Transformer-assisted PWM three-level zero-voltage soft switching inverter
阅读说明：本技术 一种变压器辅助型pwm三电平零电压软开关逆变器 (Transformer-assisted PWM three-level zero-voltage soft switching inverter ) 是由 禹健 安永泉 于 2020-04-16 设计创作，主要内容包括：本发明公开了一种变压器辅助型PWM三电平零电压软开关逆变器,在正半周期和负半周期逆变过程中,开关管S1,S2,S3和开关管S4,S5,S6互为辅助开关；本发明并未增加额外的辅助开关因此结构以及控制简单,实现了所有开关管的零电压开通,有效降低了开关管的开通损耗。(The invention discloses a transformer auxiliary PWM three-level zero-voltage soft switching inverter, wherein in the inverting process of a positive half cycle and a negative half cycle, switching tubes S1, S2 and S3 and switching tubes S4, S5 and S6 are auxiliary switches; the invention does not add an additional auxiliary switch, so the structure and the control are simple, the zero-voltage switching-on of all the switching tubes is realized, and the switching-on loss of the switching tubes is effectively reduced.)
1. The utility model provides a transformer auxiliary type PWM three-level zero voltage soft switch inverter which characterized in that: the high-voltage switch comprises a first main switch tube (S1), a second main switch tube (S2), a third main switch tube (S3), a fourth main switch tube (S4), a fifth main switch tube (S5), a sixth main switch tube (S6), a first voltage-dividing capacitor (Cd1), a second voltage-dividing capacitor (Cd2), an isolation transformer (T), a primary winding (T1), a secondary winding (T2), a clamping diode (D7), a resonant inductor (Lr), a flying capacitor (Cs), and a first main switch tube (S1)1) Source electrode, second main switch tube (S)2) The drain electrode of the switch tube is connected with a point a, and the two switch tubes form an upper bridge arm of the high-speed switch; the source electrode of the fourth main switching tube (S4) and the drain electrode of the fifth main switching tube (S5) are connected to a point b, and the two switching tubes form a high-speed switch lower bridge arm; the source electrode of the third main switching tube (S3) and the drain electrode of the sixth main switching tube (S6) are connected to a point c, and the two switching tubes form a low-speed switching bridge arm; the source electrode of the second main switching tube (S2), the drain electrode of the fourth main switching tube (S4), the negative electrode of the first voltage-dividing capacitor (Cd1) and the positive electrode of the second voltage-dividing capacitor (Cd2) are connected to a point o; the voltages at two ends of the first voltage division capacitor (Cd1) and the second voltage division capacitor (Cd2) are VDC/2 respectively; the anode of the first voltage-dividing capacitor (Cd1) is connected with the synonym end of the secondary winding (T2) of the isolation transformer (T) and the drain of the first switching tube (S1); the cathode of the second voltage division capacitor (Cd2) is connected with the anode of the clamping diode (D7) and the source of the fifth switching tube (S5); the cathode of the clamping diode (D7) is connected with the dotted terminal of the secondary winding (T2) of the transformer; one end of the resonant inductor (Lr) is connected with the point a, and the other end of the resonant inductor (Lr) is connected with the dotted end of a primary winding (T1) of the isolation transformer (T); the synonym terminal of a primary winding (T1) of the isolation transformer (T) is connected with the anode of the flying capacitor (Cs); cathode of flying capacitor (Cs)Is connected with the point b; the turn ratio of the primary winding (T1) of the isolation transformer (T) to the T2 is 1/k; one end of the load is connected to point c and the other end is connected to point o.
2. The transformer-assisted PWM three-level zero-voltage soft-switching inverter of claim 1, wherein:
when the load current is positive, the working mode and the switching time interval are as follows:
when the circuit is in steady state, S2、S3、S5In the on state, S1、S2、S4In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switching tube is in a turn-off state;
t0at time, turn off S5；
S5Delay DP1 after turn-off, turn on S4；
S4Delay DP2 after switching on, turn off S2；
S2Delay DP3 after turn-off, turn on S1；
S1Delay DP4 after switching on, turn off S4；
S4Delay DP5 after turn-off, turn on S5；
S5Delay DP6 after switching on, turn off S1；
S1Delay DP7 after turn-off, turn on S2；
The working mode and the switching time interval when the load current is negative are:
the circuit is in a steady state, S1、S4、S6In the on state, S2、S3、S5In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switching tube is in a turn-off state;
t0at time, turn off S1；
S1DN1 is delayed after the switch-off, and S is conducted2；
S2DN2 is delayed after conduction and S is turned off4；
S4DN3 is delayed after the switch-off, and S is conducted5；
S5DN4 is delayed after conduction and S is turned off2；
S2DN5 is delayed after the switch-off, and S is conducted1；
S1DN6 is delayed after conduction and S is turned off5；
S5DN7 is delayed after the switch-off, and S is conducted4；
The following parameters are all input quantities: vDCIs a dc bus voltage; t is3BShortest on time of S1 (S5); i isboostThe part of the commutation current peak value exceeding the load current; cossIs a main switch tube S1-S6Parallel absorption capacitance: coss＝C1＝C2＝C3＝C4＝C5＝C6(ii) a The following parameters can be expressed in terms of input quantity constraints; k is the turn ratio of the transformer; l isrIs a commutation inductance; l ismIs an excitation inductor; i isLm_0The excitation current value before the S5(S1) commutation is positively correlated with the load current value in each switching period;
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); t isA4_minT is the sum of the load current and the currentA-t4The time interval of (c).
