Explore the vast range of titles available.

The dynamic characteristics of hydropower unit governing systems considerably influence the stability of hydropower units and the connected power system. The dynamic performances of hydropower units with power regulation mode (PRM) and opening regulation mode (ORM) are different. This paper establishes a detailed linear model of a hydropower unit based on the Phillips–Heffron model. The damping characteristic and stability of two regulation modes with different water inertia time constants TW were analyzed. ORM tended to provide negative damping, while PRM often provided positive damping in the major parts of the frequency range within the normal frequency oscillations when TW was large. Eigenvalue analysis illustrated that PRM has better stability than ORM. To validate the analysis, a simulation under two typical faults WAS conducted based on a nonlinear model of a hydropower unit. The simulation results illustrated that the responses of units with PRM are more stable in terms of important operating parameters, such as output power, rotor speed, and power angles. For hydropower units facing challenges in stable operation, PRM is recommended to obtain good dynamic stability.

Due to the integration of more intermittent renewable energy into the power grid, the demand for frequency control in power systems has been on the rise, and primary frequency control of hydropower units plays an increasingly important role. This paper proposes an improved frequency dead zone with feed-forward control. The aim is to achieve a comprehensive performance of regulating rapidity, an assessment of integral quantity of electricity, and the wear and tear of hydropower units during primary frequency control, especially the unqualified performance of integral quantity of electricity assessment under frequency fluctuations with small amplitude. Based on a real hydropower plant with Kaplan units in China, this paper establishes the simulation model, which is verified by comparing experimental results. After that, based on the simulation of real power grid frequency fluctuations and a real hydropower plant case, the dynamic process of primary frequency control is evaluated for three aspects, which include speed, integral quantity of electricity, and wear and tear. The evaluation also includes the implementations of the three types of dead zones: common frequency dead zone, the enhanced frequency dead zone, and the improved frequency dead zone. The results of the study show that the improved frequency dead zone with feed-forward control increases the active power output under small frequency fluctuations. Additionally, it alleviates the wear and tear problem of the enhanced frequency dead zone in the premise of guaranteeing regulation speed and integral quantity of electricity. Therefore, the improved frequency dead zone proposed in this paper can improve the economic benefit of hydropower plants and reduce their maintenance cost. Accordingly, it has been successfully implemented in practical hydropower plants in China.

Stable operation is a challenge for hydropower stations with multi-turbine hydraulic coupled division systems with a common penstock. In this paper, the serious power fluctuations in a power station with such a division system are analyzed. The fluctuations occur in many conditions without any movement of the regulating system. The mathematical analysis illustrates that pressure fluctuation is responsible for power fluctuations. The computational fluid dynamics (CFD) method provided by ANSYS is used to study the flow pattern in penstocks. The vortex caused by the irrational structure of trifurcation is the reason for pressure fluctuations. Several methods are proposed to optimize the flow stability and three cases are simulated based on these measures. The calculation results of three cases prove the effectiveness of these measures. The measure of setting the new guide plate is finally conducted, and the output power fluctuations vanish. The flow calculation plays a role in the analysis and optimization of the hydraulic system of the hydropower unit. Some rules are summarized from the cases and are helpful in the design of trifurcation in a division system with a common penstock.

It is a trend for the large hydropower bases to transport the electricity to consuming center with High Voltage Direct Current (HVDC) transmission lines. The fault of HVDC has great significance impact on hydropower units in islanding sending AC grid. In this paper, a hybrid simulation system is established to analyze the dynamic characteristic of hydropower units in islanding system. The simulation system is based on Real Time Digital Simulator (RTDS) and Digital Signal Processor (DSP). The simulation of electromagnetic transient process in the generator, the load, the network and HVDC is completed by RTDS. The Hydroturbine Real Time Simulator (HRTS) based on DSP completes the simulation of hydraulic-mechanical-electrical transient process in hydroturbine, division system and governing system. The real time data communication between RTDS, HRTS and external equipment ensures the real time calculation of simulation. The simulation results show high coincidence with field data. The hybrid simulation system is an effective approach for the research of islanding system at sending terminal with HVDC.

