1. Technical background for the application of flywheel energy storage UPS
The UPS we have discussed in the past all belong to the category of static UPS. The principle is: during the operation of these UPS, in addition to Except for the cooling fan, the various electronic components and electrical components used do not have any mechanical movement. Years of static UPS operation experience show that although static UPS has made an "indispensable" contribution to ensuring the safe operation of user loads in various industries. However, it still has the following weaknesses:
(1) The efficiency of static UPS is "not high enough": Relevant statistics show that for medium and large capacity power frequency UPS, its efficiency is Only 93~94. For medium- and large-capacity high-frequency UPS models, their efficiency is only 94 to 95. For today's society that increasingly emphasizes energy conservation and environmental protection, the loss of this UPS itself is still high.
(2) The battery pack in UPS is an important factor that causes the UPS failure rate to increase and the amount of daily maintenance to increase. Moreover, the battery life is short. In addition, the disposal of used batteries that may cause serious pollution to the environment is still one of the problems that plagues us.
Therefore, one of the technical ways to solve the above problems is to use flywheel energy storage dynamic UPS to replace the double conversion online static UPS.
2. Technical advantages of flywheel UPS
In recent years, domestic and foreign data centers, semiconductor chip manufacturing, certain special military communication systems and government confidential departments are increasingly Pay attention to and choose a flywheel energy storage dynamic UPS (referred to as flywheel UPS or dynamic UPS). The following benefits can be obtained by using this kind of UPS:
(1) Further improve the efficiency of UPS: Relevant data shows that the efficiency of UPS can be increased from 92 of static UPS to 98 of flywheel UPS.
(2) Completely eliminate battery components with obviously high failure rates from the UPS. The benefits that can be obtained from this are: not only helping to improve the reliability of the UPS, but also greatly reducing the maintenance workload of the power supply personnel on duty.
For this kind of flywheel UPS, when the mains power supply is normal, it uses the mains power to supply power to users, and also passes part of the electric energy through the "synchronous compensation" with motor and generator control functions. The machine (G/M)" device stores kinetic energy in its huge flywheel.
At this time, its "synchronous compensator (G/M)" device not only assumes the function of short-term energy conversion control, but also converts the electrical energy from the mains into electricity stored in the flywheel. mechanical energy. Moreover, it is also responsible for automatic voltage stabilization and automatic compensation of harmonic currents that may be generated from the mains power grid and electrical equipment, that is, the harmonic content THDI value of the output current is adjusted to zero in real time. . When the mains power supply is interrupted, it can use the inertia-driven synchronous compensator (G/M) device that originally stored the huge kinetic energy in its flywheel to continue rotating. At this time, the synchronous compensator (G/M) device will automatically assume the control function of the generator, thereby ensuring continuous and uninterrupted power supply to various electrical equipment. The driving factors that can push flywheel UPS to a new stage of practicality are:
(1) For today's power industry, whose technology is quite mature, due to the widespread use of intelligent power supply managed by information technology, Power grid dispatching technology, and a protective design scheme that uses ATS switches to automatically perform "switching and switching" operations between dual mains input power supplies in users' power supply systems. In their mains input power supply systems, The chance of a prolonged power outage is extremely low.
This creates extremely favorable operating conditions for the practical application of flywheel UPS, which relies on kinetic inertial energy to ensure continuous power supply to the load.
① According to a survey of the U.S. power supply grid by the Electric Power Research Institute, more than 90% of power outages lasted less than 10 seconds;
② According to RWE’s survey of 9 European countries A survey of 126 power supply grids found that more than 95% of the power outage accidents lasted less than 3 seconds;
③ For user equipment that uses the automatic switching control technology of the ATS switch between the two mains input power sources , when its priority input power supply encounters a power outage, its other backup power supply can restore power to the electrical equipment within a time interval of less than 1 to 3 seconds. Theoretically, the ATS switch will cause the input power supply to be interrupted for tens to hundreds of milliseconds. This is because the typical switching time of the ATS switch is ≤200ms. The reason why the total switching time of the ATS switch may be as long as several seconds is: in order to prevent the ATS switch from performing unnecessary and frequent "mistakes" between the two mains power supplies due to occasional flash interruptions in the mains power grid. "switching" operation, resulting in annoying peak power interference at the input end of the electrical equipment and shortening the service life of the ATS switch. For this reason, it is necessary to artificially set the appropriate delay switching protection function for the ATS switch. Therefore, for users with "dual bus input" power supply conditions, they can choose the technical approach of flywheel UPS to avoid configuring a battery pack that is bulky, has a high failure rate and requires a lot of maintenance.
