JPS6355293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for a power converter capable of generating variable frequency alternating current power. The present invention relates to an improved converter for driving a commutatorless motor in order to prevent system malfunctions caused by residual magnetic flux of the transformer.

Conventionally, non-commutator motors were operated at a constant speed using commercial power, but in order to vary the speed according to the situation at the time, a variable frequency power converter can be used, or large non-commutator motors can be operated smoothly. Various systems have been considered when using a power conversion device to start and accelerate a vehicle.

The single-line system diagram shown in Figure 1 is a diagram showing a typical configuration example conventionally used.
AC power at a commercial frequency is supplied to a power conversion device 14 via a strand disconnector 12 and a transformer 13.
The power converter 14 includes a rectifier circuit 15 that converts alternating current into direct current, a direct current reactor 16 that smoothes direct current,
It consists of an inverter circuit 17 that converts direct current to alternating current of any frequency. The output of the power converter 14 is connected to a commutatorless motor 20 via a transformer 18 and a shunt breaker 19 . On the other hand, the AC power source 11 is connected to the non-commutator motor 20 via a shield breaker 21 as a bypass circuit, and the power source can be selected by switching the shield switches 19 and 21. Power converter 14
are a speed standard setting device 22, a run/stop command 23,
Speed detector 24 directly connected to commutatorless motor 20
The control circuit 25 receives the signal from the rectifier circuit 1.
5. It operates by generating a signal to control the switching elements constituting the inverter circuit 17. FIG. 2 shows a detailed circuit in which a thyristor is used as the main switching element constituting the rectifier circuit 15 and the inverter circuit 17. Now, with this configuration,
Since the output of the power conversion device 14 is an alternating current whose frequency changes, the problem is the alternating current power that can be transmitted via the transformer 18. That is, it is necessary to use the transformer 18 from low to high frequencies without saturating it, but the residual magnetic flux of the transformer 18 may cause problems in the system. Figure 3 depicts the B-H characteristics of the one-phase iron core that constitutes the transformer 18. If the voltage/frequency ratio (hereinafter referred to as v/f) is the rated value, then A→B→C →D→A
is driven through each point of , and never saturates. However, when the commutatorless motor stops driving in a certain state, the position of the residual magnetic flux is determined by the state immediately before the stop, and is difficult to control. For example, if there is residual magnetic flux at the position D', then D'→A
When changing to
In the current waveform shown in the figure, the R phase current on the power converter side
Assume that the R-phase current on the non-commutator motor side becomes I _R2 ' with respect to I _R1 . However, if the residual magnetic flux is at the position B', the change from B' to A will result in less power transmission, and for the same I _R1 , the R-phase current on the non-commutator motor side I _R2 ''. Yes, in this case time t ₁₁
Even if a start command is received, if the commutatorless motor does not rotate with the first pulse current, a start jam will occur and the system will malfunction. As a technique to improve these shortcomings, it has been proposed to flow an exciting current to the transformer 18 with the breaker 19 turned on, but if there is residual magnetic flux on the D' side from 0,
It's already close to being reset, so
A large current is required to reset to D'. Furthermore, if there is residual magnetic flux on the B' side from 0, unnecessary power may be transmitted for resetting, and depending on the state of the commutatorless motor 20, there is a risk of reverse rotation.

The purpose of this invention was to solve the above-mentioned drawbacks, and to reset the residual magnetic flux with an extremely small amount of current by opening the circuit breaker or inserting an impedance to flow an exciting current to the transformer. Therefore, it is an object of the present invention to provide a highly reliable commutatorless motor drive conversion device that is economical and can be started reliably without adding large-capacity equipment.

