JP2007295688A - Inverter control device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of a malfunction caused by a torque ripple and a current ripple which are generated when a carrier wave frequency is periodically changed without increasing an operation load. <P>SOLUTION: The sum of times (generation times Tc1 to Tc6) in one period of each current control loop and a time (a generation time Ts) in one period of a speed control loop are set to coincide with each other. In such a manner, since the displacement of an operation amount u(t) generated at each current control loop per one period of the speed control loop is considered to be constant, a speed controller 3 can perform control without correcting a proportional gain and an integrated gain of the current control loop, the occurrence of the malfunction caused by the torque ripple and the current ripple which are generated when the carrier wave frequency is periodically changed can be suppressed without increasing the operation load. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device and a control method for a power conversion device that changes an output form of a DC power supply and outputs an AC voltage, and relates to a technique for preventing occurrence of a defect caused by a change in carrier frequency.

  Conventionally, U-phase, V-phase, and W-phase currents of a three-phase AC motor (hereinafter abbreviated as “motor”) are detected, and obtained from the detected current value and the current command value output from the current controller. PID (proportional / integral / derivative) control is performed based on the deviation, and switching that configures the inverter circuit according to the magnitude relationship between the PID control value output from the current controller and the triangular wave carrier wave (hereinafter abbreviated as carrier wave) An inverter control device that switches on / off of an element is known. According to such an inverter control device, feedback control can be performed so that a sinusoidal current flows in each of the U phase, V phase, and W phase of the motor.

By the way, the inverter control device is generally called a triangular wave comparison type sine wave PWM inverter device, but it is known that EMI noise caused by the carrier frequency input to the current controller is generated. In order to reduce the peak, a method of changing the carrier frequency with time has been proposed. However, by changing the carrier frequency with time, problems such as current ripple and torque ripple occur. In order to reduce the occurrence of these current ripples and torque ripples, there is known a power converter that corrects an integration constant that is a current control gain according to a carrier frequency and makes the current control gain equivalent (for example, (See Patent Document 1).
JP 2000-184731 A

  However, since the conventional power converter suppresses an increase in current ripple or torque ripple by matching the current control gain value to the change in the carrier frequency, the processing load on the microcomputer in the current controller is enormous. Become. In addition, since the processing needs to be executed in a very short time, a microcomputer with high capability is required, which may increase the cost of the system.

  The present invention has been made to solve the above problems, and its purpose is to reduce problems caused by current ripple and torque ripple that occur when the carrier frequency is periodically changed without increasing the calculation load. There is to do.

  In order to solve the above-described problem, an inverter control device and an inverter control method according to the present invention match a predetermined number of times of a cycle time for generating a voltage command value with a predetermined cycle time for generating a current command value. An inverter control device or an inverter control method is provided.

  In the inverter control device and the inverter control method according to the present invention, the time for a predetermined number of cycle times for the current controller to generate the voltage command value is matched with the predetermined cycle time for the controller to generate the current command value. The deviation of the predetermined number of times of generating the voltage command value generated at the predetermined cycle time for generating the current command value can be regarded as a constant value. Therefore, current control can be performed without changing the current control gain in accordance with the periodic change in the carrier frequency, and problems due to current ripple and torque ripple can be reduced without increasing the calculation load.

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

  [Overall Configuration of Motor Controller] First, a block diagram of the motor controller 1 when driving the three-phase AC motor 7 according to the first embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the control apparatus 1 according to the first embodiment of the present invention mainly includes an input unit 2, a speed controller 3, a current controller 4, a PWM inverter 5, and a current sensor 6. , A three-phase AC motor 7, a speed detector 8, a carrier wave generator 9, and a carrier frequency variable unit 10.

  [Details of Each Component] The speed controller 3 is detected from the speed command value, which is the rotation speed instruction value (target value) to the three-phase AC motor 7 input from the input unit 2, and the three-phase AC motor 7. The current command value is calculated by PID control based on the difference (deviation) in rotation speed (detection value) to be output to the current controller 4. The details of the current command value will be described later.

