The UPS we discussed in the past all belong to the category of static UPS. Its principle is that in the operation of these UPS, except for the cooling fan, all kinds of electronic components and electrical components used have no mechanical movement. Years of experience in static UPS operation shows that static UPS has made great contributions to ensuring the safe operation of user loads in various industries. However, it still has the following shortcomings:
(1) Static UPS efficiency is "not high enough": Relevant statistics show that the efficiency of medium and large capacity industrial frequency UPS is only 93% ~ 94%. For high-frequency UPS with medium and large capacity, its efficiency is only 94% ~ 95%. Today, with more and more emphasis on energy conservation and environmental protection, the loss of this UPS itself is still very high.
(2) The battery pack in UPS is an important factor leading to the increase of UPS failure rate and daily maintenance. And the service life of the battery is short. In addition, the disposal of waste batteries that may cause serious pollution to the environment is still one of the difficult problems that plague us.
Therefore, as one of the technical ways to solve the above problems, the dynamic UPS with flywheel energy storage is selected to replace the static UPS with online double conversion.
2. Technical advantages of flywheel UPS
In recent years, domestic and foreign data centers, semiconductor chip manufacturing, some special military communication systems and government secret departments have paid more and more attention to and selected a flywheel energy storage dynamic UPS (referred to as flywheel UPS or dynamic UPS). The following benefits can be obtained by adopting this UPS:
(1) Further improve the efficiency of UPS: Relevant data show that the efficiency of UPS can be improved from 92% of static UPS to 98% of flywheel UPS.
(2) Completely cancel the battery components with obviously high failure rate from UPS. The benefits obtained from this are: it not only helps to improve the reliability of UPS, but also greatly reduces the maintenance workload of power supply personnel on duty.
For this kind of flywheel UPS, when the commercial power supply is normal, it uses the commercial power to supply power to users, and at the same time, it stores some electric energy in its huge flywheel in the form of kinetic energy through the "G/M" device with motor and generator adjustment function.
At this time, for its "synchronous compensator (G/M)" device, it not only undertakes the short-term energy conversion and adjustment function, but also converts the electric energy of the commercial power into the mechanical energy stored in the flywheel. Moreover, it also undertakes the adjustment function of automatic voltage stabilization and automatic compensation for harmonic current that may come from the commercial power grid and electrical equipment, that is, the value of harmonic content THDI of output current is adjusted to zero in real time. When the mains power supply is interrupted, it can use the huge kinetic energy originally stored in its flywheel to drive the synchronous compensator (G/M) device to continue to rotate. At this time, the synchronous compensator (G/M) device will automatically assume the regulation function of the generator, thus ensuring continuous and uninterrupted power supply to various electrical equipment. The driving factors that can push flywheel UPS to a new practical stage are:
(1) For today's electric power industry with quite mature technology, due to the widespread adoption of power grid dispatching technology with information management and intelligent power supply, and the protection design scheme of using ATS switch to automatically perform the "switching adjustment" operation between two mains input power supplies in the user power supply system, the probability of long-term power outage in its power supply system is extremely low.
This creates extremely favorable operating conditions for the practical application of flywheel UPS, which can ensure the continuous power supply of the load by kinetic energy inertia.
(1) According to the investigation of American power supply network by American Electric Power Research Institute, it is found that the duration of more than 90% power failure accidents is less than10s;
(2) According to RWE's survey of power supply networks in 9 European countries 126, it is found that more than 95% of the power outages last less than 3s;
(3) For the user equipment adopting the automatic switching regulation technology of ATS switching between two mains input power supplies, when the input power supply with priority power supply fails, the other standby power supply can restore power supply to the electrical equipment within a time interval of less than 1 ~ 3s. Theoretically, ATS switch will cause power interruption of input power supply for tens to hundreds of milliseconds, because the typical switching time of ATS switch is about ≤200ms or less. The reason why the total switching time of ATS switch may be as long as a few seconds is to prevent the ATS switch from unnecessary and frequent "wrong switching" between two mains due to accidental flashing of the mains power grid, which will lead to annoying peak power interference at the input end of electrical equipment and shorten the service life of ATS switch. Therefore, it is necessary to set an appropriate delay switching protection function for ATS switch artificially. Therefore, for users with "double bus input" power supply conditions, choosing flywheel UPS can save the battery pack with huge configuration, high failure rate and large maintenance.
