JPH05103479A - Load current limiting system for inverter - Google Patents

Abstract

PURPOSE:To protect a load device and an inverter body by limiting both a load current and an inverter current. CONSTITUTION:A load current limiter 8a for limiting a current for a sum of a correction current signal 6 from a voltage controller 5 and a load current feedforward signal 7 is provided. The limiter so limits that an inverter does not follow up an instantaneous overcurrent such as a rush current of a load device 16 at the time of starting and can limit a continuous overcurrent to a set value even if the signal 6 is saturated. Then, even for the sum of the output signal and a capacitor current reference of a capacitor current reference unit 3, a final inverter current command 9 is limited to an allowable current or less of an inverter body 13 by limiting the current through by an inverter current limiter 8b. Thus, the device 16 and the body 13 can be protected against the overcurrent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter load current limiting system for limiting a current applied to a load in an AC output converter such as an inverter having a filter on the output side.

[0002]

2. Description of the Related Art FIG. 3 shows a control method when an instantaneous current control is used in an inverter device having an output side LC filter. For example, a conventional current limiting method disclosed in Japanese Patent Laid-Open No. 1-3060. Is shown in the figure. In the figure, 2 is a sine wave voltage reference unit generated by the oscillator 1, 3 is a capacitor current reference unit for generating a capacitor current reference from a sine wave voltage reference, 4 is an output voltage feedback signal, 5 is a voltage control unit, 6 Is an output signal thereof, then 7 is a load current feedforward signal, and 8a is a load current limiting unit for limiting this signal. Next, 8b is a current limiting unit for limiting a signal obtained by adding the capacitor current reference, the output signal 6 and the feedforward signal 7, and the output signal 9 is an inverter current command. Reference numeral 11 is a current control unit for controlling the inverter current 10 in response to the command 9. Further, 12 is a PWM circuit, and the inverter main body 13 generates a voltage by this output signal. Then 1
Reference numeral 4 is a filter reactor, 15 is a condenser, and 16 is a load device.

Next, the principle of operation will be described. First, the sine wave voltage reference unit 2 generates a sine wave voltage reference to be supplied to the load device 16 by the oscillator 1, and then the capacitor 15 is used.
As a current to be applied to the capacitor current reference, a capacitor current reference that is 90 ° out of phase with the sine wave voltage reference is generated by the capacitor current reference unit 3 according to the capacitor capacity. The no-load voltage is established by the inverter 13 supplying this capacitor current reference to the capacitor 6. Next, the voltage control unit 5 corrects the deviation between the voltage reference and the output voltage feedback 4 so that the inverter 13 outputs the corrected current signal 6
Generate.

Next, when the load 16 is turned on, feedforward is performed so that the load current 7 flows, and the load current limiting section 8a applies load current limitation to this signal and the capacitor current reference and voltage control. The input current limiting unit 8b limits the input current to the signal obtained by adding the correction current signal 6 from the unit 5, and the output becomes the inverter current command 9 to be output by the inverter.

Next, the current control section 11 controls the inverter current command 9 so that the inverter current 10 follows the inverter current command 9 at high speed. Here, the load current limiting unit 8a limits the load current so that it does not follow an overcurrent such as an inrush current at the time of startup, and the input current limiting unit 8b limits the current limit of the inverter main body 13. By limiting the value to the value or less, the inverter body 13 is protected from overcurrent.

Next, the output signal of the current control unit 11 is compared with, for example, a triangular wave signal, and switching is performed at the intersection P.
A voltage is generated by applying this switching signal to the inverter main body 13 to the WM circuit. Next, the voltage configured by the harmonic component is supplied to the load device 16 by the filter including the reactor L14 and the capacitor 15.

[0007]

In the conventional load current limiting method described above, a limit is provided so as not to follow an instantaneous overcurrent at the time of starting the load device for the purpose of protecting the inverter itself. However, if a continuous overcurrent flows, the output voltage drops due to this current limit, and the correction current signal due to voltage control saturates.As a result, the current limit depends only on the inverter current limit. However, there is a problem that there is no protective function for the load device, such as a function that does not function as a load current limit and that may damage the load device.

