Power conversion type analysis

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Power conversion type analysis [Copy link]

*[#1202906,3142334]AC-DC alternating current to direct current*[#1202906,3142336]DCDC *[#1202906,3142342]DC-AC direct current to alternating current*[#1202906,3142344]AC-DC size and frequency changes*[#1202906,3142346]Reference link

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1. AC-DC alternating current to direct current

A circuit that converts alternating current ( AC ) input to direct current ( DC ) output.

1. Alternating Current: The acronym for Alternating Current .

AC : It is an electric current whose magnitude and polarity (direction) change periodically over time. The number of times the current polarity changes in 1 second is called frequency, expressed in Hz .

2. The acronym for Direct Current .

Direct current: Constant current is a type of direct current, which is a direct current with constant magnitude and direction. Alternating current , also known as AC , refers to current whose direction changes periodically over time, and the running average value in one cycle is zero. Current whose polarity (direction) and magnitude do not change over time is usually called DC .

② The current whose polarity does not change with time but whose magnitude changes with time is also DC .

Usually called ripple current .

3. ACDC 's low-frequency power conversion solution

AC/DC power supply is a power converter with AC input and DC output. For example, the power adapters of mobile phone chargers, notebooks, and tablet computers we often use are all this kind of power supply. This power converter contains a step-down circuit, a rectifier and filter circuit, and a voltage regulator circuit.

Low frequency power conversion solution

Common high voltage AC - low voltage DC power adapters

4. AC-DC Converter Types

Divided into: buck and buck - boost converters; flyback converters; forward converters; LLC resonant converters; PFC converters; single-phase input PFC converters; three-phase input PS ZVS FB converters, etc.

5. AC/DC Linear Power Supply vs Switching Power Supply

1. AC/DC Linear Power Supply

AC/DC linear power supplies are simple to design. They use a transformer to reduce the AC input voltage to a value more suitable for the intended application; then, they rectify the reduced AC voltage into a DC voltage; and finally, they filter it to further improve the waveform quality (see the AC/DC linear power supply functional block diagram below).

AC/DC Linear Power Supply Functional Block Diagram

Traditional AC/DC linear power supplies have limited integration in terms of efficiency, power range, and size. Since the input voltage of AC/DC linear power supplies is converted at the input, the transformer required is large and heavy. At low frequencies (such as 50Hz ), a large inductor is required to transfer a large amount of power from the primary coil to the secondary coil, requiring a large transformer core. Another limitation of AC/DC linear power supplies is voltage regulation at high powers. AC/DC linear power supplies use linear regulators to keep the voltage at the output constant. These linear regulators dissipate excess energy in the form of heat. For high powers, the amount of heat that the regulator needs to dissipate to maintain a constant output voltage is high, requiring a bulky heat sink.

2. AC/DC switching power supply

AC/DC switching power supplies create more efficient power converters without consuming extra power. In a switching AC power supply, the DC voltage is rectified and filtered at the input, and passes through a chopper, which converts the voltage into a high-frequency pulse train. Finally, another rectifier and filter convert the pulse train back to a DC ( DC ) voltage and clean up any remaining AC components that may be present before reaching the output (Switching Mode AC/DC Power Supply Functional Block Diagram).

When operating at high frequencies, the transformer inductance is able to transfer more power without reaching saturation, which means that the core can be smaller and smaller. Therefore, the size of the transformer used in an AC/DC switching power supply to reduce the voltage amplitude to the desired value can be only a fraction of the size of the transformer required for an AC/DC linear power supply.

Switch Mode AC/DC Power Supply Functional Block Diagram

AC/DC switching power converters generate a lot of noise in the system and require complex control circuits, which increases the complexity of the design. Smaller transformers and increasing regulator efficiency in AC/DC switching power supplies. The differences between AC/DC linear power supplies and switching power supplies are as follows:

Comparison between linear power supply and switching power supply

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1. DCDC

DC to DC power conversion: A power converter thatDCinputandDC

A DC/DC converter is the name of a device that converts DC to DC. It is often called a linear regulator or a switching regulator, etc., named after the conversion method.

1. DCDC topology types:

1. 1. 1. Step-down switching converter: The output voltage is lower than the input.

1. 1. 2. Boost switching converter: The output voltage is higher than the input voltage.

