CN103296896B - A kind of soft switch isolation type boost direct current converter and control method thereof - Google Patents

Abstract

The invention discloses a soft-switching isolation type step-up DC converter and a control method thereof, belonging to the technical field of power electronic converters. The converter consists of an input source (U _in ), a primary side switch circuit (10), a secondary side switch circuit (20), an inductor (L _f ), a transformer (T), a first output filter capacitor (C _o1 ), a second The output filter capacitor (C _o2 ) and the load (R _o ) are composed, wherein the primary switch circuit (10) is composed of four switch tubes, and the secondary switch circuit (20) is composed of two diodes and two switch tubes; the conversion The device realizes the control of the output voltage through the phase-shift control of the switch tubes in the primary side switch circuit (10) and the secondary side switch circuit (20); the soft switch isolation type step-up DC converter of the present invention has the ability to realize all switches within the entire load range The ability of tube soft switching can realize high-frequency and high-efficiency power conversion, can effectively reduce the volume of inductors and transformers, achieve high power density, and is simple to control, high in reliability, and easy to implement. It is an isolated and high-efficiency power conversion Key technical solutions are provided.

Description

A soft-switching isolated step-up DC converter and its control method

technical field

The invention relates to an isolated soft-switching DC boost converter and a control method thereof, belonging to the technical field of power electronic converters.

Background technique

The isolated DC boost converter is suitable for occasions that require electrical isolation of the input and output and the output voltage is higher than the input voltage. This type of converter has a wide range of applications in new energy power generation, industry, civil, aerospace and other fields.

Traditional isolated DC converters, such as forward converters, flyback converters, push-pull converters, half-bridge converters, full-bridge converters, etc., can achieve the expected boost requirements by adjusting the transformation ratio of the transformer . However, simply relying on adjusting the transformation ratio of the transformer to achieve the boost has the following problems: the voltage stress of the switching device is high, especially the voltage stress of the rectifier diode on the secondary side of the converter is much higher than the output voltage; the leakage inductance of the transformer increases, causing the switching device Voltage spikes and oscillations further aggravate the stress on switching devices, reducing reliability and efficiency. In addition, the traditional DC converter usually cannot realize the soft switching of the switching tube, which limits the efficiency of the converter. Although the full-bridge converter can achieve soft switching under specific load and input and output voltage conditions by adopting phase-shift control, the price is to increase the conduction loss of the converter, especially the circulation loss caused by leakage inductance. When the input voltage decreases When , the circulation loss will increase sharply. In addition, the phase-shifted full-bridge converter cannot realize soft switching under light load.

The step-up full-bridge isolated DC converter (also known as the current source full-bridge isolated DC converter) can achieve a higher isolation boost capability without increasing the transformer ratio. However, when the switch commutates, due to the limitation of the transformer leakage inductance If the rate of rise of the current in the transformer is limited, the filter inductance at the input will cause severe voltage spikes. In order to improve this problem, it is necessary to introduce various voltage clamping or absorbing circuits, the literature "Anmad Mousavi, Pritam Das, Gerry Moschopoulos.A comparative study of a new ZCS DC-DC full-bridge boost converter with a ZVS active-clamp converter, IEEETransactions on power electronics, vol.27, no.3, March2012, pp.1347-1358."Analysed in detail the voltage spike problem existing in the step-up full-bridge isolated DC converter, and compared and analyzed various voltages The clamping scheme, although it further proposes an improved absorption circuit scheme, these schemes increase the complexity of the circuit to varying degrees, increase the cost of the converter, increase the difficulty of control, reduce the efficiency of the converter and reduce the reliability.

Contents of the invention

Purpose of the invention:

Aiming at the deficiencies of the prior art, the invention provides an isolated soft-switching DC boost converter and a control method thereof.

