JPH11275866A - Control method of three-phase rectifier power factor improving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain stable operation of a three-phase rectifier, by changing the dead time of control pulses of control elements on positive and negative potential sides of respective arms, based on input phase voltage. SOLUTION: A dead time duration computing circuit detects input phase voltage, computes desired dead time duration so as to meet the voltage value, generates a control pulse which has generated dead time based on computed results to supply to a drive circuit. Two control signals as a pair for controlling meet one control pulse, the other control pulse is inverted by an inverting circuit to be generated, and these control pulses are applied to a control element. The dead time of the control pulses of control elements on positive and negative potential sides of the respective arms can be changed with input phase voltage. It is thus possible to attain a three-phase rectifier power factor improving circuit which can prevent failures which are caused by simultaneous on-operations of the respective arms, and has few harmonic components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control method for a three-phase rectifier power factor correction circuit.

[0002]

2. Description of the Related Art FIG. 1 shows a power factor improving circuit of a conventionally used three-phase rectifier. FIG. 2 shows a waveform of a three-phase AC input voltage. Each phase voltage when the U-phase voltage Vu is 45 ° is as shown by a dotted line of 45 ° in the figure. FIG. 3 is an example of a control pulse waveform of each phase when Vu is around 45 °. Although not described in FIG. 3, there is a non-conduction period for preventing a short circuit, a so-called dead time, between the control pulses of the control element on the positive potential side and the control element on the negative potential side of each arm. FIG. 4 is an example of a control pulse waveform (2) showing the dead time for the control elements Q3 and Q6. The width of the dead time varies depending on the type of the control element used, the switching cycle, and the like, but once set, it is constant regardless of the input voltage or the like.

The dead time is provided to prevent the control element on the positive potential side and the control element on the negative potential side of each arm from being simultaneously turned on. Therefore, considering that the ON time of the control element changes with temperature and that a design that is strong against malfunction is desirable, a wider dead time is better. In an actual three-phase rectifier power factor correction circuit, almost normal operation is performed even if the width of the dead time is considerably widened. This will be briefly described below.

FIG. 5 is an equivalent circuit showing a current flow in each switching mode of the gate signal of FIG. For example,
In the mode of FIG. 3, since the control elements of Q1, Q2, and Q3 are on, the rectifier circuit of FIG. 1 is an equivalent circuit showing a current flow as shown in FIG. Here, Q3 · D3 and Q3
Focusing on 6.D6, the current flowing through these elements is
As shown in FIG. 5, the flow direction is from the input side to the three-phase rectifier power factor correction circuit. The mode in FIG. 5 is a period in which Q3 is on, but the current flows through D3 because the current flows in the forward direction of D3. Therefore, it is considered that there is no operational problem even if Q3 remains off, and that the dead time width is maximized, and simultaneous control of the positive potential side control element and the negative potential side control element is avoided. In order to be considered the best. However, near the zero cross of the current, that is, in FIG.
In the vicinity of 60 °, there is a problem if Q3 is kept off. This will be briefly described below.

In FIG. 5, there is no change in the direction of current flow during the mode .about., But the increase and decrease of the current are repeated by the change in the state of the mode. The state of this current varies depending on (3) the input / output voltage, the state of the load, etc., for example, as shown in FIG. 6 near 60 °. 6 in FIG. 6 correspond to in FIG. Here, the portion having a waveform on the negative side is the case where the current flows from the three-phase rectifier power factor correction circuit toward the input. Therefore, in FIG. 6, in the portion where the waveform is on the negative side of the mode, the current does not flow unless Q3 is on because the direction of the current is opposite to that of D3. If Q3 remains off and no current flows to the negative side in the mode, or if the dead time is wide,
Distortion occurs in the W-phase current waveform, and the harmonic current component increases. This harmonic component is a relatively high-order component, and it is very difficult to satisfy the harmonic current standard value. This phenomenon is exactly the same for the U phase and the V phase.

[0006]

As is apparent from the above description, it is desired that the width of the dead time be as wide as possible when the input phase voltage is high and as narrow as possible when the input phase voltage is low. . However, this is not possible with the conventional control method of the dead-time fixed three-phase rectifier power factor correction circuit or the conventional three-phase rectifier power factor correction circuit control method in which the control element on either the positive or negative potential side remains off. Met. Therefore, the present invention has been made to solve the above problems, and has as its object to stably operate a three-phase rectifier by taking an appropriate dead time irrespective of input voltage fluctuations. Another object of the present invention is to realize a control method of a three-phase rectifier power factor correction circuit.

