JPH0474954B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for operating an induction motor with a brake by an inverter circuit comprising a semiconductor switch to which DC power is input.

FIG. 1 shows the circuit configuration of a system that operates an induction motor with a brake using an inverter circuit consisting of a semiconductor switch that receives DC power as input. In the figure, 1 is a DC power supply, and 2 is an inverter circuit constructed using power transistors as semiconductor switches. Note that diodes to be connected in parallel to each power transistor are omitted in the drawing. Reference numeral 3 denotes a pulse control circuit, which supplies a base current to control on/off of each of the power transistors. 4 is an induction motor with a brake, and is connected to the output of the inverter circuit 2.

Conventionally, when the pulse control circuit 3 receives a driving command signal, the control circuit 3 supplies base current to the power transistors 21 to 26, operates the inverter circuit 2, generates alternating current at the output, and outputs the alternating current. Induction motor with brake 4
was running.

Now, if we consider a system using a general induction motor instead of an induction motor with a brake, we will find that if we control the ratio of the output voltage V and output frequency f of the inverter circuit 2 to be constant, the torque It is possible to control the speed of the induction motor while keeping it constant. Therefore, it has conventionally been possible to drive the induction motor with a small capacity inverter while suppressing the rush current at startup by applying the output voltage of the inverter 2 to the induction motor while maintaining a constant V/f ratio. ing. Incidentally, in order to secure a predetermined torque in a low frequency region, in reality, control is usually performed using V=Af+B.

A typical induction motor with a brake has a built-in spring-controlled AC electromagnetic brake on the non-coupled side of the motor, and when voltage is applied to the motor, voltage is also applied to the coil of the brake electromagnet, and the attraction force of the electromagnet is applied. The control spring is pushed back to release the brake and rotate the electric motor. In this case, when the power is turned off, the brake disk is pressed against the brake lining by the brake spring, and a control torque is applied to bring the vehicle to a sudden stop. Therefore, in an induction motor with a brake, it is necessary to remove the brake before starting the motor.

A high AC voltage is required to attract the brake electromagnet, and for this reason, conventional methods have been used such as increasing the voltage of the DC power supply 1 sufficiently, or installing a transformer on the output side of the inverter 2 to boost the voltage. Ta. According to page 795 of "Electrical Engineering Handbook" (first edition published on April 10, 1978), the average value of the attractive force of an AC electromagnet is F=10 ⁷ /16πB ² gmS ...... (2) However, Bgm : Maximum value S of alternating magnetic flux in the air gap: Represented by the area of the air gap.

In addition, the attractive force of the DC electromagnet is F=2πS/δ ² (U−ΣHili) ² ×10 ^-7 ………(3) However, U: Total magnetomotive force of the magnetic path δ: Gap length Hi: Each magnet in the iron core Path magnetic field strength i: Expressed by the length of each magnetic path in the iron core.

From equations (2) and (3), find the AC applied voltage Vac and DC applied voltage Vdc necessary for the same electromagnet to obtain the same attraction force F with the same stroke.

The number of turns of the electromagnet coil is N, the winding resistance is r,
When the air gap length (stroke) is δ, the inductance of the coil is L, and by applying an AC voltage, Bgm
If Im is ^the maximum value of the current when generating a magnetic flux φm corresponding to (2) ² ………(4) However, Im=Nφm/L=NBgmS/L L=μoSN ² /δ The DC applied voltage is Vdc=rIdc...(5) However, Idc=U/NU= ^δ2 /2πs×F/ ^10-7 +ΣHili...(3) This is a modification of the equation. For example, the number of turns of the coil is 1538
When the winding resistance is 48.8 [Ω], the total product of the magnetic field strength and length of each part of the core is 308 [AT], and the stroke is 20 [mm], an electromagnet with a gap area of 12.74 [cm ² ] The voltage when generating a suction force of 2.13 [Kg weight] is N = 1538, r = 48.8 [Ω], ΣHili = 308
[AT], δ=20×10 ^-3 [m], S=12.74×10 ^-4
Substituting [m ² ], F=2.13×9.8=20.9[N] into equations (4) and (5), Im=2.97[A] L=0.189[H] Bgm=0.287[T] Idc=2.3 [A] is obtained, and when applying 30Hz AC, f = 30
[Hz] Vac (30Hz) = 127 [V] When applying direct current, it is predicted that Vdc = 112 [V].

The value of Vac calculated for f=20 to 60 [Hz] as described above is represented by the broken line a' in FIG. Furthermore, in Figure 2, the stroke of the electromagnet is 20 mm,
Special attraction voltage a, holding voltage characteristics b, of the brake electromagnet for the frequency to obtain an attraction force of 2.13 kg,
An example of the results of actually measuring the inverter output voltage characteristic c and the attraction voltage d when DC voltage is applied is shown. As is clear from the figure, when applying a DC voltage, 124V or more was required to obtain the same attraction force.
On the other hand, when an AC voltage is applied from an inverter circuit, 134V or more is required, and if this is supplied by a rectangular wave output inverter circuit, the output voltage of the DC power supply 1 is required to be approximately 181V or more. That is, in order to obtain an AC output that allows this brake electromagnet to function sufficiently, it is necessary to make the voltage of the DC power source sufficiently high, or to use means such as installing a transformer on the inverter output side to boost the voltage.

