CN103607121A - Series circuit of converter - Google Patents

Abstract

The invention discloses a series circuit of a converter. The series circuit comprises at least two same power converter primary winding units and two same voltage-sharing capacitors. Each primary winding unit is composed of identical primary windings and switch tubes controlling the primary windings to be switched on or off. Synchronous drive signals are applied to grid electrodes of all the switch tubes, and the primary windings are controlled in a same-phase mode and share magnetic cores. All the primary winding units are mutually connected in series, and all the voltage-sharing capacitors are mutually connected in series. Series points of all the primary winding units are connected with series points of all the voltage-sharing capacitors to form respective corresponding loops. Impedance components are connected between the series points of all the primary winding units and the series points of all the voltage-sharing capacitors. In each switching period, uniformity of currents flowing through the upper and low switch tubes is obviously promoted, and the three defects existing in an existing series circuit technology of the converter can be obviously improved.

Description

A kind of converter series circuit

Technical field

The present invention relates to a kind of converter series circuit, particularly a kind of DC-DC or DC-AC converter series circuit.

Background technology

When inlet highway voltage is higher, for solving the too high problem of switch tube voltage stress, can adopt the circuit structure of converter series connection.In addition, when the power output finite capacity of single inverter, can adopt equally the mode of converter series connection to increase total power output capacity.But in side circuit, mutually the parameter of the converter of series connection inevitably exists discreteness, the operating voltage skew that this may cause upper and lower switching tube, surpasses the withstand voltage of switching tube, causes the converter can not trouble free service.Can envision, in the circuit structure of converter series connection, technology of pressure equalization is one of key technology wherein.

Fig. 1 is a kind of known circuit structure with the converter series connection of automatically equalizing voltage function, and this circuit structure is published in the high pressure resistant eclipsed form flyback of the < < DC-DC converter design > > of < < electrotechnics magazine > > the 5th phase of calendar year 2001.August 24 calendar year 2001, < < by name patent for the equalizer circuit > > of supply convertor that Emerson Network Power CO., Ltd has adopted with it similarly circuit structure application, publication number is CN1126236.

The circuit theory diagrams of known pair of converter series connection as shown in Figure 1.

Be with the difference of general single-ended reverse exciting conversion, winding of converter of two converter series circuits is divided into identical two parts N1 and N2, and N1 and N2 control break-make by switching tube Q1 and Q2 respectively.The grid of Q1 and Q2 is added with synchronous driving signal.Like this, due to the consistency of N1, N2 and the synchronous working of Q1, Q2, the current potential that A is ordered is all pressed to be

$V_A=\frac{1}{2}{V}_g$... ... ... ... ... .. formula (1)

So the voltage stress that Q1 and Q2 bear is:

$V_{\mathrm{ds}}=\frac{1}{2}{V}_g+N\&CenterDot;V_o$... ... ... ... .... formula (2)

V in formula_gfor input direct voltage, V_ooutput voltage, N is winding N1 and the turn ratio of exporting main winding.

Here, C1, C2 be for set up the impartial operating voltage of pipe up and down at booting moment, and after power work, still have and all press and effect that mid-point voltage that filtering temporary disturbance causes departs from.

In Fig. 1, due to the symmetry of winding N1 and N2 with adopted identical C1 and C2, if mid-point voltage V_abe offset, circuit can be corrected automatically.

When input voltage is all pressed, upper and lower two anti exciting converter work are consistent, there is no energy exchange, only have two the former limit of anti exciting converter magnetizing inductance energy storage, its equivalent electric circuit as shown in Figure 2, wherein, Lk1, Lk2 are two corresponding leakage inductances of anti exciting converter, and Lm1, Lm2 are the magnetizing inductance of two converters.

When two converter input voltages are inconsistent, there is energy exchange in two anti exciting converters.Because two former limit Motor Winding Same Name of Ends are identical, be normal shock relation, i.e. transformer relation, energy is poured into the low Na of input voltage mono-tunnel from the high Na of input voltage mono-tunnel, realizes all and pressing.Suppose V_c1> V_c2, at this moment the equivalent electric circuit of the operating state of equalizer circuit and power flow direction are as shown in Figure 3.

