16.3 Control strategies for renewable energy sources
5 min read•august 1, 2024
Renewable energy sources require specialized control strategies to integrate smoothly with the power grid. play a crucial role, enabling efficient conversion and control of variable outputs from wind and solar sources to grid-compatible forms.
() techniques optimize energy capture from renewables under changing conditions. and coordination with conventional generators are essential for maintaining grid stability and as renewable penetration increases.
Power Electronics for Renewables
Interfacing Renewables with the Grid
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- Power electronics are used to interface renewable energy sources with the grid, enabling control of power flow and optimization of energy capture
- Power electronic converters, such as AC-DC and DC-AC converters, are essential for converting the variable output of renewable sources to a form compatible with the grid
- Example: A system uses a for MPPT and a DC-AC inverter to feed power into the AC grid
- employ AC-DC-AC converters to convert variable frequency AC from the generator to grid-compatible AC
- Power electronic devices, like IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), are used in the converters to efficiently switch and control the flow of power
Control and Grid Support Functions
- Control algorithms implemented in power electronic converters help in maximizing the power output from renewable sources and ensuring grid stability
- Example: A wind turbine converter can control the generator torque to extract maximum power from the wind
- Solar inverters can regulate the output voltage and current to maintain the desired power factor
- Power electronic converters also provide capability, reactive power support, and for renewable energy sources
- Fault ride-through ensures that the renewable source remains connected to the grid during voltage dips or faults
- Reactive power control helps in maintaining the of the grid
- Frequency regulation involves adjusting the active power output to support the grid frequency
MPPT in Wind and Solar
Solar MPPT Techniques
- MPPT is a control technique used to extract the maximum available power from wind and solar energy sources under varying environmental conditions
- For solar systems, MPPT algorithms adjust the operating voltage or current of the solar array to maintain operation at the point of maximum power on the I-V curve
- Common MPPT algorithms for solar systems include:
- (P&O): Incrementally adjusts the voltage and observes the change in power to reach the MPP
- (IC): Compares the incremental conductance (dI/dV) with the instantaneous conductance (I/V) to determine the MPP
- (CV): Maintains the solar array voltage at a fixed percentage of the open-circuit voltage, assuming the MPP occurs near that point
Wind MPPT Techniques
- In wind systems, MPPT controls the rotor speed or blade pitch angle to maintain operation at the optimal tip-speed ratio, maximizing power capture
- MPPT algorithms for wind systems include:
- (PSF): Adjusts the rotor speed based on the measured power output to track the MPP
- (OTC): Controls the generator torque as a function of the rotor speed to achieve maximum power extraction
- Perturbation and Observation (P&O): Similar to the P&O method in solar systems, it perturbs the rotor speed and observes the power output to reach the MPP
- MPPT controllers continuously monitor the output power and adjust the control variables to track the maximum power point under changing environmental conditions (wind speed, irradiance)
Reactive Power Control Strategies
Reactive Power Compensation Devices
- Reactive power control is crucial for maintaining voltage stability and power quality in the grid when integrating renewable energy sources
- Wind and solar power plants can be equipped with reactive power compensation devices to provide dynamic reactive power support
- (): Use thyristor-controlled reactors and capacitors to provide continuous reactive power control
- (): Employ voltage-source converters to generate or absorb reactive power independently of the grid voltage
Inverter-Based Reactive Power Control
- Inverter-based renewable energy sources, like solar PV and some wind turbines, can control their reactive power output by adjusting the phase angle between the voltage and current
- Reactive power dispatch strategies can be implemented in renewable energy sources to regulate the reactive power output based on grid requirements
- : Adjusts the reactive power output based on the measured voltage deviation from the nominal value
- : Maintains a constant power factor by controlling the reactive power in proportion to the active power output
- Coordination between the reactive power control of renewable sources and conventional generators is necessary to maintain the overall voltage profile and stability of the power system
Renewable vs Conventional Control Coordination
Frequency and Voltage Control Coordination
- Coordinating the control strategies of renewable energy sources with conventional generation is essential for maintaining the stability and reliability of the power system
- The variability and of renewable sources require conventional generators to provide flexibility and backup power to balance the system
- Frequency control coordination involves adjusting the power output of conventional generators to compensate for the fluctuations in renewable power generation and maintain the system frequency within acceptable limits
- Example: When renewable power generation decreases, conventional generators increase their output to maintain the supply-demand balance
- Voltage control coordination ensures that the reactive power output of renewable sources and conventional generators is properly managed to maintain the desired voltage profile across the network
- Example: If a renewable source is generating excess reactive power, conventional generators can absorb reactive power to prevent overvoltage
Power Flow and Dispatch Optimization
- Power flow control coordination aims to optimize the dispatch of renewable and conventional generation resources while considering transmission line constraints and minimizing system losses
- Example: An optimal power flow algorithm can determine the most economical and feasible dispatch of renewable and conventional generators based on their operating costs and network constraints
- Advanced control strategies, such as model predictive control or adaptive control, can be employed to enhance the coordination between renewable and conventional generation controls in real-time
- Model predictive control uses a system model to predict future states and optimize control actions over a receding horizon
- Adaptive control continuously adjusts the control parameters based on the changing system conditions and performance feedback
Key Terms to Review (35)
Ac-dc converter: An ac-dc converter is an electrical device that transforms alternating current (AC) into direct current (DC), allowing for the integration of AC power sources into DC systems. This conversion is essential for many renewable energy applications, as most renewable sources generate AC power that must be converted for efficient storage and usage in DC-based systems like batteries and electronic devices.
