Motor Drive Unit

Abstract

To provide a motor drive device and a control method thereof, capable of suppressing a rise in DC link voltage without adding a new circuit.SOLUTION: A motor drive device includes: a rectification circuit which rectifies input AC voltage to generate rectified voltage; a booster circuit which boosts the rectified voltage to generate boosted voltage; a capacitor with small capacitance which holds the boosted voltage; an inverter which converts the boosted voltage held in the capacitor with small capacitance into output AC voltage that drives a motor; an inverter control circuit which controls such that the rotational speed of the motor approaches a target rotational speed; and correction means which corrects a target q-axis current that is the target of a q-axis current flowing trough the motor and that is processed in the inverter control circuit, depending on the degree of fluctuation of the input AC voltage.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a motor drive device and a control method thereof. [Background technology]

[0002] A motor drive device is known in which a rectifier rectifies input AC power, a boost converter boosts the power rectified by the rectifier, a capacitor stores a pulsating voltage from the boost converter, an inverter having a plurality of switching elements converts AC power using the voltage across the capacitor and outputs the converted power to a motor, a regenerative power consumption unit arranged between the capacitor and the inverter consumes regenerative power from the motor, and a switching drive unit outputs a switching control signal to a switching element of the regenerative power consumption unit and an operation control signal to an inverter control unit when the voltage across the capacitor is equal to or higher than a predetermined voltage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2015 / 0354880 Summary of the Invention [Problem to be solved by the invention]

[0004] If a configuration is adopted in which the regenerative power consumption unit consumes the regenerative power from the motor to suppress the rise in the DC link voltage, it is necessary to add a new circuit to suppress the rise in the DC link voltage.

[0005] An object of the present invention is to suppress an increase in the DC link voltage without adding a new circuit. [Means for solving the problem]

[0006] With this object in mind, the present invention provides a motor drive device comprising a rectifier circuit that rectifies an input AC voltage to generate a rectified voltage, a boost circuit that boosts the rectified voltage to generate a boosted voltage, a small-capacity capacitor that holds the boosted voltage, an inverter that converts the boosted voltage held in the small-capacity capacitor into an output AC voltage that drives a motor, an inverter control circuit that controls the rotational speed of the motor to approach a target rotational speed, and correction means that corrects a target q-axis current, which is a target for the q-axis current flowing through the motor and is processed by the inverter control circuit, in accordance with the degree of fluctuation in the input AC voltage.

[0007] The correction means may use the distortion amount of the input AC voltage as the degree of fluctuation of the input AC voltage. In this case, the motor drive device may further include a calculation means for calculating the distortion amount of the input AC voltage by calculating the difference between the rectified voltage generated by the rectifier circuit and an ideal rectified voltage. Alternatively, the motor drive device may further include a calculation means for calculating the distortion amount of the input AC voltage by calculating the difference between the rectified voltage generated by the rectifier circuit and the boosted voltage generated by the booster circuit.

[0008] The present invention also provides a control method for a motor drive device that includes a rectifier circuit that rectifies an input AC voltage to generate a rectified voltage, a boost circuit that boosts the rectified voltage to generate a boosted voltage, a small-capacity capacitor that holds the boosted voltage, an inverter that converts the boosted voltage held in the small-capacity capacitor into an output AC voltage that drives a motor, and an inverter control circuit that controls the rotation speed of the motor to approach a target rotation speed, the control method for a motor drive device including the steps of detecting a degree of fluctuation in the input AC voltage, and correcting a target q-axis current, which is a target for the q-axis current flowing through the motor and is processed by the inverter control circuit, in accordance with the detected degree of fluctuation. Effect of the Invention