1. 1. 3. Buck - boost switching converter: The output voltage can be higher or lower than the input voltage. Buck - boost DC-DC converters are commonly used in battery-powered devices.

2. From the transformation type:

1. Switching DCDC Converter

Switching regulator, in English (regulatior) , some people call it regulator, voltage source. To achieve voltage stabilization, a control system ( negative feedback ) is needed. From the automatic control theory, when the voltage rises, it is lowered through negative feedback, and when the voltage drops, it is raised, thus forming a control loop. The block diagram in the figure is PWM ( pulse width control method ) , of course, there are others such as: PFM ( frequency control method ) , phase shift control method, etc.

Duty cycle: the ratio of the on time Ton to the switching period T , ton ( on time ) + toff ( off time ) = T ( switching period ) , duty cycle D = ton / T. However, we cannot use a pulse output! A method to achieve smooth energy flow is needed. By switching with many pulses at high frequency, energy will be stored during the switch on period and provided when the switch is turned off, thereby achieving a smooth voltage.

Features are as follows:

① Ability to increase voltage (boost)

② And reduce the voltage (step down) or even reverse it

③ High efficiency and power density

2. Linear DC-DC Converter

The most basic DC-DC converters are linear voltage converters. They achieve DC-DC voltage conversion by dissipating excess power into a resistor, making them a resistive voltage divider. Obviously, this is not very ideal for power conversion efficiency. Another implication of their operating principle is that they can only convert a certain input voltage to a lower output voltage of the same polarity. In other words, the value of their voltage conversion ratio is always between zero and one. The advantage of linear voltage converters is that they are fairly simple to implement. In addition, they do not usually require large and space-consuming inductors or capacitors, making them an attractive choice for monolithic integration.

advantage:

Simple design

Low number of components

Low noise

High-speed transient response

Low price

shortcoming:

Large input-output pressure difference and poor efficiency

Low efficiency and high heat generation

Sometimes you need to cool

Can only reduce blood pressure

3. Linear voltage regulation:

Fixed output linear regulators - traditional chips with positive voltage output 78xx and negative voltage output 79xx

Adjustable output linear voltage regulator - traditional chip LM317

Examples of performance characteristics of linear regulation:

4. LDO : Low dropout regulator , is a low voltage difference linear regulator. This is relative to the traditional linear regulator.

LDO is a linear regulator. Traditional linear regulators, such as 78XX series chips, require the input voltage to be at least 2V~3V higher than the output voltage , otherwise they will not work properly. Low-dropout ( LDO ) linear regulators have low cost, low noise, and low quiescent current, which are its outstanding advantages. It also requires very few external components, usually only one or two bypass capacitors. The new LDO linear regulator can achieve the following indicators: output noise 30 μV , PSRR of 60dB , quiescent current 6 μA ( TI 's TPS78001 reaches Iq=0.5uA ), and voltage drop of only 100mV (TI has mass-produced LDOs claiming to be 0.1mV ) .

Commonly used LDO devices - AMS1117

5. Switching Regulators :

The transmission device switch ( field effect transistor ) is fully turned on and completely turned off in each cycle;

l It contains at least one energy storage element, such as an inductor or a capacitor;

l Multiple topologies (buck, boost, buck - boost, etc.) .

The traditional LM2576 series is a representative of step-down switching integrated regulators.

The inductance and capacitance of the switching regulator are both related to the frequency. The lower the frequency, the more energy storage is required to have a large current output. The inductance has a great relationship with the output power.

6. A charge pump, also known as a switched capacitor voltage converter, is a type of DC-DC converter that uses so-called " flying " or " pumping " capacitors ( rather than inductors or transformers ) to store energy .

The charge pump circuit can achieve efficient energy transmission without the participation of inductors. Especially in the popular mobile phone fast charging application, the buck charge pump can achieve a conversion efficiency of nearly 98% .

Over the past decade, charge pumps have become more widely used, from unregulated single-output ICs to regulated ICs with multiple output voltages . Output power and efficiency have also been developed, so that today's charge pumps can output currents up to 250mA with efficiencies of 75% ( average ) . Charge pumps are mostly used in systems that require batteries, such as cellular phones, pagers, Bluetooth systems, and portable electronic devices.