As mentioned above, when driving an induction motor with a brake using an inverter with a constant V/f AC output voltage characteristic, it is necessary to apply a high voltage and remove the brake before starting the motor. Sometimes a large current must flow, and it is necessary to use large-capacity power transistors 21 to 26 constituting the inverter circuit 2. For this reason, it is necessary to keep V/f constant and suppress the rush current at startup while reducing the inrush current. The intention of driving a motor with a capacitive inverter cannot be achieved. In addition, particularly in the case of a small capacity, the price, volume, and weight of the storage battery used in the DC power supply 1 are not proportional to the capacity, so this system has disadvantages in terms of price, volume, and weight. In addition, even if you try to obtain the same voltage by increasing the capacity of the storage batteries, reducing the number of batteries connected in series, and inserting a step-up transformer on the output side, it is difficult to eliminate the above drawbacks because it is necessary to add a transformer. be.

The present invention was developed as a result of studying an operation control device that can operate an induction motor with a brake using a relatively small capacity storage battery and an inverter circuit.
This was done by focusing on the fact that the attraction force characteristics of brake electromagnets are different when AC voltage is applied and when DC voltage is applied, and that once attraction is achieved, the attraction state is maintained up to a considerably low voltage. The gist is that in an operation control device for an induction motor with a brake, which is composed of a DC power supply, an inverter circuit, and a pulse control circuit, the inverter circuit is composed of a plurality of semiconductor switches, takes the DC power supply as input, and its output is The pulse control circuit is connected to the coil of the induction motor and its brake electromagnet, and the pulse control circuit controls the semiconductor switch on and off, so that the output of the inverter circuit becomes DC when the induction motor with brake is started. The invention is characterized in that the output of the inverter circuit is controlled to become alternating current after a certain period of time.

The present invention will be explained below with reference to the drawings.

FIG. 3 is a diagram showing operating waveforms of the inverter circuit 2 built into the operation control device of the present invention. 1st
The DC power supply 1 in the figure is divided into two parts, and its neutral point O is set as a virtual reference potential. The time point when the pulse control circuit 3 receives the driving command signal is defined as to, and the time after a certain period of time is defined as t1. A base current is supplied so that only the power transistors 21 and 26 are turned on at time t0. Each output terminal u of inverter 2,
The voltages appearing between v, w and the neutral point O of the DC power supply 1 are Vu-o, Vv-o, and Vw-o, and the voltages appearing between each output terminal u, v, and w are Vu-v, Vv-
Let w, Vw−u. Between t0 and t1, Vu−0 is
-1/2E, Vv-o is O, Vw-o is -1/2E, Vu-v and Vv-w are O,
-E appears in Vw-u. At this time, it can be seen from FIG. 2 that the DC voltage required for the coil 42 of the brake electromagnet should be 124 V or more.

From the fixed time point t2, the pulse control circuit 3 switches control so that the output of the inverter circuit 2 becomes, for example, an AC output of 25 Hz. That is, by turning on and off the power transistors 21, 14, 22, 25, and 23, 26 with a phase difference of 120 degrees, three-phase alternating current is obtained at the output terminals u, v, and w.

As is clear from FIG. 2, the holding voltage when an alternating current voltage is applied to the brake electromagnet is sufficiently lower than the attraction voltage, so the DC power supply 1 required to maintain the holding may remain at a low voltage. The brake has already been released by applying a DC voltage sufficient for starting, and even if the application of AC voltage is switched to, the brake continues to be released due to its holding force, so that the motor starts to start. Therefore, the DC power supply 1 in the embodiment only needs to have a voltage of 124V or higher when the brake is removed and the voltage is set to 124V or higher. Any shortcomings that must be avoided are eliminated. Further, when switching the inverter circuit 2 to AC output from time t1, a method is adopted in which the ratio V/f of the output voltage V and the output frequency f is kept constant, and the induction motor is operated at a low voltage and low frequency. Therefore, it is economical to use power transistors of a large capacity type only for 21 and 26, and to use power transistors with a smaller capacity for transistors 22 to 25 than 21 and 26.

As described above, the inverter-based operation control device for an induction motor with a brake according to the present invention uses a small-capacity, low-cost storage battery as a DC power source to control a relatively small-capacity inverter circuit and operate an induction motor with a brake. It is possible and the benefits are great.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a system that operates an induction motor with a brake using an inverter circuit that receives DC power as input, and Figure 2 is a diagram showing an example of the attractive force and holding force characteristics of the brake electromagnet in the induction motor with a brake. FIG. 3 is a diagram showing operating waveforms of the inverter of the operation control device of the present invention. 1...DC power supply, 2...Inverter circuit, 21
~26...Power transistor, 4...Induction motor with brake.

Claims (1)

[Scope of Claims] 1. An operation control device for an induction motor with a brake, which is composed of a DC power supply, an inverter circuit, and a pulse control circuit, wherein the inverter circuit is composed of a plurality of semiconductor switches, and the DC power supply The output of the inverter circuit is connected to the coil of the induction motor and its brake electromagnet, and the pulse control circuit controls the semiconductor switch on and off, and when the induction motor with brake is started. An operation control device for an induction motor with a brake that controls the output of the inverter circuit to become DC, and after a certain period of time, controls the output of the inverter circuit to become AC.