To sum up, the probability of long-term power failure in the power supply network is extremely low. In this way, it lays a solid technical foundation for giving full play to the technical advantages of flywheel UPS in real-time compensation and adjustment of transient voltage fluctuation, flashover, transient interference and harmonic current that may come from commercial power grid.
(2) Compared with the traditional dual-conversion online static UPS, flywheel UPS has the following obvious technical advantages, as shown in Table 1.
As can be seen from the table, flywheel UPS is obviously superior to double-conversion online static UPS in terms of overall efficiency, maximum output power of a single machine, overload resistance, output short-circuit resistance, input power factor, load power factor, allowable working temperature range, no battery pack maintenance and high reliability. It should be noted here that the average overall efficiency of flywheel UPS power supply system is 3% ~ 4% higher than that of static UPS. The energy efficiency of vacuum magnetic levitation flywheel UPS of American Active Power Company can even be improved by 6%. This is especially obvious for energy saving, consumption reduction and greening and environmental protection in the context of the sharp rise in energy prices today. Another reason why flywheel UPS is more energy-saving is that it has its own air-cooled electric fan and does not need to be equipped with a battery pack with an ambient temperature below 25℃. Therefore, it is no longer necessary to configure air conditioning units with high consumption operation characteristics for UPS computer room. However, it should be noted that the necessary hot air exhaust system is still needed.
3. Working principle of flywheel UPS
Figure 1 shows the typical control block diagram of dynamic UPS with flywheel kinetic energy storage. Products with output power of 150, 180, 260, 400, 500, 750, 1000, 1300 and 1670kVA can be provided. As shown in the figure, UPS has two power channels * * *:
(1) Maintenance of bypass power supply channel: During normal operation, switch S2 is in off state;
(2) Main power channel: it consists of input switch S 1, input static switch, choke coil 1 and choke coil 2, power bridge and output switch S4. Among them, the power bridge consists of synchronous motor/generator set, bidirectional converter, excitation generator and energy storage flywheel. When the power supply is interrupted, its full-load power supply time is about 20s. For users who need long-term continuous power supply, it can be realized by matching diesel/gas generator sets (optional). Here, the power bridge composed of choke 1, choke 2 and synchronous motor/generator is the so-called magical isolated coupling choke control loop, which has the functions of automatic output voltage stabilization and input current harmonic compensation control. Here, the power bridge simultaneously undertakes the dual regulation functions of automatic voltage regulator and active filter. The control function of the control loop can be summarized as follows:
(1) Use current harmonics to compensate and deal with harmonic current generated by nonlinear load;
(2) Voltage harmonic compensation and treatment of input power grid voltage distortion;
③ Limit the amplitude of short-circuit current reflected to the main input power grid;
(4) The sine wave power generated by the power bridge is used to perform the automatic voltage regulation function, so as to ensure that it can output the voltage regulation accuracy to the load.
3. 1 flywheel UPS automatic voltage regulation principle of uninterrupted power supply
(1) The principle of automatic voltage regulation when the input power of flywheel UPS is normal.