Pressure equalizing specifically describes as follows: if for a certain reason, the current potential that A is ordered moves down, and occurs V_c1> V_c2situation.When switching tube Q1, Q2 driven moment, due to Q1 conducting, N1 winding voltage V₁=V_c1, again due to winding N1 and N2 close-coupled, so there is V₂> V_c2, in this case, reverse bias between the drain electrode of Q2, source electrode, the body diode Qd2 conducting of Q2, electric current reverse flow is crossed Qd2 and winding N2; Q1 forward conduction.According to the direction of flowing through of electric current, V_c1to decline, V_c2to rise, so V_c1with V_c2inconsistent being repaired.

The shortcoming that above-mentioned converter series circuit configuration has is:

1. the current-sharing poor effect of upper and lower switching tube.

When reality is used,capacitor C 1, C2 are used high-voltage electrolytic capacitor conventionally, are subject to the impact of manufacturing process, even the electrochemical capacitor of same batch, their equivalent series impedance has larger discreteness.Because equivalent series resistance there are differences and the existence of former limit peak current detecting resistance, the equiva lent impedance that equalizing current is flowed through in path N1-Q1-C1-N1 and N2-Q2-C2-N2 is unequal; And when C1, C2 are used electrochemical capacitor, equivalent series resistance (ESR) and detecting resistance are the principal elements that affects impedance loop difference.

When switch is static, on impedance loop, do not produce pressure drop, the voltage on C1, C2 and upper and lower two converters is impartial; When switch motion, can on discrepant impedance loop, produce discrepant pressure drop, thereby cause the voltage of upper and lower switching tube unequal, and then occur automatically equalizing voltage process.

Therefore, in continuous switch motion, the operating voltage of upper and lower two converters can sustainable existence difference, the process of automatically equalizing voltage can sustainable existence, thus the electric current of make to flow through Q1 and Q2 there are differences.When system adopts former limit peak current to control, probably misoperation.

The size of the upper and lower switching tube current deviation value of flowing through is:

$\mathrm{\&Delta;I}\left(t\right)=I_1\left(t\right)-I_2\left(t\right)=\frac{\mathrm{\&Delta;<figure-callout\; label="V\; R\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">V</figure-callout>}}{R_{\mathrm{eq}}}\&CenterDot;(1-e^{-\frac{{\mathrm{<figure-callout\; label="tR\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">tR</figure-callout>}}_{\mathrm{eq}}}{{\mathrm{Lk}}_1}})-\frac{\mathrm{\&Delta;V}}{R_{\mathrm{eq}2}}\&CenterDot;(1-e^{-\frac{{\mathrm{tR}}_{\mathrm{eq}2}}{{\mathrm{Lk}}_2}})$

$\&DoubleRightArrow;\mathrm{\&Delta;I}\left(t\right)=\mathrm{\&Delta;V}\&CenterDot;\frac{R_{\mathrm{eq}2}-R_{\mathrm{eq}1}}{{\mathrm{<figure-callout\; label="R\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{eq}}\&CenterDot;R_{\mathrm{eq}2}}+\mathrm{\&Delta;<figure-callout\; label="V\; R\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">V</figure-callout>}\frac{R_{\mathrm{eq}}}{}\frac{1_{}\&CenterDot;e^{-\frac{{\mathrm{tR}}_{\mathrm{eq}2}}{{\mathrm{Lk}}_2}}-R_{\mathrm{eq}2}\&CenterDot;e^{-\frac{\mathrm{<figure-callout\; label="t\; R\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">t</figure-callout>}{R}_{\mathrm{eq}}{1}_{}}{{\mathrm{Lk}}_1}}}{{\mathrm{<figure-callout\; label="R\; eq"\; filenames="HDA0000420071980000051.png,HDA0000420071980000071.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{eq}}\&CenterDot;R_{\mathrm{eq}2}}$