Wave energy converters (WEC) with the increasing capacity, which has reached a level of hundreds of kilowatts, would play a role in the connected microgrid. Due to the inherent fluctuation and randomness of wave energy, the unstable output power of WEC is a threat to the power balance of the microgrid. Machines start and stop periodically and the output power changes continuously and significantly. The previous study focused little on the power control of grid-connected WECs. In this paper, a power control strategy is proposed for WECs to achieve stable power output and regulation in various wave conditions. The power control strategy is based on a hybrid double-machine hydraulic energy storage and generating system composed of a controlled unit and an uncontrolled unit. The control strategy enables the stability control and the controllable regulation of power of WEC in various wave conditions. Simulation results of several wave conditions have validated the effect of the power control strategy. The power control strategy would contribute to the extensive deployment of WECs.

In order to ensure the performance and safety of photovoltaic grid connected inverter, based on hardware in the loop simulation technology, the design and implementation of photovoltaic grid connected inverter simulation and test platform are discussed. The system structure, principle and main functions of the platform are introduced. The simulation and test platform is composed of simulation and monitoring computer, simulation and measurement interface device, programmable power supply and test instruments. In the platform, the programmable DC power supply, the programmable AC power supply and RLC load is used to simulate the characteristics of solar panels, power grid and load respectively. The test process is controlled by LabWindows/CVI software interface, and the test data collection is completed through power quality analyser, power analyser, oscilloscope and simulation and measurement interface device. The simulation test software completes the data analysis and realizes the full-automatic detection of the grid connected inverter. The established hardware in the loop simulation test platform of photovoltaic grid connected inverter has the ability to conduct comprehensive test and detection of photovoltaic grid connected system, which can be used to verify and evaluate the photovoltaic inverter before it is connected to the power grid.

Harmonics is a widespread phenomenon in power system. With the rapid development of new energy generation, it is more urgent to monitor and suppress harmonics in power system. Considering the accuracy and real-time of harmonic detection, a novel harmonic detection method based on FFT and instantaneous reactive power theory is proposed. In this method, the harmonic frequency of the signal to be measured is first determined by windowed FFT, and then the harmonic amplitude and phase are calculated by an improved harmonic detection method based on instantaneous reactive power theory. The example results show that the proposed method has high detection accuracy and good real-time performance, and it can realize the fast detection of harmonics.

Harmonics seriously affect the safety and economy of power system. In order to control harmonics effectively, harmonic current and harmonic power must be detected quickly. Based on the analysis of the components of three-phase nonlinear current, a neural network detection method of fundamental and harmonic current in three-phase circuit is proposed. The method uses a neural network instead of the low-pass filter in the instantaneous reactive power theory. The example results show that the proposed method has the advantages of less computation, better real-time performance and high detection accuracy. The method can be used to detect the positive-sequence (negative-sequence) fundamental active current, positive-sequence (negative-sequence) fundamental reactive current, harmonic, distortion current and harmonic power.

In the field of hydropower station transient process simulation (HSTPS), characteristic graph-based iterative hydroturbine model (CGIHM) has been widely used when large disturbance hydroturbine modeling is involved. However, by this model, iteration should be used to calculate speed and pressure, and slow convergence or no convergence problems may be encountered for some reasons like special characteristic graph profile, inappropriate iterative algorithm, or inappropriate interpolation algorithm, and so forth. Also, other conventional large disturbance hydroturbine models are of some disadvantages and difficult to be used widely in HSTPS. Therefore, to obtain an accurate simulation result, a simple method for hydroturbine modeling is proposed. By this method, both the initial operating point and the transfer coefficients of linear hydroturbine model keep changing during simulation. Hence, it can reflect the nonlinearity of the hydroturbine and be used for Francis turbine simulation under large disturbance condition. To validate the proposed method, both large disturbance and small disturbance simulations of a single hydrounit supplying a resistive, isolated load were conducted. It was shown that the simulation result is consistent with that of field test. Consequently, the proposed method is an attractive option for HSTPS involving Francis turbine modeling under large disturbance condition.

The hydraulic turbine model is the key factor which affects the analysis precision of the hydraulic turbine governing system. This paper discusses the basic principle of the hydraulic turbine matrix model and gives two methods to realize. Using the characteristic matrix to describe unit flow and torque and their relationship with the opening and unit speed, it can accurately represent the nonlinear characteristics of the turbine, effectively improve the convergence of simulation process, and meet the needs of high precision real-time simulation of power system. Through the simulation of a number of power stations, it indicates that, by analyzing the dynamic process of the hydraulic turbine regulating with 5-order matrix model, the calculation results and field test data will have good consistency, and it can better meet the needs of power system dynamic simulation.