by heat exchange; a throttling device that depressurizes the refrigerant related to condensation; and A refrigerant circuit is configured by connecting a pipe with an evaporator that evaporates
A refrigeration cycle apparatus comprising the motor driving device according to any one of claims 1 to 3 for driving the compressor.   5. The pressure according to claim 4, wherein when the output frequency decreases, the opening degree of the expansion device is decreased to reduce the amount of refrigerant circulating in the refrigerant circuit, thereby reducing the pressure on the discharge side of the compressor. Refrigeration cycle equipment. A fan for encouraging heat exchange between the refrigerant and air in the condenser;
6. The refrigeration cycle apparatus according to claim 4, wherein when the output frequency is reduced, the air volume of the blower is increased to reduce the pressure on the discharge side of the compressor.

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