Wherein, R_eq1with R_eq2it is respectively the equiva lent impedance (equiva lent impedance that does not comprise leakage inductance) that equalizing current is flowed through in path N1-Q1-C1-N1 and N2-Q2-C2-N2; Δ V is V_c1with V_c2pressure reduction.From the above, work as R_eq1with R_eq2while equating, the difference between current Δ I (t) of the upper and lower switching tube of flowing through is almost nil; R_eq1with R_eq2differ larger, the difference between current Δ I (t) of the upper and lower switching tube of flowing through also can be larger.There is difference in can finally cause the flowing through peak current of Q1, Q2 of the Δ I (t) in a switch periods.Test and emulation all prove, work as R_eq1> R_eq2time, the peak current of the Q1 that flows through is less than the peak current of the Q2 that flows through; Work as R_eq1< R_eq2time, the peak current of the Q1 that flows through is greater than the peak current of the Q2 that flows through; This has a strong impact on the control of former limit peak current.Peak current difference also can make upper and lower temperature rise of switching tube there are differences, and has reduced the reliability of circuit.

Use the circuit of known Fig. 1, make maximum input voltage 600VDC, output 24VDC, the converter that output current is 0.42A, i.e. power output 10W.The agent structure of circuit is two anti exciting converter series connection of magnetic core altogether, and major parameter is:capacitor C 1, C2 are 4.7uF/400V electrochemical capacitor (their equivalent series resistance may have deviation), and Q1, Q2 are N-MOS pipe and are added with synchronous driving signal.

When the equivalent series resistance by C1 is than C2 equivalent series resistance large (be subject to the impact of high-voltage electrolytic capacitor manufacturing process, this situation completely likely exists), or other reasons, cause the equiva lent impedance R of loop N1-Q1-C1-N1_eq1compared with the equivalent series resistance R of loop N2-Q2-C2-N2_eq2during large 7.35 Ω left and right, at input 400VDC, record the current peak of the upper and lower switching tube of flowing through as shown in Table 1 under the condition of output 24V/0.42A, current waveform is as shown in Fig. 4-1, Fig. 4-2.

Table one

When the equivalent series resistance of C1 is than C2 equivalent series resistance little (be subject to the impact of high-voltage electrolytic capacitor manufacturing process, this situation equally likely exists), or other reasons, cause the equiva lent impedance R of loop N1-Q1-C1-N1_eq1compared with the equivalent series resistance R of loop N2-Q2-C2-N2_eq2during little 7.35 Ω left and right, at input 400VDC, record the current peak of the upper and lower switching tube of flowing through as shown in Table 2 under the condition of output 24V/0.42A, current waveform is as shown in Fig. 5-1, Fig. 5-2.

Table two

From above-mentioned data:

1. due to the difference of the equal hydraulic circuit impedance magnitude of upper downconverter, the upper and lower switching tube that can cause flowing through current peak there is notable difference, can have a strong impact on former limit peak current and control.

2. the peak current due to the upper and lower switching tube of flowing through there are differences, and at the switching tube Q1 of Synchronization Control and Q2, at shutdown moment, the transient peak voltage that bear at Q1 and Q2 drain-source the two poles of the earth has larger difference.

3. due to the existence ofshortcoming 1 and shortcoming 2, can cause the temperature rise situation of upper and lower switching tube inconsistent.When circuit is used for high-power output occasion, this shortcoming can reduce the reliability of circuit greatly.

Summary of the invention

Have in view of that, the object of the present invention is to provide a kind of converter series circuit, the electric current of the switching tube up and down in converter series circuit that can make to flow through is consistent to the full extent in each switch periods, improves the reliability of circuit.

For solving the problems of the technologies described above, a kind of converter series circuit, comprise supply convertor armature winding unit and equalizing capacitance that at least two groups are identical, every group of armature winding unit is comprised of identical armature winding and the switching tube of controlling this armature winding break-make, the grid of each switching tube is added with synchronous driving signal, and armature winding is with phase control and common magnetic core; Connect mutually in each armature winding unit, each equalizing capacitance is connected mutually; The series connection point of each armature winding unit is connected with all pressures series connection point of each equalizing capacitance and forms each self-corresponding loop, between the series connection point of described each armature winding unit and the series connection point of each equalizing capacitance, is connected with impedance device.