Constant Voltage: Constant voltage refers to a control strategy that maintains a steady voltage level in electrical systems, ensuring stable operation and performance. This concept is particularly important in power systems as it helps regulate the output of renewable energy sources, ensuring that they deliver consistent power despite fluctuations in generation or demand. By managing voltage levels, systems can enhance reliability, minimize losses, and optimize the integration of diverse energy resources.
Control response time: Control response time refers to the duration it takes for a control system to react to changes in input signals or disturbances within a power system. This metric is crucial for ensuring stability, especially in renewable energy sources where fluctuations in generation and demand can occur rapidly. A shorter control response time often leads to better performance in maintaining system stability and efficiency.
Dc-ac converter: A dc-ac converter, also known as an inverter, is a device that converts direct current (DC) electrical power into alternating current (AC) electrical power. This conversion is essential for integrating renewable energy sources, such as solar panels and wind turbines, into the power grid, where AC is the standard form of electricity used in homes and industries. The efficiency and control strategies of dc-ac converters are vital for optimizing energy production and maintaining grid stability.
Dc-dc converter: A dc-dc converter is an electronic device that converts direct current (DC) voltage levels from one value to another, typically used to increase (boost) or decrease (buck) voltage. This conversion is essential for efficiently powering various electronic devices, especially in renewable energy applications where voltage levels from sources like solar panels and batteries need to be adjusted to match load requirements.
Dynamic performance: Dynamic performance refers to the behavior of a power system under transient conditions, focusing on how quickly and effectively it can respond to changes such as disturbances, faults, or load variations. This concept is crucial for ensuring stability and reliability, particularly when integrating renewable energy sources, which can introduce variability and unpredictability into the system.
Fault ride-through: Fault ride-through refers to the ability of a power system, particularly renewable energy sources, to remain connected to the grid during and after a fault event, without disconnecting or tripping offline. This capability is crucial for maintaining grid stability and reliability, allowing the system to continue operating despite temporary disturbances caused by faults such as short circuits or voltage dips. Ensuring fault ride-through enhances the resilience of renewable energy systems and helps support the overall power grid during adverse conditions.
Frequency regulation: Frequency regulation is the process of maintaining the balance between electricity supply and demand to ensure that the system frequency remains within a specified range, typically around 60 Hz in North America. This process is critical for system stability and is influenced by various control mechanisms, including automatic generation control and energy management systems. Effective frequency regulation can involve different technologies and strategies that help to mitigate fluctuations in supply and demand.
Fuzzy logic control: Fuzzy logic control is a form of control system that utilizes fuzzy logic, a mathematical framework for reasoning that deals with uncertainty and imprecision, to make decisions and manage processes. This approach mimics human reasoning, allowing for more flexible and adaptive control strategies that can handle complex systems. By using linguistic variables and rules instead of precise measurements, fuzzy logic control offers significant advantages in managing dynamic conditions and improving system stability.
Grid synchronization: Grid synchronization is the process of aligning the frequency, phase, and voltage of a power source with an existing electrical grid to ensure stable and reliable operation. This alignment is crucial for integrating various energy sources, especially renewable energy systems like wind and solar, which often have variable outputs. Proper grid synchronization allows for the seamless connection of distributed generation units to the grid without causing disturbances or outages.
