JP2705081B2 - DC intermediate voltage detection method for voltage source inverter device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a voltage detection method for detecting and monitoring a DC intermediate voltage of a voltage type inverter device.

[Conventional technology]

As a conventional voltage detecting circuit of this kind, direct detection of the DC intermediate voltage is performed by comparing each divided voltage obtained by dividing the DC intermediate voltage in multiple stages for each required voltage level with each set voltage. The method by the method is known.

[Problems to be solved by the invention]

However, the fluctuation of the DC intermediate voltage during the operation of the inverter device is twice as large as the nominal voltage of the inverter device.
Therefore, the power loss in each of the voltage dividing resistors for detecting the DC high voltage is large, and the above-mentioned measures are taken by measures for radiating heat generated due to the power loss or measures for strengthening the withstand voltage of each element accompanying the high voltage. Inevitably, the overall efficiency and size of the inverter were reduced. Furthermore, the input of the detection voltage based on the resistance division of the DC intermediate voltage to the voltage comparison operation circuit or the like must be performed via a circuit insulating means such as a photocoupler, which complicates the circuit configuration. In view of this, it is an object of the present invention to provide a voltage detecting method that can easily and reliably detect the DC intermediate voltage by using a DC voltage that is insulated from the DC intermediate circuit and reduced in voltage.

[Means for solving the problem]

Means is provided for obtaining a detection voltage stepped down in proportion to the DC intermediate voltage and insulated from the circuit. That is, a rectifier circuit that converts an AC input from an AC power supply into DC, a capacitor that smoothes an output DC voltage of the rectifier circuit, and an inverter circuit that converts a DC intermediate voltage smoothed by the capacitor into a required AC. A voltage source inverter device having a flyback type DC / CD converter that outputs a flyback voltage serving as a control voltage of the inverter device and a forward voltage used as a detection voltage of the DC intermediate voltage with the DC intermediate voltage as a power supply voltage. A voltage comparison circuit that performs a comparison operation between the forward voltage and a predetermined set voltage, and indirectly detects and monitors the DC intermediate voltage based on the forward voltage.

[Action]

When switching is performed by applying a DC voltage to the primary winding of a transformer, the secondary winding having the opposite polarity to the primary winding has:
When the DC voltage is switched on, a forward voltage is induced according to a turn ratio between the primary winding and the secondary winding, and when the DC voltage is switched off, a forward voltage is induced according to a back electromotive force based on the stored energy of the transformer. And a flyback voltage.

