Harmonic analysis and solution of large-scale water electrolysis for hydrogen production

According to the Medium-and Long-term Plan for the Development of Hydrogen Energy Industry (2021-2035), the proportion of hydrogen production from renewable energy in the terminal energy consumption will be significantly increased, which will play an important role in supporting the green transformation and development of energy, and means that the proportion of electrolytic water to hydrogen production will continue to increase.

With the development of large-scale water electrolysis of hydrogen production, harmonics, an important indicator of power supply, has been more and more widely concerned by the industry.Here will be on what is harmonic, harmonic harm and how to deal with harmonics. 

1, What is a harmonic wave 

Before talking about harmonics, first introduce what is base wave. In China's AC network, 50HZ sine wave can be called "base wave", and the voltage will generate similar current waveform on the load. As shown in the figure below, "u" is voltage, and "i" is current waveform.

Figure 1 Voltage and current waveform of the linear load

However, in practical applications, the load is not completely linear. Although the grid voltage is still 50HZ sine wave, the current may produce a non-sinusoidal wave due to the nonlinear load, and the waveform may be shown in the figure below.There are many kinds of nonlinear loads, such as uninterruptible power supply, switching power supply, IGBT power supply, rectifier, frequency converter, frequency conversion air conditioning, induction heating furnace, electronic computer, charger, etc.

Figure 2. Voltage and current waveform of the nonlinear load

Although the grid input source is the same, the current waveforms of FIG. 1 and 2 are not the same. If the linear load waveform of FIG. 1 is understood as a base wave, the difference between the current waveform in FIG. 2 and the waveform of FIG. 1 is harmonic.

According to the mathematical principle, the waveform of nonlinear load can be divided into the waveform of 50Hz. Besides the base wave (50HZ), the multiple is the "number" of harmonic, common has 5 times, 7 times, 11 times, etc.Five harmonics, it can be understood as a component waveform of 5 times the frequency of 50HZ, namely the component of 250HZ.

2, The harm of harmonic wave

Harmonics produce additional losses in the public grid, reducing the efficiency of power generation, transmission and electrical equipment.A large number of three harmonics flowing through the middle line can overheat the line and even cause a fire.Harmonics will affect the normal operation of electrical equipment, motor mechanical vibration and noise; cause transformer local serious overheating; capacitors, cables and other equipment overheating, insulation aging, shorten life, and damage.Cause the power grid resonance, make the harmonic current amplification several times or even dozens of times, will form a great threat to the system, especially to the capacitor and the reactor in series, often make the capacitor and reactor burned.Harmonics can lead to relay protection, especially the microcomputer integrated protector and automatic device error action, resulting in unnecessary power supply interruption and production loss.Harmonics will also make the electrical measurement instrument measurement inaccurate, produce measurement error, and bring economic losses to the power management department or power users.

3, Harmonic related standards 

China's standard for harmonics is GB / T14549-1993 "Power Quality: Public Grid Harmonics", and the current harmonic and voltage harmonics are stipulated as follows:

Table 1

Table 2 

International standards for harmonics are IEEE 519-2014, and current and voltage harmonics are specified as follows:

Table 3

Table 4

4, Large-scale electrolysis of water and hydrogen production to reduce the harmonic measures

For large-scale water hydrogen production (500 square / hour, 1000 square / hour and above hydrogen production equipment), there are two mainstream products, one is multi-pulse thyristor rectification, the other is IGBT PWM rectification + DC / DC chopping.

The multi-pulse thyristor rectifier system designed and produced by Green Power has been used in the site of multiple 1000 square projects. Without the ideal current and voltage harmonic can be achieved by a single 24-pulse or 12-pulse + multi-pulse phase technology.Even if the hydrogen production equipment is at different loads, it can also meet the harmonic requirements.

Figure 5 Green Power 24 pulse wave thyristor rectifier cabinet

Figure 6 Green Power Zhangjiakou Winter Olympics Project site rectification cabinet

Figure 7 Baofeng project site of Intelli rectifier cabinet

Figure 8. Site rectifying cabinet of Green Power Asia Silicon Projec 

Figure 9. Field rectifier cabinet of Green Power Sinopec empirical project

According to the field test, the total distortion rate of the current harmonic when a single 24 pulse wave runs (the worst case of the harmonic) is about 3-4%, and the voltage harmonic is about 1.1%.After multiple phase shifts, the current harmonic of the non-ideal 48 pulse wave can reach about 3% even at the unbalanced load.

graph 10

graph 11

And for the application scenarios of large-scale hydrogen production, the more the hydrogen production equipment, the higher the pulse wavenumber (such as 60 pulse, 72 pulse, 96 pulse), the better the harmonic effect, the current harmonic can be controlled within 1%.No additional harmonic filter device is required, greatly saving the cost and footprint.

IGBT PWM rectifier + DC / DC chopping scheme can make the current harmonic less than 3% through PWM rectification circuit, which can also achieve the effect of low harmonic, but the cost of this scheme is high.

5, Other important indicators related to water electrolytic hydrogen rectification 

In addition to harmonics, some other indicators related to the rectifier system are also critical, such as reliability, conversion efficiency, power factor, investment cost, adaptability of different electrolytic cells, footprint, maintenance, etc.

For the electrolytic water hydrogen production equipment of more than 500 square meters, thyristor rectification can achieve power factor of 0.95 (without increasing the compensation device), efficiency of 98.5%, can meet the current demand of various electrolytic cells (currently used in the maximum current of electrolytic water hydrogen production to 35kA), mature and reliable technology, low investment cost, small area and small maintenance.

Green Powercompany has focused on the research and development, design, manufacturing and service of rectifier equipment for more than 20 years, and was rated as a special "little giant" enterprise in Hubei Province.Products including thyristor rectifying power supply, IGBT high frequency switch power, IGBT PWM rectifier power, IGBT chopper power, DC / DC photovoltaic hydrogen power supply, can provide a variety of rectification solutions for electrolytic water hydrogen production equipment, has participated in more than 70 electrolytic water hydrogen production project, and exported to Germany, the Netherlands, South Korea, Japan, Brazil, India and other countries electrolytic water hydrogen market, and domestic electrolytic water hydrogen production equipment manufacturers established long-term cooperation.

6, Green Power electrolysis water to hydrogen rectification one-stop solution

Green Power provides a one-stop rectification solution for renewable energy hydrogen production, It can cover a single 5 N m3/h to 4000 N m3/h electrolytic water hydrogen production equipment, According to the hydrogen production amount, power supply parameters, power supply characteristics, site layout and other specific conditions, Provide customized optimal performance and cost-optimal configuration scheme, Single unit power can range from 20kW to 20MW, There are 5 optional products: thyristor rectifier, PWM rectifier, IGBT chopper power supply, IGBT high-frequency switch power supply, DC / DC photovoltaic direct supply converter, Can meet the characteristics of photovoltaic hydrogen production, wind power hydrogen production, Recently, he won the bid for a number of photovoltaic hydrogen production and wind power hydrogen production and rectification projects at home and abroad.

Green Power exported to more than 50 countries and regions, for the world top five hundred enterprises rectifying products, was named special new "little giant" enterprise, in the rectifying niche, adhering to the "create customer value, carry forward the spirit of" business philosophy, adhere to the "technology first, quality, service first", provide electrolytic water hydrogen rectification one-stop solution, meet the arrival of large-scale green hydrogen era.