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Review

Review of Power Control Methods for a Variable Average Power Load Model Designed for a Microgrid with Non-Controllable Renewable Energy Sources

by
Mantas Zelba
*,
Tomas Deveikis
,
Saulius Gudžius
,
Audrius Jonaitis
and
Almantas Bandza
Department of Electric Power Systems, Kaunas University of Technology, Studentu Street 48, LT-51367 Kaunas, Lithuania
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(11), 9100; https://doi.org/10.3390/su15119100
Submission received: 30 April 2023 / Revised: 1 June 2023 / Accepted: 3 June 2023 / Published: 5 June 2023
(This article belongs to the Special Issue Smart Grid and Power System Protection)
Browse Figures
Review Reports Versions Notes

Abstract

:
Microgrid systems may employ various combinations of system designs to connect generating units, and the number of different system designs increases exponentially upon adding different brands of inverters to a system. Each of the different microgrid system designs must be set up in a way that it works in balance. An example of an unbalanced microgrid system is given in this paper, with the main issue being the non-predictive excess power, which causes a frequency rise and faulty conditions in the microgrid system. There are many simple options for controlling excess power in a microgrid system; however, none of these options solve the issue permanently while ensuring excess power control without affecting the system’s accumulated energy—the battery state-of-charge (SOC) level. Therefore, there is a need to create a variable average power load (VAPL) device to utilize the excess power at a rate it is changing to avoid a reduction in accumulated energy. The main goal of this study is to review average power control methods for the VAPL device and provide guidance to researchers in selecting the most suitable method for controlling excess power. A key finding of the paper is a suggested optimal average power control method ensuring that the VAPL device is versatile to implement, economically attractive, and not harmful to other devices in a microgrid system.

1. Introduction

As the implementation of renewable energy is growing rapidly due to various worldwide circumstances, the implementation of renewable energy sources is expanding not only at the utility and commercial scale, but also at the residential scale. Even though the importance of commercial-scale renewable energy source implementation is a major part of all integrated renewable energy sources, this article’s main focus is the implementation of renewable energy sources in microgrid systems. When designing, upgrading, or scaling microgrid systems, different issues must be faced. One of these issues is the lack of possibilities to combine different brand components in a microgrid system.
When designing a microgrid system with one brand of component supplier, in most cases, all of the components will be set up to work together, and there will be either no or simple issues; therefore, this is outside of this article’s scope. However, in cases of different brands of components being used in the same system, components might not communicate with each other, and it can be difficult to set up the communication or the communication might be not as expected, and this miscommunication may create issues. An example of such a system is shown in Figure 1, in which battery inverters with an off-grid-type photovoltaic inverter communicate, but the third inverter, which is a grid-tied type and a different brand, does not communicate with the rest of the system. This system’s master generating unit is a battery inverter, which controls the voltage, frequency, demand, and supply. Due to the lack of communication and the type of inverter itself, the grid-tied inverter causes power balance issues in this system [1].
To solve the power balance issue, there is a need to utilize the excess power in a system, because excess power is the reason for the power balance issue. There are lots of simple and well-known solutions to control the excess power in a microgrid system, such as dump load, vehicle-to-grid (V2G) and grid-to-vehicle (G2V), hydrogen storage, batteries, scheduling, pump storage, etc. However, most of these solutions have drawbacks, such as the issue only being solved temporarily, the solution to utilize excess power being complicated and not implementable, or the solution affecting the system’s accumulated energy level. Solutions to utilize the excess power in a microgrid system are reviewed in more detail in Table 1.
Due to excess power utilization at a changing rate, a solution was found in [1], namely variable average power load (VAPL). In this solution, the device is designed to utilize the excess power in a microgrid system without affecting the system’s accumulated energy (the battery SOC level) and without affecting the consumer’s comfort. VAPL is designed for a microgrid system with a non-controllable inverter, and the main source is renewable energy. Therefore, the main goal of this study is to review power control methods for the VAPL device and provide guidance to researchers in selecting the most suitable method for controlling excess power. The novelty of this article is a review of the optimum average power control method for the VAPL device, which is not currently found on the market; therefore, not only is the VAPL device novel, but its average power control method is novel as well. VAPL is a device with a working principle to change the load rate at the rate that the excess power in a microgrid is changing.
In Section 2, methods to control the average power are presented; in Section 3, power control methods are compared; in Section 4, the results are discussed; and in Section 5, all of the information is summarized.