IEEE: IEEE stands for the Institute of Electrical and Electronics Engineers, a professional association dedicated to advancing technology related to electricity. It plays a crucial role in developing standards, publishing research, and facilitating collaboration in the fields of electrical engineering, electronics, and computer science, which directly impacts control strategies for renewable energy sources.
Incremental conductance: Incremental conductance is a method used in the control of renewable energy sources to maximize power output by tracking the maximum power point of photovoltaic (PV) systems. This approach involves calculating the derivative of the power-output curve, allowing the system to adjust its operating point dynamically as environmental conditions change. It helps improve efficiency and responsiveness in power generation systems, making it crucial for effective energy management.
Intermittency: Intermittency refers to the variability and unpredictability of renewable energy sources, particularly wind and solar power, which can produce electricity only when conditions are favorable. This characteristic poses challenges for integrating these energy sources into the power grid, as it can lead to fluctuations in electricity supply. The need to manage intermittency is critical for ensuring a reliable and stable energy system that can accommodate a growing share of renewable resources.
Maximum power point tracking: Maximum power point tracking (MPPT) is a technique used to optimize the power output from renewable energy sources, particularly photovoltaic (PV) solar panels. This method dynamically adjusts the electrical operating point of the modules to ensure they produce the maximum possible power, which can vary with changes in environmental conditions such as sunlight intensity and temperature. MPPT is essential for enhancing the efficiency and performance of renewable energy systems, allowing them to respond to fluctuating conditions effectively.
Mppt: MPPT, or Maximum Power Point Tracking, is a technique used in renewable energy systems to maximize the power output from solar panels or wind turbines by adjusting the electrical load. This method ensures that the energy harvested is as efficient as possible, adapting to changing environmental conditions like light intensity and temperature. By continuously monitoring the output voltage and current, MPPT controllers can find and maintain operation at the point where the maximum power can be extracted from the renewable source.
NERC: NERC, or the North American Electric Reliability Corporation, is an organization responsible for ensuring the reliability and security of the electricity supply in North America. It develops and enforces reliability standards that utilities must adhere to in order to maintain a stable and secure power system. This is particularly important as renewable energy sources are increasingly integrated into the grid, necessitating effective control strategies to ensure reliability.
Optimal Torque Control: Optimal torque control is a control strategy used in power systems, particularly in renewable energy sources, to regulate the torque output of devices like wind turbines and electric motors for maximum efficiency. This technique adjusts the operating conditions to achieve the best possible performance while maintaining system stability and reliability. By optimizing torque, energy capture is maximized, reducing waste and ensuring that the energy generation aligns closely with demand.
Perturb and Observe: Perturb and Observe is a control strategy commonly used in renewable energy systems, particularly for optimizing power output by adjusting operating conditions based on measured responses. This approach involves making small changes to system variables and observing the resulting effect on performance, allowing for the identification of optimal settings that maximize energy production or efficiency.
Pid control: PID control stands for Proportional-Integral-Derivative control, a widely used control loop feedback mechanism that continuously calculates an error value as the difference between a desired setpoint and a measured process variable. This method adjusts the control inputs to reduce the error over time, making it essential for maintaining stability and performance in various systems, particularly in power systems involving voltage regulation and frequency control.
Power Electronics: Power electronics is the technology that deals with the conversion, control, and conditioning of electrical power using electronic devices. It plays a crucial role in improving the efficiency of power systems by enabling precise control over the flow of electrical energy, particularly in applications involving renewable energy sources such as solar and wind. By integrating power electronics with various control strategies, it enhances system performance and supports the stability of electrical grids.
Power factor control: Power factor control refers to the methods and technologies used to manage the power factor in electrical systems, ensuring that the ratio of real power to apparent power is optimized for efficiency. This is crucial in renewable energy sources, as they often face challenges in maintaining a good power factor due to their variable nature. Effective power factor control not only enhances system stability but also reduces energy losses and improves the overall performance of power systems.
Power Quality: Power quality refers to the characteristics of electrical power that affect the performance of electrical equipment. It encompasses voltage stability, frequency, and waveform distortion, which can significantly impact the reliability and efficiency of power systems, especially as renewable energy sources become more prevalent. Maintaining good power quality is essential for ensuring system stability, minimizing equipment damage, and enhancing overall operational efficiency in modern power networks.