[0009] According to the present invention, it is possible to suppress an increase in the DC link voltage without adding a new circuit. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of the configuration of a motor drive device to which an embodiment of the present invention is applied; [Diagram 2] 4 is a graph showing a waveform of an input voltage from an AC power source when the AC power source is a poor power source. [Diagram 3] 13 is a graph showing waveforms of a rectified voltage and a DC link voltage before any countermeasure is taken when the AC power supply is an inferior power supply. [Figure 4] 1 is a graph showing a comparison between an actual rectified voltage and an ideal rectified voltage. [Diagram 5] 4 is a graph showing a difference between an actual rectified voltage and an ideal rectified voltage. [Figure 6] 11 is a graph showing the timing at which an inverter consumption amount adjustment flag is turned on. [Figure 7] 7(a) is a graph showing the correction amount obtained from the graph shown in FIG. 6, and (b) is a graph showing the state when the correction amount is subtracted from the target q-axis current Iq*. [Figure 8] 11 is a graph showing waveforms of the target q-axis current Iq*, the actual q-axis current Iq, the target d-axis current Id*, and the actual d-axis current Id after the target q-axis current Iq* has been corrected. [Figure 9] 11 is a graph showing waveforms of a rectified voltage and a DC link voltage after a target q-axis current Iq* is corrected. [Figure 10] FIG. 2 is a block diagram showing an example of a functional configuration of a control device for implementing the method of the present embodiment. [Figure 11] 4 is a flowchart showing an example of the operation of a control device for implementing the method of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In recent years, the need for energy-saving products has increased due to the strengthening of environmental regulations in various countries around the world. In the air conditioner market, the demand for energy-saving products is expanding, especially in emerging countries, and the rate of inverter use is increasing. The challenges in converting home appliances to inverters are to reduce size and weight and cost. The current system is a commonly used variable transmission with vector control in an AC / DC / AC configuration. The circuit configuration of this system requires the use of an electrolytic capacitor in the DC link section, which hinders the system from being made smaller and lighter.

[0012] By the way, one method to achieve size and weight reduction is the capacitorless inverter, which replaces the electrolytic capacitor with a small-capacity film capacitor. Although electrolytic capacitors have a short lifespan, the capacitorless inverter is not subject to the limitations of this and has the advantage of having a longer product lifespan.

[0013] However, the capacitor-less inverter has drawbacks due to the pulsation of the DC link, such as the inability to secure the required operating range, and concerns over noise, vibration, and deterioration of efficiency. In particular, it is susceptible to the effects of power sources such as the effects of system impedance, instantaneous voltage fluctuations, and poor power sources.

[0014] One possible solution to this problem is to use a system that adds a boost function to the capacitor-less inverter to suppress pulsation in the DC link and increase the voltage utilization rate.

[0015] Fig. 1 is a diagram showing a configuration example of a motor drive device 1 to which the present embodiment is applied. As shown in the figure, the motor drive device 1 is connected to an AC power supply 2 and a motor 3, and includes a rectifier circuit 10, a boost circuit 20, a DC link unit 30, an inverter 40, a PFC (Power Factor Correction) control circuit 50, and an inverter control circuit 60. The AC power supply 2 is a single-phase power supply, but may be a multi-phase power supply. The motor 3 is, for example, a permanent magnet embedded synchronous motor.

[0016] The rectifier circuit 10 rectifies a single-phase AC (input AC voltage) supplied from an AC power source 2 into a DC. The rectifier circuit 10 includes a diode bridge DB. The diode bridge DB is configured by connecting directly connected diodes D11 and D12 in parallel with directly connected diodes D13 and D14. That is, the diodes D11 and D12 are connected in series at a connection point a, and the diodes D13 and D14 are connected in series at a connection point b. These are then connected in parallel between the connection points c and d. The diodes D11 to D14 are connected so that a current flows in the direction from the connection point d to the connection point c.

[0017] Furthermore, the rectifier circuit 10 includes a voltage detector 11 at the connection point c. The voltage detector 11 detects the output voltage of the rectifier circuit 10 (hereinafter referred to as the "rectified voltage").