2. Average Power Control Methods

Microgrid systems usually have a storage system to maintain the power balance in the system, and there are various types of storage, such as hydrogen [31,32,33], batteries [34,35,36,37], supercapacitors [38], electrochemical [39,40], and other types of storage [41]. The main purpose of any storage type in a microgrid system is to accumulate excess power when demand is lower than supply and use it at times when demand is greater than supply. In such a microgrid system, for storage control, conversion from alternating current (AC) to direct current (DC) and from DC to AC will likely be performed by bi-directional inverters. In a system consisting only of inverters as generating units, the reaction to the change in power in a system will generate low inertia [42,43], meaning that the microgrid system can significantly and quickly change the power due to the fact that the master generating unit in a system is an inverter.
Excess power in a microgrid system is detected by measuring frequency. Excess power causes the virtual rotating motor to rotate faster, which means that the frequency rises. The VAPL device’s main aim is to monitor the frequency and to change the average power at the rate that the frequency is changing. The VAPL device’s structure, operating function, control algorithm, location in a microgrid scheme, power electronics, and control loop schemes are provided more in detail in Reference [1]. The main scheme of the VAPL device power and control loops is visualized in Figure 2; the scheme in most of the average power control methods is the same, just the control of the switching device is different, and the four different switching control methods are reviewed.
Average power is changed by the duty cycle in the majority of cases, consisting of the on time and off time of the switched load. The higher the duty cycle is, the higher the switched-on time is compared to the off time. The duty cycle is changed in pre-designed steps; for example, if the maximum possible non-controllable excess power is 10 kW, and if there are 10 pre-designed steps, this means that each step of the average power will be 1 kW if, in such a case, the non-controllable excess power is 1.1 kW. To avoid excess power in a system, the average power load needs to be switched to 2 kW, which will cause battery discharge at a 0.9 kW rate. Therefore, the more steps of average power control there are, the more precise the excess power utilization will be.
Optimum selection for the average power control method in a microgrid system with a master generating unit consisting of an inverter is required due to a few reasons. Firstly, the VAPL device should be significantly cheaper than the inverter because it would make no sense if the cheaper solution was another inverter that could fit the needs. Secondly, the device should be versatile to implement, and it should be a plug and play solution, in order to avoid complex programming for each independent and different case. Therefore, the VAPL device should be easily adapted to different system designs. Third, the selected method should have the lowest possible impact on other devices, such as current and voltage harmonics, voltage fluctuations, etc. Only with the optimal selection of the average power control method can the VAPL device attract interest on the market. Due to these reasons, four different average power control methods are found and analyzed: burst, phase delay, pulse width modulation (PWM) on the AC side, and PWM on the DC side.

2.1. Burst Average Power Control Method

The burst control method achieves average power control by switching the load on and off within an AC sinewave period—the switching is performed at the zero crossing of the sinewave, as shown in Figure 3. The more average power is needed, the more switched-on periods there are. The more steps of average power are needed, the longer the period of the duty cycle is. In a 50 Hz system, there are 50 sinewave periods per second, and one period has positive and negative parts; for example, if 100 steps for average power control are needed, this means that the duty cycle will have a 1 s period at the shortest. On the other hand, if the average power has fewer steps of change, the duty cycle period time may be lowered accordingly. The burst power control method has low switching losses [44] compared to the phase delay and PWM methods, because the switching is performed at the zero crossing. This switching provides a lower heat and potentially a lower cooling demand in a power electronics loop. The burst control method must be used on the AC side, and depending on the non-controllable excess power source, it should be single- or three-phase. In the case of a three-phase device, three average power electronic loops should be created with one control unit.