In summary, since in the power supply grid, the probability of long-term power outage is extremely low. In this way, a solid technical foundation will be laid for the technical advantages of flywheel UPS to perform real-time compensation and control of transient voltage fluctuations, flash interruptions, transient interference, and harmonic currents that may come from the mains power grid.
(2) Compared with traditional double-conversion online static UPS, flywheel UPS has the following obvious technical advantages, as shown in Table 1.
It can be seen from the table that flywheel UPS has significant advantages in overall machine efficiency, maximum output power of a single machine, overload resistance, output short-circuit resistance, input power factor, load power factor, allowed operating temperature range, and no need for batteries. The maintenance and reliability of the unit are significantly better than the double-conversion online static UPS. It should be noted here that for a flywheel UPS power supply system, its average overall efficiency is 3 to 4 times higher than that of a static UPS. The energy efficiency of the vacuum magnetic levitation flywheel UPS from the American company Active Power can even be improved by 6. This is particularly evident in its energy-saving, consumption-reducing, greening and environmental protection effects in today's context of large increases in energy prices. Another reason why using a flywheel UPS can save more energy is because it comes with an air-cooled fan and does not need to be equipped with a battery pack that requires the ambient temperature to be less than 25°C. Therefore, there is no need to configure air conditioning units with high consumption operating characteristics for the UPS computer room. However, it should be noted that it still needs to be equipped with the necessary hot air exhaust system.
3. Working principle of flywheel UPS
The typical control block diagram of a dynamic UPS with flywheel type kinetic energy storage is shown in Figure 1. It can provide products with single unit output powers of 150, 180, 260, 400, 500, 750, 1000, 1300 and 1670kVA. As shown in the figure, there are two power supply channels unique to UPS:
(1) Maintenance bypass power supply channel: During normal operation, switch S2 is in the off state;
(2) Main power supply channel: It is composed of several major components such as input switch S1, input static switch, choke coil 1 and choke coil 2, power-bridge and output switch S4. The power bridge component is composed of main components such as synchronous motor/generator set, bidirectional converter, exciter generator and energy storage flywheel. When the mains power is interrupted, its full load power supply time is about 20 seconds. For users who need continuous power supply for a long time, this can be achieved by choosing a diesel/gas generator set (optional).
Here, the electric power bridge composed of choke coil 1, choke coil 2 and synchronous motor/generator is a so-called magical isolation that has both automatic output voltage stabilization and input current harmonic compensation and control functions. Coupling choke type control loop. Here, the power supply bridge simultaneously assumes the dual regulation functions of an automatic voltage regulator and an active filter. The control functions of this control loop can be summarized as follows:
① Compensate and control the harmonic current generated from the nonlinear load;
② Compensate and control the harmonic current from the input Compensate and control voltage harmonics according to the voltage distortion of the power grid;
③ Limit the amplitude of short-circuit current reflected to the main input grid;
④ Utilize the sine wave generated by the power supply bridge The power supply uses a waveform to perform automatic voltage stabilization and control functions to ensure that it can output high-quality power to the load with a voltage stabilization accuracy of <±1.
3.1 The control principle of automatic voltage stabilization and uninterrupted power supply of flywheel UPS
(1) When the input power supply is normal, the automatic voltage stabilization and control principle of flywheel UPS
According to the design of this UPS, during normal operation, its input switch S1 and output switch S4 are in a closed state, and the maintenance bypass switch S2 is in an open state. When the voltage of the input power supply is in the range between -20 and 15, the "input static switch" is in the on state. Under this condition, the unregulated mains power supply that may contain high-frequency interference is fed to the electrical equipment located at its output end after being filtered by choke coil 1 and choke coil 2 to resist high-frequency interference. At the same time, it also assumes the control function of the synchronous compensation machine through the generator/synchronous compensation machine (G/M machine) located in the "electric power bridge". At this time, the "electric power bridge" is in the working state of the motor. It drives a huge energy storage flywheel (speed up to 1800 ~ 3300 rpm) through the main shaft of the exciter generator in a high-speed rotating state, thereby converting part of the electric energy of the mains power grid into a high-speed rotating state. The purpose of energy conversion is the mechanical inertial kinetic energy of the flywheel. At the same time, under the control of the logic control board, the "bidirectional converter" in the "electric power bridge" located in the flywheel UPS is used to simultaneously perform automatic voltage stabilization and market stabilization of its excitation generator and synchronous generator/generator set. The control task of electrical synchronization tracking. At this time, its generator/synchronous compensator outputs a regulated power supply with a voltage stabilization accuracy of 380V±1 under the control of the bidirectional converter. At this time, chokes 1 and 2 assume the regulation function of the passive voltage harmonic compensator.
