JP3395472B2 - Motor control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for controlling the rotation speed of a motor such as a brushless DC motor. 2. Description of the Related Art When a motor such as a brushless DC motor is rotated at a set rotation speed, a rotation speed N of the motor is required.
Is detected, the difference between the detected rotation speed and the set rotation speed Ns is obtained as a speed deviation, and the drive current of the motor is controlled so as to make the speed deviation zero, and the rotation speed N of the motor is set at the set rotation speed. The speed is made to coincide with the speed Ns. As a method of controlling the electric drive current, P
WM control (pulse width control) is widely used. When the drive current is subjected to PWM control, the speed deviation is given to a PID (proportional, integral, derivative) calculation unit, and the duty ratio of the drive current required to make the speed deviation zero is calculated. The drive current is PWM-modulated by giving a drive signal that is intermittent at the calculated duty ratio to a switch element to be turned on and off to turn the switch element on and off. In this specification, the duty ratio of the drive current is a so-called on-duty ratio. When the drive current is intermittently pulse-modulated at a predetermined cycle T, the drive current is not applied to the intermittent cycle T. It means the ratio of the time Ton in which the current flows [= (Ton / T) × 100%]. [0005] As described above, when the drive current of the motor is controlled by PWM so that the rotation speed of the motor matches the set rotation speed, if the PWM control is performed immediately after the start of the motor, the rotation speed rises. I can't help but get worse. Therefore, a fixed duty control mode in which the predetermined duty control time Tx is determined and the duty ratio of the drive current is fixed to a constant value (for example, 100%) during the period from the start of the start until the fixed duty control time Tx elapses is set. After the fixed duty control time has elapsed,
A transition is made to a PID control mode in which the drive current is PWM-modulated at the duty ratio obtained by the PID calculation. [0006] As described above, the fixed duty control time is set at the time of start-up, and the fixed duty control mode for fixing the duty ratio of the drive current is performed. PI when passed
Conventionally, when the control for shifting to the D control mode is performed, the fixed duty control time Tx is fixed regardless of the set rotation speed. However, the fixed duty control time T
When x is constant, when the range of the set rotation speed to be controlled is wide, the rise of the rotation speed at startup becomes poor,
There is a problem that an overshoot of the rotation speed occurs. For example, the fixed duty control time Tx is
If the setting is made short so as to correspond to the case where the set rotation speed is low, when the set rotation speed Ns is high as shown in FIG. 3, the process shifts to the PID control at an early stage, so that the rise of the speed is deteriorated. Occurs. When the fixed duty control time Tx is set to be long so as to correspond to the case where the set rotation speed is high, as shown in FIG. 4, when the set rotation speed Ns is low, P
Since the shift to the ID control is delayed, there is a problem that a rotation speed overshoot occurs and it takes time until the rotation speed is settled at the set rotation speed. An object of the present invention is to set the fixed duty control time to an appropriate value in accordance with the set rotational speed, thereby preventing the rise of the rotational speed at start-up and the occurrence of overshoot. An object of the present invention is to propose a method for controlling an electric motor as described above. According to the present invention, a rotational speed of a motor is detected, and the detected rotational speed and a set rotational speed Ns are detected.
Is calculated as a speed deviation, and a duty ratio of a drive current of the motor required to make the speed deviation zero by performing a proportional, integral, and derivative operation on the speed deviation is calculated, and the motor is calculated using the calculated duty ratio. A PID control mode in which the drive current is PWM-modulated so as to intermittently drive the drive current so that the rotation speed of the motor matches the set rotation speed Ns, and the duty ratio of the drive current is set to a constant value when the motor is started. The present invention relates to a method for controlling a motor that performs a fixed duty control mode. In the present invention, the rate of change α of the rotational speed with respect to time from when the motor is started until the rotational speed reaches A% of the set rotational speed Ns is set. , Tx = A / (100 · α) · Ns to determine a fixed duty control time Tx. Then, the fixed duty control time T
The duty ratio of the drive current is fixed to a constant value during the period until x elapses, and the fixed duty control mode is performed. When the fixed duty control time Tx elapses, the mode is shifted to the PID control mode. If the fixed duty control time is determined for each set rotation speed as described above, the optimum fixed duty control time can be always determined for each set rotation speed. Irrespective of the above, the rate of change of the rise of the rotation speed at the time of startup can always be constant, and the rise of the rotation speed at the start of the motor can be prevented from being delayed and overshoot can be prevented. Control characteristics at the time of startup can be improved. FIG. 1 schematically shows the configuration of hardware used for implementing a control method of the present invention. In FIG. 1, reference numeral 1 denotes a motor to be controlled. In this example, the motor is a three-phase brushless DC motor. Reference numeral 2 denotes a well-known inverter circuit for applying a drive current from a DC power supply (not shown) to the three-phase armature coil of the motor 1. This inverter circuit connects PNP transistors TRu to TRw and NPN transistors TRx to TRz on the upper side of the bridge, respectively. A bridge connection is made as a switch element and a switch element on the lower side, and feedback diodes Du to Dw and Dx to Dx are respectively connected between the collectors and emitters of the transistors TRu to TRw and TRx to TRz.