[0018] The boost circuit 20 boosts the rectified voltage and includes an inductor L1, a switching element SW1, and a feedback diode Df1.

[0019] An inductor L1 has one terminal connected to a connection point c and the other terminal connected to a connection point e.

[0020] The switching element SW1 has one terminal connected to a connection point e and the other terminal connected to a connection point f. The switching element SW1 is a high-voltage power switching element. For example, a field effect transistor or an insulated gate bipolar transistor (IGBT) can be used for the switching element SW1. The switching element SW1 is a three-terminal element, and the terminal that controls on / off is called a gate.

[0021] The feedback diode Df1 is connected in parallel to the switching element SW1. The feedback diode Df1 is connected in a direction in which a current flows from the connection point f to the connection point e. The direction in which a current flows through the feedback diode Df1 is opposite to the direction in which a current flows through the switching element SW1.

[0022] The boost circuit 20 also includes a current detection unit 21 that detects the output current of the rectifier circuit 10 (hereinafter, referred to as the “rectified current”).

[0023] The boost circuit 20 may be of an interleaved type.

[0024] The DC link unit 30 includes a diode D2 and a capacitor C1. The diode D2 has one terminal (anode) connected to the connection point e and the other terminal (cathode) connected to the connection point g. The capacitor C1 is a small-capacity film capacitor, and has one terminal connected to the connection point g and the other terminal connected to the connection point h.

[0025] The DC link unit 30 also includes a voltage detection unit 31 at connection point g. The voltage detection unit 31 detects the output voltage of the DC link unit 30 (measures the voltage value). Note that connection point h in the DC link unit 30 is a reference potential, and the potential (voltage) of connection point g relative to this reference potential is sometimes referred to as a DC link voltage (boosted voltage) Vdc. In other words, the DC link voltage Vdc is the voltage of the capacitor C1 (the voltage between connection points g and h). The DC link voltage Vdc is then supplied to the inverter 40 as the output voltage of the DC link unit 30.

[0026] The inverter 40 switches the direct current supplied by the DC link unit 30 to generate an alternating current (output AC voltage) for driving the motor 3, which is a load. Here, the inverter 40 generates a three-phase alternating current (U phase, V phase, and W phase).

[0027] The inverter 40 includes switching elements SW21 to SW26 and feedback diodes (no reference numerals) connected in parallel to the switching elements. Three pairs of switching elements, each pair of which is connected in series, are connected in parallel. That is, the switching elements SW21 and SW22 are connected in series, the switching elements SW23 and SW24 are connected in series, and the switching elements SW25 and SW26 are connected in series. These are connected in parallel between the input terminals P and N of the inverter 40. The switching elements SW21 to SW26 and the feedback diodes (no reference numerals) connected in parallel to them are connected in a direction in which a current flows from the input terminal P to the input terminal N. The direction of current flow in the feedback diode is opposite to the direction of current flow in the switching elements SW21 to SW26.

[0028] The connection point of the switching elements SW21 and SW22 is connected to the motor 3 as a U-phase, the connection point of the switching elements SW23 and SW24 is connected to the motor 3 as a V-phase, and the connection point of the switching elements SW25 and SW26 is connected to the motor 3 as a W-phase.

[0029] The inverter 40 also includes a current detection unit 41 that detects three-phase AC (U phase, V phase, and W phase). The current detection unit 41 may detect the current by, for example, a one-shunt method.

[0030] The PFC control circuit 50 includes an LPF (Low-pass filter) 51, a calculator 52, a PI (Proportional Integral) control unit 53, a phase detector 54, a multiplier 55, a calculator 56, a PI control unit 57, and a PWM (Pulse Width Modulation) control unit 58.

[0031] The LPF 51 blocks high-frequency components of the DC link voltage Vdc detected by the voltage detection unit 31 and passes low-frequency components.

