Primary Frequency Modulation Research Articles

Parallel Control Method of Microgrid Inverter Based on Adaptive Droop Control

Energy is the driving force of social and economic development. With the gradual depletion of conventional energy and the increasingly prominent ecological and environmental problems, the power industry needs to find a sustainable development path. Parallel control of microgrid inverters based on adaptive droop control is an important part of future intelligent and sustainable power systems. However, with the continuous increase of power generation equipment capacity and the continuous increase of load power consumption, the form of power supply by a single inverter can no longer meet the requirements. Therefore, parallel connection of multiple inverters has been widely used in the microgrid. In this paper, a set of parallel control methods for microgrid inverters based on adaptive droop control is established. This paper is based on the inductance of the inverter’s terminal impedance, and the amplitude of the inverter terminal voltage is positively correlated with the output reactive power and has a strong correlation It is concluded that the microgrid based on adaptive droop control has the ability to automatically adjust the voltage and frequency of the microgrid. Properly reducing the droop coefficient can improve the primary frequency modulation capability of the microgrid. In this paper, an improved resistive control equation is used in a parallel system, a multi-loop control structure with a quasi-resonant controller is used for the inverter in the parallel system, and a virtual complex impedance is added to perform small signal analysis on the improved resistive control equation The overall performance of the parallel system is analyzed, and the effect of different control coefficients on the system performance is clarified. The experimental research results show that when analyzing the effect of the inductance coefficient value on the equivalent output impedance in the virtual complex impedance, the value of KL is 1 At this time, the equivalent output impedance becomes resistive again, and the property is stronger than when KL is 0.05.

Active power reserve photovoltaic virtual synchronization control technology

The photovoltaic virtual synchronous generator (PV-VSG) solves the problem of lack of inertia in the PV power-generation system. The existing PV plants without energy storage are required to participate in the power grid's frequency modulation (FM), but existing PV-VSGs with energy storage have high requirements for coordinated control. Therefore, the active power reserve PV-VSG (APR-PV-VSG) is studied. Based on the different methods to obtain the maximum power point (MPP), the peer-to-peer and master-slave APR-PV-VSG strategies are proposed. The PV inverters are deviated from the MPP to reserve active power, which is used as the virtual inertia and primary FM power. These methods equip the PV power station with FM capability. The effectiveness of the proposed control strategies is verified by simulation results.

Research on Primary Frequency Modulation of Coordinated Control System for Wind Power Generator and Thermal Power Unit

Combined with the practical problems in the development of power system, the paper introduces the technical scheme and characteristics of primary frequency modulation(PFM) for thermal power units. Aiming at the impact of the rapid development of wind power generation on the stable operation of the power grid, the PFM strategy on the coordinated control system for wind power generators and thermal power units is proposed to dynamically adjust the PFM capacity of thermal power units, which effectively make up for the adverse impact of the uncertainty of wind power generation, and improve the stable operation capacity of the power grid. It has certain reference significance on the flexible operation control optimization of the power grid in the wind power centralized area.

The solution about primary frequency modulation of thermal power generating units is proposed based on the smart grid

The performance of primary frequency modulation of thermal power generating units taking part in power grid is good or bad which may bring a direct impact on the stability of the power grid frequency. The main problem from the function of primary frequency modulation about thermal power generating units is studied in this paper, and feasible rectification solution for the pressure in front of turbine and steady-state speed regulation is proposed, which provides some technical support for vigorously developing smart grid in our country.

Primary frequency modulation characteristics of photovoltaic power station suitable for grid connection certification

Photovoltaic power station can participate in the primary frequency modulation of the power system for grid connection certification. The primary frequency modulation capability of photovoltaic power station is analyzed when the light intensity changes. According to theoretical and simulation analysis, by changing the control mode, the photovoltaic power station operated by load reduction can quickly respond to the drop and increase of frequency and reduce the change of frequency after disturbance. Overall results show that the photovoltaic power station with primary frequency control can reduce the frequency of system changes, implement the support for the frequency of the system, and make corresponding adjustment to improve the safety of power grid.