2.2. Phase Delay Average Power Control Method

The phase delay control method has a duty cycle period of half an AC sinewave period, and the main component for such a control method is a bidirectional three-electrode AC switch (TRIAC) [45]. The AC load is switched on with the delay, and the longer the delay, the less power is used, as visualized in Figure 4. The full cycle of the AC wave is applied across the load, and when the starting instant coincides with the beginning of the AC cycle, current flows through the load throughout. The average voltage applied across the load is decreased if the switching angle is delayed from zero crossing [46]. The phase delay control method faces high switching losses, which may be as high as 85% of total losses [47], resulting in waste heat in the power control loop affecting the greater need for cooling. Nevertheless, switching creates harmonics [48], and in systems with the master generating unit being an inverter, the master generating unit can react to the fast change in the system power balance and cause voltage and current spikes during the switching process. The phase angle control method, as with the burst control method, should be one-phase or three-phase, depending on the non-controllable excess power source. In the case of a three-phase device, three average power electronic loops should be created with one control unit.

2.3. PWM on AC Bus Average Power Control Method

PWM is a well-known method for inverter applications. Therefore, PWM on an AC-side bus is also possible as one of the average power control methods. The period of a duty cycle is usually a small fraction of time in the kHz scale, because it is complicated to use the conventional fixed sampling PWM method due to harmonics and the beat phenomenon when the number of switches is low [49]. Depending on the duty cycle, the on and off times of the load are changed—the longer the on time is compared to the off time, the higher the duty cycle is, and the higher the average value achieved, as depicted in Figure 5. To avoid the VAPL device employing the PWM on an AC-side bus control method impacting electricity quality, techniques such as soft-switching [50] or hardware such as filters must be applied. As with the burst and phase angle control methods, the PWM on an AC-side bus method causes the need for separate VAPL devices designed for single- and three-phase non-controllable excess power sources.

2.4. PWM on DC Bus Average Power Control Method

The final method to control the average power is a PWM on the DC side of a microgrid system. The excess power can be dissipated using a PWM-controlled device on a DC bus. The PWM’s working principle is the same as that for the AC bus; however, because of the three-phase system versus the DC bus, there is only one PWM power electronics loop, but depending on the DC bus voltage, it may need to carry more current through the switches. The average power control is achieved by means of the duty cycle, consisting of phases in which it is switched on and switched off, similar to the PWM on the AC side method. The more excess power that needs to be dissipated, the higher the duty cycle of the PWM is required to be, and the longer the switched-on time is compared to the switched-off time, as in the example given in Figure 6. PWM on the DC side, at first glance, might appear to be the option of choice for a control method, but PWM on the DC side might also cause battery aging, depending on the PWM frequency [51]. Battery aging can be monitored by estimating the battery’s state of health [52] in order to avoid the negative impact of VAPL devices on batteries. Therefore, a comparison of all of the proposed methods is required.

3. Comparison of Power Control Methods

It is important to compare all of the average power control methods in three ways in order to ensure that the VAPL device meets the market needs. This method should ensure that the VAPL device is:
  • Versatile for implementation in different systems;
  • Not harmful to other devices in a system;
  • A cost-effective solution.

