As more renewable energy sources and battery storage units are specified and integrated into power systems, consulting engineers face many challenges that can impact the overall design and performance of these solutions. Today, energy consumers can become energy producers as rooftop solar generators behind the meter and battery storage systems become more affordable and ubiquitous. Additionally, concerns about the reliability of power from traditional utilities due to their aging infrastructure, extreme weather events, and more sensitive loads have led to wider adoption of microgrids.
What is a microgrid?
A microgrid is a local power grid that can be regulated. Microgrids can be separated from the traditional grid and operated autonomously. Some microgrids can be completely off-grid and be the main source of power for the end users they serve.
Microgrids can integrate a variety of traditional and renewable energy sources, such as B. natural gas or diesel generators, wind turbines, solar panels, fuel cells and energy storage. Working with a reliable power system vendor that fully understands the power system design domain (Figure 1) can ensure a mature solution that achieves the project goals.
Components commonly found in microgrids
Technologies based on inverters and synchronous machines are often integrated into microgrids. Some components that can be used in a microgrid include the following.
photovoltaic modules.Photovoltaic or solar photovoltaic modules convert solar radiation into direct current (DC) electrical energy. Solar panels require an inverter to convert direct current to alternating current (AC) for use in most common electrical devices.
Solar panels take up a lot of shade-free physical space, but their cost has steadily decreased. Photovoltaic modules can be a valuable asset in a microgrid due to the extremely low or even non-existent marginal cost of generation. However, they are a highly intermittent power source and cannot provide continuous power on their own. Therefore, they are increasingly being combined with battery energy storage to ensure higher utilization and reliability.
battery power storage.Battery storage, combined with intermittent energy sources such as photovoltaic panels, can solve the problem of scarcity and irregularity of renewable energy sources. During the day, when solar energy is plentiful, energy produced in excess of load demand can be stored in batteries, which are discharged overnight rather than being shut down. Batteries can also be charged with mains electricity if permitted by the utility when grid charges are lower and they are discharged during peak periods or to avoid expensive demand charges. Like photovoltaic panels, batteries are a DC source and use inverters to charge or discharge an AC electrical system.
wind turbines.Microgrids can also use wind turbines. Like photovoltaic panels, wind turbines are intermittent sources that produce energy when there is sufficient wind. Geographical location has a major impact on the feasibility of harnessing wind energy in a microgrid, but in the right place, they can be very beneficial.
fuel cells.Fuel cell technology is constantly improving with greater efficiency, greater power density and reduced cost. A good understanding of expected operation and fuel availability can aid in selecting the right fuel cell technology.
investorsIn order to connect the DC output of solar, storage and fuel cells to an AC grid, the DC output must first be converted to AC power. Inverters, which are semiconductor-based electronic components, use insulated gate bipolar transistors (IGBTs) to convert direct current to alternating current by turning the IGBTs on and off in a predefined order and speed to create current pulses, which is called modulation referred to as. Additional filters and other electronic devices are used at various stages of the conversion to produce a clean sine waveform.
Investors can form the network or follow it. For line-following drives, another AC power source (e.g., the utility grid or a generator set) must provide a voltage reference for the drive to synchronize. With mains-forming drives, no reference voltage is required and the drive can set the mains voltage independently. Solar inverters generally follow the grid; while storage inverters can be network builders, network followers, or both.
Synchronmaschinen (Generator Sets).Although PV modules and batteries are DC powered devices, most electrical devices use AC power. A generator set produces AC power by its very nature and can be used directly to power AC loads if required and paralleled with other AC sources such as the utility grid.
The integration of a synchronous machine into a microgrid application brings many advantages, since they are reliable and ready-to-use energy sources that can always be used to meet the electrical load demand when fuel is available (Figure 2). Generators with their high power density can start quickly, absorb large block loads and establish a connection to grid-connected components such as photovoltaic or battery inverters. With intelligent controls on modern power generators, autonomous synchronization and load sharing can take place at the device level.
