JP2003102194A - Drive device for brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem wherein there is a risk of becoming unable to smoothly and surely start operation, and not realizing the optimization of phase difference when switching from the synchronized start-up to the operation of rotor position detecting, depending on the magnitude of the load at the start-up. SOLUTION: When switching from the synchronized start-up to the operation of rotor position detection, the electric current in a bridge inverter is reduced gradually for solving the problem, thereby enabling smooth and sure start-up since the phase difference when switching from the synchronized start-up to the operation of rotor position detecting can be rendered as being optimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor driving device, and more particularly to a brushless motor driving device that obtains a rotor position detection signal by using an induced voltage generated in an armature winding.

[0002]

2. Description of the Related Art In a drive device for a brushless electric motor that detects the position of a rotor by utilizing an induced voltage generated in an armature winding, does an induced voltage occur when starting from a stopped state? , Or even if it occurs, the voltage value is low and the position detection signal cannot be obtained. Therefore, it is necessary to start up to a rotational speed at which the position detection signal is obtained by some means.

A commonly used starting method is to operate a brushless motor as a synchronous motor. That is, this is a low-frequency synchronous startup in which the inverter circuit that drives the brushless motor is operated as a separately excited inverter circuit, and the output frequency of this inverter circuit is gradually increased. As an example of a drive device for a brushless motor by low frequency synchronous start
There is a publication of 08-223969.

[0004]

The drive device for a brushless electric motor in the above-mentioned prior art uses a digital rotor position detection, which positions the rotor at a predetermined position at the time of start-up, and also has an armature winding. After switching the energization of the wire, obtain the position detection point of the rotor and switch the energization of that phase, and at the same time, predict the position detection points of other phases by measuring the time until the position detection of the rotor It is characterized in that the energization of the armature winding is switched at that point.

However, there is no specific description regarding the magnitude of the load, and it is not clear what kind of control should be performed.

An object of the present invention is to provide a drive device for a brushless electric motor that can perform smooth and reliable startup regardless of the magnitude of the load when switching from synchronous startup to position detection operation.

[0007]

The above problems can be solved by keeping the frequency of the three-phase signal constant at the time of switching from the synchronous start to the position detection operation, and by temporarily reducing the current of the bridge inverter.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. FIG. 1 is an overall configuration diagram of this embodiment. 1 is an AC power supply, 2 is a rectifying diode, 3 is a smoothing capacitor, 4 is a bridge inverter, 6 is a current detection circuit, 7 is a current limiting circuit, 8 is a position detection circuit, 9 is a three-phase oscillation circuit,
10 is a switching circuit, 11 is a rotation speed measurement circuit, 12 is a rotation speed command circuit, 13 is a rotation speed comparison circuit, 14 is a voltage control circuit, 15
Is a gate control circuit, 16 is a modulation circuit, and 17 is a frequency upper limit signal generation circuit, which constitutes the drive device for the brushless motor. Reference numeral 5 is a brushless electric motor. Further, as a power supply unit composed of 1 AC power supply, 2 rectifying diodes, 3 smoothing capacitors, a DC power supply such as a battery is used in the case of an in-vehicle device or the like.

First, the operation of the brushless motor will be described. In the brushless electric motor 5, the magnetic field generated by the magnet attached to the rotor and the current flowing through the armature winding attracts and repels the magnetic field to generate rotational torque. At this time, the maximum rotational torque is generated when the phases of the magnet and the winding match. Therefore, when operating the brushless motor, it is necessary to control so that the phases are always in agreement. An induced voltage is generated in the armature winding as the rotor magnet rotates. The induced voltage is input to the position detection circuit 8 to detect the position of the rotor, and the bridge inverter 4 is driven via the gate control circuit 15 so that the phases always match. Further, the rotor position detection signal is input to the rotation speed measuring circuit 11 to measure the rotation speed of the brushless motor. And the rotation speed command circuit
The rotation speed command of 12 is compared by the rotation speed comparison circuit 13, and the voltage control circuit 14 determines the voltage of the brushless motor 5 based on the result and modulates it by the modulation circuit 16 to adjust the output voltage of the bridge inverter 4. , And controls the rotation speed of the brushless electric motor 5.

However, since the induced voltage is not generated or is small at the time of starting the brushless motor, the position detection circuit 8 does not operate. Therefore, a method of starting by low frequency synchronous start is generally used. FIG. 2 is a diagram for explaining the operation. The three-phase oscillation circuit 9 starts oscillating at time t = 0, and the rotation speed becomes N1 at a predetermined time t1.
During the period in which the rotation speed is temporarily increased, the three-phase oscillation output is modulated by the modulation circuit 16 through the switching circuit 9 and the gate control circuit 15 based on the voltage command from the voltage control circuit 14 to drive the bridge inverter 4. To do. Rotation speed 20 is N
When it reaches 1, the magnitude of the induced voltage becomes sufficient for the position detection circuit 7 to operate, and as described above, the phase difference between the three-phase signal and the rotor position signal becomes small, so the switching circuit 9 operates. The synchronous startup is switched to the position detection operation, and the operation is performed as a normal brushless motor.