Described impedance device is resistance or inductance.

The resistance value of described resistance is 3～6 times of impedance difference of these resistance place two adjacent loops.

The present invention can also realize by following technical measures: a kind of converter series circuit, comprise two groups of identical supply convertor armature winding unit and equalizing capacitances, every group of armature winding unit is comprised of identical armature winding and the switching tube of controlling this armature winding break-make, the grid of each switching tube is added with synchronous driving signal, and armature winding is with phase control and common magnetic core; Connect mutually in two armature winding unit, two equalizing capacitances are connected mutually; The series connection point of two armature winding unit is connected with all pressures series connection point of two equalizing capacitances, is connected in series respectively the resistance that an impedance equates all pressing between series connection point and two equalizing capacitances.

Principle of the present invention is between the series connection point of described each armature winding unit and the series connection point of each equalizing capacitance, to be connected with after impedance device the resistance value R in above-mentioned adjacent cells loop_eq1, R_eq2equal increase, | R_eq1-R_eq2| remain unchanged,

greatly reduce, thereby Δ I (t) greatly reduces, it is impartial that the peak current of the upper and lower switching tube of flowing through is tending towards.Now, circuit still has good uniform voltage function.

The invention has the advantages that between the described series connection point of each armature winding unit and the series connection point of each equalizing capacitance and be connected with after impedance device, in each switch periods, the consistency of upper and lower switching tube electric current of flowing through has obvious lifting, can make three defects that exist in existing converter series circuit technology, be significantly improved.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of two converter series circuits of prior art.

Fig. 2 is two converter series circuits of prior art equivalent electric circuits when switching tube conducting while all pressing.

Fig. 3 is the equivalent electric circuit when switching tube conducting when to be that the two converter series circuits of prior art are uneven press.

Fig. 4-1 adopts prior art circuits Fig. 1, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with large 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of the upper and lower switching tube difference between current Δ I (t) that flows through.Getting and flowing to electric capacity mid point is positive direction.

Fig. 4-2 adopt prior art circuits Fig. 1, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with large 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of flow through upper and lower switching tube Q1, Q2.

Fig. 5-1 adopts prior art circuits Fig. 1, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with little 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of the upper and lower switching tube difference between current Δ I (t) that flows through.Getting and flowing to electric capacity mid point is positive direction.

Fig. 5-2 adopt prior art circuits Fig. 1, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with little 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of flow through upper and lower switching tube Q1, Q2.

Fig. 6 is the circuit diagram of converter series circuit the first embodiment of the present invention

Fig. 7-1 adopts circuit diagram 6 of the present invention, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with large 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of the upper and lower switching tube difference between current Δ I (t) that flows through.Getting and flowing to electric capacity mid point is positive direction.

Fig. 7-2 adopt circuit diagram 6 of the present invention, when the equiva lent impedance of loop N1-Q1-C1-N1 is during compared with large 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of flow through upper and lower switching tube Q1, Q2.

Fig. 8-1 adopts circuit diagram 6 of the present invention, when the equiva lent impedance of loop N1-Q1-C2-C1-N1 is during compared with little 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of the upper and lower switching tube difference between current Δ I (t) that flows through.Getting and flowing to electric capacity mid point is positive direction.

Fig. 8-2 adopt circuit diagram 6 of the present invention, when the equiva lent impedance of loop N1-Q1-C2-C1-N1 is during compared with little 7.35 Ω of loop N2-Q2-C2-N2, and the measured waveform of flow through upper and lower switching tube Q1, Q2.

Fig. 9 is the circuit diagram of converter series circuit the second embodiment of the present invention.

Figure 10 is the enlarged capacity principle schematic diagram of circuit of the present invention.