Main applications include driving white LEDs for mobile phone backlighting and digital processors in the milliwatt range.

7. Commonly used devices - MC34063

MC34063 is a power chip that integrates Boost converter, BUCK converter and power inverter. MC34063 can use very few switching components to form a boost conversion switch, a buck conversion switch and a voltage reverse circuit. Compared with a linear voltage-regulated power supply, this switching power supply has a higher efficiency and will not decrease when the input and output voltage drops greatly. The power supply does not require a large heat sink and is small in size, making it widely used, mainly in systems based on microprocessors or single-chip microcomputers.

The main packages of MC34063 are DIP-8 and SOP-8 .

DC-DC switching converters are used to locally provide the required DC voltage and current to any component or part of the system. Depending on the application's relationship between input and output voltages, engineers must choose the best power topology - buck, boost, buck - boost, or inverting, with or without synchronous rectification. Or, they can decide to use an implementation based on a monolithic IC or with discrete power switches and controllers - or even an advanced digital implementation. Whatever they choose, the right semiconductor products are key to meeting their specific efficiency and size design goals.

8. DCDC scheme selection example:

Solution Description:

3.3V@100mA@ digital can be directly obtained from the USB input voltage through an LDO (typical voltage drop is 1.2V ). Generally, there will be a certain voltage drop when the USB port reaches the circuit board through the USB cable. The voltage drop value depends on the thickness, length, material (determines the impedance) of the USB cable and the current required by the load circuit board. In this design, we assume that the maximum voltage drop of the USB cable is 0.5V , that is, the DC power supply between 4.5V and 5V can be guaranteed at the input end of the power board . Considering the system cost, in this design, we use the most commonly used, cheap and very simple peripheral circuit 1117-3.3V LDO regulator to generate 3.3V@100mA voltage. The maximum power consumption of this circuit is 0.33W , and the efficiency is 3.3/4.5 ( 73% ) ~ 3.3 / 5 ( 66% ). If a larger current is required, you can consider using a switching voltage regulator with a conversion efficiency of more than 75% to generate 3.3V . Of course, this will cause a slight increase in the cost of the system.

1.2V@500mA@ digital must be generated by switching voltage regulator. Here we choose a cost-effective switching voltage regulator MCP1603 provided by Microchip , which can meet the requirements of the system.

+ 5V@100mA@ simulation, first adjust the DC voltage between 4.5V and 5V to + 6.5V (with switching noise) through MC34063 , and then generate a clean DC voltage of + 5V through LDO 1117-5 with a minimum voltage drop of 1.2V

-5V @100mA@ simulation, first adjust the DC voltage between 4.5V and 5V to -7.5V (with switching noise) through MC34063 , and then generate a clean DC voltage of -5V through the linear regulator 79L05 with a minimum voltage drop of 2.5V

There are many ways to generate +/- 5V . Here, two MC34063s are used to generate different output voltages. This is mainly to let everyone compare and experience the difference between 79L05 and 1117-5 , that is , the difference between conventional linear regulators and LDOs.

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1. DC-AC direct current to alternating current

A DC-AC converter is a power supply device that converts AC power into DC power. Simply put, it is a switching power supply.

The device that converts direct current ( DC ) into alternating current ( AC ) is called an inverter. It consists of an inverter bridge, control logic and filter circuit.

An inverter is an electronic device that converts low voltage ( 12 or 24 volts or 48 volts) direct current into 220 volt alternating current. The inverter gets its name because it is usually used to rectify 220 volt alternating current into direct current, and the inverter does the opposite. In an era of "mobility", mobile office, mobile communication, mobile leisure and entertainment. In a mobile state, not only low voltage direct current supplied by batteries or storage batteries is needed, but also 220 volt alternating current, which is indispensable in daily environment, is needed. Inverters can meet the needs.

The inverter is a converter that converts DC power (battery, storage bottle) into constant frequency and voltage or frequency and voltage alternating current (usually 220V, 50Hz sine wave). It consists of an inverter bridge, control logic and filter circuit. Using the PWM principle, the MOS tube generates a changing waveform, which is then converted into voltage through a transformer and then rectified for output. The conversion of AC into DC is called rectification, and the conversion of DC into AC is called inversion.