According to the design scheme of the UPS, during normal operation, its input switch S 1 and output switch S4 are in the closed state, and the maintenance bypass switch S2 is in the off state. When the input power supply voltage is in the range of -20% ~+ 15%, the "input static switch" is in the conducting state. In this case, the unstable commercial power which may contain high-frequency interference is filtered by choke 1 and choke 2 to resist high-frequency interference, and fed into the electrical equipment located at its output end. At the same time, the generator/synchronous compensator (G/M machine) located in the "power bridge" undertakes the adjustment function of the synchronous compensator. At this time, the "power bridge" is in the motor working state. It drives a huge energy storage flywheel by exciting the main shaft of the generator at high speed (the rotation speed is as high as 1800 ~ 3300 rpm), so as to achieve the purpose of converting part of the electric energy of the commercial power grid into the mechanical inertia kinetic energy of the flywheel at high speed. At the same time, under the control of the logic control board, the excitation generator and synchronous generator/generator set can simultaneously perform the control tasks of automatic voltage stabilization and synchronous tracking of the commercial power by using the "bidirectional converter" located in the "power bridge" in the flywheel UPS. At this time, its generator/synchronous compensator outputs a regulated power supply with an adjustment accuracy of 380 V 1% under the control of the bidirectional converter. At this time, chokes 1 and 2 assume the regulation function of passive voltage harmonic compensator.
(2) The principle of automatic voltage regulation control of flywheel UPS when the input power supply fails for a short time.
When the power supply fails for some reason, the excitation generator located in the flywheel UPS continues to rotate at high speed by using the inertial kinetic energy originally stored in the huge flywheel. At this time, the output power with slowly changing frequency and voltage is fed into the input end of the bidirectional converter from the generator (note: this is because with the continuous extension of the power outage time of the input power, the inertial kinetic energy originally stored in the huge flywheel is continuously consumed. In this case, the power frequency and voltage of the excitation generator output will be reduced to varying degrees. Such a power supply with poor power supply quality can output a high-quality power supply with automatic voltage stabilization and automatic frequency stabilization after being processed by a bidirectional converter. This high-quality power supply can continuously output 380 V 1% regulated power supply after being fed into the input end of synchronous motor/generator set (see figure 1b).
When the power supply fails, the duration of UPS continuous power supply depends on the mechanical energy stored in the flywheel and the load percentage of UPS. For a dynamic UPS with output power of 1670kVA, its mechanical energy storage is16.5 MW s, and the typical variation parameter values between the continuous power supply time of the UPS and the UPS load percentage are shown in Table 2.
As can be seen from the above, for flywheel UPS, in its operation, it can continuously output high-quality electric energy to the user's load under the condition that the instantaneous power supply interruption time does not exceed the above time limit. In addition, if the problem of mains power supply is not power failure, but low input voltage, the continuous power supply of UPS will be greatly extended.
Under this condition, a wide working range of input voltage can be obtained. Typical technical parameters are: when the input voltage is 380V, -20%,+15%, it can work continuously; When the input voltage drops to 380V and -30%, its power supply time is10 min; When the input voltage drops to 380V and -50%, its power supply time is 30s. Of course, users who choose diesel/gas generator option or "double bus input" power supply design with two input power supplies and +ATS switch can provide 365×24 hours uninterrupted power supply for connected loads.
The outline of a typical flywheel UPS and the structural diagram of its main components are shown in Figure 2.
3.2 Control principle of harmonic compensation characteristics of flywheel UPS
The second important technical advantage of flywheel UPS is its excellent input harmonic compensation characteristics and high system efficiency (96% ~ 98%).
When the connected 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 loaded with PC, low-grade server, DCS equipment in industrial control system, household appliances and other single-phase rectification and filtering nonlinear loads without input power factor correction (PFC), the input harmonic characteristics of these electrical equipment themselves are very poor. Although the voltage waveform of the input power supply fed into these appliances presents an excellent sine wave, the current waveform they draw from the input power supply becomes a discontinuous bell-shaped pulse train as shown in Figure 3(a) (that is, their input current waveform presents serious current distortion), resulting in the harmonic content THDI value of their input current as high as 55% ~ 77% and the input power factor PF value dropping to about 0.8.
However, after the flywheel UPS is selected to drive the above-mentioned electrical equipment, the power supply bridge composed of "choke 1+ synchronous motor/generator+bidirectional converter+choke 2" can be used to control the harmonics of this kind of nonlinear load. In this case, the reactive power provided by synchronous motor/generator connected in parallel to the main power supply line of flywheel UPS is used to realize current harmonic compensation adjustment. In this way, the input current waveform with good sine wave as shown in fig. 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. Typical values are: harmonic content of input current, THDI value; About 0.98. What needs to be explained here is that most IT equipment (middle and high-end servers, storage devices and network devices) used in today's data center computer room adopt PFC technology with input power factor correction. When flywheel UPS is used to drive these electrical equipment, the following input harmonic characteristics with the type of "green power supply" are obtained: namely, the harmonic content THDI value of its input current; About 0.99, as shown in Figure 3(b).