3. The transformer-assisted PWM three-level zero-voltage soft-switching inverter of claim 2, wherein:
the specific description of each mode and the calculation process of the interval time when the output current is positive are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S2，S3,S5In a conducting state; load current ILoadBy S2，S3Follow current, exciting current iLmBy S2，S5Free flow of value of
Mode 2 (t)0-t1)：t0At time, turn off S5(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C5 and C4;
S5voltage across
wherein:
at t1At the moment, the potential at point b resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1Time of day, S5Charging to VDC/2，D4Conducting at zero voltage; excitation inductance LmAnd a commutation inductance LrVoltage across the series isCurrent of commutation iLrAnd an excitation current iLmDecrease with the same slope; t is tAAt the moment, the current conversion current and the excitation current are reversely reduced to zero, and the primary side of the transformer is clamped to be kVDC，S4May be in the time period t1-tAThe ZVS conduction is controlled between the two switches; t is tAThen, the voltage across the commutation inductor isThe voltage at two ends of the exciting inductor is kVDC(ii) a Current of commutation iLrAnd an excitation current iLmIncrease positively with a different slope; FIG. 5 and FIG. 6 show the present mode t1-tAAnd tA-t2A segment equivalent circuit;
t1-tAthe current conversion current is:
S4the soft on-time of (d) is:
S5turn off to S4The on-time interval DP1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonant current increases to a maximum value:
iR(t2)＝Iboost+iLoadformula (27)
Wherein: i isboostIs the part of the resonant current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S4is conducted to S2The off-time interval DP2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S2Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C1Discharge C2Charging, wherein the potential of the point a starts to rise in a resonant mode; FIG. 7 is an equivalent circuit of this mode;
S2voltage across
wherein:
t3at that time, the potential at the point a rises to VDC(ii) a The mode duration is:
wherein:
mode 5 (t)3-t4):t3At the moment, the potential at the point a rises to VDC,D1Natural conduction, S1The ZVS commutation condition is met; resonant inductor current iRLinear decrease, tBTime of day, resonant inductor current iRDown to the load current iLoad(ii) a Main switch tube S1May be in the time period t3-tBControl betweenThe guidance switch-on realizes ZVS switch-on; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S2turn off to S1The on-time interval DP3 is:
the mode duration is:
S1is conducted to S4The off-time interval DP4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iRReducing to 0; excitation currentIs increased to
S4voltage acrossAnd currentThe expression is as follows:
wherein:
at t6At the moment, the potential at the point b resonates to 0, and the duration of the mode is as follows:
mode 7 (t)6-t7):t6At the moment, the potential at the point b is reduced to 0, D5Conducting naturally; t is t6-t7The exciting current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S5the soft on-time of (d) is:
S4turn off to S5The on-time interval DP5 is:
t7time of day, exciting currentIs increased to
S5is conducted to S1The off-time interval DP6 is:
mode 8 (t)7-t8):t7At time, turn off S1Load current iLoadTo C1Charging, C2Discharging, and the potential at the point a is linearly reduced; t is t8At the moment, the potential at the point a is reduced to VDC/2, diode D2Conducting naturally; s2Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DP7 is:
DP7＝T7-8formula (49)
The specific description of each mode and the calculation process of the interval time when the output current is negative are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S1，S4,S6In a conducting state; load current ILoadBy S4，S6Follow current, exciting current iLmBy S1，S4Free flow of value of
Mode 2 (t)0-t1)：t0At time, turn off S1(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C1 and C2;
S1voltage across
wherein:
at t1At the moment, the potential at point a resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1At that time, the capacitor C1 charges to VDC2, D2 zero voltage conduction; excitation inductance LrAnd a commutation inductance LrA voltage across the terminals ofCurrent of commutation iLrAnd an excitation current iLmDecreasing inversely with the same slope; t is tAAt the moment, the current conversion current and the excitation current are reversely reduced to zero, and the primary side of the transformer is clamped to be kVDC，S2May be in the time period t1-tAThe ZVS conduction is controlled between the two switches; t is tAThen, the voltage across the commutation inductor is
t1-tAthe current conversion current is:
S2the soft on-time of (d) is:
S1turn off to S2The on-time interval DN1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonant current increases to a maximum value:
iR(t2)＝Iboost+iLoadformula (58)
Wherein: i isboostIs the part of the resonant current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S2is conducted to S4The off-time interval DN2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S4Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C5Discharge C4Charging, and the potential of the point b starts to decrease in resonance; FIG. 7 is an equivalent circuit of this mode;
S4voltage acrossAnd a resonant current iRThe expression is as follows:
wherein:
t3at the moment, the potential of the point b is reduced to 0; the mode duration is:
wherein:
mode 5 (t)3-t4):t3At that time, the potential at the point a is reduced to 0, D5Natural conduction, S5The ZVS commutation condition is met; resonant current iRLinear decrease, tBTime of day, resonant current iRDown to the load current iLoad(ii) a Main switch tube S5May be in the time period t3-tBThe ZVS conduction is realized by controlling the conduction; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S4turn off to S5The on-time interval DN3 is:
the mode duration is:
S5is conducted to S2The off-time interval DN4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iLrDown to 0, exciting current iLmIs raised tot5At time, turn off S2(ii) a Excitation currentTo C2Charging C1Discharging, and the potential of the point a starts to rise in resonance; FIG. 4 is an equivalent circuit of this mode;
S2voltage across
wherein:
at t6At the moment, the potential at point a resonates to VDCThe pattern duration is:
mode 7 (t)6-t7):t6At the moment, the potential at the point a rises to VDC，D1Conducting naturally; t is t6-t7The commutation current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S1the soft on-time of (d) is:
S2turn off to S1The on-time interval DN5 is:
t7time of day, exciting current
S1is conducted to S5The off-time interval DN6 is:
mode 8 (t)7-t8):t7At time, turn off S5Load current iLoadTo C6Charging, C5Discharging, wherein the potential at the point b rises linearly; t is t8At the moment, the potential at the point b rises to VDC/2, diode D4Conducting naturally; s4Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DN7 is:
DN7＝T7-8formula (80)
According to the analysis of the circuit structure and the working principle, the switch needs to design a commutation inductor, an excitation inductor, a transformer turn ratio and a switch parallel absorption capacitor when completing zero-voltage commutation; the design of the above parameters of each element is completed as follows (analysis is performed with the output current as positive time);
when (1/2-k) VDCLess than VDCWhen the current is more than the load current, the S2 is cut off under the condition that the current conversion current is larger than a certain value, so that the switching tube can reliably complete current conversion; and the turn-off loss of the main switch is proportional to the square of the channel current at the turn-off instant [8,13 ]]Thus S2The turn-off loss of the main switch is approximately negligible (turn-off loss is less than 1/10) when the formula is satisfied:
wherein ILoad_rmsIs the effective value of the load current;
during actual circuit operation, load current detection has errors, resulting in IboostError of (2), influence commutation time T2-3And ZVT on-time T3BAfter summation of the formula IrDerivation is carried out asrThe dead time of the main switch when the formula is met can be a fixed value;
simultaneous:
thus, obtaining:
wherein the value range of beta obtained by the solution of the sum is as follows:
to ensure S5Reliable commutation and S4Enough ZVS on time, assume Lm＞＞LrObtaining the following components:
to ensure magnetizing current in commutation inductor LrAfter the linear discharge phase (t ═ t)4) And S5Before commutation (t ═ t)0) Equal in size and opposite in direction (neglecting the change of magnetizing current at the resonant commutation stage of the lower bridge arm):
t above1A，TA4Are all related to the load current, when the load current is 0, T1AAnd TA4Value of at least T1A_minTA4_minL calculated under the conditionsmAccording to the condition that S is greater than 0 when any load current is4There is a requirement for enough ZVS on-time; thus:
the excitation current can be represented by the following formula:
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); whereby each switching cycle
Technical Field
The invention relates to the technical field of power electronic conversion, in particular to a transformer auxiliary PWM three-level zero-voltage soft switching inverter.
Background
Although the topology circuit and the control principle are simple, the commonly used hard switching technology generates huge switching loss, the hard switching frequency of the high-power IGBT is severely limited to a few kHz, and in addition, the hard switching can generate high-frequency electromagnetic interference to influence the normal operation of surrounding electronic equipment. The basic idea of the soft switching technology is to make the power device perform a switching action when the voltage or current value of the power device is low or even zero by the aid of the resonant tank, so as to weaken or even completely eliminate the overlapping of the voltage and the current of the power device.
Compared with a two-level rectifier, the multi-level rectifier has many advantages, the voltage peak value born by each power switch tube is only 1/N of that of the two-level rectifier, the voltage stress of the power switch tube is reduced, and the problem that the voltage resistance of the switch tube is not high enough is solved. In addition, the multi-level rectifier has better power quality, higher voltage and power capacity and lower electromagnetic interference. Therefore, multi-level rectifiers are well suited for high power applications.
The two-level ZVT technique can be extended to three levels. However, the corresponding soft-switching three-level topology suffers from the problems of excessive auxiliary switching tubes and complicated control. In the prior art, Evaluation of soft switching technologies for the Neutral-Point-clamped (npc) Inverter summarizes four soft switching three-level circuits, wherein four circuits all have four auxiliary switching tubes, although the soft switching of the main switching tube is realized and the loss of the switching tube is reduced to a certain extent, the circuit structure and the control are complex and expensive, and the volume is large, so that the soft switching three-level circuit is not suitable for practical occasions. The prior art reduces two switching tubes on the basis of the prior art and provides a novel three-level zero-voltage switching and zero-current switching converter circuit. The technology is significantly simplified in terms of circuit structure and control compared to the technology, but the application is still relatively complicated in practice.
Disclosure of Invention
In order to solve the defects and shortcomings of the prior art, the transformer auxiliary PWM three-level zero-voltage soft switching inverter is provided, and the three-level zero-voltage soft switching circuit has the advantages of simple structure and control, realization of zero-voltage conduction of all switching tubes, effective reduction of conduction loss of the switching tubes and more easiness in practicability.