  The current controller 4 is used to turn on / off the switching element of the PWM inverter 5 based on the current command value output from the speed controller 3 and the current value (current detection value) input to the three-phase AC motor 7. Is generated by PID control and is output to the PWM inverter 5. The details of the voltage command value will be described later.

  The PWM inverter 5 is a triangular wave comparison type sine wave PWM inverter, and by turning on / off the switching element based on the voltage command value output from the current controller 4 and the carrier wave signal input from the carrier wave generator 9. The three-phase AC current is generated and output to the three-phase AC motor 7. The three-phase AC motor 7 generates a rotational force so as to realize a desired rotation speed input from the speed command value by the generated three-phase AC current.

  The current sensor 6 detects the three-phase alternating current generated by the PWM inverter 5 and feeds back the detected current value to the current controller 4.

  The speed detector 8 detects the rotational speed of the three-phase AC motor 7 and feeds back the detected rotational speed to the current controller 4. In the present embodiment, the rotational speed of the three-phase AC motor 7 is detected, but the rotation angle of the three-phase AC motor 7 may be detected.

  The carrier wave generation unit 9 outputs a carrier wave to the PWM inverter 5.

  The carrier frequency variable unit 10 changes the carrier frequency fc output from the carrier generation unit 9.

  [PID Control Performed by Speed Controller and Current Controller] Next, PID control performed by the speed controller 3 and the current controller 4 will be described with reference to FIG.

  When the control target 12 shown in FIG. 2 tries to realize output of a certain physical quantity, the difference (deviation e (t)) between the physical quantity command value (target value) and the actual physical quantity detection value is calculated. It is obtained and input to the PID controller 11. The PID controller 11 outputs the manipulated variable u (t) to the controlled object 12 so that the value of the deviation e (t) becomes small. U (t) is calculated by the following equation.

Kp represents a proportional gain, Ki represents an integral gain, and a Kd differential gain.

  Here, in the speed controller 3, the speed command value corresponds to the command value, the detection value corresponds to the speed detection value, and the operation amount corresponds to the current command value.In the current controller 4, the current command value corresponds to the command value and the detection value corresponds to the current. The detected value and operation amount correspond to the voltage command value. Further, as can be seen from Equation 1, the term including Kp, Ki, and Kd depends on the carrier cycle time that is the reciprocal of the carrier frequency fc. When performing torque control, the torque command value corresponds to the command value, and the detected value corresponds to the torque detected value.

  [Speed Control Loop and Current Control Loop] Next, a speed control loop and a current control loop performed in the motor control device 1 will be described with reference to FIG.

  In the speed control loop, first, the speed controller 3 outputs a current command value to the current controller 4. Next, based on the current command value, the three-phase AC motor 7 is driven through the current control loop, detects the rotational speed of the three-phase AC motor 7, and inputs the detected rotational speed value to the speed controller 3. Perform feedback loop control.

  In the current control loop, the current controller 4 outputs a voltage command value to the PWM inverter 5. Next, based on the voltage command value, the PWM inverter 5 generates a three-phase AC current and outputs it to the three-phase AC motor 7. Feedback loop control is performed in which a three-phase AC current output to the three-phase AC motor 7 is detected, and the detected three-phase AC current value is input to the current controller 4.

  Here, the time when the speed controller 3 generates the current command value (that is, the time of one period of the speed control loop) is the generation time Ts, and the time when the current controller 4 generates the voltage command value (that is, the current control loop 1 The period of time) is defined as the generation time Tc. The generation time Tc is the same as the cycle of the carrier wave signal output from the carrier wave generation unit 9 and is the reciprocal of the carrier wave frequency fc. The generation time Ts does not depend on the carrier wave signal and takes a certain period.

  Next, in PI control (when Kd = 0) in the current control loop, as can be seen from Equation 1 described above, the generation time Tc changes with the change in the carrier frequency fc, and therefore the terms including Ki and Kp for PI control. Also changes. Here, the integral gain Ki and the differential gain Kp are corrected so that the value of the term including Ki and Kp is constant so as not to be affected by the change in the generation time Tc. The amount of calculation becomes enormous.