Research on optimization method of primary frequency modulation capability based on different ratios of hydropower

With the continuous development of China’s cross-regional interconnected power grid, large- capacity and long-distance transmission have become an important feature of China’s power grid. As the transmission capacity of single-return transmission lines continues to increase, the risk of frequency fluctuations increases, making grid operation scheduling more concerned with the performance of the unit’s primary frequency modulation. This paper tests the frequency stability of a power system under different scenarios, in which the proportion of water and thermal power in the system is different. The results represent that a system with a large proportion of hydropower has poorer frequency stability. This paper offers a method of primary frequency modulation, which proposed to improve the frequency stability of the system by increasing the time delay of the hydropower unit’s governor. The results of simulation prove that this method is an available solution to solve the problem of poor system frequency stability when a system has a high ratio of hydropower.

Characteristics Analysis and Fuzzy Fractional-Order PID Parameter Optimization for Primary Frequency Modulation of a Pumped Storage Unit Based on a Multi-Objective Gravitational Search Algorithm

Compared with conventional hydropower units, the pumped storage unit has the characteristics of diverse working conditions and frequent switching. Therefore, the stability and regulation quality of the primary frequency modulation transition process of the regulating system is very important. Due to the “S” characteristics of the pumped storage unit (PSU), the pumped storage unit regulating system has a strong nonlinearity, and the conventional proportional-integral-derivative (PID) controller cannot provide high-quality control under low water head conditions. In this paper, the nonlinear PSU model with an elastic water hammer effect is studied, and the fuzzy fractional-order PID (FFOPID) controller is designed to improve the stability of the system. The membership function and the control parameters of the fractional-order PID are optimized based on the multi-objective gravitational search algorithm (MOGSA). The experimental results show that the optimized design of the FFOPID controller has better control quality than the traditional PID controller, the fractional-order PID (FOPID) controller, and the fuzzy PID controller (FPID) when the system is disturbed by the rotating speed under low water head.

Test of flow characteristics and parameter optimization of steam turbine DEH

The characteristics of steam turbine high pressure cylinder intake valve directly affect the performance of AGC and primary frequency modulation, In DEH system, the nonlinear characteristics of the high valve flow need to be corrected to ensure a smooth and linear relationship between the integrated valve level instruction and the steam flow of the turbine. When the nonlinear correction of the high valve flow is not correct, there may be nonlinear intervals such as “dead zone”, “jump”, and “inflection point” between the valve comprehensive opening instruction and the steam turbine flow, The valve integrated opening command mutates the gain of steam turbine flow, causing the valve to be insensitive or oscillating when the valve is in a certain opening range under the coordinated control system of the furnace and machine.

Research on the Unit’s Control Strategy of On-line Primary Frequency Modulation

This paper introduces the basic principle and control structure of primary frequency modulation on the thermal power units, at the same time gives the forming method of primary frequency modulation compensation instruction. Combined with the actual power production and aiming at the actual problems of primary frequency modulation, this paper presents the flexible limiting control method of primary frequency modulation instruction and on-line automatic correction method, which can effectively improve the primary frequency modulation performance on the thermal power units and ensure the safe operation of power grid. This scheme provides reference for other units to improve the primary frequency modulation optimization.

Optimization of Sliding Pressure Curve of Thermal Power Unit Based on Economical and Primary Frequency Modulation Characteristics

According to the thermal economic characteristics and primary frequency modulation characteristics of the thermal power unit’s variable working conditions, the nozzle distribution steam turbine unit is taken as the research object to meet the primary frequency modulation capacity and reduce the unit heat consumption rate. The influence of the valve position on the economics of the unit and the primary frequency modulation capability is used to provide a richer adjustment basis for the technical and economic comparison between different operating modes of the unit, and the obtained sliding pressure running curve can meet the requirements of primary frequency regulation of the power grid. The throttling loss generated during the operation of the unit is minimized, and the optimal configuration between the grid operation and the power economy is realized.