3.1. Versatility Comparison of Power Control Methods

The versatility meaning in this article is presented as a function of an end VAPL device prototype. The VAPL device should be easily adopted to different system designs, and the device itself should be designed like a plug and play solution in order to avoid complex programming for different applications or system designs. Therefore, power control methods are compared in a presented meaning of versatility.
All average power control methods must have a duty cycle control loop, where the average power needed should be calculated and respective control should be given to the average power control device. The evaluation of the required average power is completed by measuring the frequency on the AC bus, where the excess power is detected. Therefore, each method of average power control must have a connection to an AC bus to calculate the required average power to utilize the excess power at the rate it is changing without affecting the system’s accumulated energy level.
Burst control, phase delay, and PWM on AC bus methods switch on and off the load on the AC bus; therefore, the versatility of integrating such power control methods will be similar for all three methods. A VAPL device controlled by one of three methods must be connected to an AC bus of a system. Nevertheless, the duty cycle is calculated by the connection to the AC bus as well; therefore, the main connections of the VAPL device itself could be combined. This causes the VAPL device to have a simplified solution for connection to any AC system where the excess power is causing issues. Due to the burst control, phase delay, and PWM on AC bus methods being used on the AC side, it represents a versatile solution for implementation in any AC system with any inverter brand or type.
The versatility of a VAPL device controlled by PWM on a DC bus method is affected by a few factors. First, the indicator of excess power in a system is the frequency, and the average power of a VAPL device must change at the rate that the frequency changes, and therefore, PWM on a DC bus as a VAPL device control method must be considered in combination with the AC connection. In different system designs, it might cause the installation of the VAPL device to be complicated. Secondly, its versatility would be negatively affected because of the different voltage levels of battery systems, and the method for adapting it to all battery rated voltages, ranging from 12 V DC to 48 V, and up to 400 V DC and even more. This means that separate devices should be created for each voltage level of a battery system. Third, in some cases, battery inverters and batteries are communicating with each other, and additional programming might be needed to integrate the VAPL device on a DC bus. Fourth, due to the transient conditions while quickly switching the load on and off, the DC bus battery aging might be affected [53], and therefore, filters should be applied to avoid aging or a non-harmful switching frequency should be selected for the batteries, which would make the system even less versatile to implement in different systems.
Due to the VAPL device design being dependent on each power control method, the VAPL device circuit board and the integration into different systems are affected. It is accepted that the highest versatility of the VAPL device would be achieved if one of three power control methods were adopted: burst control, phase delay, or PWM on AC bus.

3.2. Not Harmful to Other Devices in a System

In an experimental system visualized in Figure 1 and described in Ref. [1], we tested if switching performed during high voltages of a sinewave causes transient processes in a system. Switching on an AC bus during high voltages of a sinewave without filters causes voltage spikes in an off-grid system, as shown in Figure 7 and Figure 8.
As seen from measurement data in Figure 7, the whole sinewave period is 20 ms; however, fast switching on high voltages of a sinewave in an off-grid system causes a transient process. The transient process period is dependent on the voltage level of the sinewave at the switching time, but the transient process period might take up to 1.2 µs, as seen in Figure 8. Voltage spikes in a transient process might reach over 200 V, and due to the voltage, current spikes also appear. Therefore, phase delay and PWM on AC bus methods cause undesirable voltage and current spikes which affect the quality of electricity and may damage the AC appliances in the off-grid system.
Less harmful effects but similar issues are faced with the direct PWM control method on a DC bus. Direct fast switching on a DC bus might affect battery aging [53] due to the transient conditions while switching on and off, and therefore, filters should be applied to avoid aging or a non-harmful switching frequency should be selected for the batteries.
The Burst power control method will have little or no transient process while switching, because switching is carried out near 0 V. PWM on a DC bus also has little or no transient process on the AC side, because switching is performed on the DC side. Therefore, the burst control method and PWM on a DC bus are accepted to have very little or no harmful effects on other devices in a system.
Phase delay and PWM on AC side average power control methods with no additional components were compared. The comparison was performed to understand which of the methods causes less total harmonic distortion (THD) and the need for alternative components in the VAPL device, such as filters. The results of the comparison suggest which methods require fewer additives while having a low impact on other system components. The comparison’s main evaluation parameter is THD, which is simulated and calculated with the MATLAB Simulink software (The MathWorks, Inc., Kaunas, Lithuania, version R2022b). Additionally, the results are given in Figure 9. The burst control method is not seen in the results of Figure 9, because THD is dependent only on the load itself and the system’s capabilities for transient conditions, and switching is performed at 0 V; therefore, in the simulation, THD has a value of 0. In the burst control method, all values from 0 to 100% of the duty cycle are equal to 0% of THD. PWM on the DC-side bus is also hardly seen in Figure 9, because switching is performed on a DC bus, which has no effect on the AC bus simulated, and therefore, the THD value is also 0% at any duty cycle range.
Even though PWM on the AC bus would dissipate the power evenly through the sinewave and over operation time, it would create the largest current and voltage harmonics, according to Figure 9, which leads to the biggest possible expenses related to adding filters. The phase delay method causes lower harmonics compared to the PWM on the AC bus method, but this difference is not significant, and it would create an inrush voltage and current spikes when switching on and off the load.
The burst control method’s advantages are as follows: it has no voltage harmonics; the current harmonics are relatively small or not detected at all, depending on the system model; and the switching is performed at or near 0 V, which causes low switching losses. One of the downsides of this method is that it may cause audible noise [54] when the duty cycle is low; another downside may be voltage fluctuations, which can affect electricity quality and consumer comfort due to flickering lights. Another minor downside may be incorrect timing of switching on or switching off the load, which might cause sinewave distortion near the zero crossing [55].
The phase delay method’s main advantage is that it provides no voltage fluctuations (flickering lights) caused by switching. On the other hand, the phase delay control method causes current and voltage harmonics, which might cause the neutral wire to heat up, as well as radio frequency (RF) interference and inrush current spikes during turning on and off [56,57,58]. Since system design varies, there may be a need for individual filters designed for individual systems to reduce the transient process affecting the electricity quality.
One of the main advantages of the PWM average power control method on the AC bus is that it provides evenly distributed power in the whole sinewave period and whole operation time, and therefore, it performs better than the burst and phase delay control methods. PWM on an AC-side bus represents the best solution technically compared to the burst and phase delay methods; however, due to the constant fast switching, filters must be applied [59,60].
The PWM average power control method on the DC-side bus has multiple advantages. Firstly, the average power is distributed evenly across all three phases and across the whole operation time. Second, there are no voltage fluctuations on the AC side and no inrush current or voltage in the sinewave, and therefore, this solution is not harmful to other AC devices in the system.
The best fits for the VAPL device out of the four control methods regarding the effects on other appliances in the system are the burst method and the PWM on a DC bus average power control method.