Embodiment

Fig. 6 is first embodiment of the invention, as shown in Figure 6, is in series resistor R between converter armature winding unit mid point and equalizing capacitance mid point from prior art circuits Fig. 1 different, and the main body of circuit is inverse excitation type converter, and the operation principle of circuit is:

A winding of converter is divided into identical two parts N1 and N2, and N1 and N2 control break-make by switching tube Q1 and Q2 respectively.The grid of Q1 and Q2 is added with identical driving signal.Between converter series connection mid point and capacitances in series mid point A, by resistance R, be connected, due to the consistency of N1, N2 and the synchronous working of Q1, Q2, the current potential that A is ordered by equal pressures is

$V_A=\frac{1}{2}{V}_g$Formula (3) so, the voltage stress that Q1 and Q2 bear is:

$V_{\mathrm{ds}}=\frac{1}{2}{V}_g+N\&CenterDot;V_o$Formula (4)

V in formula_gfor input direct voltage, V_ooutput voltage, N is winding N1 and the turn ratio of exporting main winding.

Here, C1, C2 be for set up the impartial operating voltage of pipe up and down at booting moment, and after power work, still have and all press and effect that mid point that filtering temporary disturbance causes departs from.

Because the symmetry of winding N1 and N2 and adopted identical C1 and C2, if mid-point voltage V_abe offset, circuit can be corrected automatically.Its automatically equalizing voltage principle is consistent with aforesaid known circuits Fig. 1.

When reality is used, due to the equivalent series resistance of C1, C2, the impedance of N1, N2 winding, and the existence of the otherness of the conducting resistance of switching tube and former limit peak current detecting resistance, cause the equiva lent impedance R of loop N1-Q1-R-C1-N1_eq1compared with the equivalent series resistance R of loop N2-Q2-R-C2-N2_eq2inevitably there is difference | R_eq1-R_eq2|.Have above-mentioned analysis known, now, the upper and lower switching tube electric current of flowing through can there are differences.

When after converter mid point is connected in series impedance R with equalizing capacitance mid point, | R_eq1-R_eq2| value still remains unchanged, R_eq1, R_eq2the impedance that equal increase resistance R has.When the impedance of R | R_eq1-R_eq2| suitably get when large, preferentially get the impedance of R | R_eq1-R_eq2| large 3～6 times, can make

enough little; Thereby reduce to a great extent the value of Δ I (t), guarantee that upper and lower switch has good current-sharing effect.

The effect of the present embodiment is described with two groups of actual test datas below.

As shown in Figure 6, make equally input voltage 600VDC, output 24VDC, the converter that output current is 0.42A, i.e. power output 10W.The agent structure of circuit is two anti exciting converter series connection of magnetic core altogether, major parameter is:capacitor C 1, C2 are 4.7uF/400V electrochemical capacitor, Q1, Q2 are N-MOS pipe and are added with synchronous driving signal, resistance R is value 33 Ω in the present invention, and other parameters are consistent during all with test known circuits shortcoming.Like this, compare the equiva lent impedance R of loop N1-Q1-C1-N1 with known circuit diagram 1_eq1equiva lent impedance R with loop N2-Q2-C2-N2_eq2difference DELTA R remain unchanged, but R_eq1, R_eq2all impartial increase by 33 Ω,greatly reduce.

When the equivalent series resistance by C1 is than C2 equivalent series resistance large (be subject to the impact of high-voltage electrolytic capacitor manufacturing process, this situation completely likely exists), or other reasons, cause the equiva lent impedance R of loop N1-Q1-C1-N1_eq1compared with the equivalent series resistance R of loop N2-Q2-C2-N2_eq2during large 7.35 Ω left and right, at input 400VDC, record the current peak of the upper and lower switching tube of flowing through as shown in Table 3 under the condition of output 24V/0.42A, current waveform is as shown in Fig. 7-1, Fig. 7-2.

