JP2001086759A - Control method for inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a control method for inverter in which the output voltage of an inverter is controlled by varying the carrier frequency, while compensating for variation of voltage level. SOLUTION: A DC voltage is switched through the switching element in an inverter and applied to a load, i.e., a motor, and the output voltage of an inverter is controlled by driving the switching element with a PWM signal having an on-width of a predetermined carrier pulse. When the r.p.m. of the motor is lower than a target value and the carrier frequency is varied for PWM control, the carrier frequency is fixed at a low frequency value h1 and the on-width of the carrier pulse is increased. When the on-width of the carrier pulse reaches a predetermined value k, the on-width is fixed and the carrier frequency is increased. When the carrier frequency reaches a high frequency value h2, it is fixed and the on-width of the carrier pulse is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique of a voltage type inverter for controlling a load motor (for example, a brushless DC motor) and the like, and more particularly, to a technique for compensating a change in an output voltage of the inverter due to a change in a carrier frequency. The present invention relates to a method of controlling an inverter to be controlled.

[0002]

2. Description of the Related Art In inverter control, for example, FIG.
The following control device is required. In FIG. 4, a DC power supply DC is switched by a switching element of an upper and lower arm of an inverter circuit 1 to form a three-phase rectangular wave voltage, which is applied to, for example, a three-phase four-pole motor 2 of a load, and a drive current is supplied to the motor 2. Get rotational torque.

At this time, the position of the rotor is determined by the position detection circuit 3.
The position detection signal is obtained based on, for example, an induced voltage waveform generated in a non-conducting phase, and the position detection signal is input to a control circuit (microcomputer) 4. Switching element U
a, Va, Wa, X, Y, and Z are driven to switch the energization of the armature winding of the stator.

In the PWM control method, the control circuit 4 switches the energization of the armature winding based on the position detection signal, and, for example, when the rotation speed of the motor 2 is increased to the target rotation speed, the output voltage is commanded. The on / off state of the carrier pulse is determined by comparing the waveform reference to be performed with a carrier having a higher frequency than the same waveform reference, and the carrier pulse on / off signal (PWM signal) is supplied to the inverter circuit 1 via the base amplifier circuit 5. Output to Then, the inverter circuit 1
Are turned on and off in a predetermined manner, whereby a rectangular wave voltage corresponding to the output voltage command is applied to the motor 2.

When the carrier frequency of the voltage-type inverter is changed, the output width of the inverter circuit 1 is controlled by adjusting the ON width of the carrier pulse (ON of the PWM signal) according to the rate of the change. For example, when the rotation speed of the motor 2 is set to a predetermined rotation speed or when the rotation speed of the motor 2 is increased to a target rotation speed, the carrier frequency is changed and the carrier pulse is turned on in accordance with the change rate of the carrier frequency. By adjusting the width, the output voltage of the inverter circuit 1 is increased or decreased.

[0006]

However, in the above-described motor control method, a delay occurs between the output of the PWM signal of the control circuit 4 and the arm driving of the inverter circuit 1 due to the switching element. If the ON width of the carrier pulse is also changed, the delay of the switching element cannot be ignored, and the output voltage of the inverter circuit 1 fluctuates when the carrier frequency changes.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a method of controlling an inverter capable of changing a carrier frequency while compensating for fluctuations in the output voltage of the inverter. It is in.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for switching a direct current voltage by a switching element of an inverter and applying the switching voltage to the load, and applying the switching element with a PWM having an ON width of a predetermined carrier pulse. In an inverter control method for controlling an applied voltage (output voltage of an inverter) of the load by driving with a signal,
When at least the carrier frequency is changed to perform the WM control, when the carrier frequency is at a low frequency value or a high frequency value, the carrier frequency is fixed and the ON width of the carrier pulse is changed, and the ON width of the carrier pulse is changed. Is equal to a predetermined value, the ON width is fixed, and the carrier frequency is changed to a high frequency value or a low frequency value.

According to the present invention, a DC voltage is switched by a switching element of an inverter and applied to the motor, and the switching element is applied with a predetermined carrier pulse width P.
In an inverter control method for controlling an applied voltage (output voltage of an inverter) of the motor by driving with a WM signal, a carrier frequency for performing the PWM control is increased because a rotation speed of the motor is lower than a target rotation speed. In the case, when the ON width of the carrier pulse does not reach a predetermined value, the carrier frequency is fixed to a low frequency value, the ON width of the carrier pulse is increased, and when the ON width of the carrier pulse reaches a predetermined value, The carrier frequency is increased by fixing the ON width, and when the carrier frequency becomes a high frequency numerical value, the carrier frequency is fixed to increase the ON width of the carrier pulse. Thus, when the carrier frequency increases, the control of the output voltage becomes smooth, and the fluctuation of the output voltage is compensated.

