The hottest pwmbu based on SG3525 voltage regulati

2022-08-11
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PWM Buck three-level converter based on SG3525 voltage regulation chip

Abstract: This paper expounds the interleaving control of PWM Buck three-level converter with SG3525 voltage regulation chip. Compared with the interleaving control of PWM Buck three-level converter using discrete components, this control method is simple and easy to implement, and can better solve the problem of asymmetry of three-level waveform. The SG3525 voltage regulation chip is introduced in detail, and the specific design method of PWM Buck three-level converter based on SG3525 voltage regulation chip is given. Finally, the PWM Buck three-level converter with input voltage of 120V (90 ~ 180V), output of 48v/4a and switching frequency of 50KHz is experimentally verified

key words: PWM Buck three-level converter; SG3525 voltage regulation chip; Discrete components

Introduction

three level converter has the following advantages:

the voltage stress of the switch is half of the input voltage

can greatly reduce the size of energy storage elements

The voltage stress of the freewheeling diode is half of the input voltage

therefore, the three-level converter is very suitable for high-power applications in high input voltage. Literature [1] analyzes the topology of isolated and non isolated three-level converters in detail

due to the large number of switches of three-level converter, it is complex to implement effective control. Traditionally, comparator, operational amplifier and RS trigger are used to control PWM three-level converter. However, due to the large number of discrete components required to achieve the above control, the two sawtooth waves cannot be completely matched, and the driving circuits of the two switches cannot be exactly the same. Therefore, there must be a certain difference in the duty cycle of the two switches, and the energy provided by the DC isolation capacitor CB cannot be equal in one cycle, resulting in the asymmetry of the three-level waveform

in this paper, the voltage regulation chip SG3525 is used to realize the control of PWM Buck three-level converter, which can greatly reduce the problem of three-level waveform asymmetry caused by the implementation of discrete components. The implementation method is simple and effective

1 buck three-level converter

1.1 two kinds of three-level hydraulic oil will oxidize the coking switch unit during long-time operation

literature [2] analyzes the derivation process of three-level dc/dc converter: two switches are connected in series to replace one switch to reduce the voltage stress, and a clamping diode and a clamping voltage source (which are equally divided into two equal voltage sources) are introduced to ensure the voltage stress balance of the two switches. The connection method between the clamping voltage source and the clamping diode is also different with the position of the switch in the circuit. Two three-level switching units are extracted as shown in Figure 1 below. In Figure 1 (a), the anode of the clamping diode is connected to the midpoint of the clamping voltage source, which is called an anode unit; In Figure 1 (b), the cathode of the clamping diode is connected to the midpoint of the clamping voltage source, which is called the cathode unit

(a) three-level anode unit (b) three-level cathode unit

Figure 1 two three-level switching units

1.2 buck three-level converter

in order to ensure that the voltage stress of the two switches is equal, the three-level converter is generally composed of the above two switching units. The derivation idea of half bridge three-level converter analyzed in reference [2] can be extended to all DC converters, and a family of three-level converter topologies are proposed. Figure 2 shows the main circuit topology of Buck three-level converter and its four working modes

mode 1 is shown in Figure 2 (a). At the time of t=0, trigger the switch S2 to make S2 conductive, and the diode D2 is reverse biased and cut off. The voltage source VIN charges the inductor L through the DC isolating capacitor CB

mode 2 is shown in Figure 2 (b). At time t=t1, turn off S2, then D2 is on, the circuit is freewheeling by D1 and D2, and the inductance L discharges

mode 3 is shown in Figure 2 (c). Until t=t2, the control circuit turns on S1, the diode D1 is reverse biased and cut off, and the DC isolating capacitor CB discharges to the inductor L

mode 4 is shown in Figure 2 (d). When t=t3, turn off S1, then D1 is on, the circuit is freewheeling by D1 and D2, and the inductance L discharges, which is similar to the working process of mode 2

(a) mode 1

(b) mode 2

(c) mode 3

(d) mode 4

Figure 2 buck three-level converter

2.1 voltage regulation chip sg352 build an independent intellectual property and technical standard system of environmental protection and high-performance surface materials. 5

voltage regulation chip SG3525 is an integrated PWM voltage control chip with excellent performance, comprehensive functions and strong versatility. It has the characteristics of external synchronization of oscillator, built-in reference voltage source, dead time regulation, PWM latch and the best design of output stage

sg3525 is a 16 pin chip, and the specific internal structure and packaging are shown in Figure 3. Among them, pin 16 is the reference voltage source output of SG3525, and the accuracy can reach (5.11%) V. It adopts temperature compensation and is equipped with overcurrent protection circuit. There is a double threshold comparator in pin 5, pin 6 and pin 7. The internal capacitance charge and discharge circuit, together with the external resistance capacitance circuit, constitute the oscillator of SG3525. The oscillator is also equipped with an external synchronous input (pin 3). Pin 1 and pin 2 are the inverting input and in-phase input of the on-chip error amplifier respectively. The amplifier is a two-stage differential amplifier with a DC open-loop gain of about 70dB. According to the dynamic and static characteristics of the system, an appropriate feedback compensation network should be added between the output pin 9 and pin 1 of the error amplifier

(a) internal structure diagram (b) package diagram

figure 3sg3525 internal structure diagram and package diagram

because SG3525 can output two driving signals with equal duty cycle and phase difference of 180, it is suitable for realizing the control of non isolated PWM three-level converter

one thing to note is that the SG3525 can only output a drive signal with a duty cycle of 50%, so it can only achieve the duty cycle of 50% of the non isolated three-level converter. In order to realize the working requirement of 50% duty cycle of the converter, the output of SG3525 cannot directly drive the switch, but some links must be added, which will not be repeated in this paper