Technical solutions:

The present invention adopts following technical scheme for realizing above-mentioned purpose of the invention:

The isolated soft-switching DC boost converter consists of an input source (U _in ), a primary side switch circuit (10), a secondary side switch circuit (20), an inductor (L _f ), a transformer (T), and a first output filter The capacitor (C _o1 ), the second output filter capacitor (C _o2 ) and the load (R _o ), the primary switch circuit (10) consists of the first switch tube (S ₁ ), the second switch tube (S ₂ ), the Three switch tubes (S ₃ ) and a fourth switch tube (S ₄ ), the secondary switch circuit (20) consists of a first diode (D ₁ ), a second diode (D ₂ ), a fifth switch tube (S ₅ ) and the sixth switching tube (S ₆ ), the transformer (T) includes a primary winding ( _NP ) and a secondary winding ( _NS );

The anode of the input source (U _in ) is respectively connected to the drain of the first switch (S ₁ ) and the drain of the third switch (S ₃ ), and the source of the first switch (S ₁ ) is respectively connected to The drain of the second switching tube (S ₂ ) and one end of the inductor (L _f ), the other end of the inductor (L _f ) is connected to the same-named end of the primary winding ( _NP ) of the transformer (T), and the transformer (T) The non-identical end of the primary winding ( _NP ) is connected to the source of the third switch (S ₃ ) and the drain of the fourth switch (S ₄ ), and the source of the fourth switch (S ₄ ) is connected to The source of the second switch (S ₂ ) and the negative of the input source (U _in );

The terminal with the same name of the secondary winding ( _NS ) of the transformer (T) is connected to the anode of the first diode (D ₁ ), the cathode of the second diode (D ₂ ) and the fifth switching tube (S5) Drain, the non-identical end of the secondary winding ( _NS ) of the transformer (T) is connected to the drain of the sixth switch tube (S ₆ ), one end of the first output filter capacitor (Co1) and the second output filter capacitor (Co2 ), the other end of the first output filter capacitor (Co1) is respectively connected to the cathode of the first diode (D1) and one end of the load (Ro), and the other end of the load (Ro) is respectively connected to the second output filter The other end of the capacitor (Co2) is connected to the anode of the second diode (D2), and the source of the fifth switch (S5) is connected to the source of the sixth switch (S6).

The inductance (L _f ) in the isolated soft-switching DC boost converter of the present invention can be replaced by the leakage inductance of the transformer (T).

The first switching tube (S ₁ ) and the second switching tube (S ₂ ) in the isolated soft-switching DC boost converter of the present invention conduct complementary conduction, and the third switching tube (S ₃ ) and the fourth switching tube (S ₄ ) Complementary conduction, the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ) are complementary conducting, the first switching tube (S ₁ ), the second switching tube (S ₂ ), the third switching tube ( S ₃ ), the fourth switching tube (S ₄ ), the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ) have the same duty cycle, and the first switching tube (S ₁ ) and the fourth switching tube ( S ₄ ) is turned on and off at the same time, the second switch tube (S ₂ ) and the third switch tube (S ₃ ) are turned on and off at the same time, and the first switch tube (S ₁ ) is turned on no later than The turn-on time of the sixth switch tube (S ₆ ), the turn-on time of the third switch tube (S ₃ ) is no later than the turn-on time of the fifth switch tube (S ₅ ), by adjusting the first switch tube (S ₁ ) and the second switch tube (S 1 ) The phase shift angle between the conduction moments of the six switch tubes (S ₆ ) realizes the control of the output voltage.

The present invention has following technical effect:

(1) The voltage of all switching devices is directly clamped by the input voltage or output voltage, and the voltage stress of the switching devices is low;

(2) All switching devices can realize soft switching in the full load range, and the conversion efficiency is high;

(3) The leakage inductance of the transformer is effectively utilized, and there is no problem of circulating current or voltage spike caused by leakage inductance

(4) The converter can work with high-frequency switching, thereby effectively reducing the volume and weight of the inductor and transformer, and achieving high power density

(5) The topological structure is concise and the control is simple.