  Therefore, in the inverter control device according to the first embodiment of the present invention, the time of one speed control loop (that is, the generation time Ts) and the time corresponding to a predetermined number of times of one period of the current control loop (that is, each generation time Tc1). The total time of ~ Tcn) is made to coincide. That is, the generation times Tc1 to Tcn are determined so that the following formula 2 is satisfied (Ts is constant).

  FIG. 4 shows the relationship between the time of one cycle of the current control loop (generation time Ts) and the time of one cycle of the speed control loop (generation time Tc). The time of one cycle of the speed control loop and the current control loop 1 It is configured so that the sum of the times of the periods is the same, and has a relationship satisfying the following expression.

  In this case, the order may be different as long as the sum of the time of one current control loop (generation time Tc1 to Tc6) matches the time of one period of the speed control loop (generation time Ts). As described above, since the deviation of the operation amount u (t) generated in each current control loop per cycle of the speed control loop can be considered to be constant, it is possible to correct the proportional gain and integral gain of the current control loop. Thus, the speed controller 3 can perform control, and it is possible to suppress problems caused by torque ripple and current ripple that occur when the carrier frequency fc is periodically changed without increasing the calculation load.

  Next, the configuration of the inverter control apparatus according to the second embodiment of the present invention will be described. Since the configuration of the inverter control device according to the second embodiment of the present invention is the same as that of the inverter control device according to the first embodiment of the present invention, the change in the generation time Ts will be described below with reference to FIG. The relationship of the generation time Tc will be described.

  As shown in FIG. 5, the relationship between the generation time of the current control loop and the generation time of the speed control loop of the inverter device according to the second embodiment of the present invention is the sum of the generation times Tc1 to Tc6 with respect to Ts. And the order of their appearance appears in the same order. In such a relationship, the generation time Ts and the carrier frequency change period Tm are equal, and the generation time Ts can be made equal to an integer multiple of the carrier change period Tm. In contrast, it is not necessary to synchronize the start time and end time of one cycle of the speed control loop. In this case, since the change period Tm of the carrier wave is constant, the start time of one period of the speed control loop may be any time, for example, the start time is the generation time of the current control loop Tc2 or the generation of the current control loop Tc4 Even during the period, all the same generation times Tc1 to Tc6 are included once in one period of the speed control loop. Therefore, the carrier frequency change period Tm can be set according to the generation time Ts.

  Next, the configuration of the inverter control apparatus according to the third embodiment of the present invention will be described. Since the configuration of the inverter control apparatus according to the third embodiment of the present invention is the same as that of the inverter control apparatus according to the first embodiment of the present invention, the generation time of the current control loop will be described below with reference to FIG. The relationship between the change in Ts and the generation time Tc of the speed control loop will be described.

  As shown in FIG. 6, the carrier frequency fc for PID control changes to a sine wave shape of full wave rectification. By changing the carrier frequency fc in this way, the time of the one-dot chain line shown in FIG. 6 is used as the start timing of the speed control loop, the generation time Ts is set to an integral multiple of a half cycle of the carrier frequency change period Tm, A relationship satisfying Equation 2 can be realized. Therefore, according to the period of the speed control loop, it is possible to further appropriately define the change period of the carrier frequency fc for preventing the occurrence of problems due to the carrier frequency fc.

  Next, the configuration of the inverter control apparatus according to the fourth embodiment of the present invention will be described. Since the configuration of the inverter control apparatus according to the fourth embodiment of the present invention is the same as that of the inverter control apparatus according to the first embodiment of the present invention, hereinafter, a current control loop will be described with reference to FIGS. The relationship between the change in generation time Ts and the generation time Tc of the speed control loop will be described.

  As shown in FIG. 7, the carrier frequency fc for PID control changes in a triangular waveform. By changing in this way, the carrier frequency fc at the time of the one-dot chain line shown in FIG. 7 is the maximum value (peak position) or minimum value (valley position) and the start time of the speed control loop generation time Tc. Synchronize.