Widely used in air conditioners, home theaters, electric grinding wheels, electric tools, sewing machines, DVDs , VCDs , computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting, etc. In foreign countries, due to the high penetration rate of cars, the inverter can be connected to the battery to drive electrical appliances and various tools when going out for work or travel. The car inverter output through the cigarette lighter is 20W , 40W , 80W , 120W to 150W power specifications.

The common method of inverter power supply is to modulate a sine wave waveform through SPWM , and then switch the output voltage polarity through an H- bridge, which requires the switching of the H- bridge to be synchronized with the SPWM circuit. It is technically complex, but highly efficient, and many inverters on the market use this method.

SPWM : Sinusoidal Pulse Width Modulation The signal wave of sinusoidal PWM is a sine wave, that is, the sine wave is equivalent to a series of rectangular pulse waveforms with equal amplitude and unequal width (consistent with the drawing in our courseware). This waveform composed of n rectangular pulses of equal amplitude and unequal width is equivalent to the half-cycle waveform of the sine wave, which is called the SPWM waveform.

Formation of Unipolar Pulse Width Modulation Wave

SPWM is a control method that uses a sine wave as the reference wave (modulation wave) and uses a series of equal-amplitude triangle waves (carriers) to compare with the reference sine wave to generate a PWM wave. When the reference sine wave is higher than the triangle wave , the corresponding switch device is turned on ; when the reference sine wave is lower than the triangle wave , the corresponding switch device is turned off. Therefore , the output voltage waveform of the inverter is a pulse train , which is characterized by: the pulses in half a cycle are equidistant, equal in amplitude and unequal in width , always wide in the middle and narrow on both sides , and the area of each pulse is proportional to the area under the sine wave in the interval. This pulse wave can be low-pass filtered to obtain a sine wave with the same frequency as the modulation wave , and the amplitude and frequency of the sine wave are determined by the amplitude and frequency of the modulation wave.

The operation of the inverter circuit can be further broken down into: first, the oscillation circuit converts direct current into alternating current; second, the coil boosts the voltage to convert irregular alternating current into square wave alternating current; finally, rectification converts the alternating current into sinusoidal wave alternating current via a square wave.

The working principle is as follows:

Classification of inverters:

Half-bridge inverter architecture

UPS is a power protection device that contains energy storage devices and uses inverters as main components to stabilize voltage and frequency output. When the mains power is input normally, UPS stabilizes the mains power and supplies it to the load. At the same time, it charges the internal battery and stores energy in the battery. When the mains power is interrupted (power outage due to various reasons) or input failure occurs, UPS will convert the energy of the internal battery into 220V AC power to continue to supply the load, so that the load can maintain normal operation and protect the load software and hardware from damage.

The full-bridge inverter architecture is as follows:

Work efficiency:

The inverter itself also consumes some electricity when working, and its input power must be greater than its output power. The efficiency of the inverter is the ratio of the inverter output power to the input power, that is, the inverter efficiency is the output power divided by the input power. If an inverter inputs 100 watts of DC power and outputs 90 watts of AC power, then its efficiency is 90% .

Main features of inverter

1. High conversion efficiency and fast startup;
2. Good safety performance: the product has five protection functions : short circuit, overload, over / under voltage, and over temperature ;
3. Good physical properties: The product adopts an all-aluminum shell with good heat dissipation performance, hard-oxidized surface, good friction resistance, and can resist extrusion or impact of a certain external force;
4. Strong load adaptability and stability

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   Rectification circuit: mainly composed of a rectifier bridge; the AC power (mains power) is rectified into DC power through a full bridge. For three-phase 380V AC power, after rectification, the theoretical value of the DC voltage is 380X1.414 ≈ 537V ; and for single-phase 220V AC power, after rectification, the theoretical value of the DC voltage is 220X1.414 ≈ 310V .

   Buffer circuit: suppresses the impact current at the moment of power-on. According to the working principle of electrolytic capacitors, when the inverter is powered on, the voltage at both ends of the capacitor will not change suddenly, but the current at both ends of the capacitor will change suddenly, and the two ends of the capacitor are equivalent to a short circuit. If there is no buffer circuit (charging resistor), the rectifier bridge will be damaged due to excessive current. The buffer circuit plays a role in protecting the rectifier bridge.