The transformer auxiliary PWM three-level zero-voltage soft switching inverter comprises a first main switching tube (S1), a second main switching tube (S2), a third main switching tube (S3), a fourth main switching tube (S4), a fifth main switching tube (S5), a sixth main switching tube (S6), a first voltage division capacitor (Cd1), a second voltage division capacitor (Cd2), an isolation transformer (T), a primary winding (T1), a secondary winding (T2), a clamping diode (D7), a resonant inductor (Lr), a flying capacitor (Cs), and a first main switching tube (S1)1) Source electrode, second main switch tube (S)2) The drain electrode of the switch tube is connected with a point a, and the two switch tubes form an upper bridge arm of the high-speed switch; a source electrode of the fourth main switching tube (S4),The drain electrode of a fifth main switching tube (S5) is connected to a point b, and the two switching tubes form a high-speed switching lower bridge arm; the source electrode of the third main switching tube (S3) and the drain electrode of the sixth main switching tube (S6) are connected to a point c, and the two switching tubes form a low-speed switching bridge arm; the source electrode of the second main switching tube (S2), the drain electrode of the fourth main switching tube (S4), the negative electrode of the first voltage-dividing capacitor (Cd1) and the positive electrode of the second voltage-dividing capacitor (Cd2) are connected to a point o; the voltages at two ends of the first voltage division capacitor (Cd1) and the second voltage division capacitor (Cd2) are VDC/2 respectively; the anode of the first voltage-dividing capacitor (Cd1) is connected with the synonym end of the secondary winding (T2) of the isolation transformer (T) and the drain of the first switching tube (S1); the cathode of the second voltage division capacitor (Cd2) is connected with the anode of the clamping diode (D7) and the source of the fifth switching tube (S5); the cathode of the clamping diode (D7) is connected with the dotted terminal of the secondary winding (T2) of the transformer; one end of the resonant inductor (Lr) is connected with the point a, and the other end of the resonant inductor (Lr) is connected with the dotted end of a primary winding (T1) of the isolation transformer (T); the synonym terminal of a primary winding (T1) of the isolation transformer (T) is connected with the anode of the flying capacitor (Cs); the cathode of the flying capacitor (Cs) is connected with the point b; the turn ratio of the primary winding (T1) of the isolation transformer (T) to the T2 is 1/k; one end of the load is connected to point c and the other end is connected to point o.
As a further improvement of the above scheme, when the load current is positive, the operation mode and the switching time interval are as follows:
when the circuit is in steady state, S2、S3、S5In the on state, S1、S2、S4In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switching tube is in a turn-off state;
t0at time, turn off S5；
S5Delay DP1 after turn-off, turn on S4；
S4Delay DP2 after switching on, turn off S2；
S2Delay DP3 after turn-off, turn on S1；
S1Delay DP4 after switching on, turn off S4；
S4Delay DP5 after turn-off, turn on S5；
S5Delay DP6 after switching on, turn off S1；
S1Delay DP7 after turn-off, turn on S2；
The working mode and the switching time interval when the load current is negative are:
the circuit is in a steady state, S1、S4、S6In the on state, S2、S3、S5In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switching tube is in a turn-off state;
t0at time, turn off S1；
S1DN1 is delayed after the switch-off, and S is conducted2；
S2DN2 is delayed after conduction and S is turned off4；
S4DN3 is delayed after the switch-off, and S is conducted5；
S5DN4 is delayed after conduction and S is turned off2；
S2DN5 is delayed after the switch-off, and S is conducted1；
S1DN6 is delayed after conduction and S is turned off5；
S5DN7 is delayed after the switch-off, and S is conducted4；
The following parameters are all input quantities: vDCIs a dc bus voltage; t is3BShortest on time of S1 (S5); i isboostThe part of the commutation current peak value exceeding the load current; cossIs a main switch tube S1-S6Parallel absorption capacitance: coss＝C1＝C2＝C3＝C4＝C5＝C6(ii) a The following parameters can be expressed in terms of input quantity constraints; k is the turn ratio of the transformer; l isrIs a commutation inductance; l ismIs an excitation inductor;
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); t isA4_minT is the sum of the load current and the currentA-t4The time interval of (c).