  In all of the above-described embodiments, the speed control loop and the current control loop can each be realized by using interrupt processing of a microcomputer. FIG. 8 is a diagram showing the timing of the speed control interrupt and the current control interrupt for realizing the carrier frequency fc change in FIG. In this case, the speed control interrupt is synchronized with a current control interrupt in which the carrier frequency fc is the maximum value or the minimum value. With such a configuration, it becomes possible to easily synchronize the change period of the speed or torque control loop and the carrier frequency fc.

  In the description using the embodiment of the present invention, only the motor drive to which the speed control is applied has been described. However, the present invention is not limited to the speed control, and the motor drive to which the torque control is applied is also described. It is possible to carry out similarly. In this case, the same explanation can be made by changing the speed control to the torque control in the above description.

FIG. 2 is a block configuration diagram of motor control according to the first embodiment of the present invention. It is a block block diagram of PID control performed by a speed controller or a current controller. It is a block block diagram of current control loop control and speed control loop control. FIG. 5 is a diagram illustrating a relationship between a time change of a carrier frequency, a generation time Tc of a current control loop, and a generation time Ts of a speed control loop according to the first embodiment of the present invention. It is a figure showing the relationship between the time change of the carrier frequency based on 2nd Example of this invention, the generation time Tc of a current control loop, and the generation time Ts of a speed control loop. It is a figure showing the relationship between the time change of the carrier frequency which concerns on the 3rd Example of this invention, the generation time Tc of the current control loop, and the generation time Ts of the speed control loop. It is a figure showing the relationship between the time change of the carrier frequency which concerns on the 4th Example of this invention, the generation time Tc of the current control loop, and the generation time Ts of the speed control loop. It is a figure showing the interruption time of the speed control loop based on the 4th Example of this invention.

Explanation of symbols

1: Control device 2: Speed controller 3: Current controller 4: PWM inverter 5: Current sensor 6: Three-phase AC motor 7: Speed detector 8: Carrier wave generator 9: Carrier frequency variable unit 10: PID controller 11 : Control target

Claims (5)

An AC motor driven by AC current;
An input unit for inputting a command value so as to obtain a desired rotation speed or torque to the AC motor;
A detection unit for detecting a rotation speed or a rotation angle of the AC motor;
A current detection unit for detecting a current input to the AC motor;
A carrier generation unit for generating a carrier;
A carrier frequency variable unit that varies the frequency of the carrier;
A controller that generates a current command value or a torque command value based on the command value and the detected rotation speed or the command value and the detected rotation angle;
A current controller that generates a voltage command value based on a change in the carrier signal;
And the inverter control is performed so that a time corresponding to a predetermined number of cycle times for the current controller to generate the voltage command value matches a time corresponding to a predetermined cycle for the controller to generate the current command value. Inverter control device to perform.   2. The inverter control device according to claim 1, wherein the time for which the controller generates the current command value is an integral multiple of a period of the change waveform of the carrier frequency.   The change waveform of the carrier frequency is a waveform that is turned back every half cycle centering on a predetermined time, the start time of the generation cycle of the current command value is made coincident with the predetermined time, and the generation cycle is set to the carrier frequency The inverter control device according to claim 2, wherein the inverter control device is set to an integral multiple of a half cycle of the change waveform.   The change waveform of the carrier frequency has a triangular wave shape, and the start time of the generation period of the current command value coincides with the time when the maximum value or the minimum value of the change waveform of the carrier frequency becomes a triangular wave shape. The inverter control device according to claim 3. A step of inputting a command value so as to obtain a desired rotational speed or torque to the AC motor;
Detecting the rotation speed or rotation angle of the AC motor;
Detecting a current input to the AC motor;
Generating a carrier wave;
Varying the carrier frequency;
Generating a current command value or a torque command value based on the command value and the detected rotation speed or command value and the detected rotation angle;
Generating a voltage command value based on a change in the carrier signal;
An inverter control method for performing inverter control so that a time corresponding to a predetermined number of cycle times in which the current controller generates a voltage command value and a time corresponding to a predetermined cycle in which the controller generates a current command value are matched .

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