Description of drawings

Accompanying drawing 1 is the circuit schematic diagram of the isolated type soft-switching DC boost converter of the present invention;

Accompanying drawing 2 is the main waveform diagram of the isolated soft-switching DC boost converter of the present invention under the continuous operation mode of the inductor current;

Accompanying drawing 3～accompanying drawing 6 are the equivalent circuit diagrams of each switching mode of the isolated soft-switching DC boost converter of the present invention in the continuous operation mode of the inductive current;

Accompanying drawing 7 is the main waveform diagram of the isolated soft-switching DC boost converter in the inductor current discontinuous working mode of the present invention;

Accompanying drawing 8～accompanying drawing 11 are the equivalent circuit diagrams of each switching mode of the isolated soft-switching DC boost converter of the present invention under the inductive current discontinuous working mode;

The symbol names in the above drawings: U _in is the input source; 10 is the primary side switch circuit; 20 is the secondary side switch circuit; _{L f} is the inductance; _T is the transformer; side winding and secondary winding; _n is the ratio of transformer (T) secondary winding ( _NS ) turns to transformer (T) primary winding turns (NP ); C _o1 and C _o2 are the first and second Two output filter capacitors; R _o is the load; S ₁ , S ₂ , S ₃ , S ₄ , S ₅ and S ₆ are the first, second, third, fourth, fifth and sixth switch tubes respectively; D ₁ and D ₂ are the first and second diodes respectively; U _o is the output voltage; u _DS1 , u _DS4 and u _DS6 are the first switching tube (S ₁ ), the fourth switching tube (S ₄ ) and the The voltage between the drain and source of the six switching tubes (S ₆ ); u _S is the voltage between the same-named end and the non-identical end of the secondary winding ( _NS ) of the transformer (T); i _Lf is the inductance (L _f ) current; i _S1 , i _S2 , i _S3 and i _S4 are the currents flowing into the drains of the first, second, third and fourth switch tubes respectively; t, t ₀ , t ₁ , t ₂ , t ₃ and _t4 is time.

Detailed ways

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the isolated soft-switching DC boost converter of the present invention consists of an input source (U _in ), a primary side switch circuit (10), a secondary side switch circuit (20), an inductor (L _f ), A transformer (T), a first output filter capacitor (C _o1 ), a second output filter capacitor (C _o2 ) and a load (R _o ), the primary switch circuit (10) consists of a first switch tube (S ₁ ), a second Two switch tubes (S ₂ ), a third switch tube (S ₃ ) and a fourth switch tube (S ₄ ), the secondary switch circuit (20) consists of a first diode (D ₁ ), a second diode (D ₂ ), the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ), the transformer (T) includes a primary winding ( _NP ) and a secondary winding ( _NS ); the input source ( The anode of U _in ) is respectively connected to the drain of the first switch (S ₁ ) and the drain of the third switch (S ₃ ), and the source of the first switch (S ₁ ) is respectively connected to the second switch (S ₂ ) drain and one end of the inductance (L _f ), the other end of the inductance (L _f ) is connected to the same-named end of the transformer (T) primary winding (N _P ), the transformer (T) primary winding (N The non-identical end of _P ) is connected to the source of the third switch (S ₃ ) and the drain of the fourth switch (S ₄ ), and the source of the fourth switch (S ₄ ) is connected to the second switch ( The source of S ₂ ) and the negative pole of the input source (U _in ); the terminal with the same name of the secondary winding ( _NS ) of the transformer (T) is connected to the anode of the first diode (D ₁ ), the second diode The cathode of the tube (D ₂ ) and the drain of the fifth switching tube (S5), the non-identical terminal of the secondary winding ( _NS ) of the transformer (T) is connected to the drain of the sixth switching tube (S ₆ ), the first One end of the output filter capacitor (Co1) and one end of the second output filter capacitor (Co2), and the other end of the first output filter capacitor (Co1) are respectively connected to the cathode of the first diode (D1) and the load (Ro) One end, the other end of the load (Ro) is respectively connected to the other end of the second output filter capacitor (Co2) and the anode of the second diode (D2), and the source of the fifth switch tube (S5) is connected to the sixth switch The source of the tube (S6).

