JPH0327788A - Dynamic brake for brushless synchronous motor - Google Patents

Abstract

PURPOSE:To inexpensively brake a motor in a motor low speed rotating range without necessity of a mechanical unit at a motor shaft by adding a device for consuming generating energy of a brushless synchronous motor to an inverter for driving the motor. CONSTITUTION:When a braking transistor 6 ia turned ON by a brake controller 9, 3-phase induction voltages are three-phase full-wave rectified by flywheel diodes DX-DZ and rectifying diodes DX'-DZ'. Further, a braking resistor 5 consumes as thermal energy due to the flow of a current by a full-wave rectified voltage. Accordingly, since a deceleration torque is consumed as generating energy via the resistor, braking time can be shortened as compared with the case in which it is stopped only by mechanical loss.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a brushless synchronous motor, and particularly to a braking device suitable for shortening the time during deceleration of a brushless synchronous motor.

[Conventional technology]

Regarding the braking of brushless synchronous motors, see the literature Basics and Applications of Brushless Servo Motors, pages 200 to 203.
As described on the page, there are friction brakes that apply external frictional force to the motor shaft to perform braking, and a conductive cylinder that is directly connected to the motor shaft and a DC current passed through a separate excitation coil to generate magnetic flux. When the above-mentioned cylinder rotates in this magnetic flux, eddy currents are generated in each part of the cylinder, and the electromagnetic force generates braking force in the eddy current brake and the conductive disk used in the eddy current brake. There are hysteresis brakes that use hysteresis materials, and regenerative braking in which when the motor rotates above the no-load speed, the motor generates electricity as a generator, and this electricity is regenerated to the power source to use the motor as a brake. ．． [Problem to be solved by the invention] The above conventional technology requires a mechanical device on the motor shaft to perform braking, or a device that regenerates the generated energy into a power source. It is difficult to install a braking device in the case of a high-speed rotating shaft or a floating rotating shaft, and for the latter, the braking force is weak in the low-speed rotating region.
Both methods have the problem that they require special equipment and are expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a braking device for a brushless synchronous motor that does not require a mechanical device on the motor shaft to perform braking and can perform braking at low cost in a low-speed motor rotation range.

[Means to solve the problem]

The above object can be achieved by adding a device that consumes the energy generated by the brushless synchronous motor to an inverter device that drives the brushless synchronous motor.

[Effect]

A brushless synchronous motor has a rotor made of permanent magnets. When the rotor is free running, it induces a voltage in the stator coil. This is called induced voltage, and 3
In the case of a phase motor, the voltage is a three-phase sine wave voltage. Further, the braking control circuit determines whether the motor rotation speed has reached the braking rotation speed. The rectifier circuit rectifies this three-phase induced voltage and converts it into direct current. Braking force can be obtained by consuming the induced voltage rectified by the rectifier circuit, that is, the generated energy, as heat through the resistance, and converting the rotational energy of the motor rotor into thermal energy.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall structure of an inverter transistor, a braking circuit, and its control circuit.

In FIG. 1, 1 is a brushless synchronous motor, and 2 is an inverter, consisting of transistors QU-QZ and flywheel diodes DU-DZ. 3 is a rectifier diode consisting of DX' to DZ'. 5 is a braking resistor that consumes the energy generated by the motor. 6 is a braking transistor that turns the braking resistor 5 on and off. 7 is a rotor position detection circuit, which is a circuit for detecting the frequency and phase of the motor rotor. 8 is a speed control circuit, which is a circuit that controls the rotation speed of the brushless synchronous motor 1. Reference numeral 9 denotes a braking control circuit, which determines the braking rotational speed based on the speed signal from the speed control circuit 8 and turns on the braking transistor 6. Figure 2 shows the induced voltage waveform of the brushless synchronous motor 1.
Since the motor is three-phase, it is a three-phase sine wave.