According to the present invention, a DC voltage is switched by a switching element of an inverter and applied to the motor, and the switching element is turned on by a predetermined carrier pulse width P.
In an inverter control method for controlling an applied voltage (output voltage of an inverter) of the motor by driving with a WM signal, a carrier frequency for performing the PWM control is reduced because a rotation speed of the motor is higher than a target rotation speed. When the ON width of the carrier pulse has not reached the predetermined value, the carrier frequency is fixed to a high frequency value to reduce the ON width of the carrier pulse, and when the ON width of the carrier pulse has reached the predetermined value, the ON frequency becomes low. The carrier frequency is lowered by fixing the width, and when the carrier frequency becomes a low frequency value, the carrier frequency is fixed to reduce the ON width of the carrier pulse. As a result, when the carrier frequency falls,
The control of the output voltage becomes smooth, and the fluctuation of the output voltage is compensated.

[0011]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described in detail with reference to FIG. In FIG. 2,
The same parts as those in FIG.

In FIGS. 1 and 2, the control device to which the inverter control method of the present invention is applied increases the carrier pulse on-width (PWM) when increasing the carrier frequency.
When the ON width of the signal is in the low output region of the section A shown in FIG. 1, the carrier frequency is fixed to the low frequency value h1, and the ON width of the carrier pulse is changed, and the ON width of the carrier pulse becomes B shown in FIG. When the intermediate output area of the section is reached, the ON width is fixed at a predetermined value k and the carrier frequency is changed. The carrier frequency is C
When the high output area of the section is reached, the carrier frequency is fixed at the high frequency value h2 to change the ON width of the carrier pulse, and when the carrier frequency is decreased, the control circuit follows a path reverse to the above-described course. (Microcomputer) 10.

When the ON width of the carrier pulse is changed, a value (ratio) of the ON width of the carrier pulse / the carrier period is calculated.
The change range of the ON width (for example, the range to be increased; see the sections A and C in FIG. 1) is increased. The changing speed of the carrier frequency is adjusted so as to be the same as the changing range of the ON width of the carrier pulse (see the slope of the section B in FIG. 1).

Further, the control of the output voltage is performed by adjusting the ON width of the carrier pulse. Specifically, the control is performed by the routine shown in the flowchart of FIG. Note that the control circuit 10 also has the function of the control circuit 4 shown in FIG.

The operation of the control device having the above configuration will be described in detail with reference to the flowchart of FIG. The number of rotations of the motor 2 is set as a target number of rotations.
H1 to h2 or h2 to h1 shown in FIG.

First, the control circuit 10 calculates the current speed (current F.) based on the position detection signal, and compares the target speed (target F.) with the current speed. If the result of the comparison is that current rotation speed <target rotation speed, step S
The process proceeds from T1 to ST2 to determine a section (A, B or C section) corresponding to the ON width of the current carrier pulse. When the ON width of the current carrier pulse is smaller than the predetermined value k,
The section is determined to be section A, and the process proceeds from step ST2 to ST3, where the carrier frequency is fixed at the low frequency value h1, the ON width of the carrier pulse is increased, and the output voltage (the so-called applied voltage of the motor 2) is controlled. The ON width of the carrier pulse is increased by a predetermined value at each predetermined step.

Subsequently, when the ON width of the carrier pulse reaches a predetermined value k, the steps ST1 and ST2 are repeated.
Proceed to T4. That is, the ON width of the current carrier pulse reaches the predetermined value k and enters the section B. Then, the ON voltage of the carrier pulse is fixed to a predetermined value k, and the output voltage is controlled by increasing the carrier frequency by a predetermined value every predetermined step.

Subsequently, the carrier frequency is changed to a high frequency value h2.
Is reached, the steps ST1, ST2 and ST
Go to 5. That is, the current carrier frequency is the high frequency value h
This is because it reaches 2 and enters section C. Then, while fixing the carrier frequency to the high-frequency numerical value h2, the ON width of the carrier pulse is increased by a predetermined value every predetermined step,
When the current rotation speed reaches the target rotation speed, the increase of the ON width of the carrier pulse is stopped. That is, the ON width of the carrier pulse is maintained, and the routine ends.

If the result of the comparison is that the current rotational speed is greater than the target rotational speed, the process proceeds from step ST1 to ST6 to determine the section (A, B or C section) corresponding to the ON width of the current carrier pulse. When the ON width of the current carrier pulse is larger than the predetermined value k, it is determined that the section is C, and the process proceeds from step ST6 to ST7, where the carrier frequency is fixed at the high frequency value h2 to reduce the ON width of the carrier pulse to control the output voltage. . In this case, the ON width of the carrier pulse is reduced by a predetermined value every predetermined step.

