Projects:2019s2-25201 Evaluating the Capabilities of the Existing Synchronous Generators for Ancillary Services Provision in the NEM in various Renewable Penetration Scenarios

Abstract here

Introduction

Our power system is going through dramatic changes. With renewable generation resources in the grid, more synchronous generators are retiring. Traditionally, the synchronous machines were the main sources of ancillary services to compensate imbalances between generation and demand in order to keep the frequency within the acceptable range. However, renewable resources (such as photovoltaic and wind) are very uncertain, unpredictable, and representing huge up and down ramping events. In this study, we want to see if the existing synchronous generators of different types and properties (such as coal- and gas-fired and hydro power plants) are able to provide the kind of AS that is needed in different penetration levels of renewables. We use the information from AEMO to identify the existing synchronous machines, their availability for AS (eight FCAS markets), and specific characteristics related to providing AS. We also analyse the ramping requirements under various renewable (PV + wind) generation scenarios.

Project team

Project students

• Khairul Azwari Adnan
• Aina Afrina Hasram
• Wenkang Li

Supervisors

• Ali Pourmousavi Kani
• David Vowles

Objectives

• Study technical characteristics of existing synchronous generators available in the market.
• Quantifying the ancillary services requirements of the system under different scenarios of intermittent renewable generation.
• Analyze the ramping requirements of under various intermittent generation scenarios.

Background

Supply & Demand

Figure 1: Installed and forecasted wind and solar

Basically, the electric supply is from renewable and non-renewable sources. Electricity demand is the electricity used by the consumers and the amount is varies. The balancing of supply and demand is very important to make sure the performance of the power system is in stable state. Frequency is one of the important parameters in the power system and it is totally depending on the balancing of supply and demand. The standard frequency limit in the power system is ±50 Hz. As the supply is higher than demand, the frequency is lower and vice versa.

Intermittent Generation

Intermittent energy is a kind of energy cannot continuously generate power, cannot accurately set or plan the capacity of power generation. In renewable energy specifically refers to wind and solar power. These two intermittent energy source increasing is the main factor of the Supply & Demand unbalance and the frequency deviation. Thus, this project will not study others renewable energy soucre(such as Hydropower).The figure 1 is installed wind and solar capacity in the NEM for 2019, with 2025 and 2040 forecasts from the Draft 2020 ISP Central and Step Change generation builds[1]. Obviously, the proportion of wind and solar will continuously increasing. Hence, due to uncertainty and variability characteristics from these two sources, there will be more occurrences in frequency drop/rise event.

Table 1: Frequency Control Ancillary Services (FCAS) markets

Ancillary Services

Ancillary service is functioning to help in maintaining the performance of the power system. There are three types of ancillary services, Frequency Control Ancillary Service (FCAS), Network Support Control Ancillary Service (NSCAS) and System Restart Ancillary Service (SRAS). For this project, the team is focusing on the FCAS only.

Frequency Control Ancillary Services (FCAS)

Frequency control is necessary in order to guarantee that the system frequency in the grid system is in the nominal frequency. FCAS is required to get back the frequency to its standard frequency and make sure the frequency is always in the range. Other than that, Australia has a huge number of intermittent sources such as wind and solar, that supply electricity to the power system in the grid. These intermittent sources have affected the performance of the frequency in the power system.

There are two types of FCAS services, regulation services and contingency services. Regulation services is provided by the participated generators based on the Automatic Generator Control (AGC) while contingency is provided based on the frequency deviation in the power system [1]. From these two services, there are eight products in the FCAS market, Raise Regulation, Raise 6-Second, Raise 60-Second, Raise 5-Minute, Lower Regulation, Lower 6-Second, Lower 60-Second, and Lower 5-Minute. All these products perform a different services. Table 1 shows the description of each product in the FCAS market.

For every FCAS products, there are different characteristics and different purposes. It will depends on the situation of contingency event. In Regulation service, there are two which are raise and lower. A signal from AGC will alter the generation output so that it can match with the supply and demand. For contingency, there are three speed, 6 seconds(fast), 60 seconds (slow), and 5 minutes (delayed). For the fast service, it will arrest the major drop/rise frequency issue immediately. While the 60 seconds is to stabilise following major drop/rise in frequency and the last one, 5 minutes will recover frequency to the normal operating band following the major drop/rise in frequency.

Methodology

Figure 2: Project Planning

Figure 2 shows the project planning of the project. Date retrieving is taken from NEMreview apps https://app.nemreview.info/index.html#/ for 3 years of all FCAS products. The data for regulation services is observe in the whole NEM which are South Australia, Victoria, New South Wales, Queensland, and Tasmania, while for contingency, the observation is only focus in the South Australia since the contingency services is being controlled by local generator. Once the data is completely being retrieved, correlation testing is conducted to all parameters to find the relationship with the intermittent sources generation over past three years. There are two factors being tested which are FCAS prices and FCAS requirements. This correlation testing is done in MATLAB. Figure 2 and Figure 3 show the correlation between requirement and availability of raise contingency. It can be seen that the correlation for for intermittent renewable generation with the FCAS requirements are stronger comparing to FCAS prices. Hence, to proceed the next stage, we just focus on FCAS requirements data and analyse from it.