Functional Location Analysis of Inertia Support and Primary Frequency Modulation of Virtual Synchronous Generator in Power System

With the continuous improvement of renewable energy penetration, the inertia and primary frequency modulation capability of synchronous power grid are declining. If the virtual synchronous generator (VSG) technology is used for renewable energy generation, it can make due contribution to reducing the frequency variation and frequency deviation of the system under the impact of high power gap. The inertia support and primary frequency modulation function positioning in VSG research are not clear. In this paper, the inertia support function of VSG and its physical significance are analyzed, the expression of inertia support power of VSG is deduced, the location distinction between inertia support function of VSG and primary frequency modulation function is analyzed, and the different control function pairs of VSG in the process of large synchronous power grid frequency accident are simulated and analyzed,and study the effect of system frequency variation.

Minimum Frequency and Voltage Stability Constrained Unit Commitment for AC/DC Transmission Systems

An increased use of the high-voltage direct current (HVDC) technologies can have important effects on frequency performance and voltage stability of the receiving-end grid during normal operation as well as during blocking failure. The main reasons are the inherent characteristics of the HVDC such as its much larger capacity than thermal plants and lack of voltage supporting ability to the alternating current (AC) grid. These has led to new challenges for AC/direct current (DC) power grid operators in terms of ensuring power system security. To address these challenges, a unit commitment (UC) of the receiving-end in the AC/DC hybrid grid is presented in this paper. In the proposed model, primary frequency modulation constraints are added to provide sufficient capacity for HVDC blocking. Besides, grid security constraint after secondary frequency regulation is also considered because HVDC blocking failure would cause large range power transfer and transmission lines overload. Meanwhile, voltage stability constraints are employed to guarantee enough voltage supporting capacity from thermal plants at the HVDC feed-in area. Based on the characteristics of the model, Benders decomposition and mixed integer programming algorithm are used to get the optimal transmission power of the HVDC and schedule of thermal units. The study is done by considering the IEEE-39 and Jiangsu power grid in eastern China, containing two HVDC transmission projections respectively. The results are also validated by simulation of different HVDC blocking failure scenarios.

Analysis and optimization of frequency modulation strategy for hydropower units

Analysis the deficiencies of typical control strategies for AGC regulation and primary frequency regulation on conventional hydropower units. The logical relationship between primary frequency regulation and AGC is optimized. A new regulation method is proposed and applied in a hydropower plant. Practice shows that the method can avoid contradiction between AGC load adjustment and primary frequency modulation, and improve the frequency modulation performance of the unit. The optimization finally satisfy the requirements of power grid assessment.

Simulation Analysis of Frequency Regulation

Frequency is one of the most important parameters reflecting the operation quality of the system. When the system is in steady-state operation, the frequency of the generator in the system is equal under steady-state operation. Because the load is changing at any time, this kind of balance is dynamic. The only way to maintain dynamic balance is to adjust the input power of the generator, so that the actual output of the generator can closely track the change of the load and keep the balance between supply and demand of active power. The essence of frequency control is to regulate and control the active power of all generators in power grid. In this paper, the principle of frequency fluctuation is analyzed, and the physical models of the primary and secondary frequency modulation are established. The simulation results verify the differential regulation of the primary frequency modulation and the no-difference regulation of secondary frequency modulation. It provides an effective basis for the later research of AGC control strategy.

A Disturbance Source Location Method Based on the Initial Oscillation Period

In order to improve the accuracy and rapidity of the disturbance source location, a new method based on variational mode decomposition (VMD) for forced power oscillation disturbance source location is proposed. Using the active power and frequency of the transient phase of an oscillation, the dominant mode of electrical components is extracted by VMD. Then, the oscillation energy using the variation is calculated to achieve the disturbance source location. Taking the forced power oscillation accident caused by too strong primary frequency modulation as an example, the effectiveness and feasibility of the proposed method is verified.