Subsequently, when the ON width of the carrier pulse reaches a predetermined value k, steps ST1, ST6 to S6 are executed.
Proceed to T8. That is, the ON width of the current carrier pulse reaches the predetermined value k and enters the section B. Then, the ON voltage of the carrier pulse is fixed to a predetermined value k, and the output voltage is controlled by lowering the carrier frequency by a predetermined value at each predetermined step.

Subsequently, the carrier frequency is changed to a low frequency value h1.
Is reached, the steps ST1 and ST6 to ST6 are performed.
Go to 9. That is, the current carrier frequency is the high frequency value h
This is because it reaches 1 and enters section A. Then, while fixing the carrier frequency to the low frequency value h1, the ON width of the carrier pulse is reduced by a predetermined value every predetermined step,
When the current rotational speed reaches the target rotational speed, the reduction of the ON width of the carrier pulse is stopped. That is, the ON width of the carrier pulse is maintained, and the routine ends.

As described above, the output voltage of the inverter is controlled such that the ON width of the carrier pulse is not changed when the carrier frequency is changed and the carrier frequency is not changed when the ON width of the carrier pulse is changed. The output voltage can be controlled by changing the carrier frequency while compensating for the fluctuation of the output voltage of the inverter without being affected by the delay of the switching element of the circuit 1.
In the above embodiment, the case where the motor 2 is used as the load of the inverter has been described, but the present invention can be applied to other devices.

[0023]

According to the present invention described above, the following effects can be obtained. The inverter control method according to the present invention includes:
When the carrier frequency is changed to perform the PWM control, when the carrier frequency becomes a low frequency value or a high frequency value, the carrier frequency is fixed and the ON width of the carrier pulse is changed. When the predetermined value is reached, the same ON width is fixed and the carrier frequency is changed to a high frequency value or a low frequency value.When the carrier frequency is changed, the ON width of the carrier pulse is not changed, and when the ON width of the carrier pulse is changed, Since the carrier frequency is not changed, the carrier frequency can be changed while compensating for the fluctuation of the output voltage of the inverter, and there is an effect that the control of the output voltage becomes smooth.

[Brief description of the drawings]

FIG. 1 is a schematic time chart for explaining a method of controlling an inverter according to the present invention.

FIG. 2 is a schematic block diagram of a control device to which the inverter control method of the present invention is applied.

FIG. 3 is a schematic flowchart for explaining the operation of the control device shown in FIG. 2;

FIG. 4 is a schematic block diagram of a conventional inverter control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter circuit 2 Motor (load) 3 Position detection circuit 4,10 Control circuit (microcomputer) h1 Low frequency value h2 High frequency value k Predetermined value

Claims (3)

[Claims] 1. A DC voltage is switched by a switching element of an inverter and applied to the load, and the switching element is driven by a PWM signal having an ON width of a predetermined carrier pulse to apply a voltage to the load (an output voltage of the inverter). The method of controlling an inverter for controlling
When at least the carrier frequency is changed to perform the WM control, when the carrier frequency is at a low frequency value or a high frequency value, the carrier frequency is fixed and the ON width of the carrier pulse is changed, and the ON width of the carrier pulse is changed. Wherein the carrier frequency is changed to a high-frequency value or a low-frequency value when the ON-state width reaches a predetermined value. 2. A DC voltage is switched by a switching element of an inverter and applied to the motor, and the switching element is driven by a PWM signal having an ON width of a predetermined carrier pulse to apply a voltage to the motor (an output voltage of the inverter). In the method of controlling the inverter, the rotation speed of the motor is lower than the target rotation speed.
When increasing the carrier frequency for performing the M control, when the ON width of the carrier pulse does not reach a predetermined value, the carrier frequency is fixed to a low frequency value, and the ON width of the carrier pulse is increased. When the ON width reaches a predetermined value, the ON frequency is fixed to increase the carrier frequency, and when the carrier frequency becomes a high frequency value, the carrier frequency is fixed and the ON width of the carrier pulse is increased. A method for controlling an inverter, the method comprising: 3. A DC voltage is switched by a switching element of an inverter and applied to the motor, and the switching element is driven by a PWM signal having an ON width of a predetermined carrier pulse to apply a voltage to the motor (an output voltage of the inverter). In the method of controlling the inverter, the rotation speed of the motor is higher than the target rotation speed.
When lowering the carrier frequency for performing the M control, if the ON width of the carrier pulse does not reach a predetermined value, the carrier frequency is fixed to a high frequency value to reduce the ON width of the carrier pulse, When the width reaches a predetermined value, the ON width is fixed and the carrier frequency is lowered, and when the carrier frequency becomes a low frequency value, the carrier frequency is fixed and the ON width of the carrier pulse is reduced. A method for controlling an inverter, comprising: