JP2002247856A - Load voltage detector for inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To indirectly detect the voltage of a load, since high-voltage noises are superposed on a detection signal, if the load voltage becomes high, and a malfunction caused by this occurs in some cases, when the voltage of the load driven by an inverter is detected and transmitted to an inverter controller. SOLUTION: A value obtained by multiplying a value corresponding to the inductance of a reactor 6 with the differentiated value of a detected output current value of the inverter is subtracted from a detected output voltage of the inverter, or from a computed output voltage value of the inverter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to one or more series circuits in which a plurality of semiconductor switches are connected in series between the positive and negative sides of a DC power supply. The present invention relates to an inverter load voltage detector for measuring a load voltage indirectly without directly measuring a load voltage in an inverter.

[0002]

2. Description of the Related Art In order to control the output current or output voltage of an inverter to a value corresponding to the current or voltage required by a load, it is necessary to accurately grasp the load current or load voltage. However, when the load driven by the inverter is exposed to a voltage higher than the inverter output voltage by a reactor or the like connected in series, the signal line that transmits the detected value of the load voltage to the inverter side is based on the high potential. Noise is superimposed.

Referring to the drawings, FIG. 3 shows a conventional inverter load voltage detection system, in which a DC power supply 1 is used.
The semiconductor switches 2 and 3 and 4 and 5 typified by a transistor and an anti-parallel diode are connected in series and then connected in parallel between the positive and negative sides to form an inverter.

[0004] A reactor 6 and a capacitor 7 constituting a series resonance circuit and a load 8 are connected to the inverter, and a high voltage based on the series resonance is applied to the load 8. In general, the load voltage V2 having a higher value than the inverter output voltage is detected by the voltage detector 21 and given to the control circuit 11 as a load voltage detection value V2 ^* , so that the control circuit 11 sets the load voltage to a desired value. Supplies control pulse signals G2, G3, G4 and G5 to the semiconductor switches 2 to 5, respectively.

The semiconductor switches 2 and 3 or 4 and 5 are alternately turned on (ON) with a so-called dead time in which both are turned off (OFF). As shown in FIG. 4, when the control pulse signal G2 of the semiconductor switch 2 and the control pulse signal G5 of the semiconductor switch 5 are ON, a positive voltage + E is output to the inverter output terminal.
When the control pulse signal G4 and the control pulse signal G3 of the semiconductor switch 3 are ON, a negative voltage -E is output to the inverter output terminal.

[0006] In order to keep the load voltage V2 at a desired voltage value irrespective of fluctuations in the DC power supply or the load, a control circuit 11 often installed at a position away from the load is provided with a voltage control circuit 11 installed near the load. A load voltage detection value is obtained from the detector 21,
This is compared with a load voltage reference value, and a control pulse signal based on the difference is output.

[0007]

The problem here is that when the load voltage V2 to be detected is high, the signal line for transmitting the detected load voltage value to the control circuit has to be routed close to the high voltage portion. In this case, the detection signal is influenced by an electromagnetic field generated from the high-voltage portion, so that an inductive noise is generated in the detection signal, whereby the control device may malfunction.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a device capable of detecting a load voltage without being affected by a high voltage in an inverter of the type described at the outset.

[0009]

According to the present invention, the above-mentioned object is achieved by calculating the load voltage by calculation on the inverter side without directly detecting the load voltage.

More specifically, according to the invention described in claim 1 of the present application, one or a plurality of series circuits in which a plurality of semiconductor switches are connected in series between the positive and negative of a DC power supply are connected. An inverter that converts a DC voltage into an AC voltage pulse by turning on and off a semiconductor switch;
In a power converter including a series circuit of a reactor and a load connected to the output of the inverter, and a control circuit for controlling ON / OFF of the semiconductor switch, an inverter output voltage detector, an inverter output current detector, ,
A differentiation circuit for differentiating an inverter output current detection value detected by the inverter output current detector, and a subtractor for subtracting the output value of the differentiation circuit from the inverter output voltage detection value detected by the inverter output voltage detector. By providing the load voltage calculation circuit, the above-mentioned problem can be solved.

According to a second aspect of the present invention, in the above-mentioned power converter, an inverter output voltage for outputting a polarity discrimination signal of an inverter output voltage based on an on / off signal of the semiconductor switch. An inverter output voltage detector including a polarity discriminator, a multiplier for multiplying a DC voltage detection value of the DC power supply by an output of the inverter output voltage polarity discriminator, an inverter output current detector, and the inverter output current detector. Voltage calculation circuit, comprising: a differentiation circuit for differentiating an inverter output current detection value detected by an inverter; and a subtractor for subtracting an output value of the differentiation circuit from the inverter output voltage detection value detected by the inverter output voltage detection circuit. The above problem can be solved also by providing.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit connection diagram showing an embodiment according to the first aspect of the present invention. The same circuit elements as those in FIG. 3 are denoted by the same symbols or reference numerals to avoid duplication of description. Reference numeral 12 denotes an output current detector of the inverter, and a detection value I ₀ of the output current I ₀ detected thereby.
^* And the detected value V1 ^* of the inverter output voltage V1 detected by the inverter output voltage detector 13 are input to the load voltage calculation circuit 14.

The load voltage calculating circuit 14 includes a differentiating circuit 15 and a subtractor 16. The differentiating circuit 15 differentiates the detected inverter output current I ₀ ^* , and this differentiated value corresponds to the inductance L of the reactor 6. by multiplying a _{^{value, V3 * = L (dI 0}} * / dt) (1) comprising calculating the terminal voltage V3 ^* of the reactor 6 of the formula.

The subtractor 16 subtracts the calculated reactor terminal voltage V3 ^* from the inverter output voltage detection value V1 ^* to obtain a load represented by the following formula: V2 ^* = V1 ^* -V3 ^* (2) The voltage V2 is calculated.

The detected value of the current detector 12 and the voltage detector 13
Since the detected value has only the potential of the output voltage level of the inverter at most, and is not affected by the high potential on the load side,
The load voltage calculation value obtained by calculation from these detection values is not affected by high voltage noise or the like.

FIG. 2 is a circuit connection diagram showing an embodiment according to the second aspect of the present invention. The same circuit elements as those in FIGS. 1 and 3 are denoted by the same reference numerals or symbols to avoid redundant description. The circuit of FIG. 2 differs from the circuit of FIG. 1 in that a voltage detector 17 for detecting a DC voltage and an inverter voltage detection circuit 18 are provided instead of the voltage detector 13 for detecting the output voltage of the inverter. .

The inverter voltage detecting circuit 18 comprises an inverter output voltage polarity judging circuit 19 and a multiplier 20. The inverter output voltage polarity discriminating circuit 19 outputs +1 V when the control pulse signals G2 and G5 shown in FIG. 4 are both at the signal level for turning on the semiconductor switches 2 and 5, and the control pulse signals G3 and G4 are both semiconductor. When the signal level turns on the switches 3 and 4, -1V is output, and in other cases, 0V is output.

The output of the inverter output voltage polarity determination circuit 19 and the detection value E of the DC voltage detected by the voltage detector 17
^* And by multiplying by the multiplier 20, the inverter output voltage V1 ^* is determined.

The load voltage calculation circuit 14 calculates the inverter output current detection value I ₀ ^* and the inverter output voltage detection value V 1 ^*.
From the equation (2) to calculate the load voltage V2
^* Is calculated and given to the control circuit 11.

[0020]

As described above, according to the present invention, the load voltage can be estimated without transmitting the measured value on the load side having a high potential to the control circuit side having a low potential.
It is possible to reduce the possibility of malfunction due to induction noise or the like.

[Brief description of the drawings]

FIG. 1 is a circuit connection diagram showing an embodiment according to the invention of claim 1;

FIG. 2 is a circuit connection diagram showing an embodiment in the invention of claim 2;

FIG. 3 is a circuit connection diagram in the related art.

FIG. 4 is an operation time chart of a semiconductor switch constituting an inverter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2-5 Semiconductor switch 6 Reactor 7 Capacitor 8 Load 11 Control circuit 12 Current detector 13 Voltage detector 14 Load voltage calculation circuit 15 Differentiation circuit 16 Subtractor 17 Voltage detector 18 Inverter voltage detection circuit 19 Inverter output voltage polarity Discrimination circuit 20 Multiplier 21 Voltage detector G2 to G5 Control pulse signal

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2G035 AA27 AB02 AC01 AC16 AD02 AD04 AD13 AD18 AD20 AD22 AD31 AD57 5H007 AA01 AA12 CA01 CB02 CB05 CC09 DB02 DC02 DC05

Claims (2)

[Claims] 1. A series circuit in which a plurality of semiconductor switches are connected in series between the positive and negative of a DC power supply,
An inverter for converting a DC voltage into an AC voltage pulse by an on / off operation of the semiconductor switch, a series circuit of a reactor and a load connected to an output of the inverter, and a control circuit for controlling on / off of the semiconductor switch An inverter output voltage detector, an inverter output current detector, a differentiation circuit for differentiating an inverter output current detection value detected by the inverter output current detector, and the inverter output voltage detector. A load voltage calculating circuit comprising a subtractor for subtracting the output value of the differentiating circuit from the detected inverter output voltage detection value. 2. One or a plurality of series circuits in which a plurality of semiconductor switches are connected in series between positive and negative DC power supplies,
An inverter that converts a DC voltage into an AC voltage pulse by an on / off operation of the semiconductor switch, a series circuit of a reactor and a load connected to an output of the inverter, and a control circuit that controls on / off of the semiconductor switch An inverter output voltage polarity determination circuit that outputs a polarity determination signal of an inverter output voltage based on an on / off signal of the semiconductor switch; a DC voltage detection value of a DC power supply; and the inverter output voltage polarity. An inverter output voltage detection circuit comprising a multiplier for multiplying the output of the discrimination circuit; an inverter output current detector; a differentiation circuit for differentiating an inverter output current detection value detected by the inverter output current detector; Before the inverter output voltage detection value detected by the output voltage detection circuit Inverter load voltage detector, characterized in that a, a load voltage calculating circuit and a subtracter for subtracting the output value of the differential circuit.