A wide range of generator sets are available in various power ratings, handling different types of fuel, operating at different duty cycles and producing a variety of noise and emission levels to meet specific project requirements. Generator sets also add inertia to a microgrid system that inverter-based power supplies cannot provide, thus contributing to overall system stability. For example, some microgrids composed of synchronous and photovoltaic generators require a minimum capacity of always-on synchronous generators to maintain inertia.
Two common concerns when using generator sets for microgrid and conventional applications are noise and emissions, with increasing pressure to be environmentally and socially responsible. Modern generator sets are available that produce exceptionally low emissions due to advances in combustion and aftertreatment technologies. In addition, low-carbon fuels such as renewable natural gas (RNG) and biogas can be used for carbon-neutral operation. Noise can be solved by heavily muffled offices and buildings. Site-level noise and emissions can also be minimized through intelligent controls that optimize the use of each asset to minimize duration and uptime.
Parallel AC power supplies
In order to connect parallel or alternative power supplies, various characteristics of the AC output voltage must be equal or within an acceptable range. It is important that the waveform and phase sequence are the same. In addition, the frequency, phase angle, and amplitude of the voltage must be within the acceptable range for safe and effective parallel AC sources.
Synchronous generators naturally generate AC voltage and can be in load sharing mode (similar to grid-forming inverters) or in load regulation mode (similar to grid-following inverters). Load sharing is the proportional sharing of the total load in kW and kVAR across multiple generator sets in a parallel system and is essential to avoid overloads and stability problems. In load sharing, gensets regulate their voltage and frequency and can be isochronous, where voltage and frequency remain constant at 100% regardless of load, or droop, where voltage and frequency vary as the load changes.
Isochronous load sharing provides constant voltage and frequency but requires the sources to communicate with each other. Dip control requires no communication but results in varying voltage and frequency as the load varies.
The load control function is applied when a generator set or multiple sets are connected in parallel to a utility or the grid. Because the grid voltage and frequency are fixed, gensets regulate their kW and kVAR output and not their frequency and voltage.
The paralleling controls onboard the synchronous generator are expected to have built-in paralleling and protection functions and be responsible for all of the following:
- parallel functions.
- Initial Commencement of Arbitration.
- Synchronization (Ø, V and Hz).
- Load sharing (kW and kVAR).
- Schutz
- measure up
- Alarm
- Built-in safe manual concurrency.
Inverters are responsible for lower level timing, protection and metering. However, an essential aspect of the parallel connection is the load sharing between all sources. Load sharing between synchronous generators is easily achieved through the built-in paralleling control. When it comes to load sharing with inverters, one approach would be to configure the gensets to work as utilities (load sharing/grid forming) and the inverters would follow the grid and act as a constant PQ. Source. And an external control system would send these PQ commands to the inverter.
Microgrid-Controller
At the heart of any microgrid power system must be autonomous control. At a minimum, the microgrid controller is expected to:
- Optimize energy production from all energy sources to meet demand.
- Maximize energy production from renewable sources.
- Control loads through load aggregation and load shedding.
- Minimize emissions and fuel consumption.
- Get the lowest levelized cost of electricity (LCOE) and lowest total cost of ownership (TCO) for any asset.
- Enable asset monetization through network support and demand-response programs.
- Ensure that system resources are used optimally.
- Adapt to changing weather conditions (e.g. cloud cover, wind speed and other conditions).
- Operate the system completely or partially off-grid.
- Monitor and/or control assets remotely with real-time notifications.
What is not expected from the microgrid controller are lower-level machine-to-machine operations such as synchronization, load balancing and protection. By shifting these processes to individual machines, the single point of failure is eliminated and thus reliability is increased. The failure of the autonomous microgrid controller does not affect the reliability of the microgrid power system. All failures need to be analyzed and mitigated for safe and reliable operation, which is typically done by the microgrid controller vendor.
Designing a well-functioning microgrid
Microgrids can offer significant benefits in terms of resiliency, sustainability and cost savings. Each project should begin with a feasibility study and stability analysis to determine the best mix and size of assets to achieve project goals (Figure 3). The operating sequence must be written to ensure system recoverability and power quality with mitigated failure modes. Integrated parallel and protection controls for synchronous generator sets and the microgrid controller are critical components to ensure trouble-free operation, system recovery, failure mode analysis and system optimization.
