Miniature PV Inverter

1, micro-inverter design quality assessment

Is it possible that the micro-inverters with increasing geometrical levels may pose potential safety hazards?

There are two huge differences between the basic characteristics of the micro-inverter based on the component power level (300 watts) and the components themselves:

A component is a single diode structure (simple semiconductor), and an inverter is a combination of multiple active and passive devices and has embedded software devices (complex electronics). The reliability of the two is essentially unmatched. . A single component can be easily implemented for 25 years. It is not easy to achieve 25 years of inverters with multiple component combinations.

2 The difference in power systems in different countries is enormous. It is the inverter that bears this difference, namely the inverter has become the firewall of the component. Therefore, the components are insensitive to the grid, and one certification can be used universally; and the inverter must be differently certified for each country's power grid to meet the different requirements of the grid, such as voltage, frequency, safety specifications and so on.

The number of micro-inverters has increased by an order of magnitude compared to the smallest power level centralized inverter (3000 watts), and for large-scale centralized inverters (250 kW), the number of micro-inverters has increased. Three orders of magnitude (1000 times). This huge amount of change will inevitably lead to some fundamental changes at the power plant level and the power grid level. This so-called quantitative change leads to qualitative change. Therefore, the assessment criteria for the design quality of micro-inverters are much more complex and demanding than the evaluation criteria for components (certainly also centralized inverters).

The first level of design quality is the assessment of the electrical specifications of the product itself, such as power, voltage, efficiency, weight, total harmonic content THD, power factor PF, appearance, price, and durability. Unfortunately, most micro-inverter manufacturers only stop at this level.

The second level of design quality is to design for the power system and safety regulations of different countries on a global scale, through its certification and verification in the application. In Australia, because of the low standard threshold, Chinese manufacturers there gather; North America has adopted a network of standards for micro-inverters due to its relative backwardness in the distributed power generation industry and standards, as well as support for local companies. "Open side" attitude. For example, North American standards have abandoned the requirement of “mechanical disconnection” as special equipment and have low requirements for leakage current and DC component, and have not proposed to make micro-inverters responsible for the social responsibility of the power system. "Frequency change regulates output power" requirement. Therefore, just passing the certification in Australia or North America, there is still a long way to go before the requirements of the global market. Moreover, we believe that with the increase in the scale of distributed photovoltaic power plants in Australia and North America, they will inevitably reflect on and raise the corresponding standards, and will be aligned with the standards of Europe (such as Italy and Germany). North America's request for reactive power to photovoltaic power plants has actually released a strong signal.

Ying Weili has comprehensively and systematically studied typical power plants in countries around the world in a spirit that is not afraid of difficulties and endures loneliness, and has completed certifications in many countries including North America, Australia, Germany, Italy, the United Kingdom, Northern Europe, Spain, Mexico, and South Korea. (Looking around each of the micro-inverter manufacturers, almost all of them come from the semiconductor industry. Only Ying Weili is led by experts who really understand the power system).

The third level of design quality is user testing with a certain amount of scale and extensive representation. Both are indispensable. If it is only tested in Australia, then the reliability of even the 100,000 test results represents far less than the credibility of 10 million sets in 10 countries in Europe, Asia, Africa, and the United States. The test is also not comparable to the two-year test.

Ying Weili completed testing of nearly 20,000 units in more than 40 countries in nearly two years. However, Company A and Company N only tested and sold in only one or two countries in less than one year, although the total amount may be larger. Due to the relative shortness of time and the relative unity of electricity, geography, climate, and even the human environment, Company A, Company N, and even Company E do not have the ability to ship products in bulk globally.

We do not comment too much on the business strategies of Company A and Company N. However, from the standpoint of design quality control, this approach is not rigorous or scientific. Due to the relatively short time and the similarity of test conditions, many potential problems cannot be revealed. This has been fully demonstrated in our testing experience. For this purpose, Ying Weili has done a lot of work to formulate a power grid for each country. Different requirements. Therefore, many potential problems in the design of Company A and Company N will remain lurking. These problems ultimately require someone to pay the bill.

Finally, the assessment of quality design requires a comprehensive and continuous monitoring and improvement at three different levels and at different levels. This is a long-term, long-span, geographically distributed, multi-complex climate environment. This kind of comprehensive test and improvement process of grid adaptability. Any attempt to skip these necessary stages is extremely dangerous and will certainly be costly. Many pioneers have become martyrs, and the reasons are mostly similar. Looking at the way IT and EVs (EVs) have travelled over the past decade, it has profound implications for the healthy development of distributed smart grids.

