JPH06160438A - Inverter output current detection method - Google Patents

Abstract

PURPOSE:To detect the output current of an inverter with an AC current transformer over the full variable extent of the output frequency of the inverter including direct currents. CONSTITUTION:An AC current transformer(ACCT) 5 having two inputs on its primary side is made to function as if the ACCT 5 has a normal current transforming function against the output current of a voltage type inverter in the full frequency region of the inverter irrespective of the positive and negative polarity of the output current and almost irrespective of the frequency of the output current by changing the resultant magnetic flux in the iron core of the ACCT 5 in accordance with the period of a carrier frequency supplying the currents respectively supplied to the upper arm composed of a transistor 1 and diode 2 and lower arm composed of a transistor 3 and diode 4 in one arbitrary phase of the main circuit bridge constitution of the ivnerter to the primary-side two windings of the ACCT 5 with opposite polarities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting method for detecting an output current of an inverter including an extremely low output frequency region by an AC current transformer.

[0002]

2. Description of the Related Art Conventionally, in the output current detection of an inverter whose output frequency variable range is extremely wide, if an AC current transformer is used as a current detection element, for example, the frequency value on the low frequency side such as zero to several H _Z can be determined. In some cases, iron core saturation of the AC current transformer may occur and accurate current detection may not be possible. In this case, it is known to use a DC current transformer instead of the AC current transformer.

Incidentally, FIG. 3 is a circuit diagram showing an embodiment of the conventional method as described above, showing the case of detecting an output current of any one phase in the main circuit bridge configuration of the voltage source inverter, and 1 is the above An upper arm transistor for switching in any one phase, 2 is an upper arm diode for commutation connected in parallel to this transistor 1 in reverse polarity,
Reference numeral 3 is a lower arm transistor for switching in any one phase, 4 is a lower arm diode for commutation antiparallel to the transistor 3, and 6 is the arbitrary one taken out from a series connection point between the upper and lower arm transistors. It is an AC current transformer (ACCT) that transforms and detects the inverter output current in the phase.

[0004]

However, the DC current transformer used in the above case is more expensive than the AC current transformer, and the use of the DC current transformer requires the inverter as a device. It had to be expensive.
In view of this, the present invention provides a current detection method capable of detecting an output current of an inverter, which has a wide variable range of its output frequency and whose minimum value is extremely small, using an AC current transformer in the same manner as a DC current transformer. The purpose is.

[0005]

In order to achieve the above object, an inverter output current detecting method according to the present invention is a method for detecting an output current in an arbitrary phase of a voltage source inverter, and a primary side thereof. A primary and secondary input type AC current transformer having two sets of windings with the same number of turns is provided for each current detection phase in the main circuit bridge configuration of the inverter, and two sets of the primary side of the current transformer are provided. In each of the windings, the output currents of the upper and lower arms in the current detection phase of the bridge configuration are made to flow so as to have opposite polarities, and the inverter output current is transformed from the secondary winding of the current transformer in the current detection phase. Let's get the output.

[0006]

In the main circuit bridge structure of the voltage type inverter, the switching elements such as power transistors forming the upper and lower arms of each phase are controlled so as to perform an opening / closing operation conjugate with each other while following the cycle of the carrier frequency. That is,
When the upper arm element is ON (closed), the lower arm element is OFF (open), and conversely, when the upper arm element is OFF, the lower arm element is ON. To be done.

Further, the inverter output current in an arbitrary phase taken out from the series connection point between the upper and lower arm elements in the bridge structure is synthesized by the upper and lower arm currents in the corresponding phase flowing into the series connection point at different timings. Are formed. On the other hand, if the polarity of the DC power supply applied to both ends of the series connection of both arms is taken as a reference and the arm current polarity in the direction from the positive pole to the negative pole of this power supply is made positive, the currents flowing through the upper and lower arms will reverse each other. It will have the same polarity.

That is, the inverter output current is a combination of the upper and lower arm currents having positive and negative inversion polarities and shifted by a period corresponding to the cycle of the carrier frequency, and the polarity is specified at the time of combination. Either positive or negative. For example, when the polarity of the inverter output current is positive, that is, in the outflow direction from the inverter to the load, the inverter output current is equal to the positive upper arm current passing through this element when the upper arm element is ON, Upper arm element is OFF and lower arm element is ON
Sometimes the negative lower arm current passing through the anti-parallel commutation diode to the lower arm element and the negative lower arm current are combined at the series connection point between the both arm elements at different times, and have the positive definite polarity. It will form the inverter output current.

Therefore, in the primary and secondary input type AC current transformer, the two currents having the same number of turns are supplied with currents of both upper and lower arms in opposite polarities to the respective current transformers. The alternating current transformer is related to the positive and negative polarities of the inverter output current by generating an alternating magnetomotive force with respect to the alternating current magnetomotive force and changing the synthetic magnetic flux in the current transformer iron core due to the alternating magnetomotive force according to the cycle of the carrier frequency. It has a normal current-changing function for the inverter output current in the entire frequency range regardless of whether the frequency is high or low. That is, the AC current transformer functions like a DC current transformer in its low frequency range.

