Instant Closing of Permanent Magnet Synchronous Motor Control Systems at Open-Loop Start

Round 1

Reviewer 1 Report

1. It is a meaningful and complete work.

2. The title of Figure 9 is truncated after "when closing is".

3. The conclusion has to be modified, to figure out the contributions of the proposed controller in academic study and engineering application.

Author Response

Dear reviewer,

Thank you for the high evaluation of my manuscript. Please, find the responses to your comments below.

 

1. It is a meaningful and complete work.

Thank you for your appreciation, I did my best.

 

2. The title of Figure 9 is truncated after "when closing is".

Thank you for your attention! The picture boundaries were modified.

 

3. The conclusion has to be modified, to figure out the contributions of the proposed controller in academic study and engineering application.

The paper uses conventional PI-controller, however it suggests the way of its reinitialization for instant switch between different control algorithms. Considering you comment, the conclusion was modified as follows.

“This paper proposes an algorithm for instant and seamless closing of control systems of synchronous motors after open-loop starting. The author reviewed and discussed existing methods of the sensorless motor starting and considered existing techniques utilized for transition from the open-loop mode to the sensorless vector control. After conclusions of inapplicability of the existing methods, the new method was proposed and implemented. In this algorithm PI-controllers start operation in the open-loop synchronous frame and operate until decision to close the control systems. After that, all internal variables of PI-controllers are reinitialized to operate in the estimated synchronous reference frame, where control system works after starting. The proposed algorithm suggests several approaches to calculate motor torque and perform seamless closing. Furthermore, the author proposes several ways to switch the system from the operational point used before closing to the optimal operational point, used in further work. These ways differ in complexity of implementation and speed transients, thus the most convenient solution may be selected for the developing project, depending on the requirements. The experimental results proved its feasibility and absence of the undesired transients.”

Reviewer 2 Report

Congratulations on the well-prepared manuscript. However, from my point of view, there is some improvement that may improve the manuscript.

 

1. Figure 8 must be improved for clarity. The label is not clear. On top of that, it should come with a block diagram so that the reader can understand the connection of each system used.
2. How the result presented in Figures 10 and 11 proves improvement of the proposed control technique should be explained further.
3. An extensive explanation for the result presented in Table 2 is essential to prove the proposed control technique improvise the overall system performance compared to the traditional technique.
4. There is so much explanation on the theoretical aspect presented in this manuscript. However, the correlation between the findings and the theory is not properly discussed. 

Author Response

Dear reviewer,

Thank you for the high evaluation of my manuscript. Please, find the responses to your comments below.

 

Congratulations on the well-prepared manuscript. However, from my point of view, there is some improvement that may improve the manuscript.

Thank you for your appreciation, I did my best. I have carefully considered all your comments and modified my manuscript correspondingly. I hope, you will find modifications satisfactory.

 

1. Figure 8 must be improved for clarity. The label is not clear. On top of that, it should come with a block diagram so that the reader can understand the connection of each system used.

Thank you for your opinion. The color of labels was modified for better readability. The figure was also enhanced with a block diagram for better understanding the structure of motor drive. The paper was modified as follows:

“The experimental system used for verification of the proposed technique is shown in Figure 8, where Figure 8a demonstrates view of installation and Figure 8b depicts its schematic. In this figure inverter 1 supplies compressor 2, which pumps a refrigerant. Air condenser 4 cooling the pressurized refrigerant, while evaporator 6 decreases pressure and temperature of the refrigerant. Valve 5 controls operation of the compressing circuit by setting pressure of the refrigerant. Manometers 3 and 7 are used to control high and low pressures, respectively.”

Figure 8. Experimental set-up. a) Picture; b) schematic

 

2. How the result presented in Figures 10 and 11 proves improvement of the proposed control technique should be explained further.

The main criterion is speed transients right after closing. It can be clearly seen, that the speed transient in Fig. 10 is higher than in Fig.9, but is still acceptable for the overwhelming majority of systems. At the same time, the speed transient in Fig. 11 are absent, which illustrates perfect operation. In order to clarify it, section “Discussion” added to the manuscript.

“7. Discussion

The experimental results provided above demonstrate that the proposed technique is superior to the conventional algorithms. It can perform instant reinitialization of system controllers from open-loop reference frame used at starting to the estimated synchronous reference frame, where control system operates after closing. At the same time, conven-tional techniques involve cross-over functions, which require about 0.5 ~ 0.8 s for switch-ing. In this interval the conventional control system may not execute external commands, which results in poor controllability. Furthermore, due to the usage of cross-over func-tions, the transients are higher and longer.

The proposed algorithm reinitializes system controllers the way, that their new state corresponds to the system state in a new reference frame. This action is performed in one calculation step, therefore, there are no undesired transients and system is ready to pro-cess external commands right after reinitialization.