In practice, the inductance (L _f ) can be completely or partially replaced by the leakage inductance of the transformer (T), which means that the leakage inductance of the transformer (T) will be effectively utilized, and after the leakage inductance is used as an energy transmission inductance, the The converter no longer has voltage spikes or loss problems caused by leakage inductance in series-isolated converters.

The first switching tube (S ₁ ) and the second switching tube (S ₂ ) in the isolated soft-switching DC boost converter of the present invention conduct complementary conduction, and the third switching tube (S ₃ ) and the fourth switching tube (S ₄ ) Complementary conduction, the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ) are complementary conducting, the first switching tube (S ₁ ), the second switching tube (S ₂ ), the third switching tube ( S ₃ ), the fourth switching tube (S ₄ ), the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ) have the same duty cycle, and the first switching tube (S ₁ ) and the fourth switching tube ( S ₄ ) is turned on and off at the same time, the second switch tube (S ₂ ) and the third switch tube (S ₃ ) are turned on and off at the same time, and the first switch tube (S ₁ ) is turned on no later than The turn-on time of the sixth switch tube (S ₆ ), the turn-on time of the third switch tube (S ₃ ) is no later than the turn-on time of the fifth switch tube (S ₅ ), by adjusting the first switch tube (S ₁ ) and the second switch tube (S 1 ) The phase shift angle between the conduction moments of the six switch tubes (S ₆ ) realizes the control of the output voltage.

In specific implementation, a reasonable dead time must be set between the switching signals of the first switching tube (S ₁ ) and the second switching tube (S ₂ ) to realize the first switching tube (S ₁ ) and the second switching tube ( For soft switching of S ₂ ), a reasonable dead time must be set between the switching signals of the third switching tube (S ₃ ) and the fourth switching tube (S ₄ ) to realize the third switching tube (S ₃ ) and the fourth switching tube (S 3 ) The soft switching of the tube (S ₄ ), and there is no need to set any dead time between the switching signals of the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ).

In actual implementation, all switching tubes should be semiconductor switching devices with parasitic body diodes, such as metal oxide semiconductor field effect transistors. If the selected switching tube does not have a parasitic body diode, antiparallel diodes should be connected across its drain and source.

From the circuit structure of the isolated soft-switching DC boost converter of the present invention shown in Figure 1, it can be seen intuitively that the switching devices on the primary side of the converter are directly clamped by the input voltage, that is, the voltage stress is equal to the input voltage. Voltage, while the switching devices on the secondary side of the converter are directly clamped by the output voltage, that is, their voltage stress is equal to the output voltage, all switching devices on the primary side and secondary side do not have voltage spikes, and the voltage stress of the switching devices is low .

Assuming that all inductors, capacitors, switch tubes and diodes are ideal devices, ignoring the voltage ripple on all capacitors, the sum of the voltages of the first and second output filter capacitors C _o1 and C _o2 is equal to the output voltage U _o . According to the working state of the inductor (L _f ), the isolated soft-switching DC boost converter (hereinafter referred to as the converter) of the present invention can work in the inductor current continuous mode or the inductor current discontinuous mode. The working principles of the converter in the two working modes are analyzed separately below.

When the output power is large, the converter usually works in the continuous mode of the inductor current. Figure 2 is the main working waveform of the converter in the inductor current continuous mode. In this mode, there are four switching modes in half a switching cycle.

Switching mode 1 [t ₀ , t ₁ ]: Before time t ₀ , the switches S ₂ , S ₃ and S ₅ are turned on, but the current in the switch S ₅ is zero, the diode D ₂ is turned on, and the inductor L _f The current i _Lf is negative, and the input source U _in transmits power to the load through the inductance L _f ; at t ₀ , S ₂ and S ₃ are turned off, and the current of the inductance L _f commutates to the body diodes of S ₁ and S ₄ , _The voltage drop _of the switch tubes S1 and S4 is 0, therefore, S1 and S4 have the condition of zero _- voltage turn _- on, and at the same time, the current i _Lf of the inductor _Lf decreases linearly under the action of the input and output voltages, the model The state equivalent circuit is shown in Figure 3.