As with all specifications, the microgrid specification should be function and performance based. Working with a trusted power system supplier that fully understands the design domain of power systems can ensure a mature solution that achieves project goals.
—Jaimie Hamilton-AntonsonHe is a technical advisor to Cummins Power Generation's Energy Management Solutions team, focusing on microgrids and hydrogen applications. Prior to this role, he has supported lean gas generators since 2014, focusing on renewable fuel projects and unique and complex applications. Jaimie holds a BS in Mechanical Engineering from Loyola Marymount University and an MS in Mechanical Engineering from the University of Minnesota, Twin Cities.
FAQs
Why is synchronous generator important? ›
Synchronous generators are commonly used for variable speed wind-turbine applications, due to their low rotational synchronous speeds that produce the voltage at grid frequency. Synchronous generators can be an appropriate selection for variable speed operation of wind turbines [166,167].
Where do we use synchronous generator? ›Three phase synchronous generators are used in almost all commercial power plant; the less common type is the induction generator. Generators convert the mechanical energy provided by the prime mover (steam turbine, gas turbine, water turbine etc.) into electrical energy.
What are the characteristics of a synchronous generator? ›Synchronous generators also are called alternators. In synchronous generator rotor's winding is supplied by a DC power source, generating a magnetic field. When rotor rotates in synchronous speed, a sinusoidal AC voltage is induced in each stator's phase winding. This is the principle of electromagnetic induction.
What are the advantages of micro grid? ›Microgrids can help deploy more zero-emissions energy sources, make use of waste heat, reduce energy lost through transmission lines, help manage power supply and demand, and improve grid resilience to extreme weather.
Why synchronous generators are better than induction generators? ›E) Synchronous generators have the advantage of being able to generate at a predetermined power factor into the grid, through the use of a power factor controller. F) An induction generator draws KVAR's at a lagging power factor from the public utility grid to provide excitation.
How efficient are synchronous generators? ›The study showed that the efficiency of single-phase synchronous generating set of low power is small. The maximum one was 16.1%. The highest value of efficiency is achieved at the load with an output power close to the rated power of generator.
Which is the main application of synchronous? ›Synchronous motors are normally used in applications in which a constant and precise speed is required. Typical applications of these low power motors are positioning machines. They are also used in robot actuators. Synchronous motors are also used in ball mills, watches, record players, and turntables.
Which is better synchronous or asynchronous generator? ›Synchronous generators (large ones at least) are more efficient than asynchronous generators. Synchronous generators can more easily accommodate load power factor variations. Synchronous generators can be started by supplying the rotor field excitation from a battery.
What are the advantages of using synchronous generators in parallel to supply loads? ›Running generators in parallel can allow the emergency backup power system to remain active even during maintenance. With an N+1 parallel configuration, one generator can be completely offline for maintenance while the remaining generator handles the required loads.
What is the principle of synchronous generator? ›The principle of operation of synchronous generator is electromagnetic induction. If there exits a relative motion between the flux and conductors, then an emf is induced in the conductors.
How does synchronous generator improve power factor? ›
A Synchronous Motor can be made to operate at unity and leading power factor by just increasing its excitation voltage i.e. by increasing the field current. This advantage of Synchronous Motor is used to improve the power factor.
What is the difference between grid and microgrid? ›As the name suggests, the microgrid is engineered to work in small community areas. On the other hand, the smart grid is designed to handle power supply for large communities and is the digital technology used for two-way communication between utilities and their customers, and sensors along transmission lines.
What are the two components of microgrid? ›A microgrid is a local energy system which incorporates three key components; Generation, Storage and Demand all within a bounded and controlled network. It may or may not be connected to the grid. Different end-users have a range of requirements from their energy supply systems.
Which is better AC or DC microgrid? ›... DC microgrid systems are preferred over AC microgrid systems because they are more effective due to the lack of converter requirements. Energy losses occur during each conversion phase thus more energy losses occur in the AC microgrid system compared to the DC microgrid (Shuai et al., 2018; Hossain et al., 2019) .