[0032] The calculator 52 calculates a predetermined target DC link voltage (hereinafter referred to as the "target DC link voltage") Vdc *The differential between this and the DC link voltage Vdc output by the LPF 51 is calculated, and the result is output.

[0033] The PI control unit 53 calculates a current value A for making the difference output by the calculator 52 approach zero by PI control, and outputs the result. Hereinafter, the PI control unit 53 is referred to as "AVR", and the gain used in the PI control in this AVR is referred to as "AVR gain".

[0034] The phase detector 54 detects the phase θ of the AC power supply 2, and outputs the absolute value |cos θ| of the cosine wave of the detected phase θ.

[0035] Multiplier 55 multiplies the current value A output by PI control unit 53 by the absolute value |cos θ| of the cosine wave output by phase detector 54, and outputs the result A×|cos θ|.

[0036] The calculator 56 sets the multiplication result A×|cosθ| output by the multiplier 55 as a target rectified current, calculates the difference between this target rectified current and the rectified current detected by the current detection unit 21, and outputs the result.

[0037] The PI control unit 57 calculates a duty for bringing the difference output by the calculator 56 closer to zero by PI control, and outputs the result. Hereinafter, the PI control unit 57 is referred to as "ACR", and the gain used in the PI control in this ACR is referred to as "ACR gain".

[0038] The PWM control unit 58 controls the timing of switching the switching element SW1 on / off in accordance with the duty output by the PI control unit 57.

[0039] The inverter control circuit 60 includes a speed estimation unit 71, an angle estimation unit 72, a three-phase to two-phase conversion unit 73, a calculator 74, a PI control unit 75, and a multiplier 76. The inverter control circuit 60 also includes a calculator 81, a PI control unit 82, a calculator 83, a PI control unit 84, a two-phase to three-phase conversion unit 85, and a PWM control unit 86.

[0040] The speed estimation unit 71 estimates the actual angular speed ωrm of the motor 3 and outputs the result. Here, the actual angular speed ωrm of the motor 3 may be estimated using a known method.

[0041] The angle estimator 72 estimates the angle of the motor 3 based on the actual angular velocity ωrm of the motor 3 estimated by the velocity estimator 71, and outputs the result.

[0042] The three-phase to two-phase conversion unit 73 generates and outputs an actual d-axis current (hereinafter referred to as the "actual d-axis current") Id and an actual q-axis current (hereinafter referred to as the "actual q-axis current") Iq based on the three-phase AC (U phase, V phase, and W phase) detected by the current detection unit 41 and the angle of the motor 3 output by the angle estimation unit 72.

[0043] The calculator 74 calculates a target angular velocity ωrm of the motor 3 that is determined in advance. * and the actual angular velocity ωrm of the motor 3 output by the speed estimation unit 71, and outputs the result.

[0044] The PI control unit 75 calculates a current value B by PI control for bringing the difference output by the calculator 74 closer to zero, and outputs the result.

[0045] The multiplier 76 multiplies the current value B output by the PI control unit 75 by the absolute value |cos θ| of the cosine wave output by the phase detector 54, and outputs the result B×|cos θ|.

[0046] The calculator 81 converts the multiplication result B×|cosθ| output by the multiplier 76 into a target q-axis current (hereinafter referred to as the "target q-axis current") Iq * Then, the target q-axis current Iq * and the actual q-axis current Iq output by the three-phase to two-phase conversion unit 73 is calculated, and the result is output.

[0047] The PI control unit 82 calculates, by PI control, the q-axis voltage to be applied to the motor 3 in order to bring the difference output by the calculator 81 closer to zero, and outputs the result.

[0048] The calculator 83 calculates a predetermined target d-axis current (hereinafter referred to as the "target d-axis current") Id * and the actual d-axis current Id output by the three-phase to two-phase conversion unit 73, and outputs the result.

[0049] The PI control unit 84 calculates, by PI control, the d-axis voltage to be applied to the motor 3 in order to bring the difference output by the calculator 83 closer to zero, and outputs the result.