In accordance with the above, according to the present invention, one primary and two input type AC current transformer having two sets of windings with the same number of turns on the primary side is provided for each current detection phase in the main circuit bridge configuration of the inverter. A secondary winding of the current transformer is provided by energizing the two primary windings of the current transformer so that the output currents of the upper and lower arms in the current detection phase have opposite polarities. By this, the transformed output of the inverter output current in the current detection phase is obtained.

[0011]

1 is a circuit diagram of an embodiment of the present invention and FIG.
2 will be described with reference to the operation waveform diagram of FIG. In FIG. 1, constituent elements having the same functions as those in the embodiment of the prior art shown in FIG. 3 are designated by the same reference numerals. In FIG. 1, the ACCT (alternating current transformer) 6 in the circuit diagram of FIG. 3 is removed, and the connections of the transistors 1 and 2 of the upper arm and the lower arm are separated at the series connection point of the two, and In place of the ACCT 6, 5 primary and 2 input type ACCTs are provided, and the currents of the upper and lower arms are made to have opposite polarities to the two sets of primary windings having the same number of turns (the number of turns is 1 in the figure) in the ACCT 5. They are connected so that they are energized.

With the connection as described above, the magnetomotive force to the ACCT 5 due to the electric currents flowing through the upper and lower arms becomes an alternating magnetomotive force that changes according to the cycle of the carrier frequency to change the synthetic magnetic flux in the current transformer core. The AC current transformer ACCT5 has a normal current transformer function for the inverter output current in the entire frequency range regardless of the positive / negative polarity of the inverter output current and almost regardless of the level of the frequency of the output current. In the low frequency range, it functions like a DC current transformer.

Next, in the operation waveform diagram of FIG. 2, the figure (a) shows the ON (closed) / OFF (opened) state of each of the upper and lower arms due to the controlled conjugate opening / closing operation of the transistors 1 and 2. Is. The OFF state of each of the two arms is not shown as a pair with each ON state, but the OFF state of the upper arm is at the same level as the ON state of the lower arm, for example.

Further, FIG. 2B shows an output current pattern in an arbitrary phase of the inverter obtained as a result of the opening / closing operation of the upper and lower arms shown in FIG.
The figure shows a state in which, for example, a positive constant polarity is maintained while including a pulsating component according to the cycle of the carrier frequency. Further, FIG. 3C shows an alternating current obtained when the upper and lower arm currents having different generation timings according to the cycle of the carrier frequency are combined according to their positive and negative polarities, and the alternating current transformer ACCT5 It represents the equivalent combined current of the primary input current of the current transformer corresponding to the magnetomotive force of the alternating combined magnetic flux that is generated.

The inverter output current shown in FIG. 6B is obtained by inverting the negative component of the alternating current shown in FIG. 3C and adding it to the positive component.

[0016]

According to the present invention, there is provided a method for detecting an output current in an arbitrary phase of a voltage source inverter, which is No. 1
The primary and secondary input type AC current transformer having two sets of windings with the same number of turns on the secondary side is provided for each current detection phase in the main circuit bridge configuration of the inverter, and two sets of the current transformers are provided. The output currents of the upper and lower arms in the current detection phase of the bridge configuration are applied to the primary windings so that the output currents have opposite polarities, and the inverter output in the current detection phase is output from the secondary winding of the current transformer. By obtaining the transformed output of the current, the variable range of the output frequency is wide and the minimum value becomes extremely small.It becomes possible to detect the normal current transformation in the entire frequency range of the output current of the inverter. It is not necessary to use a DC current transformer in the range, and it is possible to significantly reduce the cost of equipment related to the detection of the inverter output current.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter output current detection circuit showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of various components of the circuit shown in FIG.

FIG. 3 is a circuit diagram of an inverter output current detection circuit showing an embodiment of the prior art.

[Explanation of symbols]

 1 Upper Arm Transistor 2 Upper Arm Diode 3 Lower Arm Transistor 4 Lower Arm Diode 5 ACCT (Primary 2 Input AC Current Transformer) 6 ACCT (Primary 1 Input AC Current Transformer)

Claims (1)

[Claims] 1. A method for detecting an output current in an arbitrary phase of a voltage type inverter, wherein the inverter comprises a primary / secondary input type AC current transformer having two sets of windings having the same number of turns on its primary side. One is provided for each current detection phase in the main circuit bridge configuration, and the output currents of the upper and lower arms in the current detection phase of the bridge configuration are set to have opposite polarities to each of the two primary windings of the current transformer. The method for detecting an output current of an inverter is characterized in that a transformed output of the inverter output current in the current detection phase is obtained from the secondary winding of the current transformer.