What is the main advantage of a synchronous motor over an induction motor? ›In a synchronous motor, the rotor turns at the same speed (in sync) with the stator rotating magnetic field. Unlike an induction motor that relies on rotor slip to induce current into the rotor to generate torque, in synchronous motors there is no induced current and subsequent rotor losses.
What is the difference between induction generator and synchronous generator? ›The fundamental difference between these two motors is that the speed of the rotor relative to the speed of the stator is equal for synchronous motors, while the rotor speed in induction motors is less than its synchronous speed. This is why induction motors are also known as asynchronous motors.
What are the advantages and disadvantages of induction generator over synchronous generator? ›Advantages of Induction Generators
It is relatively cheaper. It possesses a small size per kW output power that means high energy density. It runs in parallel without hunting. Like a synchronous generator, it needs no synchronization to the supply line is required.
Synchronous transmission has the advantage that the timing information is accurately aligned to the received data, allowing operation at much higher data rates. It also has the advantage that the receiver tracks any clock drift which may arise (for instance due to temperature variation).
What are the advantages and disadvantages of synchronous transmission? ›Synchronous communication is happening in the exact moment, while asynchronous communication goes over a period of time. In other words, synchronous communicating is fast, while asynchronous is slow. The right implementation of both of them affects team productivity and sprint velocity.
What are the advantages and disadvantages of a synchronous motor? ›The advantages of the synchronous motor are the ease with which the power factor can be controlled and the constant rotational speed of the machine, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.
Which among these is the advantage of synchronous? ›
ANSWER: Helps in achieving the stepless control of power factor.
What is the function of synchronous? ›A Synchronous function is a function that does not return until the work is completed or has failed. So all of the functions that we wrote for the last couple of days have been synchronous functions because that's how they work.
What is synchronous generator operating alone? ›If stand alone operation is used, a generator is connected to a load and is responsible for supplying all power and reactive power required by the load. A simple three-phase schematic diagram is shown below: Assuming a balanced load, each supply line from the generator will carry the same current.
Which is faster synchronous or asynchronous? ›In the synchronous counter, the operation is faster. In Asynchronous counter the operation is slower. 3. Synchronous counter is also known as Parallel counter.
What is difference between synchronous and asynchronous grid? ›An important feature of large synchronous generators is that they can be used to black start the AC grid. ASYNCHRONOUS ELECTRITY GENERATION: An asynchronous generator uses the signal on the AC line as its frequency and phase reference.
Why are synchronous generators connected in parallel to the grid? ›As the load increases beyond the generated capacity of the connected units, additional generators are parallel to carry the load. Similarly, if the load demand decreases, one or more machines are taken off the line as per the requirement. It allows the units to operate at a higher efficiency.
What is one advantage of a synchronous motor? ›Advantages of Synchronous Motor
It operates at a constant speed (i.e., synchronous speed) from no-load to full-load. Power factor of a synchronous motor can be easily controlled by changing the excitation of the motor. For low speed (< 300 RPM) applications, synchronous motors are more economical than induction motors.
Synchronization matches various parameters of one alternator (or generator) to another alternator or to the bus bar. The process of synchronization is also called as Paralleling of Alternators or Generators.
What is the speed of synchronous generator? ›6000 r.p.m.
What is the main purpose of synchronous motor? ›In higher power industrial sizes, the synchronous motor provides two important functions. First, it is a highly efficient means of converting AC energy to work. Second, it can operate at leading or unity power factor and thereby provide power-factor correction.
Is synchronous generator is self starting? ›
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator.
What are the four important parameters needed in synchronizing the generator? ›- Phase Sequence.
- Voltage Magnitude.
- Frequency.
- Phase Angle.
The power factor rating of most synchronous generators is typically between 0.8 lagging to 0.95 lagging. By convention, a synchronous generator operating with a lagging power factor is producing vars, while one operating with a leading power factor is consuming vars.
Is solar a synchronous generator? ›Wind and solar are asynchronous generators. Wind turbines also use rotation to generate electricity, but spin at variable speeds (i.e. asychronously relative to the grid frequency) and slower speeds than synchronous generators.
