JPS623384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting intermittent load current, and more particularly to a current intermittent detection device suitable for controlling load current of a power conversion device.

2. Description of the Related Art Power conversion devices that supply power from a power source to a load by controlling a power conversion circuit consisting of a semiconductor switch such as a thyristor are widely used in various fields. For example, there are cases where voltage is applied to a DC motor by controlling the phase of a three-phase bridge circuit in which an AC power source is configured with a thyristor. In such a power conversion device, a motor current control system is generally configured in order to protect the motor and the power conversion circuit, and to improve the responsiveness of the motor speed control system.
In this case, the motor current may be continuous or intermittent depending on operating conditions such as motor rotation speed and ignition phase. For example, as shown in Figure 1, a three-phase AC power supply
In a power conversion device consisting of an AC, thyristors S ₁ to _{S 6} , and a DC motor DCM, the characteristics between the firing phase α of the thyristors S ₁ to _{S 6} , the DC current I _d and the DC voltage E _d are shown in Figure 2. It's becoming like that.

From Figure 2, I _d when the current is continuous and when the current is intermittent.
It can be seen that the characteristics between -E and _d are significantly different. Note that a broken line A indicates a boundary line between when the current is continuous and when the current is intermittent. The response characteristics differ depending on whether such current is continuous or intermittent. As a countermeasure for this, it has been proposed to detect that the current is in an intermittent state and control the current by changing the control method between the intermittent state and the continuous state. In this case, it is necessary to detect that the current is intermittent.

Conventionally, discontinuity has been detected by detecting the instantaneous value of the motor current and processing its waveform. However, since this method makes judgments based on the instantaneous waveform of the current, it is susceptible to disturbances and noise and is prone to malfunction. In particular, if a malfunction occurs when a large current is flowing, the control system becomes unstable, which has a large effect.

The purpose of the invention is to detect the average value of the operating state,
A means for determining whether the current is intermittent or continuous is provided, and the reliability of the detection signal is increased by checking the rationality of the conventional method for detecting intermittent current, and then outputting that the current is intermittent. An object of the present invention is to provide a current intermittent detection device for a power conversion device that can output a signal with improved performance.

That is, in the present invention, the current intermittent determination means is provided with the characteristics shown by the broken line _A in FIG _. A rationality check is performed when a signal with intermittent detection is generated.

An embodiment of the present invention will be described below with reference to FIG. 3 and subsequent figures. FIG. 3 shows an embodiment of the present invention. 1 is a power conversion circuit composed of thyristors shown by S ₁ to S ₆ in Fig. 1, 2 is a filter for smoothing and detecting the DC voltage E _d , and 3 is a DC transformer for detecting the motor current. (hereinafter referred to as DCCT) 4 is a filter for smoothing and detecting the DC current _Id ;
Reference numeral 5 indicates a function generator indicated by the broken line A in FIG. As shown in the figure, it is composed of a comparator 9, a monostable multivibrator 10, a resistor R, a capacitor C, and an OR circuit 11.

In this configuration, the motor current i _d detected by the DCCT 3 is smoothed by the filter 4 to become I _d . When this signal I _d is passed through the function generator 5, an output E _da shown by the broken line A in FIG. 2 is output. On the other hand, the DC voltage e _d is smoothed by the filter 2 and becomes E _d . Therefore, the comparator 6 compares E _d and E _da .
Now, if E _d > E _da , the current i _d is continuous, and the output of the comparator 6 becomes "0" level. Furthermore, when E _d ≦E _da , the current i _d is intermittent, and the output of the comparator 6 becomes "1" level.

On the other hand, the output i _d of the DCCT directly becomes an input to the current intermittent detection circuit 8 . This circuit is, for example, a circuit as shown in FIG. The comparator 9 generates a signal d which is at the "1" level in the period where the output i _d of the DCCT is zero, as shown in FIG. The monostable multivibrator 10 generates a "1" level signal for a certain period of time in synchronization with the falling edge of the signal d. For this reason, when a signal like d in FIG. 5 is input, the waveform becomes like e. Further, the signal d is input to the OR circuit 11 via a filter composed of a resistor R and a capacitor C. As a result, the output signal f of the OR circuit has a waveform as shown in FIG. This waveform provides a signal that detects that the current is intermittent.

The signal f obtained in this manner and the output signal g of the comparator 6 are input to an AND circuit 7, and a signal h is obtained which becomes the "1" level only when the two match and indicate current interruption. This signal h is used as a signal indicating that the current is intermittent.

As explained above, in the embodiment shown in FIG. 3, even if the current intermittent detection circuit 8 malfunctions, the comparator 6
Since the rationality is checked by the output g of , highly reliable current intermittent detection can be performed.

In the embodiment shown in FIG. 4, I _d and E _d are used as input signals when determining whether the current is intermittent, but instead of E _d , the ignition phase α, motor rotation speed, or induced voltage is used. The second thing that can be done using etc.
It is clear from the characteristics of the figure. Furthermore, when the current control system is implemented by a digital arithmetic processing device such as a microprocessor, the processing of the function generator 5 and comparator 6 shown in FIG. 3 can be performed by the microprocessor, which simplifies the hardware.

Furthermore, although Fig. 3 shows the case of detecting the motor current of a DC motor, it also applies to cases where current is flowing to a load via a power conversion circuit, and where the load current is intermittent or continuous. It is obvious that this method can be applied as a load current detection method in many cases.

As described above, according to the present invention, it is possible to detect intermittent current with high reliability.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a power conversion device, Fig. 2 is a characteristic diagram showing the relationship between the average value of the load current of the power conversion device in Fig. 1 and the average value of the output voltage of the power conversion circuit, and Fig. 3 4 is a detailed circuit diagram of an example of the current intermittent detection circuit of FIG. 3, and FIG. 5 is a time chart showing the operation of FIG. 4. 1...Power conversion circuit, 2...Filter, 3...
DCCT, 4...Filter, 5...Function generator, 6
...Comparator, 7...AND circuit, 8...Current intermittent detection circuit.

Claims (1)

[Claims] 1. A power conversion device configured with a thyristor, a detection means for detecting a DC voltage of the power conversion device,
It has a current intermittent judgment means that judges whether the load current is continuous or intermittent based on the output of the detection means, and a current intermittent detection means that detects the instantaneous value of the load current and detects the current intermittent state from its waveform. A current intermittent detection device for a power conversion device that detects that a load current is intermittent when both the current intermittent determining means and the current intermittent detecting means determine that the load current is intermittent.