   Filter circuit: The withstand voltage of a general electrolytic capacitor is 400V ; and the theoretical value of the DC voltage of a three-phase 380V AC power after rectification is about 537V . Therefore, the filter capacitor can only be made up of two electrolytic capacitors in series. Since the capacity of the electrolytic capacitors cannot be absolutely the same, the voltage distribution on the two electrolytic capacitors after series connection is unbalanced, which will result in different service lives of the two electrolytic capacitors. In order to solve the problem of voltage imbalance, equalizing resistors with the same resistance value need to be connected in parallel at both ends of the two electrolytic capacitors.

   Inverter circuit: A power electronic circuit that converts direct current (DC bus) into alternating current. It is composed of multiple IGBTs in the inverter bridge . Each IGBT integrates a freewheeling diode, which provides a circuit for the motor's stator winding to feedback energy (motor power generation). When the motor is in the power generation state, its electric energy can flow to the DC circuit through the freewheeling diode and charge the electrolytic capacitor.

   Since the voltage and frequency of power grids in different countries are different, the technical performance of exported and imported products needs to be tested according to the voltage and frequency of different countries. Variable frequency power supply can simulate the power supply voltage and frequency of countries around the world.

   The input power of the variable frequency power supply is AC. Generally, the three-phase AC power in China is 380V , the single-phase AC power is 220V , and the voltage in the United States, Japan and other countries is 110V (check the voltage frequency of various countries in the world). The variable frequency power supply can imitate the standard voltage and frequency of electricity in various countries in the world, so many manufacturers of exported electrical appliances use variable frequency power supplies to test the use of exported electrical appliances. The standard frequency of electricity in each country is different. The standard frequency of electricity in different countries: the voltage standard of various countries in the world

   

   National voltage frequency

   The following table lists the single-phase voltage values for some countries or regions.

   

   Examples of general parameters of high-power variable-frequency power supplies that we commonly use

   

   

   Frequency converters are classified according to modulation methods:

   PAM : Plus Amplitude Modulation

   Pulse Width Modulation ( PWM ) : Plus Width Modulation

   

   The variable frequency power supply converts the AC power in the mains into a pure sine wave through AC-DC-AC conversion. The output frequency and voltage are adjustable within a certain range. It is different from the variable frequency speed controller used for motor speed regulation and also different from the ordinary AC voltage stabilized power supply. The characteristics of an ideal AC power supply are stable frequency, stable voltage, zero internal resistance, and a pure sine wave voltage waveform (no distortion). The variable frequency power supply is very close to the ideal AC power supply. Therefore, advanced and developed countries are increasingly using variable frequency power supplies as standard power supplies to provide the best power supply environment for electrical appliances and facilitate objective assessment of the technical performance of electrical appliances.

   The basic original variable frequency power supply is the core part of the AC resonant withstand voltage test system . It requires independent voltage regulation and frequency regulation , output voltage of 0 ~ 400 V, frequency of 30 ~ 300 Hz, high stability , and strong anti-interference ability in the field environment.

   With the emergence of fully controlled fast switching devices such as GTR , IGBT , and MOSFET , PWM has gradually developed . Since the voltage amplitude can be adjusted by adjusting the duty cycle of the PWM wave , the inverter link can simultaneously complete the voltage regulation and frequency regulation tasks , the rectifier does not need to be controlled , the equipment structure is simpler , and the control is more convenient. The output voltage is improved from a square wave to a PWM wave , which reduces the low-order harmonic content of the output voltage.

   Current status of inverter power supply research

   The general power supply is connected to the load. From the relevant literature, we know that the current research on inverter power supply mainly focuses on the following aspects:

   1. Topological form

   At present, the commonly used inverter circuit topologies are: conventional inverter circuit topology, soft switching inverter circuit topology, multi-power inverter circuit topology,

   Flat inverter circuit topology, etc.

   Conventional inverter circuit topology

   Conventional inverter circuit topology can be divided into single-phase half-bridge, single-phase bridge, three-phase bridge circuit, etc. According to the properties of the DC side power supply,

   It can also be divided into voltage source inverter circuit ( VSTI ) and current source inverter circuit ( CSTI ).