To sum up, compared with the traditional dual-conversion online static UPS, it can only solve the problem of its input current harmonics and output harmonics. Flywheel UPS can compensate and adjust its input current harmonics and output harmonics at the same time, 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 its excellent dynamic response characteristics. As shown in Figure 4, when the load connected to UPS suddenly loads, the parallel power bridge composed of "synchronous motor/generator set+choke coil 2" provides transient and supplementary active power to the connected load to ensure that the output terminal of UPS can obtain excellent automatic regulation output characteristics. Its typical dynamic response characteristics are:
Here, the circuit composed of input static switch, choke coil 1 and choke coil 2 in flywheel UPS can be regarded as the main channel of power transmission in commercial power grid, while the power supply bridge composed of "flywheel+excitation motor+bidirectional converter+synchronous motor/generator" can be regarded as a voltage-stabilized energy storage with its output terminals connected in parallel, which can dynamically adjust the output power of flywheel UPS in order to quickly respond to later-stage electrical 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 with input voltage harmonic content of 96%;
Input voltage range: 380V, -20% ~+ 15%, long-term operation; 380V, -30%, supporting running time10 min; 380V, -50%, supporting running time of 2min.
Output voltage: 380 volts
Output short-circuit resistance: 300%, 5s; 1400%， 10ms；
The mean time between failures (MTBF) of uninterruptible power supply is 65438+300,000 hours;
Number of UPS connected in parallel allowed: 16.
4. Concluding remarks
To sum up, for users with good commercial power environment, flywheel UPS is obviously superior to dual-frequency online static UPS in the following technical performance. They are: the efficiency of the whole machine, the maximum output power of a single machine, the ability to resist output short circuit, the input power factor, the output power factor, the allowable working temperature range, reliability and EMC electromagnetic compatibility. Moreover, because there is no need to configure a battery pack, the maintenance workload of UPS and the occupied area of the computer room are greatly reduced. Among them, the battery pack with high reliability, remarkable effect of energy saving and consumption reduction, and high failure rate without configuration is particularly eye-catching. In view of this, it has been applied in some semiconductor chip factories and military systems in the United States, Europe and Taiwan Province Province. In recent years, it has attracted more and more attention from China people. It is reported that flywheel UPS may be included in the standards of data center construction in China. This is because, as a rapidly developing technology in recent years, Flywheel UPS can achieve both economic and environmental benefits while building a green data center. However, it should be noted that this UPS is not perfect.
Although there are still some shortcomings in flywheel UPS, up to now, for those users who have "double bus input" power supply conditions and are worried about battery application, by taking technical measures, the possible disadvantages of battery pack with high configuration failure rate and heavy maintenance workload can be completely eliminated, because its expected service life can be as long as 15 ~ 20 years. At present, large data centers abroad generally use flywheel UPS to ensure power supply, especially in the field of magnetic suspension flywheel UPS system. In contrast, the service life of a battery is only a few thousand times, and it usually takes several years to replace the battery.
About micro-control new energy
Shenzhen Micro-control New Energy Technology Co., Ltd. (referred to as micro-control or micro-control new energy) is a global leader in physical energy storage technology. The company is headquartered in Shenzhen, covering North America, Europe, Asia, Latin America and other regions. With the "safe, reliable and efficient" global leading magnetic levitation energy technology, its products and services are widely trusted by many Fortune 500 companies such as Huawei, GE, ABB, Siemens and Emerson.
Facing the three major trends of "cleaner, high-density and digital" energy in the future, the company continues to provide systematic solutions for energy transportation, storage, recycling and data management for strategic emerging industries.