As a further improvement of the above scheme, the specific description of each mode and the calculation process of the interval time when the output current is positive are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S2，S3,S5In a conducting state; load current ILoadBy S2，S3Follow current, exciting current iLmBy S2，S5Free flow of value of
Mode 2 (t)0-t1)：t0At the moment of time, the time of day,off S5(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C5 and C4;
S5voltage acrossAnd currentThe expression is as follows:
wherein:
at t1At the moment, the potential at point b resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1Time of day, S5Charging to VDC/2，D4Conducting at zero voltage; excitation inductance LmAnd a commutation inductance LrVoltage across the series is
t1-tAthe current conversion current is:
S4the soft on-time of (d) is:
S5turn off to S4The on-time interval DP1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonant current increases to a maximum value:
iR(t2)＝Iboost+iLoadformula (27)
Wherein: i isboostIs the part of the resonant current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S4is conducted to S2The off-time interval DP2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S2Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C1Discharge C2Charging, wherein the potential of the point a starts to rise in a resonant mode; FIG. 7 is an equivalent circuit of this mode;
S2voltage across
wherein:
t3at that time, the potential at the point a rises to VDC(ii) a The mode duration is:
wherein:
mode 5 (t)3-t4):t3At the moment, the potential at the point a rises to VDC,D1Natural conduction, S1The ZVS commutation condition is met; resonant inductor current iRLinear decrease, tBTime of day, resonant inductor current iRDown to the load current iLoad(ii) a Main switch tube S1May be in the time period t3-tBThe ZVS conduction is realized by controlling the conduction; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S2turn off to S1The on-time interval DP3 is:
the mode duration is:
S1is conducted to S4The off-time interval DP4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iRReducing to 0; excitation current
S4voltage across
wherein:
at t6At the moment, the potential at the point b resonates to 0, and the duration of the mode is as follows:
mode 7 (t)6-t7):t6At the moment, the potential at the point b is reduced to 0, D5Conducting naturally; t is t6-t7The exciting current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S5the soft on-time of (d) is:
S4turn off to S5The on-time interval DP5 is:
t7time of day, exciting currentIs increased to
S5is conducted to S1The off-time interval DP6 is:
mode 8 (t)7-t8):t7At time, turn off S1Load current iLoadTo C1Charging, C2Discharging, and the potential at the point a is linearly reduced; t is t8At the moment, the potential at the point a is reduced to VDC/2, diode D2Conducting naturally; s2Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DP7 is:
DP7＝T7-8formula (49)
The specific description of each mode and the calculation process of the interval time when the output current is negative are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S1，S4,S6In a conducting state; load current ILoadBy S4，S6Follow current, exciting current iLmBy S1，S4Free flow of value of
Mode 2 (t)0-t1)：t0At time, turn off S1(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C1 and C2;
S1voltage across
wherein:
at t1At the moment, the potential at point a resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1At that time, the capacitor C1 charges to
t1-tAthe current conversion current is:
S2the soft on-time of (d) is:
S1turn off to S2The on-time interval DN1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonant current increases to a maximum value:
iR(t2)＝Iboost+iLoadformula (58)
Wherein: i isboostIs at resonancePart of the current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S2is conducted to S4The off-time interval DN2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S4Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C5Discharge C4Charging, and the potential of the point b starts to decrease in resonance; FIG. 7 is an equivalent circuit of this mode;
S4voltage acrossAnd a resonant current iRThe expression is as follows:
wherein:
t3at the moment, the potential of the point b is reduced to 0; the mode duration is:
wherein:
mode 5 (t)3-t4):t3At that time, the potential at the point a is reduced to 0, D5Natural conduction, S5The ZVS commutation condition is met; resonant current iRLinear decrease, tBTime of day, resonant current iRDown to the load current iLoad(ii) a Main switch tube S5May be in the time period t3-tBThe ZVS conduction is realized by controlling the conduction; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S4turn off to S5The on-time interval DN3 is:
the mode duration is:
S5is conducted to S2The off-time interval DN4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iLrDown to 0, exciting current iLmIs raised to；t5At time, turn off S2(ii) a Excitation current
S2voltage across
wherein:
at t6At the moment, the potential at point a resonates to VDCThe pattern duration is:
mode 7 (t)6-t7):t6At the moment, the potential at the point a rises to VDC，D1Conducting naturally; t is t6-t7The commutation current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S1the soft on-time of (d) is:
S2turn off to S1The on-time interval DN5 is:
t7time of day, exciting current
S1is conducted to S5The off-time interval DN6 is:
mode 8 (t)7-t8):t7At time, turn off S5Load current iLoadTo C6Charging, C5Discharging, wherein the potential at the point b rises linearly; t is t8At the moment, the potential at the point b rises to VDC/2, diode D4Conducting naturally; s4Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DN7 is:
DN7＝T7-8formula (80)
According to the analysis of the circuit structure and the working principle, the switch needs to design a commutation inductor, an excitation inductor, a transformer turn ratio and a switch parallel absorption capacitor when completing zero-voltage commutation; the design of the above parameters of each element is completed as follows (analysis is performed with the output current as positive time);
when (1/2-k) VDCLess than VDCWhen/2, the S is cut off under the condition that the commutation current is larger than the load current by a certain value2Ensuring that the switching tube reliably completes current conversion; and the turn-off loss of the main switch is proportional to the square of the channel current at the turn-off instant [8,13 ]]Thus S2The turn-off loss of the main switch is approximately negligible (turn-off loss is less than 1/10) when the formula is satisfied:
wherein ILoad_rmsIs the effective value of the load current;
during actual circuit operation, load current detection has errors, resulting in IboostError of (2), influence commutation time T2-3And ZVT on-time T3BAfter summation of the formula IrDerivation is carried out asrThe dead time of the main switch when the formula is met can be a fixed value;
simultaneous:
thus, obtaining:
wherein the value range of beta obtained by the solution of the sum is as follows:
to ensure S5Reliable commutation and S4Enough to get ZVS onOn time, assume Lm＞＞LrObtaining the following components:
to ensure magnetizing current in commutation inductor LrAfter the linear discharge phase (t ═ t)4) And S5Before commutation (t ═ t)0) Equal in size and opposite in direction (neglecting the change of magnetizing current at the resonant commutation stage of the lower bridge arm):
t above1A，TA4Are all related to the load current, when the load current is 0, T1AAnd TA4Value of at least T1A_minTA4_minL calculated under the conditionsmAccording to the condition that S is greater than 0 when any load current is4There is a requirement for enough ZVS on-time; thus:
the excitation current can be represented by the following formula:
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); whereby each switching cycleDifferent.