Next, the operations of the frequency upper limit signal generating circuit 17 and the current limiting circuit 7 will be described. The current flowing through the bridge inverter 4 during the synchronous operation period is I1. Figure 3
Shows the positional relationship between the armature winding and the rotor during synchronous startup. The rotor is in phase with the winding. When the rotor rotates from the state of FIG. 3 (a) and reaches the position of FIG. 3 (b), commutation occurs and the state of FIG. 3 (c) is obtained. In this way, synchronous operation is performed. When the load torque is small, the advance is large, and conversely, when the load torque is large, the advance is small. Even if the advance becomes zero, if a torque commensurate with the load torque is not generated, a lag phase occurs and a step out occurs. When the brushless motor 5 is started, when the load torque is large, it is necessary to flow a sufficiently large current so as not to be out of step even at the load torque. This current value is I1. When the current corresponding to the maximum starting load is supplied to start in this way, when the load is small, synchronous operation is performed with a large lead angle, and smooth and reliable switching is performed when switching from synchronous start to position detection operation. I may not be able to. Therefore, the rotation speed for synchronous activation is N1.
When the frequency upper limit signal generation circuit 17 is activated and the rotation speed becomes constant, the current limiting circuit 7 is activated from t2 when a predetermined time has elapsed and the current is temporarily reduced. The lead angle becomes smaller by temporarily reducing the current. When the load is large, the optimum switching state is set at time t3 and current I3. When the load is small, the optimum switching state is set at time t4 and current I4.

By the above-mentioned operation, it is possible to smoothly switch from the synchronous start to the position detection operation regardless of the load of the start, and to perform the reliable start.

[0013]

According to the present invention, since the phase at the time of switching from the synchronous start to the position detection operation can be optimized, smooth and reliable start can be performed.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation of low frequency synchronous activation.

FIG. 3 is an operation explanatory diagram of synchronous operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Rectifying diode, 3 ... Smoothing capacitor, 4 ... Bridge inverter, 5 ... Brushless motor, 6 ... Current detection circuit, 7 ... Current limiting circuit, 8 ... Position detection circuit, 9 ... Three-phase oscillation circuit, 10 ... Switching circuit, 11 ... Rotation speed measurement circuit, 12 ... Rotation speed command circuit, 13 ... Rotation speed comparison circuit, 14 ... Voltage control circuit, 15 ... Gate control circuit, 16 ... Modulation circuit, 17 ... Frequency upper limit signal generation circuit, 21 ... Armature winding, 22 ... Magnet.

Claims (4)

[Claims] 1. An AC power supply, a rectifier circuit connected to the AC power supply, a smoothing capacitor connected to an output terminal of the rectifier circuit, a bridge inverter connected to the smoothing capacitor, and a bridge inverter connected to the smoothing capacitor. A brushless motor, a position detection circuit for detecting a rotor position of the brushless motor from an induced voltage of its armature winding to generate a rotor position signal, an oscillation circuit for generating a three-phase signal for synchronous starting, A switching circuit that switches between the output of the oscillation circuit and the output of the position detection circuit, a gate control circuit that controls the gate of the bridge inverter based on the output signal of the switching circuit, and a switching element that constitutes the bridge inverter. A modulation circuit for modulating a current period with a modulation signal having a frequency higher than the output frequency of the bridge inverter, and changing a conduction ratio of the modulation signal. A voltage control circuit for adjusting the output voltage of the bridge inverter, a rotation speed measurement circuit for measuring the rotation speed of the brushless motor, a rotation speed command circuit for generating a predetermined rotation speed command, and a rotation speed of the brushless motor for a predetermined value. In a drive device for a brushless motor, which comprises a rotation speed control circuit for outputting a voltage command for controlling the value to the voltage control circuit, a frequency for generating a frequency upper limit signal when the oscillation frequency of the oscillation circuit exceeds a predetermined upper limit value. An upper limit signal generation circuit,
A drive device for a brushless motor, comprising a current limiting circuit for limiting a current flowing through the brushless motor during a synchronous operation period. 2. An air conditioner comprising the drive device for the brushless electric motor according to claim 1. 3. A refrigerator provided with the drive device for the brushless electric motor according to claim 1. 4. A refrigerator comprising the drive device for the brushless electric motor according to claim 1.