(2) When the input power supply has a "short-term power outage"/flash failure for some reason, the automatic voltage stabilization and control principle of the flywheel UPS
When the mains power has a "short-term power outage" for some reason When a "momentary power outage"/flash (power supply interruption on the order of tens of milliseconds) fails, the exciter generator located in the flywheel UPS continues to rotate at high speed by utilizing the inertial kinetic energy originally stored in the huge flywheel. At this time, the output power from the generator, whose frequency and voltage are in a slowly changing state, is fed to the input end of the bidirectional converter (Note: This is due to the fact that as the power outage time of the input power continues to extend, the original storage The inertial kinetic energy in the huge flywheel is continuously consumed. Under this condition, the frequency and voltage of the output power from the exciter generator will decrease to varying degrees). After such a power supply with poor power supply quality is processed by a bidirectional converter, it can output a high-quality power supply with automatic voltage stabilization and automatic frequency stabilization operating characteristics. After such high-quality power is fed to the input end of the synchronous motor/generator unit, it can continuously output a regulated power supply of 380V±1 (see Figure 1b).
When the mains power fails, the length of time this UPS continues to provide power depends on the amount of mechanical energy stored in the flywheel and the load percentage of the UPS. For a dynamic UPS with an output power of 1670kVA, its mechanical energy storage is 16.5MW·s. Typical variation parameter values ??between the duration of the UPS and the load percentage of the UPS are listed in Table 2.
From the above, it can be seen that for flywheel UPS, during its operation, if the instantaneous power supply interruption time of the mains power does not exceed the above time limit, it can continuously output high-quality power to the user's load. power supply. In addition, if the mains power problem encountered is not a power outage, but a low input voltage, the continuous power supply of this UPS will be greatly extended.
Under this condition, a wide input voltage working range can be obtained. Its typical technical parameters are: when the input voltage is 380V, -20, 15, it can work continuously; when the input voltage drops to When the input voltage is 380V and -30, the power supply time is 10min; when the input voltage drops to 380V and -50, the power supply time is 30s. Of course, for users who choose the diesel/gas generator option or the "dual bus input" power supply design using a two-way input power ATS switch, they can provide 365×24 hours of uninterrupted power to the subsequent loads. of power supply.
The appearance and structural diagram of the main components of a typical flywheel UPS are shown in Figure 2.
3.2 Principle of regulating harmonic compensation characteristics of flywheel UPS
The second important technical advantage of flywheel UPS is: It has excellent input harmonic compensation characteristics and high System efficiency (96~98).
When the subsequent load is resistive, its input power factor PF value is 1, and the THDI value of the input current harmonic component is almost zero. When it is used with single-phase rectifier filter nonlinear loads such as PCs, low-end servers and other IT equipment, DCS equipment in industrial control systems and household appliances without input power factor correction function (PFC), the input of these electrical equipment itself The harmonic characteristics are very poor. Although the voltage waveform fed to the input power supply of these electrical devices at this time exhibits an excellent sinusoidal waveform, the current waveform they draw from the input power supply becomes a discontinuous bell shape as shown in Figure 3(a) Pulse train (that is, they show severe current distortion on their input current waveform), resulting in the harmonic content of their input current having a THDI value as high as 55 to 77, and the input power factor PF value dropping to about 0.8.
However, after selecting a flywheel UPS to drive the above electrical equipment, you can use a system consisting of "Choke 1, Synchronous Motor/Generator Bidirectional Converter Choke 2", etc. Power bridges are used to control harmonics for this type of nonlinear load. Under this condition, the reactive power provided by the synchronous motor/generator connected in parallel to the main power supply line of the flywheel UPS is used to perform current harmonic compensation regulation. In this way, the input current waveform with an excellent sinusoidal waveform as shown in Figure 3(a) can be obtained again at the input end of the flywheel UPS.
In this context, the harmonic characteristics of its input current can be greatly improved. Its typical values ??are: the harmonic content of the input current THDI value lt; 5, the input power factor PF value gt; about 0.98. What needs to be explained here is: Since the vast majority of IT equipment (medium and high-end servers, storage equipment, network equipment) used in today's data center rooms adopt input power factor correction technology (PFC), when using flywheel UPS When driving these electrical equipment, the following "green power" input harmonic characteristics are obtained: that is: the harmonic content of their input current THDI value lt; 3. The input power factor PF value gt; about 0.99, such as As shown in Figure 3(b).