[0050] The two-phase to three-phase conversion unit 85 calculates three-phase (U phase, V phase, and W phase) voltages based on the q-axis voltage applied to the motor 3 output by the PI control unit 82, the d-axis voltage applied to the motor 3 output by the PI control unit 84, and the angle of the motor 3 output by the angle estimation unit 72, and outputs the result.

[0051] The PWM control unit 86 generates and outputs a signal that controls the timing of switching on / off of the switching elements SW21 to SW26 so that the three-phase (U phase, V phase, and W phase) voltage output by the two-phase to three-phase conversion unit 85 can be applied to the motor 3.

[0052] Incidentally, the configuration of the motor drive device 1 described above is a general one, and the operation thereof is also a general one, so a detailed description of the operation thereof will be omitted.

[0053] Although the suppression of pulsation in the DC link unit 30 by using a system in which a boost function is added to a capacitor-less inverter has been described above, pulsation in the DC link unit 30 cannot be completely suppressed by this alone.

[0054] Therefore, here, we consider measures to be taken when voltage fluctuations occur in the AC power supply 2. Voltage fluctuations in the AC power supply 2 include, for example, instantaneous voltage fluctuations and voltage fluctuations when the AC power supply 2 is an inferior power supply.

[0055] 2 is a graph showing the waveform of the input voltage from the AC power source 2 when the AC power source 2 is an inferior power source. In this graph, voltage fluctuation occurs in the input voltage, and the maximum value of the input voltage is about 410V.

[0056] 1 uses a small-capacity film capacitor as capacitor C1, so there is a possibility that the DC link voltage will jump up if a voltage fluctuation occurs in the AC power supply 2. In addition, there is a possibility that the boost control by the boost circuit 20 will have an adverse effect and increase the jump. If the DC link voltage jumps up, it is necessary to stop operation to protect the elements.

[0057] Figure 3 is a graph showing the waveforms of the rectified voltage and DC link voltage before countermeasures are taken when the AC power source 2 is an inferior power source. In the figure, the thin line indicates the rectified voltage, and the thick line indicates the DC link voltage. For example, if an overvoltage error occurs and operation is stopped when the DC link voltage continues to be 430V or higher, in this graph, the maximum value of the DC link voltage is about 435V, so an overvoltage error occurs and operation is stopped.

[0058] However, continued operation of the motor drive device 1 is beneficial to the customer. Therefore, in this embodiment, a method for suppressing an increase in the DC link voltage is proposed.

[0059] Specifically, when a voltage fluctuation of the AC power supply 2 is detected, the target q-axis current Iq * For example, the target q-axis current Iq * By subtracting the correction amount from, the power consumption of the inverter 40 can be temporarily reduced, thereby suppressing an increase in the DC link voltage Vdc. Here, for example, the distortion amount of the voltage of the AC power supply 2 may be used as the degree of voltage fluctuation of the AC power supply 2. Methods for calculating the distortion amount of the AC power supply 2 include a first method for calculating the magnitude of the difference between the actual rectified voltage and the ideal rectified voltage (the distortion amount for each frequency) and a second method for calculating the magnitude of the difference between the actual rectified voltage and the DC link voltage (the distortion amount for each frequency).

[0060] The specific contents of the first method will be described below by taking the first method as an example.

[0061] 4 is a graph showing a comparison between the actual rectified voltage and the ideal rectified voltage. In the figure, the thin line shows the waveform of the actual rectified voltage, and the thick line shows the waveform of the ideal rectified voltage.

[0062] In this first method, the difference between the actual rectified voltage and the ideal rectified voltage is then calculated.

[0063] Figure 5 is a graph showing the difference between the actual rectified voltage and the ideal rectified voltage. In the figure, the thin line shows the difference waveform obtained by subtracting the ideal rectified voltage waveform from the actual rectified voltage waveform, and the thick line shows the low-pass differential waveform after only the low-frequency components are extracted from the difference waveform with a low-pass filter.