   The advantages of single-phase inverter circuit are simplicity, fewer components, and it is often used in small power inverters below a few kW .

   Phase bridge inverter power supply is widely used.

   Soft-switching inverter circuit topology

   In order to obtain a better AC output waveform, the inverter power supply will increase the switching frequency of the fully controlled power electronic devices .

   Switching loss will also increase, circuit efficiency will be seriously reduced, and electromagnetic interference will also increase, so simply increasing the switching frequency is not enough. To address these problems, soft switching technology has emerged. It is an auxiliary commutation method based on resonance, which solves the switching loss and switching noise problems in the circuit and greatly increases the switching frequency. Soft switching technology can generally be divided into two categories: zero voltage ( ZVS ) and zero current (ZCS) . According to the order of their appearance, they can be divided into three categories: quasi-resonance, zero switching PWM and PWM . Each category includes topology and many derived topologies.

   Three-level or multi-level inverter circuit topology

   The idea of multi-level inverter was first proposed by Nabae of Japan in the early 1980s .

   The step wave voltage close to the sinusoidal output is synthesized through multiple DC levels. Its advantage is to reduce the inverter output harmonics and reduce the voltage stress of the switch tube. There are many types of multi-level topologies, but they can be roughly divided into three types: diode clamped, flying capacitor and independent DC power supply cascade multi-level. These three multi-level topologies have their own advantages, among which the most widely used is the diode clamped multi-level topology.

   

   

   Full-wave rectification and half-wave rectification ( AC/DC conversion) There are two rectification methods for converting AC (alternating current voltage) to DC (direct current voltage). In both cases, the forward current flow characteristics of the diode are used for rectification.

   

   Full-wave rectification is to convert the negative voltage component of the input voltage into a positive voltage through a diode bridge circuit structure and then rectify it into a DC voltage (pulse voltage). Half-wave rectification is to use a diode to eliminate the negative voltage component of the input and then rectify it into a DC voltage (pulse voltage).

   

   2. The development trend of variable frequency power supply technology research

   In the application of power electronics technology and various power supply systems, variable frequency power supply technology is at the core.

   The development of the next generation variable frequency power supply technology mainly shows the following trends:

   (1) High frequency

   Increasing the switching frequency of the variable frequency power supply can effectively reduce the size and weight of the device .

   The volume and weight are reduced by removing the bulky power frequency isolation transformer, adopting high frequency isolation, and eliminating the audio noise of the transformer and inductor, while improving the dynamic response capability of the output voltage.

   (2) High performance

   High performance mainly refers to the high performance of output voltage characteristics, which is mainly reflected in the following aspects : good voltage regulation performance, no-load and

   The effective value of the output voltage should be stable when loaded; the waveform quality should be high, not only requiring a good waveform when no-load, but also a good waveform when loaded, and strong resistance to nonlinear loads; the transient response characteristics of the output voltage should be good when the load is suddenly increased or decreased; the voltage modulation amount should be small; the frequency stability of the output voltage should be good; for common-phase power supplies, the phase voltage imbalance should be small when carrying unbalanced loads.

   (3) Modularity

   The development trend of today's inverter power supply is high power and high reliability . Although we can now produce large-scale inverters with a capacity of several thousand KVA,

   Inverter power supply can fully meet the occasions with high power requirements. However, the reliability of the entire system is completely determined by a single power supply, and the reliability cannot be very high anyway. In order to improve the reliability of the system, modularization must be achieved. Modularization means that users can easily combine small-capacity modular power supplies to form a larger-capacity variable-frequency power supply. Modularization requires solving the parallel connection problem between inverter power supplies. The parallel connection of variable-frequency power supplies is more complicated than that of DC power supplies. It faces many problems such as load distribution, circulating current compensation, and on-off control.

   (4) Digitalization

   Now digital signal processing technology is becoming more and more perfect and mature, showing more and more advantages : easy to process and control by computer, avoiding

   It avoids the distortion of analog signals, improves the anti-interference ability of the system, facilitates the debugging of software packages and remote sensing, telemetry and adjustment, and is also convenient for the implantation of self-diagnosis, fault-tolerant and other technologies, while also facilitating the development of parallel technology of power supplies.