The present invention uses a DC intermediate voltage of an inverter device as a DC voltage for applying a primary winding of the transformer, and controls the applied intermediate voltage by switching the duty ratio of a semiconductor switching element to control the secondary winding of the transformer. Flyback type in which the flyback voltage induced in the line is controlled at a fixed value and the smoothed voltage is used as the control voltage of the inverter device.
Take out the secondary side forward voltage of DC / DC converter,
The rectified and smoothed voltage of the forward voltage is used as a detection voltage which is insulated from the DC intermediate voltage of the inverter device and is proportionally lowered, and a comparison operation between the detection voltage and a predetermined set voltage is performed to perform an indirect calculation. Then, the DC intermediate voltage is detected and monitored.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are a forward voltage detection circuit diagram and a voltage comparison circuit diagram of the forward voltage of the flyback type DC / DC converter, respectively. FIG. 3 is a diagram showing the DC / D converter corresponding to FIG.
FIG. 4 is an operation waveform diagram of a flyback voltage and a forward voltage of the C converter, and FIG. 4 is an example of an inverter device system overall circuit diagram. First, in FIG. 4, 1 is a three-phase AC power supply, 2 is an inverter device that converts an AC input received from the AC power source and outputs an AC having a predetermined frequency and voltage, and 3 is an output AC of the inverter device. This is an induction motor driven at a variable speed. The inverter device 2 includes a rectifier circuit 4 that converts an AC input from the AC power supply 1 into a direct current, and a capacitor that smoothes an output direct current voltage of the rectifier circuit and stabilizes a direct current intermediate voltage E _dc of the inverter device 2. C, an inverter circuit 5 for converting the DC intermediate voltage E _dc into a required AC, and a flyback voltage E as a control voltage of the inverter device 2 using the DC intermediate voltage as a power supply voltage.
a flyback DC / DC converter 6 to output a forward voltage E _fw used as _fb and the detection voltage of the DC intermediate voltage E _dc, the voltage comparator circuit 7 for comparing the forward voltage B _fw with a predetermined set voltage Consists of Next, in FIG. 1, the flyback type DC / DC converter 6 converts a primary winding 8a and a shared voltage of the winding in accordance with the respective winding ratios and the winding polarities indicated by ● in the figure. Wire 8b and feedback winding 8c
A transformer 8 having three windings, a switching transistor TR, and a base voltage control circuit of the transistor as main components, and a primary terminal of the converter.
When the voltage E _dc is applied between P _m and N _m, the collector current of the transistor TR that has started conducting by the base current via the oscillation starting resistor R ₁ is the primary winding 8 a of the transformer 8.
A voltage proportional to the rate of change of the collector current induces in, the induced voltage by the voltage induced in the feedback winding 8c is its differential voltage applied to the differentiating circuit consisting of resistor R ₃ and capacitor C ₃ Metropolitan positive The resistor R ₁
The transistor is quickly added to the fully switched-on state when added to the base voltage via On the other hand, the rate of change of the collector current decreases with the ON state of the transistor, and accordingly, the induced voltage in the primary winding 8a and the feedback winding 8c of the transformer 8 decreases, and thus the base voltage decreases and the collector voltage decreases. When the current starts decreasing, the state further progresses, and when the polarity reversal of the induced voltage in the windings 8a and 8c occurs, the base voltage shifts from a decrease in the forward direction to a reverse bias state, and as a result, the transistor becomes It switches off quickly. It said switching on and off operation and the differentiating circuit time constant R ₃ C ₃ wherein the two windings 8a
It is repeated with a period related to the turns ratio of 8c, and the corresponding frequency is several tens KHz. Therefore, the induced voltage in the primary winding 8a (winding n ₁ ) of the transformer 8 whose polarity is inverted in accordance with the switching on / off state is the secondary winding.
8b (winding n ₂ ), separated by diodes D ₁ and D ₂ every half-wave according to their respective polarities, and then smoothed by a parallel circuit of capacitors C ₁ and C ₂ and a resistor R ₂ , respectively. A flyback voltage E _fd and a forward voltage E _fw are output from the secondary terminals Pc and O of the converter 6 and between O and Nd. Here, the flyback voltage E _fb corresponds to the switching-off state of the transistor TR, and similarly, the forward voltage E _fw corresponds to the switching-on state, and the turns ratio n ₂ / n ₁ is a proportional coefficient. _Is obtained as a value proportional to the voltage _Edc . The automatic voltage adjusting circuit 9 controls the flyback voltage E _fb used as a control constant voltage at a constant value.
An output voltage corresponding to a deviation between _fb and its set voltage is given as a correction control voltage for the base of the transistor TR. FIG. 3 is an operation waveform diagram showing a state where the voltages E _fb and E _fw are generated. Here, FIG. 7A shows the switching on / off state of the transistor TR, and FIG. 7B corresponds to FIG. 7A, and the two voltages E _fb and E _fb having different polarities.
Indicates _fw . Figure 2 is a voltage comparator circuit diagram for detecting the variation of the DC intermediate voltage detecting indirectly the DC intermediate voltage variation pattern of the forward voltage E _fw obtained as a value proportional to E _dc of the above as an inverter device Where CP ₁ and CP ₂ are voltage comparators, R _{4 to} R ₈ are resistors, S ₁ and S ₂ are voltage setting devices,
ZD is a constant voltage diode. For example, voltage detection level L ₁
Looking at the detection operation, the diode ZD and the resistor R ₄
The diode constant voltage across corresponding to the level L ₁ in the setter S ₁ in addition to the from the intermediate terminal divides taken out the comparator CP ₁ of + terminal, whereas the two voltages in the series connection of the The difference between E _fb and E _fw is _divided by the resistors R ₅ and R ₆ and the midpoint voltage of the series connection of the two resistors is compared to the comparator CP _1.
Bruno - applied to the terminal, der to output as the detection level L ₁ to determine the magnitude of the two pairs of voltage which is the input voltage at the CP _1. The even detector of the comparator CP ₂ by the level L ₂ is the same as that of the level L _1, and also an increase in the detected level stages are readily by number increase, such as described above.

〔The invention's effect〕

According to the present invention, in the detection of a DC intermediate voltage of an inverter device, a flyback type DC using the intermediate voltage as a power supply
By using the secondary-side forward voltage of the DC / DC converter as a detection voltage that is proportionally reduced to the intermediate voltage and is insulated from the circuit, the resistance loss accompanying the detection operation is reduced, and the circuit insulation on the withstand voltage becomes unnecessary. It is possible to improve the overall efficiency of the inverter device and reduce the size of required equipment.

[Brief description of the drawings]

FIGS. 1 and 2 show an embodiment of the present invention, respectively, showing a forward voltage detection circuit diagram of a flyback type DC / DC converter and a voltage comparison circuit diagram of the forward voltage.
FIG. 4 is an operation waveform diagram of a flyback voltage and a forward voltage of the converter, and FIG. 4 is an overall circuit diagram of the inverter device system. 1 ... AC power supply, 2 ... Inverter device, 3 ... Induction motor, 4 ... Rectifier circuit, 5 ... Inverter circuit, 6 ...
DC / DC converter, 7: Voltage comparison circuit, 8: Transformer, 8a: Primary winding, 8b: Secondary winding, 8c: Feedback winding, 9: Automatic voltage adjustment circuit , C, C ₁ ~C ₃ ...... capacitors, CP _1, CP ₂ ...... voltage comparator, D _1, D ₂ ...... diodes,
R ₁ ~R ₈ ...... resistance, S _1, S ₂ ...... voltage setter, ZD ...... constant voltage diode.

Claims (1)

(57) [Claims] 1. A rectifier circuit for converting an AC input from an AC power supply into a DC power, a capacitor for smoothing an output DC voltage of the rectifier circuit, and an inverter for converting a DC intermediate voltage smoothed by the capacitor to a required AC. A voltage source inverter having a circuit, and a flyback type DC / C that outputs a flyback voltage serving as a control voltage of the inverter device and a forward voltage used as a detection voltage of the DC intermediate voltage, using the DC intermediate voltage as a power supply voltage. A voltage type inverter device comprising a DC converter and a voltage comparison circuit for performing a comparison operation between the forward voltage and a predetermined set voltage, wherein the DC intermediate voltage is indirectly detected and monitored by the forward voltage. DC intermediate voltage detection method.