Power Signal Feedback: Power signal feedback is a control mechanism that uses real-time measurements of power signals to adjust and stabilize the performance of electrical systems. This feedback loop allows for the continuous monitoring and optimization of power flow, ensuring that renewable energy sources operate efficiently and reliably under varying conditions.
Ramp Rates: Ramp rates refer to the speed at which a power generation source can increase or decrease its output. This characteristic is crucial for balancing supply and demand in real-time, especially as renewable energy sources, like solar and wind, can exhibit rapid fluctuations in generation due to changes in weather conditions. Understanding ramp rates helps to optimize control strategies for these renewable sources and assess their impact on overall system stability.
Reactive power control: Reactive power control is the management of reactive power in electrical systems to maintain voltage stability and optimize the performance of power systems. This control is crucial for ensuring that electrical equipment operates efficiently and effectively, particularly in environments with variable loads and renewable energy sources. By regulating reactive power, systems can enhance stability, reduce losses, and improve the quality of power delivered to consumers.
SCADA Systems: SCADA systems, or Supervisory Control and Data Acquisition systems, are vital tools used in industrial automation for monitoring and controlling infrastructure and facility-based processes. They play a crucial role in gathering real-time data from various sensors and devices, enabling operators to make informed decisions and ensure efficient operation. SCADA systems are instrumental in integrating renewable energy sources into the power grid and also pose challenges related to cyber-physical security.
Smart grid technology: Smart grid technology refers to an advanced electrical grid that utilizes digital communication and automation to improve the efficiency, reliability, and sustainability of electricity services. By integrating renewable energy sources, real-time monitoring, and advanced control systems, smart grids enhance the overall operation of power systems and enable better management of energy resources.
Solar pv: Solar PV, or solar photovoltaic, refers to the technology that converts sunlight directly into electricity using semiconductor materials. This process harnesses solar energy, which is renewable and abundant, making it a key player in the transition to sustainable energy solutions.
STATCOMs: STATCOMs, or Static Synchronous Compensators, are advanced power electronic devices used to regulate voltage levels in electrical power systems. They enhance system stability and improve the quality of power delivery by providing reactive power support during disturbances, particularly in systems integrating renewable energy sources such as wind and solar power.
Static Synchronous Compensators: Static synchronous compensators, or STATCOMs, are advanced power electronic devices that provide dynamic reactive power support to the electrical grid. They help regulate voltage levels, enhance stability, and improve power quality by rapidly injecting or absorbing reactive power. By responding quickly to changes in the grid, they play a crucial role in maintaining system reliability and accommodating fluctuations caused by renewable energy sources.
Static Var Compensators: Static Var Compensators (SVCs) are devices used in power systems to control voltage levels by providing or absorbing reactive power. They enhance the stability and performance of electrical grids by dynamically adjusting the reactive power output, which helps maintain voltage stability during various load conditions and disturbances. By stabilizing voltage and improving power factor, SVCs play a critical role in ensuring that power systems operate reliably and efficiently.
SVCs: Static Var Compensators (SVCs) are devices used in power systems to control voltage levels by providing or absorbing reactive power. They play a vital role in maintaining stability in power systems, particularly in integrating renewable energy sources, which can be intermittent and lead to voltage fluctuations. By adjusting reactive power dynamically, SVCs help improve the reliability and efficiency of electrical grids.
Voltage Droop Control: Voltage droop control is a control strategy used in power systems, particularly in renewable energy sources, to regulate voltage levels by allowing the output voltage to decrease as the active power output increases. This method helps maintain system stability by providing a natural response to changes in load demand and generation, thus promoting better integration of distributed energy resources into the grid.
Voltage Stability: Voltage stability refers to the ability of a power system to maintain steady voltage levels at all buses in the system after being subjected to a disturbance. This concept is crucial because voltage instability can lead to voltage collapse, where voltages drop significantly, causing widespread outages and affecting system reliability.
Wind turbines: Wind turbines are devices that convert the kinetic energy of wind into mechanical energy, which can then be transformed into electrical energy. These machines play a crucial role in harnessing renewable energy sources and contribute significantly to reducing greenhouse gas emissions, promoting sustainability, and enhancing energy independence.