What are the three 3 conditions that are needed in paralleling synchronous generators? ›- Matched/proper frequency.
- Matched/correct phase rotation.
- Phase voltages in phase and within specified voltage range.
2.3 Losses in synchronous generators
Most of the losses generated in the machine are resistive losses, iron losses on the pole surface and iron losses in the stator core. Resistive losses in the stator and rotor represent approximately 50-60% of the total losses in a generator.
Stability, reliability, and protection are the key issues of microgrids due to reverse power flows of distributed generation units, local oscillations, transient modes of microgrid, severe frequency deviations in islanded mode operation, and economical and supply‐demand uncertainties of microgrid.
What are the main types of sources in microgrid? ›A microgrid utilizes renewable energy sources such as solar panels, wind turbines, battery storage, diesel gensets and combined heat and power (CHP) modules–operating separately or in parallel. Diesel or gas generator sets may also be included, along with battery banks to store electricity and deliver it when needed.
Which relay is essential in microgrid? ›Multifunction protective relays are an economical choice for microgrid controls because the hardware is commonly required at the point of interface (POI) to the electric power system (EPS) and at each distributed energy resource (DER).
Is a generator a microgrid? ›At the core, a microgrid is a miniature power grid system that is set up to manage distributed energy resources and can include renewables (solar, wind, and/or hydro) with other non-renewable sources (such as diesel generators, gas turbines, etc.).
What are the 3 major components of a power grid? ›
The grid consists of countless complex interconnections, however there are three main sections—electricity generation, transmission and distribution.
What is power quality in microgrid? ›Abstract: The actual direction of increasing the efficiency of distributed generation and renewable energy resources is the aggregation of low-power sources in a microgrid or virtual power plant.
What is the difference between mini grid and microgrid? ›Microgrids are used by small residential or commercial consumers; minigrids are larger configurations, which can power large commercial outlets, universities, factories ane even islands. Microgrids or minigrids can: complement the conventional power grid when electricity demand is high.
What are the disadvantages of microgrids? ›- Electrical energy needs to be stored in batteries which require space and maintenance.
- Re-synchronization with the main grid can be a problem.
- Issues such as standby charges as well as net metering are obstacles for microgrids.
Testing of synchronous generators (SGs) is performed to obtain the steady-state performance characteristics and the circuit parameters for dynamic (transients) analysis.
Why is synchronous motor important? ›The advantages of the synchronous motor are the ease with which the power factor can be controlled and the constant rotational speed of the machine, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.
What happens if generators are not synchronized? ›Poor synchronizing can: Damage the generator and the prime mover because of mechanical stresses caused by rapid acceleration or deceleration, bringing the rotating masses into synchronism (exactly matched speed and rotor angle) with the power system.
What happens if two generators are not synchronized? ›An improper synchronization can affect the healthy power system and results in electrical and mechanical transients that can damage the prime mover, generator, transformers and other power system components.
Why are synchronous motors more efficient? ›Synchronous motors generally have a higher power density than induction motors of comparable size, allowing them to provide more power at a smaller volume. This is great for size-constrained applications and is a reason to choose a synchronous motor over an induction motor.
What are the four condition of synchronization? ›There are five conditions that must be met before the synchronization process takes place. The source (generator or sub-network) must have equal line voltage, frequency, phase sequence, phase angle, and waveform to that of the system to which it is being synchronized.
Why generators are connected in parallel and not in series? ›
Generators are used in parallel to increase the total system size and increase redundancy. It may also be more cost effective to combine several smaller units in preference to one larger unit.
What will happen if a synchronous generator operates with a lagging power factor? ›Operating a synchronous generator with a lagging power factor does not require additional power from the prime mover. It does, however, reduce the amount of real power that the generator can produce by increasing the stator winding current.
Why are synchronous generators operated in parallel? ›Resource management: generators can be located and operated to best meet the generating conditions, instead of having to be located and operated to meet the requirements of a local load.
What happens if excitation fails in synchronous generator? ›· Gas/Steam turbine generators
When a synchronous generator loses excitation, it will overspeed and operate as an induction generator. It will continue to supply some power to the system and it will receive its excitation from the system in the form of VARs.