Table three

When the equivalent series resistance sum of C1 is than C2 equivalent series resistance sum little (be subject to the impact of high-voltage electrolytic capacitor manufacturing process, this situation equally likely exists), or other reasons, cause the equiva lent impedance R of loop N1-Q1-C1-N1_eq1compared with the equivalent series resistance R of loop N2-Q2-C2-N2_eq2during little 7.35 Ω left and right, at input 400VDC, record the current peak of the upper and lower switching tube of flowing through as shown in Table 4 under the condition of output 24V/0.42A, current waveform is as shown in Fig. 8-1, Fig. 8-2

Table four

With table three, contrast with the data of table one, table two respectively with the data of table four, can see, under equal input/output condition, converter series circuit of the present invention is compared with existing converter converter series circuit, in each switch periods, upper and lower switching tube has very significantly current-sharing effect.

From the weaknesses analysis of known circuits, after circuit of the present invention has improved the current-sharing effect of converter series circuit, can there is certain improvement to above-mentioned shortcoming 2 and shortcoming 3 equally.

In addition, in HF link, the capacitive reactance that electric capacity has, and the induction reactance impedance that inductance has has identical effect with resistance.Therefore, above-mentioned R should only not comprise resistance.In fact, when R is replaced to an inductance, be conducive to equally improve current-sharing effect.

Above-described embodiment is the analysis to two groups of series unit circuit, in the situation that more than two groups series units forms, as long as be connected impedance device between the series connection point of each armature winding unit and the series connection point of each equalizing capacitance, can realize same effect.

Fig. 9 is the circuit diagram of converter series circuit the second embodiment of the present invention, all pressing between series connection point and two equalizing capacitances of series unit, is connected in series respectively the resistance that an impedance equates.Specifically between the negative electrode of mid point A and C1, be connected in series impedance R1, between the anode of mid point A and C2, be connected in series impedance R2.When R1, R2 impedance equate, | R_eq1-R_eq2| remain unchanged, R_eq1, R_eq2equal increase, can reduce equally

value.And then reach the effect of improving upper and lower switching tube current-sharing.

Figure 10 is the enlarged capacity principle schematic diagram of circuit of the present invention.When input voltage is very high, may be a plurality of converter armature winding units in series, for the electric capacity of all pressing, also want a plurality of electric capacity packet chain to be unified into a pressure unit.Between the tie point of armature winding unit and the tie point of pressure unit, with resistance, be connected.Its principle is identical with embodiment mono-, and its power capacity increases.

Below be only the preferred embodiment of the present invention, it should be pointed out that above-mentioned preferred implementation should not be considered as limitation of the present invention, protection scope of the present invention should be as the criterion with claim limited range.For those skilled in the art, without departing from the spirit and scope of the present invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.Principle in execution mode is known, and any being conducive to reduces

the method of value all has above-mentioned beneficial effect.

Claims (5)

1. a converter series circuit, comprise supply convertor armature winding unit and equalizing capacitance that at least two groups are identical, every group of armature winding unit is comprised of identical armature winding and the switching tube of controlling this armature winding break-make, the grid of each switching tube is added with synchronous driving signal, and armature winding is with phase control and common magnetic core; Connect mutually in each armature winding unit, each equalizing capacitance is connected mutually; The series connection point of each armature winding unit is connected with all pressures series connection point of each equalizing capacitance and forms each self-corresponding loop, it is characterized in that: between the series connection point of described each armature winding unit and the series connection point of each equalizing capacitance, be connected with impedance device.

2. a kind of converter series circuit according to claim 1, is characterized in that: described impedance device is resistance.

3. a kind of converter series circuit according to claim 1, is characterized in that: 3～6 times of the impedance difference that the resistance value of described resistance is these resistance place two adjacent loops.

4. a kind of converter series circuit according to claim 1, is characterized in that: described impedance device is inductance.

5. a converter series circuit, comprise two groups of identical supply convertor armature winding unit and equalizing capacitances, every group of armature winding unit is comprised of identical armature winding and the switching tube of controlling this armature winding break-make, the grid of each switching tube is added with synchronous driving signal, and armature winding is with phase control and common magnetic core; Connect mutually in two armature winding unit, two equalizing capacitances are connected mutually; The series connection point of two armature winding unit is connected with all pressures series connection point of two each equalizing capacitances, it is characterized in that: be connected in series respectively the resistance that an impedance equates all pressing between series connection point and two equalizing capacitances.

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