JPH06261550A - Power converter - Google Patents

Abstract

PURPOSE:To obtain stable inverter output voltage and current comprising a means of leading out inverter output current and a means of adjusting output current so that input power corresponding to this output current can be obtained. CONSTITUTION:A control circuit 8 consisting of a mean value operating means 81, a modulation factor and phase operating means 82, and a gate pulse generating means 83 on-off controls control switching devices of converters 3a,3b in a predetermined order via a gate signal processing circuit 9 by the output. Even when there is unbalance between DC output currents 1i1, 1i2 of smoothing capacitors Cd and Cd2 for some reason in circuit action, DC voltages Ed1 and Ed2 can be kept at set values by operating input power. As a result, output currents of smoothing capacitors connected in series at the input stage of the invertor are different, current is controlled to adjust every smoothing capacitor, so that stable voltage can be supplied to a multilevel inverter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, and more particularly, to an AC-current converter having a plurality of converters and a multi-level inverter for inputting the DC output voltage of the converters and converting the voltage into a variable-voltage / variable-frequency AC. Regarding AC power conversion.

[0002]

2. Description of the Related Art When driving an M level inverter from an AC input, power supply by an M level converter is considered. For example, there is a three-level converter + three-level inverter system described on pages 570 to 571 of the Proceedings of the 1992 National Conference of Industrial Applications of the Institute of Electrical Engineers of Japan.

[0003]

In the conventional multi-level converter / inverter system, the multi-level converter and the DC output of this converter have the same number of output levels as those of the converter through the smoothing capacitor group connected in series. Circuit configurations have been used to power multi-level inverters. In such a circuit configuration, if there are variations in the elements that make up the converter and the inverter, or if there is a bias in the operation of the inverter, the input current and output of the capacitors that make up the smoothing capacitor group that is the voltage source of this inverter The average value of the current difference does not become zero. Therefore, the capacitor is continuously charged or discharged, and the voltage of the capacitor fluctuates. As a result, the voltage between the capacitors varies, and the output voltage of the multilevel inverter becomes unstable.

An object of the present invention is to keep the voltage of each capacitor of the smoothing capacitor group, which is the voltage source of the multilevel inverter, constant and obtain a stable inverter output voltage and current.

[0005]

In the present invention, (M-1) two-level converters for converting AC to DC and DC outputs of these converters are connected in series (M-1).
Connected to each capacitor of a smoothing capacitor group consisting of a plurality of smoothing capacitors, an M level inverter fed by this smoothing capacitor group, a means for deriving an output current of the inverter, and an input power corresponding to the output current. Means are provided for adjusting the output current of the converter as obtained. For example, in order to suppress fluctuations in the individual smoothing capacitor voltages of the smoothing capacitor group due to the imbalance of the output power of the multilevel inverter, two levels are set so as to be balanced with the inverter output current and the inverter input current determined by the switching state of the inverter. Controls the output current of the converter.

[0006]

As a result, the input / output currents of the capacitors are balanced, the capacitor voltage becomes constant, and a stable voltage can be supplied to the multilevel inverter.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention. A circuit of a control device for an induction motor by a converter / inverter system, 1 is an AC power supply, 2 is a transformer, 3
a and 3b are 2-level PWM converters that convert AC into DC, 4 is a smoothing capacitor group formed by filter capacitors 4a and 4b for smoothing DC voltage, 5 is a 3-level inverter device, and 6 is an inverter 5 It is an induction motor driven by. Reference numerals 7a and 7b are current detection means, 8 is a control circuit composed of an average value calculation means 81, a modulation factor and phase calculation means 82, and a gate pulse generation means 83. The output of the control circuit 8 causes the gate signal processing circuit 9 to Through the converters 3a and 3b in a predetermined order.
Control ON / OFF of the switching element is controlled.

FIG. 2 is an equivalent circuit of one converter set of the two converter circuits shown in FIG.
21 is a secondary voltage of the transformer 2, 22 is an equivalent reactor of the transformer 2, 3 is a two-level converter, 4'is a DC smoothing capacitor, 10 is a current source I equivalent to the inverter output current.
_i is shown.

FIG. 3 is a vector diagram showing the relationship between the converter input voltage and the current when the power factor of the input current is 1.0. When the converter input voltage E _C is set as shown with respect to the secondary voltage E _S , the difference between the two becomes the reactor voltage E _L applied to the reactor 22. Here, since the input current I _S and the reactor voltage E _L have an orthogonal relationship,
The input current I _S is as shown. Therefore, the imaginary axis component E _Ci of the input AC voltage (component orthogonal to the secondary voltage E _S )
By operating the input current I _S active ingredient (secondary voltage E _S-phase component) is controlled in converter input current by operating the real axis component E _Cr of the input AC voltage E _S I _S
The phase (fundamental wave power factor) of is controlled. Then, a DC current I _c obtained by rectifying the input current I _S is output to the DC side. A difference current I _d between this and the inverter input current I _i flows into the capacitor. The terminal voltage of the smoothing capacitor 4 is determined by this current.