3.3. Cost Evaluation of Power Control Methods

If the price for the VAPL device solution is approximately the same as a new inverter, the end consumer will possibly choose to buy a new or different inverter which would fit the needs of a system instead of buying a VAPL device to solve the excess power issue. Such a VAPL device would attract little interest on the market; therefore, a cost evaluation of power control methods and their required additives is important.
The burst control method’s first advantage considering the prime cost of the VAPL device is switching losses. Switching is performed at or near 0 V, which causes low heat dissipation and leads to a reduced need for a cooling system. The switching does not cause neither voltage harmonics nor current harmonics—harmonics are relatively small or not detected at all. Due to the lack of a need to reduce harmonics, there is no need for filters or a cooling system. Therefore, the burst average power control method is accepted as one of the best solutions to minimize the prime cost of a VAPL device.
Phase delay and PWM on AC bus average power control methods switch at high voltages of a sinewave, so there are higher switching losses compared to the burst method, and therefore, this method’s power electronics loop will have a greater need for a cooling system. Despite the need for cooling, filters will be needed to avoid voltage and current spikes. The phase delay and PWM on AC bus methods consist of parts that are not needed in the burst control method, and are therefore seen as less suitable methods for the VAPL application, because they will potentially lead to a higher prime cost of the VAPL device. Due to the high initial costs of implementing phase delay or PWM on an AC-side bus for the VAPL device, such methods will result in the end VAPL device cost being approximately the same price as a new inverter. Therefore, such a solution would have low interest on the market.
In addition to the pros and cons of the PWM on an AC bus average power control method, there is also the possibility to control the duty cycle period time according to the load power connected [61] for the excess power dissipation. This option could set the optimal duty cycle automatically and independently of the switched load resistance; such an option would be useful for the required application because it would increase the versatility of such a device, but would possibly also increase the prime cost even more.
Finally, PWM on the DC-side bus creates no harmonics, and therefore, the need for filters is eliminated, in combination with the lower prime cost of the VAPL device. However, due to different battery system voltage levels, different devices should be created for every different voltage and power level, which would potentially raise the prime cost of the device.
In conclusion, the burst average power control method is selected to fit the needs best compared to the other methods, while keeping the prime cost low. PWM on a DC-side bus also might be considered as an option to control the VAPL device’s average power with a low impact on raising the prime cost.