Dz is connected in parallel. The respective collectors of the transistors TRu to TRw and the transistor T
The connection points of the collectors Rx to TRz with the respective collectors are U, V, and W three-phase output terminals, and these output terminals are connected to the three-phase input terminals of the electric motor 1.
The common connection point of the emitters of the transistors TRu to TRw is connected to the positive output terminal of a DC power supply (not shown), and the common connection point of the emitters of the transistors TRx to TRz is connected to the negative terminal of the DC power supply (not shown). The electric motor 1 is provided with a position sensor (PS) 3 for detecting the rotational angle position of the rotor, and the output of the position sensor 3 is input to the microcomputer 4. The electric motor 1 is also provided with a rotary encoder (RE) 5 for generating a pulse for detecting a rotation speed, and a pulse obtained from the encoder is input to a speed detection unit 6 and converted into a speed detection signal. A speed detection signal obtained from the speed detector 6 is input to the microcomputer 4. The microcomputer 4 includes the position sensor 3
Pattern output unit 4A that supplies a phase pattern signal that determines a phase in which a drive current flows according to a position detection signal given from
A speed setting unit 4B for providing a set rotation speed according to a speed setting signal given by speed setting means (not shown);
A speed deviation detecting unit 4C for calculating a difference between a speed detection signal given from the speed detecting unit 6 and a speed setting signal given from the speed setting unit 4B to obtain a speed deviation;
A PID calculation unit 4D for performing a proportional, integral and differential operation (PID operation) on the speed deviation given from C to generate a PWM signal for giving a duty ratio of a drive current of the electric motor necessary to make the speed deviation zero; To achieve. The phase pattern signal is provided to the drive unit 7. The drive unit 7 is configured to select one of the switch elements TRu to TRw on the upper side of the inverter circuit 2 and one of the switch elements TRx to TRz on the lower side in accordance with the phase pattern signal. A drive signal is supplied to the motor and a drive current is supplied to an armature coil of a predetermined phase of the motor, and the drive current is commutated to a U-phase or W-phase armature coil of the motor in accordance with a change in the phase pattern signal. P output from the microcomputer 4
The WM signal is provided to the PWM control unit 8. The PWM signal is a signal having a pulse waveform intermittent at the duty ratio calculated by the PID (the duty ratio of the drive current necessary to reduce the speed deviation to zero), and the PWM control unit 8 responds to the PWM signal. By intermittently driving the drive signals u to w or the drive signals x to z applied to the upper switch elements of the inverter circuit, the duty ratio of the drive current applied to the motor 1 from the inverter circuit 2 is reduced. PWM modulation is performed so as to be equal to the duty ratio of the PWM signal. The microcomputer 4 further includes a fixed duty control time calculating section 4E for calculating a fixed duty control time Tx, and a duty ratio of a PWM signal output from the PID calculating section during the fixed duty control time Tx when the motor is started. Is fixed to a constant value (for example, 100%),
A fixed duty control mode in which the duty ratio of the drive current is fixed to a constant value is performed, and when the fixed duty control time has elapsed, the drive speed is set equal to the duty ratio calculated by the PID to set the rotation speed. A mode switching unit 4F that switches the control mode so as to shift to the PID control mode for controlling to match the speed is realized. An appropriate load 9 is connected to the electric motor 1. In the present invention, the fixed duty control time Tx is set such that the rate of change of the rotational speed at the time of startup with respect to time is set to a set value irrespective of the set rotational speed. Calculate. As shown in FIG. 2, when the set rotational speed Ns is Ns1, Ns2 and Ns3 (in the example shown, Ns1 = Ns2 / 2,
Ns3 = 2Ns2), and the rotation speed after start-up is A% of the set rotation speed (80% in the illustrated example).
, The duty ratio of the drive current is fixed at a constant value. The rotation speed is A% of the set rotation speed.
The rotation speed is linearly changed at a constant rate of change α [rpm / sec] with respect to time until the rotation speed reaches the predetermined rotation speed.