[0064] In this first method, the timing for turning on the inverter consumption adjustment flag is then calculated.

[0065] FIG. 6 is a graph showing the timing to turn on the inverter consumption adjustment flag. In the figure, the thin solid line shows the waveform of the low-pass difference obtained by subtracting the ideal rectified voltage waveform from the actual rectified voltage waveform and extracting only low-frequency components with a low-pass filter from the difference waveform obtained by subtracting the ideal rectified voltage waveform from the actual rectified voltage waveform. Also, the thin dashed line shows the threshold for turning on the inverter consumption adjustment flag, and the thick solid line shows the state in which the inverter consumption adjustment flag is turned on. For example, looking at the section from time S1 to time T2, the low-pass difference is below the threshold at time S1, but the inverter consumption adjustment flag is not turned on immediately at this time, but is turned on at time T1 when the low-pass difference has been below the threshold for a certain period of time. Also, the low-pass difference is above the threshold at time S2, but is not turned off immediately at this time, but is turned off at time T22 when the low-pass difference has been above the threshold for a certain period of time.

[0066] Fig. 7(a) is a graph showing the correction amount obtained from the graph shown in Fig. 6. In the figure, the solid curved line shows the correction amount. The correction amount is set for the section from time T1 to time T2, the section from time T3 to time T4, etc., where the inverter consumption adjustment flag was on in Fig. 6.

[0067] Figure 7(b) shows the target q-axis current Iq * 1 is a graph showing the state when a correction amount is subtracted from the target q-axis current Iq * The thick line indicates the waveform of the target q-axis current Iq * This shows the waveform after subtracting the correction amount from the target q-axis current Iq * By reducing the current, the power consumption of the inverter 40 is temporarily reduced, thereby minimizing the consumption of the power stored in the capacitor C1.

[0068] Figure 8 shows the target q-axis current Iq in Figure 7(b). * After correction, the target q-axis current Iq * , actual q-axis current Iq, target d-axis current Id * , and the actual d-axis current Id. In the figure, the thin solid line represents the target q-axis current Iq * The thick solid line shows the waveform of the actual q-axis current Iq, and the thin dashed line shows the waveform of the target d-axis current Id * The thick dashed line indicates the waveform of the actual d-axis current Id.

[0069] Figure 9 shows the target q-axis current Iq in Figure 7(b). * 1 is a graph showing the waveforms of the rectified voltage and the DC link voltage after correction. In the figure, the thin line indicates the rectified voltage, and the thick line indicates the DC link voltage. For example, if an overvoltage error occurs and operation stops when the DC link voltage continues to be 430 V or higher, in this graph, the maximum value of the DC link voltage is about 423 V, so operation can continue.

[0070] In the above, when the rectified voltage is low, the target q-axis current Iq *However, this is not limited to the above. When the rectified voltage is high, the target q-axis current Iq * A correction amount may be added to

[0071] Also, the second method differs from the first method only in that the DC link voltage is used instead of the ideal rectified voltage, and therefore a detailed description thereof will be omitted.

[0072] 10 is a block diagram showing an example of the functional configuration of a control device 90 for implementing the method of this embodiment. As shown in the figure, the control device 90 includes a rectified voltage receiving unit 91, a voltage fluctuation amount calculating unit 92, and a target q-axis current correcting unit 93.

[0073] The rectified voltage receiving unit 91 receives the rectified voltage from the voltage detecting unit 11 (see FIG. 1).

