The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine. It also has the same inertia, damping, frequency, voltage regulation, and other external performance as the generator. It is the key technology to realize new energy grid connections’ stable and reliable operation. This project studies a dynamic simulation model of an extensive new energy power system based on the virtual synchronous motor. A new energy storage method is proposed. The mathematical energy storage model is established by combining the fixed rotor model of a synchronous virtual machine with the charge-discharge power, state of charge, operation efficiency, dead zone, and inverter constraint. The rapid conversion of energy storage devices absorbs the excess instantaneous kinetic energy caused by interference. The branch transient of the critical cut set in the system can be confined to a limited area. Thus, the virtual synchronizer’s kinetic and potential energy can be efficiently converted into an instantaneous state. The simulation of power system analysis software package (PSASP) verifies the correctness of the theory and algorithm in this paper. This paper provides a theoretical basis for improving the transient stability of new energy-connected power grids.

In recent years, with the rapid development of technologies such as cloud computing and big data, various large energy companies have gradually established their own cloud-based big data centers. It consumes more and more energy. Both the government and enterprises are beginning to study the low energy consumption of cloud data centers, advocating low-carbon, environment-friendly life, and green cloud computing. The resource scheduling and allocation method uses commercial servers supporting dynamic voltage and frequency adjustment technology to adjust the voltage used to save energy. Due to the increasing popularity of new energy sources, the proportion of conventional synchronous generators is getting smaller and smaller. The relative reduction of rotating reserve capacity and moment of inertia in the power system reduces the power grid's stable support and self-regulation ability against disturbance. This puts severe demands on the safety and stability of the power system. Energy storage systems based on power electronic devices have been widely used in power generation due to their adjustable characteristics. Reference [

Establishing a model that can reflect the operating characteristics of a large-scale battery energy storage system is crucial for studying the security and stability of the power grid after large-scale energy storage is connected to the grid. The transient stability research of a high-permeability power grid needs to establish a low-order, high-precision, open energy-mechanical transient mathematical model. Existing energy storage and grid characteristics simulations are mostly based on detailed models. It performs corresponding dimension reduction processing according to specific research objects. Reference [

A virtual machine consists entirely of software. It does not contain any hardware components. Virtual machines offer many unique advantages over physical hardware. This paper proposes an electromechanical transient modeling method for energy storage under the control of a virtual generator set, which is suitable for transient stability analysis of large-scale power systems. A virtual generator set controller is constructed based on the virtual governor and virtual excitation controller as the core, combined with the mathematical models of rotor mechanics and stator electricity. Corresponding simplification methods are proposed for multiple timing components such as the energy storage primary body model, current inner loop controller, and converter. According to the node current injection method, the energy conversion between the modules is carried out, and the transient model of the energy storage system based on the branch transient potential energy control is constructed. By controlling the transient potential energy of the branch, the ability to withstand the transient potential energy of the system is improved to improve the transient stability of the system. The electromechanical transient simulation of new energy grid-connected based on a virtual machine proposed in this paper is compatible with the power system.

Furthermore, it exists independently of the hardware system. So, the virtual machine does not need to control the transient potential energy of the entire network, and the method only needs to use energy storage to control the transient potential energy of the critical branch. The control signal is easy to extract, and the energy ratio index is further improved to evaluate the energy storage and control energy effect.

Virtual synchronous generator technology simulates the grid-connected inverter so that the new energy unit has the characteristics of inertia, damping, frequency regulation, and voltage regulation. This provides frequency and voltage support for new energy units. Thus, the operation adaptability, safety, and stability of new energy units connected to the power grid can be improved. A virtual synchronous generator (VSG) topology is shown in

It can be seen from

The reactive power control of VSG is also a virtual magnetic field regulator. It is expressed in

The VSG electromagnetic part is modeled on the stator electrical part. The electromagnetic wave equation in

The transmission line must be inductive to decouple VSG’s active and reactive power. Therefore, if the hypothetical resistance value

Active power and reactive power injected by the grid-connected converter can be obtained by expanding the above equation:

The structure of the energy storage virtual synchronous machine is shown in

In

The fundamental voltage at the exit of the inverter is expressed in the equation

The equation for calculating the phase voltage base wave amplitude

Substituting

Substituting

The energy storage device can adjust charging and discharging power in real-time and has a peak clipping capability, twice its installation capacity. For both the AC grid and the DC grid, the energy storage power station has a solid ability to improve the stability and flexibility of the grid. For the former energy storage power station, it can reduce valley charging, adjust the system frequency, and provide reactive voltage support. For the latter, the electrochemical energy storage power plant can also provide sufficient reactive power for the converter station and enhance the ability of the converter station to resist commutation failure. The energy storage power station mainly comprises a battery room, transformer booster box, 10 kV confluence box, intelligent main control room, SVG room, substation, and other supporting equipment. The power station has a station-side monitoring system, intelligent network load interactive terminal, synchro phasor measurement device, anti-islanding protection and frequency voltage emergency control device and intelligent auxiliary control system. Synchronous motors need to be used for reactive power compensation of the grid, and they operate in a unique way of no-load operation when connected to the grid. This mode of operation can improve power factor and improve power supply performance. It can be seen from the analysis that the energy storage virtual synchronous machine also has the special operation mode of the synchronous machine. In response to DC commutation failure, the energy storage virtual synchronous machine can continuously provide reactive power to the system to support the DC bus voltage and prevent commutation failure when the DC bus voltage drops rapidly when the system fails. In the HVDC system, the thyristor on the rectifier side has sufficient turn-off time. The thyristor on the inverter side has insufficient turn-off time, which will cause the two ends of the thyristor that were not completely turned off to bear the forward voltage. The thyristor will be turned on again, so the commutation failure mainly Occurs in the thyristor of the converter station on the inverter side. If the commutation voltage drop of the HVDC system is supported, the commutation failure can be significantly suppressed.

The electromechanical transient energy storage system model includes a control, ontology, and model interface. Energy storage and conversion device is an integral part of energy storage. Its main objective is to realize effective voltage control by inverter-frequency, amplitude, and phase. The direct current energy of the energy storage unit is converted to the alternating current energy suitable for the power grid. It can be divided into outer ring regulation and inner ring regulation. The outer loop control system of the equipment is the central control system. Read bus frequency

The internal loop control architecture of the converter is shown in

Axis

It can be converted into a first-order inertia chain by using the pole-zero cancellation principle, and the power characteristic equation can be expressed as

According to the above virtual synchronous machine control model and simplified inner loop control, the energy storage converter control model can be used, as shown in

The active regulation mainly includes the virtual governor, rotor mechanical equation and active power output. OMB here represents the frequency of the bus.

The energy storage unit differs in charge and discharge rate, power grade and other parameters. The influence of charging conditions on energy storage units is considered in the range of force-electric short time. This paper proposes a nonlinear and time-invariant theoretical model of battery charging and discharging characteristics and parameters based on transient responses of power electronic systems. A linear line can represent its external properties. The modeling of the energy accumulator is equivalent to the setting of the related limit link of the frequency converter [

(1) The charged state of energy storage refers to the percentage of the available power and the maximum power in the rechargeable pool group. It reflects the power of the battery. It plays an essential role in battery utilization efficiency and service life. The system on chip (SOC) is estimated by ampere-hour measurement, open-circuit voltage, neural network, Kalman filter, etc. A new ampere-hour calculation method with wide application and simple operation is presented [