2.2 drive circuit

in order to improve the efficiency of the circuit and the reliability of the power device, it is generally necessary to power amplify the output signal of the control circuit. In this paper, mc3452 plus isolation transformer drive method is used to design the drive circuit

mc34552 has simple peripheral circuit and convenient application. It is an 8-pin in-phase push-pull drive chip. The specific internal structure and packaging are shown in Figure 4. Pin 2 and pin 4 are two control signal inputs. After the push-pull amplification of this part in the chip, two driving signals in phase (pin 7 and pin 5) are directly output. In order to make the chip work more stably, a ceramic chip capacitor that filters out high-frequency interference and an electrolytic capacitor that filters out low-frequency interference are generally connected in parallel at the power end of the chip

(a) internal structure diagram

(b) package diagram

Figure 4 mc34552 internal structure diagram and package diagram

when the power of the circuit is large and the working frequency is high, it is generally necessary to isolate the control circuit from the main circuit. Therefore, this paper adopts isolation transformer to realize isolation. The output of mc34552 can be directly input to the primary side of the isolation transformer after passing through a DC isolation capacitor

the driving circuit designed in this paper is simple and feasible, and the driving waveform is ideal: it has a fast rising edge and a certain overshoot to accelerate the opening and reduce the opening loss; At the same time, there is reverse bias cut-off voltage, which provides enough inverse gate drive and reduces the falling time

2.3 pwmbuck three-level converter based on SG3525

the system block diagram of pwmbuck three-level converter based on SG3525 is shown in Figure 5

Fig. 5 experimental results and analysis of pwmbuck three-level converter based on SG3525

in order to verify the control feasibility of PWM Buck three-level converter based on SG3525, the appropriate device parameters were selected to verify the circuit. The input voltage is dc90 ~ 180V, the output voltage is DC48V, the rated output current is 4a, and the switching frequency is 50KHz

Figure 6 shows the experimental waveform of PWM Buck three-level converter based on SG3525

(a) ch1 - dead band waveform; ch2-vgs1; ch3-vgs2

(b)ch4-vcd; ch2-vgs1; ch1-vds1

(c)ch1-vds2; ch2-vgs2; ch3-vab; ch4-vds1

(d)ch1-Io; CH2 - vo

Figure 6 experimental results of PWM Buck three-level converter

it can be seen from Figure 6 that it is feasible to use SG3525 to realize the control of PWM Buck three-level converter

in Figure 6 (a), the maximum duty cycle of the two outputs vgs1 and vgs2 of SG3525 is about 48.5%. The dead time can be adjusted arbitrarily according to the needs of the circuit. In the PWM Buck three-level converter, the switching frequency is 50KHz. It can be seen from the figure that the frequency of the driving signal is the required frequency. In order to adjust the frequency of the driving signal, it becomes very simple. You only need to adjust the oscillator frequency of SG3525

in Figure 6 (b), the input voltage Vin is dc120v, and the constant current electronic IO load is 4a. VCD is the voltage waveform at both ends of the DC isolation capacitor CB, and its average value is vin/2, which is half of the input voltage. In the experiment, the waveform of VCD has tiny spikes. This is caused by the opening and closing of switch S2. Vgs1 is the driving waveform of switch S1. Vds1 is the drain source voltage waveform of switch S1 when it works. There is no big spike at the time of opening and closing, so it is an ideal waveform for the switch

in Figure 6 (c), the input voltage Vin is DC 120V, and the constant current electronic load IO is 4a. From the waveforms of vds1 and VDS2, we can clearly see the working conditions of the two switches: switches S1 and S2 are complementary on, and there is a common off period. During this period, diodes D1 and D2 are followed by current, which well verifies the working conditions of the four modes analyzed in this paper. Vgs2 is the driving waveform of switch S2. VAB is a three-level waveform, and its frequency is twice the switching frequency. Thus, the size of the filter element is greatly reduced. Literature [3][4] analyzes in detail a kind of zero voltage and zero current switching composite full bridge three-level dc/dc converter. The high-frequency AC component of the output rectified voltage of the converter is very small, which can reduce the output filter and improve the dynamic performance of the converter; At the same time, the input current ripple is very small, which can reduce the input filter. Reference [1] discusses in detail the analysis and comparison of filter parameter design of Buck three-level converter outside the United States and traditional buck converter

in Figure 6 (d), the input voltage is DC 120V. The figure shows the transient response curve of the output voltage Vo when the constant current electronic load IO jumps from 2a to 4a. It can be seen that the PWM Buck three-level converter circuit has strong anti load disturbance ability and can be quickly stabilized at the rated output voltage vo=48v

4 Conclusion

this paper first briefly discusses the derivation process of three-level converter topology; Then the main circuit topology of Buck three-level converter and its four working modes when the duty cycle is less than 50% are introduced. How to realize the control of PWM Buck three-level converter based on voltage regulation chip SG3525 is analyzed in detail. Finally, the experiment proves that the control of PWM Buck three-level converter based on SG3525 is effective, which can greatly reduce the problem of three-level waveform asymmetry caused by the implementation of discrete components, and the method is simple. Similarly, the voltage control method based on SG3525 can be extended to other non isolated PWM three-level converters

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