The time required to reach% is defined as T1, T2 and T3, respectively. At this time, the following equation is established. Ns1 × (A / 100) = αT1 (1) Ns2 × (A / 100) = αT2 (2) Ns3 × (A / 100) = αT3 (3) Equations (1) to (3) T1 = T3 = {A / (100α)} × Ns2 (4) T1 = {A / (100α)} × Ns1 (4) T2 = {A / (100α)} × Ns2 (5) (6) Accordingly, assuming that the set speed is Ns and the fixed duty control time is Tx, Tx = {A / (100α)} × Ns (7) That is, if the fixed duty control time Tx is calculated by the equation (7) and the duty ratio of the drive current is fixed to a constant value during the calculated fixed duty control time Tx, the set rotation speed Ns Regardless of the manner, the starting can be performed with the rate of change α of the rotation speed with respect to time being constant. The value of A can be appropriately set according to the characteristics of the electric motor, but generally, A = 80. In the present invention, the values of α and A are determined according to the characteristics of the motor to be controlled, and when the set rotation speed Ns is given by the speed setting means, the expression (7) is obtained by the microcomputer. To calculate the fixed duty control time Tx. Then, the motor is started by performing the fixed duty control mode in which the duty ratio of the drive current is fixed to a constant value during the calculated fixed duty control time Tx, and the PID control mode is set when the fixed duty control time Tx has elapsed. Then, the rotation speed is set to the set rotation speed. The value of the duty ratio in the fixed duty control mode is appropriately set according to the change rate α of the rotation speed at the time of starting. When control is performed using a microcomputer, the value of α and the value of A may be externally provided at the time of startup, or may be stored in a ROM in advance. Generally, the value of A is fixed at 80% or around 80% even if the characteristics of the motor change, so that when the characteristics of the motor are different, in most cases, α
You only need to change the value of In the above description, the microcomputer calculates the fixed duty control time Tx using the equation (7). However, the fixed duty control time Tx that satisfies the relation of the equation (7) for each set rotational speed is used. Is stored in the form of a table in the ROM or EEPROM of the microcomputer, and when the set rotational speed is given, the fixed duty control time for the given set rotational speed is read out or read out from the table. The fixed duty control time may be obtained by performing an interpolation operation on the calculated value. When the fixed duty control time for each set rotation speed is stored in the form of a table, if the fixed duty control time is finely determined for many set rotation speeds, the storage capacity of the ROM is required. Is unavoidable to be larger, but the above-mentioned equation (7)
Is used to calculate the fixed duty control time Tx, the fixed duty control time can be finely determined with respect to the set rotational speed without using a memory having a large capacity. When the fixed duty control time is obtained using the arithmetic expression, the rate of change α of the rotational speed and the coefficient A [%] for determining the rotational speed at the end of the fixed duty control can be set. Therefore, it is possible to easily cope with a case where the characteristics of the electric motor are changed. The present invention can also be applied to a case where speed control is performed using an analog arithmetic circuit without using a microcomputer. In this case, for example, a timer circuit configured to change the operation time according to the set rotation speed is provided, and the duty ratio of the drive current is controlled while the timer circuit performs the time operation when the electric motor is started. When the timer circuit completes the timed operation, the PID is fixed to a fixed value.
What is necessary is just to shift to control. In the above example, the case where the brushless DC motor is controlled is taken as an example. However, the duty ratio of the drive current of the DC motor with brush is controlled to control the rotation speed to match the set rotation speed. The present invention can be applied to the case. As described above, according to the present invention, the fixed duty control time is obtained by calculation for each set rotational speed, so that the optimum fixed duty control time is always optimum for each set rotational speed. By setting the duty control time, regardless of the set rotation speed, the rate of change of the rotation speed at startup can be made constant, and when the motor starts, the rise of the rotation speed is delayed or overshoot occurs. And the rise of the rotation speed when the motor is started can be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration schematically showing a configuration of an apparatus for implementing a control method of the present invention. FIG. 2 is a diagram showing start-up characteristics obtained when the control method of the present invention is performed. FIG. 3 is a graph showing a starting characteristic obtained when the fixed duty control time is set to a value corresponding to a low set rotational speed in the conventional control method and the start is performed by increasing the set rotational speed. FIG. FIG. 4 is a graph showing a starting characteristic obtained when the fixed duty control time is set to a value commensurate with a high set rotational speed in a conventional control method and the start is performed at a low set rotational speed. FIG. [Description of Signs] 1 Brushless DC motor 2 Inverter circuit 3 Rotor position detector 4 Microcomputer 4A Phase pattern output unit 4B Speed setting unit 4C Speed deviation detection unit 4D PID calculation unit 4E Fixed duty control time calculation unit 4F Mode switching unit 5 rotary encoder 6 speed detector 7 drive unit 8 PWM control unit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 5/00 H02P 5/17 H02P 6/06 H02P 6/20

Claims (1)

(57) [Claim 1] A rotation speed of an electric motor is detected, and a difference between the detected rotation speed and a set rotation speed Ns is obtained as a speed deviation. An arithmetic operation is performed to calculate a duty ratio of the driving current of the electric motor necessary to make the speed deviation zero, and the driving current is PWM-modulated so that the driving current of the electric motor is intermittently operated at the calculated duty ratio. A PID control mode for controlling the rotation speed of the motor to match the set rotation speed Ns, and a fixed duty control mode for fixing the duty ratio of the drive current to a constant value when the motor is started. A change rate α of the rotation speed with respect to time until the rotation speed reaches A% of the set rotation speed Ns after the motor is started is set, and for the set change rate α, x = A /
A fixed duty control time Tx determined by the formula (100 · α) · Ns is obtained, and the duty ratio of the drive current is fixed at a constant value during a period from the start of the motor start until the fixed duty control time Tx elapses. A fixed duty control mode, and when the fixed duty control time Tx has elapsed, a transition to the PID control mode.