2. Micro-inverter-based distributed systems: far more than microinverters

Generator or power plant? this is a problem.

The micro-inverter and the components together form an ideal alternator, and multiple generators form a power plant. The beauty of the micro-inverter is that it has a commercially available (static) alternator at a power level of 300 watts, providing a complete solution for distributed generation. This is a milestone in the history of human electrical civilization. This further makes it possible for individuals to generate electricity that is truly and commercially significant. It is a pity that its profound connotation and complete extension are not even clear to the pioneers. However, like many other technological innovations, this is normal.

Distributed generation systems have two levels: the distribution of benefits and the distribution of risks. Both must be taken into consideration, but the focus will be different depending on the size of the power plant.

Smaller systems for residential roofs (less than 10 kW) are more focused on the former, while large systems (above 300 kW) are more focused on the latter. The risk of electric shock is provided by the leakage protection mechanism, and the risk of transformer damage is provided by the DC component detection mechanism of the current.

In the era of centralized inverters, generators and power plants are integrated, and all revenue control and risk control are concentrated on the inverter. Therefore, centralized inverters require leakage protection and DC component protection. It's also taken for granted (and can be affordable). In the era of micro-inverters, generators and power plants are no longer the same entity. The combination of multiple qualified generators (micro-inverters) does not equal a qualified power plant. The most direct reason is that as a micro-inverter for generators, the certification body does not need to detect its leakage current and DC component (and can not afford it at cost), but the power plant needs these two mandatory safety protections: People are serious safety accidents, and the DC component burning the distribution transformer will directly endanger the safety of the power system. Both of these are great responsibilities that power plant owners must bear.

The systems of company E, company A, and company N, because they do not have eGate, can not perform distributed, intelligent detection and timely protection of the leakage current and DC components, so their solution is only applicable to small systems, plus Third-party protection (thus resulting in uncontrollable costs). Strictly speaking, they are only "generator suppliers", and only Ying Weili is the "power plant supplier." The difference between the words is a thousand miles away. In fact, our competitors are not aware of the power system (their senior executives and technical teams are mainly in the semiconductor industry). They have not yet solved the 100 kilowatt-class, megawatt-class distributed micro-inverse system solutions. Preparation.

The Infineon three-phase eGate+ micro-inverter system is a complete 16x3x0.25kW=12kW power plant that perfectly meets all the electrical safety requirements for a distributed power plant: secondary lightning protection, dual mechanical electrical shocks Open, leakage current detection and safe power-off/automatic recovery, grid-connected current DC component detection and safe power-off/automatic recovery. Based on such a complete distributed power plant unit, users can easily build distributed power plants at any power level just like children can use Lego Blocks.

At present, as far as the author knows, only Infineon's eGate+ micro-inverter system can be used worldwide to realize a truly modular, intelligent power distribution photovoltaic system of any power class. This is inextricably linked to the author's rich experience accumulated in the field of power systems, motor control, and advanced power electronic converters for more than 20 years.

Whether it is a component plant or an inverter plant, it is only consciously or unconsciously concerned about the "generator" (ie inverter) itself, and the grid company is more concerned about whether the power plant as a whole meets the grid connection requirements.

To provide end-users with distributed solutions based on micro-inverters, from the perspective of revenue, they benefit from it. However, so far, the vast majority of micro-inverter manufacturers seem to only pay attention to and meet the interests of end-user customers, but ignored the basic respect for the power grid companies: Grid companies did not get from the additional benefits of distributed generation Any benefits. On the contrary, for power plants with the same power level, the power system has to face many more generators than the centralized inverter (micro-inverter): the surge in the number of generators in a distributed power plant makes the reliability of the power system It became more complex than ever before.

For example, J Company's Fengxian Plant's one megawatt (1MW) project selected Yingwei's 4,200 micro-inverters, or 4,200 generators. If a 250kW centralized inverter is used, only 4 generators are needed. The additional generation of 4,200 micro-generators has brought better benefits to J Company's Fengxian plant, but potential safety problems posed by these generators have been left to the grid if not handled properly. In addition to conventional over- and under-voltage, over-frequency and under-frequency protection, frequency regulation power, island protection, and lightning protection, there are two serious safety issues that must be addressed: 1. Leakage current protection; 2. DC component protection. Leakage can endanger personal safety (its importance is self-evident); DC components can jeopardize the safety of step-up transformers. Leakage currents endanger life, which can be sued by victims and insurance companies; DC components can lead to abnormal heating up of distribution transformers, and even burning them, which can be severely punished by power grid companies.