3.4. Summary of Comparison of Power Control Methods

There are more than four presented average power control methods available, such as phase delay. In this paper, the presented phase delay method delays the time when the load is switched on, and the load is switched off when the sine crosses zero. In a similar method to phase delay, just in the opposite order, the load is switched on when the sinewave crosses zero and the load is switched off with a delay, as much as the average power is needed. There are more similar average power control methods to the presented ones, but we believe they result in similar performances.
All four average power control methods were compared and the summarized comparison is provided in Table 2. Even though PWM on an AC bus would dissipate the power evenly through the sinewave and over operation time, it would create the largest current and voltage harmonics according to Figure 9, which leads to the biggest possible expenses related to adding filters. The phase delay method causes lower harmonics compared to the PWM on an AC bus method, but this difference is not significant, and it would most likely create an inrush voltage and current spikes when switching on and off. Therefore, filters for the phase delay method and PWM on an AC-side bus would be needed, which would potentially increase the VAPL device prime cost and reduce the interest in such a device. PWM on a DC bus fits the needs best; however, its difficult integration into different systems with different battery voltage levels and frequency measurements leads to it being viewed as a non-versatile solution.
The VAPL device, when comparing power control methods, should be versatile to implement and a plug and play solution, and compared to other methods, the burst power control method is similar to the phase-angle and PWM on the AC bus methods. Therefore, considering all three requirements—versatile to implement in different systems, a cost-efficient solution, and not harmful to other devices in a system—the burst average power control method is preferred as the best-suited one. In the end, the burst power control method is seen as a simple and versatile solution which does not require any special additives to fulfill all three targets.

4. Discussion

Excess power in a microgrid system causes a rise in frequency; therefore, the VAPL device measures and reacts to the change in frequency, and if it reaches and goes above the set limit, the VAPL device switches on and starts to utilize the non-controllable excess power with the required average power. The VAPL working algorithm changes the average utilized power at the rate that the excess power is changing; therefore, the VAPL device does not affect the system’s accumulated energy level or the electricity quality in the system.
The average power of the VAPL device should be changed in as small steps as possible regarding the control method; due to the smaller power steps, non-controllable excess power will be utilized in a more precise way. Nevertheless, for all the control methods, the VAPL device should have different models separately designed for a one- or three-phase non-controllable excess power source, except for the PWM on a DC bus control method.
The comparison results suggest that the power control method best suited to the VAPL application is the burst control method. The burst method may cause voltage fluctuations in a system with a rotating master generating unit, but with an inverter-based master generating unit, it should not cause voltage fluctuations. Therefore, the authors believe that the burst control method should not have a significant impact on the electricity quality in the system; however, all four methods should still be modeled and simulated in the MATLAB Simulink environment with the working microgrid system. After simulation, a real-life system example should be created to prove the primary results and assumptions of the proposed method and the solution itself.

5. Conclusions

Any microgrid system consisting of at least one generating unit not controlling its generated power according to the system needs might experience excess power issues, leading to rising system frequency and non-stable conditions of the whole system. This issue topic becomes more serious if this non-controllable generating unit is an unpredictable renewable energy source. To solve this excess power issue without affecting the system’s accumulated energy level, a VAPL (variable average power load) device is required, and the device should be controlled under one of four presented methods: burst, phase-angle, PWM on an AC bus, or PWM on a DC bus.
Considering the requirements of the device, the application, and the capabilities, the burst control method is suggested as the best method to control the average power in a microgrid system with a non-controllable excess power source without affecting the accumulated energy level of the microgrid system. The burst control method can influence the end VAPL device to have the lowest prime cost of all compared methods, with a low impact on the system and its components, and sufficient performance while utilizing the excess power. Further research should be performed, testing the burst control method in simulated microgrid systems and real-life prototype examples.