[0074] The voltage fluctuation calculation unit 92 calculates the amount of fluctuation in the voltage of the AC power source 2 based on the rectified voltage received by the rectified voltage receiving unit 91. Specifically, the voltage fluctuation calculation unit 92 calculates the amount of distortion for each frequency of the AC power source 2 by calculating the difference between the actual rectified voltage and the ideal rectified voltage. Alternatively, the voltage fluctuation calculation unit 92 may calculate the amount of distortion for each frequency of the AC power source 2 by calculating the difference between the actual rectified voltage and the DC link voltage. In the latter case, the control device 90 receives the DC link voltage from the voltage detection unit 31 (see FIG. 1). In this embodiment, the voltage fluctuation calculation unit 92 is provided as an example of a calculation means for calculating the amount of distortion of the input AC voltage by calculating the difference between the rectified voltage generated by the rectifier circuit and the ideal rectified voltage, and as an example of a calculation means for calculating the amount of distortion of the input AC voltage by calculating the difference between the rectified voltage generated by the rectifier circuit and the boosted voltage generated by the booster circuit.

[0075] The target q-axis current correction unit 93 corrects the target q-axis current Iq calculated by the calculator 81 in accordance with the amount of fluctuation in the voltage of the AC power source 2 calculated by the voltage fluctuation amount calculation unit 92. * Specifically, the amount of correction is determined according to the amount of fluctuation in the voltage of the AC power source 2. Then, the calculated target q-axis current Iq *with the determined correction amount. In this embodiment, a target q-axis current correction unit 93 is provided as an example of a correction means for correcting a target q-axis current, which is a target of the q-axis current flowing through the motor and is processed by the inverter control circuit, in accordance with the degree of fluctuation in the input AC voltage.

[0076] The control device 90 is included in the motor drive device 1 and may be realized by, for example, a microcomputer. In this case, a CPU (not shown) loads a program stored in a ROM (not shown) into a RAM (not shown) and executes the program, thereby realizing a rectified voltage receiving unit 91, a voltage fluctuation amount calculating unit 92, and a target q-axis current correcting unit 93.

[0077] FIG. 12 is a flowchart showing an example of the operation of the control device 90.

[0078] As shown in the figure, in the control device 90, first, the rectified voltage receiving unit 91 receives the rectified voltage from the voltage detecting unit 11 (see FIG. 1) (step 901).

[0079] Next, the voltage fluctuation calculation unit 92 calculates the amount of fluctuation in the voltage of the AC power supply 2 based on the rectified voltage received in step 901 (step 902).

[0080] Finally, the target q-axis current correction unit 93 corrects the target q-axis current Iq set by the calculator 81 in accordance with the amount of fluctuation in the voltage of the AC power source 2 calculated in step 902. * is corrected (step 903).

[0081] In this manner, in this embodiment, the control device 90 controls the target q-axis current Iq * This makes it possible to suppress the rise in the DC link voltage without adding any new circuitry. [Explanation of symbols]

[0082] 1...motor drive device, 10...rectifier circuit, 11...voltage detection unit, 20...booster circuit, 30...DC link unit, 40...inverter, 50...PFC control circuit, 60...inverter control circuit, 81...arithmetic unit, 90...control device, 91...rectified voltage receiving unit, 92...voltage fluctuation calculation unit, 93...target q-axis current correction unit

Claims

[Claim 1] A rectifier circuit for rectifying an input AC voltage to generate a rectified voltage; a boost circuit that boosts the rectified voltage to generate a boosted voltage; a small-capacity capacitor for holding the boosted voltage; an inverter that converts the boosted voltage held in the small-capacity capacitor into an output AC voltage that drives a motor; an inverter control circuit that controls the rotation speed of the motor so as to approach a target rotation speed; a correction means for correcting a target q-axis current, which is a target of a q-axis current flowing through the motor and is processed by the inverter control circuit, in accordance with a degree of fluctuation of the input AC voltage; Equipped with the correction means uses an amount of distortion of the input AC voltage as a degree of fluctuation of the input AC voltage, a calculation means for calculating an amount of distortion of the input AC voltage by determining a difference between a rectified voltage generated by the rectifier circuit and the boosted voltage generated by the boost circuit.

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