The invention has the beneficial effects that:
compared with the prior art, in the transformer auxiliary PWM three-level zero-voltage soft switching inverter, in the inversion process of the positive half period and the negative half period, the switching tubes S1, S2 and S3 and the switching tubes S4, S5 and S6 are auxiliary switches; the invention does not add an additional auxiliary switch, so the structure and the control are simple, the zero-voltage switching-on of all the switching tubes is realized, and the switching-on loss of the switching tubes is effectively reduced.
Drawings
The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings, in which:
FIG. 1 is a transformer-assisted PWM three-level zero-voltage soft-switching inverter circuit of the present invention;
FIG. 2 is a state diagram of the circuit of the present invention for each mode within one PWM switching period when the output current is positive;
FIG. 3 is a state diagram of the circuit of the present invention in each mode during a PWM switching cycle when the output current is negative;
FIG. 4 is an equivalent circuit diagram of
FIGS. 5 and 6 are equivalent circuit diagrams of patterns 3t1-tA and t1-tA in one PWM switching period according to the present invention;
FIG. 7 is a schematic diagram of the equivalent circuit of
FIG. 8 is a schematic diagram of the equivalent circuit of mode 5 in one PWM switching cycle in accordance with the present invention;
FIG. 9 is a schematic diagram of the equivalent circuit of
FIG. 10 is a waveform diagram of the driving pulse signal and the main node voltage and the branch current of each switching tube in a PWM switching period when the output current is positive in the circuit of the present invention;
FIG. 11 is a waveform diagram of the driving pulse signal and the main node voltage and current of each switching tube in a PWM switching period when the output current is negative.
Detailed Description
As shown in fig. 1-11, the transformer-assisted PWM three-level zero-voltage soft switching inverter of the present invention includes a first main switching tube S1, a second main switching tube S2, a third main switching tube S3, a fourth main switching tube S4, a fifth main switching tube S5, a sixth main switching tube S6, a first voltage-dividing capacitor Cd1, a second voltage-dividing capacitor Cd1A capacitor Cd2, an isolation transformer T, a primary winding T1, a secondary winding T2, a clamping diode D7, a resonant inductor Lr, a flying capacitor Cs, a first main switch tube S1Source electrode and second main switch tube S2The drain electrode of the switch tube is connected with a point a, and the two switch tubes form an upper bridge arm of the high-speed switch; the source electrode of the fourth main switching tube S4 and the drain electrode of the fifth main switching tube S5 are connected to a point b, and the two switching tubes form a high-speed switch lower bridge arm; the source electrode of the third main switch tube S3 and the drain electrode of the sixth main switch tube S6 are connected to the point c, and the two switch tubes form a low-speed switch bridge arm; the source electrode of the second main switching tube S2, the drain electrode of the fourth main switching tube S4, the negative electrode of the first voltage division capacitor Cd1 and the positive electrode of the second voltage division capacitor Cd2 are connected to a point o; voltages at two ends of the first voltage division capacitor Cd1 and the second voltage division capacitor Cd2 are VDC/2 respectively; the anode of the first voltage division capacitor Cd1 is connected with the synonym terminal of the secondary winding T2 of the isolation transformer T and the drain of the first switching tube S1; the cathode of the second voltage division capacitor Cd2 is connected with the anode of the clamping diode D7 and the source of the fifth switching tube S5; the cathode of the clamping diode D7 is connected with the dotted terminal of the transformer secondary winding T2; one end of the resonant inductor Lr is connected with the point a, and the other end of the resonant inductor Lr is connected with the dotted end of a primary winding T1 of the isolation transformer T; the synonym terminal of a primary winding T1 of the isolation transformer T is connected with the anode of the flying capacitor Cs; the cathode of the flying capacitor Cs is connected with the point b; the turn ratio of the primary winding T1 of the isolation transformer T to the T2 is 1/k; one end of the load is connected to point c and the other end is connected to point o.