   (5) Greening

   绿色电源的含义有两层:首先是显著节电， 这意味着发电容量的节约， 而发电是造成环境

   The main cause of pollution. In order to make the power supply system green, the power supply should be equipped with a high-efficiency filter, and the power factor correction technology and soft switching technology should be used at the input end of the power grid. Improving the input power factor is of great significance. It can not only reduce the pollution to the power grid, reduce the reactive power loss of the mains, and achieve the effect of environmental protection and energy saving, but also reduce the corresponding investment and improve the operation reliability. The traditional method to improve the power factor is to use passive power factor correction technology. The more advanced method is : the single-phase input uses active power factor correction technology, and the three-phase input uses SPWM high-frequency rectification to improve the power factor. In the future, power supply technology will develop in the direction of high efficiency, high power factor and high reliability, and continuously achieve low harmonic pollution, low environmental pollution, low electromagnetic interference, miniaturization and lightweight. This will provide a strong technical guarantee for the development of green power products and equipment in the future, which will also be the inevitable result of the development of modern power supplies.

   3. Difficulties in the digital development of variable frequency power supply

   Digitalization is the main direction of the development of variable frequency power supply, but the following problems still need to be solved :

   (l) The output of the variable frequency power supply needs to track a given signal that changes according to the sinusoidal law. It is different from the general switching power supply.

   Under closed-loop control, the time difference between the given signal and the feedback signal is reflected as an obvious phase difference, which is related to the load, which brings difficulties to the design of the controller.

   (2) The output filter of the variable frequency power supply has a great influence on the system model. The fluctuation amplitude of the input voltage and the nature of the load,

   大小的变化范围往往比较大， 这些都增加了控制对象的复杂性， 使得控制对象模型的高阶性、不确定性、 非线性显著增加。

   (3) The variable frequency power supply power electronic conversion device is a discrete, coupled, nonlinear dynamic system.

   In order to meet the static and dynamic index requirements of the load on the power supply, the power electronic conversion device is generally designed as a closed-loop automatic control system. Engineering and technical personnel are familiar with the correction and synthesis of linear systems, but are somewhat unable to control such a system. Therefore, if a mathematical model of the system can be established, especially the transfer function from control to output, it will help the design and system analysis of engineering and technical personnel, reduce the debugging time of blindly selecting parameters, and solve the linear control problem of essentially nonlinear systems.

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1. Reference Links

https://www.rohm.com.cn/electronics-basics/dc-dc-converters/dcdc_what2

https://www.eetree.cn/wiki/ps_design_case

https://www.51wendang.com/doc/0fd6704dc3141d949cd4671c

https://www.ti.com.cn/sitesearch/zh-cn/docs/universalsearch.tsp?langPref=zh-CN&searchTerm=%E5%BC%80%E5%85%B3%E7%94%B5%E6%BA%90%E5%9F%BA%E7%A1%80%E7%9F%A5%E8%AF%86&nr=592#q=Basic knowledge of switching power supply &numberOfResults=25

https://zhuanlan.zhihu.com/p/386508094

https://baijiahao.baidu.com/s?id=1714224305606135668&wfr=spider&for=pc

http://www.360doc.com/content/20/0620/22/61974897_919625297.shtml

http://www.360doc.com/myfiles.aspx

https://www.docin.com/p-2019723694.html

https://baijiahao.baidu.com/s?id=1722210500244950108&wfr=spider&for=pc

https://wenku.baidu.com/view/7b2b451e930ef12d2af90242a8956bec0875a5db.html

https://www.doc88.com/p-7377709840122.html

https://www.doc88.com/p-9052856936219.html

https://www.doc88.com/p-84687429490893.html

http://www.360doc.com/content/22/0118/19/21901291_1013830883.shtml

se7ens

Great work, first praise and then watch

okhxyyo

se7ens posted on 2022-5-13 18:22 Great work, first like and then read

Haha, it's not me. I'm just a porter. The hard work is done by our colleagues who search for information, sort it out, and organize it in their own language. Haha. I'll accept this like for others~~

combat

Thank you for your hard work and the compilation. It is very well organized. It would be more convenient

okhxyyo

combat posted on 2022-5-30 11:17 Thank you for your hard work and the compilation. It is very well organized. It is more convenient to download a complete document. ...

Got it~ I will pack it and upload it to the download center later