The present invention has been made in order to solve the above-mentioned problems, and has a limit value for both instantaneous overcurrent at the time of starting the load device and continuous one. It is an object of the present invention to obtain a load current limiting system for an inverter having a protective function of a load device by limiting the load current as described above.

[0009]

According to the load current limiting method for an inverter of the present invention, a deviation between a reference voltage generator for generating a reference voltage to be supplied to the load of the inverter and an inverter output voltage fed back to the reference voltage. And a voltage control unit that generates a correction current signal according to the current to be output by the inverter in order to correct the deviation, and an addition value of the correction current signal and the load current output by the inverter is set to a predetermined value. Inverter current based on the sum of the load current limiter that generates and outputs a signal limited to a value less than or equal to the value, the output signal of the load current limiter, and the signal that corresponds to the no-load output current of the inverter generated according to the reference voltage A current command generator for generating a command is provided.

[0010]

According to the present invention, even if the correction current is saturated to correct the load voltage to the reference voltage due to an instantaneous overcurrent generated when the load device is started, the correction current is corrected by the load current limiting unit. Is limited to a predetermined value, and the inverter current command is generated based on the limited correction current, so that the load current can be limited according to the set value and the load device can be protected.

[0011]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to FIG.
Shown in. In the figure, those having the same functions as those in FIG. 3 described above are designated by the same reference numerals, and the description thereof will be omitted, and the operation of the present embodiment will be described.

A load current limiting unit 8a for limiting the current of the signal obtained by adding the correction current signal 6 output from the voltage control unit 5 and the load current feedforward signal 7 is provided. This current limitation is performed so that the inverter does not follow an instantaneous overcurrent such as a rush current at the time of starting the load device 16, and the correction current signal 6 is temporarily saturated with respect to a continuous overcurrent. Can also be restricted according to the set value. Next, the inverter current limiting unit 8b also limits the current of the output signal and the signal obtained by adding the capacitor current reference by the capacitor current reference unit 3 so that the final inverter current command 9 is sent to the inverter main body 13. It is limited to the allowable current or less and is protected from overcurrent.

In this way, the load device 16 and the inverter current limit are doubled to limit the current.
Also, the inverter body is protected from overcurrent, and the current limit value can be set independently on the load side and the inverter side.

Example 2. The current limiting method of FIG. 1 described above can be applied not only to a single-phase inverter, a three-phase inverter, or an inverter but also to other instantaneous control type converters such as a cycloconverter.

Further, in the above embodiment, the construction method in the case of being applied to the follow-up control system in which the voltage reference of the sine wave is input has been described. In FIG. 2, the constant value control system using the dq axis synchronous rotation coordinate system. A configuration diagram when current limitation is applied to is shown.

In this case, it is a big difference that three three-phase / two-phase converters 18a, 18b, 18c and one two-phase / three-phase converter 19 are dealt with in comparison with FIG. Similarly, it is possible to provide a load and an inverter current limit, and the same effect is obtained.

[0017]

As described above, since the current limiting method in the present invention is configured to limit both the load current and the inverter current, it is possible to protect the control device and the load device, and to provide a highly reliable device. Further, there is an effect that both limit values can be designed separately.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a current limiting method according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a current limiting system showing another embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional current limiting method.

[Explanation of symbols]

 1 Oscillator 2 Sine wave voltage reference part 2a Voltage reference part 3 Capacitor current reference part 4 Voltage feedback signal 5 Voltage control part 6 Correction current signal 7 Load current feed forward 8a Load current limiting part 8b Inverter current limiting part 9 Inverter current command 13 Inverter Main unit 16 load device

Claims (1)

[Claims] 1. A reference voltage generating unit for generating a reference voltage to be supplied to a load of an inverter, and a deviation between the reference voltage and the inverter output voltage fed back are input, and the inverter should output to correct the deviation. A voltage control unit that generates a correction current signal according to the current, and a load current limiting unit that generates and outputs a signal in which the addition value of the correction current signal and the load current output by the inverter is limited to a predetermined value or less, A load current limiting unit, and a current command generating unit that generates an inverter current command based on a sum value of a signal corresponding to the no-load output current of the inverter generated according to the reference voltage. Inverter load current limiting method.