Figure 3: Correlation of intermittent renewable generation with FCAS prices

Figure 4: Correlation of intermittent renewable generation with FCAS requirements

Figure 5: Output table of Python

Figure 6: The Linear Graph

Due to aiming for better resolution of data, 5-minutes intervals of data are chosen. Hence, there will be 3 years of historical data of 5-minutes intervals for each FCAS products. From this, our interest is to study the most critical intervals for each product. Hence, the calculation of the critical factor of each FCAS services is required. To find the most critical intervals, the data sorting process is required. This sorting process is done using Python. The lowest critical factor followed by big capacity of FCAS requirements will prove the criticality of that time intervals. This can be done using assessment table method by categorising it into safe and critical zone. The figure 5, this is the example output from assessment table method resulted from analysis made using Python.

After that, create a data modelling based on the highest critical zone for each products. This data modelling is create by applying a linear function to the 3 years average data. This was done by using average data for each years 2017, 2018 and 2019 for FCAS requirements and percentage of intermittent generation. Figure 6 shows the graph with the linear equation for one of the product. This linear equation is used to predict the future requirement of FCAS products and observe whether availability in the FCAS still can support when the penetration of intermittent increase until 70%. This can be done for contingency cases only, but the regulation will brings the different result. As mentioned earlier in the background, regulation is always needed as it only correct minor changes and are required most of the times. Hence, there will be no critical time intervals for both lower and raise services.

From the prediction of FCAS requirements, by plotting the latest FCAS resources which are 2019, normal distribution curve will be mapped onto the graph to see the difference in area between two. This can help in estimation of how many percentage the resources available to accomodate if the such penetration intermittent generation is happening. This estimation is done approximately hence the accuracy could be improved in future planning.

Results

Table 2 shows the result of prediction for requirement based on the linear equation of 3 years data. The prediction is done by using the data of availability for 2019. So, as the penetration of intermittent sources increase, the requirement also increase. The percentage of how many the FCAS availability can support the requirement is based on the assumption of area under the distribution curve minus the area of histogram. Figure 7 shows the distribution curve for requirement of FCAS that has been plotted on the histogram of availability.

Figure 7: Distribution Plot of Requirement Prediction on Histogram Availability in 2019 (Raise 60-Second)

Conclusion

Frequency control ancillary services is a service that is responsible to counter the imbalance supply and demand in the power system. In simple words, when the sun shines, solar PV systems will generate electricity while when the wind blows, wind farms will generate electricity. As explained in Section 1.2.1, the variable sources of electricity lead to difficulty in predicting the generation. As a result, it will increase the potential for imbalances between supply and demand that will cause frequency disturbances. We’re losing frequency control capability over the years. Hence, this problem creates a challenge for NEM in frequency control and AEMO to maintain the security of the power system. The ancillary services style must make some changes for a better preparation for these changes. AEMO needs to re-evaluate the framework of frequency control services. To operate NEM with high wind and solar penetration will be a huge challenge yet still feasible to accomplish with proper approaches and planning. It will require more efficient co-ordination of all resources and better information-sharing across operators and participants. A proper solution is compulsory in countering the uncertainty issue. This is because, we need to predict the right resources so that it can be scheduled at the right time efficiently. AEMO needs to minimize and impact on market operation resulting from this planning.

As the conclusion, the availability of raise regulation can support until 30% penetration of intermittent sources, while the availability of lower regulation can support until 100% penetration of intermittent sources. The availability of raise contingency can support until 50% penetration of intermittent sources, while the availability of lower contingency can support until 40% penetration of intermittent sources.

Future Planning

Due to time constraints, the study of ramping requirements was unable to undergo. In future, the ramping requirements of the intermittent generation can be continuing for a more comprehensive research. Plus, 3 years historical data might not be sufficient to approximate a high accuracy result in FCAS requirements. Global market operator has arranged strategy to operate power systems with gradually reducing the synchronous generation. A comparative methodology could be considered in Australia. AEMO has recently recommended changes to the regulatory framework in the NEM to require PFT from all participated generators. In both Texas and Ireland, they have employed inertia requirements that are always applicable. But in NEM, inertia and RoCoF requirements are only active under certain cases. Analyze the ramping requirements under various intermittent generation scenarios.

References

[1] Renewable Integration Study: Stage 1 report, AEMO
[2] Guide to Ancillary Services in the National Electricity Market, AEMO