An Improved Low Frequency Oscillation Disturbance Source Localization Method in Control Devices of Generator

In this paper, an improved oscillation disturbance source localization method in control devices of generator is investigated. Using the dominant component of the electrical signals by the fast Fourier transform (FFT), the oscillation energy for governor system and excitation system is obtained separately. Then, based on the direction of the non-periodic component of the oscillation energy for the two systems, the control device level locating of the oscillation disturbance source is realized. Taking the forced power oscillation accident caused by too strong primary frequency modulation as an example, the oscillation energy based on FFT for the two systems show that the proposed method can locate the disturbance source accurately.

Calculation Method of PFC Assessment Index Based on Time Point Comprehensive Processing

With the increase of DC power supply scale and the increase of new energy output ratio, higher requirements are put forward for the PFC(primary frequency control) performance of thermal power units. Through the introduction of the inherent characteristics of PFC, aimed at the problems of insufficient adjustment range and unable to effectively maintain the adjustment load in the actual modulation process of thermal power units, one calculation method of PFC assessment index based on the comprehensive processing of time points is proposed. This method can calculate the multi-point speed difference rate in accordance with the national standard, improve the effectiveness and accuracy of primary frequency modulation assessment index, ensure that the unit meets the power grid’s demand for the rapidity and stability of PFC action, and ensure the safe and stable operation of the power grid.

Study on the Improved Evaluation Method of Primary Frequency Modulation for Grid-connected Units

The primary frequency modulation function of generating units is an important means to maintain the frequency stability of the power grid. The reasonable assessment criteria help to regulate the primary frequency modulation performance of generating units and enhance the enthusiasm of units to participate in frequency modulation auxiliary services. On the basis of mastering primary frequency modulation principle, the response characteristics of the electro-hydraulic governor and the turbine under frequency excursion are analysed in detail. Aiming at the shortcoming of the current primary frequency modulation evaluation standard, an integral electricity algorithm with different weights added according to the contribution of primary frequency modulation is proposed. Finally, based on the concrete example, the correctness and rationality of the improved method are verified.

Dynamic Performance Assessment of Primary Frequency Modulation for a Power Control System Based on MATLAB

The primary frequency modulation (PFM) performance of a power control system (PCS) is an important factor affecting the security and stability of a power grid. The traditional control method is proportional integral (PI) control. In order to improve its dynamic control performance, a control method based on the combination of internal model control (IMC) and PI is proposed. Using the method of theoretical assessment and system identification, a simple simulated model of the typical PCS is established. According to the principle of system identification and the least square estimation (LSE) algorithm, the mathematical models of a generator and a built-in model are established. According to the four dynamic performance indexes, the main and auxiliary assessment index of the PCS are defined, and the benchmark and the result of the performance assessment are given. According to three different structures, the PFM dynamic performance of the PCS is analyzed separately. According to the dynamic performance assessment index of PFM, the structure of the control system and the influence of different parameters on the performance of the PCS are analyzed under ideal conditions. The appropriate control structure and controller parameters are determined. Secondly, under the non-ideal condition, the influence of the actual valve flow coefficient on the performance of the control system is studied under two different valve control modes. The simulation results show that the internal model combined with PI has better dynamic control performance and stronger robustness than the traditional PI control, and it also has better application prospects for thermal power plants.

Coordinated Optimization of Multi Control System for Steam Turbine Generator Unit

A method of the coordinated optimization of multi control system for steam turbine generator unit was proposed in this paper. The primary frequency modulation performance and dynamic stability of the power system were taken into account in the method. The multi-control system to be optimized includes the excitation regulation system, the power system stabilizer (PSS), the speed control system and the boiler-turbine coordinated control system (CCS). And the taboo search (TS) algorithm was introduced as a means to obtain the optimal values of the system control parameters. The simulation result shows that the method can coordinate the primary frequency modulation performance and the dynamic stability of the system, and can effectively prevent the low frequency oscillation caused by the improper multi control system parameters setting.