Figure 3 shows the overall configuration of the braking circuit, and shows the part related to braking in Figure 1. In FIG. 1, when the brushless synchronous motor 1 is decelerated, the motor rotation speed is determined from the rotor position detection circuit 7 and the speed control circuit 8, and is used as a speed signal. The braking control circuit 9 determines from the speed signal that the braking starting rotation speed has been reached, and provides an on signal to the braking transistor 6. The operation of the braking circuit will be explained below with reference to FIGS. 2 and 3.

Since the brushless synchronous motor 1 has a rotor made of a permanent magnet, when free running, it generates a triwa sine wave voltage as shown in FIG. The amplitude and frequency of this voltage are proportional to the motor rotation speed, and the higher the motor rotation speed, the larger the amplitude and the higher the frequency. Therefore, it can be considered as a three-phase power supply as shown in FIG. Here, when the braking transistor 6 is turned on by the braking control circuit 9, the Sanwa induced voltage is three-phase full-wave rectified by the flywheel diodes DX to DZ and the rectifying diodes DX' to DZ', as shown in FIG. A full-wave rectified waveform is obtained as shown in FIG. 2, and a current flows through the braking resistor 5 according to its resistance value and the full-wave rectified voltage, and is consumed as thermal energy by the braking resistor 5.
Here, if the resistance value of the braking resistor 5 is R, the penetrating moment of the motor rotor is J, the motor induced voltage coefficient is Kω, the motor braking start angular velocity is ωH, and the deceleration angular velocity is ωL, then the braking torque is as follows.

From τ=-Jdω/dt, Ka・(Ll”/(RX(&))=-J dω/d
t Therefore, d t=-J − R/(Kω2・ω)Xdω,
By integrating the above equation, the braking time T is calculated as T=-J aR/K(
1)"X 12n (ωo/ωL). Let T' be the deceleration time due to mechanical loss only, and T' - T is the time shortened by adding this braking circuit.

In FIG. 5, the braking transistors constituting the braking circuit in FIG. 1 are replaced with mechanical contacts, and it is easy to isolate the main circuit including the inverter section transistor from the control circuit. Figure 6 shows the braking circuit shown in Figure 1 with an overcurrent/overload protector installed in case the current flowing through the braking resistor becomes an overcurrent or the generated energy increases and the braking resistor becomes overloaded. This protects the braking circuit in the event of a load condition.

〔Effect of the invention〕

According to the present invention, since the deceleration torque is consumed as generated energy by the braking resistance, the braking time can be shortened compared to the case where the vehicle stops due to mechanical loss alone. Further, the braking circuit according to the present invention can be configured inside an inverter device that drives a brushless synchronous motor, and in order to control the on/off of the braking resistor,
The structure can be easily and inexpensively constructed. In addition, when used in high-speed rotating bodies such as turbo-type vacuum pumps, especially when non-contact bearings such as electromagnetic bearings are used in the future, friction loss is extremely small, and since the rotor is in a vacuum, there is no friction with the air. No loss.

Therefore, it is very difficult to install a mechanical braking device, but according to the present invention, the structure can be simplified because no mechanical mechanism is required.

Furthermore, the braking force can be varied by changing the resistance value and capacity of the braking resistor.

[Brief explanation of drawings]

The drawings are explanatory diagrams related to the present invention, and FIG. 1 is a diagram showing the overall structure of an inverter including a braking circuit for a brushless synchronous motor;
Fig. 2 is a Sanwa induced voltage waveform diagram, Fig. 3 is a diagram of the structure of the braking circuit, Fig. 4 is a full-wave rectified waveform diagram of Sanwa induced voltage, and Figs. 5 and 6 are braking circuit diagrams. It is a diagram showing the structure of a circuit. l: Brushless synchronous motor, 2: Inverter transistor, 3: Rectifier diode, 5: Braking resistor, Z Figure 3 Figure 4 Figure 5 Figure Atsushi 6 Figure

Claims (1)

[Claims] 1. In a brushless synchronous motor, a means for determining a motor braking rotation speed, a means for rectifying a motor back electromotive voltage,
A dynamic braking device for a brushless synchronous motor, characterized by comprising means for consuming energy generated by the motor.