In order to keep the capacitor voltage E _d constant,
The modulation factor K of the converter and the phase difference θ between the converter input end voltage E _C and the secondary voltage E _S are determined as follows.

The relationship between the input and output power of the converter in FIG.

[0012]

[Equation 1] E _s · I _s = E _d · I _c (Equation 1) The fundamental wave power factor of the input current I _S is the imaginary axis component E of the input AC voltage.
_Assuming that _Ci is operated so that the phase becomes 0 ° (power factor 1.0), the relationship between the modulation factor K and the phase angle θ is as follows.

[0013]

[Equation 2]

[0014]

[Equation 3]

If E _d is constant, that is, I _d is zero, then the following equation 4 holds.

[0016]

## EQU00004 ## I _i = I _C (Equation 4) Substituting the equation (1) which is the power relational equation and the relational equation of the input / output current into the equations (2) and (3), the relational expression between the modulation factor K and the phase angle θ becomes the equation (5).
And are modified as shown in Equation 6.

[0017]

[Equation 5]

[0018]

[Equation 6]

The modulation factor obtained by these equations is K,
By controlling the converter with the phase angle of θ, the capacitor current I _d becomes zero, that is, E _d becomes constant.

Further, the same control can be performed during power regeneration when the output current of the inverter becomes negative.

Such control is performed by the converter 3a shown in FIG.
By performing separately for and 3b, the respective current output current I _i1, I _i2 smooth some reason the circuit operation capacitor C _d1 and C _d2 be imbalance there, the capacitor C _d1, C _d2 By manipulating the input power, the DC voltages E _d1 and E _d2 can be maintained at set values, and a stable voltage can be supplied to the multilevel inverter.

As described above, the present invention includes a 2-level 2-converter and a 3-level converter.
Although the embodiment of the case of the level-one inverter has been described, the present invention is a combination of other converters and multi-level inverters, and generally, a two-level (X-1) converter and an X-level inverter (X is an integer of 3 or more). ) Is also applicable to the control circuit, as shown in FIG.
The capacitor voltage can be kept constant by detecting the capacitor voltage E _d , taking the deviation from the target value E _d *, and controlling the converter to eliminate the deviation.

[0023]

According to the present invention, even if the operation of the multi-level inverter is biased and the output currents of the smoothing capacitors connected in series to the input stage of this inverter are different,
By operating each converter independently and controlling the current of each smoothing capacitor, each smoothing capacitor voltage can be adjusted and a stable voltage can be supplied to a multilevel inverter.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the converter unit shown in FIG.

FIG. 3 is a vector diagram showing the relationship between input / output voltage and current of the converter.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 ... AC power supply, 2 ... Transformer, 3 ... PWM converter circuit, 4 ... Smoothing capacitor, 5 ... 3-level PWM inverter, 6 ... Induction motor, 7 ... Current detector, 8 ... Control circuit,
9 ... Gate signal processing circuit, 10 ... Inverter output equivalent current.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H02M 7/17 9180-5H

Claims (3)

[Claims] 1. A power converter including a forward converter for converting AC to DC, a smoothing capacitor group, and an inverse converter for converting DC to AC, wherein the inverse converter is an M level inverter (M is 3). The integer above), and the smoothing capacitor group is composed of (M-1) capacitors connected in series,
The power converter, wherein the forward converter is composed of (M-1) two-level converters connected in series. 2. A power converter including a forward converter for converting AC to DC, a smoothing capacitor group, and an inverse converter for converting DC to AC, wherein the inverse converter is an M level inverter (M is 3). The integer above), and the smoothing capacitor group is composed of (M-1) capacitors connected in series,
The forward converter is composed of (M-1) two-level converters connected in series, and controls each of the two-level converters so as to keep the voltage across the terminals of the capacitors constant. Converter. 3. A power converter including a forward converter for converting AC to DC, a smoothing capacitor group, and an inverse converter for converting DC to AC, wherein the inverse converter is an M level inverter (M is 3). The integer above), and the smoothing capacitor group is composed of (M-1) capacitors connected in series,
The forward converter is composed of (M-1) two-level converters connected in series, means for detecting a terminal voltage of each capacitor, means for calculating an average value of the terminal voltage, and the terminal. An electric power converter comprising means for controlling a converter according to a deviation between an inter-voltage and a target voltage.