[0007]

According to the present invention, a rectifier input is formed by connecting the inductance of each phase of a three-phase AC input, and a diode is connected in anti-parallel to each control element constituting a three-phase bridge. In the connected three-phase rectifier power factor correction circuit, the dead time of the control pulse of the control element on the positive potential side and the control element on the negative potential side of each arm is changed according to the input phase voltage. It is a control circuit of a three-phase rectifier power factor improvement circuit. One means for achieving this is to detect each phase voltage and provide a dead time of the arm corresponding to the phase voltage.

[0008]

FIG. 7 shows an embodiment of a control system according to the present invention. FIG. 7 is a control block for one arm of the control elements Q1 and Q4 in FIG. Therefore, the three-phase circuit as a whole has the same block as that of FIG. 7 with three blocks, with the voltage control system and the sawtooth wave generator as common parts. In FIG. 7, when the absolute value of the input phase voltage is large, the dead time width is large, and the dead time width is large.
When the absolute value of the input phase voltage is small, the calculation is performed so that the dead time width becomes narrow.

Referring to FIG. 7, the operation will be described. An input phase voltage is detected, and a dead time width calculation circuit calculates a desired dead time width according to the detected voltage value. And
Based on the calculation result, a control pulse that generates a dead time is generated and supplied to the drive circuit. Control pair 2
The control signal of one control element is generated corresponding to one control pulse, and the other control pulse is inverted by an inversion circuit. Then, these control pulses are applied to the control elements Q1 and Q4. Other paired control elements (Q2, Q5)
And (Q3, Q6). The dead time of the control pulses of the control element on the positive potential side and the control element on the negative potential side of each arm can be varied according to the input phase voltage value. Specifically, when the absolute value of the input phase voltage is high, the dead time width is wide, and when the absolute value of the input phase voltage is small, the dead time width is narrowed.

Of course, when the input phase voltage is high, there may be a case where one of the control elements is turned off as a result of an increase in the dead time width. The present invention also includes a case where the set dead time width is generated when the absolute value of the input voltage becomes equal to or less than a certain value, and the control element on one side is turned off in other periods. . (5)

[0011]

As is apparent from the above description, according to the present invention, it is possible to prevent a failure due to simultaneous turning on of each arm,
It is possible to provide a three-phase rectifier power factor improvement circuit with less harmonic components.

[Brief description of the drawings]

FIG. 1 is a power factor correction circuit of a three-phase rectifier.

FIG. 2 is a waveform of a three-phase AC input phase voltage.

FIG. 3 is a gate drive waveform of each phase when the U-phase voltage Vu is around 45 °.

FIG. 4 is a control pulse waveform example showing a dead time.

FIG. 5 is an equivalent circuit showing a current flow in each switching mode.

FIG. 6 is an example of an input current waveform.

FIG. 7 shows an embodiment of the present invention.

[Brief description of reference numerals]

 Q1 to Q6 Control elements D1 to D6 Diode CO Output smoothing capacitor C1 to C3 Input smoothing capacitor L1 to L3 Input inductor Vu U-phase phase voltage Vv V-phase phase voltage (6) Vw W-phase phase voltage Ec Reference triangular wave GQ1 to GQ6 Control pulse for control elements Q1 to Q6 Eu Comparison voltage for controlling GQ1 and GQ4 Ev Comparison voltage for controlling GQ2 and GQ5 Ew Comparison voltage for controlling GQ3 and GQ6 DT Dead time

Claims (2)

[Claims] In a three-phase rectifier power factor improving circuit, an inductance is connected to each phase of a three-phase AC input, and a diode is connected in anti-parallel to each of control elements constituting a three-phase bridge. A dead time of a control pulse is not constant during one cycle of a commercial input voltage, wherein the control element on the positive potential side and the control element on the negative potential side are both non-conductive. control method. 2. The control method according to claim 1, wherein the dead time of the control element on the positive potential side and the control element on the negative potential side of each arm are determined according to the phase voltage connected to each arm. Control method for a three-phase rectifier power factor correction circuit, characterized in that