Because of the cost, the micro-inverter itself does not have active leakage protection and DC component protection. These two important electrical safety indicators, if handled badly, will leave huge hidden dangers to the safety of the entire system. Imagine that one of the 4,200 micro-inverters in the Fengxian project of company J had a leakage or excessive DC component. What will happen?

Our competitors, the systems of company E, company A and company N, can only join third party leakage protection and DC component protection. However, they immediately face two dilemmas: Are these protections concentrated in the central distribution box or are they distributed throughout?

If a third party's leakage current and DC component protection are to be centrally added to the central distribution box, then if there is a micro-inverter or a cable leakage, then only the 4000 or more micro-inverters can be completely removed. One by one, because there is no leakage fault location system, it is impossible to accurately locate where the fault occurred.

If you want to add third-party leakage current and DC component protection devices throughout, then, although this can manually locate the leakage fault, the cost of doing so will greatly exceed the cost of the eGate solution. The most unacceptable to customers is that they spent distributed money and bought a “semi-automatic” pseudo-distributed system. The frequent manual interventions and complicated maintenance brought by such systems far exceeded ( Traditional) centralized system required maintenance. With Infinity's eGate system, any problem can be located in real-time on 16 (a set of) micro-inverters and corresponding cables, including conventional electrical isolation, leakage protection, DC components, and lightning protection.

The safety and intelligence of incomplete distributed systems are worse than centralized ones. We will call it "pseudo distributed system" for the time being.

The photovoltaic industry should also take seriously the potential harm to the owner and the power system caused by this “pseudo distributed system”. The real meaning of the component-level, intelligent distributed system, only the Infineon eGate+ micro-inverter is the best solution.

3. Micro-inverter-based smart grid: far beyond data acquisition

Smart Grid: The trouble is just beginning.

Five years ago, Infineon began to develop a micro-inverter: an advanced digital power supply (generator). Looking back on this five-year journey today, what Yingwei Li finally delivered to its customers was a complete smart grid system. This leaps, if not explained, many people cannot realize.

First, because of the relatively small number of centralized inverters, wired communication is used. The LAN of a large number of micro-inverter systems can only use wireless or virtual wireless solutions. The application of wireless and virtual wireless to industrial-grade high-real-time and high-reliability designs is a new and challenging task in itself.

We do not discuss the applications of smart grids such as power interventions, billing certifications, geographic information, meteorological information, industrial power distribution information, virtual power plants, power quality analysis, data mining based on expert systems, participation in peak and valley adjustments, Harmonic control, low-voltage traversing, reactive power compensation and so on, in terms of data acquisition, real-time and safety are two eternal themes that must be strictly protected. How does the local area network based on PLCC guarantee the real-time data and security of the data, according to the author's understanding, company A and company N have the problem of insufficient understanding of this requirement.

Firstly, both A company and N company adopt Shenzhen R company's plan, and it is a kind of "transmission" "total package solution". That is, R company provides a full set of protocol encapsulation of data link layer, only opening interface parameters to A company and N company. R company's product design, all around the remote meter reading developed, that is, one monthly data (small amount of data, the frequency of transmission is very low). For this application, real-time performance and security are not the issues they need to consider. Because of "outsourcing", the "communications group" of both company A and company N has weaker capabilities, while Infineon is equipped with more than a dozen teams of communication engineers (with experience in wireless communication and factory automation), engaged in basic theory and application. Research. Ying Weili has realized the growth from pure power electronic converters to smart grid systems, from simple power electronics technology to industrial LANs and remote database technology, and further development of settlement and advanced applications. Ying Weili has grown into a company that provides complete smart grid solutions, while Company A and Company N are just power electronics companies.

On the primary side of the power system (ie on the power generation and transmission side), the ethical relationship of the power system is clear and fixed. Low-speed power line carrier communication (PLCC) based on BFSK (Binary Frequency Shift Keying) has been the first choice due to its excellent safety and economy. Moreover, due to the natural attenuation of the distribution transformer, the physical signals in the power line carrier communication (PLCC) used on the primary side (ie, on the power generation and transmission side) are relatively closed, and their interference by the outside world is very small. Therefore, this clear system structure and closeness determine that the technical conditions for the application of power line carrier communication (PLCC) on the primary side of the power system (ie, power generation and transmission side) are relatively easy to meet to ensure communication quality (uninterrupted and safe). Sexual).