Parameter | Numerical value |
---|---|

Overall operation efficiency of energy storage system |
0.89 |

Initial battery state |
0.63 |

The minimum battery charge state is |
0.21 |

The maximum charged state of the battery is |
0.83 |

Rated power downtime |
208.33 |

Minimum frequency dead band |
52.04 |

Frequency dead band maximum |
52.12 |

Active power

The comparison of experimental results shows that the experimental data obtained from the experimental platform constructed in this article is consistent with the simulated data. When using this control method, they can all meet the output requirements of the system, but compared to using model predictive control, its output voltage control effect is worse than using model predictive control, which can also be seen from the output voltage. At the same time, due to the introduction of inertia and damping in the VSC system control, the output current overshoot will be smaller when the load is switched than when using conventional control, but there will still be some overshoot phenomenon, and the output power overshoot will also be smaller. The advantage of the new VSC is that the new optimization objective function can ensure the accuracy of voltage tracking while also taking into account the error of current tracking, thereby ensuring the accuracy of voltage tracking and improving the accuracy of current tracking. In addition, due to the introduction of the VSC system control output tracking voltage reference and the setting of current limiting limits in the cost function, its output current and output power are shallow during load switching. Therefore, it can handle load switching well, achieving better power tracking and ensuring the safe and stable operation of the system. The experiment shows that this method is correct and effective.

The energy storage process’s dynamic characteristics are simulated using the WEPRI7 node system. A three-phase short circuit fault occurs on the side of line B4-B3 near bus B4 at 0 s. The fault was removed 0.06 s later. Install an energy storage device on the busbar B1. The maximum power is 100 megawatts. It has a capacity of 1000 megajoules. The initial SOC value is 0.

The response curve of the energy storage device under different grid-connection times is shown in

Simulation and analysis of energy storage using PSASP software. The unit is a typical structure. The three-phase short-circuit fault is set in busbar 3, line 2^{*}–12 and line 15–16^{*}, respectively. The “^{*}” indicates the failed near-end busbar. The defect elimination rate of this method is 0.18, 0.22, 0.17 s. Set the maximum energy storage power at 500 MW. It has a capacity of 8 gigajoules.

Furthermore, install it on buses 1, 9. The relative power Angle curve and energy ratio index ERI curve of the generator before and after the energy storage system is connected based on time domain simulation, which is shown in

Critical branch | Bus 3 | Line 2^{*}–12 |
Line 15–16^{*} |
|||
---|---|---|---|---|---|---|

No energy storage | Stored energy | No energy storage | Stored energy | No energy storage | Stored energy | |

1–3 | 0.0143 | 3.8361 | 0.0101 | 2.7496 | 0.0014 | 4.0859 |

8–5 | 0.0004 | 3.6557 | 0.0074 | 2.8209 | 0.0071 | 5.9655 |

1–9 | 2.8438 | 4.2042 | 2.8182 | 3.5840 | 3.8501 | 7.8957 |

9–4 | 3.9820 | 7.0944 | 3.8950 | 6.1999 | 4.5469 | 4.9268 |

5–7 | 2.6617 | 20.1263 | 3.0741 | 17.3990 | 2.8165 | 34.7721 |

6–11 | 0.1089 | 17.2310 | 4.2846 | 8.4796 | – | – |

21–26 | – | – | – | – | 0.0231 | 7.7371 |

It can be seen from ^{*}–12 fail, the system presents two significant instability graphs. However, when the 15–16^{*} line fails, it shows multigroup instability. Whether the system is two-group unstable or multi-machine group unstable, the instability situation of the system can be effectively suppressed after the energy storage is added [

A new method of modeling energy storage devices using synchronous virtual machines is proposed. Examples simulate the transient characteristics of the power system under various control modes. The force-machine transient mathematical model of an energy storage system based on a virtual synchronous motor is established. The designed energy storage device is simulated in PSASP software. It has a more accurate trend of external characteristics by simulating various working conditions and analyzing transient characteristics. The results show that the energy storage model is correct and effective. This model can reflect the transient performance and energy storage performance of synchronous motor wells. The “virtual synchronous generator” technology can make the energy storage and its converter have the characteristics of a synchronous generator. It can realize real-time adjustment of output power and voltage, effective smoothing of power fluctuations, active power, and reactive power without changing the control strategy-maintenance of work and power balance, adjustment of grid frequency and voltage.

None.

The authors received no specific funding for this study.

The authors acknowledge the contributions to this article as follows: Study conception and design: Shichao Cao; Data collection: Yonggang Dong; Results analysis and interpretation: Xiaoying Liu; Manuscript preparation: Shichao Cao. All authors reviewed the results and approved the final version of the manuscript.

The data supporting this study’s findings are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

The authors declare no conflicts of interest to report regarding the present study.