Author Contributions

Conceptualization, methodology, formal analysis, software, writing—original draft preparation, writing—review and editing, investigation, M.Z.; validation, resources, S.G.; supervision, data curation, T.D.; project administration, A.J.; visualization, funding acquisition, A.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The scheme of a microgrid system with a grid-tied inverter.
Figure 1. The scheme of a microgrid system with a grid-tied inverter.
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Figure 2. The scheme of a VAPL device.
Figure 2. The scheme of a VAPL device.
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Figure 3. Burst control operation mode. Blue parts of the waveform represent the output of the load.
Figure 3. Burst control operation mode. Blue parts of the waveform represent the output of the load.
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Figure 4. Phase delay control operation mode. Blue parts of the waveform represent the output of the load.
Figure 4. Phase delay control operation mode. Blue parts of the waveform represent the output of the load.
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Figure 5. PWM on AC-side bus control operation mode.
Figure 5. PWM on AC-side bus control operation mode.
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Figure 6. PWM control on the DC-side bus operation mode. The more excess power that needs to be dissipated, the higher the duty cycle of the PWM is required to be, and the longer the switched-on time is compared to the switched-off time, as in the example given in the figure.
Figure 6. PWM control on the DC-side bus operation mode. The more excess power that needs to be dissipated, the higher the duty cycle of the PWM is required to be, and the longer the switched-on time is compared to the switched-off time, as in the example given in the figure.
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Figure 7. Voltage spikes are caused by switching on high voltages, expanded sinewave.
Figure 7. Voltage spikes are caused by switching on high voltages, expanded sinewave.
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Figure 8. Voltage spikes are caused by switching on high voltages, expanded transient process.
Figure 8. Voltage spikes are caused by switching on high voltages, expanded transient process.
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Figure 9. THD comparison of average power control methods.
Figure 9. THD comparison of average power control methods.
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Table
Table 1. Excess power utilization options.
Table 1. Excess power utilization options.
Excess Power Utilization OptionReferenceDrawback
Heat/thermal storage[2,3,4,5]Excess power is utilized in fixed power, and therefore, fixed power causes microgrid system battery discharge.
Pump storage[6,7,8,9]Complicated to implement both at the commercial and residential scale.
Scheduling[10,11,12,13,14,15,16]Excess power is utilized at the cost of consumer comfort.
V2G/G2V; fuel cell[17,18,19,20,21,22]It expands the accumulated energy level in a microgrid system, and therefore, it solves the issue only temporarily.
Dump load[23,24,25]Excess power is utilized in fixed power, and therefore, fixed power causes microgrid system battery discharge.
Inverter/system control via communication[26,27,28,29,30]Complicated to implement in different designs of systems. Not feasible to create a plug and play solution.
Table
Table 2. Comparison of average power control methods.
Table 2. Comparison of average power control methods.
Power Control MethodVersatileCost-EfficientNo Filtering Needed
BurstYesYesYes
Phase delayYesNoNo
PWM AC busYesNoNo
PWM DC busNoYesYes
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Zelba, M.; Deveikis, T.; Gudžius, S.; Jonaitis, A.; Bandza, A. Review of Power Control Methods for a Variable Average Power Load Model Designed for a Microgrid with Non-Controllable Renewable Energy Sources. Sustainability 2023, 15, 9100. https://doi.org/10.3390/su15119100

AMA Style

Zelba M, Deveikis T, Gudžius S, Jonaitis A, Bandza A. Review of Power Control Methods for a Variable Average Power Load Model Designed for a Microgrid with Non-Controllable Renewable Energy Sources. Sustainability. 2023; 15(11):9100. https://doi.org/10.3390/su15119100

Chicago/Turabian Style

Zelba, Mantas, Tomas Deveikis, Saulius Gudžius, Audrius Jonaitis, and Almantas Bandza. 2023. "Review of Power Control Methods for a Variable Average Power Load Model Designed for a Microgrid with Non-Controllable Renewable Energy Sources" Sustainability 15, no. 11: 9100. https://doi.org/10.3390/su15119100

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