Further improved, when the load current is positive, the working mode and the switching time interval are as follows:
when the circuit is in steady state, S2、S3、S5In the on state, S1、S2、S4In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switching tube is in a turn-off state;
t0at time, turn off S5；
S5Delay DP1 after turn-off, turn on S4；
S4Delay DP2 after switching on, turn off S2；
S2Delay DP3 after turn-off, turn on S1；
S1Delay DP4 after switching on, turn off S4；
S4Delay DP5 after turn-off, turn on S5；
S5Delay DP6 after switching on, turn off S1；
S1Delay DP7 after turn-off, turn on S2；
The working mode and the switching time interval when the load current is negative are:
the circuit is in a steady state, S1、S4、S6In the on state, S2、S3、S5In an off state; clamping diode D7、D8、D9And the anti-parallel diode of the switch tube is in turn-off stateA state;
t0at time, turn off S1；
S1DN1 is delayed after the switch-off, and S is conducted2；
S2DN2 is delayed after conduction and S is turned off4；
S4DN3 is delayed after the switch-off, and S is conducted5；
S5DN4 is delayed after conduction and S is turned off2；
S2DN5 is delayed after the switch-off, and S is conducted1；
S1DN6 is delayed after conduction and S is turned off5；
S5DN7 is delayed after the switch-off, and S is conducted4；
The following parameters are all input quantities: vDCIs a dc bus voltage; t is3BIs the most S1(S5)Short turn-on time; i isboostThe part of the commutation current peak value exceeding the load current; cossIs a main switch tube S1-S6Parallel absorption capacitance: coss＝C1＝C2＝C3＝C4＝C5＝C6(ii) a The following parameters can be expressed in terms of input quantity constraints; k is the turn ratio of the transformer; l isrIs a commutation inductance; l ismIs an excitation inductor;the excitation current value before the S5(S1) commutation is positively correlated with the load current value in each switching period;
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); t isA4_minT is the sum of the load current and the currentA-t4The time interval of (c).
Further improved, when the output current is positive, the specific description of each mode and the calculation process of the interval time are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S2，S3,S5In a conducting state; load current ILoadBy S2，S3Follow current, exciting current iLmBy S2，S5Free flow of value of
Mode 2 (t)0-t1)：t0At time, turn off S5(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C5 and C4;
S5voltage across
wherein:
at t1At the moment, the potential at point b resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1Time of day, S5Charging to VDC/2，D4Conducting at zero voltage; excitation inductance LmAnd a commutation inductance LrVoltage across the series isCurrent of commutation iLrAnd an excitation current iLmDecrease with the same slope; t is tATime of day, current of changeThe current and the exciting current are reversely reduced to zero, and the primary side of the transformer is clamped to kVDC，S4May be in the time period t1-tAThe ZVS conduction is controlled between the two switches; t is tAThen, the voltage across the commutation inductor isThe voltage at two ends of the exciting inductor is kVDC(ii) a Current of commutation iLrAnd an excitation current iLmIncrease positively with a different slope; FIG. 5 and FIG. 6 show the present mode t1-tAAnd tA-t2A segment equivalent circuit;
t1-tAthe current conversion current is:
S4the soft on-time of (d) is:
S5turn off to S4The on-time interval DP1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonant current increases to a maximum value:
iR(t2)＝Iboost+iLoadformula (27)
Wherein: i isboostIs the part of the resonant current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S4is conducted to S2The off-time interval DP2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S2Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C1Discharge C2Charging, wherein the potential of the point a starts to rise in a resonant mode; FIG. 7 is an equivalent circuit of this mode;
S2voltage across
wherein:
t3at that time, the potential at the point a rises to VDC(ii) a The mode duration is:
wherein:
mode 5 (t)3-t4):t3At the moment, the potential at the point a rises to VDC,D1Natural conduction, S1The ZVS commutation condition is met; resonant inductor current iRLinear decrease, tBTime of day, resonant inductor current iRDown to the load current iLoad(ii) a Main switch tube S1May be in the time period t3-tBThe ZVS conduction is realized by controlling the conduction; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S2turn off to S1The on-time interval DP3 is:
the mode duration is:
S1is conducted to S4The off-time interval DP4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iRReducing to 0; excitation current
S4voltage acrossAnd current
wherein:
at t6At the moment, the potential at the point b resonates to 0, and the duration of the mode is as follows:
mode 7 (t)6-t7):t6At the moment, the potential at the point b is reduced to 0, D5Conducting naturally; t is t6-t7The exciting current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S5the soft on-time of (d) is:
S4turn off to S5The on-time interval DP5 is:
t7time of day, exciting current
S5is conducted to S1The off-time interval DP6 is:
mode 8 (t)7-t8):t7At time, turn off S1Load current iLoadTo C1Charging, C2Discharging, and the potential at the point a is linearly reduced; t is t8At the moment, the potential at the point a is reduced to VDC/2, diode D2Conducting naturally; s2Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DP7 is:
DP7＝T7-8formula (49)
The specific description of each mode and the calculation process of the interval time when the output current is negative are as follows:
mode 1 (t)<t0): the circuit is in a steady state, S1，S4,S6In a conducting state; load current ILoadBy S4，S6Follow current, exciting current iLmBy S1，S4Free flow of value of
Mode 2 (t)0-t1)：t0At time, turn off S1(ii) a FIG. 4 is an equivalent circuit of this mode; excitation inductance LmAnd a commutation inductance LrThe series connection resonates with the capacitors C1 and C2;
S1voltage across
wherein:
at t1At the moment, the potential at point a resonates to VDCAnd/2, the duration of the mode is as follows:
mode 3 (t)1-t2)：t1At that time, the capacitor C1 charges to
t1-tAthe current conversion current is:
S2the soft on-time of (d) is:
S1turn off to S2The on-time interval DN1 is:
tA-t2the increment of the resonance current, namely the part of the commutation current not including the excitation current (namely the current participating in the S1 commutation) is as follows:
t2at the moment, the value of the resonance current increases to the maximumThe value:
iR(t2)＝Iboost+iLoadformula (58)
Wherein: i isboostIs the part of the resonant current exceeding the load current
Simultaneous, charging mode (T)A2) The duration of (c) is:
S2is conducted to S4The off-time interval DN2 is:
mode 4 (t)2-t3):t2At the moment, the main switch S4Off, resonant current iRPart I of the medium excess load currentboostTo the capacitor C5Discharge C4Charging, and the potential of the point b starts to decrease in resonance; FIG. 7 is an equivalent circuit of this mode;
S4voltage acrossAnd a resonant current iRThe expression is as follows:
wherein:
t3at the moment, the potential of the point b is reduced to 0; the mode duration is:
wherein:
mode 5 (t)3-t4):t3At that time, the potential at the point a is reduced to 0, D5Natural conduction, S5The ZVS commutation condition is met; resonant current iRLinear decrease, tBTime of day, resonant current iRDown to the load current iLoad(ii) a Main switch tube S5May be in the time period t3-tBThe ZVS conduction is realized by controlling the conduction; FIG. 8 is an equivalent circuit of this mode;
thus, obtaining: the duration of the ZVS on mode of the main switch is as follows:
S4turn off to S5The on-time interval DN3 is:
the mode duration is:
S5is conducted to S2The off-time interval DN4 is:
mode 6 (t)4-t6) At t4Time of day, resonant current iLrDown to 0, exciting current iLmIs raised to；t5At time, turn off S2(ii) a Excitation current
S2voltage across
wherein:
at t6At the moment, the potential at point a resonates to VDCThe pattern duration is:
mode 7 (t)6-t7):t6At the moment, the potential at the point a rises to VDC，D1Conducting naturally; t is t6-t7The commutation current increases reversely, and fig. 9 is an equivalent circuit of the present mode;
the excitation current in the mode is as follows:
S1the soft on-time of (d) is:
S2turn off to S1The on-time interval DN5 is:
t7time of day, exciting current
S1is conducted to S5The off-time interval DN6 is:
mode 8 (t)7-t8):t7At time, turn off S5Load current iLoadTo C6Charging, C5Discharging, wherein the potential at the point b rises linearly; t is t8At the moment, the potential at the point b rises to VDC/2, diode D4Conducting naturally; s4Can be at t8Then controlling the conduction;
the mode duration is:
S1turn off to S2The on-time interval DN7 is:
DN7＝T7-8formula (a)80)
According to the analysis of the circuit structure and the working principle, the switch needs to design a commutation inductor, an excitation inductor, a transformer turn ratio and a switch parallel absorption capacitor when completing zero-voltage commutation; the design of the above parameters of each element is completed as follows (analysis is performed with the output current as positive time);
when (1/2-k) VDCLess than VDCWhen/2, the S is cut off under the condition that the commutation current is larger than the load current by a certain value2Ensuring that the switching tube reliably completes current conversion; and the turn-off loss of the main switch is proportional to the square of the channel current at the turn-off instant [8,13 ]]Thus S2The turn-off loss of the main switch is approximately negligible (turn-off loss is less than 1/10) when the formula is satisfied:
wherein ILoad_rmsIs the effective value of the load current;
during actual circuit operation, load current detection has errors, resulting in IboostError of (2), influence commutation time T2-3And ZVT on-time T3BAfter summation of the formula IrDerivation is carried out asrThe dead time of the main switch when the formula is met can be a fixed value;
simultaneous:
thus, obtaining:
wherein the value range of beta obtained by the solution of the sum is as follows:
to ensure S5Reliable commutation and S4Enough ZVS on time, assume Lm＞＞LrObtaining the following components:
to ensure magnetizing current in commutation inductor LrAfter the linear discharge phase (t ═ t)4) And S5Before commutation (t ═ t)0) Equal in size and opposite in direction (neglecting the change of magnetizing current at the resonant commutation stage of the lower bridge arm):
t above1A，TA4Are all related to the load current, when the load current is 0, T1AAnd TA4Value of at least T1A_minTA4_minL calculated under the conditionsmAccording to the condition that S is greater than 0 when any load current is4There is a requirement for enough ZVS on-time; thus:
the excitation current can be represented by the following formula:
wherein T isA4T is the sum of different load currentsA-t4The time interval of (c); whereby each switching cycle
The forward direction of reference for each electrical variable in the loop coincides with the direction of the arrow in fig. 1.
The input parameters are shown in table 1:
input DC voltage (V)DC)
400V
Switching frequency (f)sw)
20KHz
Coss
100pF
Iboost
2A
T1A_min
10ns
T3B
10ns
TABLE 1 input parameters
Specific values of inductance and transformer calculated from constraints of input parameters are shown in Table 2
Commutation inductance (L)r)
1.6uH
Excitation inductor (L)m)
40.3uH
Transformer turn ratio k
0.4
TABLE 2
Calculating the sum of each duration according to the parameter table of the specific componentRelationship to load current:
DP3＝DN3＝(22.9+5)×10-9formula (93)
The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments may be combined with each other into a new embodiment. The above embodiments are only for illustrating the technical solutions of the present invention and are not limited thereto, and any modification or equivalent replacement without departing from the spirit and scope of the present invention should be covered within the technical solutions of the present invention.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：模块化并联四电平变换器系统及方法