The secondary side of the power system (ie, the power-side end of the power distribution system) is a very new research topic based on the communication system of the distributed power generation system. There are many technical, economic and even social and legal systems issues that need to be further studied. The Power Line Carrier Communication (PLCC) scheme for the distributed power generation system at the bottom of the distribution network at the secondary side of the power system is currently under study. No matter whether it is the physical layer, data link layer or application layer, it has not yet been studied. Industry Standard. Ying Weili is the only company that has put forward this topic and put it into practical research, and has implemented and applied mature technology solutions.

Relative to the power line carrier communication (PLCC) environment of the medium and high voltage side of the power system, the low voltage distribution network (ie, the power grid where the micro-inverter is located) faces more technical problems. First, the primary side of the power system (that is, the power generation and transmission side) is a stable closed network in terms of high-frequency impedance, while the secondary side is an open network (the access of its load is almost unlimited), and in turn high frequencies. Impedance cannot be controlled. Second, harmonic pollution in the secondary-side power distribution network is increasingly serious (such as the instantaneous current change caused by the unstable power supply of household appliances), and it is an increasing trend in such systems. The electromagnetic environment of Power Line Carrier Communication (PLCC) cannot be guaranteed. If the broadband PLCC scheme with strong anti-interference is adopted, its high-tech threshold and high cost will limit its wide application. The application of low-voltage PLCC based on narrow-band technology is still mainly limited to meter reading systems and street lamp control, where the data volume is small and real-time requirements are not high. Thirdly, in the centralized power generation system, the flow of electricity is one-way. The emphasis of the power information system is on relay protection and power quality analysis. The system can give mandatory instructions, and the affiliation of the power system (power system ethics). It is clear. And fundamentally changing the micro-distribution power generation of the power grid ecology, the affiliation in the system is no longer clear, the system can not only give mandatory instructions, even if the acquisition of pure technical information must also consider the different power generation Legal protection regulations for factory and personal information, and user acceptance of information sharing and data security.

Therefore, in the distributed generation system, there are many problems in which the information transmission medium is unstable and uncontrollable, which requires high real-time data, and poses potential risks to the public information security. In this system, the application is based on narrow-band technology. The low-voltage power line carrier communication (PLCC) technology is indeed a brand new technical challenge. The openness of the physical layer signal of the R company's solution will face a huge risk of disclosure of personal business information of the user; at the same time, the R company's framework based on the Ethernet protocol is also difficult to use in the application of multi-power plants and complex electrical environments. (The high degree of unreliability of data transmission, which has become prominent in the actual application of the customers of company A and company E, and has given rise to "not providing communication functions" or "long data times" in the market strategies and applications of these manufacturers. The strange phenomenon of not changing, and the original intention of the "micro-inverter system can monitor the power generation status of each component in real time and continuously."

We must also give more serious consideration to changes in the ecology and ethics of the power system caused by smart grids. The communication problems of the new energy grid-connected system must comprehensively consider various aspects of technical, economic and social factors. Within the microgrid, the most suitable communication technology should be selected as narrow-band power line carrier technology; at the interface between the microgrid and the public power network, high-frequency filters and impedance matching networks can be installed to make the signal-noise environment on the power line inside the microgrid. The impedance stability is guaranteed, which in turn ensures reliable, low-cost communications; the interconnection between the microgrids can be based on industrial bus technology LAN or wireless network solutions; the external uplink and downlink communications from the microgrid to a remote central database should be preferred Commercial communications networks, especially the Internet.

One hundred years ago, the beginning of the electrical age (all analogs) created GM and Siemens. Thirty years ago, the mid-electrical era (information digitization) created IBM, Microsoft, and Google. Today, the electrical age has entered its late stage (energy digitization) and it can be predicted that anyone who has mastered the core technology of the smart grid will be able to take the initiative in this electrical industry.

With the development of smart grids, distributed generation information systems can break the physical boundaries of traditional power suppliers and make it possible for the global power system to be interconnected on the information loop. At the same time, it has constructed a special Internet of Things framework that crosses the border. With the continuous improvement of infrastructure based on this technology, more business models and business values ​​will be excavated and created.

Before strategically entering the field of micro-inverters, the author thinks that it is very necessary to follow the above thinking and fully consider issues from generators (micro-inverters), power plants, and power grids, from technology, system standards, and laws to extensions. The three propositions that have been continuously expanded and the connotation is deepening have been comprehensively and profoundly considered:

1. Three levels of design quality assessment of the generator (micro-inverter) itself;

2. When the generator function is distributed, it must consider the intelligent and distributed implementation of the power plant's electrical safety.

3. All applications under the framework of the smart grid must be developed on the basis of comprehensive assurance of real-time data and information security.