FIG. 5 shows an embodiment of the present invention. The difference between this diagram and Figure 1 is that in response to the signal _S1 from the operation/stop command 23, a command is given to close the shield breaker 19.
S ₂ , a control that generates a signal S ₃ that gives a gate pulse to the rectifier circuit 15 and the inverter circuit 17 of the power converter 14 to instruct the excitation current to flow, and a signal S ₄ that instructs the control circuit 25 to perform normal operation. circuit 26
The point is that A time chart of signals S ₁ to S ₄ is shown in FIG. In the same figure, from time _t21 until time _t22 when the operation command is issued, the ladder and disconnector 19 are open and excitation current flows, and at time _t22 , the excitation current is reduced to zero, and at time _t23 , Insert the disconnector 19,
Starting operation begins after time t ₂₄ . FIG. 7 shows the phases in which the excitation current should flow. In the figure, it is shown that a small excitation current is flowing during the period from time t ₂₁ to time t ₂₂ , but at time t ₂₄
In subsequent startup operations, the exciting current is passed with a phase advance of 180° relative to the initial current phase.

Here, the initial current phase when entering the starting operation can be known from the signal of the speed detector 20, as is well known. That is, in the case of a non-commutator motor, since it is well known that the position detector is also used as the speed detector 20, the speed detector 2
From the signal of the position detector which also serves as 0, it is possible to know the initial current phase and phase when entering the startup operation. The configuration of the iron core of the transformer determines which phase the excitation current should be in to achieve the most effective reset; in the case of a single-phase transformer, it will advance 180 degrees, and in the case of a three-phase transformer, it will advance 180 degrees. When configuring it with a 60° to 80° advance, it is effective. Figure 8 shows the path through which the residual magnetic flux is reset by this excitation current, and the residual magnetic flux is B', 0,
No matter where it is in D′, B′(0, D′)→C′→
It is reset with D'. The reason why this reset is performed using a small excitation current is to open the shield breaker 19 and remove the current flowing to the load, and all the current flowing from the power converter to the transformer becomes the excitation current. The residual magnetic flux can be completely reset by flowing a current corresponding to the excitation current that obtains the rated v/f.

FIG. 9 shows another embodiment of the invention. The difference between this figure and FIG. 5 is that a control circuit 27 is provided that inverts the signal S ₂ during operation, and when the shroud breaker 19 opens due to the signal S ₂ ′, the breaker 28 and the impedance 29 open. The point is that a bypass circuit is provided. According to this embodiment, some load current may flow to the non-commutator motor via the transformer 18 and the impedance 29, but if the impedance is made large enough, the same effect as the embodiment shown in FIG. 5 can be obtained. be able to.

From the above explanation, in a configuration in which a transformer and a breaker are installed between a variable frequency power converter and a non-commutator motor, it is possible to disconnect the breaker or insert an impedance at that time. To provide a converter for driving a non-commutated motor having the following features by making the impedance of the transformer sufficiently high even if the transformer bypasses the breaker and passing an excitation current that resets the residual magnetic flux of the transformer. be able to.

(1) It is economical because the residual magnetic flux can be reset with an extremely small excitation current without adding any special equipment, or even if it is added, just by adding equipment whose capacity is sufficiently small compared to the capacity of the main circuit. It is a power conversion device.

(2) Even if the current is extremely small, most of it becomes excitation current, so it is a highly reliable power conversion device that can reliably reset the magnetic flux.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional device, Fig. 2 is a detailed view of a part of Fig. 1, Figs. FIG. 6, FIG. 7, and FIG. 8 are diagrams for explaining the operation of the present invention, and FIG. 9 is a configuration diagram showing another embodiment of the present invention. 11... AC power supply, 12, 19, 21, 28... Line breaker, 13, 18... Transformer, 14... Power converter, 15... Rectifier circuit, 16... DC reactor, 1
7... Inverter circuit, 20... Commutatorless motor, 2
2...Speed standard setter, 23...Run/stop command, 2
4... Speed detector, 25, 26, 27... Control circuit,
29...Impedance.

Claims (1)

[Claims] 1. In a non-commutator motor drive converter that drives a non-commutator motor via a transformer and a circuit breaker, the first current flows at the start of the commutator-less motor prior to starting the commutator-less motor. means for controlling the converter to supply an excitation current that is 60° to 180° ahead of the phase of the phase current for a predetermined time;
A device comprising: a means for turning on the shield breaker after the predetermined time has elapsed and starting the converter; and a bypass circuit for switching the commutatorless motor to the commercial power supply side and operating the converter after the start is completed. Commutator motor drive conversion device.