Switching mode 2 [t ₁ , t ₂ ]: At time t ₁ , the switches S ₁ and S ₄ are turned on with zero voltage, and the current of the inductor L _f continues to decrease until the time t ₂ i _Lf decreases to 0, and the secondary diode D ₂ natural shutdown, the modal equivalent circuit is shown in Figure 4.

Switching mode 3 [t ₂ , t ₃ ]: at time t ₂ , the body diode of switch tube S ₆ is turned on naturally, and the current at both ends of S ₆ naturally drops to 0, creating conditions for the zero-voltage turn-on of S ₆ , starting from t ₂ From time to time, the currents of the switch tubes S5 and _S6 gradually increase from zero, and the current of the inductor _Lf increases positively from ₀ under the action of the input source _Uin , until the switch tube _S5 is turned off at the time _t3 , the model The modal equivalent circuit is shown in Figure 5. It is worth noting that the longer the mode lasts, the greater the peak value of the inductor current, and the greater the power that the converter can transmit to the load, that is, the output voltage or output power of the converter is proportional to the duration of the mode .

Switching mode 4[t ₃ , t ₄ ]: At time t ₃ , the switch tube S ₅ is turned off and S ₆ is turned on, but since S ₅ is turned off, no current flows in S ₆ , and the secondary winding current naturally commutates To the diode D ₁ , the input source U _in jointly transmits energy to the load through the inductance L _f , and the current of the inductance L _f decreases linearly. The modal equivalent circuit is shown in Figure 6.

After time _t4 , the second half of the switching cycle starts, and the working process is similar, so the description will not be repeated.

Summarizing the working process in the continuous mode of inductor current, we can see that in the continuous mode of inductor current, all switches can be turned on at zero voltage, and the current of the two diodes naturally decreases to 0 and naturally increases from 0, so there is no Diode reverse recovery problem, therefore, all switching devices are soft switching working state.

When the output power is low, the converter usually works in the inductor current discontinuous mode. Figure 7 is the main working waveform of the converter in the inductor current discontinuous mode. In this mode, there are four switching modes in half a switching cycle.

Switching mode 1[t ₀ , t ₁ ]: Before time t ₀ , the switches S ₂ , S ₃ and S ₅ are turned on, but because the current i _Lf of the inductance L _f has dropped to 0, the current flowing through all the switches Both are 0, and the _two diodes D1 and D2 _on the secondary side are both in the off state. At time t ₀ , S ₂ and S ₃ are turned off, and the current of the inductor L _f remains at 0 state. The equivalent circuit of the modal converter is shown in Fig. 8 .

Switching mode 2[t ₁ , t ₂ ]: At time t ₁ , the switches S ₁ and S ₄ are turned on with zero current, the body diode of the switch S ₆ is turned on naturally, and the current at both ends of S ₆ naturally drops to 0, which is S ₆ The zero-voltage turn-on of the circuit creates the conditions. From the moment _t1 , the currents of the switch tubes S5 and _S6 increase gradually from zero, the current of the inductor _Lf increases linearly from ₀ , and the secondary diode D1 is naturally turned _on . The state equivalent circuit is shown in Figure 9.

Switching mode 3 [t ₂ , t ₃ ]: At time t ₂ , the switch tube S ₅ is turned off and S ₆ is turned on, but since S ₅ is turned off, no current flows in S ₆ , and the secondary winding current naturally commutates To the diode D ₁ , the input source U _in jointly transmits energy to the load through the inductance L _f , and the current of the inductance L _f decreases linearly. The modal equivalent circuit is shown in Fig. 10 .

Switching mode 4[t ₃ , t ₄ ]: At time t ₄ , the current of the inductor L _f naturally decreases to 0, and the diode D ₁ is naturally turned off. The equivalent circuit of this mode is shown in Figure 11.

After time _T4 , the second half of the switching cycle starts, and the working process is similar, so the description will not be repeated.