In summary, it can be seen that compared with the traditional double-conversion online static UPS which can only solve the problem of its input current harmonics and output harmonics, the flywheel UPS can simultaneously solve its input current harmonics and output harmonics. The output harmonics are controlled by harmonic compensation, and its technical advantages are self-evident.
3.3 Flywheel UPS has excellent output dynamic response characteristics
Another important technical advantage of flywheel UPS is that it has excellent dynamic response characteristics. As shown in Figure 4, when the UPS When the subsequent load is suddenly loaded, the parallel power supply bridge composed of "synchronous motor/generator set choke 2" provides transient, supplementary active power to the subsequent load to ensure the output of the UPS. The terminal can obtain excellent automatic voltage stabilizing output characteristics. Its typical dynamic response characteristics are: lt; 5, recovery time 10ms (0→100 load→0). On the contrary, when the subsequent load of the UPS suddenly reduces its load, the parallel power supply bridge composed of the "synchronous motor/generator set choke 2" will quickly absorb the transient "abundance" from the main output line of the UPS. "Active power to ensure excellent automatic voltage stabilization output characteristics at the UPS output.
Here, the circuit consisting of the input static switch, choke coil 1 and choke coil 2 located in the flywheel UPS can be regarded as the main channel of power transmission in the mains power grid, which will be The power bridge composed of "flywheel excitation motor, bidirectional converter, synchronous motor/generator", etc. is regarded as a voltage-stabilized electric energy storage device connected in parallel to its output end, which dynamically adjusts the power output from the flywheel UPS. , in order to quickly respond to dynamic changes in real-time power consumption of downstream power equipment.
3.4 Typical technical parameters of flywheel UPS
Output power: 150, 180, 260, 400, 500, 750, 1000, 1300, 1670kVA;
Input Power factor: 0.96 ~ 0.99; THDV value of input voltage harmonic content lt; 2; efficiency: gt; 96;
The input voltage range is: 380V, -20 ~ 15, long-term operation; 380V, -30, the supported running time is 10min; 380V, -50, the supported running time is 2min;
Output voltage: 380Vlt; ±1; Peak ratio is 5:1;
Output short-circuit resistance: 300, 5s; 1400, 10ms;
UPS single unit mean time between failures (MTBF): 1.3 million hours;
Allowed number of parallel UPSs : 16 units.
4. Conclusion
In summary, for users with good mains power environment, flywheel UPS is significantly better than double-conversion online static in the following technical performances: UPS. They are: overall machine efficiency, maximum output power of a single machine, output short-circuit resistance, input power factor, output power factor, allowed operating temperature range, reliability, EMC electromagnetic compatibility, and the UPS is greatly reduced because there is no need to configure a battery pack. reduce the maintenance workload and reduce the area occupied by the computer room. Among them, it is particularly eye-catching because of its high reliability, significant energy saving and consumption reduction effect, and the fact that it does not need to configure a battery pack with a high failure rate. For this reason, it is used in some semiconductor chip factories and military systems in the United States, Europe and Taiwan. In recent years, it has also attracted increasing attention from the Chinese people. It is reported that it is possible that flywheel UPS will be included in the standards for the construction of data centers in my country. This is because flywheel UPS, as a technology that has developed extremely rapidly in recent years, can provide us with both economic and environmental benefits when building green data centers. However, it should be noted here that for this UPS, it is not perfect.
Although flywheel UPS still has some shortcomings, today, for those users who have "dual bus input" power supply conditions and are troubled by battery applications, they can definitely choose The technical measures of flywheel UPS are used to eliminate various disadvantages that may be caused by the battery pack with a high failure rate and heavy maintenance workload. This is because its expected service life can be as long as 15 to 20 years.
At present, it is common for large foreign data centers to use flywheel UPS to ensure power supply. The magnetic levitation flywheel UPS system is particularly outstanding in this field. In contrast, the service life of the battery is only a few thousand times of charge and discharge, and it usually only takes a few years to be replaced. Battery.
About Microcontrol New Energy
Shenzhen Microcontrol New Energy Technology Co., Ltd. (referred to as Microcontrol or Microcontrol New Energy) is the global leader in physical energy storage technology. The company's global headquarters is located in Shenzhen, and its business covers North America, Europe, Asia, Latin America and other regions. With its "safe, reliable and efficient" world-leading magnetic levitation energy technology, its products and services are widely used by Huawei, GE, ABB, Siemens, Emerson Trusted by many Fortune 500 companies.
Facing the three major trends of "cleaner, high-density, and digital" energy in the future, the company continues to be committed to providing system solutions for energy transportation, storage, recycling, and data management for strategic emerging industries.