The speed and current transients, which happen in the experimental system are cause by the change of operational point. The system moves from starting point, which corresponds to higher stator current and lower efficiency, to the optimal working point with the lowest current and highest efficiency, as shown in Figure 7. This process may be uncontrolled, so current controllers set commanded current the fastest way, which results in slight deviation from torque loci curve and minor transients. These transients are ac-cepted for the overwhelming majority of motor drives, however, if transients are undesired the currents may be controlled to follow torque loci curve. In this case, the system moves from one operational point to another without transients.”

 

3. An extensive explanation for the result presented in Table 2 is essential to prove the proposed control technique improvise the overall system performance compared to the traditional technique.

Thank you for the valuable comment. In order to provide better explanation and emphasize improvements, section “Discussion” was added. The modifications are shown in p.2.

 

4. There is so much explanation on the theoretical aspect presented in this manuscript. However, the correlation between the findings and the theory is not properly discussed.

Thank you for your opinion. In order to clarify this issue, section “Discussion” was added to the manuscript. The modifications are shown in p.2.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Author,

Kindly address the review comments mentioned below

1. There is no clear justification about the type of the controller used and how it is operating/controlling at the required speed conditions

2. Mention parameters in Figure 9 and the figure title is also is not justified

3. In some cases irrelevant data is presented which is not at all a part of the paper please ensure relevant topics are covered and also justify figure 10 as it seems to be same like fig 9 and there is no difference

4. Rather than PI controllers there are many effective controllers that can be implemented for controlling purpose. Mention your reason.

5. Lacks novelty in the paper, as we came across many of these type of controlling devices based on the mass production equipment’s.

Author Response

Dear reviewer,

Thank you for the high evaluation of my manuscript. Please, find the responses to your comments below.

 

Dear Author,

Kindly address the review comments mentioned below

Thank you for the careful reading of my paper. Please find all your comments addressed below.

 

1. There is no clear justification about the type of the controller used and how it is operating/controlling at the required speed conditions

Thank you for your opinion. The proposed paper mainly focuses on the closing algorithm and reinitialization of the controller. In this paper, a PI type controller is considered, because it is the most popular type of controller for electrical drives and power electronics. However, the suggested algorithm of reinitialization maybe easily extended to controller of other types, say PID. In order to clear this issue, the paper was modified as:

“Let’s consider PI type controller as the most popular type of controller for electrical drives and power electronics. Simultaneously, the suggested algorithm of reinitialization maybe easily extended to controller of other types, say Proportional-Integral-Differential (PID) type. This paper does not pay attention to the tuning of controllers and selection of their gains, because it depends on exact project and is out of scope of this manuscript. At the same time, the values of controllers’ gains are not important for reinitialization, which does not depend on them.”

 

 

 

 

 

2. Mention parameters in Figure 9 and the figure title is also is not justified

Thank you for your attention! The picture boundaries were modified.

The parameters of transient were included into Table 2

Table 2. Comparison of the proposed and existing methods
Parameter Method	Cross-over time	Speed deviation	Current deviation
Proposed (Equation 4, Figure 9)	Instant	30 rpm	0.3 A
Proposed, trajectory (Figure11)	Instant	< 8 rpm	< 0.05 A
Cross-over (Eq. 1)	0.5 s	50 rpm	0.2 A
Cross-over (Eq. 2)	0.8 s	45 rpm	0.15 A

 

 

3. In some cases irrelevant data is presented which is not at all a part of the paper please ensure relevant topics are covered and also justify figure 10 as it seems to be same like fig 9 and there is no difference

Figure 9 illustrates transients, where motor torque is calculated using theoretical dependency, which may be hard for calculation. At the same time, transients are shorter and overshooting is lower. Figure 10 illustrates transients, where motor torque is calculated using simplified formula, which contains about 10% error, however is much easier for calculations. As it can be clearly seen, the transients are longer and overshooting is higher, however it is acceptable for the overwhelming majority of motor drives.

 

 

4. Rather than PI controllers there are many effective controllers that can be implemented for controlling purpose. Mention your reason.

You are absolutely right! Many controllers of other types may be used for control of motor drives and power electronics. This paper considers PI type controller as the most popular one, however the proposed algorithm of reinitialization may be easily extended into controllers of other type.

The paper was modified as follows:

“Let’s consider PI type controller as the most popular type of controller for electrical drives and power electronics. Simultaneously, the suggested algorithm of reinitialization maybe easily extended to controller of other types, say Proportional-Integral-Differential (PID) type. This paper does not pay attention to the tuning of controllers and selection of their gains, because it depends on exact project and is out of scope of this manuscript. At the same time, the values of controllers’ gains are not important for reinitialization, which does not depend on them.”

 

 

5. Lacks novelty in the paper, as we came across many of these type of controlling devices based on the mass production equipment’s.

This paper does not focus on controller itself. It proposes algorithm of controller reinitialization, which properly modifies all its internal variables in order to instantly switch from open-loop reference frame to estimated synchronous reference frame, where control system works after starting. The novelty is instant and seamless switching, while the competitive techniques propose cross-over functions to perform this switch. The competitive approach requires time for switching and provide poorer control in tansients.

 

Author Response File: Author Response.pdf