Summarizing the working process in the inductor current discontinuous mode, it can be seen that in the inductor current discontinuous mode, the four switching tubes on the primary side of the converter can naturally realize zero-current turn-on, and even the two switching tubes on the secondary side can naturally realize zero-voltage turn-on , the currents of the two diodes naturally decrease to 0, and naturally increase from 0, so there is no diode reverse recovery problem, so all the switching devices are also in the soft switching state.

Claims (3)

1. An isolated type soft-switching DC boost converter, characterized in that: The isolated soft-switching DC boost converter consists of an input source (U _in ), a primary side switch circuit (10), a secondary side switch circuit (20), an inductor (L _f ), a transformer (T), and a first output filter The capacitor (C _o1 ), the second output filter capacitor (C _o2 ) and the load (R _o ), the primary switch circuit (10) consists of the first switch tube (S ₁ ), the second switch tube (S ₂ ), the Three switch tubes (S ₃ ) and a fourth switch tube (S ₄ ), the secondary switch circuit (20) consists of a first diode (D ₁ ), a second diode (D ₂ ), a fifth switch tube (S ₅ ) and the sixth switching tube (S ₆ ), the transformer (T) includes a primary winding ( _NP ) and a secondary winding ( _NS ); The anode of the input source (U _in ) is respectively connected to the drain of the first switch (S ₁ ) and the drain of the third switch (S ₃ ), and the source of the first switch (S ₁ ) is respectively connected to The drain of the second switching tube (S ₂ ) and one end of the inductor (L _f ), the other end of the inductor (L _f ) is connected to the same-named end of the primary winding ( _NP ) of the transformer (T), and the transformer (T) The non-identical end of the primary winding ( _NP ) is connected to the source of the third switch (S ₃ ) and the drain of the fourth switch (S ₄ ), and the source of the fourth switch (S ₄ ) is connected to The source of the second switch (S ₂ ) and the negative of the input source (U _in ); The terminal with the same name of the secondary winding ( _NS ) of the transformer (T) is connected to the anode of the first diode (D ₁ ), the cathode of the second diode (D ₂ ) and the fifth switching tube (S5) Drain, the non-identical end of the secondary winding ( _NS ) of the transformer (T) is connected to the drain of the sixth switch tube (S ₆ ), one end of the first output filter capacitor (Co1) and the second output filter capacitor (Co2 ), the other end of the first output filter capacitor (Co1) is respectively connected to the cathode of the first diode (D1) and one end of the load (Ro), and the other end of the load (Ro) is respectively connected to the second output filter The other end of the capacitor (Co2) is connected to the anode of the second diode (D2), and the source of the fifth switch (S5) is connected to the source of the sixth switch (S6). 2. An isolated soft-switching DC boost converter according to claim 1, characterized in that: the inductance (L _f ) is replaced by the leakage inductance of the transformer (T). 3. A control method based on the isolated soft-switching DC boost converter according to claim 1, characterized in that: The first switching tube (S ₁ ) is complementary to the second switching tube (S ₂ ), the third switching tube (S ₃ ) is complementary to the fourth switching tube (S ₄ ), and the fifth switching tube (S ₅ ) and the sixth switch tube (S ₆ ) are complementary conduction, the first switch tube (S ₁ ), the second switch tube (S ₂ ), the third switch tube (S ₃ ), and the fourth switch tube (S ₄ ) , the duty cycle of the fifth switching tube (S ₅ ) and the sixth switching tube (S ₆ ) are equal, the first switching tube (S ₁ ) and the fourth switching tube (S ₄ ) are turned on and off at the same time, the second The second switch tube (S ₂ ) and the third switch tube (S ₃ ) are turned on and off at the same time, and the turn-on time of the first switch tube (S ₁ ) is not later than the turn-on time of the sixth switch tube (S ₆ ), The turn-on time of the third switch (S ₃ ) is no later than the turn-on time of the fifth switch (S ₅ ), by adjusting the time between the turn-on of the first switch (S ₁ ) and the sixth switch (S ₆ ) The phase shift angle realizes the control of the output voltage.